Over the past several years the literature has accumulated a number of publications in the discussion of materials and process problems associated with DUV photoresist materials. Many authors have discussed a number of issues including contaminants that can adversely effect performance, the addition of `suicide' bases to enhance stability and issues related to manufacturing implementation. The requirement to overcome the obstacles that can reduce this technology's viability to become the workhorse of future semiconductor programs is similar. Unfortunately, there are a number of additional concerns that are unique to photoresist development and manufacturing implementation. Developments in negative resists have demonstrated a significant role in the production of semiconductors and their ease of use over their predecessors has created a higher level of acceptance in the semiconductor fab. Additional developments in positive tone deep ultraviolet resist systems over recent predecessor's has eliminated some of the problems associated with image stability and substrate compatibility. Additionally, stepper and track manufacturers have researched further safeguards in the filtration and neutralization of contaminants that adversely effect chemically amplified systems. In this paper the author discusses issues related to materials concerns for positive and negative DUV photoresists. Issues such as reflectivity control, etch concerns, process control for positive and negative photoresist, fab space considerations, and quality control for DUV photoresists for 0.25 micrometers manufacturing are discussed.

The stabilization toward airborne contamination of chemical amplification resists can be achieved by annealing to reduce the free volume of resist films. Our new positive resist consisting of a thermally and hydrolytically stable polymer and acid generator can be baked above its glass transition temperature and is thus environmentally stable. However, the high temperature bake processes place a stringent demand on the selection of the acid generator (and of course on the resist polymer). In addition to the airborne contamination, evaporation of acid generators and/or photochemically generated acids during the bake processes can result in the T-top formation, especially when the acid generator is small in size and the bake temperatures are high. This paper describes the thermal stability of several acid generators and the influence of the acid generator structure on the T-top formation in our environmentally stable chemically amplified positive resist. The careful selection of a bulky acid generator provided excellent 0.25 micrometers lithography with the depth-of-focus of 1.2 micrometers and the exposure latitude of 20%.

The chemical amplification resist system composed of partially tBOC-protected PVP, a dissolution inhibitor, and an acid generator are investigated as EB resists. As dissolution inhibitors, hydroquinone protected with tert-butoxycarbonyl group (B-HQ) and isophthalic acid protected with tert-butyl group (B-IP) are utilized. It is found that dissolution rate of the resist consisting of B-IP is faster than that of B-HQ in the exposed area. B-HQ and B-IP as dissolution inhibitors convert into HQ and IP as dissolution promoters after exposure, respectively. The pKa of IP is smaller than that of HQ. It is considered that the acidity of IP is higher than that of HQ, so the ability of the dissolution promotion of IP is much larger than that of HQ. IP enhances the solubility of the matrix resin to the alkaline developer larger than HQ. The resist consisting of B-IP has a high dissolution rate ratio between the exposed and unexposed areas, so it is considered that it results in a much improved patten profile. A 0.14 micrometers lines-and-spaces pattern is successfully fabricated at 17.5 (mu) C/cm² using 50 keV. EB.

The development of a new DUV positive resist, XP-9493, is reported. XP-9493 was designed for the Micrascan II exposure system. Its absorbance over the 245 - 252 nm wavelength range is 0.48/micrometers , substantially higher than that of APEX-E, which is approximately 0.2/micrometers . The dissolution selectivity, tan ((phi) ), of XP-9493, 7.7, is much higher than that of APEX-E, 4.1. Thus, XP-9493 is capable of higher resolution than APEX-E with better swing curve control. It is shown that the deprotection rate of this resist is proportional to the pK_a of the photogenerated acid. This result leads to the prediction that protonation of the protected polymer may determine the rate of the deprotection reaction. Further study of the photospeed vs PEB temperature showed a two-tier activation energy for the deprotection reaction. At high PEB temperatures, >= 95 degree(s)C, the deprotection reaction is diffusion-limited, where the protonation step is rate limiting. The activation energy, E_a, under diffusion limited conditions is only 7.6 kJ/mole. At lower PEB temperatures, < 95 degree(s)C, the deprotection reaction is reaction-limited, where the deprotection of the protonated protected polymer is rate-limiting. E_a under these conditions is 26.3 kJ/mole. This behavior leads to lower linewidth shifts per unit PEB temperature change, (Delta) CD/(Delta) T, at the recommended process conditions. For XP-9493, (Delta) CD/(Delta) T is approximately 6 nm/ degree(s)C for 300 nm line/space pairs. XP- 9493 resolves 0.225 micrometers line/space pairs at 19 mJ, and 0.25 micrometers contact holes at 27 mJ. The 0.25 micrometers process window for XP-9493 is >= 1.0 micrometers depth-of-focus, with 25% exposure latitude on a MSII exposure tool.

In the present study, protecting groups of moderate stability, such as acetals and ketals, were investigated as pendant blocking groups in polyvinyl phenols. Polymers were obtained by reacting enol ethers with the phenolic side groups to form acetal or ketal blocked phenols. Decomposition temperatures, glass transition temperatures, and molecular weights of the resulting polymers were monitored and correlated with the protecting group structure. Stability of the protecting groups can be explained by protonation occurring at either of the two oxygen sites, making two cleavage routes possible. Secondary reactions of the released protecting groups in the resist film were investigated and discussed. The structure of the protecting group was designed in order to meet basic resist properties such as resolution/linearity, DOF, post exposure delay latitude and thermal stability. A Canon FPA 4500 (NA equals 0.37) and a GCA XLS exposure tool (NA equals 0.53) were used for the optimization process. A preoptimized resist formulation based on the above criteria exhibits 0.23 micrometers line/space resolution, 0.8 micrometers focus latitude at 0.25 micrometers resolution and approximately two hours post exposure delay latitude.

Deep-UV chemically amplified (CA) resists are among the leading candidates for the manufacture of semiconductors at 0.25 micron ground rules. In systems of this type, a latent image of photogenerated acid is produced in the resist film on pattern-wise exposure to UV light. The subsequent post-exposure bake (PEB) step drives a thermal reaction, causing a change in the aqueous base solubility of the resist in the exposed regions. Due to the fact that the photochemical and thermal images are decoupled it is important to understand the details of the resist thermal chemistry in order to understand how process conditions affect properties such as linewidth control and resolution. We describe here in-situ, high data-rate, accurate measurements of the chemical kinetics that occur in CA resists during post-exposure bake (PEB). The experimental methodology employs IR or UV spectroscopic measurement under carefully controlled isothermal conditions to determine resist film composition as a function of time. The acid-catalyzed deprotection reactions of two candidate deep-UV resist materials, poly(t-butoxy carbony-loxystyrene)(PTBOC) and poly(t-butyl methacrylate)(PTBMA), were characterized. We propose a model for the acidolysis reactions for both polymer systems and extract coefficients using a stochastic kinetics simulator. This model explicitly addresses the effects of photo-acid strength on the efficiency of the deprotection step. Excellent agreement between the model and experimental data is obtained. The derived rate coefficients are shown to be useful for quantitative prediction of the chemical kinetics of related resist systems. Mechanistic implications of the values of the derived rate coefficients are discussed. The influence of chemical kinetics on the resist's lithographic properties is examined.

The dissolution kinetics of a 3-component chemically amplified DUV positive resist (base resin; t-BOC protected polyhydroxystyrene, PAG; benzenesulfonic acid derivative, dissolution inhibitor; t-BOC protected bisphenol A;) was investigated under various conditions. Particularly, the effects of the dissolution inhibitor on the dissolution rate characteristics together with the effect of the t-BOC protection ratio of the base resin were studied. Moreover, in order to obtain ideal dissolution characteristics, a resist profile simulation analysis was carried out. The dissolution rate contrast as well as the slope N of log(dissolution rate)-log(exposure dose) plots increased with increasing inhibitor concentrations. However, a very high inhibitor concentration induced a severe standing wave effect and T-topping profile, resulting in the deterioration of resist performance. Therefore, it was discovered that inhibitor concentration has an optimum value in this resist system. These results are similar to those of t-BOC protection ratio in base resin. According to resist simulation, the slope N was closely related to resist performance, but the dissolution rate contrast was not. A slope value of more than 15 was necessary for 0.25 micrometers patterning (focus margin > 1.3 micrometers ). In addition, the acid diffusion length was one of the key factors: suitable diffusion length was essential for achieving a good resist profile; short diffusion length induces a severe standing wave profile and a long diffusion length deteriorates resolution capability. Based on the analysis of the dissolution characteristics and resist profile simulation, it was concluded that the optimization of the base resin structure and inhibitor concentration is effective for modifying the dissolution parameter. Moreover, it was also found that a steep slope (> 15), moderate dissolution contrast (approximately 10,000) and adequate acid diffusion length (approximately 35) can bring about ideal dissolution characteristics leading to 0.25 micrometers pattern formation.

For the achievement of the 0.25 micrometers design rule technology, the CD variations must not exceed +/- 25 nm; this has to be ensured by a high performance reproducible process. The resolution capability of DUV lithography at 248 nm has already been demonstrated. However, positive tone DUV materials and their associated processes are still under optimization. Among the various process steps to be optimized, the baking steps are of great importance. Taking into account the conclusions drawn on SB mechanisms in a previous work, the role of PEB has been studied in order to obtain better linewidth control and process reproducibility. For this study, the BASF ST2 resist has been chosen as a typical example of advanced DUV positive resists. The lithographic experiments have been performed in a 200 mm DUV lithographic cell, including an ASM-L 5500/90 DUV stepper and a MARK 8 TEL track. Two main conclusions can be drawn. Firstly, the experimental results obtained clearly demonstrate that the PEB temperature is directly correlated with the viscoelastic properties (Tg) of the resist material: two diffusion regimes, below and above Tg, can be observed. Secondly, the process latitude as well as CD reproducibility are increased for PEB temperatures below Tg.

Microbridge formation in a CAMN photoresist we have developed is dependent on the ratio of dose to print (DTP) to dose to gel (DTG) as well as resist contrast. Photoresists formulated with poly(p-hydroxystyrene) (PHS) have a very high tendency to form microbridges when developed in 2.38 wt% TMAH due to high contrast and high DTP/DTG ratio. When photoresists formulated from PHS were developed in 1.2 wt% TMAH contrast and DTP/DTG ratio were reduced resulting in microbridging being nearly eliminated. Using this observation we developed an I-line CAMN photoresist with PHS type thermal stability and high resolution capabilities which can be developed in industry standard 2.38 wt% TMAH.

Design criteria for the development of the high resolution photoresists comprising novolak resin and DNQ-PAC are proposed by studying the dissolution behavior of photoresists across film thickness. We propose a new analytical method for the dissolution behavior, with which the dissolution rate curves at surface, middle, and bottom parts in a photoresist film can be analyzed separately. From the experimental results obtained by using this new analytical method, we established the following design criteria: (1) To obtain a large separation DOF, the photoresist has to show a steep slope and a large contrast of dissolution curve at the bottom part in some practical exposure dose range of clear region. (2) A small difference of dissolution rate between the surface part and bottom part is necessary to obtain a large profile DOF. In order to adjust a dissolution behavior taking account of the new criteria, we examined the effects of photoresist components. It was found that some phenolic additives were very useful to control the dissolution behavior. The results of the spectroscopic study suggest that such a strong effect is caused by the interaction between phenolic additive and PAC or developer. A photoresist developed by adopting these design criteria for the dissolution behavior control shows wide DOF at 0.35 micrometers L&S with good pattern profile.

The mechanisms of the formation of microgroove and protuberance defects in novolac/diazonaphthoquinone resists were studied and found to be influenced by the resist composition, the degree of substrate silylation, and the developer composition. Low molecular chains in the novolac polymer and high PAC contents promote the formation of microgrooves and protuberances. A mechanism is proposed wherein short polymer chains migrate toward the substrate interface and PAC migrates away from the substrate during post-bake; this migration enhances the dissolution rate near the substrate, leading to an undercut. The possibility that the migration of developer along the resist/substrate interface occurs through percolative diffusion is explored. Developer-induced hydrolysis of trimethylsilyl groups from the silylated substrate is shown to be a contributory mechanism in the formation of microgrooves. Adding select surfactants to the developer is shown to reduce the rate of substrate desilylation and inhibit microgroove formation.

Novolak resins are the most complex and important polymers used in photoresists for microlithography. We have developed methods for fractionation of novolak resins based on supercritical fluid technology to afford polymers with molecular weights distributions (M_W/M_N) approaching 1.0. Properties (glass transition, dissolution, and lithographic) of monodisperse novolak resins demonstrate extremely exaggerated molecular weight effects. I- line resists formulated from these ultra-fractionated resins show extraordinarily diverse lithographic properties, ranging from low-to-high contrast, the absence or presence of microgrooving and residue, and photospeed and thermal properties that are highly controllable. Ultimately, a prototype resist formulation based on mixtures of fractions combining high resolution (0.35 microns) and fast photospeed (125 mJ/cm²) was demonstrated. New rules for the influence of novolak molecular weight on photoresist performance are presented.

The dissolution properties of nearly monodisperse fractions of metacresol novolac resin in aqueous potassium hydroxide solutions has been investigated. A relationship between the molecular weight of the fractions and dissolution rate was examined for a range of developer concentrations. Deliberate and calculated blending of the various fractions afforded an opportunity to investigate the fundamental relationship between molecular weight and dissolution characteristics over a range of developer concentrations.

This study evaluates the effect of dyes, including photosensitive dyes, on resist performance such as: swing curve reduction, resist dissolution rate, resolution, dose and focus latitude, scumming, etc. The paper demonstrates good correlation between modeling of the dyed resist performance and experimental results.

The influence of PAC structure and morphology on the surface induction in novolak based resist systems was investigated. Variation in surface induction for a given PAC is caused by changes in the morphology between the surface and the bulk of the resist film resulting from solvent depletion and is characteristic of the novolak. PAC structure, particularly its functionality [i.e., maximum amount of diazonaphthoqunione (DNQ) esterifiable OH], was found to greatly influence the amount of surface inhibition.

Interactions between diazonaphthoquinone (DNQ)-photoactive compounds (PACs) and phenolic resins with different degrees of ortho, ortho-bonding have been investigated using solid state nitrogen-15 nuclear magnetic resonance (NMR) and vibrational (infrared and Raman) spectroscopic techniques. A specifically nitrogen-15 labeled PAC was synthesized to facilitate solid state nitrogen-15 NMR experimentation, and to resolve ambiguities in vibrational spectra. Comparison of vibrational spectra of the ¹⁵N-labeled PAC and its natural abundance ¹⁴N analog showed conclusively that Fermi resonance as well as hydrogen-boding resin-PAC interactions influence changes in the out-of-phase diazo stretching region near 2100 cm^-1. Solid state nitrogen-15 NMR of the ¹⁵N-labeled PAC in poly(p-hydroxystyrene), in a m-cresol 3,5-xylenol novolak, and in a mainly m,p- cresol novolak showed the binding situation in the resins to be diffuse, but quite similar. Although the three resins examined are lithographically very different, the observed nitrogen- 15 shifts were small compared to the broadening of the resonances, and did not show major differences due to ortho, ortho-bonding effects.

In the original percolation model of novolak resists, dissolution inhibition was through to occur through the blocking of hydrophilic (phenolic) percolation sites by the inhibitor. Closer analysis revealed that mere site blocking cannot account for the size of the inhibition effect observed in practical systems; a more profound reorganization of resin structure is needed. In this communication it is suggested that hydrogen bonding between OH-groups leads to the formation of phenolic clusters in concentrated novolak solutions, and these clusters are preserved in the solid films. The introduction of the strong acceptor groups of inhibitors reinforces the cohesion in the clusters and concentrates the OH-groups. In this way the inhibitor creates a deficit of hydrophilic sites in other areas of the percolation field, thereby lowering the dissolution rate.

An ArF single layer resist based on alicyclic polymer has been developed. Our work centers on improving the solubility of the base polymer in an aqueous base solution. The solubility is the most significant point in using alicyclic polymer. A suitable developer is obtained by adding isopropyl alcohol to the standard TMAH solution with a proper mixing ratio. This mixture greatly enhances the dissolution rate and allows the alicyclic polymer to act as a highly sensitive resist. Over-top coating has also been used to improve the pattern profile. We applied these processes to a resist based on a copolymer of 3-oxocyclohexyl methacrylate and adamantyl methacrylate. The results of ArF lithography are encouraging. There is a high sensitivity of about 10 mJ/cm², and a high resolution of 0.17 micrometers lines and spaces is achieved. This shows that by enhancing the solubility the lithographic characteristics of the resist based on the alicyclic polymer are effectively improved.

A new positive chemically amplified resist which consists of a novel photoacid generator NEALS (new alkylsulfonium salt) and methacrylate terpolymer with tricyclodecanyl group (TCDA) has been developed. NEALS shows good thermal stability up to 151 degree(s)C, high transparency and high acid generation efficiency for an ArF excimer laser exposure. A new base polymer with TCDA groups demonstrated high transparency (69.3%/micrometers ), high thermal stability up to 141 degree(s)C, a good dry-etching resistance and high solubility for an aqueous base (tetramethylammonium hydroxide) developer. A 0.20 micrometers lines and spaces pattern has been resolved using an ArF excimer laser exposure system (NA equals 0.55).

The VUV-absorption spectrum of aromatic compounds can be red-shifted toward longer wavelengths to make the window of absorption align with 193 nm by extending the conjugation length of the double bonds. Based on this observation, the new concept of absorption band shifting is proposed as a way to increase the transparency of resist components for 193 nm ArF excimer laser exposure. A chemically amplified single-layer ArF excimer laser resist consisting of naphthalene-containing photoacid generator, a dissolution inhibitor, and base polymer has been newly developed. Using this resist, a 0.17 micrometers line/space pattern with a vertical resist profile was resolved by a prototype 0.55 NA projection lens for ArF excimer laser exposure, and a resolution limit of 0.16 micrometers was achieved.

We have optimized a positive-tone silylation process using polyvinylphenol resist and dimethylsilyldimethylamine as the silylating agent. Imaging quality and process latitude have been evaluated at 193 nm using a 0.5-NA SVGL prototype exposure system. A low- temperature dry etch process was developed that produces vertical resist profiles resulting in large exposure and defocus latitudes, linearity of gratings down to 0.175 micrometers , and resolution of 0.15-micrometers gratings and isolated lines.

This paper describes the silylation properties and the lithographic performance of ArF (193 nm) surface imaging process with bis(dimethylamino)methylsilane [B(DMA)MS]. The silicon concentration of silylated region with B(DMA)MS in liquid phase is much higher (2 times) than that for the conventional silylation with dimethylsilyldimethylamine (DMSDMA) in vapor phase. The excellent resolution of 0.12 micrometers L/S and practical DOF (1.0 micrometers in a range for 0.18 micrometers L/S) have been achieved using ArF exposure system with a conventional binary mask under a normal illumination. Further, the resolution of 0.088 micrometers has been obtained with a Levenson-type phase shifting mask.

The problem of deep ultraviolet (DUV) resist footing on titanium nitride (TiN) substrates has been studied using three different photoresists and TiN films of various stoichiometries. Multiple characterization techniques have been used to characterize the TiN films including auger electron spectroscopy, atomic force microscopy, Rutherford backscattering and reflectivity measurements. Resist footing was compared for process delay experiments, softbake temperature changes, and pretreatments to the TiN substrates. Based on these results and information previously published, it is concluded that detrimental surface and interface states exist on the TiN substrate which are principally reasonable for the footing.

We fabricated resist patterns on a silicon nitride (Si₃N₄) substrate using a KrF excimer laser stepper and a positive chemically amplified resist. The cross-sectional views of the resist patterns revealed `footing,' so we carried out experiments to find the cause of this. We investigated the relationship between the resist profile and the Si₃N₄ film thickness, or the storage time of the substrate. We also tried to improve the footing profile with some substrate treatments. As a result, we revealed that substrate treatment using oxygen plasma is extremely effective in diminishing footing. Therefore, the effects of substrate treatment were investigated using electron spectroscopy for chemical analysis (ESCA) and gas-chromatograph mass-spectrometry (GC-MS). From these results, we studied the cause of footing.

Incorporation of organic salt additives consisting of an organic acid and organic base improves the resist stability. The sensitivity of a t-BOC resist without the salt decreased to 1/4 after standing for one hour after deep-UV exposure. Typical T-top patterns were obtained on this resist by a KrF excimer laser stepper (NA equals 0.45), and a half-micron resolution was barely obtained. On the other hand, a t-BOC resist, with an organic salt, consisting of p- toluenesulfonic acid and dicyclohexylamine (PTS/DCHA), showed no change in sensitivity after one hour. The resist with the PTS/DCHA achieved a 0.3-micrometers resolution line-and- space pattern without environmental control or a protective topcoat.

The effect of amine additives in chemical amplification resists is discussed. Phenolic amines such as 4-aminophenol and 2-(4-aminophenyl)-2-(4-hydroxyphenyl) propane were investigated as model compounds from the viewpoint of sensitivity, diffusion and resolution. Equal molar amounts of acid and amine deactivated at the very beginning of post-exposure bake, and could not participate in decomposing the inhibitor as a catalyst. Only the acid which survived from the deactivation diffuses in the resist, decomposing the inhibitors from the middle to late stage of PEB. The basic additives reduce the diffusion range of the acid, especially for long-range diffusion, resulting in higher contrast at the interfaces between the exposed and unexposed areas. In addition, the amine concentration required is found to be less than the concentration which causes the resist sensitivity to start decreasing.

The cost of expendable chemicals in the resist process is increasing and with this the economic impetus to conserve usage. The volume of liquid resist dispensed (shot size) determines the consumption rate and disposal volumes of liquid resist. The choice of resist solvent can influence the shot volume. Three formulation factors influence the shot size: (1) the surface tension of the resist and the interfacial energy of the coating surface, (2) the viscosity of the resist formulation, and (3) the evaporation rate of the solvent. The suitable resist formulation and subsequent solvent choice should be of the lowest surface tension and lowest viscosity and be balanced by an evaporation rate which allows a minimum shot volume to be spread on the surface without significant solvent loss. Of all the solvents examined, ethyl 3-ethoxy propionate (EEP) gave the lowest shot size relative to the old resist solvent standard of 2- ethoxy ethyl acetate (ECA).

A track-mounted, in-situ dissolution rate monitor (DRM) is used to study the impact of exposure variations on g-line, i-line and DUV positive chemically amplified resists. In the i- line case, a comparative study between constant spray and a spray/puddle process was undertaken. In all cases, modeling parameters were extracted from the track-mounted DRM data and entered into 2D and 3D simulators using an experimentally generated development rate vs. PAC concentration table. Simulated profiles were compared with actual SEM cross- sections. Whenever possible, DRM traces were used to analyze standing waves, surface inhibition effects and quantify resist performance by calculating contrast. For the g-line case, the impact of PEB temperature upon the standing wave effects, as quantified by the in-situ DRM data, was studied.

A method for thick film photoresist resolution enhancement was investigated which involves treatment of photoresist films with solutions of cationic surfactants prior to development. By utilizing a surfactant surface treatment process, resist contrast is improved and better image resolution can be achieved. The effectiveness of the surfactant treatment is dependent on a number of factors including structure and concentration of surfactant, pH of the solution, mode and duration of treatment, and effect of other additives. The mechanism of the process has been investigated and the results suggest that the critical factors are the attachment of the surfactant to the top surface of the resist and the detachment of surfactant depending on film acid concentration.

The glass transition temperature (Tg) is related to the two main concerns encountered with chemically amplified resists, namely delay-time and contamination effects. However, Tg is often convoluted with the deprotection reaction and cannot be determined using conventional thermal analysis techniques (e.g., DSC). This problem can nevertheless be circumvented using the wafer curvature measurement technique (WCM). Thus, DSC and WCM appear to be complementary techniques for the complete thermal characterization of DUV resists. Each technique provides one of the two temperature boundaries of an optimum process window. Various DUV positive resists, representative of different cases, are investigated.

Supercritical fluid (SCF) technology is investigated as a dry technique for photoresist developing. Because of their unique combination of gaseous and liquid-like properties, these fluids offer comparative or improved efficiencies over liquid developers and, particularly carbon dioxide, would have tremendous beneficial impact on the environment and on worker safety. Additionally, SCF technology offers the potential for processing advanced resist systems which are currently under investigation as well as those that may have been abandoned due to problems associated with conventional developers. An investigation of various negative and positive photoresist systems is ongoing. Initially, supercritical carbon dioxide (SC CO₂) as a developer for polysilane resists was explored because the exposure products, polysiloxanes, are generally soluble in this fluid. These initial studies demonstrated the viability of the SCF technique with both single layer and bilayer systems. Subsequently, the investigation focused on using SC CO₂ to produce negative images with polymers that would typically be considered positive resists. Polymers such as styrenes and methacrylates were chemically modified by fluorination and/or copolymerization to render them soluble in SC CO₂. Siloxane copolymers and siloxane-modified methacrylates were examined as well. The preliminary findings reported here indicate the feasibility of using SC CO₂ for photoresist developing.

We report on two different all-dry resist schemes for 193-nm lithography, one negative tone and one positive tone. Our negative tone resist is an extension of our initial work on all-dry photoresists. This scheme employs a bilayer in which the imaging layer is formed by plasma enhanced chemical vapor deposition (PECVD) from tetramethylsilane (TMS) and deposited onto PECVD carbon-based planarizing layers. Figure 1 shows SEMs of dark field and light field octagons patterned in projection on Lincoln Laboratory's 0.5-NA 193-nm Micrascan system. These 0.225-micrometers and 0.200-micrometers line and space features were obtained at a dose of approximately 58 mJ/cm². Dry development of the exposed resist was accomplished using Cl₂ chemistry in a helicon high-ion-density etching tool. Pattern transfer was performed in the helicon tool with oxygen-based chemistries. Recently, we have also developed an all-dry positive-tone silylation photoresist. This photoresist is a PECVD carbon-based polymer which is crosslinked by 193-nm exposure, enabling selective silylation similar to that initially reported by Hartney et al., with spin-applied polymers. In those polymers, for example polyvinylphenol, the silylation site concentration is fixed by the hydroxyl groups on the polymer precursors, thus limiting the silicon uptake per unit volume. With PECVD polymers, the total concentration of silylation sites and their depth can be tailored by varying plasma species as a function of time during the deposition. This affords the possibility of greater silicon uptake per unit volume and better depth control of the silylation profile. Figure 2 shows a SEM of 0.5-micrometers features patterned in plasma deposited silylation resist.

Disilanes are used as silylating reagents for near-surface imaging with deep-UV (248 nm) and EUV (13.5 nm) lithography. A relatively thin imaging layer of a photo-cross-linking resist is spun over a thicker layer of hard-baked resist that functions as a planarizing layer and antireflective coating. Photoinduced acid generation and subsequent heating crosslinks render exposed areas impermeable to an aminodisilane that reacts with the unexposed regions. Subsequent silylation and reactive ion etching affords a positive-tone image. The use of disilanes introduces a higher concentration of silicon into the polymer than is possible with silicon reagents that incorporate only one silicon atom per reactive site. The higher silicon content in the silylated polymer increases etching selectivity between exposed and unexposed regions and thereby increases the contrast. The synthesis and reactivity of `smaller' disilanes, N,N-dimethylamino-1,2-dimethyldisilane, (DMADMDS), and N,N-diethylamino-1,2- dimethyldisilane also are described. Additional silylation improvements that minimize flow during silylation also are discussed including the addition of bifunctional disilanes to the monofunctional DMAPMDS. This causes the crosslinking to occur during silylation which minimizes flow. We have resolved high aspect ratio, very high quality 0.20 micrometers line and space patterns at 248 nm with a stepper having a numerical aperture (NA) equals 0.53 and have resolved <EQ 0.15 micrometers line and spaces at 13.5 nm.

We have developed a unique chemically amplified negative-type resist composed of poly(t- butoxysiloxane) and photoacid generator, the GPR (glass precursor resist), which can be converted into inorganic silicate glass. Poly(t-butoxysiloxane) is a specially designed SiO₂ precursor masked by t-butoxyl groups. To confirm the mechanism of condensation to SiO₂ an intermediate trapping experiment was carried out. GPR exposed at a low dose is fully developed by alkaline solution to give a positive tone; on the other hand, high-dosage GPR gives negative tone by means of organic solvent development. They correspond to the formation of poly(hydroxysilane) and SiO₂ respectively. Deprotection proceeds readily even at low temperature, whereas condensation requires thermal assistance. Decreasing the content of t-butoxyl groups enhances the sensitivities to electron beam exposure. Precursor polymers with several degrees of branching were synthesized. The high-branching polymer provides high sensitivity because its network grows abruptly with condensation. GPR has high resolution and high sensitivity. The fine patterns can be resolved with the practical dose latitude using an electron beam direct-writing system.

An efficient synthetic route for the synthesis of t-Boc protected poly (p-hydroxy styrene-alt- carbon monoxide) utilizing a Pd(II) catalyst is reported. The polymer was deprotected by thermolysis or acidolysis of the tert-butoxycarbonyl protecting group to give the p- hydroxystyrene/CO copolymer. This material should lend itself well to lithographic applications because of our ability to control the molar mass of the material with a narrow molar mass distribution (which should lend to high development efficiencies). Preliminary lithographic evaluation of the copolymer is reported herein.

Thin films composed of the copolymer of glycidyl methacrylate-ethyl acrylate and a cobalt(III)-am(m)ine tetraphenylborate salt undergo crosslinking upon deep-UV irradiation and subsequent heating. The mechanism of this process involves the efficient photoredox decomposition of the cobalt salt with the release of multiequivalents of Lewis base. In a thermally activated step, the base then crosslinks the copolymer via nucleophilic attack on the epoxide rings. Near-UV irradiation of Pt(acac)₂ (acac is the acetylacetonate anion) and Ru(Cp)₂ (Cp is the cyclopentadienide anion) dissolved in ethyl (alpha) -cyanoacrylate initiates rapid anionic polymerization of the acrylate monomer. The active initiating species is acac in the former system, while the radical anion of the monomer is a likely candidate in the latter system.

Electron-beam (e-beam) lithography is one technique that offers subquarter micron resolution. Advancements in tool design and resist materials make it possible to print nanometer structures. In this paper, we focus on the process optimization of an e-beam positive tone chemically amplified resist. The resist system is based on protected polyhydroxystyrene and an acid generator. The exposures were performed on an e-beam system equipped with a variable- shape spot operating at 50 keV. The process was examined with a statistical experimental design. The process parameters considered in this evaluation are softbake time, softbake temperature, developer concentration, and developer time. The lithographic responses studied are: linewidth variation with dose, contrast (gamma), unexposed film loss, profile angle, bulk sensitivity, and writing bias. A central composite design with 4 independent variables and 25 experimental runs was employed. Statistical analysis of data yielded a significance level of the different process parameters and their interactions. Also, regression analysis fit each response in terms of the process parameters. These relationships were used to define process parameters, yielding the desired responses. The optimized process yielded subquarter micron images in 0.8 micrometers resist film with nearly vertical profiles. The resist exhibited a high contrast (> 50) and a large develop latitude. The resist resolution and linearity extended to below 250 nm for the nested features. In addition, the resist exhibits excellent environmental stability, withstanding long delays (> 24 hr) between different process steps. A detailed discussion of the resist performance and process latitude is presented. This material performed well in this application with 0.25 micrometers design rules and has the potential of performing well at smaller linewidths.

This paper examines the effects of latent acid formation and acid diffusion into dark regions of images in determining resist behavior during post exposure bake. Results of two new experiments, consisting of diffusion from an exposed into an unexposed resist film, the deliberate introduction of flare in patterned exposures, and re-examination of FTIR measurements of flood and patterned exposed samples show that a sharp diffusion front is the dominant mechanism determining resist image formation with post exposure bake times, and similar front velocities of 33 nm/min, 35 nm/min, and 31 nm/min were obtained for each experiment, respectively. In addition, quantitative modeling of toploss in unexposed samples due to acid diffusion from a top-to-top contact bake with an exposed sample show that Fickean diffusion cannot account for the experimental observations and suggest deprotection dependent diffusion fronts in positive DUV resists are important in modeling lithographic performance.

Infrared spectroscopy is a powerful tool for studying chemical reactions which take place in photoresist films. It provides information about functional groups present in the material, is nondestructive to the sample, can be used to monitor reactions in real-time, and can be used as a monitor for real-time process control. Transmission spectroscopy has been used for determination of rate constants for the post exposure bake (PEB) step in both positive and negative chemically amplified x-ray resists, but in transmission the IR beam must pass through the wafer in order to reach the detector. Reflection spectroscopy is more suitable for on-line monitoring because all the optics are located on the same side of the wafer; however, traditional reflection spectra of thin films contain interference fringes which make quantitative analysis difficult. We have developed a method, called mirror-backed infrared reflection- absorption spectroscopy (MBIRRAS), that eliminates the problem of interference fringes in reflection spectra. The method is capable of providing quantitative information about the concentration of functional groups in resist films and produced a linear calibration curve for a commercial crosslinker (hexamethoxymethylmelamine) in a Novolac matrix over a 20% by weight range of concentrations. MBIRRAS was also used to monitor the height of an IR peak corresponding to formation of crosslinks in Shipley negative-tone resist SAL 605 at various processing conditions. The results of this experiment show that PEB time and temperature, prebake time and temperature, and delay between exposure and PEB, all have statistically significant effects on the extent of crosslinking during PEB. In order to explain the observed effect of prebake conditions on the amount of crosslinking during the PEB step and to define the acceptable range of prebaking conditions for resist/wafer adhesion studies, another experiment was performed to demonstrate that thermally generated crosslinking occurred during an additional prebake step without any exposure to x rays. In fact, an additional prebake for 60 seconds at 110 degree(s)C can generate the same number of crosslinks as an x- ray dose of 4 mJ/cm², while baking for 60 minutes at 110 degree(s)C is equivalent to an x-ray dose that is greater than the resist sensitivity (42 mJ/cm²). Noticeable changes in crosslink concentration were detected at 30 seconds. This suggests that crosslinking occurs during the normal prebake step and explains the dependence of linewidth on prebake time. Finally, a correlation was demonstrated between printed linewidth and MBIRRAS peak height corresponding to crosslink formation in SAL 605. This correlation, along with the demonstrated precision of the MBIRRAS method (3 sigma <EQ 3%), suggests that MBIRRAS can be used as an on-line monitor for adaptive control of the processing of SAL 605, thus reducing critical dimension (CD) variation from wafer to wafer for 0.25 micrometers lithography.2438

Improvements in modeling of chemically amplified resists are necessary to increase the capability of doing `What if' simulations and to help interpret experimental data. One method to minimize the difference between modeled and experimental results is to use an underlying database of experimentally determined bulk dissolution rates as the source of the input parameters for the imaging engine of the lithographic model. In this paper, a R(E,z) to R(m,z) converter is discussed. The converter takes into account the amplification factor, kinetic effects and acid loss. The underlying data consist of a positive acting chemically amplified resist, XP-9402, that was processed using various post exposure bake conditions. With conversion to R(m,z), the energy of activation and Arrhenius coefficient for both the deprotection reaction and acid loss, the rate of photoacid formation, C, the chemical amplification factor for a given thermal dose and the ratio of deprotection rate constant to acid loss rate constant can be determined. These parameters are then used in the lithographic simulator PROLITH/2 version 4.1a. Results are used to understand lithographic results for photoresist that had been processed at different temperatures.

Chemical changes within a resist material (for example, resulting from the exposure and subsequent chemical reactions during post exposure bake) will in general, result in a change in diffusivity of components within that material. In the case of positive chemically amplified resists, the diffusivity of the photo-generated acid changes as a function of the extent of polymer deprotection. The deprotection reaction leads to the generation of small reaction product molecules, some of which are volatile. The liberation of these reaction products causes an increase in the free volume and changes in the chemical behavior in the exposed area. These changes, primarily the increase in free volume, results in an increase in the diffusivity of the acid. Low exposure areas have lower acid diffusivity, leading to a lower efficiency of reaction. This results in a contrast enhancement of the latent image due to the concentration dependent diffusivity of the acid. In this paper, a concentration dependent diffusivity expression is incorporated into a lithography simulator to explore these effects on lithographic performance. Using the assumption of free volume, suitable expressions for the diffusivity are examined and compared to experimentally measured values. The experimental work consists of XP-9402 positive acting, chemically amplified resist that was imaged using different thermal doses.

In this paper we present a technique utilizing intense UV exposure to alter the chemical properties of an organic antireflective material such that dry etch performance is improved. By monitoring the ARC thickness before and after UV exposure, it can be demonstrated that prolonged UV exposure coupled with a specific range of substrate temperatures can result in a dramatic reduction in ARC thickness. Similar measurements taken before and after ARC etch reveal an improvement in etch rate in ARC samples previously subjected to intense UV exposure. Changes in ARC structure and etch performance are presented as functions of UV wavelengths, substrate temperature, and exposure time.

During implementation of a chemically amplified I-line negative resist (INR) into the eight- inch-wafer manufacturing line at IBM's facility in Essex Junction, Vermont we found that the resist profiles were being undercut during development on silicon-nitride surfaces. The undercut was attributed to a `poisoning' of the photoacid generated in the resist during exposure by the nucleophilic characteristics of the silicon-nitride surface. A second-generation negative resist has since been formulated by IBM, which greatly reduces these undercut effects but does not eliminate them. This newer version of INR is referred to as INR2. To further understand the effects of silicon nitride on the I-line negative-resist profiles, we used Prolith/2 (v3.05)³ to model the underlying stack and evaluate the performance of INR2. Silicon monitors with oxide and different nitride thicknesses were patterned with INR2 using 4-Mb DRAM manufacturing ion-implant block masks and associated photo processing. The results indicated that the undercut observed by this chemically amplified negative resist on silicon nitride was not only chemical in nature, but related to the optical properties of the nitride substrate. Simulation results obtained using Prolith/2 are give and compared with resist profiles obtained from wafers processed with INR2; the accuracy of the Prolith/2 model to predict slope profiles for INR2 is also discussed.

LOCOS processes use nitride layers in the range of 1000 - 2000 angstrom for oxidation barriers. The thicknesses are optimized for the stiffness needed to control the `bird's beak' and for stress which effects the subsequent gate oxide quality. We have found that CD control is generally poor on the active mask and that the resist profile is prone to `footing.' Simulation and experiments have shown that resist footing is dependent on the exposure dose at the resist/nitride interface. This, in turn, depends on the nitride thickness. This resist foot is not reproducible because of normal variations in the nitride thickness and it introduces CD variation. In addition the foot may produce problems with the nitride etch and contributes to the resist to final etched CD bias. Here we report on studies of the effect of nitride thickness on active masking. Optimizing the LOCOS film stack results in improved resist profiles and CD control.

We considered that contaminant control could best be addressed from the processing side. A KrF excimer stepper and a track system were physically integrated and equipped with chemical filter units. The atmosphere where wafers were transported from exposure to postexposure bake (PEB) was enclosed. The measured ammonia concentration was always less than 0.5 (mu) g/m³ everywhere within the enclosed atmosphere. We patterned resists with an ammonia concentration of 0.2 (mu) g/m³. They showed no T-tops and the deviation rates of line width against PEB were within the range of 0.56 to 0.80 nm/min for line and space patterns between 0.30 to 0.35 micrometers . These low deviation rates were considered to be acceptable for manufacturing purposes.

A novel simulator using the Monte-Carlo method, which simulates molecular-like movements and reactions in chemically amplified resist systems, has been developed in order to clarify the mechanism of amine additive. The simulation program simulates diffusion phenomena with random-walked acids and amine molecules, and reactions of deactivation (neutralization) and inhibitor cleavage in every movement of the molecules. It was found that the amine in the exposed area was rapidly deactivated, and the concentration profile of the remaining amine was rapidly changed to an inversely shaped profile of that of the acid. This means that the remaining amine prevents diffusion of acids outside the exposed area by functioning as a barrier during almost the whole period of post-exposure bake (PEB). These concentration profiles lead to an enhancement of stability of pattern sizes and reduction of edge roughness of the pattern. Environmental stability was also calculated, and amine additive was also found to prevent contamination from the environment in the initial period of the PEB.

Airborne contamination in chemically amplified resist films was evaluated by monitoring deprotection reaction using an IR spectrometer. T-BOC protected (20, 50 and 100 mol%) m- and p-cresol novolak resins and triphenyltriflate were used as a matrix polymer and a photoacid generator (PAG), respectively. Three levels of clean environments whose base contaminant (NH₄⁺) concentrations were 50 - 80, 5 - 10 and less than 1 ppb, were prepared for the experiments. In order to determine the delay effects precisely, other processes including baking, exposure, and storage during process intervals were conducted in a base-free environment. The PEB delay effect as well as radiation sensitivity without delay depended on the t-BOC content, and the best results were obtained at 50% and 25 - 50% t- BOC contents in m-cresol novolak and p-cresol novolak systems, respectively.

Chemically amplified DUV photoresists have a sensitivity to certain airborne chemical contaminants. Processing these resists requires control of the environment within the process tooling. This study explores the contamination threshold levels to meet minimum established lithography criteria as well as the effectiveness of the equipment in providing such an environment. A DUV lithography cluster consisting of a SVGL MICRASCAN-II linked to an SVG Series 90 track are the platform for this study. Both the stepper and track utilize Donaldson stacked carbon filters, each is sized to design air flow rate. Measurement and control of two (2) known contaminants, n-methyl2-pyrolidone (NMP) and ammonia (NH₃), are investigated in the stepper chamber, the track chamber, and the surrounding environment. Gas chromatography (GC) and ion mobility spectrometry (IMS) are used to measure NMP and NH₃ levels, respectively, and provide the basis for the data presented. Criteria for resist profile, critical dimension (CD) and post exposure delay (PED) in a single layer resist system i.e., without resist top-coat (RTC), were set such that contamination effects are of no consequence. Contaminant threshold levels to meet this lithography criteria have been determined. Data that underscores the trade-off between having a single purpose filter or a dual purpose filter design that removes both NMP, an organic, and NH₃, an inorganic, are analyzed. The effectiveness (efficiency and life time) of this dual purpose filter in reducing the contaminants to low enough levels for maintaining lithography acuity, as established by the criteria, are summarized. A cost analysis highlighting the economic trade-off of using either RTC in a non-filtered environment or providing a conducive filtered environment for single layer resist processing are analyzed. Conclusions based upon data from ambient conditions, both inside and outside the lithography cluster and the performance of the equipment are made. Recommendations are made on what constitutes a `clean' environment and when the use of RTC may become necessary.

Recent advances in computer hardware and software have provided the capability to simulate complex mixtures of compounds on a molecular level. These tools provide the potential for exploration of resist chemistry and mechanism on a molecular level with visual feedback. However, there are still limitations of software and hardware and time which require simplification of the simulations. Thus extensive methods development will be required to be able to produce simulations useful to predict resist properties. This paper discusses the basics of photoresist molecular simulation techniques, limitations of the current techniques, and the potential for using molecular simulations to explore various aspects of photoresist performance, particularly novolac-novolac and novolac-diazonaphthoquinone photoactive compound (DNQ PAC) hydrogen bonding.

Recent advances in computer hardware and software have provided the capability to simulate complex mixtures of compounds on a molecular level. These tools provide the potential for exploration of resist chemistry and mechanism on a molecular level with visual feedback. Molecular simulations of a DNQ novolac resist were used in an unsuccessful attempt to visualize and study PAC diffusion during PEB. Simulation of PAC molecules allowed the calculation of the Connolly surface and hence the volume of space occupied by the PAC molecule. A reasonable correlation of the Connolly volume with the decrease in standing waves after PEB as measured from DRM curves was observed. This supports a PAC diffusion mechanism for PEB reduction of standing waves.

The interesting phenomenon of CD undersizing has been predicted by simulations to occur in high contrast/high exposure margin resists imaged with high numerical aperture steppers. Under these conditions the out-of-focus images of dense arrays, which are 1:1 at best focus, print too small. The phenomenon is particularly prevalent at geometries which are larger than those near the resolution limit of the imaging tool, and is most apparent when the resist surface is moved away from the focal plane. In this study CD undersizing is demonstrated experimentally and explored in more detail using computer simulation for both actual state-of- the-art i-line resist/imaging systems, and for hypothetical resist systems having monotonically increasing contrast. The origin of the effect is due to the characteristics of the aerial image intensity profile of partially coherent illumination. In particular, the relative intensity at the mask edge may increase with defocus depending upon the spatial frequency (linewidth), partial coherence, and numerical aperture of the imaging system. This results in an `over-exposure' condition and hence undersizing of the out-of-focus images may occur. The same aerial image characteristics give rise to the familiar `pipe-bowl' effect observed in the (zero defocus) mask- linearity plots, which are frequently used to characterize positive resists. The magnitude of undersizing decreases with increase in partial coherence, increases with resist contrast and may lead to retrograde profiles.

Changes in phenolic-formaldehyde resin properties are described in terms of thermal exposure. At high temperature, resin molecular weight, dissolution properties and chemical composition change depending on the presence or absence of monomers. Without monomer in the resin melt at 220 degree(s)C, resin molecular weight increases with a corresponding decrease in dissolution rate. In the presence of monomer, molecular weight generally decreases. Dissolution rate may fluctuate depending on the monomer mixture. Three,five- Xylenol and 2,3,5-trimethylphenol co-monomers induced the most extreme changes in resin properties with thermal treatment. Resin degradation-recombination processes suggest a classical Friedel-Craft rearrangement mechanism.

As critical dimensions become smaller, a greater demand is being placed on existing i-line lithographic capability to support 0.35 micrometers technology. One method that is gaining wider acceptance is the use of a top side anti reflective coating (TARC). The effect of the TARC is to reduce the interference effects occurring in the film stack so that critical dimension (CD) variation as a result of topography is minimized. Unfortunately, the TARC provides no improvement with other lithographic responses that define the process window of a resist. Another approach is to use a contrast enhancement material (CEM). It is well known that a CEM can improve the depth of focus and resolution of a given resist system, and it is suspected that it may also possess some of the interference reduction properties of conventional TARCs. The purpose of this work is to investigate how effective the CEM acts as a TARC, and to determine any additional lithographic improvements which will increase the overall 0.35 micrometers process window. Process optimization of the CEM and TARC revealed that similar processing schemes could be used for both materials, but that it was necessary to remove the CEM (w/ a water rinse) prior to post exposure bake (PEB). The bulk photospeed swing ratio of the SPR3000 alone, was compared to SPR3000/Aquatar and SPR3000/CEM. Results showed that the Aquatar reduced the Eo swing ratio by 75%, while the CEM reduced the Eo swing ratio by about 55%. Similar improvements were seen with 0.35 micrometers CD swing ratio data. Exposure latitude and focus latitude (0.35 micrometers lines/spaces) data was generated using the same resist/enhancement schemes mentioned above at thicknesses corresponding to an Emax and Emin. Results of the lithography at each thickness were overlaid to determine the process window. Results showed the Aquatar and CEM processes to provide improved 0.35 micrometers windows, and that using a contrast enhancement material as a TARC is another alternative which can be used to increase the capability of commercially available i-line resists.

This paper investigates the dielectric properties and chemical changes occurring in electron beam cured photoresist and how they compare with photoresist cured with standard thermal bake. The material used in the investigation is AZ P4620, a positive tone photoresist based on diazonapthoquinone (DNQ)/novolak chemistry and formulated mostly for thick film applications. The photoresist was spun on silicon wafers and exposed at different doses using an electron beam curing system. The dielectric properties and chemical changes of the exposed films were then evaluated and compared with photoresist films cured with a standard thermal cure. The dielectric properties that were evaluated were dielectric constant and breakdown voltage. The chemical changes were analyzed by FT-IR. For the electron beam cured photoresist, preliminary results indicate that the photoactive compound undergoes both decomposition and crosslinking during the process. The dielectric properties as well as the chemical changes as a function of dose are discussed.

The use of i-line photolithography is finding increased importance in generating today's advanced semiconductor devices. The requirements in this area have led to the recent development of wide field i-line steppers whose large field sizes permit higher device throughput. The introductions of these wide field i-line steppers generate additional demands on the photoresist used in the manufacturing process. This paper describes the development of an advanced i-line photoresist for use in high-throughput applications. The requirements of this photoresist are high photospeed of the order of 75 mJ/cm² to achieve targeted throughput requirements at low lamp power densities, high resolution of approximately 0.80 micrometers at NA equals 0.24 to satisfy device critical dimension requirements, and high resistance to thermal flow to permit further processing stages. The photoresist's formulation and processing were optimized to produce the desired performance characteristics. Exposure, focus latitude, photosensitivity, and resistance to thermal flow were determined and correlated with resin dissolution characteristics, relative photosensitizer concentration, softbake and post exposure bake temperatures.

Iodine containing diazoquinone photoactive compounds (PAC) were synthesized and formulated with novolak and other resins in an effort to develop a positive photoresist for the synchrotron beam line at IBM's Advanced Lithography Facility. The studies focused on the effect of synchrotron radiation on the PACs themselves and in various halogenated resins. These materials were tested by exposing the resist materials to various doses of radiation and then measuring the loss of diazo from the PAC. An enhanced sensitivity x-ray (ESX) photoresist system was developed by combining an iodinated PAC with a novolak resin. ESX was compared to a conventional DQ/novolak photoresist system TNS. ESX was able to print at approximately half the dose needed for TNS. Features as small as 175 nm resolved. These set of experiments demonstrate the potential of significantly improving the photospeed of DQ/novolak photoresist system by utilizing a more x-ray efficient PAC.

Our approach to the design of positive, single layer resists for 193 nm lithography is discussed. Phenolic resins, the archetype in positive photoresist materials, cannot be used at this wavelength due to optical opacity. Methacrylate polymers combine the required optical transparency at 193 nm with easily tailored properties, however. The methacrylate polymer materials used in our 193 nm resists are completely different from phenolics used in traditional (248 nm) chemically amplified resists but the imaging chemistry is very similar. With a design based on methacrylate terpolymers, we have recently developed a high resolution positive resist for 193 nm lithography with excellent imaging at both 193 and 248 nm. Our recent work has centered on gaining further insight into methacrylate polymer structure/property relationships, improving the imaging performance and finally increasing the etch resistance. Towards that end, we have developed a class of dissolution inhibitors for 193 nm resists that are combined with methacrylate polymers to provide 3-component resists. A family of B- steroid dissolution inhibitors that also increase etch resistance is described. Imaging and etch performance of four versions of our resist are disclosed. These methacrylate resists show resolution capability below 0.25 micron, etch rates 20% higher than novolak resins, good environmental stability in contrast to traditional DUV resists and dual wavelength (193/248) imaging.

There is increasing interest in chemically amplified (CA) single-layer photoresist for 193 nm excimer laser lithography as a route to sub-quarter micron imaging. A quantitative understanding of the factors that limit the ultimate resolution of CA resists requires a detailed knowledge of both the kinetics of the acid-catalyzed chemical reaction and the diffusion properties of the photogenerated acid. Information of this type is key to the accurate modeling of all CA resists regardless of exposure wavelength. We have investigated the exposure, thermal processing and dissolution behavior of a methacrylate terpolymer-based 193 nm resist. The chemical reactions occurring during post-exposure bake were monitored by FTIR microscopy over a range of PEB temperatures and exposure doses. Using the FTIR data and dissolution contrast curves, parameters for a model of the exposure, the post-exposure bake and the development were extracted. The model was implemented in the SAMPLE lithography simulation tool to predict resist profiles and process latitudes of methacrylate resists on a 193 nm step and scan tool. Excellent agreement between the simulated photoresist profiles and SEM cross-sections was obtained.

Silicon dioxide is the primary dielectric fabric of silicon integrated circuits, and the need to pattern it accounts for a large percentage of all photolithographic operations. As shrinking device dimensions place extreme demands on both lithography and etching, patterned oxide films are finding yet additional applications as intermediate `hard masks.' For example, polysilicon gate and metal layers may be etched with greater selectivity and linewidth control through a thin patterned oxide mask, rather than through a thicker photoresist layer (which is used to pattern the oxide and removed before pattern transfer). However, any advantages of such schemes must be weighed against the costs of increasing process complexity. We recently reported a new all-dry photolithographic process based on the plasma deposition and patterning of organosilicon resists. These materials, as best exemplified by plasma polymerized methylsilane (PPMS), possess amorphous Si-Si bond backbone structures and undergo efficient photo-oxidation to give glasslike siloxane network material. Patterns are developed using chlorine plasma etching to selectively remove unexposed regions, providing a negative tone image. In previous papers we have demonstrated the use of these materials in bilevel processes, using oxygen reactive ion etching to transfer patterns in thin PPMS layers through underlying organic planarizing layers. Using 248 nm deep UV exposure tools, such schemes afford sub-0.25 micrometers design rule capabilities and are well suited for difficult device topography. Here we describe the discovery and development of a fundamentally different application unique to PPMS: a new direct approach to patterned silicon dioxide.

Requirements of materials for lithography at 193 nm limit single layer resist candidates to those with high optical transmission. A random copolymer of trimethylsilymethyl methacrylate (SI) and chloromethyl styrene (CMS), [P(SI-CMS)], has been shown to be highly sensitive negative 193 nm resist in both bi-layer and single layer modes. Such resists show maximum sensitivity with an optical absorbance of the coating of log₁₀e, or 0.434. Through control of the mole ratio of the monomers in the P(SI-CMS) copolymer, absorbance values have been optimized for film thicknesses of 0.2 - 0.3 micrometers for 90:10 SI:CMS, 0.35 - 0.45 micrometers for 95:5 SI:CMS and 0.55 - 0.65 micrometers for 98:2 SI:CMS. Optical absorbance of the CMS is at a maximum in the 190 to 205 nm range, allowing the copolymer to be tailored for a large degree of crosslinking at a relatively low CMS concentration. Spray development of these materials is performed with ethanol, followed by a two step methanol/isopropanol-water rinse. Sensitivities are on the order of 4 to 20 mj/cm² at M_w near 40,000 g/mol. Furthermore, these ratios have been found to produce optimum O₂ etch resistance.

This paper investigates the plasma etch characteristics of electron beam processed photoresist. A standard positive novolak photoresist, as well as an advanced deep-UV photoresist, are evaluated. Etch characteristics are determined for an oxide etch application. Etch selectivity of the photoresist is determined as a function of electron beam dose. Photoresist undercut and wall slope variation are also determined as a function of dose. The performance of the electron beam processed photoresist is evaluated for line and via formation. The etch characteristics of the electron beam processed photoresist are compared with the etch characteristics for untreated and thermally processed photoresist. In most cases there is an improvement in photoresist profile integrity with increasing electron beam dose. Interaction of the processed photoresist with the plasma chemistry, and its effect on post process removal, are also presented. Finally, a process model is presented for using the electron beam process in current production plasma etch applications.

In this paper, a new method to calculate the silylation profile in the PRIME process is presented. New software modules have been added to the 2D simulator SLITS in order to simulate the silylation and dry developed profiles in the PRIME process. The silylation and dry developed profiles for the PRIME process are simulated and compared to experimental results. Simulations were carried out for both e-beam and DUV exposures. Under e-beam exposure, the maximum percentage error between the simulated and experimental results was 13%. Under DUV exposure, the silylation depth at the mask edge can be reduced by increasing the dose thus effectively controlling the resist linewidth. The depth of focus was found to be 0.4 micrometers .

The lithographic properties of the vacuum vapour deposited thin films based on the benzo[a]phenoxazine derivatives applied in the "all-dry" lithography process with laser patterning (2 =266nm) have been studied. As shown, film sensitivity and resolution, line-edge profile, dry etch resistance and stability under storage and ion implantation depend highly on the chemical structure of the side substitutes. It was found that the treatment of the films with B and p ions with dose equal to or more than 1.8*10 'ion/cm2 and energy equal to 30 keV results in the formation of thin carbonized surface film layer. Its chemical structure includes phosphorous compounds such as PhP3, (PhO)3P0, (PhO)3P in the case of P ion treatment. Modified films display higher dry etch resistance. The fluorination of the vacuum vapour deposited and modified films in C3F8 plasma is under consideration. Keywords: vacuum vapour deposited organic films, laser photolithography, film surface modification, line-edge element profile, etch resistance, ion implantation.

Vacuum vapor deposited films (0.8 - 1.2 micrometers thickness) of perylene-3,4,9,10- tetracarboxylic acid (PTA) derivatives studied permit masks to be produced by laser vacuum projection lithography (LVPL) technique. The masks have submicron elements (0.4 - 0.6 micrometers ) and selectivity ranging from 7 to 15 during plasma chemical etching of Si, SiO₂ and Al. Films based on diphenyl- and di-(p-chlorophenyl)-diimides possess the best lithographic and masking properties.

We investigate an all dry etching process of the development-free vapor photolithography (DFVP) with 315 XeF excimer laser. After masked exposure, SiO₂ on a silicon wafer and beneath a photoaccelerator polymer layer can be directly etched by etching vapor which is a mixture of HF, water and N₂. Ultimately, patterns with 0.4 micron resolution were obtained. We have investigated the effect of the etching temperature and time, exposure energy and 5-ni-troacenaphthene concentration on the resolution and discussed the mechanism of DFVP.

The relationships of contact angle among different substrates, the role of dehydrating bake on photoresist profile and the relationship between contact angle and photoresist profile are addressed in this paper. Generally speaking, when the HMDS priming time increases, the contact angle of all the substrates increases no matter what the adhesion priming temperature and dehydrating bake time/temperature used. Among these substrates, tungsten silicide always has the largest contact angle and its minimum acceptable priming time is about 5 seconds. Regarding the priming temperature, largest contact angle is obtained with priming temperature around 50 degree(s)C for doped poly, bare silicon, and tungsten silicide substrates, while for Teos substrates there is no significance difference on priming temperature as it's beyond larger than 30 degree(s)C. In terms of dehydration temperature, lower baking temperature results in larger contact angle. However, as far as the photoresist profile is concerned, higher contact angle does not guarantee that profile is vertical without undercut or tailing problems. In view of improving the photoresist profile, the dehydrating bake is unavoidable and the temperature should be around 100 degree(s)C.

A novel process for the fabrication of T-gates (mushroom gates) with a base dimension of 0.2 micrometers (gate length) and a top dimension of 0.6 micrometers is presented. We developed a two- layer resist system, in which first the bottom of the gate structure is patterned with a one-layer e-beam resist P(MMA/MAA) and then the top of the structure is patterned with an optical wafer stepper exposure and development of an experimental i-line negative resist (LMB 7011). The crosslinked bottom resist (prebake temperature 170 degree(s)C) is exposed with our Leica e-beam system EBPG-5HR. The top resist is patterned with our i-line wafer stepper ASM-L 2500/40. For this exposure we use a rim phase shift reticle to increase the resolution limit of the stepper from 0.7 to 0.5 micrometers . During exposure of the top resist, there is light reflection from the alloyed ohmic contacts (source and drain electrodes) into the unexposed region of the T-gate. To avoid this effect we use a top antireflective coating (TAR). The thickness and the prebake conditions of this TAR are very important to decrease the swing curve of the i-line negative resist. A comparison between the swing ratio with and without an antireflective coating is given. This additional layer also reduces the exposure dose of the i-line negative resist, which is very useful to get a re-entrant resist profile for the lift-off process of the gate metal. Electrical results on test devices and microwave transistors also are presented. S- parameter measurements, up to 75 GHz, were performed on T-gate transistors with our standard HEMT-structure.

A unique spin coat process was developed which improves the coating uniformity and extends the range of applicable resist thicknesses typically encountered for a one viscosity photoresist. This spin coat process involves a high speed, short term initial coat followed by a low speed dry cycle. Advantages are seen in better standard deviation of coating uniformity and coating thicknesses achieved over a 1 micron range (1.2 to 2.4 microns) for positive photoresists on 6' wafers. In this paper the authors discuss the application of this unique resist processing approach to three types of photoresists which differ in solvent composition (utilizing ethyl lactate, propylene glycol mono methyl ether acetate, and 3-ethoxy-ethyl propionate). Comparison of coating uniformity at various resist thicknesses with a standard coating process is made and emphasis is placed on analysis of residual solvent and PAC content in resist films.

The validity of a photolithographic develop process in a manufacturing environment is measured by critical-dimension control, photo defects, chemical usage, cycle time, functional test yield, and rework. Due to the rapid pace of change in the semiconductor industry and the trend toward ever tighter ground rules, the demands that these parameters place on the develop process are never constant. A process that worked in the past may suddenly become inadequate for a new product design with specific performance, throughput and cost requirements. This paper details the techniques used for engineering support of the photocluster single-wafer develop processes in the IBM Microelectronics Division's semiconductor production facility near Burlington, Vermont. Unique analysis procedures have been established for baselining spray- and puddle-develop processes and for identifying the sources of sudden process deviations or defect occurrences. Effective engineering support can maintain the required process performance while also ensuring that all other production considerations are met.

The environmental specifications for submicron photolithographic processes on photocluster tools have traditionally demanded strict setpoint control with very little variation in temperature and humidity. In an effort to reduce support costs, the need for such tight tolerances on relative humidity is being examined. This paper discusses the effects of relative- humidity variation on photoresist thickness after spin-coating and on the final printed-image linewidth after full processing through the photocluster. Two different photoresists are compared using spray- and puddle-develop processing. When the resist thickness is varied by changing the humidity setpoint, the swing-curve correlation between printed-image linewidth and resist thickness is equivalent to one typically generated by changing the photoresist thickness with different casting speeds.

This paper describes an engineering approach that was taken to improve an existing edgebead removal process which used acetone exclusively. Production problems were encountered after exposure and develop of positive photoresist: after the UV bake step. These problems were manifested by popping photoresist. The approach taken here was to evaluate acetone by itself as an edgebead remover and compare it with a commercially available EBR. Specifically, a combination of ethyl lactate and 2-pentanone. The improved edgebead removal process is presented as a function of photoresist popping after the UV bake step for our CMOS process.

In recent years, increased activity in micromachining has driven the need for high aspect ratio thick films resist systems. This paper discusses a new epoxy based resist that can be used to achieve high aspect ratios (> 10:1) using UV lithography. The resulting negative resist system provides sharp, clean images in thick films (> 200 micrometers ). Because of the high aspect ratio and short exposure times, this material may be a viable candidate for producing the images required for micromachined parts. The resist images exhibit straight sidewalls and developed patterns, have excellent thermal stability, good adhesion, and chemical resistance. The high aspect ratio and high thermal stability make these epoxy resists suitable for other packaging applications such as plating stencils and optical wave guides.

The process capability of a commercially available positive diazonaphthoquinone (DNQ) photoresist, SJR 3000 series from Shipley, was evaluated. This photoresist at a film thickness of 7 - 8 microns was found to have a large process latitude and focus budget while maintaining nearly vertical wall profiles. The high contrast found with this thick film photoresist was due to a low loading of a monofunctional DNQ sensitizer which also has a high dissolution inhibition. The photoresist formulation was compatible with both AZ 400K and Microposit (MP) 2401 developers when using either a stepper or scanner exposure system. SJR photoresist was shown to provide an effective photoresist frame for electroplating metals such as copper and permalloy.

Planar waveguide gratings are finding applications in wide band signal processing for imaging and location radars. Advanced forms may take the form of a `blased' topology, in which height as well as line and space dimensioning are engineered. This allows more complicated beam steering and wave interaction along the grating, promising better control over efficiency and more diverse engineering application. Planar lenses are being investigated as a method of coupling optical signals to the substrate. Realizing these devices also requires modification of the host substrate in three dimensions and is a difficult technological hurdle. Inherently low contrast resists can be shaped with the aid of clever processing techniques and have been classically used to obtain smaller line widths than the lithography technique would have normally allowed. In this work we utilize an experimental negative tone resist formulation to realize three dimensional features on GaAs substrates. The negative tone resist of interest, P(SI-CMS)-20, is under development (AT&T Bell Labs, Murray Hill, NJ) as a high performance single component system to be used in the fabrication of x-ray masks. Its properties include high resolution and the more unusual ability to faithfully retain a post processed film thickness that is primarily dependent upon e-beam dose, while using a fixed post exposure processing methodology. A curve of film thickness retention versus dose is then selected to define a required post exposure processed film thickness. A nominal 200 nm thick film is first spun onto the GaAs host wafer and softbaked. A Leica EBMF-10.5 vector scan electron beam lithography tool working at 25 KeV beam energy is used for patterning. A saw tooth or step ramping in processed resist height may now be achieved with a series of single pass lines or small areal features of successively higher dose density. The minimum dose corresponds to the minimum incipient gel of the resist and clears the foot of the saw tooth ramp. Successive features of increasing dose will build an increasingly thicker ramp of resist. Images are developed in ethanol, a first rinse in methanol and a final rinse in IPA/H₂O. Planar lenses may also be attempted in this way by again doing a piece-wise construction of the shape, using a varying dose. The processed 3-D resist pattern is then transferred to the wafer by a magnetron RIE dry etch in an argon and boron trichloride atmosphere. Etching of the resist pattern and the wafer is performed so that protected areas of the wafer receive the least etch and the smallest relief. Etching selectivity may in part be set by choosing an appropriate mix in the etching atmosphere.

Diffractive optical elements (DOE) are becoming important as optical signal processing elements in increasingly diverse applications. These elements, fabricated on quartz, may be used as phase shift type masks or as embedded components that implement a transfer function within a processing network. A process is under development for the fabrication of a DOE implementing a Jervis error diffusion kernel for research in half tone image processing. Dry etching is performed after lithography and pattern transfer through a nickel mask. This results in etched areal features on the substrate. An optical diffraction medium is thus created. Lithographic patterning is done by e-beam lithography (EBL) to realize small features, but also offers the important advantage of a large depth of field which relaxes the problem of complex surface topology. The recent availability of high energy (100 KeV) lithography tools provides a capability for precision overlay, small feature resolution, and enhanced image contrast through a lower induced proximity effect. Patterning by EBL on insulating substrates is complicated by the necessity of providing a vehicle for the avoidance of charge buildup on the surface. In a previously presented paper a methodology was shown for the use of TQV-501 (Nitto Chemical) antistatic compound as a final spin on film for use with PMMA and SAL-601 (Shipley). In this current work, a process is described using EBL and a high performance positive resist working with a final film layer of antistatic TQV-501 on a nickel coated wafer. The process may then be reapplied to realize additional lithographic levels in registration, for multilevel DOE components. High energy (100 KeV) EBL is used to provide high quality pattern definition. The e-beam sensitive resist, ZEP-320-37 (Nagase Chemical) in dilution, together with a top film layer of TQV-501 serves as a bilevel resist system and is used for patterning the desired image before definition of the nickel mask through a wet etch. ZEP- 320-37 in 1:1 dilution with the native solvent is spin applied and softbaked for 2 hours at 120 degree(s)C, after which the antistatic film is spin applied and softbaked for 10 minutes at 70 degree(s)C. After exposure, the TQV film is removed within the development procedure itself. The image is developed in xylene followed by a thorough IPA rinse. The pattern is then transferred to the nickel film via a dilute HCl etch bath. Finally, magnetron RIE is performed on the substrate through the defined nickel mask, after which the nickel film is completely removed in HCl.2438

An intralevel mix match resist technology is described using modeling and simulation methods. The two dimensional description of the process contains a Monte-Carlo calculation for the e-beam exposure, a model for the interaction of electrons with the resist, a simulation of the i-line exposure, a calculation for the silylation and for a final dry development step (O2-RIE). The simulation is supported by experiments where a structuring down to 50 nm is achieved.

Conventional acid catalyzed, chemically amplified DUV photoresists are susceptible to environmental contamination and post exposure delay effects resulting in `T-topping' and linewidth variation. These phenomena are directly relatable to uncontrolled diffusion of the photoactive acid generator within the photoresist or from the diffusion of basic contaminants into the resist. The diffusion process can be controlled by a combination of materials and processing optimization. This paper describes a new positive tone DUV photoresist based on poly(4-hydroxystyrene) protected with the isopropyloxycarbonyl (i-POC) functionality. This protecting group is considerably less acid labile than the tert-butyloxycarbonyl (t-BOC) group and the resulting polymer is considerably more thermally stable than a t-BOC protected poly(4-hydroxystyrene). As such, the i-POC based polymer is more amenable to processing at higher temperatures.

A series of AZ-compatible negative photoresists composed of a novolak resin and azide sensitizers for the micro and nano-lithography is presented. The ma-N 2400 and ma-N 300 are sensitive to light of the deep UV region (248 nm, 254 nm, 308 nm), the ma-N 400 and ma-N 1400 are sensitive to light of the mid UV region, the latter has a high sensitivity to the i-line (365 nm). The thickness of the resist layers prepared by spin coating is up to 8 micrometers depending on the composition of the resist solution. All resists are non-swelling during aqueous alkaline development after exposure. Using special lithography, these photoresists have a resolution capability up to 0.1 micrometers . The resistance to wet etch solutions and to dry etch gases is superior and higher than that of the most positive resists based on novolak.

The definition of `Moore's Law' has come to refer to almost anything related to the semiconductor industry that when plotted on semi-log paper approximates a straight line. I hesitate to review its origins and by doing so restrict its definition. However, this paper is a review of the history and past performance relative to predictions and shows where the advances have come from. I will leave the future performance up to you. Certainly continuing on the same slope doesn't get any easier. It presents a difficult challenge to the industry.

ULSI has heavily depended on developments in optical lithography. However, optical lithography is now facing a major obstacle due to exposure wavelength limitations. To overcome this obstacle, not only the use of shorter wavelengths, but also such new technologies as super-resolution techniques, electron beams, and x-ray lithography are being intensively investigated. This paper reviews recent developments in these technologies and discusses the major issues. The difference in lithographic activities between Japan and the U.S. is also discussed. Finally, recent developments in lithography for experimental 1-Gb DRAMs are presented.

In 1994, The National Technology Roadmap for Semiconductors was revised, updated to reflect the latest information, and published in December 1994. Lithography continues to be a cornerstone for semiconductor process and productivity. The roadmap activity is sponsored by the SIA. The Technical Working Group (TWG), which does the actual work of updating the roadmap, is comprised of members from SEMATECH, SEMATECH FTABs, SRC, industry, universities and government. One of SEMATECH's key goals is to insure that the activities we pursue are well-aligned to the roadmap. The roadmap is focused on requirements and needs of the industry. SEMATECH is focused on solutions. The lithography roadmap makes clear the desire of semiconductor manufacturers to stay with optics as long as possible since shifts to non-optical technology are viewed as much higher investment and risk. It is perceived that optics can be a viable manufacturing solution through at least the 0.18 micrometers generation. The TWG and SEMATECH FTAB meetings highlighted the need for greatly increased emphasis and resources on 193 nm technology to bring it to pilot production in 1998 for the 0.18 micrometers generation. SEMATECH has since worked with the industry to define more detailed needs and requirements for a successful 193 program and is working with industry and the government to insure that the technology is available when needed in manufacturing. The needs are clear...cost-effective lithography for each generation. The challenges are...how to get there from here.