A brief overview of a model for the dissolution of resists is given. The glassy film is first converted into a swollen gel, whereupon entangled coils disengage from the network into the developer solution. The glass/gel interface movement is governed by stress-induced Case II diffusion, whereas polymer dissociation from the gel-like network at the gel/solvent interface is best described by a reptation type process. Transient stress and concentration profiles between these two moving boundaries provide a link between the interface kinetics. Polymer molecular weight, polymer-solvent compatibility, free volume state of the glassy matrix, and diffusivity of the solvent in the gel layer are all properly reflected in the basic scheme of the model. Preliminary results exhibit behavior consistent with experimental observations using an in-situ psi-meter. Effects of individual process parameters on the final structure will be explored in a future publication detailing comparison of full model predictions and systematic experimental data.

A new general method for measuring dissolution kinetics of thin films has been developed. This technique employs a quartz crystal microbalance to measure the mass of the dissolving thin film. The method allows the measurement of very rapid dissolution rates, and can also be used to study the dissolution kinetics of thick or opaque films. The technique has several advantages over alternative in situ methods based on optical interferometry or capacitance. This instrument has been used to examine the effects of photoproducts on the dissolution kinetics of positive photoresist. The influence of photolytically generated carboxylic acid, and the nitrogen byproduct entrapped in the film, have been independently assessed by comparing the solubility of films of novolac resin, and films of resin plus carboxylic acid photoproduct, with that of exposed photoresist. Our results indicate that the acid does not significantly influence the solubility of the resin, and that entrapped gaseous photoproducts exert a rate-enhancing effect.

Dissolution rates are measured conveniently and accurately using a simple laser inter-ferometer. The apparatus is inexpensive and reliable and yields various kinds of information about the dissolving polymer and its interactions with the solvent or solvent mix-ture. Measurements have been made recently of the polymer of maleic anhydride with alphamethylstyrene. These can be compared with the more extensive reports of past work with poly(methylmethacrylate) and some other polymers. The dissolution process which is desirable is one which proceeds without appreciable swelling of undissolved material. Various thermodynamic anu kinetic parameters are suggested as shedding light on the proper selection of solvents to achieve the best developing systems.

A new analytical model of the exposure and development of optical positive resists is used to quantitatively evaluate process control. Using this model, a new method is described that allows for the rapid extraction of the characteristics parameters that describe the exposure and development of resists. Characteristic parameters were measured for AZ 1300SF in two concentrations of AZ 351 and AZ developers, respectively. Line width variations that would result from specific process variations were calculated for the different developers. It is clearly shown that dilute developers operating at optimal exposure doses give the best control.

A method of characterizing and simulating spun-on resist coating contours is described. A low-pass frequency filter is applied to the uncoated contour (topography). Two parameters, P. and a, describe the low-pass frequency filters that estimate the coating contours of different spun-on solutions. The frequency filter parameters are derived solely from step-height measurements of coated isolated-line features. Radial flow-induced coating anomalies are also discussed. These anomalies produce different coating contours for features at different orientations and positions with respect to the centrifugal center of the substrate. A simulated coating contour on a three-dimensional device structure is presented to show the typical thickness changes produced by spun-on positive resist films. A correction for film shrinkage is sometimes required for this simulation procedure.

We derive a general relation that exhibits the interdependence of the exposure and development processes in determining the contrast and the sensitivity curve of any photo-resist. We show,that for several limiting cases, the contrast is given by the reciprocal of the (pre-or post-expose) optical density of the resist, in agreement with the measured contrasts for PR102, AZ2400 and Dupont 2041 Elvacite PMMA resists. We also calculate the dependence of the threshold exposure energy D/35, and the dose Dp required to completely develop the resist, and hence, the contrast, on development time for a hypothetical solvent and simulate the results obtained using MF314 developer.

Silicon wafers coated with 1.0 micrometer of ACCULITH® P-6010 positive photoresist were exposed at 436 nm and processed in three different developers known to produce different levels of contrast. From experimental thickness vs. time curves, development parameters required as input to SAMPLE were determined. These parameters are preliminary in that they have yet to be optimized over the entire exposure range. Within a limited energy range however, information on relative trends in exposure and development latitude as a function of contrast has been determined. The effect of adding an antireflective coating between the silicon and the resist was briefly examined.

A model for image formation in the Ag2Se/GexSe1-x resist systems had been proposed by Tai et al.1 The first step of the process consists of forming a thin latent image of photodoped Ag in the top layer of the GexSe_l-x film. This Ag doped layer then serves as a mask for the anisotropic wet chemical etching of the undoped GexSe_l-x structure with a bicomponent etchant. Anisotropic chemical etching results from an unusual, interlocked, phase-separated columnar structure of the GexSe_l-x film. The formation of such phase-separated columnar structures depends on the composition of the Germanium-Selenium film. We examine here the dependence of film microstructure on film composition and describe the relationship bewtween etching characteristics and the concentration ratios of a bicomponent developer.

Soft X-ray absorption spectra and spectral sensitivity of X-ray resist are studied using synchrotron radiation. A measurement technique for spectral sensitivity named X-ray Excited Ion Mass Analysis is newly developed. Spectral sensitivity is evaluated from the fragment yield of the decomposed resist during exposure to monochromatized synchrotron radiation. Using this technique, the spectral sensitivity of poly-2-methylpentene-1-sulfone is measured. The sensitivity is found to be enhanced at shorter wavelengths despite a low absorption coefficient.

Several kinds of silicon-containing resist materials for bi-layer resist systems devel-oped in our' Laboratories are reported. For negative working resists, poly(trimethylsilylstyrene-co-chloromethylstyrene) ( P(SiSt-CMS) ) and a mixture of poly(triallylphenylsilane) with bisazide ( TAS ) have been developed. P(SiSt-CMS) was designed for EB or deep UV exposure. TAS suits to use in near UV lithographic tools. For positive working resists, SIPR (a partly trimethylsilyl-methylated resorcinol-formaldehyde resin mixed with naphthoquinonediazide) was developed. Syntheses, lithographic data and applications to bi-layer systems of these resists are given.

A series of polysiloxane-based negative resists will be described which are applicable to both electron-beam and ion-beam lithography. Compositional changes have been made to nary the Fisitivitg to 20 keV electrons from 40 to 180 μC/cm² . A sensitivity of 9.4 tiC/cm (2.5 x 10¹² ions/cm² ) has been obtained with 150 keV silicon ions for the 40 iiC/cm E-beam resist. The resists have high glass transition temperaWes and re effective top layers of a bilevel resist system. A thin polysiloxane layer (400Å to 1000Å) makes an effective mask layer over 1 to 2 μm AZ type leveling layer. After the polysiloxane pattern was developed, the images were transferred to the AZ layer by reactive ion etching with oxygen. By properly adjusting the etching parameters, extremely high anisotropy and excellent selectivity (25:1 ratio between bottom and top layers) were achieved. Using this polysiloxane-topped bilevel system, good quality images have been prepared using both electron-beam lithography (EBL) and focused ion-beam lithography (FIBL). With a 600 -700w thick polysiloxane layer over 1 pm of AZ1370 we have produced a 6000 wide gap with parallel side walls in a 2 pm pitchimage by EBL. The same process has also demonstrated high quality images over 5000A steps. For FIBL a resist system consisting of 400w of polysiloxane over 1 pm AZ1370 was used with a focused 50 keV gallium ion beam2 Resist lines 0.12 pm wide and 1 μm high were produced with an exposure of 8 x 10¹² ions/cm².

A phenolic resist system was formulated with a selected anti-reflective dye tuned for use with stepper exposure equipment in the 400-436 nm region. High exposure latitude and better than 1.25 micrometer resolution were demonstrated over highly reflective aluminized topography. Excellent 200^oC. resist image stability was enhanced by deep UV treatment to endure prolonged heating at 400°C. It is felt that this resist is a good candidate for use in high temperature processes such as sputtering applications.

A plasma-enhanced chemically vapor deposited (PECVD) silicon oxynitride (Si-O-N) was used in a 3-layer resist system in combination with a 0.42 na lens to provide device process developers with a means for extending photolithography down to 0.5 pm feature size. This delayed the need for using more expensive lithography alternatives. In this paper, the procedures used for forming the 3-layer structure are outlined. Typical plasma deposition conditions are cited. Results from the comparison among Si-N-0 films of differing composition are described in terms of refractive index, stress, and pinhole densities for varying ratios of S:N:O. Etch rates and their ratios pertinent to transferring the image into base resist are reported. Lift-off profiles were obtained and a pol*mide was used for a base which remains soluble in common solvents after being baked at 200^oC. Scanning electron micrographs (SEMs) of sub-micron image profiles are shown and linewidth measurement data are presented to show linewidth precision and constant bias into the 0.7 μm range. The latter demonstrates the adequacy of this technique for sub-micron device development.

Multi-level resist systems are rapidly becoming essential in the drive towards submicron lithography. Such systems offer many inherent advantages over single level schemes, such as planarization of underlying substrate, higher resolution and formation of high aspect ratio patterns. Other advantages, particular to specific exposure technologies, can also be found. These include minimization of backscatter and proximity effects for electron beam lithography or reduction of standing wave effects and depth of focus problems for photolithography.

Although many attempts have been made to prevent the formation of the interfacial layer between the toplayer resist and the bottom layer resist PMMA, an interfacial layer always seems to be more or less present. After an extra treatment it is sometimes possible to re-move this thin layer. It would be an advantage if such an extra process step could be avoided by means of applying a toplayer photoresist which does not cause the formation of an interfacial layer. We therefore tried to gain a basic understanding of the parameters which have effect on the origin of the interfacial layer. From the investigation of the effects of the resin composition and its molecular weight (distribution), the solid content, the solvent composition and the prebake temperature on the interfacial layer formation it appeared that all these parameters are concerned in the origin of the interfacial layer. Prebake temperatures should be as low as possible, 450°C for novolak based resists (which results in bad resolution) and 480°C for a polyhydroxy-styrene based positive resist. The low and high molecular weight fraction of novolak are causing thicker interfacial layers than the medium molecular weight fraction. If cyclohexanone or ethylcellosolve were used as solvents and polyhydroxystyrene as the resin a positive near UV photoresist could be composed which can be used as the toplayer resist for the bilevel deep UV system in the capped mode with a negligible interfacial layer.

An aqueous developable two layer resist system has been developed using a poly(dimethylglutarimide) (PMGI) based planarizing layer. This material offers better resistance to dry etching and thermally induced flow than PM M A. The PMGI layer is highly solvent resistant so no interfacial mixing with conventional positive resist top layers is observed. The pattern transfer exposure wavelengths for the PMGI are 240 - 280 nm. Dyes were added to the novolak based top layer to ensure optimum deep UV masking for thicknesses less than one micron.

When a patterned surface is coated with a polymer solution and dried or cured, the resulting surface is not completely flat (contrary to most drawings illustrating the planarization layer in multilayer resist schemes.) In order to understand the thickness variation of the polymer film, it is useful to define local planarization as the reduction in height of a single step and global planarization as the long range effects of different pattern densities. It has been determined that the efficiency of planarization depends on the thickness of the polymer coating, the shrinkage of the polymer solution, the flow properties of the polymer during the cure cycle, and the dimensions of the patterns on the surface. The degrees of both local and global planarization can be predicted by straightforward calculations.

A positive-working electron resist, poly-(methacryloyl chloride), which has sensitivity ≈5 μC/cm² at 20 keV is described. The resist is slightly more resistant to erosion in a carbon tetrachloride-based plasma than is poly-(methyl methacrylate). Its erosion rate in the plasma can be further reduced by treating developed film patterns with suitable reagents to introduce into the resist structure aromatic groups or metals. Erosion rates can be reduced to values near those of negative resists containing aromatic groups.

A comparative study on the lithographic behavior of this azide-phenolic resin resist in deep UV and electron beam exposures is presented in this paper. Despite the broadening of resist line base exposed to electron beam, its submicron resolution capability and sensi-tivity of ≈16 μC/cm² are demonstrated. This system offers image profile variations in deep UV exposure mode through controlled exposure and development conditions. Excellent linewidth control of ± 0.1 micrometers was obtained with adequate development latitude and high thermal and plasma resistance. Preliminary results also showed the feasibility of using 0.5-0.6 micrometer coatings of this resist as a high resolution conformable mask in multilevel systems.

Copolymers of allyl methacrylate and propargyl methacrylate have very high speed as electron-beam and x-ray resists. They produce polymers of a structural complexity not often encountered in addition polymerization. The structural variety available in allyl methacrylate polymers gives them unusual properties, which consequently enhance their microlithographic performance.

Plasma-developable positive and negative resists with a high etching rate ratio between exposed and unexposed areas have been developed for electron-beam lithography. The negative resist systems are composed of radiation-degradation polymers such as poly-alkylmethacrylate and low molecular weight phenylsilane compounds such as triphenylsilane and diphenylsilandiol. Electron-beam exposure induces the formation of nonvolatile silicone compounds through chemical reaction between decomposition products of polyalkylmethacrylate and added silicone compound. The negative resist patterns are obtained by RIE 0₂ plasma development after removing the added silicone compound from unexposed areas by a relief treatment. Since the surface of the exposed area is covered with a plasma resistant layer produced from the nonvolatile silicone compound, the etching rate ratio between exposed and unexposed area is very high. The sensitivity of these resist systems depends on the glass transition temperature (Tg) of polyalkylmethacrylate and species of silicone compound. The range of sensitivity is 7 to 70 μC/cm² and the resolution is better than 1.0 μm. These resist systems are applicable to bi-level or tri-level resist processes, and high aspect ratio patterns are obtainable. The positive resist systems comprise crosslinking polymers such as chloromethylatedpoly-styrene and the same silicone compounds. Positive resist patterns are obtained by electron-beam exposure and subsequent RIE 0₂ plasma development. Electron-beam exposure reduces resist film thickness by a few percent as a result of the crosslinking of polymer, then, the added silicone compound is separated as minute particles from uniformly mixed resist film. The exposed areas show less resistance to RIE 0₂ plasma than unexposed areas. The sensitivity of the typical resist system is about 60 μC/cm², and resolution is 0.4 μm for 1.0 μm original resist film thickness.

A negative deep UV resist MRS is successfully applied to 1:1 projection printings. The MRS has high resolution capability due to the absence of swelling in the developer, and resolves 1 μm patterns. Because of its intense absorption characteristics, the MRS is insensitive to variation in underlayer reflectivity, so the linewidth of the surface part of the MRS is well controlled. A further consequence is image profile variation depending on development 'conditions and resist thickness over steps. Anisotropic etching with high selectivity to resist may mitigate this effect. We are currently applying the MRS to obtain 1 pm-thick Al-Cu-Si metallization patterns realizing 1.5 μm spaces over 0.7 μm stepped substrates by the use of reactive ion etching. The MRS is reliable enough to apply to a single-layer resist process for production of 1.0 μm - 1.5 μm feature size devices. It is found that, using the MRS as a top layer for a tri-layer resist structure, 0.7 μm line and space patterns can be obtained with 1:1 deep UV projection printing. In our tri-layer resist process, the surface part of the MRS acts as a mask to etch the second thin SiO layer, which becomes the final mask pattern of the polymer bottom layer. The MRS tri-layer resist process has excellent resolution and controllability of linewidth compared with that of conventional positive resists.

In recent years there has been considerable interest in inorganic resist systems based on the photo-doping of amorphous chalcogenide films, the majority of the research being devoted to Ge-Se films. This paper presents a detailed investigation of inorganic resists based on the photo-doping of Ag into As-S films. It is shown that high resolution patterns can be produced in such resists using holography or optical lithography and that they are compatible with wet-chemical or plasma etching. Structural studies using Raman spectro-scopy indicate that for best resolution the composition of the As-S film should be close to AS33S67 since on photo-doping it will yield a single-phase homogeneous material. A possible mechanism for the photo-doping process is described based on a tarnishing-type photo-chemical reaction. It is shown that the actinic radiation initiating the photo-dissolution effect is absorbed primarily in the photo-doped layer, close to the interface with the undoped As-S region.

A new class of alkyl silane copolymers with relatively facile self-developing behavior under deep UV exposure has been examined. These materials can reproduce 0.8 μ features by projection lithography with a KrF excimer light source. The mechanism of material removal is primarily photochemical in nature and yields chemically inert volatile siloxanes as the major photoproducts, via a high quantum yield silylene expulsion/oxidation process.

To date the use of photoimagable polyimide systems has been limited by lack of photo-speed, excessive volume contraction, and by shelf-life problems. These shortcomings have now been improved to the point where a practical, usable system has become available. Through the use of novel high quantum yield sensitizers, tailored to the g-line (436 nm) of the mercury spectrum, it is now possible to lower exposure times markedly and to reduce the amount of layer shrinkage that occurs in the final cure. Layers up to 70 microns and more of final cured polyimide can be photostructured at high resolution with an exposure energy of less than 1 J/cm². The system presented is particularly useful for relatively thick layer applications as, for example, alpha particle protection, but can be used also for thin layer applications with accordingly shorter exposure times.

A series of new type of negative photoresists composed of a phenolic resin and azide sensitizers has been developed. RD-2000N is sensitive in the deep UV region, RU-1000N in the mid UV region and RG-3000N in the mid UV to visible region. These resists are non-swelling aqueous developable, and give higher resolution compared to conventional cyclic rubber based negative resists. Resolution in less than 1 μm can be obtained by 1 : 1 projection or 10 : 1 reduction projection aligning method. Adequate exposure doses to define submicron patterns are 50 mJ/cm4(at 254nm),70 mJ/cm° (at 365 nm) and 180 mJ/cm²(at 436nm) for RD-2000N, RU-1000N and RG-3000N, respectively. The resistance to dry etch gases is also superior to conventional negative resists, and comparable with novolak resin based positive resists. Intense absorption of irradiating light by these resists makes them insensitive to reflected light from the substrate, resulting in a high resolution on stepped substrates without any antireflective layers which are necessary in positive resist applications.

Two kinds of negative photoresists, MRL(N) and MRG have been obtained by sensitizing poly-vinylphenol with aromatic azides synthesized by condensing isophorone with p-azidobenz-aldehyde and p-azidocinnamaldehyde. The sensitivity of MRG to g line (436 nm), expressed by the dose necessary for 50 % film thickness to remain on the substrate after development (D1°) is 55 mJ/cm2. MRL(N) is less sensitive to g line than MRG, however, its ID" value to i line (365 nm) is 13 mJ/cm². Both resists do not swell in aqueous alkaline developer, and conse-quently have high resolution capability. The quantum efficiency of photodecomposition of azide has been determined. The values ranged from 0.10 to 0.24. The photoinsolubilization of resist is considered to be mainly due to the increase in molecular weight of polyvinylphenol by the recombination of polymer radicals with each other.

In the struggle to attain denser and higher speed devices through reducing feature sizes companies are facing thresholds beyond which conventional photolithography cannot transcend. Enormous financial commitments have been made by semiconductor device fabricators in their drive to produce devices centered on 1.5μ design rules. The purchase of ever more sophisticated alignment and peripheral processing equipment, costly photoresist changes, and massive investments in engineering has enabled many companies to participate in this race. This compulsory buying of next year's model will not necessarily bring companies through the difficult technological times ahead!

Photoresist linewidth profiles for optical projection printing with high performance stepper lenses were simulated using the SAMPLE program. Profile slopes and linewidth variations of resist structures on profiled surfaces (silicon and aluminum substrates) have been investigated in dependance on photoresist parameters such as optical absorption coefficient and thickness of the photoresist as well as exposure/development time. The study also discusses the influence of exposure wavelength (g-line vs. h-line vs. i-line) on line edge slope and standing wave effects.

Control of optically printed linewidths becomes increasingly difficult as diffraction effects degrade image quality. If, during development, the exposed film thickness is monitored by optical detection of interference fringes, it is possible to find the time at which the photoresist breaks through to the substrate. When this time is related to the total development time needed to print a given feature size, it is possible to automatical-ly adjust the total development time to correct for process drifts in dose, resist thickness or soft bake temperature. This paper will describe a method for in-line, automatic linewidth control for both spray and puddle development. This equipment can also be used in a process diagnostic mode to evaluate such photoresist parameters as the resist dissolution rate or initiation time before development actually begins. The implications of this tool for fully automated photoresist processing will be discussed.

Linewidth control and resolution have become increasingly more difficult for optical lithography in the one micron region because of reflective substrates and severe topography. Recently, much attention has been given to spin-on Antiretlective Coatings (ARC) as an easily implemented solution to standing waves and scattered reflections. This leads to improved linewidth control and better resolution for the same aligner and resist system. This paper investigates ARC undercutting and its effect on the final etched image for popular anisotropic plasmas as used to etch polysilicon gates, silox contact holes, and aluminium interconnections. Brewer ARC-PN4, ARC-PN2, and Waycoat 204 positive photoresist were used and imaged using a THE 800-SLR 10X stepper. It was found that final etched features were insensitive to spin-on ARC baking and developing conditions making this a useful technique for production in the one micron region.

The trend towards continued miniaturization in integrated circuits has placed enormous demands on both equipment and materials used in the fab lines. As a result, the higher technology fab lines have shifted away from the currently available cyclized polyisoprene negative resists to the novolac-based positive types. At the same time, the desirability of having a high performance negative photoresist has been mentioned in the literature.' We are presenting a new family of organic solvent developed negative photoresists, the key feature of which is the ability to maintain resist images with virtually no swelling. This is demonstrated by the presence of standing waves in the side walls. Being based on a proprietary new chemistry, the new resists provide the advantage of having independent degrees of freedom in such critical properties such as the double bond content, glass transition temperature and aromatic content of the resin. These properties allow for high ultimate crosslink density, limited plastic flow up to 230°C, and high plasma/RIE resis-tance. The photoresist is sensitized for either 365 nm to be used in mirror projection, contact or proximity printing, for 254 rim (deep UV) , or for 405-436 nm to be used in stepper prin-ting. In contact mode the resolution obtained was 1 micron (submicron for under exposure), in scanning projection 1.25 microns. The one micron features were transfered into silicon oxide by RIE with a better than 5:1 selectivity. All these innovations allow for a significant advancement in the state-of-the-art in negative resist microlithography.

A new resin system, comprising a thermoplastic polymer backbone with chemically stable imide functionality, has been adapted for use in three different positive resist product types. These include an advanced bilayer system, a near, mid and deep UV monolevel resist; and an antireflective coating. The key features of the imide polymer system which are utilized for the new resist products are: 1. Novolac-like solubility in aqueous base. This property allows formulation of resists, including the planarizing layer of a bilevel system, with conventional types of positive resist photoactive compounds and aqueous base developers, unlike the situation with PMMA which is not base soluble. 2. Transparency to wavelengths above 260nm. This permits use of the polymer as the matrix for systems which utilize mid and deep UV exposure, including the planarizing layer for a bilevel system and mid and deep UV monolayer resists. This is in contrast to novolac resin wHch absorbs strongly in the deep UV region. 3. Insolubility in solvents used for conventional positive resists. This property is critical to use of the resin in planarizing layers of bilevel systems, including antirefiective coatings. It eliminates the intermixing problems which represent a major problem in conventional PMMA bilevel systems. 4. High Tg (185°C). This value is about 80°C higher than that of PMMA and allows higher temperature processing without pattern distortion. 5. Chemical stability and plasma resistance. Unlike conventional reactive polyimide resins the subject polymer is chemically unreactive and is stable to temperatures above 300°C. Further, the polymer has significantly greater resistance to plasma than does PMMA.

The effect of positive photo resist's unbleachable absorbance on standing wave effects, reflective notching, scumming, exposure latitude and time, bleaching rates, and resist contrast has been evaluated using both theoretical simulation and experimental data. The addition of unbleachable dye to the resist film is shown to reduce reflective notching and the variation of dose with changing resist thickness. Adding dye also leads to a larger standing wave toe on the resist profiles and to increased exposure times. Bleaching rates are reduced and resist profiles are decreased from the vertical. Data is presented showing the improved CD control using dyed resist on interconnect layers.

The combined effects of diffraction, refraction, reflection, and interference often result in the notching of photoresist lines at steps in the substrate. Dyes have been added to photoresists in order to minimize the notching problem. However, it has not been clear whether the improvement has been due to the optical absorbance of the dye, the effect of the dye on the dissolution rate of the resist or both. The objective of the work reported here is to gain insight into the nature of the problem and its solution in order to allow the most efficient approaches to be utilized. The Dill model of exposure and development is used as a tool to evaluate the effects of various dye additions to a conventional positive photoresist. The functional absorbances, nonfunctional absorbances, and photo-decomposition rates are compared at 436 nm and 405 nm. Dissolution rate versus relative inhibitor concentration curves are compared for both metal ion containing and metal free developers. Characteristic curves are presented which demonstrate the effects of the dyes on photospeed and contrast. These effects are separated into the portion due to the optical absorbance of the dye and the portion due to the effect of the dye on the dissolution rate of the resist.

This paper discusses the functional performance features of a new positive photoresist designated as ULTRAMAC' PR78T that can be subjected to temperatures up to 220°C. without any changes in the critical dimensions (CD's). No deep UV stabilization, intermediate post bakes, or other stabilization techniques are required to achieve high temperature thermal stability (220°C.). This high temperature positive photoresist is based on a diazo-coupled alkali soluble resin. The resolution and photospeed of this resist, ULTRAMAC' PR78T, are shown to be in the order of 1 micron using a 1.5 microns resist film thickness at 44 mJ/cm². This resist also has submicron capabilities using step-and-repeat exposure equipment (10:1) utilizing monochromatic 436 nanometer light. ULTRAMAC' PR78T resist shows optimum sensitivity in the 300 - 500 nanometer UV spectral range. In contact or projection exposure equipment, resolution in the order of 1 micron can be achieved using a 1 micron resist film with exposure energies of about 35 mJ/cm². For steppers using monochromatic light at 436 nanometers, typical exposure energies are in the order of 160 to 180 mJ/cm², using either metal-ion-free or buffered metal based developers. Contrast (gamma) curves are shown for both metal-ion-free developer, ULTRAMAC' MF72A, and buffered metal containing developer, ULTRAMAC" D71A. High current ion implant data is also presented, showing no resist degradation. Anisotropic plasma/RIE etching selectivity data is also shown on SiO₂ and aluminum alloy substrates.

Previous work has shown Microposit 1400-27/MF-314 resist/developer systems to have high chemical contrast, Gamma >3, and that the contrast was tunable o some degree.' This high contrast was thought to be the result of an inhibition effect. However, SEM analysis of overdeveloped resist images did no show the characteristic underigutting associated with systems which exhibit this effect. Dissolution studies of S140027/MF-314 in immersion mode of development showed appreciable inhibition at low exPosure dose, but contrast was not as high as observed in spray. The latter result suggested the inhibition effect was being masked and that dissolution studies must be conducted during spray development to de-termine its magnitude. To do this work a HeNe laser dissolution rate monitoring aooaratus was attached to a GCA 9000 aspirated spray developer module. Using this apoaratus, the develonment of S1400-27 in both MF-314 and MF2312 CD-27 was examined during spray and puddle modes of develooment. Also, to gather more information on contrast tuning, MF-314 was examined in a spray/puddle process. In this study, it is shown that S1400-27 photoresist developed with MF-314 does exhibit appreciable inhibition during development in spray and puddle. However at higher exposure dosage, except for enhanced dissolution rates, the inhibition effect with MF-314 is comparable to MF-312 CD-27 developer. It is also shown that resist developed with MF-3l2 CD-27 behaves similarly in both spray and immersion modes of development. A brief description of the dissolution monitoring apparatus is also included.

The literature dealing with contrast in positive photoresists is reviewed. Pertinent definitions are relayed followed by a survey of the various methods proposed for the measurement of contrast. The processing techniques used to improve contrast are also enumerated along with the advantages and disadvantages of each.

Post Exposure Bake (PEB), also known as diffusion bake or deferred bake, has been widely accepted in the industry as a means of reducing standing wave effects in positive photoresists. The basic process involves a bake cycle after exposure, but prior to development. A typical sequence is a soft bake of 50°C - 70°C, exposure, a PEB of 90 -110°C, followed by development. We investigated the presumed role of diffusion in the PEB process through experiments with different size sensitizer molecules and the possible role of phase transition. These investigations revealed a previously unappreciated degree of freedom in the PEB process. A new process variation is presented using AZ 4000 positive photoresist where the PEB is conducted at a much higher temperature, for example, 150°C. We named the process, High Temperature Post Exposure Bake (HTPEB). Though developing conditions must be adjusted, we have found several benefits from use of the HTPEB process: o Improved contrast, photolithographic process latitude and working resolution. o Thermal stability at least equal to the HTPEB temperature. o Improved control of standing waves and other reflective phenomena. o Elimination of micro-peeling and residue problems common to metal ion free developers. Though not presented in this paper, we have demonstrated in our laboratory one practical use of the HTPEB process in opening 1.25μm contact holes having controllable wall angles in the 50° and 70° range.

For the past several years the trend in VLSI technology has been toward attaining higher and higher pattern densities, which requires the ability to print him and smaller geometries over steps. Concurrently, the increasing use of step and repeat technology has allowed placing less emphasis on throughput and more on process control. It has been predicted that the ability to achieve contrasts during processing of greater than 5 would allow wet processing to give more nearly vertical wall angles and minimize the variation in linewidth over steps. This paper will discuss one such system having a contrast value greater than 10, demonstrating the strengths and weakness of such a material. This system has shown the capability of patterning less than 0.5μm features on planar substrates at full film thickness and substantial exposure latitude, with reduced linewidth variation over steps as compared to more conventional materials. The impact of various processing parameters will be discussed, including agitation and temperature. The ability of this system to generate a lift-off profile in one step will also be examined.

An oxygen plasma assisted photoresist process has been developed to allow fabrication of reliable, high performance, low noise GaAs mixer diodes. Plasma tailoring of the photo-resist solved two critical processing problems. Plasma processing of the photoresist was repeatable and required minimal additional processing time. A matrix array of diodes having diameters from 1.5 to 5.0 microns were fabricated. Devices, having excellent ideality factors and low series resistance, were produced. Noise figures as low as 3.5 dB at 60 GHz were observed, and the devices were capable of withstanding temperature stress in excess of 300°C for an extended period of time.

The functional performance of ULTRAMAC PR914 positive resist on a 10:1 wafer stepper using monochromatic light at 436 nanometers was described in detail at the last SPIE Conference (March 1984). Submicron resolution capabilities in the order of 0.6 micron with edge wall profiles greater than 85° were shown, using the metal-ion-free developer, ULTRAMAC' MF62. This follow-up paper details the functional performance of ULTRAMAC' PR914 positive resist with a new metal-ion-free developer, ULTRAMAC" MF62A. When used at 1:1 dilution, ULTRAMAC' MF62A reduces the exposure energy necessary to obtain high contrast PR914 images by approximately 50% as compared to a 1:1 dilution of ULTRAMAC' MF62, making it a "fast" photoresist system by accepted industry standards. Data is shown with contact, projection and step-and-repeat alignment equipment. Also, a mechanism is proposed to explain the significant reduction in standing waves when ULTRAMAC' PR914 resist is developed with MF62 or MF62A. New data is shown on a modified version of PR914 resist, designated as ULTRAMAC" PR914 AR, for use on highly reflective surfaces, particularly over nonplanar (stepped) features. Deep UV stabilization of both ULTRAMAC' PR914 and PR914 AR, offering excellent thermal stability of critical dimensions, is also shown. Selectivity data of PR914 resist in plasma/RIE etch conditions is presented in comparison with other resists. The effect of high current ion implant (phosphorus and arsenic) on PR914 resist is also reported.

EBR-9, a positive E-beam resist, was developed in Japan as a possible replacement for PBS with wider processing latitude. The MIBK/IPA develope5 systems took 8-15 minutes in immersion development to yield sensitivities below 1 uC/cm² at 10 kV at temperatures of 25-30^oC. The newer developer, Developer V, can be used either with immersion or heated nitrogen-assisted spray development to give similar sensitivity but with higher contrast, at shorter development time. Solubility rate data are also presented. Our results show this to be another milestone toward a resist system with more process latitude than the standard PBS process.

Two anti-reflective coatings have been developed which eliminate linewidth variation of HPR-204 and HX-256 over stepped highly reflective topography. These anti-reflective coatings are composed of non-photoactive modified polyimides and laser dyes. Thin coatings exhibit the following desirable properties; strong absorption of 436nm light, the ability to dry etch, resistance to flow at 200°C, and good planarization properties.