This paper reports on the evaluation of XP SU-8 4000NPG for potential use in nanoimprint applications using hot UV imprint lithography. The use of this material is advantageous in that it can be imprinted, exposed and sufficiently cured all at the same temperature without any temperature cycling providing an isothermal process leading to short cycle times. Uncured XP SU-8 4000NPG has a Tg below 10ºC, yet its films are sufficiently robust to be handled at temperatures from 40 to 70ºC. This resist exhibits excellent flow properties in this temperature range, which is also a range where the post exposure bake of the exposed areas is sufficient to lock in the imprinted patterns and allow easy stamp removal. Wafers can be spin coated with the 4000NPG to provide films of less than 100nm thickness to more than 500 nm and subsequently baked to remove the residual coating solvent. Precoated wafers are introduced into the imprint tool and placed on a pre-heated chuck for a few seconds to reach the set temperature, and then the imprint stamp is applied under pressure for 30-60 sec to allow adequate time to properly fill the mold. While still in the mold, the resist is exposed through the transparent stamp and simultaneously cured for as little as 10 sec in order to remove the stamp without tearing or pattern deformation. The wafer can then be immediately removed from the imprint tool. The optimal temperature is a balance between resist flow, cure rate and the thermal stresses imparted into the cured film at the higher operating temperatures.
This paper describes a modification of the standard MIMIC technology, solving its main drawbacks, to define arrays of spherical or ellipsoidal microlenses. Perfectly symmetrical meniscuses have been obtained by using a XP SU-8 NO-2 layer beneath the PDMS mold. Moreover, the photostructurable properties of this polymer allow obtaining self-alignment structures for adequate fiber optics positioning. Microchannels ended with these meniscuses have been filled with standard SU-8 to obtain 3D microlenses. Agreement between theory and experimental results allows confirming the validity of the proposed technology.
Alkaline soluble maleimide based tetrapolymers which were prepared by free radical copolymerization are found to be suitable for use as non-imaginable resists in multilevel photolithographic processing. These materials offer widely variable undercut rates because of the ability to vary the composition during free radical polymerization and show little or no scumming when used in lift-off resist. This new polymer system may also be used as the base soluble resin in a photoresist formulation or a base soluble antiflective coating composition as well as used in making lift-off resists.
Thin film imaging processes such as top surface imaging (TSI) are candidates for sub-150 nm lithography using 193 nm lithography. Single component, non-chemically amplified, positive tone TSI photoresists based on phenolic polymers demonstrate good post-etch contrast, resolution, and minimal line edge roughness, in addition to being the most straightforward thin film imaging approach. In this approach, ArF laser exposure results directly in radiation- induced crosslinking of the phenolic polymer, followed by formation of a thin etch mask at the surface of the un- exposed regions by vapor-phase silylation, followed by reactive ion etching of the non-silylated regions. However, single component resists based on poly(para-hydroxystryene) (PHS), such as MicroChem's Nano MX-P7, suffer from slow photospeed as well as low silylation contrast which can cause reproducibility and line-edge-roughness problems. We report that selected aromatic substitution of the poly(para- hydroxystryene) polymer can increase the photospeed by up to a factor of four relative to un-substituted PHS. In this paper we report the synthesis and lithographic evaluations of four experimental TSI photoresists. MX-EX-1, MX-EX-2, MX- EX-3 and MX-EX-4 are non-chemically amplified resists based on aromatic substitutions of chloro- and hydroxymethyl- groups and PHS. We report optimized lithographic processing conditions, line edge roughness, silylation contrast, and compare the results to the parent PHS photoresist.
It is well known that onium salt structure has an influence on resist resolution and post exposure delay stability as well as solubility in typical resist solvents. As a result of our study, it was found that resists have higher contrast when t-butylphenyl substituents replaced phenyl or alkyl substituents in the cation segment of onium-type photoacid generators in both iodonium and sulfonium systems. Dissolution inhibition appeared to play a primary role. In this paper we also report the results of our investigation into onium-type photoacid generators possessing reduced diffusion, lower volatility and suitable acidity to cleave common protecting groups such as t-butoxycarbonyl, acetal and t-butyl. Substituted benzene sulfonic acids were very useful for cleaving common protecting groups in polyhydroxystyrene based Deep-UV resist systems. The addition of alkyl groups to the ring had only slight effect on acid diffusion. Perfluoro sulfonic acids were required to cleave adequately, the acid stable leaving groups in methacrylate resist systems.
Exposures leading to 0.18 micrometer or better resolution are now being demanded by IC development. Photolithography using 193 nm exposure tools is the leading technology for the development of these next generation of devices. We are reporting on our development efforts on the TER resist system, which is a single layer resist designed for image evaluation applications at 193 nm exposure wavelengths. The TER-system has been developed to allow equipment manufacturers to evaluate their equipment, to provide R&D lithographers with materials to qualify their 193 nm equipment and to determine process control parameters. The TER-system is a chemically amplified methacrylate resist terpolymer. It is composed of methyl methacrylate (MMA), methacrylic acid (MAA) and an acid labile acrylic ester. We have evaluated different leaving groups as the acid labile component and we report on the initial results of several. We also examined different onium salts as the PAG component. One such example is di(t- butylphenyl)-iodonium p-toluenesulfonate and we report on other examples which were used. We evaluated the thermal stability of the resins and thermal analysis showed they start to decompose at about 125 degrees Celsius when tetrahydropyranyl methacrylate is used. Other more thermally stable systems were also evaluated. Post apply bake (PAB) temperatures of 100 - 125 degrees Celsius were preferably used with the tetrahydropyranyl ester. Other more thermally stable esters, such as tetrahydro-4-methyl-2-oxo-2H-pyran-4-yl methacrylate (mevalonic lactone), ethoxy-ethyl methacrylate and 3-oxo-cyclohexyl methacrylate, also are described. Exposures in the range of 5 - 50 mJ/cm2 were typical and varied depending on the ester, the PAG, and other processing parameters. The acid catalyzed reaction rates after exposure were observed to be rapid. In all cases, post exposure bake (PEB) was typically carried out at 10 degrees Celsius or lower. Initial exposure evaluations at 193 nm and 248 nm show good resolution and image fidelity. The TER-system produced better than 0.225 micrometer resolution using 248 nm exposure equipment (NA equals 0.55) suggesting that better than 0.18 micrometer resolution is possible with 193 nm exposures. Results of resist synthesis, formulation and evaluation are presented.
Results are presented from a study undertaken to evaluate resist casting solvent composition and molecular weight variation in PMMA for electron beam exposure. PMMA cast in several solvent systems have been evaluated for lithographic performance. Additionally, formulations in chlorobenzene with minor variations in molecular weight have been evaluated for batch-to- batch uniformity. A 10 KeV MEBES electron beam system has been used to study resist sensitivity, contrast, and process latitude. Using a two-factor, three level factorial designed experiment, prebake and development time have been varied as controlled process factors. Samples with varying molecular weights were shown to have wide process latitude. These samples gave comparable performance while their molecular weights varied from 539 K to 614 K, and polydispersity varied from 3.3 to 6.1. Resist samples with chlorobenzene, PGMEA (propylene glycol monomethyl ether acetate), and anisole as the casting solvent resulted in equivalent performance.
This paper describes the use of a 193 nm surface imaging resist in a new small-field, deep-UV projection exposure system. The 193 nm surface imaging technology utilizes commercial photoresists, in conjunction with a small field step-and-repeat exposure system. Typical processing characteristics of the imaging chemistry are presented, along with a detailed description of the projection exposure system. The resist uses vapor phase silylation with oxygen RIE developing and has been shown to provide wide focus latitude and better than 0.2 micrometers resolution. The imaging system uses a catadioptric lens with 0.5 NA for 0.20 images.
It is no longer possible to have just the best technology in the semiconductor equipment and materials market and remain successful. Each product tends to last for only one generation of IC devices. This high rate of imaging technology change means that the material or equipment manufacturer must have a large base of expertise to keep up with the rapidly changing needs and requirements of the technology. Also necessary is a large source of capital to finance development, manufacturing, and testing equipment. Unfortunately, the sequence of short business cycles, with limited lifetimes for each lithographic technology, is expected to continue for at least another ten years, until some technology or technologies, with long lifetimes through a large number of device generations, is firmly in place.
The intent of this paper is to compare the potential IC manufacturing requirements, product timing, and the technological capabilities of i-line, DUV (248 nm), VUV (193 nm), and x-ray. From this we intend to project the technological potential of each. To do this we intend to determine the limiting resolution and DOF of each technology, evaluate the resist and processing capabilities, examine the engineering requirements. We will evaluate the impact of phase shift mask technology, surface imaging, and planarization and their impact on lithographic potential. From this information we will provide a comparison of these four technologies. This data will then be compared to IC device requirements and timetables from which a lithographic product need and lifetime relationship can be determined for each technology.
A variety of novolac-based polymers and blends with photoactive compounds were studied for their suitability as resists in a 193-nm positive-tone silylation process. The addition of photoactive compound was found to reduce the sensitivity of the resist and to hinder the diffusion of the silylating agent. Pure meta-cresol novolacs and polyvinylphenols, both of which can be polymerized to high (> 10,000) molecular weights show the best sensitivity for this process. Diffusion rates correlate with the molar volume of the silylating agent, although the activation energy does not. Resolution of 0.2-micrometers line-and-space gratings has been achieved with the polyvinylphenol and meta-cresol novolac resins.
This paper studies e effects of process conditions and dye additives on sidewall profiles using RS—1 designed experiments. We have explored the mechanism of forming negative sidewall profiles (above 90) in a positive photoresist, the dependence of depth of focus (DOF) and exposure latitude upon sidewall angle The resist studied is a positive, dual purpose (g—, i—line) resist, ULTRAMAC EL2015. The study presented in this paper was done in i—line but similar phenomena were observed in g—line as well. The effect of two different actirtic dyes in various concentrations on wall angle control is demonstrated. The two dyes investigated are both soluble in resist solvent but their solubility in developer is very different and their effect on required exposure energy is different. The contribution of the dyes to the absorption of the resist, their effect on swing curve and surface inhibition is evaluated and compared. The surface inhibition effect of undyed resist has been determined to be the most critical parameter influencing profiles, as increased post exposure bake temperature increases sidewall profile angle.
The accelerated drive toward 0.5 and 0.3 urn optical imaging is putting severe
pressure on both the equipment and photoresist vendors. Materials must give
both high resolution and high process latitude. These needs led to the develop-
ment of EL2015 positive photoresist series. This is a high contrast, high
resolution photoresist series based on the same chemical concepts used in our
PR1O24MB resists. This new resist contains a 2,1,5-naphthoquirionediazidesulfonate
ester of a special novolac as its photoactive component. This is combined with
an improved novolac resin for better film integrity. EL2015 is a versatile
positive resist optimized for g-, h-, i-line, and broadband exposure tools.
Resolution of better than 0.50 urn has been routinely obtained with current
0.40 NA i-line steppers and 0.40 urn resolution at best focus. A focus latitude
of greater than 1.5 urn for 0.5 urn images with an exposure latitude of 30-50%
has been demonstrated on i-line equipment. Finally, the thermal stability
and plasma etch resistance of EL2015 has been found to be comparable to current
high resolution g-line photoresists.