EP0855050A1

EP0855050A1 - Water-processable, chemically amplified resist compositions and processes

Info

Publication number: EP0855050A1
Application number: EP96931943A
Authority: EP
Inventors: Joseph Graham Davidson Darling; Alexander Maxovitch Vekselman
Original assignee: Martinex R&D Inc
Current assignee: Martinex R&D Inc
Priority date: 1995-10-13
Filing date: 1996-10-11
Publication date: 1998-07-29
Also published as: WO1997014079A1; GB9520950D0; CA2234512A1

Abstract

Solvent-processable chemically amplified resists have a photoresist layer on a substrate; the layer comprises a solvent-soluble, non-light scattering film of polymer which bears vicinal dicarboxylic acid or monoesterified dicarboxylic acid groups, and a photoinitiator as a source of acid catalyst; the dicarboxylic acid or ester groups are acid catalyzably dehydrated or dealcoholated by the acid catalyst to acid anhydride groups which render the polymer insoluble, in a solvent in which the original polymer is soluble, or soluble in a solvent in which the original polymer is insoluble. The resist is exposed in an image-wise manner, for example, to UV radiation which results in release of the acid catalyst in the exposed areas; on heating, the acid catalyzes the dehydration or dealcoholation of the dicarboxylic acid or ester groups to acid anhydride groups whereby an image is defined by solvent-insoluble and solvent-soluble zones of the layer. Alternatively a reverse image is defined if the resist is first thermally dehydrated or dealcoholated, then exposed, then rehydrolyzed or alcoholyzed in exposed areas. This system enables the use of water and/or alcohol developers in many cases.

Description

WATER-PROCESSABLE. CHEMICALLY AMPLIFIED RESIST COMPOSITIONS AND PROCESSES

BACKGROUND OF THE INVENTION

Background ofthe Art

This invention relates to a chemically amplified resist, a process of producing such a resist, and a method for microlithographic production or reproduction of an image. The invention is more especially concerned with such resists which are water-processable.

Background ofthe Art

Production of resists for photolithography is described in U.S. Patent 5,384,220 and in Larry F. Thompson, C. Grant Willson, Murrae J. Bowden (Eds) "Introduction to Microhthography", 2nd ed.; American Chemical Society: Washington, D.C, 1994.

A new generation of "Chemically Amplified" (CA) resists is entering pilot and mass-volume lines for production of semiconductor devices with sub-micron features (Reichmanis, E. et al., "Chemical AmpUfication Mechanisms for Microhthography," Polymers in Microelectronics, L.F. Thompson, CG. Willson and S. Tagawa, Editors, 1994, ACS, Washington, D.C. USA, pp. 2-24). One mechanism of chemical ampUfication is to first photo-produce (photogenerate) a small amount of catalyst, in most cases an acidic material such as an acid or acid salt. In a subsequent step of heating, such acid induces a cascade of material-alteration reactions, so that the primary photogeneration of acid effect of the irradiation is amplified a thousand times. Patterned irradiation, either through a mask or by Laser Direct Imaging (C. Decker and B. Elzaouk, "AcryUc Photoresists for Laser Direct Imaging", Polym. Mater. Sci. Eng. Vol. 72, 1995, pp. 406-407; G.M. Wallraff, R.D. Allen, W.D. Hinsberg, CG. Wilson, L.L. Simpson, S.E. Webber and J.L. Stutevant, "A chemically amplified photoresist for visible Laser Direct Imaging", J. Imaging Sci. Technol. vol. 36(5), 1992, pp. 468-476), followed by overall heating, thus creates areas of altered and unaltered material in a resist coating. A subsequent development step then removes either the exposed areas to give a negative-tone image, according to the composition of the resist, and often on the method of processing. Thus in a leading CA resist composition of poly-(4-[t- butoxycarbonyloxy]-styrcne) and onium salt (PtBOCOSt resist) that employs "polarity alteration" chemistry (as shown in Scheme I), developing with aqueous alkali (optionally with added alcohol) removes exposed areas to give positive-tone images, while a less polar organic solvent removes only unmodified areas to produce negative-tone imaghes (H. Ito, "Polarity Change for the Design of Chemical Amplification Resists," Irradiation of Polymeric materials, E. Reichmanis, CW. Frank and J. M. O'Donnell, Editors, 1993, ACS, Washington, D.C. pp. 197-223). Such prior art CA resists have so far been based upon especially designed and synthesized, and thus expensive, specialty polymers. Moreover, all of them require organic solvents to cast their films, and often to develop and strip them off. It would be desirable to provide a CA resist that could be processed entirely with less expensive and hazardous liquids, in particular, with pure water. An example of a water-developable CA resist is poly(methylacrylamidoglycolate methyl ether) or poly(MAGME), but since it works by crosslinking instead of a polarity-alteration, swelling ofthe undissolved material is a problem (Anders Hult, Otto Skooling, Sven Gothee and Ulla Mellstrom, "A New Higher-Sensitivity, Water-Developable Negative Photoresist," Polym. Mater. Sci. Eng., vol. 55, pp. 594-595.

It would be desirable to provide a chemically amplified resist which is relatively inexpensive to produce, and which, in particular embodiments, can be produced from readily available chemicals.

A CA resist with high sensitivity, low cost and water-processabiUty would also be useful for other appUcations besides micro-lithography that use resists, that are not so demanding in resolution but are very high in volume. These include phototypesetting and other photo-mechanical printing processes, such as reviewed in: Michael H. Bruno, "Photomechanical Printing Processes", in John M. Sturge (Ed.) "Neblette's Handbook of Photography and Reprography - Materials, Processes and Systems", 7th ed.; Van Nostrand Reinhold Company: Toronto, 1977, pp. 481-495 (which describes the printing and packaging industry in the United States in 1975 as being worth over 70 bilhon dollars, or 5% of the GNP). These other appUcations also include printed circuit manufacturing, as described in: Raymond H. Clark "Handbook of Printed Circuit Manufacturing", MacMillan of Canada: Agincourt, Ont. Canada, 1985. Another review of resists for many applications is contained in: D. Winkelmann et al "Imaging Technology", in B. Elvers et al (Eds.) "Ullmann's Encyclopedia of Industrial Chemistry", vl3, p571-660.

Still further, the invention describes a chemically amplified resist which may be solvent-processable and especially water-processable, and a method for production ofthe resist.

Current resists require organic or alkah solutions to remove film not removed under developing conditions. The resists ofthe invention can often be stripped with warm or hot water (failing that, methanol, n-butanol or other alcohol).

Orgamc solvents are expensive and pose disposal or recycling problems. Aqueous alkali, except for quaternary ammonium (which is also expensive or toxic), can contaminate semiconductor substrates with inorganic ions. Pure water is inexpensive, safe, and non-contaminating. Methanol or ethanol are also reasonably inexpensive and biodegradable, though somewhat less desirable than pure water.

U.S. Patents Nos. 5,017,461 (May 21, 1991) and 5,252,435 (Oct. 12, 1993) describe water-soluble resists involving other compositions and reactions than those ofthe present invention..

BRIEF DESCRIPTION OF THE INVENTION In accordance with one aspect ofthe invention, there is provided a chemically amplified resist comprising: a substrate having a photoresist layer comprising a water-soluble non-Ught scattering, film of polymer, said polymer bearing vicinal dicarboxylic acid or mono-esterified dicarboxyUc acid groups, and a photoinitiator which releases a species which can convert or catalyze the conversion of said acid or monoesterified acid group to acid anhydride groups. One mechanism for this is to provide a species which lowers the pH such as an acid which on exposure in an image-wise manner, said dicarboxyUc acid or mono-esterified dicarboxylic acid groups are acid catalyzably dehydrated or dealcoholated to acid anhydride groups. These acid anhydride groups rendering said polymer insoluble in a solvent in which the acid or ester group-containing polymer is soluble, or rendering said polymer soluble in a solvent in which the acid or ester-group containing polymer is insoluble. Compositions of anhydride polymers and onium salts are also dislosed which can be used in the formation of positive-tone images.

DETAILED DESCRIPTION OF THE INVENTION In accordance with another aspect ofthe invention there is provided a method for microlithographic production or reproduction of an image with a resist of the invention comprising exposing the photoresist layer in an image-wise manner to convert said acid groups or monoesterified acids groups to anhydride groups, as by release of an acid from the photoinitiator in exposed zones of the layer, and subjecting the exposed layer to a temperature effective for the formation of the anhydride, as by acid catalyzed dehydration or dealcoholation of said dicarboxylic acid or said monoesterester groups to acid anhydride groups, said acid anhydride groups rendering said polymer insoluble in a solvent in which the acid or monoester group containing polymer is soluble (or dispersible), or soluble (or dispersible) in a solvent in which the acid or monoester-group containing polymer is insoluble, whereby an image is developed which is defined by solvent insoluble zones and solvent soluble (or dispersible) zones of said layer.

In accordance with still another aspect of the invention there is provided a process for producing a solvent-processable chemically amplified resist comprising: i) applying to a substrate, a photoresist layer comprising: a) a solvent-soluble, non- light scattering film forming polymer, said polymer bearing vicinal dicarboxylic acid or mono-esterified dicarboxyUc acid groups, b) a photoinitiator which releases a species, as noted before, such as an acid on exposure in an image-wise manner, and c) a solvent for said polymer, and ii) drying the photoresist layer to remove said solvent, said dicarboxylic acid or ester groups being convertible to anhydride groups by a species released by the photoinitiator, as with an acid or ester group which are acid catalyzably dehydratable or dealcoholatable with said acid from said exposed photoinitiator, to form acid anhydride groups rendering said polymer insoluble in a solvent in which the acid or ester group containing polymer is soluble, or soluble in a solvent in which the acid or ester group containing polymer is insoluble.

In accordance with another aspect of the invention there is provided a solvent-processable chemically amplified resist comprising: a substrate having a photoresist layer comprising a solvent-soluble non-Ught scattering film of polymer, said polymer bearing vicinal dicarboxyUc acid or mono-esterified dicarboxylic acid groups, and a photoinitiator which releases a species, as noted above, such as an acid on exposure in an image-wise manner, said dicarboxylic acid or ester groups being dehydratable or dealcoholatable to acid anhydride groups. In accordance with yet another aspect of the invention there is provided a method for microUthographic production or reproduction of an image comprising: i) providing a resist as defined in the preceding paragraph, ii) dehydrating or dealcoholating the dicarboxylic acid or monoester groups to acid anhydride groups which render the polymer insoluble in a solvent in which the acid or monoester group-containing polymer is soluble (or dispersible), or soluble in a solvent in which the acid or ester group containing polymer is insoluble, iii) exposing the photoresist layer in an image-wise manner to release the acid from the photoinitiator in exposed zones of the layer, iv) treating the film with water or alcohol, whereby an image is developed which is defined by solvent-soluble-zones and solvent-insoluble zones of said layer.

Step ii) in this latter method may suitably be achieved by heating at an elevated temperature, for example, greater than 75°C (for at least 2 minutes), more preferably greater than 100 °C (for 2 minutes), and more preferably at or above 160°C for 2 minutes in the case of vicinal dicarboxylic acid groups or 190°C for 2 minutes for ethyl monoester groups.

In step iv) the anhydride groups are acid-catalyzably hydrated or alcoholated to diacid or ester acid groups to form the latent image.

For example, this hydration or alcoholation may be achieved by treatment with steam or water vapour at 100-130°C, preferably about 120°C for 2 minutes, or vapours from boiling ethanol at about 78°C for 2 minutes; this may typically be followed by reUef development of the image with pure water, i.e., positive-tone development by water or an alcohol.

In especially preferred embodiments, the resist is water-processable and is derived from a water soluble non-light scattering film forming polymer bearing vicinal dicarboxyUc acid groups. Alternatively, a non-light-scattering surface treatment or coating may be apphed above and or below the layer, as long as the layer does not interfere with the solubility requirements of the resist process (e.g., a top layer would be totally developable or compatibly photosensitive with the resist layer). In such case the solvent for the polymer is preferably an aqueous solvent, especially water, and the dehydration to form acid anhydride groups renders the polymer water-insoluble.

It is especially advantageous to be able to use water as the processing or stripping liquid. The film-forming polymer may also be one bearing vicinal mono-esterified dicarboxylic acid ester groups. In such case one of the acid groups may be esterified. In this case the (acid) catalyzed reaction produces acid anhydride groups with loss ofthe alcohol ofthe ester groups. Film-forming polymers which are not soluble in water but are soluble in alcohols, especially lower alcohols such as methanol, or other non-toxic, relatively inexpensive solvents are also contemplated by the invention where these produce other advantages. Thus, for example, film-forming styrene-maleic acid copolymers and styrene-maleic acid ester copolymers may not be water-processable but have an advantage of containing plasma-resistant phenyl groups.

Suitable water-soluble film forming polymers include copolymers of dicarboxylic acids with comonomers. One suitable dicarboxyUc acid is maleic acid which forms water-soluble copolymers with comonomers such as ethylene, vinylacetate and methyl vinyl ether. Other suitable monomers that contain vicinal dicarboxylic groups, which can be homopolymerized, or copolymerized with maleic anhydride include itaconic anhydnde, 3- or 4-vinylphthalic anhydride, cis-1,2,3,6- tetrahydrophthalic anhydride, or cis-5-norbene-endo-2,3-dicarboxylic anhydride (N.G. Gaylord, A.B. Deshpande and M. Martan, "Cyclopolymers of cyclopentadiene and maleic anhydride", J. Polm. Sci. Polym, Lett. Ed. vol. 14, 1976, pp. 679-682, and references therein). The last two monomers or comonomers provide for resists that are particularly advantageous for microlithography with submicron resolution, with polymer structures that contain alicyclic units that do not absorb vacuum-UV (<200 nm), yet that confer resistance to many plasma etching conditions (Kunz, R.R., S.C. Palmateer, et al. (1996). "Limits to etch resistance for 193-nm single layer resists." "Advances in Resist Technology and Processing Xiπ, Sanat Clara, CA, U.S.A., Proc. SPIE, vol. 2724)." Dehydration of the dicarboxyUc acid groups in these copolymers, to acid anhydride groups, renders the copolymers water- insoluble.

The ratio ofthe dicarboxylic monomer to co-monomer can be 100:0 to 20:80, or sufficient for its structure or state (i.e. anhydride or otherwise) to affect the overall solubility or other properties of the resist. Typically the ratio is near 50:50 due to a tendency towards alternating copolymerization of maleic anhydride, particularly with electron-rich monomers like methyl vinyl ether or styrene. As with other polymer resists, the molecular weight is generally between 5,000 or 8,000 up to 70,000 weight average molecular weight, while preferred molecular weights are 10,000- 40,000 g/mol: sufficient to form a strong enough coated film, but not so high that its spin-coating solution becomes unacceptably viscous and development or stripping unacceptably slow. The copolymer is suitably appUed to the substrate as a clear aqueous or alcoholic solution of 1-40 wt.%, preferably 5-20 wt.% of the copolymer together with the photoinitiator. One suitable photoinitiator is diphenyl iodonium triflate (DPI-Tr) which suitably may be employed in an amount of 1 to 20 wt.%, preferably 2.5 to 10 wt.% based on the copolymer. Silver triflate (Agθ3SCF3) is another example of acid photogenerator that is water-dispersable, though less sensitive. It is suggested that any water-dispersible (or water-soluble) photogenerators which release an acid anion species within at least a pKa of 10 (towards the base range) of triflate can perform well in the practice of the present invention. Substances which are acidic or mre acidic than HOTf would also be suitable. While such obvious candidate materials as triphenylsulfonium triflate is insufficiently dispersible in water to itself perform, substitution ofthe phenyl groups with hydrophilic groups or highly ionic groups should increase the dispersibility sufficiently to enable the derivatives to perform in the aqueous environment. Additional references which describe water-soluble photoacid generators which release triflic acid are described in "Water-soluble onium salts: a new class of acid generators for chemical amplification positive resists" T. Sakimizu, H. Shiraishi and T. Ueno in E. Reichmanis et al., Ed. "Microelectronics Technology: Polymers for Advanced Imaging and Packaging," ACS Symp. Ser. 614, 1995, pp. 124-136.

Not all photoinitiators are spectrally sensitive to useful ranges of the elctromagnetic spectrum or insufficiently sensitive to perform readily. It is well known in the art to use spectral sensitizers to broaden the spectral response range or to enhance the speed of the response. Spectral sensitizers are selected appropriately for each of the classes of photoinitiators used, as sensitizers behave differently for each of the initiator classes. Sensitizers for the iodonium and sulfonium salts are well described in U.S. Patent Nos. 4,250,053 and 4,386, 154.

The solution or polymer melt (free of substantive amounts of solvent) is appUed to the substrate, for example, a silicon wafer, for example, by conventional coating methods including, but not limited to, gravure coating, slot coating, curtain coating, meniscus coating and spin-coating, to form a clear, smooth film of 0.05 to 500 μm, preferably 0.5-2 μm thickness for micro-electronic appUcations, and up to 1000 μm or more for circuit board patterning or phototypesetting.

The concentration of components is selected within this range, in conjunction with the coating (e.g., spin) rate, and molecular weight of the polymer to achieve a desired thickness of the resist film.

In the manufacturing process leading to the negative tone development in water or alcohol, the film is dried only enough to remove solvent, with the drying conditions controlled so as to not provoke further conversion to anhydnde; suitably this may be achieved in a Post-Applied Baking (PAB) step at above 80°C, but below 160°C, e.g., at 100-130°C for a short time, for example, 30 seconds.

The coating solution ofthe copolymer may be formed from the corresponding maleic anhydride copolymer. For example, solid ethylene, vinyl acetate or methyl vinyl ether-maleic anhydride copolymers are available which will dissolve in water with hydrolysis to the corresponding water-soluble maleic acid copolymer, or, together with styrene-maleic anhydride copolymer, in alcohol with alcoholysis to the corresponding alcohol-soluble mono-esterified maleic acid copolymer. These copolymers of maleic anhydride are readily available commercially. The anhydride form of the polymer used in combination with the onium salt in the positive-tone system for development in water may be formed by applying the anhydnde form and the onium salt in a solution of (aprotic) solvent, or as the melt, as well as being formed in situ by heating the diacid or monoester acid form. The compositions of the invention, whether the acid or monoester with the initiator or the anhydride with the onium salt may be provided in a commercially useful form as a solution, melt, solid film or coating, or powder. Other anhydride monomers besides maleic anhydride which can be employed to provide the vicinal dicarboxyUc acids or mono-esterified dicarboxylic acid groups in the said copolymers include mono-substituted maleic anhydrides, for example, 2- methylbutenedioic anhydride or citraconic anhydride or disubstituted maleic anhydrides, for example, 2,3-dimethylmaleic anhydride, though these would be more expensive and copolymerize with greater difficulty. The comonomers are particularly selected to confer UV-transparency and water-solubihty, for example, ethylene, methyl vinyl ether, or resistance to fluorocarbon plasma etch, for example, styrene and substituted styrene (e.g., with alkyl, alkoxy or other aliphatic substituents of 1 to 10 carbon atoms), as well as cyclopolytmerizing cyclopentadiene and furan (both 1:2 with maleic anhydrides), 4-vinyl- and 4-allyl-cyclopentene and cyclcohexene.

The polymer may be one in which one ofthe vicinal dicarboxylic acid groups is esterified with an alcohol. The alcohol may be selected from a wide range of alcohols, for example, lower aliphatic alcohols, especially methanol or ethanol, and alcohols providing an aromatic content, for example, benzyl alcohol, as well as HOCH2COOH and other hydroxyl alkyl or arylcarboxylates for increased water solubility so that the polymer bears vicinal mono-esterified dicarboxylic acid groups. The chemistry of maleic anhydride copolymers, includ ng hydrolysis to diacid form and alcoholysis to ester-acid form is reviewed in Manfred Ra zsch "Alternating Maleic Anhydride Copolymers", Progr. Polym. Sci. yl988, vl3, p277-337.

Exposure of the photoresist layer to deep UV radiation, longer wavelength radiation to which the photoinitiator has been spectrally sensitized, an electron beam or X-rays results in release of the active species, e.g., the acid catalyst from the photoinitiator. This can be carried out in an image-wise manner so that the release of acid occurs in zones of the layer corresponding to a positive or negative image. By way of example exposure may be with>15, preferably >20, and more preferably >25 mJ/cm^ of deep UV (below 350nm) radiation for sufficient contrast, but not requiring > lOOmJ/ cm-2, and preferably not requiring > 50mJ/ cπ f°^r sufficient sensitivity

The thus exposed layer is subjected to a temperature, typically in a Post- Exposure Baking (PEB) effective for the (e.g., acid) catalyzed dehydration of the dicarboxylic acid groups, or dealcoholation of mono-esterified dicarboxylic acid groups, to acid anhydride groups, without thermal dehydration of dicarboxylic acid or mono-esterified dicarboxyUc acid groups without acid groups. Typically this may be achieved at 125 to 135°C for 30-60 seconds.

It will be understood that thermal dehydration of the polymer during the preparation or coating phase, as previously noted, is to be avoided or maintained at a minimum (e.g., less than 5% or 2%, preferably less than 1%, and more preferably less than 0.5% of available groups which can be dehydrated) insofar as such thermal dehydration is not confined to the same zones subject to acid catalyzed dehydration in the negative-tone system developed in water or alcohol. The dehydration is the basis ofthe image formation and thus must be confined to the zones of acid catalysis based on the image-wise exposure. In this way, a latent image is produced which is easily developable in water or alcohol within seconds, for example, stripping the water-soluble zones from the substrate to leave an image defined by the water-insoluble zones.

IR and TGA studies show that under such conditions non-irradiated areas still consist of water-soluble or alcohol-soluble acidic forms of copolymer. But, heating this with photo-produced triflic or other acid causes sufficient dehydration to alter the solubility of the exposed versus unexposed areas sufficiently to enable good contrast for the relief-developed images. As a guideline, it has been found that at least 20% conversion of functional groups (the acid or monester acid, or the enhydride groups) should be transfomed. It is desirable that at least 20-60% of the hydrophilic/hydrophobic groups ne transformed. It is idealized to practice almost complete dehydration towards the less hydrophihc anhydride form or vice evrsa to the more hydrophilic acid or monoester acid form. Besides this relief developing, the difference in reactivity and hydrophobicity between exposed and non-exposed areas also allows functional developing, e.g., introduction of inorganic ions, polyamino aromatic, or other compounds selectively only into non-exposed areas to confer fluorocarbon etch resistance or for other purposes.

Alternatively, the photoresist layer is first heated, for example at 160°C for 2 minutes, sufficiently to convert, by heat alone and without acid catalyst, vicinal dicarboxylic acid or monoesterified dicarboxylic acid groups to anhydnde groups. It is then exposed in an image-wise manner to release acid from the photoinitiator in exposed zones of the layer. It is then treated with water or alcohol vapours, under conditions effective for the acid-catalyzed hydrolysis or alcoholysis of the acid anhydride to dicarboxyUc acid or monoesterified dicarboxylic acid groups, but not effective for such hydrolysis or alcoholysis in the absence of acid, for example, with steam at 120°C for 2 minutes. This produces a positive latent image that is, for the same image-wise exposure, resist composition and developing solvent, the reverse of that formed using the procedure described above.

Maleic anhydride and maleic acid copolymers with ethylene, styrene, vinyl acetate and methyl vinyl ether are mass-produced items. Along with good mechanical and film casting properties, such copolymers possess highly reactive anhydride moiety, that is transformable into acid, salt, amide, etc. by appropriate reagents. Particularly in microhthography, some MA copolymers have been used, but only as a protection layer against basic contaminants. Recent research (CH. Zhang, A.M. Vekselman, G.D. Darling, Chem Mater. vol. 7, 1995, pp. 850-855) shows that poly-(di-butyl fumarate-co-styrene) easily undergoes thermoacidolysis at 100-130°C towards poly-(fumaric acid-co-styrene), which was rapidly soluble in aqueous alkali to form positive relief images. But above 130°C, a detectable reaction of dehydration to give cyclic anhydride increased hydrophobicity of the matrix and depressed dissolution. As strong acids catalyze a variety of rearrangements, it appeared that photo-produced acid would promote dehydration at PEB temperatures, and such areas would be dissolved slower or not at all in alkali or polar solvents (Scheme II). Onium salts are standard Photo- Acid Generators (PAG) in microlithography, but the existence and appUcability of their solubility of some in water have been neglected. Some onium salts are in fact fairly soluble in alcohols and alcohol/water mixtures, and thus might be dispersable in a water-soluble polymer, which might also help in dissolving them or their photoproducts.

Materials and Instruments.

Polymers were used as received from SP Scientific Polymer Inc: methyl vinyl ether-co-maleic anhydride (I, cat.# 317, CAS# [9011-16-9]), methyl vinyl ether-co-maleic acid (H, cat# 374) and poly(acτylic acid) (HI, cat# 026), whose nominal molecular weights specified as "medium", "low" and 250 K, respectively. Poly-ethylene-co-maleic anhydride (IV) was from Aldrich (cat.# 18,805-0, CAS# [9006-26-2]), nominal M_w = 100-500 K. 2,6-diaminopyridine (cat.# D2.440-4; CAS# [141-86-6]) and 1,10-diaminodecane (cat.# Dl,420-4) were used as received from Aldrich. Onium salts: diphenyl iodonium triflate (DpI-Tr) and hexafluoroantimonate (DPI-Sb), as well as triphenyl sulfonium hexafluoroantimonates (TPS-Sb) were synthesized by ion-exchange or other known methods. Analytical reagent grade acetone was from BDH. Distilled water was used to dissolve copolymers and an onium salt (2-10 wt% vs copolymers) to 5-20 wt% concentration. Distilled water was used for rehef developing as well. Post-apply baking (PAB) and post-exposure baking (PEB) were performed on a hot plate at 50- 160°C for 10-120 s. UV illumination was done with wideband 100 W Hg lamp with 256 nm narrowband filter controlled by a timer, or using a homemade system with 1 KW Hg lamp in an ORIEL housing with consensing lenses, through water to absorb IR radiation but without any UV filter. An REK/73 step tablet (from Optoline- Fluroware) was used with several areas of 0-100% transparency. For image evaluation, the following items of apparatus were used: UV-VIS Shimadzu 210-UV spectrophotometer, Brooker IF-48 FTER spectrophotometer, Seiko TGA-7 station, and optical microscope (200X and 400X) with attached 35-mm camera.

Results and Discussion.

Solubility of onium salt in water. To check solubility of several commonly used onium salts in pure water, about 25 mg of fine crystals were shaken in 5 ml of water for overnight. More "ionic" DPI-Tr dissolved completely to give transparent solution. Only a small number of crystals were left in clear solution of DPI-Sb, while a lot of crystals were left in cloudy TPS-Sb solution. All three solutions after filtration (0.8 and 0.2 μm subsequently) showed enormous peaks (»3 absorption units) in the deep-UV region due to aryl moieties of onium salts. Thus, even TPS-Sb salt has some solubility in water. Addition into the same vials (without filtration) of ca. 5 wt% of I and shaking for 30 min gave clear solution with both DPI salts and slightly cloudy solution with TPS-Sb, but without big crystals (Table I). Thus, addition of polymer of medium polarity with both water soluble (acidic and methoxy moieties) and hydrophobic (hydrocarbon . backbone) units improved onium salt solubility in such polymeric water solution.

Table 1 Solubility of Oni u Salts.

Onium Salt Pure Water Water plus 5 wt% of I

DPI-Tr + + + +

DPI-Sb +- + +

TPS-Sb -+ +- (++) clear, (+-) clear with some crystals, (-+) cloudy with crystals

Resist processing. Spin-coating onto siUcon wafers at 600-2000 RPM gave smooth optically clear films of 0.3-2 μm thickness without visible phase separation. Ca. 1 μm films, cast from water/I/DPI-Tr (100/10/1 wt) system were subjected to brief sensitivity evaluation with variation in PAB and PEB conditions. After 2 min of PAB at 60, 100, 130 and 160°C, samples were exposed through step tablet at 254 nm and heated another 2 min at 100, 130 or 160°C After brief cooling, samples were immersed in water for 30 s, spin-dried and sensitivity was estimated by identifying the apparently unaffected area with lowest UV-dose (Table H). The only baking conditions good for producing negative relief images was PAB 100-130°C, then later PEB around 130°C Both irradiated and non-irradiated areas appeared to be insoluble (presumably dehydrated) after baking at 160°C Insufficient low temperature of PAB <100°C and PEB <130°C left all areas water-soluble, again regardless of exposure. The simplest explanation is that insufficient prebaking leaves too much water, which slows down acid-catalyzed reactions.

Table II. Sensitivity ofthe resist in various PAB and PEB processing conditions.

120 s 120 s PEB at PAB at 100° 130°C 160°C

60°C all soluble all soluble n a

100°C all soluble 25 mJ/cm² all insoluble

130°C all soluble 25 ml/cm² all insoluble

160°C all insoluble n/a n/a

"soluble" and "insoluble" refer to water solubihty of exposed and non- exposed areas

In fixed processing conditions of PAB 130°C for 10 s and PEB 130°C for 40 s, compositions with I and 10.0, 5.0 or 2.5 wt% of DPI-Tr showed sensitivities of 25, 42 and ca. 100 mJ/cm² respectively. 1.0 wt% of the PAG was too low to get any image with less than 300 mJ/cm . Thus, without sentiziser, ca. 5 wt% of the PAG was needed to absorb enough DUV (Deep UV, e.g., below 300 nm) energy and produce enough acid to alter the matrix.

Ethyleneco-maleic copolymer IV shows the same behavior as methyl vinyl ether analog in similar conditions. Lower molecular mass methyl vinyl ether- comaleate II behaved worse than I, in that even its catalytically dehydrated areas were too quickly eroded by water. A brief test of compositions with onium salt and polyacrylic acid III failed to produce any image under the same readily accessible processing conditions of PAB and PEB at 130°C for 1 min and DUV dose <100 mJ/cm². Unlike DPI-Tr, other onium salts DPI-Sb and TPS-Sb also failed to produce any developable image with I, possibly due to too great a phase separation of PAG from copolymer, or lesser efficiency of hexafluoroantimonic vs. triflic acid, although both are very strong.

IR Monitoring of the Resist Transformation. FTIR spectra of the resist (I:DPI-Tr 10:1 wt%) films after different DUV doses for PAB 110°C for 30 s and PEB 130°C foi 30 s weie provided on the samples. Increased UV dose resulted in a steady decrease of DR. signal from COOH groups at 1720 cm^"1 and increase of cyclic anhydride carbonyl peaks at 1780 and 1850 cm-1. The latter exactly match those from 5-membered rings of starting maleic anhydride copolymer, that are much more sterically favourable than intermolecular or 6-membered ring intramolecular anhydrides. Other characteristic anhydride peaks appear at ca. 920 and 970 cm-1. The peak at 1120 cm^*1 from methyl ether was stable under such conditions. Thus, the main process here is acid-promoted dehydration of almost completely hydrolyzed diacid form of the copolymer into cyclic anhydnde form. Semi-quantitative evaluation ofthe curves show that the matrix is soluble in water at a diacid:anhydride ratio of ca. 2:1, but is insoluble (within tens of seconds) with the ratio ca. 1:1.

TGA of the Resist THERMO-GRAVIMETRIC ANALYSIS (TGA) curves taken from samples of pure copolymer I (curve A, 1.5 mg) and from resist formulation I:DPI-Tr 10:1 (B, 1.1 mg, and C, 0.17 mg) were informative. Sample A was not baked, sample B was subjected to PAB 110°C for 30 s, and sample C was subjected to similar PAB, exposure to 50 mJ/cm² at 256 nm, and PEB 130°C for 30 s. For the pure copolymer, TGA shows drying at 50-80°C Next mass loss, ca. 10%, occurs at 130-180°C (160°C max.) and evidently corresponds to dehydration to cyclic anhydride (calculated at 12.7 wt% for complete dehydration of a 1:1 copolymer). Next ca. 30 wt% are lost at 210-300°C (max. at 250°C), and then only mild decomposition continues until 500°C Curve B shows that after a given PAB, the resist was almost completely dry, and maximum dehydration occurs at 156°C, similar to pure copolymer. An important feature of curve C is a 35°C decrease in dehydration temperature in the presence of photo-generated acid. Thus, according to TGA, precise control of PAB temperature in 120-140°C range and baking time would give best contrast between exposed and unexposed areas.

These results of preliminary sensitivity evaluation well agree with FTTR and TGA experiments. Interestingly, the presence of starting and photo-decomposed DPI-Tr alters TGA curves at higher temperatures, possibly due to eventual thermodecomposition of the salt, accompanied by further acid or heat-catalyzed reactions like methanol elimination, decarboxylation and possibly crosslinking.

Resists Patterns. Even with a homemade illumination system, resolution 1- 2 μm was obtained with negative images with I:DPI-Tr resist. Patterns were clean without any residue in unexposed areas, and without detectable swelling of exposed areas. The resist showed good adhesion to the substrate, probably due to high COOH content, and calculated shrinkage was less than 2.5% in any direction (10% by volume).

Resists Stripping. Although a resulting relief pattern was water-stable for minutes, a couple of hours was enough for water to dissolve all areas at room temperature. But all resist residue disappeared within seconds in hot water at ca. 70°C These results and the IR study preclude any possible crosslinking by esterification between methoxy and acidic or anhydride moieties. Thus, all steps - casting, developing and stripping - can be accomplished with water. Positive Developing with Organic Solvents. Although it does not fit with the all-water objective, it is possible to develop positive relief image by treatment with organic solvent(s). As exposed areas turn from diacid into anhydride, the developer must be nonionic and of medium polarity. Figure 5 shows contrast curve of I/DPI-Tr (20:1 wt.) resist after developing with acetone for 10 s. Functional Development With the appearance of various microdevices for opto-electronics and biological applications, there is an increasing demand to place compounds of interest within submicron pattems. Recently, it has been shown that poly(t-butyl fumarate-co-styrene) works as an excellent template for selective sorption of dyes, aminocompounds, polymers and metal ions. Similarly, with MA copolymers, exposure and subsequent heating turn hydrophilic highly reactive acidic functions into rather hydrophobic and less reactive anhydride moieties. Several amino compounds were tested. As was expected, from water solution both 2,6- diaminopyridine (DAP) and 1,10-diaminodecane selectively entered only un-exposed areas containing mostly COOH groups. Loading of aminocompounds is well controlled by (i) UV dose, (ii) concentration of modification solution and (iii) contacting time. It was observed that a more concentrated (2.5 wt%) solution of DAP penetrated the matrix faster and more exclusively in exposed areas, than less concentrated one (1 wt%). Polyfunctional amino compounds form multiple ammonium salts linkages, that heavily crosslink a matrix to prevent its dissolution.

Areas that have selectively incoφorated aryl or heterocyclic amines after such "functional development" should sufficiently resist fluorocarbon plasma to enable "dry etch" methods of pattem transfer to underlying substrate, without the need to remove other areas of resist in a "relief development" step. Similar behavior was observed with aqueous solutions of nickel and cobalt chlorides; such loading with inorganics can permit O2-RIE development for high resolution and aspect ratio. Such structures can be used in space-directed biosynthesis, or to create micron-scale lines of organic-polymer or inorganic- polymer composites with various optical, thermal, electrical etc. properties.

Table I. List of chemicals

chemicals abbreviation source'" and CAS ff specification poly(methyl vinyl ether-aΛ-maleic PMVEMAn SP2, cat# 317, [9011-16-9] M_w = "medium" anhydride) 1 poly(methyl vinyl ether-αώ-maleic PMVEMAn ISP, Gantrez AN- 119, M_w = 50 K anhydride) 2 [9011-16-9] poly(methyl vinyl ether-α/r-maleic PMVEMAc SP2, cat# 374, [25153-40-6] M_w = "low" acid) poly(acrylic acid) PAAc SP2, cat# 026, [9003-01-4] M_w = 250 K poly(ethylene-<2//-maleic PEMAn Aid., cat# 18,805-0, [9006- M_w = 100-500 K anhydride) 26-2]

PMAn POLY, cat# 02348, [24937-72-2] - poly(itaconic acid) PIAc POLY, cat# 09534, [25119- - 64-6]

PMVEMAc monoethyl ester MEE Aid., cat# 41,629-0, [25087- 50 wt % in

06-3] ethanol

PMVEMAc mono-/-propyl ester MIPE Aid., cat# 41,639-8, [31307- 50 wt % in i-

95-6] propanol

PMVEMAc mono-π-butyl ester MNBE Aid., cat# 41,630-4, [25119- 50 wt % in

68-0] ethanol poly(styrene-α /-maleic anhydride) PSMAn SP2, cat# 456, [9011-13-6] M_w = 100-500 K

2,6-diaminopyridine DAP Aid., cat# D2.440-4, [141- *" 86-6]

1 , 10-diaminodecane DAD Aid., cat# Dl,420-4, [646 - - 25-3] silver triflate Ag-oπ Aid., cat# 17,643-5, [2923- 99+ % purity 28-6]

' SP2 = SP2 Scientific Polymer Inc.; ISP = International Specialty Products (known also as GAF); Aid. = Aldrich Chemical Corporation; POLY = Polyscience, Inc.

Table 3. Evaluation of resists based on MAc monoesters (see structures in Scheme 1)

R' ROH PAG solvent : polymer : PAG PAB, PEB sensitivity w:w:w ("C.seconds)

Ph ethanol DPI-OTf 1000:100:5 130.30, 140.30 50

Ph methanol TPS-SbF₆ 1000:100:7 130.30, 130.30 18

Ph methanol DPI-OTf 1000:100:7 130.30, 130.30 22

Ph malic acid DPI-OTf 1000:100:5 130.30, 140.30 35

Ph lactic acid DPI-OTf 1000:100:7 120.20, 130.40 30-33

OMe ethanol DPI-OTf 1000:100:5 130.30, 130.30 ca. 40

OMe i- DPI-OTf 1000:100:5 130.30, 150.30 ca. 35 propanol

EXAMPLES

1. A CA resist (PAB or PEB) with silver triflate as PAG. Films of ethylene or methyl vinyl ether copolymers with maleic anhydride, containing 3, 5 and 10 wt.% (vs polymer) of silver triflate, prepared by spin-coating from water as described before, were made water-insoluble after irradiation with an unfiltered 150 W Hg lamp at 30 cm for 200, 140 and 90 s, respectively. No such water- insolubilization was seen after 300 s uradiation with the same light filtered by an aryl polyester film (cutoff 340 nm), or by a 254 nm bandpass filter.

2. Functional developments with metal ions. Poly(ethylene-co-maleic anhydride) (PEMA), poly(methyl vinyl ether-co-maleic anhydride) (PMVEMA) and poly-(acrylic acid) (PAA; for comparison) were subjected to spin-coating and PEM as described above, then treated with aqueous solutions of different salts of polyvalent cations at different pH. Above a minimum concentration of polyvalent metal cation, the film was ionically crosslinked (as seen by FTTR) instead of being dissolved (see Table below). Salt Minimum salt concentration to prevent film dissolution, mol/L (pH)

PEMA PMVEMA PAA

CeCl₃ 0.1 (5.0) > 1.0 (5.0) <0.004 (5.5)

CuCl₂ 0.2 (4.0) > 1.0 (4.0) 0.01 (4.5)

FeCl₃ 0.25 (1.0) 0.05 (1.5) 0.02 (2.0)

ZnCl₂ 1.0 (6.0) > 1.0 (6.0) 0.1 (6.5)

NiCl₂ 1.0 (6.0) 1.0 (6.0) 0.4 (6.5)

CaCl₂ > 1.0 (7.5) > 1.0 (7.5) 0.4 (7.5)

CoCl₂ > 1.0 (6.0) > 1.0 (6.0) 1.0 (6.0)

The presence of metal ions in the polymer film can allow it to resist etching by oxygen plasma during a later O2RIE dry development (I.E., Oxygen Reactive Ion Etching) step (producing relief images with vertical profiles, that can be transfened to an underlying planarizing layer that is a non-photoactive organic polymer), through formation of a refractory metal oxide surface layer. Another way of doing this with our resists would be to react their anhydride form with aminopropyltrimethylsilane or similar aminoalkyl-silane, similar to the reaction described in: H. Anne, S. Birkle, H. Borndoerfer, R. Leuschner, M. Sebald (to Siemens AG), EP 492256 1992.07.01, U.S. Patent 5,384,220; 1995.01.24. Silylation of polymer films, such as poly(hydroxystyrene) obtained by photoacid- caralyzed cleavage of poly(tBOCO-styrene), for such purposes is known .

UV transparency of the polymer film, such as a 1.3 μm film of poly(methyl vinyl ether-co-maleic anhydride) in both diacid and anhydride form is desirable. The lack of an aryl moiety in such polymers during exposure is an advantage for extremely high-resolution imaging with deep and vacuum UV.

3. CA resists based on product of poly(styrene-co-maleic anhydride) (PSMA) with lactic and glycolic acids. 1 g of PSMA was dissolved in 10 ml of bis(methoxyethyl) ether (diglyme), and 3 g of lactic (2-hydroxy-propanoic) or glycolic (hydroxyacetic) acid was added. The solution was then heated ovemight at ca. 75-80°C Several cycles of precipitation in excess of diethyl ether and redissolution in methanol give ca. 0.5 g of white product. IR spectra show both strong acid and ester carbonyl peaks at 1710 and 1735 cm"--, respectively, and almost no lack of anhydride peaks at 1850 and 1780 cm"¹. The PSMA monoester with lactic acid appeared to be water-insoluble, but easily dissolved soluble in methanol, acetone and other organic solvents. Its mixture with 10 wt.% of diphenyl iodonium triflate was spin-coated from 1 -propanol onto a silicon wafer at 1200 rpm, followed by PAB at 120°C for 20 s, then exposure at 256 nm, and PEB at 140°C for 40 s. Acid, ester and anhydride FTIR peak intensities change (since acid and ester C=O peaks overlap each other, these results are only semiquantative) vs. dose, as do contrast curves for development in either methanol or aqueous base (1.5 wt.% K2CO3; dissolution was faster and cleaner than with methanol). FTTR and solubility changes obviously correlate. As with PMVEMA and PEMA, thermoacidolysis led exclusively to intramolecular anhydride formation. Acetone worked as a stripping solvent.

4. Process for reverse images. An approximately 1 μm film of PMVEMA with 10% of DPI-Tr was obtained by spin-coating, then heated at 160°C for 2 minutes to convert completely to anhydride form by FTIR. After patternwise exposure, sample was exposed to water vapours by holding above boiling water in beaker for 2 minutes. In this step water hydrolyzed anhydride moieties only in exposed areas (containing photo-released acid) by FTTR. The sample was then developed in pure water at room temperature for 20 s to remove exposed zones ofthe layer given a postive-tone image.

For the first time, an all-water processable CA resist with micron-scale resolution was presented. In the presence of photo-produced acid, water-soluble carboxylic polymer(s) undergo dehydration to water-insoluble products, at 30-50°C lower temperature than without the acid. Careful choice of processing conditions (formulation, PAB, UV dose and PEB) can make possible the production of negative-tone images with 1 μm or better linespace (L/S) resolutions. Positive-tone performance was also shown with organic solvent (acetone), or by thermal dehydration followed by photoacid-catalyzed rehydration. Other abbreviations used in the present discussion include TPS (triphenyl sulfonium cation), DPI (diphenyl iodonium cation), Poly (TBOCST) (poly-[di-t- butyloxycarbonyloxystyrene]), PSF (poly-styrene-cσ-fumaryl), DSC (differential scanning calorimietry), Otf (triflic acid, anion), PDBFS (poly-di-t-butyl fumarate-cø- styrene), RIE (reactive ion etching), TBOC (t-butyloxycarbonyloxy) and 4TS (4- (phenylthio)phenyldiphenyl sulfonium cation).

The general schemes for photolithographic processes with the resists of the invention is illustrated by reference to Schemes I and II

Mechanism of acid-catalyzed reactions of maleic diacid/ester-acid copolymers (arrows show mechanism of reactions from left to right; they are reversed for right to left).

R is selected for ROH to react quickly with cyclic anhydride in the presence of acid, but slowly in its absence; for ROH to be volatile to leave the polymer during

PAB or PEB; to maintain or increase solubility in water or other polar solvents (for example, containing -COOH groups); or instead to confer fluorocarbon etch resistance (for example, PI1CΗ2OH).

5. A CA resist based on an alicyclic copolymer cis-5-Norbornene-e«<fo-2,3- dicarboxylic anhydride (5.0 g, 30 mmol) and maleic anhydride (3.0 g, 30 mmol) were melted together in a 25 mL round flask at 100°C under nitrogen. A solution of benzoyl peroxide (0.5 g, 2 mmol) in 0.5 mL xylene was then injected, and the mixture stirred. After forty minutes, the viscous mixture was precipitate filtered, washed with pentane, xylene, penatne, then dried under vacuum. A portion of the dried product was dissolved in boling water to 20 wt% to give a noticeably viscous solution, to which was added 10 wt% diphenyliodonium triflate (versus the weight of the polymer), and the solution was spread onto a Si wafer, with drying at ca. 120°C for 1 minute to a smooth coating ca. 2 micrometers thick. This was exposed through a mask using an unfiltered Cole-Palmer UV lamp at 40 cm distance (60-80 mJ at 254 nm), then the wafer was heated until the appearance of a latent pattem (ca, 1 minute at 120°C), and rinsed in 25°C water for 10 s, at which time unexposed areas of resist had dissolved away, and exposed areas remained.

These anhydrides are formed from vicinal carboxylic acid groups, which insures that they are intramolecular, forrning 5-membered rings (e.g., succinic acid derivatives), unlike poly(acrylic acid). Scheme 1. Design for CA resists based on copolymers of maleic anhydride.

Scheme 1.

hv

Photo-Acid Generator H⁺ and other products

R = H, alkyl R^* -= H, OCH3, Ph

Scheme 2. Probable A_AC2-mechanism for acid-catalyzable formation of 5-member ring anhydride (only one direction is shown for this reversible cycle). Scheme 2.

PAG

Claims

1. A solvent-processable chemically amplified resist comprising: a substrate having a photoresist layer comprising a solvent-soluble film of polymer, said polymer bearing vicinal dicarboxylic acid or mono-esterified dicarboxylic acid groups, and a photoinitiator which releases an acid on exposure in an image-wise manner, said dicarboxylic acid or ester groups being convertible to acid anhydride groups by said acid from said photoinitiator, said acid anhydride groups rendering said polymer more insoluble in a solvent in which the acid or ester group containing polymer is soluble, or more soluble or dispersible in a solvent in which the acid or ester-group containing polymer is insoluble.

2. A resist according to claim 1, which is water-processable, said film beinga non-light scattering film of a water-soluble or water dispersible polymer bearing vicinal dicarboxylic acid or monoesterified dicarboxylic acid groups, and said acid anhydride groups rendering said polymer water insoluble or water-nondispersible.

3. A resist according to claim 2, wherein said photoinitiator releases an acid catalyst for dehydration of said dicarboxylic acid or monoesterified dicarboxylic acid or 2-methyl, 2,3-dimethyl, 2-chloro, 2,3-dichloro- or 2,3-dibromo derivatives, and groups to acid anhydride groups, on exposure to UV radiation, radiation to which said photoinitiator is spectrally sensitized, electron beams or X-rays.

4. A resist according to claim 2, wherein said photoresist layer has a thickness of 0.5 to 2 μm.

5. A resist according to claim 2, wherein said water soluble film of polymer is a maleic acid or monoesterified maleic acid copolymer.

6. A resist according to claim 5, in which said copolymer is a copolymer of maleic acid or monoesterified maleic acid and a comonomer selected from ethylene, vinyl acetate, styrene and methyl vinyl ether, cyclopentadiene, cis-5-norbornene- e/ι o-2,3-dicarboxylic anhydride, furan, 7-oxa-cw-5-norbornene-e/iιio-2,3- dicarboxylic acid anhydride, 4-vinylcyclopenetene, 4-allylcyclopentene, 4- vinylcyclohexene and 4-allylcyclohexene.

7. A method for microlithographic production or reproduction of an image comprising: i) providing a resist as defined in claim 1 , ii) exposing the photoresist layer in an imagewise manner to release the acid from said photoinitiator in exposed zones of said layer, iii) subjecting the exposed layer to a temperature effective for the acid catalyzed dehydration or dealcoholation of said dicarboxyUc acid or ester groups to acid anhydride groups, said acid anhydride groups rendering said polymer more insoluble in a solvent in which the acid or ester group-containing polymer is soluble, or more soluble in a solvent in which the acid or ester group-containing polymer is insoluble, whereby an image is developed which is defined by solvent insoluble zones and solvent soluble zones of said layer.

8. A method according to claim 7, in which said resist is water-processable, said non-Ught scattering film being of a water-soluble polymer bearing vicinal dicarboxylic acid or monoesterified dicarboxylic acidgroups, and said acid anhydride groups rendering said polymer water insoluble.

9. A method according to claim 8, wherein said photoinitiator releases acid catalyst for the acid catalyzed dehydration or dealcoholation of said dicarboxylic acid or monoesterified dicarboxylic acid groups to acid anhydride groups, on exposure to UV radiation, an electron beam or X-rays.

10. A method according to claim 9, wherein step ii) comprises exposing said layer in an image-wise manner to UV radiation, an electron beam or X-rays effective to release said acid catalyst from said photoinitiator and step iii) comprises a post- exposure bake effective for said acid catalyzed dehydration or dealcoholation without thermal dehydration or dealcoholation of said dicarboxylic acid or monoesterified dicarboxylic acid groups.

11. A method according to claim 10, wherein said post-exposure baking is at 125-135°C for 30 to 60 seconds.

12. A method according to claim 7, 8, 9, 10 or 11, wherein step ii) comprises exposure to >25 mJ/cm^ of deep UV radiation.

13. A method according to claim 7, 8, 9, 10, 11 or 12, wherein said water- soluble film forrning polymer is a copolymer of maleic acid with a comonomer selected from ethylene, vinyl acetate, styrene and methyl vinyl ether, cyclopentadiene, c/j-5-norbornene-encfo-2,3-dicarboxylic anhydride, furan, 7-oxa- cis-5-norbornene-enιio-2,3-dicarboxyUc acid anhydride, 4-vinylcyclopenetene, 4- allylcyclopentene, 4-vinylcyclohexene and 4-allylcyclohexene.

14. A method according to claim 7, 8, 9, 10, 11, 12 or 13, including a step of iv) developing said image by stripping water-soluble zones from said substrate, with water.

15. A process for producing a solvent-processable chemically amplified resist comprising: i) applying to a substrate, a photoresist layer comprising: a) a solvent-soluble, non-light scattering film forming polymer, said polymer bearing vicinal dicarboxylic acid or monoesterified dicarboxylic acid groups, b) a photoinitiator which releases an acid on exposure in an image-wise manner, and c) a solvent for said polymer, and ii) drying the photoresist layer to remove said solvent, said dicarboxylic acid or monoesterified dicarboxylic acid groups being acid catalyzably dehydratable or dealcoholatable with said acid from said photoinitiator, to form acid anhydride groups rendering said polymer solvent-insoluble.

16. A process according to claim 15, in which said resist is water-processable, said film forming polymer being water soluble and bearing vicinal dicarboxylic acid or monoesterified dicarboxylic acid groups, and said solvent being an aqueous solvent.

17. A process according to claim 15 or 16, wherein said layer has a thickness of 0.5 to 2 μm.

18. A process according to claim 15, 16 or 17, wherein step ii) comprises baking at 100-130°C to remove said solvent.

19. A solvent-processable chemically amplified resist comprising: a substrate having a photoresist layer comprising a solvent-soluble non-light scattering film of polymer, said polymer bearing vicinal dicarboxylic acid or mono¬ esterified dicarboxylic acid groups, and a photoinitiator which releases an acid on exposure in an image-wise manner, said dicarboxylic acid or monoesterified dicarboxylic acid groups being dehydratable or dealcoholatable to acid anhydride groups.

20. A method for microlithographic production or reproduction of an image comprising: i) providing a resist as defined in claim 19, ii) before exposure, thermally dehydrating or dealcoholating the dicarboxylic acid or monoesterified dicarboxylic acid groups to acid anhydride groups, iii) exposing the photoresist layer in an image-wise manner to release the acid from the photo-initiator in exposed zones ofthe layer, whereby an image is developed which is defined by solvent-soluble zones and solvent-insoluble zones of said layer.

21. A method according to claim 20, wherein step iii) comprises exposing the photoresist layer with water or alcohol vapours, acid catalyzably hydrating or alcoholating the anhydride group to diacid or ester acid groups.

22. A method according to claim 20, wherein the acid released in step ii) catalyzes the hydrolysis or alcoholysis of the anhydride groups in the exposed zones so that said exposed zones are solvent soluble.

23 A method for microlithographic production or reproduction of an image comprising: i) providing a resist comprising: a substrate having a photoresist layer comprising a solvent-soluble film of polymer, said polymer bearing vicinal dicarboxylic acid or mono-esterified dicarboxylic acid groups, and a photoinitiator which releases an active species on exposure in an image-wise manner, said dicarboxylic acid or ester groups being convertible to acid anhydride groups by said active species from said photoinitiator, said acid anhydride groups rendering said polymer more insoluble in a solvent in which the acid or ester group containing polymer is soluble, or more soluble or dispersible in a solvent in which the acid or ester-group containing polymer is insoluble, ii) exposing the photoresist layer in an imagewise manner to release the active species from said photoinitiator in exposed zones of said layer, iii) subjecting the exposed layer to a temperature effective for the conversion of said dicarboxylic acid or ester groups to acid anhydride groups, said acid anhydride groups rendering said polymer more insoluble in a solvent in which the acid or ester group-containing polymer is soluble, or more soluble in a solvent in which the acid or ester group-containing polymer is insoluble, whereby an image is developed which is defined by solvent insoluble zones and solvent soluble zones of said layer.

24 A solvent-processable chemically amplified resist comprising: a substrate having a photoresist layer comprising a solvent-soluble film of polymer, said polymer bearing vicinal anhydride groups, and a photoinitiator which releases an acid on exposure in an image-wise manner, said polymer becoming either more or less insoluble in a solvent in which a counterpart acid or ester group containing polymer is soluble, or more soluble or dispersible in a solvent in which a counterpart acid or ester-group containing polymer is insoluble.