1. Field of the Invention
The invention relates to radiation-sensitive and acid-cleavable compounds and to a radiation-sensitive mixture which is positive-working, i.e., which becomes soluble as a result of irradiation, and which contains these compounds. The mixture contains p1 (a) a binder which is insoluble in water and soluble or at least swellable in aqueous alkaline solutions, and
(b) a compound which generates a strong acid under the action of actinic radiation and which has at least one acid-cleavable C--O--C bond. PA1 R.sup.2 is a hydrogen atom, an unsubstituted or substituted alkyl radical, or unsubstituted or substituted aryl radical, (R.sup.1 --SO.sub.2 --O--).sub.n X--, or R.sup.3 O--, PA1 R.sup.3 and R.sup.4 are identical or different and are unsubstituted or substituted alkyl, cycloalkylalkyl, cycloalkenylalkyl or aralkyl radicals, in which 1 to 3 aliphatic CH.sub.2 or CH groups are optionally replaced by one or more of NR.sup.5, O, S, CO, CO--O, CO--NH, O--CO--NH, CO--NH--CO, NH--CO--NH, SO.sub.2, SO.sub.2 --O or SO.sub.2 --NH, or unsubstituted or substituted alkenyl, alkynyl, cycloalkyl or cycloalkenyl radicals, or R.sup.3 and R.sup.4 are mutually linked to form a heterocyclic ring, PA1 R.sup.5 is an acyl radical, PA1 n is an integer from 1 to 3, and PA1 X is an alkylene, cyloalkylene, or arylene group if n is 1 or X is a(n+1)-valent radical of an alkane, cycloalkane, or arene if n is 2 or 3. PA1 a. at least one binder which is insoluble in water and soluble or at least swellable in aqueous alkaline solutions, and PA1 b. at least one compound of the formula I, which generates a strong acid under the action of actinic radiation and which has at least one acid-cleavable C--O--C bond. PA1 R.sup.1 is an alkyl radical which has 1 to 6 carbon atoms and may be highly fluorinated, i.e. in which at least 50% of the hydrogen atoms are replaced by fluorine atoms, or an aryl radical which has 6 to 12 carbon atoms and PA1 R.sup.2 is a hydrogen atom or an R.sup.3 O radical. PA1 R.sup.3 and R.sup.4 are preferably identical and especially are alkyl, cycloalkylalkyl, cycloalkenylalkyl or aralkyl groups having less than 16 carbon atoms, it being possible for 1 to 3 aliphatic CH.sub.2 or CH groups to be replaced by NR.sup.5, O, S, CO, COO, CONH, OCONH, CONHCO, NHCONH, SO.sub.2, SO.sub.2 O or SO.sub.2 NH, or alkenyl, alkynyl, cycloalkyl or cycloalkenyl radicals. If R.sup.3 and R.sup.4 together form a heterocyclic ring, this is preferably a 1,3-dioxolane or 1,3-dioxane ring. PA1 R.sup.5 can especially be an alkanoyl or aroyl, an alkyl-, alkenyl-, analkyl- or aryl-sulfonyl or an alkyl-, alkenyl-, aralkyl- or aryl-phosphonyl radical having up to 12 carbon atoms, particularly preferably an alkanoyl radical having 2 to 6 carbon atoms or an aroyl radical having 7 to 10 carbon atoms. PA1 X preferably is an alkylene group having 2 to 10 carbon atoms, a cycloalkylene group having 4 to 10 carbon atoms or an arylene group having 6 to 12 carbon atoms, each substituted by 1 to 3 sulfonyloxy groups R.sup.1 --SO.sub.2 --O--. PA1 R.sup.1 is a methyl, ethyl, trifluoromethyl or hexafluoroisopropyl radical or a phenyl radical which may be substituted by 1 to 3 alkyl or alkoxy groups having 1 to 3 carbon atoms, 1 to 3 halogen atoms, 1 or 2 nitro, cyano or trifluoromethyl groups or appropriate combinations thereof and PA1 X is an arylene group which is substituted by 1 to 3 sulfonyloxy groups R.sup.1 --SO.sub.2 --O--. PA1 R.sup.2 is a hydrogen atom and PA1 X is an aromatic six-membered ring substituted by 1 to 3 sulfonyloxy groups R.sup.1 --SO.sub.2 --O. PA1 a) a binder which is insoluble in water and soluble or at least swellable in aqueous alkaline solutions and PA1 b) a compound which generates a strong acid under the action of actinic radiation and which has at least one acid-cleavable C--O--C bond, PA1 (1) compounds having at least one orthocarboxylic acid ester grouping and/or carboxylic acid amide-acetal grouping, the compounds also having a polymeric character and it being possible for the said groupings to occur as linking elements in the main chain or as substituents in side chains (see DE-A 2,610,842 and 2,928,636), PA1 (2) oligomeric or polymeric compounds with recurring acetal and/or ketal groupings in the main chain (see DE-A 2,306,248 and 2,718,254), PA1 (3) compounds having at least one enol ether grouping or N-acyliminocarbonate grouping (see EP-A 0,006,626 and 0,006,627), PA1 (4) cyclic acetals or ketals of .beta.-ketoesters or .beta.-ketoamides (see EP-A 0,202,196), PA1 (5) compounds having silyl ether groupings (see DE-A 3,544,165 and 3,601,264), PA1 (6) compounds having silylenol ether groupings (see DE-A 3,730,785 and 3,730,783), PA1 (7) monoacetals and monoketals, whose aldehyde or keto component respectively has a solubility of between 0.1 and 100 g/l in the developer (see DE-A 3,730,787), PA1 (8) ethers based on tertiary alcohols (see U.S. Pat. No. 4,603,101) and PA1 (9) carboxylic acid esters and carbonates of tertiary alcohols, allylic alcohols or benzylic alcohols [see U.S. Pat. No. 4,491,628 and J. M. Frechet et al., J. Imaging Sci. 30, 59-64 (1986)]. PA1 6.0 p.b.w. of a styrene/p-hydroxystyrene copolymer (molar ratio 30:70) having a mean molecular weight of 27,000, PA1 1.5 p.b.w. of a cresol/formaldehyde novolak having a softening range from 105.degree. to 120.degree. C. and PA1 2.0 p.b.w. of 4-(toluene-4-sulfonyloxy)benzaldehyde bis(2-phenoxyethyl)acetal (Compound No. 1) in PA1 42 p.b.w. of propylene glycol monomethyl ether-acetate. PA1 5.3 p.b.w. of sodium metasilicate.times.9 H.sub.2 O, PA1 3.4 p.b.w. of trisodium phosphate.times.12 H.sub.2 O, PA1 0.3 p.b.w. of sodium dihydrogen phosphate and PA1 191 p.b.w. of deionized water. PA1 7.5 p.b.w. of a styrene/p-hydroxystyrene copolymer (molar ratio 20:80) having a mean molecular weight of 32,000 and PA1 2.0 p.b.w. of 3,4-bis(toluene-4-sulfonyloxy)benzaldehyde bis(2-succinimidoethyl)acetal (Compound No. 3) in PA1 42 p.b.w. of propylene glycol monomethyl ether acetate. PA1 7.5 p.b.w. of the copolymer indicated in Example 2 and PA1 2.0 p.b.w. of 4-(toluene-4-sulfonyloxy)benzaldehyde bis(2-phenoxyethyl)acetal (Compound No. 1) in PA1 42 p.b.w. of propylene glycol monomethyl ether-acetate. PA1 7.5 p.b.w. of a 3-methyl-4-hydroxystyrene homopolymer having a mean molecular weight of 25,000 and PA1 2.0 p.b.w. of 4-(toluene-4-sulfonyloxy)benzaldehyde-bis(2-phenoxyethyl)acetal (Compound No. 1) in PA1 42 p.b.w. of propylene glycol monomethyl ether-acetate. PA1 7.5 p.b.w. of the copolymer indicated in Example 2 and PA1 2.0 p.b.w. of 4-methanesulfonyloxybenzaldehyde bis[2-(N-propylcarbamoyl)ethyl]acetal (Compound No. 2) in PA1 42 p.b.w. of propylene glycol monomethyl etheracetate. PA1 7.5 p.b.w. of a styrene/maleimide copolymer (molar ratio 1:1) having a softening range from 165.degree. to 180.degree. C. and PA1 2.0 p.b.w. of 3,4,5-tris(toluene-4-sulfonyloxy)benzaldehyde bis(3-phenylpropyl)acetal (Compound No. 4) in PA1 42 p.b.w. of cyclohexanone. PA1 7.5 p.b.w. of the copolymer indicated in Example 8 and PA1 2.0 p.b.w. of 2-(toluene-4-sulfonyloxy)benzaldehyde) bis(3-phenylpropyl)acetal (Compound No. 7) in PA1 42 p.b.w. of propylene glycol monomethyl ether acetate. PA1 7.5 p.b.w. of the copolymer described in Example 2 and PA1 2.0 p.b.w. of trisphenethyl 4-methanesulfonyloxyortho-benzoate in PA1 42 p.b.w. of propylene glycol monomethyl ether-acetate.
The invention also relates to a radiation-sensitive recording material which has been produced from this mixture and which is suitable for producing photoresists, electronic components, printing plates or for chemical milling.
2. Description of Related Art
The continuing reduction in the size of the structures, for example in chip manufacture down into the range of less than 1 .mu.m, requires modified lithographic techniques. To form images of such fine structures radiation of a short wavelength is used, such as high-energy UV light, electron beams and X-rays. The radiation-sensitive mixture must be adapted to the short-wave radiation. A compilation of the requirements to be met by the radiation-sensitive mixture is given in the article by C. G. Willson "Organic Resist Materials--Theory and Chemistry. [Introduction to Microlithography, Theory, Materials, and Processing, editors L. F. Thompson, C. G. Willson, M. J. Bowden, ACS Symp. Ser., 219, 87 (1983), American Chemical Society, Washington].
There is therefore an increased demand for radiation-sensitive mixtures which can be used in the more recent technologies, such as mid-UV or deep-UV lithography [exposure, for example, with excimer lasers at wavelengths of 305 nm (XeF), 248 nm (KrF), 193 nm (ArF)], electron beam lithography or X-ray lithography, and which, furthermore, are preferably sensitive in a wide spectral range and correspondingly can also be used in conventional UV lithography.
Positive-working radiation-sensitive mixtures for producing radiation-sensitive recording materials are known. For example, mixtures which contain o-quinone-diazide derivatives in binders soluble in aqueous alkaline media, for example novolaks or polyhydroxystyrenes, are commercially available. However, the sensitivity of these materials to actinic radiation, and especially to high-energy short-wave radiation, such as light from a KrF-excimer laser having a wavelength of 248 nm or electron beams, is inadequate.
Positive-working radiation-sensitive mixtures are also known in which an acid is generated by the action of actinic radiation on a photoinitiator contained in this mixture and this acid then, in a subsequent reaction, renders an acid-cleavable compound likewise contained in the mixture which is soluble in the irradiated areas under the action of an appropriate, preferably aqueous alkaline, developer. Such materials are in general distinguished by an enhanced sensitivity to actinic radiation.
Numerous mixtures are known which contain a polymeric binder soluble in aqueous alkaline solutions, a solubility-inhibiting compound and a compound which, on irradiation, generates the acid required for cleavage. The binder is in most cases a novolak resin. Many of these mixtures have a high sensitivity to actinic radiation. They are designated as chemically amplified, photocatalytic 3-component systems.
Of these mixtures, those whose acid-cleavable component contains one or more acetal units have especially gained commercial importance. These mixtures have, however, certain disadvantages. Particularly, they demonstrate only a limited stability on the substrate materials to which they have to be applied, and thus lead to unsatisfactory, not reducible reproduction of the image original. This can be improved only by introducing additional protective layers, for example, according to DE-A 3,621,376 equivalent to U.S. Pat. No. 4,840,867. The causes of the deterioration in the image reproduction are not known in detail and have not been adequately investigated. For example, the process window, i.e., the processing latitude, for the exposure of these mixtures is very narrow and frequently not unambiguously reproducible. In particular, the quality of the image reproduction greatly depends on the time difference between exposure and development, the so-called delay time. In principle, it must be assumed that diffusion processes which cause this behavior are not easily controllable. In addition, however, it may be presumed that during drying of the mixture on a substrate material partial vaporization of the photoinitiator or of the acid-unstable compound, or segregation of the individual mixture constituents, takes place. This is observed with particular frequency in the case of acid-unstable compounds having a low solubility in the usual coating solvents.
It is also known from the papers by C. C. Petropoulos [J. Polym. Sci., Polym. Chem. Ed., 15, 1637 (1977)] that aromatic acetals which carry a nitro group in the vicinal position, are photodecomposable by high-energy UV radiation without acid catalysis, and can be used in positive-working radiation-sensitive recording materials. The photosensitivity of these compounds is however inadequate for applications in practice, since their photoreaction cannot be chemically amplified.
In DE-A 3,721,741 equivalent to U.S. Pat. No. 4,883,740, radiation-sensitive mixtures are described which contain a polymeric binder insoluble in water and soluble in aqueous alkaline solutions, and an organic compound which contains at least one acid-cleavable grouping and a grouping which generates a strong acid under the action of radiation. The radiation-sensitive groups described are exclusively onium salt groups, in particular sulfonium salt groups.
The use of onium salts, such as diazonium, phosphonium, sulfonium and iodonium salts of non-nucleophilic acids such as HSbF.sub.6, HAsF.sub.6 or HPF.sub.6 as photolytic acid generators involves disadvantages which drastically restrict their possible uses in various fields of application. For example, many of the onium salts are toxic. Their solubility is inadequate in many solvents, which is why only a few solvents are suitable for preparing a coating solution. Furthermore, when the onium salts are used, undesired foreign atoms are sometimes introduced which can cause interference with the process, especially in microlithography. Moreover, the onium salts form Bronstedt acids, which have a very severe corrosive action, in the photolysis. These acids attack sensitive substrates, so that the use of such mixtures leads to unsatisfactory results. Halogen compounds such as trichloromethyltriazine derivatives or trichloromethyloxadiazole derivatives also form hydrohalic acids which have a severely corrosive action.
In more recent papers by F. M. Houlihan et al., SPIE 920, 67 (1988), it was shown by reference to positive-working systems that, in addition to the above-mentioned acid generators, nitrobenzyl tosylates, which on exposure generate sulfonic acids having a low migration tendency, can be used in certain acid-unstable resist formulations. It can be deduced from these results that such compounds can also be used for photo-curable systems. However, the sensitivities thus achieved with these compounds, especially to UV radiation from 350 to 450 nm, and the thermal stability of the photoresists have proven to be inadequate.
There is thus a demand for radiation-sensitive mixtures which do not have the disadvantages described above and which possess a reactivity suitable in practice.