Mixed ester O-quinone diazide photosensitizers and process of preparation

Abstract

The invention relates to new mixed ester photosensitive compounds and photosensitizer compositions comprised thereof. The photosensitive compounds and photosensitizer compositions are prepared by condensing phenolic compounds with a 1,2-naphthoquinonediazide-5-sulfonic acid halide and an organic acid halide in specific ratios. Photoresist compositions comprising the photosensitive compounds and photosensitizer compositions are also disclosed. The photosensitizer compositions exhibit excellent solution stability and resistance to precipitation when formulated in alkali-soluble resin photoresist compositions. The photoresist compositions have enhanced lithographic properties.

Description

BACKGROUND OF THE INVENTION The present invention relates generally to photosensitive compositions and radiation sensitive positive photoresist compositions and particularly to compositions containing novolak and polyvinyl phenol resins together with naphthoquinone diazide sensitizing agents.

It is well known in the art to produce positive photoresist formulations such as those described in U.S. Pat. Nos. 3,666,473, 4,115,128, 4,173,470 and 4,550,069. These include alkali-soluble novolak resins together with light-sensitive materials, usually a substituted naphthoquinone diazide compound. The resins and sensitizers are dissolved in an organic solvent or mixture of solvents and are applied as a thin film or coating to a substrate suitable for the particular application desired.

The novolak resin component of these photoresist formulations is soluble in aqueous alkaline solutions, but the naphthoquinone sensitizer acts as a dissolution rate inhibitor with respect to the resin. Upon exposure of selected areas of the coated substrate to actinic radiation, however, the sensitizer undergoes a radiation induced structural transformation and the exposed areas of the coating are rendered more soluble than the unexposed areas. This difference in solubility rates causes the exposed areas of the photoresist coating to be dissolved when the substrate is immersed in alkaline developing solution while the unexposed areas are largely unaffected, thus producing a positive relief pattern on the substrate.

In most instances, the exposed and developed substrate will be subjected to treatment by a substrate-etchant solution. The photoresist coating protects the coated areas of the substrate from the etchant and thus the etchant is only able to etch the uncoated areas of the substrate, which in the case of a positive photoresist, correspond to the areas that were exposed to actinic radiation. Thus, an etched pattern can be created on the substrate which corresponds to the pattern of the mask, stencil, template, etc., that was used to create selective exposure patterns on the coated substrate prior to development.

The relief pattern of photoresist on substrate produced by the method described above is useful for various applications including, for example, as an exposure mask or a pattern such as is employed in the manufacture of miniaturized integrated electronic components.

The properties of a photoresist composition which are important in commercial practice include the photospeed of the resist, development contrast, resist resolution, and resist adhesion.

Photospeed is important for a photoresist, particularly in applications where a number of exposures are needed, for example, in generating multiple patterns by a repeated process, or where light of reduced intensity is employed such as in projection exposure techniques where the light is passed through a series of lenses and mono-chromatic filters. Thus, increased photospeed is particularly important for a resist composition employed in processes where a number of multiple exposures must be made to produce a mask or series of circuit patterns on a substrate. Development contrast refers to a comparison between the percentage of film loss in the exposed area of development with the percentage of film loss on the unexposed area. Ordinarily, development of an exposed resist coated substrate is continued until the coating on the expoeed area is substantially completely dissolved away and thus, development contrast can be determined simply by measuring the percentage of the film coating loss in the unexposed areas when the exposed coating areas are removed entirely.

Resist resolution refers to the capability of a resist system to reproduce the smallest equally spaced line pairs and intervening spaces of a mask which is utilized during exposure with a high degree of image edge acuity in the developed exposed spaces.

In many industrial applications, particularly in the manufacture of miniaturized electronic components, a photoresist is required to provide a high degree of resolution for very small line and space widths (on the order of one micron or less).

The ability of a resist to reproduce very small dimensions, on the order of a micron or less, is extremely important in the production of large scale integrated circuits on silicon chips and similar components. Circuit density on such a chip can only be increased, assuming photolithography techniques are utilized, by increasing the resolution capabilities of the resist.

In order to achieve the desired sensitivity and contrast, it is necessary to have a sufficiently high concentration of photosensitive compounds in the photoresist to prevent dissolution of the unexposed resist during development. High concentrations photosensitizer may be achieved by dissolving a mixture of highly soluble and less soluble photosensitizers in the photoresist solution or by supersaturating the photoresist solution with a photosensitizer.

However, solution concentration of photosensitizer near saturation can lead to a short shelf life due to solution instability and precipitation of the sensitizer prior to or during the use of the product. This phenomenon is referred to in U.S. Pat. Nos. 4,397,937 and 4,526,856, both of which are hereby incorporated by reference.

Clecak et al. in U.S. Pat. No. 4,397,937 discloses improved solubility by using as a sensitizer a bisester of 1-oxo-2-diazonaphthalene sulfonic acid and an unsymmetrical primary or secondary aliphatic diol which is a mixture of geometric and diastereoisomers. Esterification of the aliphatic diol at one end with a diazonaphthoquinone molecule having the acid group in the 5 position and at the other end with a diazonophthoquinone molecule having the sulfonyl group in the 4 position is disclosed. However, the patent emphasizes the importance of limiting the invention to unsymmetrical aliphatic diols. Clecak et al. does not disclose mixed esters of o-quinone diazide acids and non-light-sensitive organic acids.

According to Lewis et al. in U.S. Pat. No. 4,526,856, the problem of obtaining higher concentrations of sensitizer was addressed by modifying the solvent system of the photoresist formulations. The solvent composition which consist of cyclopentanone, or cyclopentanone and cyclohexanone with an aliphatic alcohol, when used in certain critical ratios provides good solubility.

In contrast, the present invention provides photosensitizers which are the condensation products of 1,2 naphthoquinonediazide-5-sulfonic acid and organic acids with aromatic diols and polyols. The photosensitizer compositions of the invention exhibit excellent solubility and resistance to precipitation when formulated in photoresist compositions. Also they may be dissolved into photoresist compositions at higher solution concentrations than previously known comparable photosensitizers. The photoresist compositions of the invention exhibit excellent solution stability and an improved shelf life. At the same time they also exhibit excellent photosensitivity and contrast properties.

SUMMARY OF THE INVENTION

The invention relates to new mixed ester photosensitive compounds and photosensitizer compositions comprised thereof. The photosensitive compounds and photosensitizer compositions are prepared by condensing phenolic compounds with a 1,2-naphthoquinonediazide-5-sulfonic acid halide and an organic acid halide in specific ratios. Photoresist compositions comprising the photosensitive compounds and photosensitizer compositions are also disclosed. The photosensitizer compositions exhibit excellent solution stability and resistance to precipitation when formulated in alkali-soluble resin photoresist compositions. The photoresist compositions have enhanced lithographic properties.

According to the present invention there is provided: photosensitive compounds represented by the general formulae (1), (2) or (3): ##STR1## wherein R is H, --X--R.sub.b or ##STR2## X is a single C--C bond, --O--, --S--, --SO.sub.2 --, ##STR3## n is 1 or 2, R.sub.a is H, --OH, --OY, --OZ, halogen or lower alkyl, with at least one R.sub.a radical being --OY and at least one thereof being --OZ, R.sub.b is H, alkyl, aryl, substituted alkyl, or substituted aryl; ##STR4## wherein R.sub.1 is H, or , ##STR5## R.sub.c is H, --OH, --OY or ##STR6## --OZ, with at least one R.sub.c radical being --OY and at least one thereof being --OZ; and ##STR7## wherein R.sub.2 is H, alkyl, aryl, substituted alkyl, or substituted aryl, R.sub.d is --OH, --OY or --OZ with at least one R.sub.d radical being --OY and at least one thereof being --OZ; wherein Y is 1,2-naphthoquinonediazide-5-sulfonyl and Z is --W--R.sub.3, where W is ##STR8## or --SO.sub.2 --, and R.sub.3 is alkyl, aryl, substituted alkyl or substituted aryl.

According to the present invention there is provided: a photosensitizer composition comprising the condensation product of:

(I) a phenolic compound selected from the group consisting of: ##STR9## wherein R is H, --X--R.sub.b, or ##STR10## R.sub.a is H, --OH, halogen or lower alkyl, with at least two and not greater than six R.sub.a radicals being --OH, X is a single C--C bond, --O--, --S--, --SO.sub.2 --, ##STR11## n is 1 or 2, R.sub.b is H, alkyl, aryl, substituted alkyl or substituted aryl; ##STR12## wherein R.sub.1 is H or ##STR13## R.sub.c is H or --OH with at least two R.sub.c radicals being --OH; and ##STR14## wherein R.sub.2 is H, alkyl, aryl, substituted alkyl, or substituted aryl; (II) a 1,2-naphthoquinonediazide-5-sulfonic acid (Diazo); and (III) an organic acid halide represented by the formula: W--R.sub.3 wherein W is ##STR15## or --SO.sub.2 --V, V is halogen, R.sub.3 is alkyl, aryl, substitted alkyl or substituted aryl; wherein the molar ratio of the amount of Diazo reacted to the amount of organic acid reacted is in the range of from about 1:2 to about 19:1.

According to the present invention there is provided:

a process for preparing a photosensitizer composition comprising: condensing a phenolic compound represented by the general formulae (A), (B) or (C): ##STR16## wherein R is H, --X--R.sub.b, or ##STR17## R.sub.a is H, --OH, halogen or lower alkyl, with at least two and not greater than six R.sub.a radicals being --OH, X is a single C--C bond, --O--, --S--, --SO.sub.2 --, ##STR18## n is 1 or 2, R.sub.b is H, alkyl, aryl, substituted alkyl or substituted aryl; ##STR19## wherein R.sub.1 is H or ##STR20## R.sub.c is H or OH with at least two R.sub.c radicals being --OH; and ##STR21## wherein R.sub.2 is H, alkyl, aryl, substituted alkyl or substituted aryl, with a 1,2-napthoquinonediazide-5-sulfonic acid (Diazo) and with an organic acid halide represented by the formula W--R.sub.3, wherein W is ##STR22## or --SO.sub.2 --V, V is halogen, R.sub.3 is alkyl, aryl, substituted alkyl or substituted aryl; wherein the molar ratio of the amount of Diazo to the amount of organic acid halide to be reacted is in the range of from about 1:2 to about 19:1.

According to the present invention there is provided: a photoresist composition comprising in admixture a novolak or polyvinyl phenol resin, a photosensitive compound as described above, and a solvent.

According to the present invention there is provided: a photoresist composition comprising in admixture a novolak or polyvinyl phenol resin, a photosensitizer composition as described above, and a solvent.

According to the present invention there is provided: a method for producing an article which comprises coating a photoresist composition as described above onto a substrate; imagewise exposing said composition to sufficient ultraviolet radiation to render said imagewise exposed portions substantially soluble in an aqueous alkaline solution; and then removing the thusly exposed composition portions from said substrate with an aqueous alkaline developing solution.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It has been found that by substituting an organic acid for a portion of the 1,2-naphthoquinonediazide-5-sulfonyl groups (Diazo) in photosensitizer compositions consisting essentially of 1,2-naphthoquinonediazide-5-sulfonyl esters of phenolic compounds, novel mixed ester photosensitive compounds and photosensitizer compositions may be obtained. These Diazo/organic acid mixed esters and photosensitizer compositions thereof may be formulated in positive-acting alkali-soluble novolak or polyvinyl phenol resin photoresist compositions which exhibit excellent solution stability. The photoresist compositions of the invention exhibit higher contrast than comparable heretofore available photoresist compositions and a longer "induction period" is observed when they are developed with metal-ion-free developer solutions.

The photosensitive compounds and photosensitizer compositions may be obtained by condensing phenolic compounds with a mixture of Diazo and organic acid halides. The molar ratio of the amount of Diazo to the amount of organic acid halide in the mixture may be in the range of from about 1:2 to about 19:1, preferably from about 2:3 to about 19:1 or more preferably from about 7:8 to about 9:1. For example, one mole of 2,3,4-trihydroxybenzophenone may be condensed with a mixture of 1.4 moles of Diazo and 1.6 moles of methanesulfonyl chloride to yield a photosensitizer composition comprising compounds having the formula: ##STR23## where R.sub.1, R.sub.2 and R.sub.3 may independently be either 1,2-naphthoquinonediazide-5-sulfonyl (Diazo) or methanesulfonyl.

Thus, in one aspect, the invention provides photosensitive compounds useful in photosensitizer compositions. The photosensitive compounds may be represented by general formulae (1), (2) and (3): ##STR24## wherein R is H, --X--R.sub.b or ##STR25## X is a single C--C bond, --O--, --S--, --SO.sub.2 --, ##STR26## n is 1 or 2, R.sub.a is H, --OH, --OY, --OZ, halogen, preferably Cl or Br, or lower alkyl, preferably lower alkyl having 1-4 carbon atoms, with at least one R.sub.a radical being --OY and at least one thereof being --OZ, R.sub.b is H, alkyl, aryl, substituted alkyl, or substituted aryl; preferably alkyl having 1-20 carbon atoms, more preferably 1-12 carbon atoms, preferably aryl being phenyl or naphthyl, alkyl or aryl may be substituted with lower alkyl having 1--4 carbon atoms, lower alkoxy having 1-4 carbon atoms, or halogen, preferably Cl or Br; ##STR27## wherein R.sub.1 is H, or ##STR28## R.sub.c is H, --OH, --OY or --OZ, with at least one R.sub.c radical being --OY and at least one thereof being --OZ; and ##STR29## wherein R.sub.2 is H, alkyl, aryl, substituted alkyl, or substituted aryl, the alkyl radicals R.sub.2 may be straight-chain or branched and may be substituted with halogen atoms or lower alkoxy groups having 1-4 carbon atoms, preferably the alkyl radicals have 1-20 carbon atoms; the aryl radicals R.sub.2 are preferably mononuclear and may be substituted with lower alkyl or alkoxy groups having 1-4 carbon atoms or with halogen atoms, preferably the aryl radicals have 1 to 10 carbon atoms; compounds in which R.sub.2 is an aryl radical are particularly preferred and compounds in which the aryl radical is a phenyl radical are especially preferred; R.sub.d is --OH, --OY or --OZ with at least one R.sub.d radical being --OY and at least one thereof being --OZ;

wherein Y is 1,2-naphthoquinonediazide- 5-sulfonyl and Z is --W--R.sub.3, where W is ##STR30## or --SO.sub.2 --, and R.sub.3 is alkyl, aryl, substituted alkyl or substituted aryl; the alkyl radicals R.sub.3 may be straight-chain or branched and may be substituted with halogen atoms, preferably Br or Cl, or lower alkoxy groups having 1-4 carbon atoms, preferably alkyl having 1-20 carbon atoms; the aryl radicals R.sub.3 are preferably mononuclear and may be substituted with lower alkyl or alkoxy groups having 1-4 carbon atoms or with halogen atoms, preferably Br or Cl, preferably aryl radicals having 6-10 carbon atoms; phenyl radicals are preferred; alkyl radicals are particularly preferred and lower alkyl radicals having 1-6 carbon atoms are especially preferred.

These photosensitive compounds may be prepared, for example, in the manner as herein described for the preparation of the photosensitizer compositions. The compounds may be isolated and purified as desired.

Another aspect of the invention provides photosensitizer compositions comprising inter alia the photosensitive compounds disclosed herein. The photosensitizer compositions may be obtained by condensing phenolic compounds with a mixture of Diazo and organic acid halides. The Diazo component and the organic acid halide component of the mixture may be condensed either sequentially or concurrently with the phenolic compounds.

The Diazo/organic acid mixture may be reacted preferably in stoichiometric quantities with the hydroxyl-bearing compounds. However, the phenolic compounds need not be completely esterified and less than stoichiometric quantities of the Diazo and organic acid halide compounds may be condensed with the phenolic compounds provided that the molar ratio of Diazo to organic acid halide reacted is within the ranges specified herein. The total amount of Diazo and organic acid halide reacted with the phenolic compounds should be sufficient to produce a photosensitizer composition capable of inhibiting the dissolution rate of an alkali-soluble resin.

The phenolic compounds which may be condensed with the Diazo/organic acid mixture are represented by the general formulae (A), (B) and (C): ##STR31## wherein R is --H, --OH, --X--R.sub.b, or ##STR32## R.sub.a is H, --OH, halogen, preferably Cl or Br, or lower alkyl, preferably lower alkyl having 1 to 4 carbon atoms; with at least two and not greater than six R.sub.a radicals being --OH, X is a single C--C bond, --O--, --S--,--SO.sub.2 --, ##STR33## n is 1 or 2, R.sub.b is H, alkyl, aryl, substituted alkyl or substituted aryl; preferably alkyl having 1-20 carbon atoms, more preferably 1-12 carbon atoms, preferably aryl being phenyl or naphthyl, alkyl or aryl may be substituted with lower alkyl having 1-4 carbon atoms, lower alkoxy having 1-4 carbon atoms, or halogen atoms, preferably Cl or Br; ##STR34## wherein R.sub.1 is H or ##STR35## R.sub.c is H or --OH with at least two R.sub.c radicals being --OH; and ##STR36## wherein R.sub.2 is H, alkyl, aryl, substituted alkyl, or substituted aryl; the alkyl radicals R.sub.2 may be straight-chain or branched and may be substituted with halogen atoms or lower alkoxy groups having 1-4 carbon atoms, preferably the alkyl radicals have 1-20 carbon atoms; the aryl radicals R.sub.2 are preferably mononuclear and may be substituted with lower alkyl or alkoxy groups having 1-4 carbon atoms or with halogen atoms, preferably the aryl radicals have 1 to 10 carbon atoms; compounds in which R.sub.2 is an aryl radical are particularly preferred and compounds in which the aryl radical is a phenyl radical are especially preferred.

Among the phenolic compounds represented by the general formula (I) are: hydroxyl-bearing benzene compounds such a 1,2-dihydroxybenzene, 1,3-dihydroxybenzene, 1,4-dihydroxybenzene, 1,2,3-trihydroxybenzene, 1,2,4-trihydroxybenzene, 1,3,5-trihydroxybenzene, and the like; dihydroxybenzophenones such as 2,2'-dihydroxybenzophenone, 2,3'-dihydroxybenzophenone, 2,4dihydroxybenzophenone, 2,4'-dihydroxybenzophenone, 2,5dihydroxybenzophenone, 3,3'-dihydroxybenzophenone, 4,4'dihydroxybenzophenone, and the like; trihydroxybenzophenones such as 2,2',6-trihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone, 2,4,6-trihydroxybenzophenone, 3,4,5-trihydroxybenzophenone, and the like; tetrahydroxybenzophenones such as 2,2'3,4-tetrahydroxybenzophenone, 2,2',4,4'tetrahydroxybenzophenone, 2,2'4,6'-tetrahydroxybenzophenone, 2,2',5,6'-tetrahydroxybenzophenone, 2,3',4,4'-tetrahydroxybenzophenone, 2,3',4,6-tetrahydroxybenzophenone, 2,4,4',6-tetrahydroxybenzophenone, 3,3',4,4',-tetrahydroxybenzophenone, and the like; pentahydroxybenzophenones; hexahydroxybenzophenones; dihydroxy- and trihydroxy- phenyl alkyl ketones such as 2,4dihydroxyphenyl alkyl ketones, 2,5-dihydroxyphenyl alkyl ketones, 3,4-dihydroxyphenyl alkyl ketones, 3,5-dihydroxyphenyl alkyl ketones, 2,3,4-trihydroxyphenyl alkyl ketones, 3,4,5-trihydroxyphenyl alkyl ketones, 2,4,6-trihydroxyphenyl alkyl ketones, and the like, preferably alkyl having 1-12 carbon atoms such as methyl, ethyl, butyl, n-hexyl, heptyl, decyl, dodecyl, and the like; dihydroxyphenyl aralkyl ketones; trihydroxyphenyl aralkyl ketones; dihydroxydiphenyls; trihydroxydiphenyls such as 2,2',4-trihydroxydiphenyl; tetrahydroxydiphenyls such as 2,2',4,4'-tetrahydroxydiphenyl; dihydroxydiphenyl oxides; dihydroxydibenzyl oxides; dihydroxydiphenyl alkanes, preferably lower alkanes such as methane, ethane, propane or the like; dihydroxybenzoic acid; trihydroxybenzoic acids; dihydroxy- and trihydroxy- benzoic acid alkyl esters, alkyl preferably having 1 to 12 carbon atoms, such as n-butyl 2,4-, 2,5-, 3,4- and 3,5-dihydroxybenzoate, 2,4,4-trimethylpentyl 2,4-dihydroxybenzoate, and the like; dihydroxy- and trihydroxy- benzoic acid phenyl esters; dihydroxy-, trihydroxy-, and tetrahydroxy- diphenyl sulfides such as 4,4'-dihydroxydiphenyl sulfide; dihydroxydiphenyl sulfones; and dihydroxy- and trihydroxy- phenyl naphthyl ketones such as 2,3,4-trihydroxyphenyl naphthyl ketone; and the like.

Examples of compounds of general formula (I) where at least one R.sub.a radical is halogen or lower alkyl include 2,4-dihydroxy-3,5- dibromobenzophenone; 5-bromo-2,4-dihydroxybenzoic acid and esters; 2,4,2',4'-tetrahydroxy-3,5,3',5'-tetrabromodiphenyl; 4,4'-dihydroxy-2,2'dimethyl-5,5'-di-tert.-butyl diphenyl; 4,4'-dihydroxy-2,2'dimethyl-5,5'-di-tert.-butyl diphenyl sulfide; 2,4,2',4'-tetrahydroxy-3,5,3'5'-tetrabromodiphenyl sulfone; and the like.

The preferred phenolic compounds of general formula (I) are the hydroxyl-bearing benzenes and benzophenones and the especially preferred compounds are the trihydroxybenzophenones.

Among the phenolic compounds represented by general formula (II) are: dihydroxynaphthalenes such as 1,2-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 1,8-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, and the like; dihydroxydinaphthylmethanes such as 2,2'dihydroxydinaphthylmethane, and the like. The dihydroxynaphthylenes are preferred. The hydroxyl groups of the dihydroxynaphthylenes may be either on the same nucleus or on different nucleii of the naphthalene moiety.

Among the phenolic compounds represented by general formula (III) are bis-(3-benzoyl-4,5,6-trihydroxyphenyl)-methane; bis-(3-acetyl-4,5,6-trihydroxyphenyl)-methane; bis-(3-propionyl-4,5,6-trihydroxyphenyl)-methane; bis-(3-butyryl-4,5,6-trihydroxyphenyl)-methane; bis-(3-hexanoyl-4,5,6-trihydroxyphenyl)-methane; bis-(3-heptanoyl-4,5,6-trihydroxyphenyl)-methane; bis-(3-decanoyl-4,5,6-trihydroxyphenyl)-methane; bis-(3-octadecanoyl-4,5,6-trihydroxyphenyl)-methane; and the like.

The organic acid halides which may be used to modify the Diazo ester compounds may be represented by the formula:

W--R.sub.3 wherein W is ##STR37## or --SO.sub.2 --V, V is halogen, preferably Cl or Br, and R.sub.3 is alkyl, aryl, substituted alkyl or substituted aryl; the alkyl radicals R.sub.3 may be straight-chain or branched and may be substituted with halogen atoms, preferably Br or Cl, or lower alkoxy groups having 1-4 carbon atoms, preferably the alkyl radicals have 1-20 carbon atoms; the aryl radicals R.sub.3 are preferably mononuclear and may be substituted with lower alkyl or alkoxy groups having 1-4 carbon atoms or with halogen atoms, preferably Br or Cl, preferably the aryl radicals have 6 to 10 carbon atoms, phenyl radicals are especially preferred; compounds in which R.sub.3 is an alkyl radical are particularly preferred and compounds in which the alkyl radical is lower alkyl radical having 1-6 carbon atoms are especially preferred.

Among the organic acid halides represented by the above formula are alkyl sulfonyl halides such as methanesulfonyl chloride, ethanesulfonyl chloride, propanesulfonyl chloride, n-butanesulfonyl chloride, dodecanesulfonyl chloride, and the like; arylsulfnyl chlorides such as benzenesulfonyl chloride, naphthalenesulfonyl chlorides, and the like; acyl halides such as acetyl chloride, butanoyl chloride, valeryl chloride, benzoyl chloride, benzoyl bromide, naphthoyl chlorides, and the like.

The preferred organic acid halides are lower alkyl sulfonyl halides and lower alkyl acyl halides having 1-6 carbon atoms, and benzenesulfonyl halides and benzoyl halides. These acid halides may be substituted or unsubstituted.

The following examples are presented solely to illustrate the invention and should not be considered to constitute limitations on the invention, many variations of which are possible without departing from the spirit or scope thereof.

Preparation of Photosensitizer Compositions

The preparation of naphthoquinonediazide photosensitizers is described in U.S. Pat. Nos. 3,046,118, 3,106,645 and 4,397,937, which are hereby incorporated by reference. The photosensitizer compositions of this invention may be obtained by condensing the desired naphthoquinonediazide sulfonyl halide and organic acid halide with a phenolic compound which has more than one hydroxyl group in the presence of an acid scavenger. The resulting sensitizer composition may be purified as desired.

Solvents for the reaction may include, but are not limited to, acetone, p-dioxane, tetrahydrofuran, methylene chloride, pyridine, or the like.

The acid scavenger may be inorganic, such as sodium carbonate, or the like, or organic, such as sodium salts of weak acids, tertiary amines such as triethyl amine, pyridines, or the like.

A preparative example follows:

EXAMPLE 1

23.0 grams of 2,3,4-trihydroxybenzophenone and 37.6 grams of 1,2-naphthoquinonediazide-5-sulfonyl chloride (Diazo) are stirred together in 165 ml acetone. 20.5 grams of methanesulfonyl chloride are added in. 34.0 grams of triethylamine are slowly dropped in while maintaining an internal temperature of about 30.degree. C. The reaction mixture is filtered, the salt cake washed with 165 ml acetone, and the acetone solution drowned in 2.97 liters of 1 normal hydrochloric acid. The product is filtered off, washed with water, and dried in an air oven at .ltoreq.40.degree. C. The yield obtained is 67.8 grams, 99.7% of theory.

The product thusly obtained may be purified as desired.

The method of synthesis shown in this example is not the only way to make such photosensitizer compositions, as those skilled in the art may obtain comparable products by simply varying solvents, bases or reaction conditions. Several other examples are set forth in Table 1.

TABLE 1______________________________________ Diazo Diazo Methane- Diazo Trisester 3,4 Bisester Sulfonate NitrogenSensitizer.sub.1 (%) (%) Trisester (%) (%)______________________________________A 30.5 3.0 16.6 6.20B 30.1 4.2 13.8 6.38C 29.0 4.7 11.2 6.28D 12.2 1.6 9.3 6.09E 12.8 1.7 7.9 6.09F 13.1 0.8 9.9 5.99G 12.2 1.0 9.6 6.11H 14.3 1.9 10.3 6.20I 12.7 0.7 6.6 6.60J 10.3 0.7 6.4 6.36K 12.8 1.9 6.9 6.47L 13.2 1.9 9.2 6.53M 12.4 1.7 6.8 6.40N 12.7 1.8 7.6 6.50O 14.9 -- 7.6 6.38P 11.9 0.7 7.7 6.41______________________________________ .sup.1 Sensitizers A, B and C were prepared by reacting the Diazo with 2,3,4trihydroxybenzophenone first and then adding in the methanesulfonyl chloride. Sensitizers M and 0 were prepared by reacting the methanesulfonyl chloride with 2,3,4trihydroxybenzophenone first and then adding in the Diazo. Sensitizers D through L, N and P were prepared by condensing the Diazo and methanesulfonyl chloride concurrently with 2,3,4trihydroxybenzophenone.

EXAMPLE 2

A photosensitizer composition is prepared by condensing 1,2,3trihydroxybenzene with 90 mole percent Diazo and 10 mole percent methanesulfonyl chloride in a 1 to 3 molar ratios. 0.74 grams of the resulting sensitizer is formulated in 24.26 grams of a solution comprising 28.4 percent novolak resin and 71.6 percent AZ Thinner, a solvent mixture comprising cellosolve acetate, butyl acetate and xylene available from American Hoechst Corporation, Somerville, N.J. The lithographic properties are measured and it is found that at an absorptivity of 0.740 l/g-cm at 398 nm, the photoresist has a dark erosion rate of 0.004 .mu.m/minute, a photosensitivity of 31.0 mJ/cm.sup.2 determined under 350-450nm broad band exposure measured at 405 nm, and a contrast value of 2.50. The photoresist composition remains in a stable solution for at least two weeks when stored at room temperature. In contrast, an unmodified photosensitizer obtained by condensing 1,2,3-trihydroxybenzene with Diazo in a 1 to 3 molar ratio could not be formulated in a stable solution with the above resin and solvent mixture.

Comparative Example

Comparative examples are prepared by condensing 2,3,4-trihydroxybenzophenone with 1,2-naphthoquinonediazide-5-sulfonyl chloride in a molar ratio of 1 to 1.4. A photosensitizer composition is obtained having diazide trisester content of about 36 to 40 by weight, a 3,4-bisester content of about 18 to 20 percent by weight and a 2,3,4-trihydroxybenzophenone content of about 9 to 10 percent by weight. In the following tables, this photosensitizer composition is designated as "X".

Preparation of Positive Photoresist Systems

The photoresist composition may be prepared by formulating the photosensitizer compositions of this invention with alkali-soluble resins, solvents and, if desired, other additives. Alkali-soluble resins which may be used include, for example, novolak resins, polyvinyl phenol resins, and the like.

Alkali-soluble novolak resins, which may be used for preparing photosensitive compositions, are known in the art. A procedure for their manufacture is described in Chemistry and Application of Phenolic Resins, Knop, A. and Scheib, W.; Springer Verlag, New York, 1979 in Chapter 4 which is incorporated herein by reference.

The photoresist compositions of this invention are prepared by dissolving the above-mentioned novolak or polyvinyl phenol resins and the photosensitizer compositions of the invention in a solvent. Suitable solvents for this purpose include, for example, propylene glycol methyl ether acetate and the like; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and the like; cellosolve acetates such as methyl cellosolve acetate, ethyl cellosolve acetate and the like; esters such as ethyl acetate, butyl acetate and the like; ketones such as methyl ethyl ketone, cyclopentanone, cyclohexanone and the like; and aromatic hydrocarbons such as toluene, xylene and the like. It is also possible to use mixtures thereof. The choice of solvent, or mixture of solvents, will depend upon the coating method intended, layer thickness, drying conditions and consideration of the solubilities of the constituents, vaporization speed of solvent after coating the photoresist composition on a substrate, and the like.

Optionally, additives such as colorants, dyes, anti-striation agents, plasticizers, adhesion promoters, speed enhancers and such surfactants as non-ionic surfactants may be added to the photoresist composition before it is coated onto a substrate.

In the preferred embodiments, the solid parts of the photoresist compositions, that is the novolak or polyvinyl phenol binder resin and photosensitizer composition, preferably ranges from 15% to about 99% novolak or polyvinyl phenol binder resin and from about 1% to about 85% photosensitizer composition. A more preferred range of binder resin would be from about 50% to about 97% and most preferably from about 65% to about 93% by weight of the solid resist parts. A more preferred range of photosensitizer composition would be from about 3% to about 50% and most preferably from about 7% to about 35% by weight of the solid resist parts. In preparing the resist composition the binder resin and photosensitizer composition are mixed with the solvent such that the solvent is present in an amount of from about 40% to about 90% by weight of the overall resist composition. A more preferred range is from about 60% to about 85% and most preferably from about 65% to about 80% by weight of the overall resist composition.

Examples of dye additives that may be used together with the photoresist compositions of the present invention include Methyl Violet 2B (C.I. No. 42535), Crystal Violet (C.I. 42555), Malachite Green (C.I. No. 42000), Victoria Blue B (C.I. 44045) and Neutral Red (C.I. No. 50040) at one to ten percent weight levels, based on the combined weight of novolak and sensitizer. The dye additives help provide increased resolution by inhibiting back scattering of light off the substrate.

Anti-striation agents may be used up to five percent weight level, based on the combined weight of novolak and sensitizer.

Plasticizers which may be used include, for example, phosphoric acid tri-(.beta.-chloroethyl)-ester; stearic acid; dicamphor; polypropylene; acetal resins; phenoxy resins; and alkyl resins at one to ten percent weight levels, based on the combined weight of novolak and sensitizer. The plasticizer additives improved the coating properties of the material and enable the application of a film that is smooth and of uniform thickness to the substrate.

Adhesion promoters which may be used include, for example, .beta.-(3,4-epoxy-cyclohexyl)-ethyltrimethoxysilane; p-methyl-disilane-methyl methacrylate; vinyltrichlorosilane; and .gamma.-amino-propyl triethoxysilane up to a 4 percent weight level, based on the combined weight of novolak and sensitizer.

Speed enhancers that may be used include, for example, picric acid, nicotinic acid or nitrocinnamic acid at a weight level of up to 20 percent, based on the combined weight of novolak and sensitizer. These enhancers tend to increase the solubility of the photoresist coating in both the exposed and unexposed areas, and thus they are used in applications when speed of development is the overriding consideration even though some degree of contrast may be sacrificed; i.e., while the exposed areas of the photoresist coating will be dissolved more quickly by the developer, the speed enhancers will also cause a larger loss of photoresist coating from the unexposed areas.

Non-ionic surfactants that may be used include, for example, nonylphenoxy poly(ethyleneoxy) ethanol; octylphenoxy (ethyleneoxy) ethanol; and dinonyl phenoxy poly(ethyleneoxy) ethanol at up to 10 percent weight levels, based on the combined weight of novolak and sensitizer.

Solubility and Solution Stability

Photoresist compositions were prepared according to the method outlined above. The photosensitizer compositions from the examples are dissolved in a prefiltered solution of resin and propylene glycol methyl ether acetate (PGMEA) or AZ Thinner solvent.

The compositions of the solutions is set forth in Table 2.

The prepared photoresist test solutions are filtered through an Alsop 175 filter pad, then through a 0.2 .mu.m Fluoropore filter (available from Millipore Corporation). The test solutions are protected from light and stored in a constant temperature air oven at 50.degree. C. for a period of seven days and then examined for visible precipitate. If precipitate is visible in a test solution, the sample has failed the solution stability test. The photoresist solutions are also tested for solution stability at room temperature. The solutions are preiodically examined for visible crystallization, precipitation and color change.

TABLE 2______________________________________ Diazo N.sub.2 Photosensitizer Contrast Composition of PhotoresistExample (% weight) Resin Solution Composition______________________________________3 9.12% A 24% novolak/76% 0.565% PGMEA4 8.86% B 24% novolak/76% 0.565% PGMEA5 9.00% C 24% novolak/76% 0.565% PGMEA6 9.29% D 24% novolak/76% 0.565% PGMEA7 9.3% E 24% novolak/76% N/A PGMEA8 9.3% F 24% novolak/76% N/A PGMEA9 9.3% G 24% novolak/76% N/A PGMEA10 9.3% N 24% novolak/76% N/A PGMEA11 9.3% O 24% novolak/76% N/A PGMEA12 9.3% P 24% novolak/76% N/A PGMEA13 8.825% N 25.6% novolak/ N/A 74.4% AZ Thinner14 8.825% O 25.6% novolak/ N/A 74.4% AZ Thinner15 8.825% P 25.6% novolak/ N/A 74.4% AZ Thinner______________________________________

The photoresist compositions of the invention have excellent solution stability and good color. The photoresist composition of Examples 3 through 15 show no visible precipitation after storage at 50.degree. C. for one week. At room temperature, no visible precipitate is observed for Examples 3-10, 12, 13 and 15 after seven months. Example 11 precipitated at four months and Example 14 precipitated at six months. The solution color is exceptionally clear and light in comparison to photoresists prepared with type X photosensitizers of the comparative examples.

The choice of the solvent system may affect the ability to formulate a particular photosensitizer composition. For example, a photosensitizer may be difficult to formulate in one solvent system, but readily formulated in another. However, where the modified and unmodified photosensitizer compositions can be formulated, the unmodified composition will generally precipitate before the modified composition.

The solubility of the photosensitizer compositions may be tested by dissolving the photosensitizer in a solvent at various concentrations and observing the solution over several days. A photosensitizer of type G dissolved in acetone shows no crystallization at concentrations as high as 30 percent. In contrast, a photosensitizer of type X crystallizes overnight at 30 percent and 15 percent concentrations. A small amount of flocculant is observed at the 5 percent concentrations of the type X photosensitizer.

Photosensitivity, Contrast and Unexposed Film Loss

The prepared resist solution, can be applied to a substrate by any conventional method used in the photoresist art, including dipping, spraying, whirling and spin coating. When spin coating, for example, the resist solution can be adjusted as to the percentage of solids content in order to provide coating of the desired thickness given the type of spinning equipment utilized and the amount of time allowed for the spinning process. Suitable substrates include silicon, aluminum or polymeric resins, silicon dioxide, doped silicon dioxide, silicon nitride, tantalum, copper, polysilicon, ceramics and aluminum/copper mixtures.

The photoresist coatings produced by the above described procedure are particularly suitable for application to thermally grown silicon/silicon dioxide-coated wafers such as are utilized in the production of microprocessors and other miniaturized integrated circuit components. An aluminum/aluninun oxide wafer can be used as well. The substrate may also comprise various polymeric resins especially transparent polymers such as polyesters.

After the resist composition solution is coated onto the substrate, the substrate is baked at approximately 80.degree. to 105.degree. C. until substantially all the solvent has evaporated and only a thin coating of photoresist composition on the order of a micron in thickness remains on the substrate. The coated substrate can then be exposed to actinic radiation especially ultraviolet radiation in any desired exposure pattern produced by use of suitable masks, negatives, stencils, templates, etc.

The exposed resist-coated substrates are next substantially immersed in alkaline developing solution. The solution is preferably agitated, for example, by nitrogen burst agitation.

The substrates are allowed to remain in the developer until all, or substantially all, of the resist coating has dissolved from the exposed areas.

After removal of the coated wafers from the developing solution, a post-development heat treatment or bake may be employed to increase the coating's adhesion and chemical resistance to etching solutions and other substances. The post-development heat treatment can comprise the oven baking of the coating and substrate below the coating's softening point. In industrial applications, particularly in the manufacture of microcircuitry units on silicon/silicon dioxide-type substrates, the developed substrates may be treated with a buffered, hydrofluoric acid base etching solution. The resist compositions of the present invention are resistant to acid-base etching solutions and provide effective protection for the unexposed resist-coating areas of the substrate.

The following specific examples will provide detailed illustrations of the methods of producing and utilizing compoitions of the present invention. These examples are not intended, however, to limit or restrict the scope of the invention in any way and should not be construed as providing conditions, parameters or values which must be utilized exclusively in order to practice the present invention.

EXAMPLES

Resist formulations are prepared with the photosensitizer compositions of this invention. The sensitizer to be tested is dissolved in a pre-filtered stock solution of resin and solvent. The resist solutions are then filtered. The photoresist composition are spin coated on several silicon wafers at a constant, predetermined spin speed to obtain 2.0 .mu.m layers of dried resist film. The wafers are then baked at 90.degree. C. for 30 minutes.

The initial film thicknesses of the resist coatings are measured by a Rudolf Film Thickness Monitor. The wafers are then exposed to varied amounts of UV light energy (350-450 nm). The resists are developed for 1 minute at 25.degree. C. using AZ 400K alkali developer, AZ alkali developer or AZ 312 MIF alkali developer, available from American Hoechst Corporation, Somerville, N.J. diluted with deionized water. The remaining film thicknesses are then remeasured by the Rudolf Film Thickness Monitor to determine film loss for the particular energy dose. Photosensitivity is measured by generating a characteristic curve, as described in Wake, R. W. and Flanigan, M. C., "A Review of Contrast in Positive Photoresists", SPIE Vol. 539, Advances in Resist Technology and Processing II (1985), p. 291, which is herein incorporated by reference, wherein film thickness loss after one minute of development is plotted against the logarithm of the UV exposure dose. By interpolation of this plot to 1.0 .mu.m film loss, the photosensitivity value in mJ/cm.sup.2 is obtained. The slope of the linear portion of the plot is the contrast.

The results of photosensitivity, contrast and dark erosion rate testing of several photoresist compositions prepared with photosensitizer compositions of this invention are set forth in Table 3 and compared with photoresists prepared with unmodified photosensitizer compositions.

TABLE 3__________________________________________________________________________Ex- Developeram- Photosensitizer Resin Absorptivity Strength Dark Erosion Photosensitivity.sup.2 Con-ple (% weight) Solution (1/g-cm) Developer.sup.1 (ratio to H.sub.2 O) (Rate .ANG./min.) (mJ/cm.sup.2) trast__________________________________________________________________________16 3.9% X 30% novolak 0.741 AZ 1:1.5 40 43.1 1.48 70% AZ Thinner17 4.9% D 30% novolak/ 0.727 AZ 1:1 30 43.2 1.90 70% AZ Thinner18 3.9% X 30% novolak/ 0.745 AZ 400K 1:5 80 27.6 2.27 70% AZ Thinner19 4.9% D 30% novolak/ 0.736 AZ 400K 1:4 40 33.6 2.55 70% AZ Thinner20 6.9% X 30% novolak/ 1.30 AZ 400K 1:4 40 14.2 3.04 70% AZ Thinner21 8.8% D 30% novolak/ 1.35 AZ 400K 1:2 40 15.1 4.03 70% AZ Thinner22 6.9% X 30% novolak/ 1.30 AZ 312 MIF 1:1.5 60 26.3 2.21 70% AZ Thinner23 6.9% X 30% novolak/ 1.30 AZ 312 MIF 1:1.5 70 26.1 2.29 70% AZ Thinner24 6.87% X 25.6% novolak/ 1.31 AZ 312 MIF 1:1.5 80 24.1 2.23 74.4% AZ Thinner25 7.16% X 30% novolak/ 1.33 AZ 312 MIF 1:1.5 90 25.2 2.37 70% AZ Thinner26 7.12% X 30% novolak/ 1.31 AZ 312 MIF 1:1.5 20 38.7 2.04 70% AZ Thinner27 7.12% X 25.6% novolak/ 1.31 AZ 312 MIF 1:1.5 80 25.8 2.38 74.4% AZ Thinner28 8.66% B 30% novolak/ 1.32 AZ 312 MIF 1:1 90 21.2 4.00 70% AZ Thinner29 8.8% D 30% novolak/ 1.35 AZ 312 MIF 1:1 150 29.9 3.71 70% AZ Thinner30 8.8% D 30% novolak/ 1.35 AZ 312 MIF 1:1 50 27.5 4.18 70% AZ Thinner31 8.82% D 25.6% novolak/ 1.33 AZ 312 MIF 1:1 50 29.9 3.74 74.4% AZ Thinner32 8.82% D 30% novolak/ 1.35 AZ 312 MIF 1:1 80 27.4 4.09 70% AZ Thinner33 8.82% D 25.6% novolak/ 1.36 AZ 312 MIF 1:1 60 29.5 4.02 74.4% AZ Thinner34 9.24% D 30% novolak/ 1.32 AZ 312 MIF 1:1 60 30.6 4.42 70% AZ Thinner35 9.24% D 30% novolak/ 1.32 AZ 312 MIF 1:1 60 31.8 4.54 70% AZ Thinner36 9.24% E 30% novolak/ 1.34 AZ 312 MIF 1:1 50 31.0 4.50 70% AZ Thinner37 9.24% F 30% novolak/ 1.33 AZ 312 MIF 1:1 50 31.4 4.41 70% AZ Thinner38 9.24% G 30% novolak/ 1.32 AZ 312 MIF 1:1 60 31.5 4.57 70% AZ Thinner39 8.82% N 24.6 novolak/ 1.36 AZ 312 MIF 1:1 80 30.0 4.17 74.4% AZ Thinner40 8.82% O 24.6% novolak/ 1.35 AZ 312 MIF 1:1 90 30.9 3.89 74.4% AZ Thinner41 8.82% P 24.6% novolak/ 1.35 AZ 312 MIF 1:1 70 31.2 3.88 74.4% AZ Thinner__________________________________________________________________________ .sup.1 AZ 400K Developer, AZ Developer and AZ 312 MIF Developer are available from American Hoechst Corporation, Somerville, New Jersey. The AZ 400K Developer is an aqueous inorganic alkali developer, the AZ Developer is a buffered aqueous inorganic alkali developer, and AZ 312 MI is a metalion-free aqueous alkali developer containing a quaternary ammonium salt. .sup.2 The broadband exposure energy levels were measured at 365 nm.

The data show that the photoresist compositions of the invention exhibit higher contrast values than the comparative examples at similar photospeeds when an aqueous alkali developer is used.

An increase n the induction period of up to about 50 percent over the induction period of the comparative examples was observed for the photoresist compositions of the invention when a metal-ion-free developer is used. The induction period is the threshold period before which the exposed portions of a resist will dissolve during development. The induction period may be measured by plotting the film loss against the logarithm of the energy dose.

Claims

1. A photosensitive compound represented by the general formulae (1): ##STR38## wherein R is ##STR39## X is a single C--C bond, --O--, --S--, ##STR40## n is 1 or 2, R.sub.a is H, --OH, --OY, --OZ, halogen or lower alkyl, with at least one R.sub.a radical being --OY and at least one thereof being --OX;

wherein Y is 1,2-naphthoquinonediazide-5-sulfonyl and Z is --W--R.sub.3, where W is ##STR41## or --SO.sub.2 --, and R.sub.3 is alkyl, aryl, substituted alkyl or substituted aryl; and the total amount of Diazo and organic acid halide reacted with the phenolic compound is that amount sufficient to produce a photosensitizer condensate capable of inhibiting the dissolution rate of an alkali soluble resin when mixed with said resin.

2. A photosensitizer comprising the condensation product of:

(I) a phenolic compound having the formula: ##STR42## wherein R is ##STR43## R.sub.a is H, --OH, halogen or lower alkyl, with at least two and not greater than six R.sub.a radicals being --OH, X is a single C--C bond, --O--, --S--, --SO.sub.2 --, ##STR44## n is 1 or 2 and (II) a 1,2-naphthoquinonediazide-5-sulfonic acid (Diazo); and

(III) an organic acid halide represented by the formula:

W--R.sub.3

wherein W is ##STR45## or --SO.sub.2 --V, V is halogen and R.sub.3 is alkyl, aryl, substituted alkyl or substituted aryl;

wherein the molar ratio of the amount of Diazo reacted to the amount of organic acid reacted is in the range of from about 1:2 to about 19:1; and the total amount of Diazo and organic acid halide reacted with the phenolic compound is that amount sufficient to produce a photosensitizer condensate capable of inhibiting the dissolution rate of an alkali soluble resin when mixed with said resin.

3. A method of preparing a photosensitizer condensate comprising:

condensing a phenolic compound represented by the general formulae (A): ##STR46## wherein R is ##STR47## R.sub.a is H, --OH, halogen lower or lower alkyl, with at least two and not greater than six R.sub.a radicals being --OH, X is a single C--C bond, --O--, --S--, --SO.sub.2 --, ##STR48## n is 1 or 2; with a 1,2-naphthoquinonediazide-5-sulfonic acid (Diazo) and with an organic acid halide represented by the formula W--R.sub.3, wherein W is ##STR49## or --SO.sub.2 --V, V is halogen, R.sub.3 is alkyl, aryl, substituted alkyl or substituted aryl; wherein the molar ratio of the amount of Diazo to the amount of organic acid halide to be reacted is in the range of from about 1:2 to about 19:1; and the total amount of Diazo and organic acid halide reacted with the phenolic compound is that amount sufficient to produce a photosensitizer condensate capable of inhibiting the dissolution rate of an alkali soluble resin when mixed with said resin; wherein said condensing is conducted in a solvent medium in the presence of an acid scavenger; and then subsequently isolating said photosensitizer condensate.

4. A photosensitizer according to claim 2, wherein the ratio of the amount of Diazo reacted to the amount of organic acid halide reacted is in the range of from about 2:3 to about 19:1.

5. A photosensitizer according to claim 2, wherein the ratio of the amount of Diazo reacted to the amount of organic acid halide reacted is in the range of from about 7:8 to about 9:1.

6. A photosensitizer according to claim 2, wherein the phenolic compound is a trihydroxybenzene, a dihydroxybenzophenone, a trihydroxybenzophenone or a tetrahydroxybenzophenone; and said organic acid halide is a lower alkyl sulfonyl halide, a benzene sulfonyl halide, a lower alkyl acyl halide or a benzoyl halide.

7. A photosensitizer according to claim 4, wherein the phenolic compound is a trihydroxybenzene, a dihydroxybenzophenone, a trihydroxybenzophenone or a tetrahydroxybenzophenone; and said organic acid halide is a lower alkyl sulfonyl halide, a benzene sulfonyl halide, a lower alkyl acyl halide or a benzoyl halide.

8. A photosensitizer according to claim 5, wherein the phenolic compound is a trihydroxybenzene, a dihydroxybenzophenone, a trihydroxybenzophenone or a tetrahydroxybenzophenone; and said organic acid halide is a lower alkyl sulfonyl halide, a benzene sulfonyl halide, a lower alkyl acyl halide or a benzoyl halide.

9. A photosensitizer according to claim 2, wherein the phenolic compound is 2,3,4-trihydroxybenzophenone.

10. A photosensitizer according to claim 4, wherein the phenolic compound is 2,3,4-trihydroxybenzophenone.

11. A photosensitizer according to claim 5, wherein the phenolic compound is 2,3,4-trihydroxybenzophenone.

12. A method according to claim 3, wherein said ratio of the amount of Diazo reacted to the amount of organic acid halide reacted is in the range of from about 2:3 to about 19:1.

13. A method according to claim 3, wherein said ratio of the amount of Diazo reacted to the amount of organic acid halide reacted is in the range of from about 7:8 to about 9:1.

14. A method according to claim 3, wherein the phenolic compound is a trihydroxybenzene, a dihydroxybenzophenone, a trihydroxybenzophenone or a tetrahydroxybenzophenone; and the organic acid halide is a lower alkyl sulfonyl halide, a benzene sulfonyl halide, a lower alkyl acyl halide or a benzoyl halide.

15. A method according to claim 12, wherein the phenolic compound is a trihydroxybenzene, a dihydroxybenzophenone, a trihydroxybenzophenone or a tetrahydroxybenzophenone; and the organic acid halide is a lower alkyl sulfonyl halide, a benzene sulfonyl halide, a lower alkyl acyl halide or a benzoyl halide.

16. A method according to claim 13, wherein the phenolic compound is a trihydroxybenzene, a dihydroxybenzophenone, a trihydroxybenzophenone or a tetrahydroxybenzophenone; and the organic acid halide is a lower alkyl sulfonyl halide, a benzene sulfonyl halide, a lower alkyl acyl halide or a benzoyl halide.

17. A method according to claim 3, wherein the phenolic compound is 2,3,4-trihydroxybenzophenone.

18. A method according to claim 12, wherein the phenolic compound is 2,3,4-trihydroxybenzophenone.

19. A method according to claim 13, wherein the phenolic compound is 2,3,4-trihydroxybenzophenone.