WO1988002878A1

WO1988002878A1 - Image reversal system and process

Info

Publication number: WO1988002878A1
Application number: PCT/US1987/002743
Authority: WO
Inventors: Chava Gal; Giora Ben-Shushan; Eitan Shalom
Original assignee: Macdermid, Incorporated
Priority date: 1986-10-20
Filing date: 1987-10-16
Publication date: 1988-04-21
Also published as: EP0288533A4; EP0288533A1; AU8173487A; JPH01501176A

Abstract

A light-sensitive composition and method which can be used to produce photoresist images. The composition comprises a mixture of a novolak resin, a 1,2-quinonediazide sensitizer and sufficient quantities of one or more organic stabilizing compounds to render the total composition soluble in alkaline developer. In producing a negative image the composition is exposed imagewise to actinic radiation, thereafter heated to render the exposed image insoluble to alkaline developer, and the unexposed composition is then removed using alkaline developer without the necessity to subject the unexposed composition to exposure to actinic radiation prior to the development stage.

Description

IMAGE REVERSAL SYSTEM AND PROCESS

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a photoresist system and is more particularly concerned with light-sensitive photoresist compositions which can be employed to produce negative relief images and with processes for preparing such images.

2 . Description of the Prior Art Photores ist systems which give rise to positive resist images and photoresist systems which give rise to negat ive res ist images are well-known in the art . However , the two types of system are generally very different from each other in composition and behavior. Thus , positive resist systems generally comprise a base-soluble polymer such as a novolak resin and a photosensitizer containing diazo and keto groups on adj acent positions in a benzenoid structure . Exposure o f the compos ition to actinic radiation serves to convert the diazo-keto configuration of the sensitizer to a σarboxyl group thereby rendering the exposed composition soluble in alkaline developers . In con¬ trast , negative resist systems generally comprise a polymer in association with a sensitizer which initiates cross -linking of the polymer upon exposure to actinic rad i at ion . The exposed image is thereby rendered insoluble in developer solvents and is developed by dissolving away the unexposed portions of the resist system. More recently , photores ist systems have been described which are capable of being processed in the negative as well as the positive modes. Illustratively, Kaplan et al. U.S. Patent 4,007,047 describes a process by which a negative image can be produced using a system based on an alkali-soluble resin and a diazo-ketone sensitizer which normally is employed in the positive mode. In order to produce a negative resist image using such a system a layer of the composition is exposed imagewise to actinic radiation to convert the diazo-keto sensitizer to an alkali soluble carboxyliσ acid, the exposed image is treated with mild aqueous acid (which treatment apparently converts the alkali soluble form of the sensitizer to an alkali-insoluble form by decarboxyl- ation) , and then the layer so treated is subject to a blanket exposure which converts the sensitizer in the previously unexposed portions of the layer to the carboxylic acid form. The negative image is then developed using an alkaline developer which removes the originally unexposed portions of the photosensitive layer which have been rendered alkali soluble by the blanket exposure.

Stahlhofen U.S. Patent 4,581,321 describes a vari¬ ation of the above process in which the material in the exposed image layer is rendered insoluble in alkaline developer by a post exposure bake of the image after which the previously unexposed portions of tlie photo¬ sensitive layer are blanket exposed to radiation as in the previous process and the negative image developed using alkaline developers. A hexamethylmelamine ether is included in the composition employed in the process and its function is said to be that of a cross-linker for the polymeric resin in the composition. The cross-linking takes place during the post-exposure bake and is said to be catalyzed by the acid generated in the portion of the photosensitive layer which has been exposed to the actinic radiation. Chiong et al., IBM Technical Disclosure Bulletin 27. No. 1A, June 1984 teach a modification of the above type of process in which the post-exposure bake is avoided. The imagewise exposure step is carried out using deep-UV radiation and is followed immediately, without a post-bake step, by blanket exposure using near-UV light.

Spak et al. Seventh International Technical Conference on Photopolyaers, Ellenville, New York, October, 1985, pp. 247-269 describe the properties of, and theoretical background relating to operation of, a typical image reversal system based on a diazo keto sensitizer and a novolak resin, which system is avail¬ able commercially under the name AZ^R5214. The description given by Spak et al. of the procedure for use of this system in the negative mode corresponds to that set forth in the aforesaid '321 with the exception that no mention is specifically made of the need for a second blanket exposure prior to development of the negative image. However, the system is basically designed to operate in the positive mode. It is not yet known whether it can be utilized satisfactorily in the negative mode without the need for a second blanket exposure and or other process or formulation modifica- tions.

It has now been found that the need for a blanket exposure prior to development of a negative image using image reversal systems such as those described above can be avoided by improvements in formulation of the system which will be described hereinafter. The elimination of the blanket exposure step represents a significant sav¬ ing in energy and labor costs. Additional improvements in performance of the system have also been found and will be described hereinafter. SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved image reversal system and an improved process for preparing negative photoresist images using such a system.

It is a further object of the invention to provide an improved photoresist system which does not require a blanket exposure of the unexposed portions of the system prior to development of the image in the negative mode. It is yet another object of the invention to provide an improved resin composition for use in an image reversal system.

These objects, and other objects which will become apparent from the description which follows, are achieved by the composition and process of the inven¬ tion. Thus the invention, in one embodiment, comprises an improved process for producing a negative image on a substrate comprising the steps of: coating said substrate with a layer of a lightsensitive composition comprising in admixture

(a) a phenolic resin (b) a 1,2-quinonediazide sensitizer; exposing said light-sensitive layer imagewise to actinic radiation; heating said layer, after said exposure, to a temperature and for a time sufficient to render said imagewise exposed portions of said layer insoluble in alkaline developer; and thereafter dissolving the unexposed portions of said layer in an alkaline developer; wherein the improvement comprises incorporating in said light-sensitive composition at least one organic solubilizing agent in an amount sufficient to render soluble in alkaline developer the portions of said layer which have not been exposed to actinic radiations. The invention also comprises a l ight-sensitive im a g e r ev e r s i b l e ph o to re s i st compos it i on wh i ch comprises , in admixture , (a) at least one novolak resin , (b ) a 1 , 2-quinonediazide sensitizer, and (c) at least one organic solubili z ing agent present in an amount sufficient to render said total composition soluble in alkaline developer.

The term " image reversible photoresist composi¬ tion" means a light-sensitive composition which can be employed in either the positive or negative image mode .

DETAILED DESCRIPTION OF THE INVENTION

The light-sensitive image reversible photoresist compositions of the invention in the broadest embodiment thereof comprise a phenolic resin, a 1,2-quinonediazide sensitizer, and, as the novel component, at least one organic solubilizing agent. By "organic solubilizing agent" is meant an organic compound, or a mixture of two or more such compounds, which serves to render soluble in alkaline developers the total combined components of the photosensitive compositions of the invention when the latter are present in the areas of a coating of the same which have not been exposed to actinic radiation but have been subjected to a post-image bake as herein¬ after discussed. The solubilizing agents employed in the compositions of the invention are compatible with the other components of the compositions, i.e., do not enter into chemical reaction therewith or interfere in any way with the desired operation of the photosensitive composition other than to render it soluble in the unexposed state in alkaline developers, and are stable on storage in admixture with the other components. The extent to which the solubilizing agents render the compositions of the invention alkali soluble is con¬ sidered adequate if the total composition, without exposure to actinic radiation but after being subjected to a post-image bake, is completely soluble in conven¬ tional alkaline developers in a reasonable length of time, i.e., up to about five minutes but preferably from 1 to 2 minutes in the case of a layer of the composition having an average thickness up to about 10 microns.

Illustrative of such organic solubilizing agents are compounds which contain phenolic and or carboxylic groups. The latter compounds are inclusive.of -organic compounds which contain (a) at least one phenolic group and preferably two or more phenolic groups in a benze- noid ring or rings or (b) at least one, and preferably two or more, carboxylic acid groups or (c) at least one phenolic group and at least one carboxylic group in the molecule. Illustrative of such compounds are phenolic compounds such as mono, di, and trihydroxybenzophenone, resorσinol, 1,3 ,4-xylenol, hydroquinone, catechol, pyrogallol, phlorogluσinol, polymeric phenolic resins such as poly(vinylphenol), orcinol, 1,2,4-benzentriol, 4-methylcateσhol, 2-methylresorcinol, 2,2*4,4'-tetra- hydroxybenzophenone, picric acid, coniferyl alcohol, and the like; weak carboxylic acids such as abietic acid, cinnamic acid, 9-anthroic acid, 3-methyladipic acid, pimelic acid, 1-methyl-l-cyclohexane carboxylic acid, linolenic acid, and the like, and compounds containing both carboxylic and phenolic groups such as salicylic, protocatechuic, m-hydroxybenzoic, vanillic, p-hydroxy- benzoic, 2-hydroxy-3-naphthoic, gallic, 3-hydroxy-4- methoxycinnamic, 4-hydroxy-3-methoxycinnamic, 3-hydroxy-4-methoxymandelic, 4-hydroxy3-methoxymandelic, homovanillic, p-hydroxymandeliσ, acids and the like.

The solubilizing agents employed in the composi¬ tions of the invention also include diazoles and triazoles particularly benzotriazole and substituted benzotriazoles, such as l,2,3,4tetrachlorobenzotriazole, 1,2,3-trichlorobenzotrazole, 1,2dichlorobenzotriazole, 1-chlorobenzotriazole and the like.

Preferred compounds for use in the compositions of the invention are poly (vinylphenols) , polyhydroxybenzophenone, abietic acid, benzotriazole and mixtures of two or more such compounds.

As set forth above the amount of the organic solubilizing agent employed, singly or in mixtures of two or more, in the compositions of the invention is at least such that, when employed as a thin coating (up to about 10 microns) , the total composition without exposure to actinic radiation is rendered completely soluble in a reasonable length of time in conventional alkaline developers such as aqueous sodium or potassium hydroxide solution, sodium meta silicate, sodium orthophosphate, sodium hydrogen phosphate, and the like.

The actual amount of the organic solubilizing agent or agents which is necessary to achieve the desired rate of solubilization of the composition will depend principally, in any given instance, upon the particular mode, i.e., positive or negative image, in which the composition is to be employed. Thus, as discussed more fully below, in the positive mode of operation the exposed image and the unexposed photo¬ resist composition are both soluble to different degrees in aqueous alkaline developer. In order to develop an image under these circumstances it is clearly necessary that the rate of dissolution of the exposed image in the developer must be significantly greater than the rate of dissolution of the unexposed material in the same developer. This difference in rates is generally referred to as development contrast and can be measured in any given instance simply by measuring the percentage of the film coating loss in the areas which remain after the more soluble areas have been removed entirely. In the case of the compositions of the invention which are to be used in the positive mode the develop¬ ment contrast is advantageously such that the percentage of film coating remaining in the unexposed areas, when the exposed area has been completely removed, can be as high as about 50 percent. Preferably the amount of film coating remaining in the unexposed areas is of the order of about 70 percent. The concentration of the organic solubilizing agent or agents, which is present in the compositions of the invention in order to achieve development contrast in the above range will obviously depend to some degree on the particular solubilizing agent or agents employed but can be determined readily in any given instance by a process of trial and error. In general the total amount of such agent or agents employed in the compositions of the invention is of the order of about 1 to about 20 percent by weight based on weight of phenolic resin present in the compositions.

When the compositions of the invention are employed in the negative mode the requirement that there be development contrast still holds but in this case, as will be discussed in more detail below, the exposed image has been rendered substantially insoluble in the alkaline developers. Accordingly, in this mode, it is only necessary that the amount of organic solubilizing agent or agents be sufficient to render the unexposed areas of the composition completely soluble in conven¬ tional alkaline developers within a reasonable period of time, advantageously about 10 seconds to about 5 minutes and preferably about 1 minute for a thickness of film of the order of about 1 - 5 microns. The concentration of the above solubilizing agent or agents necessary to achieve such a degree of solubility can be readily determined in any given instance by a process of trial and error. In general the amount of solubilizing agent, or the total amount if two or more agents are used, is of the order of about 2 to about 20 percent by weight based on weight of phenolic resin present in the total composition. Any of the phenolic resins convention¬ ally employed in positive photoresist compositions can be employed in the compositions of the invention. Such resins are generally prepared by acid condensation of formaldehyde and phenol or an alkylsubstituted phenol under conditions described, for example, in Chemistry and Application of Phenolic Resins, Knop et al.. Chapter 4, Springer Verlag, New York, 1979. A particularly preferred group of resins for use in the compositions of the invention is the group of novolak resins derived from m-cresol alone or from a mixture of phenols in which m-cresol is the major component, i.e., is present in an amount greater than 50 percent and preferably greater than about 90 percent by weight. Advantageously the resins employed, including the preferred group, have average molecular weights in the range of about 600 to about 1600 and preferably from about 800 to about 1500. The 1,2-quinonediazide sensitizers employed in the compositions of the invention can be any of those conven¬ tionally employed in positive photoresist compositions available in the art. Such sensitizers comprise the esters and amides of naphthoquinone-(1,2)-diazide-(2)-4- sulfonic acid and naphthoquinone- (1,2)-diazide-(2)-5- sulfoniσ acid. The esters are generally those derived from polyhydric phenols such as 2,3,4 trihydroxybenzo- phenone, 2,4-dihydroxybenzophenone, 4-decanoylresorσin- ol, 4,4-bis(4-hydroxyphenyl)valeric acid butyl ester and the like. A preferred group of such esters are the esters of the above two acids with 2,3,4-trihydroxy- benzophenone. The amides of the above two acids which can be employed in the compositions of the invention are those derived from long chain aliphatic primary amines or from aromatic primary amines. The proportion of such sensitizers employed in the compositions of the invention is advantageously of the order of about 2 percent to about 20 percent by weight and preferably about 2 to about 8 percent by weight, based on weight of total constituents of the composi¬ tions other than solvents. The optimum proportion to employ in any given instance can be determined readily by a process of trial, and error.

Similarly, the proportion of phenolic resin employed in the compositions of the invention is advantageously of the order of about 2 percent to about 45 percent by weight, and preferably about 2 to about 20 percent by weight, based on weight of total constituents of the composition other than solvents. The compositions of the invention generally also comprise a solvent or a mixture of solvents. The solvent or solvents employed are generally selected based on compatibility, volatility, inertness with respect to the components of the photoresist and like considerations. Illustrative of solvents employed alone or admixture in the compositions of the invention are ketones such as methylethylketone, methylisopropylke- tone, diethylketone and the like; chlorinated hydro¬ carbons such as trichloroethylene, 1,1,1-trichloroethane and the like; aliphatic alcohols such as ethanol, n-propyl alcohol, n-butyl alcohol, n-hexyl alcohol and the like; aliphatic esters such as n-butyl acetate, n-hexyl acetate, cellosolve acetate and the like; glycol ethers such as ethylene glycol monomethyl ether, propy- lene glycol monomethyl ether and esters thereof such as the acetates, propionates and the like; and aromatic hydrocarbons such as toluene, xylene and the like. A preferred group of solvents are the aliphatic alcohols, aliphatic esters, glycol ether esters and aromatic hydrocarbons and mixtures of two or more such solvents. The amount of solvent or mixture of solvents employed is generally such as to represent from about 50 to about 80 percent by weight, and preferably from about 60 to about 70 percent by weight, based on total weight of the compo¬ sitions of the invention. The compositions of the invention may also com¬ prise other optional components conventionally employed in the art such as surfactants, adhesion-promoters, finely-divided pigments and the like. In a particular embodiment the compositions of the invention also comprise one or more cross-linking agents such as hexamethylolmelamine alkyl ethers, 2 , 6-bis (hydroxyl- ethyl) -4methylphenol, resoles, epoxy resins, and the like. Such crosslinking agents may be employed in a concentration of about 0.5 to about 20 percent by weight, and preferably in a concentration of about 1 to about 10 percent by weight, based on total components other than solvents present in the 'compositions of the invention. The optimum concentration for use in any given instance can be readily determined by a process of trial and error.

In carrying out the process of the invention the substrate is coated with a layer of a photosensitive composition of the invention using any of the coating techniques conventional in the art. Illustrative of such techniques are spin-coating, spraying, dipping, roller coating and the like. The substrate can be metallic such as aluminum, copper and the like or non- metallic such as reinforced epoxy resins, silicon wafers and the like. The surface of the substrate is generally chemically pretreated, depending on the substrate material, by use of appropriate compositions such as hexamethyl disilizane and the like compositions conventionally employed in the art.

The thickness of the coating applied to the substrate is generally in the order of about 0.5 to about 10 microns but higher or lower thicknesses can be employed in any given instance. The layer of photo¬ sensitive composition applied to the substrate in the above manner is then treated to remove the solvent present in the layer in any conventional manner. Generally speaking this step is achieved by baking the coated substrate at a temperature less than that which would result in decomposition of the sensitizer. A temperature of the order of about 90 to llO'Cis usually satisfactory and reduced pressures can be employed if desired in order to facilitate removal of solvent.

The resulting coated substrate is then exposed imagewise to actinic radiation. If the composition is being employed in the positive resist mode the image is then developed using aqueous alkaline developer until the exposed material has been completely removed. Any of the alkaline developers commonly employed in the art, such as those exemplified above, can be used. Prefer¬ ably the developer has a pH within the range of about 11 to about 14. If the composition coated on the substrate is being used in the negative mode, the coated substrate, after imagewise exposure to actinic radiation but prior to development, is subjected to a post-exposure bake. This step is conducted at a temperature and for a time such that the exposed image portions of the coating are rendered insoluble in alkaline developer. The bake temperature necessary to achieve this result is gener¬ ally within the range of about 115'C to about 140°C and preferably within the range of about 120"C to about 135"C. The temperature is chosen preferably to avoid any significant decomposition of the sensitizer present in the unexposed portions of the light-sensitive layer. The time required to achieve the desired result, i.e., insolubilization of the exposed image, will vary depend- ing upon the particular composition which is being employed and the heating mode used. In general the time required is of the order of about 5 to about 60 minutes in an oven and 1 to 3 minutes when a hot plate is used. The optimum time required in any given instance can be readily determined by a process of trial and error. The process which takes place in the exposed image portions of the photosensitive layer during the exposure and subsequent post-exposure baking is believed to be as follows. The exposure of the sensitizer to actinic radiation is believed to result in conversion of the diazo-keto function of the sensitizer to an indene carboxylic acid illustrated schematically as follows:

During the post-exposure bake the acid function of the indene carboxylic acid produced in situ as shown above s believed to serve to catalyze cross-linking of the novolak resin in the exposed image portions of the photosensitive coating. The cross-linking is facilitat¬ ed by the presence of the cross-linking agent or agents in the photosensitive compositions of the invention. The unexposed portions of the photosensitive layer do not undergo cross-linking since no carboxylic acid has been produced in situ therein during imagewise exposure of the layer to actinic radiation. Accordingly, the unexposed portions of the photosensitive layer remain solubl e in alkal ine developer whereas the exposed portions become insoluble due to the exposure followed by post exposure baking. Hence the negative image is produced by dissolving out the unexposed portions of the l ayer using alkaline developers as hereinbefore described. It is to be understood that the above theory is offered for purposes of explanation only and is not to be construed as limiting the scope of the invention in any manner whatsoever. • As will be understood by one skilled in the art, the composition and process of the invention represent significant advances over those hitherto available in the art since the omission of the second flood or blanket exposure, hitherto necessary in the compositions and processes employed in the art, is not required. Elimination of this step results in the elimination of one or more work stations with attendant savings in space, equipment and labor. Further the compositions of the invention give rise to markedly improved aspect ratio and resulting definition of the image produced and are also characterized by outstanding performance in the various steps of the processes of the invention.

The following examples illustrate the process of the invention and the best mode known to the inventors of carrying out the same but are not to be construed as limiting.

Example 1

A composition in accordance with the invention was prepared by dissolving the following components in the proportions shown in the solvent shown.

Parts by Weight novolak resin¹ 5 sensitizer² 4 poly(vinylphenol)³ 15 picric acid 1.5

2,6-bis(hydroxymethyl)-4-methyl phenol 3 propylene glycol monomethyl ether acetate. 75 benzotriazole 0.14 Footnotes:

1: acid catalyzed formaldehyde-meta-σresol condensate average M.W. = 1000.

2: Ester of naphthoquinone- (1, 2) -diazide- (2) -4-sulfoniσ acid with trihydroxybenzophenone

3: Maruzen resin (Maruzen Oil Co.: Average M.W. =

5000) .

A copper plate, previously cleaned, was coated with a layer approximately 5 microns thick of the above composition. The resulting layer was baked at 80"C for

30 minutes before being cooled and exposed imagewise to

UV light in a broad band contact exposure mode

(156mJ/cm²) using an Oriel printer. Exposure took place over 120 seconds. After exposure the coated plate was baked at 115 - 118* C for 30 minutes before the negative image was developed by immersion for 75 seconds in a 20 percent by weight solution of a commercially available alkaline developer [XD5071: MacDermid Inc., Waterbury, Ct.]. The resulting image was observed to be well-defined.

Example 2

The process described in Example 1 is repeated us¬ ing a composition in accordance with the invention which had been prepared by dissolving the following components in the proportions shown in the solvent shown.

Parts by weight) novolak resin¹ 6 sensitizer² 3 poly(vinylphenol) 10 p-hydroxymandelic acid 2

2,6-bis(hydroxymethyl)-4- methy1phenol 4 propylene glycol monomethylether acetate 70 benzotriazole 0.14 Footnotes :

1 : Same as Example 1

2 : Same as Example 1

Example 3 The process . described in Example 1 is repeated using "a compos ition in accordance with the invention which had been prepared by dissolving the following components in the proportions shown in the solvent shown^'

Part by weight novolak resin¹ 20 sensitizer² 2.5

1-methyl-l-σyσlohexane carboxylic acid 2.5 ethylene glycol monoethyl ether acetate 68

2,6-bis (hydroxymethyl)-4- methylphenol 2.5 benzotriazole 0.14-

Footnotes: 1: Same as Example 1

2: Ester of naphthoquinone-(1,2)-diazide-(2)-5-sulfonic acid with sec.-butylphenol.

Example 4

A composition in accordance with the invention was prepared by dissolving the following components in the amounts shown in 71 parts by weight of a mixture of propylene glycol monomethyl ether acetate, n-butanol, p-butylacetate and xylene.

Part by weight novalak resin¹ 3 sensitizer² 2 poly(vinylphenol) 17 trihydroxybenzophenone 2.5 abietic acid 1.5

2,6-bis(hydroxymethyl)-4- methylphenol 3.0 benzotriazole 0.14 Footnotes:

1: Same as Example 1

2: Same as Example 1

Example 5 A composition of the invention was prepared in the same manner and using the same ingredients as in Example 4 with the exception that the amount of sensitizer was increased to 5 parts by weight.

Example 6 This Example illustrates the use of a typical composition of the invention to fabricate a positive resist image.

A silicon wafer was spin-coated at 5000 rpm with a layer of the composition of Example 4. The average thickness of the coating was 1.35 microns. The result¬ ing layer was baked at 110*C for 50 seconds on a hot plate to evaporate solvents before being cooled and exposed imagewise to UV light in a broad band contact exposure mode (150mJ/cm²) using an Oriel printer. The image was developed using a positive photoresist alka¬ line developer [MF-62: MacDermid Inc., Waterbury, Ct.] which had been diluted with water to 20 percent of the original concentration. The time required for complete clearing of the non-image areas was observed and the average loss in layer thickness of the image was measured after development was completed.

The above process was repeated two additional times with the exception that the developer had been diluted to 21 percent of original concentration in one run and to 22 percent of original concentration in the other. The time taken to clear the non-image areas and the average thickness loss in the developed image in each of these runs was as follows:

Concentration of Time to Clear Image Thickness/ Developer .Seconds) Loss

20 150 0.25 microns

21 75 0.30 microns

22 60 0.50 microns In all three cases the image resolution was found to be good to 0.8 microns.

Example 7

This example illustrates the use of a typical composition of the invention to fabricate a negative resist image employing a silicon wafer as a substrate. The wafer was coated, baked, cooled, and exposed using the composition and method described in Example 6. After exposure, the wafer was baked at 130 ^β C for 20 minutes in an oven. The wafer was then developed by immers ion for one minute in an alkaline developed [MF- 62 ; diluted with water to 35% of the original concentration] . The resulting image was well-defined.

Claims

What is claimed is:

1. In a process for producing a negative resist image on a substrate which comprises the steps of: coating said substrate with a layer of a light- sensitive composition comprising in admixture (a) a phenolic resin and (b) a 1,

2 quinone diazide sensitizer; exposing said light-sensitive layer imagewise to actinic radiation; heating said layer, after said exposure, to a temperature and for a time sufficient to render said imagewise exposed portions of said layer insoluble in alkaline developer; and thereafter dissolving the unexposed portions of said layer in an alkaline developer; the improvement which comprises incorporating in said light-sensitive composition at least one organic solubilizing agent in an amount sufficient to render soluble in alkaline developer the portions of said layer which have not been exposed to actinic radiation.

. A process in accordance with claim 1 wherein said organic solubilizing agent is selected from the group consisting of benzotriazole, σhoro-substituted benzotriazoles and compounds containing phenolic and or carboxylic acid groups.

3. A process in accordance with claim 2 wherein said compound containing phenolic and or carboxylic acid groups comprises a poly(vinylphenol) .

4. A process in accordance with claim 2 wherein said compound containing phenolic and or carboxylic acid groups comprises abietic acid.

5. A process in accordance with claim 2 wherein said compound containing phenolic and or carboxylic acid groups comprises trihydroxybenzophenone.

6. A process in accordance with claim 1 wherein at least a major portion of said novolak resin comprises a novolak resin derived from a-cresol.

7. A process in accordance with claim 1 wherein said 1,2-quinone diazide sensitizer is an ester of naphtho- quinone(l, 2) -diazide-(2) -4-sulfonic acid or naphtho¬ quinone- (1, 2) diazide- (2) -5-sulfoniσ acid.

8. A process in accordance with claim 7 wherein said ester is an ester of 2,3,4-trihydroxybenzophenone.

9. A process in accordance with claim 1 wherein said 1 ightsensitive composition also comprises a cross-linking agent.

10. A process in accordance with claim 9 wherein said cross-linking agent comprises 2 ,6-b is (hydroxymethyl) -4-methylphenol .

11. A process according to claim 1 wherein said light-sensitive composition also comprises a solvent.

12. A process according to claim 1 wherein said light-sensitive composition also comprises a surfactant.

13. A process according to claim 1 wherein said post-exposure heating of said light-sensitive layer is carried out at a temperature within the range of about 115 "C to about 140 C for a period of about 5 minutes to about 60 minutes.

14. A light-sensitive image reversible photoresist composition which comprises, in admixture, (a) at least one phenolic resin (b) a 1,2-quinonediazide sensitizer and (c) at least one organic solubilizing agent present in an amount sufficient to render said composition soluble in alkaline developer.

15. A composition in accordance with claim 14 which also comprises a solvent.

16. A composition in accordance with claim 14 wherein said component (c) is selected from the group consisting of benzotriazole, chlorinated benzotriazole and com¬ pounds containing phenolic acid or carboxylic acid groups.

17. A composition in accordance with claim 14 wherein said component (c) comprises a mixture of trihydroxy- benzophenone, abietic acid, benzotriazole and a poly (vinylphenol) .

18. A composition in accordance with claim 14 wherein said component (a) comprises a novolak resin derived from m-cresol.

19. A composition in accordance with claim 14 wherein said component (b) comprises an ester of naphthoquinone- (1,2) -diazo(2)-4-sulfonic acid or naphthoquinone-(1,2)- diazo-(2)-5-sulfonic acid.

20. A composition in accordance with claim 19 wherein said ester is an ester of 2,3,4-trihydroxybenzophenone.

21. A composition in accordance with claim 14 which also comprises a cross-linking agent.

22. A composition in accordance with claim 21 wherein said cross-linking agent comprises 2, 6-bis(hydroxy¬ methyl)-4-methylphenol.

23. A composition in accordance with, claim 14 wherein said component (a) is present in an amount from about 0.5 to about 40 percent by weight based on total weight of the composition.

24. A composition in accordance with claim 14 wherein said component (b) is present in an amount from about 2 to about 20 percent by weight based on total weight of the composition.

25. A light-sensitive image reversible photoresist composition which comprises, in admixture,

(a) at least one novolak resin derived from m-cresol; ^' (b) an ester of 2-diazo-l,2-napthoquinone-4- or

-5-sulfonic acid;

(c) a mixture of trihydroxybenzophenone, abietic acid, benzotriazole and a poly(vinylphenol) , said mixture being present in an amount sufficient to render said composition soluble in alkaline developer; and

(d) a cross-linking agent.

26. A composition in accordance with claim 25 wherein said component (b) is an ester of said acid with 2 , 3 , 4 -trihydroxybenzophenone.

27. A composition in accordance with claim 25 which also comprises a solvent.

28. A composition .in accordance with claim 25 wherein s. a i d c r o s s - l i n k i n g a g e n t c o m p r i s e s

2 , 6-bis (hydroxymethyl) -4-methylphenol.