Radiation sensitive compositions comprising polymer having acid labile groups

The invention provides a radiation sensitive composition having a polymer binder of phenolic and cyclic alcohol units. At least a portion of the phenolic units and/or cyclic alcohol units of the polymer are bonded to acid labile groups. High solubility differentials between exposed and unexposed regions are realized with only moderate substitution of the binder with the acid labile groups.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to radiation sensitive compositions such as 
photoresists that provide high solubility differentials between exposed 
and unexposed regions, and increased transparency to activating radiation. 
2. Background Art 
Photoresists are photosensitive films used for transfer of an image to a 
substrate. They may be negative or positive acting. After a coating of a 
photoresist is formed on a substrate, the coating is selectively exposed 
through a photomask to a source of activating energy such as ultraviolet 
light. The photomask has areas that are opaque to activating radiation and 
other areas that are transparent to activating radiation. The pattern in 
the photomask of opaque and transparent areas define a desired image to be 
transferred to a substrate. 
In the case of a negative photoresist, exposed portions of a photoresist 
coating become less soluble in a developer as the result of a 
photochemical reaction, thereby resulting in differential solubility 
between the exposed and unexposed portions. This difference in solubility 
allows for the selective removal of unexposed portions of the photoresist 
coating and the subsequent transfer of an image to a substrate. 
In the case of a positive acting photoresist, exposed portions of the 
photoresist coating become more soluble in developer than unexposed 
portions as the result of a photochemical reaction allowing for selective 
removal of exposed areas by development. 
Following development of a photoresist coating, portions of the substrate 
bared by development may be altered such as by etching. The historical 
background, types and processing of conventional photoresists are 
described by Deforest, Photoresist Materials and Processes, McGraw Hill 
Book Company, New York, Chapter 2, 1975 and by Moreau, Semiconductor 
Lithography, Principles, Practices and Materials, Plenum Press, New York, 
Chapters 2 and 4, 1988, both incorporated herein for their teaching of 
photoresist compositions and methods of making and using the same. 
Most commercial photoresist formulations, both positive and negative, 
comprise a film forming binder and a radiation sensitive component. Many 
of these film forming binders are phenolic resins. For example, many 
positive acting photoresists currently in commercial use comprise a 
novolak resin and a naphthoquinone diazide sulfonic acid ester photoactive 
compound where the novolak resin is the reaction product of formaldehyde 
and a phenol. Examples of such photoresists are disclosed in U.S. Pat. 
Nos. 4,377,631 and 4,404,272, incorporated herein by reference. Another 
class of positive acting photoresists comprise a poly(vinylphenol) and a 
naphthoquinone diazide sulfonic acid ester. Examples of these photoresists 
are disclosed in U.S. Pat. Nos. 3,869,292 and 4,439,516, both incorporated 
herein by reference. 
An important property of a photoresist is image resolution. A developed 
image of fine line definition having vertical side-walls is highly desired 
to permit transfer of the fine line image to an underlying substrate. 
Another important property of a photoresist is photospeed. Photospeed is a 
common way of describing the sensitivity of a photoresist or other 
radiation sensitive compositions to activating radiation. Enhanced 
photospeed is especially important in applications where a number of 
exposures are needed, for example, in generating multiple patterns by a 
step and repeat process, or where activating energy of reduced intensity 
is employed. Increased photospeed also permits reduction in the radiation 
sensitive component of the photoresist and/or a decrease in the required 
energy of exposure for image formation. 
Some cationic photoinitiators have been used to induce selective 
photogenerated acidic cleavage of certain "blocking" groups pendant from a 
photoresist binder, or cleavage of certain blocking groups that comprise a 
photoresist binder. See, for example, U.S. Pat. Nos. 4,968,581; 4,883,740; 
4,810,613 and 4,491,628, and Canadian Patent Application 2,001,384, all of 
which are incorporated herein by reference for their teaching of the 
described binders and acid labile blocking groups, and methods of making 
and using the same. Such cleavage is reported to create different 
solubility characteristics in exposed and unexposed areas of the polymer. 
Upon selective cleavage of the blocking group through exposure of the 
photoresist, a polar functional group is said to be provided, for example, 
carboxyl or imide. 
It has been found that these reported systems have limitations. For 
example, to realize significant solubility differentials between exposed 
and unexposed regions (and thereby provide high resolution of the 
developed image), known systems generally require that a somewhat large 
portion of the photoresist binder contain acid labile blocking groups. 
That is, a large portion of the polar functionalities of the resist are 
substituted with blocking groups so that a sufficient solubility 
differential is provided between exposed and unexposed regions of the 
resist. Consequently, exposure results in cleavage of a significant mass 
of the resist. This can result in shrinkage of the photoresist in exposed 
regions and thereby compromise resolution of the image patterned in the 
photoresist coating layer. 
Other problems can arise upon subsequent etching of the substrate that 
underlies the developed photoresist image. For example, to etch an 
aluminum or silicon oxide substrate rather stringent conditions are often 
employed. Aluminum chlorine gas is frequently used to etch such substrates 
and extensive localized heating often occurs during the etching sequence. 
As a consequence, the patterned photoresist coating on the substrate can 
experience shrinkage as the acid labile groups of the unexposed resist 
pattern undergo thermally induced cleavage. This can result in the imaged 
photoresist lines having a wrinkled or roughened surface, a condition 
known in the art as reticulation and which can be undesirable, 
particularly for high resolution applications. 
In U.S. Pat. No. 5,128,232, incorporated herein by reference, a photoresist 
composition is described, the composition having a resin binder comprising 
a polymer having a major portion of phenolic units and a minor portion of 
cyclic alcohol units. This application discloses that by employing cyclic 
alcohol units in the binder, the resist composition exhibits enhanced 
transparency to activating radiation. This application also discloses that 
the concentration of the cyclic alcohol units should be limited to retain 
developer solubility of an exposed layer of the resist composition. 
It would be desirable to have a photoresist binder that could provide high 
solubility differentials upon exposure with only a moderate substitution 
of the binder with acid labile groups. It also would be desirable to have 
a photoresist binder that contained acid labile groups but was resistant 
to reticulation during stringent processing steps. It would be further 
desirable to have a radiation sensitive composition that was highly 
transparent to activating radiation. 
SUMMARY OF THE INVENTION 
The present invention provides a radiation sensitive composition that 
comprises a resin binder that comprises a polymer having pendant acid 
labile blocking groups and a radiation sensitive component that generates 
acid upon exposure to activating radiation. The polymer comprises both 
phenolic and cyclic alcohol units. 
It has been discovered that high solubility differentials between exposed 
and unexposed regions of a coating layer of the composition of the 
invention are realized with only modest levels of substitution of the 
binder with acid labile blocking groups, including where about 1 percent 
of the hydroxyl groups of the polymer are blocked with acid labile groups. 
Preferably from about 5 to 35 percent of the hydroxyl groups of the binder 
are blocked with acid labile groups. This is in contrast to prior systems 
where significantly greater portions of available polar groups of the 
binder are substituted with blocking groups. High solubility differentials 
between exposed and unexposed regions, with relatively low levels of 
blocking group substitution are possible because the cyclic alcohol units 
of the binder are less polar relative to the phenolic groups, effectively 
limiting solubility of unexposed regions in aqueous alkaline developers, 
but enabling high solubility of those regions in suitable organic 
developers. Thus, a radiation sensitive composition is provided where a 
comparatively smaller mass of blocking groups is liberated upon 
photoinduced cleavage, thereby avoiding problems of prior systems such as 
shrinkage of the composition layer. 
Reticulation of patterned resist lines that can arise during post-exposure 
processing steps such as substrate etching is also generally avoided by 
use of the composition of the invention. By providing a binder having a 
relatively small mole percent of acid labile groups, thermally induced 
cleavage can only liberate a relatively smaller mass of acid labile 
groups, thus reducing reticulation of the patterned resist. 
It has been further discovered that by employing suitable blocking groups, 
a phenol-containing polymer binder comprising a high concentration of 
cyclic alcohol units may be employed. This is accomplished by the highly 
polar groups that can be grafted onto the binder by the sequential steps 
of blocking at least a portion of the binder's hydroxyl units, followed by 
photocleavage of the blocking groups. For example, photocleavage of a 
t-butyl acetate acid labile group provides the acetic acid ether moiety 
(--OCH.sub.2 COOH). Such polar groups render exposed regions soluble in a 
polar developer where the polymer has a cyclic alcohol concentration of 50 
mole percent or greater, including concentrations of cyclic alcohol units 
in the polymer 60 mole percent or greater of the total polymer, and even 
concentrations of cyclic alcohol units in the polymer of 70 mole percent 
or greater of the total polymer. By utilizing such a polymer binder that 
has a high mole percent of cyclic alcohol units, a radiation sensitive 
composition is provided that exhibits exceptional optical clarity, i.e., 
decreased radiation absorption during exposure of the composition to 
activating radiation. Consequently, the radiation sensitive composition 
has increased photospeed. 
The radiation sensitive compositions of the invention can be either 
positive acting or negative acting. The high solubility differentials 
discussed above enable selective removal of exposed regions of a film of 
the composition with an aqueous alkaline solution, and selective removal 
of unexposed regions with suitable organic developers. 
The radiation sensitive compositions of the invention may additionally 
comprise dissolution inhibiting compounds to further control dissolution o 
an exposed coating layer of the composition. The compositions may also 
comprise sensitizer compounds to expand the spectral sensitivity of the 
composition. 
Various methods may be used to form the polymer of the phenol and cyclic 
alcohol units. One method comprises copolymerizing a cyclic alcohol with 
phenol. A preferred method involves hydrogenation of a preformed phenolic 
resin. The acid labile groups are then grafted onto to the reactive 
hydroxyl sites of the polymer, typically by a base-catalyzed condensation 
reaction. 
It should be appreciated that by using a polymer of a cyclic alcohol and a 
phenol in place of a phenolic polymer in the formulation of a radiation 
sensitive composition, less energy is absorbed by the binder during 
exposure and therefore, given a constant exposure energy, more energy is 
available for activation of the radiation sensitive component of the 
composition. The improvements resulting from the use of the binder polymer 
of a cyclic alcohol and a phenol will vary for differing compositions 
dependent upon the energy required for activation. For example, it is 
known that the greatest absorption by a conjugated bond is within the deep 
UV range. Therefore, use of the polymer binder described herein as a 
binder for a composition activated by deep UV radiation (i.e, radiation 
having a wavelength of from about 100 to 300 nm) exposure can be more 
efficacious than the use of the same polymer in a composition activated at 
an exposure energy other than deep UV. 
The use of the polymer binder described herein in a radiation sensitive 
composition results in increased photospeed. In addition, it has been 
found that radiation sensitive compositions using the subject polymer 
exhibit improved image resolution following development. Relief images 
formed using compositions of the invention are capable of fine line 
resolution (including images of submicron widths) and possess vertical 
side walls known by the art to be highly desirable for transfer of fine 
line images to underlying substrates. 
The present invention also provides processes for the production of relief 
patterns and relief images using the described radiation sensitive 
compositions, and related articles of manufacture.

DETAILED DESCRIPTION OF THE INVENTION 
The polymer binder of the invention comprises phenolic and cyclic alcohol 
units. The preferred polymers for purposes of this invention are those 
formed by the hydrogenation of a phenol formaldehyde (novolak) or a 
poly(vinylphenol) resin. 
Procedures for the preparation of conventional novolak and 
poly(vinylphenol) resins used as photoresists binders are well known in 
the art and disclosed in numerous publications including those discussed 
above. Novolak resins are the thermoplastic condensation products of a 
phenol and an aldehyde. Examples of suitable phenols for condensation with 
an aldehyde, especially formaldehyde, for the formation of novolak resins 
include phenol; m-cresol; o-cresol; p-cresol; 2,4-xylenol; 2,5-xylenol; 
3,4-xylenol; 3,5-xylenol and thymol. An acid catalyzed condensation 
reaction results in the formation of a suitable novolak resin which may 
vary in molecular weight from about 500 to 100,000 daltons. The preferred 
novolak resins conventionally used for the formation of photoresists are 
the cresol formaldehyde condensation products. 
Poly(vinylphenol) resins are thermoplastic polymers that may be formed by 
block polymerization, emulsion polymerization or solution polymerization 
of the corresponding monomers in the presence of a cationic catalyst. 
Vinylphenols useful for the production of poly(vinylphenol) resins may be 
prepared, for example, by hydrolysis of commercially available coumarin or 
substituted coumarins, followed by decarboxylation of the resulting 
hydroxy cinnamic acids. Useful vinylphenols may also be prepared by 
dehydration of the corresponding hydroxy alkyl phenols or by 
decarboxylation of hydroxy cinnamic acids resulting from the reaction of 
substituted or non-substituted hydroxybenzaldehydes with malonic acid. 
Preferred poly(vinylphenol) resins prepared from such vinylphenols have a 
molecular weight range of from about 2,000 to about 100,000 daltons. 
As noted, preferred resins for purposes of this invention are polymers of 
phenols and nonaromatic cyclic alcohols analogous in structure to the 
novolak resins and poly(vinylphenol) resins. These polymers may be formed 
in several ways. For example, in the conventional preparation of a 
polyvinyl phenol resin, a cyclic alcohol may be added to the reaction 
mixture as a comonomer during polymerization reaction which is thereafter 
carried out in normal manner. The cyclic alcohol is preferably aliphatic, 
but may contain one or two double bonds. The cyclic alcohol is preferably 
one closest in structure to the phenol. For example, if the resin is a 
polyvinyl phenol, the comonomer would be vinyl cyclohexanol. 
The preferred method for formation of the polymer comprises partial 
hydrogenation of a preformed novolak resin or a preformed polyvinyl phenol 
resin. Hydrogenation may be carried out using art recognized hydrogenation 
procedures, for example, by passing a solution of the phenolic resin over 
a reducing catalyst such as a platinum or palladium coated carbon 
substrate or preferably over Raney nickel at elevated temperature and 
pressure. The specific conditions are dependent upon the polymer to be 
hydrogenated. More particularly, the polymer is dissolved in a suitable 
solvent such as ethyl alcohol or acetic acid, and then the solution is 
contacted with a finely divided Raney nickel catalyst and allowed to react 
at a temperature of from about 100.degree. to 300.degree. C. at a pressure 
of from about 50 to 300 atmospheres or more. The finely divided nickel 
catalyst may be a nickel-on-silica,. nickel-on-alumina, or 
nickel-on-carbon catalyst depending upon the resin to be hydrogenated. 
Hydrogenation is believed to reduce the double bounds in some of the 
phenolic units resulting in a random polymer of phenolic and cyclic 
alcohol units randomly interspersed in the polymer in percentages 
dependent upon the reaction conditions used. 
A preferred polymer binder comprises units of a structure selected from the 
group consisting of: 
##STR1## 
where unit (1) represents a phenolic unit and unit (2) represents a cyclic 
alcohol unit; (Z) is an alkylene bridge having from 1 to 3 carbon atoms; A 
is a substituent on the aromatic ring replacing hydrogen such as lower 
alkyl having from 1 to 3 carbon atoms, halo such as chloro or bromo, 
alkoxy having from 1 to 3 carbon atoms, hydroxyl, nitro, amino, etc.; a is 
a number varying from 0 to 3; B is a substituent such as hydrogen, lower 
alkyl having from 1 to 3 carbon atoms, halo such as chloro or bromo, 
alkoxy having from 1 to 3 carbon atoms, hydroxyl, nitro, amino, etc.; a is 
a number varying from 0 to 3; B is a substituent such as hydrogen, lower 
alkyl having from 1 to 3 carbon atoms, halo such as chloro or bromo, 
alkoxy having from 1 to 3 carbon atoms, hydroxyl, nitro, amino, etc., 
provided that at least 3 of said B substituents are hydrogen; b is an 
integer varying between 6 and 10; and X is the mole fraction of the units 
(1) in the polymer. 
In accordance with the invention, at least a portion of available hydroxyl 
moieties of the above polymer binder are bonded to suitable acid labile 
blocking groups. Suitable blocking groups in general are those that upon 
photocleavage provide a moiety that is more polar than hydroxyl. Further, 
the acid labile groups should be generally stable to any pre-exposure 
softbake and should not substantially interfere with photoactivation of 
the composition. 
The percentage of cyclic alcohol units of the polymer preferably is not so 
high as to prevent development of an exposed film layer of the radiation 
sensitive composition in a polar developer solution. The polymer may have 
a major portion of phenolic units and a minor portion of cyclic alcohol 
units, i.e., less than about 50 mole percent of cyclic alcohol units. 
However, as it has been found that transparency of the compositions of the 
invention increases with the concentration of cyclic alcohol units in the 
polymer binder, it can be desirable to employ a polymer having a major 
portion of cyclic alcohol units and a minor portion of phenolic units. 
This can be achieved by using suitable blocking groups which upon acid 
catalyzed hydrolysis provide polar functional groups, rendering exposed 
regions highly soluble in polar developer solutions. Thus, to provide a 
radiation sensitive composition having high transparency, the percentage 
of cyclic alcohol units of the subject polymer binder is about 50 mole 
percent or greater; and to further enhance clarity of the composition the 
percentage of cyclic alcohols groups is about 60 mole percent or greater 
of the total polymer; and to still further enhance the transparency of the 
composition to activating radiation the percentage of cyclic alcohol 
groups may be about 70 percent or greater of the total polymer binder. 
The acid labile blocking groups are generally employed in accordance with 
the below Scheme in which a preferred polymer binder is condensed with a 
compound that comprises an acid labile group (R) and a suitable leaving 
group (L). 
##STR2## 
In the Scheme, unit (1) represents a phenolic unit and unit (2) represents 
a cyclic alcohol unit; A is a substituent on the aromatic ring replacing 
hydrogen such as lower alkyl having from 1 to 3 carbon atoms, halo such as 
chloro or bromo, alkoxy having from 1 to 3 carbon atoms, hydroxyl, nitro, 
amino, etc.; a is a number varying from 0 to 3; B is a substituent such as 
hydrogen, lower alkyl having from 1 to 3 carbon atoms, halo such as chloro 
or bromo, alkoxy having from 1 to 3 carbon atoms, hydroxyl, nitro, amino, 
etc. provided that at least 3 of said B substituents are hydrogen; b is an 
integer varying between 6 and 10; 
R is an acid labile blocking group; L is a leaving group; P is the group 
provided upon acidic cleavage of the acid labile blocking group R; and 
W is the mole fraction of the units (1) in the copolymer; X is the mole 
fraction of units (2) in the copolymer; Y is the mole fraction of units 
(1) blocked by a group R; and Z is the mole fraction of units (2) blocked 
by a group R. 
The acid labile group (R) is typically provided by an alkaline condensation 
reaction with the preformed polymer and a compound that comprises the acid 
labile group R and a suitable leaving group L, for instance a halogen such 
as bromide or chloride. For example, where R is the particularly preferred 
t-butoxy carbonyl methyl group, t-butyl haloacetate (e.g., t-butyl 
chloroacetate) is added to a solution of the polymer and a suitable base, 
and the mixture stirred typically with heating. A variety of bases may be 
employed for this condensation reaction including hydrides such as sodium 
hydride and alkoxides such as potassium t-butoxide. The condensation 
reaction is typically carried out in an organic solvent. A variety of 
organic solvents are suitable as is apparent to those skilled in the art. 
Tetrahydrofuran and dimethylformamide are preferred solvents. Suitable 
conditions of the condensation reaction can be determined based on the 
constituents used. For example, an admixture of sodium hydride, 
t-butylchloroacetate and a partially hydrogenated poly(vinylphenol) is 
stirred for about 15 to 20 hours at about 70.degree. C. 
The percent substitution of the polymer binder with the acid labile groups 
can be controlled by the amount of the acid labile compound that is 
condensed with the binder. The percent substitution of hydroxyl sites of 
the polymer binder can be readily ascertained by proton and 13C NMR. 
It has been found that the polymer binder can be condensed with mixtures of 
two or more acid labile groups to provide a mixture of acid labile groups 
bonded pendant to the polymer backbone. If the polymer is condensed with 
two or more acid labile groups, then groups R and P of the above formula 
will be a mixture of different groups. For example, if the subject polymer 
of phenolic groups and cyclic alcohol groups is o first condensed with a 
compound of the formula R'L, and then condensed with a compound of the 
formula R''L, where R' and R'' of said formulas are two different acid 
labile moieties, and L is a leaving group, the polymer will comprise a 
mixture of R' and R'' acid labile groups. 
As shown in the above Scheme, exposure to radiation produces an acid which 
is generated by a radiation sensitive component admixed with the polymer. 
Suitable photoacid generating compounds are described below and are 
generally well known to those skilled in the art. 
It has been found that the acid labile groups add predominately to the more 
reactive phenolic groups, rather than the cyclic alcohol groups, of the 
above described polymer binder when a hydride base such as sodium hydride 
is employed in the condensation reaction. That is, primarily only the 
phenolic groups of the binder are bonded to above defined groups R and P 
and the cyclic alcohol groups are substantially free of acid labile 
groups. It is believed that acid labile groups will add to both the 
phenolic and cyclic alcohol groups of the binder by use of stronger bases 
such as butyllithium or other alkyllithium reagents. 
The polymer binder shown in the above Scheme provides a radiation sensitive 
composition that exhibits excellent solubility differentials upon exposure 
with the mole fraction of blocked groups in the polymer (i.e., the sum of 
the values Y and Z as those values are defined above) being extremely low 
relative to prior systems, including values of about 0.01. Preferably, the 
mole fraction of blocked hydroxyl groups in the binder varies from about 
0.01 to 0.5; more preferably the mole fraction of blocked hydroxyl groups 
varies from about 0.05 to 0.35. To alternatively state these same ranges, 
preferably from about 1 to 50 percent of the total hydroxyl sites of the 
polymer are bonded to acid labile groups, and more preferably from about 5 
to 35 percent of the total hydroxyl sites of the polymer are bonded to 
acid labile groups. When the binder has a percentage of blocked hydroxyl 
blocked groups within these preferred ranges, significant shrinkage upon 
imaging of a coating layer of the composition of the invention is believed 
to be generally avoided. The mole fraction of blocked hydroxyl groups can 
be greater than 0.5 if desired. 
Suitable acid labile groups include acetate groups such as acetate groups 
of the formula --CR.sup.1 R.sup.2 C(.dbd.O)--O--R.sup.3, where R.sup.1 and 
R.sup.2 are each independently selected from the group of hydrogen, an 
electron withdrawing group such as halogen, lower alkyl having from 1 to 
about 10 carbon atoms, and substituted lower alkyl having from 1 to about 
10 carbon atoms; and R.sup.3 is substituted and unsubstituted lower alkyl 
having from 1 to about 10 carbon atoms, substituted and unsubstituted aryl 
having from 1 to about 10 carbon atoms, substituted or unsubstituted 
benzyl having 7 to about 13 carbon atoms. The substituents can be, for 
example, one or more halogen, lower alkyl, lower alkoxy, aryl or benyzl. 
R.sup.1 and R.sup.2 suitably are each hydrogen. It has been found that if 
R.sup.1 and/or R.sup.2 are halogen or other suitable electron-withdrawing 
group, upon acidic cleavage of the acetate group a highly polar moiety is 
provided along with enhanced solubility differentials between exposed and 
unexposed regions of a coating layer of the subject composition. The 
difluoro group (i.e., R.sup.1 and R.sup.2 both fluoro) is particularly 
suitable for such purposes and provides extremely high dissolution 
differentials between exposed and unexposed regions with only modest 
levels of substitution of hydroxy groups of the polymer binder. This 
difluoro group can be provided by alkaline condensation of the polymer 
with t-butyl chlorodifluoroacetate (ClCF.sub.2 
C(.dbd.O)OC(CH.sub.3).sub.3). As noted above, R.sup.3 is preferably 
tert-butyl (i.e., R is the tert-butyl acetate group). Acid degradation of 
this group liberates isobutylene to provide the polar acetic acid ether 
moiety pendant to the polymer backbone. 
It is understood that a wide range of acid labile groups are suitable, 
including many of the groups described in the patents incorporated herein 
by reference. For example, suitable acid labile groups include oxycarbonyl 
groups of the formula --C(.dbd.O)--O--R.sup.3, where R.sup.3 is the same 
as defined above. Preferably, R.sup.3 is tert-butyl or benzyl (i.e, R is 
the t-butoxy carbonyl or benzyloxy carbonyl group). 
The acid generator compound used in combination with the above-described 
binder may be chosen from a wide variety of compounds known to form acid 
upon exposure to activating radiation. One suitable class of radiation 
sensitive compositions of this invention are compositions that use the 
polymer of the phenol and cyclic alcohol with acid labile groups as a 
binder and an o-quinone diazide sulfonic acid ester as a radiation 
sensitive component. The sensitizers most often used in such compositions 
are naphthoquinone diazide sulfonic acids such as those disclosed by 
Kosar, Light Sensitive Systems, John Wiley & Sons, 1965, pp. 343 to 352, 
incorporated herein by reference. These sensitizers form an acid in 
response to radiation of different wavelengths ranging from visible to 
X-ray. Thus, the sensitizer chosen will depend, in part, upon the 
wavelengths used for exposure. By selecting the appropriate sensitizer, 
the photoresists can be imaged by deep UV, E-beam, laser or any other 
activating radiation conventionally used for imaging photoresists. 
Preferred sensitizers include the 2,1,4-diazonaphthoquinone sulfonic acid 
esters and the 2,1,5-diazonaphthoquinone sulfonic acid esters. 
Other useful acid generator include the family of nitrobenzyl esters, and 
the s-triazine derivatives. Suitable s-triazine acid generators are 
disclosed, for example, in U.S. Pat. No. 4,189,323, incorporated herein by 
reference. 
Non-ionic photoacid generators are suitable including halogenated 
non-ionic, photoacid generating compounds such as, for example: 
1,1-bis [p-chlorophenyl]-2,2,2-trichloroethane (DDT); 
1,1-bis [p-methoxyphenyl]-2,2,2-trichloroethane; 
1,2,5,6,9,10-hexabromocyclododecane; 
1,10-dibromodecane; 
1,1-bis[p-chloropehnyl]-2,2-dichloroethane; 
4,4'-dichloro-2-(trichloromethyl) benzhydrol (Kelthane); 
hexachlorodimethyl sulfone; 
2-chloro-6-(trichloromethyl) pyridine; 
0,0-diethyl-0-(3,5,6-trichloro-2-pyridyl)phosphorothionate; 
1,2,3,4,5,6-hexachlorocyclohexane; 
N(1,1-bis [p-chlorophenyl]-2,2,2-trichloroethyl)acetamide; 
tris [2,3-dibromopropyl] isocyanurate; 
2,2-bis [p-chlorophenyl]-1,1-dichloroethylene; 
tris [trichloromethyl] s-triazine; 
and their isomers, analogs, homologs, and residual compounds. Suitable 
photoacid generators are also disclosed in European Patent Application 
Nos. 0164248 and 0232972, both incorporated herein by reference. 
Residual compounds are intended to include closely related impurities or 
other modifications of the above halogenated organic compounds which 
result during their synthesis and may be present in minor amounts in 
commercial products containing a major amount of the above compounds. 
Acid generators that are particularly preferred for deep UV exposure 
include 1,1,-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT); 
1,1-bis(p-methoxyphenol)-2,2,2-trichloroethane; 
1,1-bis(chlorophenyl)-2,2,2-trichloroethanol; 
tris(1,2,3-methanesulfonyl)benzene; and tris(trichloromethyl) triazine. 
Onium salts are also suitable acid generators. Onium salts, with weakly 
nucleophilic anions have been found to be particularly suitable. Examples 
of such anions are the halogen complex anions of divalent to heptavalent 
metals or non-metals, for example, Sb, Sn, Fe, Bi, Al, Ga, In, Ti, Zr, Sc, 
D, Cr, Hf, and Cu as well as B, P, and As. Examples of suitable onium 
salts are diaryldiazonium salts and onium salts of group Va and B, Ia and 
B and I of the Periodic Table, for example, halonium salts, quaternary 
ammonium, phosphonium and arsonium salts, aromatic sulfonium salts and 
sulfoxonium salts or seleonium salts. Examples of suitable preferred onium 
salts can be found in U.S. Pat. Nos. 4,442,197; 4,603,101; and 4,624,912, 
all incorporated herein by reference. 
A particularly suitable group of acid generating compounds useful in the 
compositions of the invention are the iodonium salts. A preferred group of 
iodonium salts are those resulting from the condensation of aryl 
iodosotosylates and aryl ketones as disclosed, for example, in U.S. Pat. 
No. 4,683,317, incorporated herein by reference. 
Another group of suitable acid generators is the family of sulfonated 
esters including sulfonyloxy ketones. Suitable sulfonated esters have been 
reported in J. of Photopolymer Science and Technology, vol. 4, no. 3, 
337-340 (1991), incorporated herein by reference, including benzoin 
tosylate, t-butylphenyl alpha-(p-toluenesulfonyloxy)-acetate, and t-butyl 
alpha-(p-toluenesulfonyloxy)-acetate. 
Dissolution inhibitor compounds may be added to the radiation sensitive 
compositions of the invention to further control dissolution of an exposed 
coating layer of the composition. Suitable dissolution inhibiting 
compounds include, for example, t-butyloxycarbonato-bis-phenol-A and 
t-butylacetoxy-bis-phenol-A. The dissolution inhibiting compounds may be 
suitably in a concentration of about 5 to 10 weight percent of total 
solids of a photoresist formulation. 
In addition to the components described above, other conventional additives 
known to the art may be added to the radiation sensitive compositions of 
this invention. Such additives typically include dyes, adhesion promoting 
agents, solubility modifiers, other resins for specific purposes, 
materials to improve chemical resistance, flexibility, etch resistance, 
electrical properties, coating characteristics, exposure speed, 
development and resolution characteristics, etc. 
As noted, use of a polymer of a phenol and a cyclic alcohol as a resin 
binder for a radiation sensitive composition in accordance with the 
invention improves optical properties because the binder contains fewer 
conjugated bonds, it being known that such bonds absorb at activating 
radiation, especially at wavelengths below 350 nm. In addition, it is 
believed that optical properties are improved due to elimination of 
quinone type impurities in said resins when hydrogenation is the means 
selected to form the polymer binder. 
Use of the polymer binder containing phenol and the cyclic alcohol and 
having acid labile moieties provides another advantage. Following exposure 
and development of a photoresist prepared in accordance with the 
invention, the relief image generated is of improved resolution and 
possesses an improved profile. The relief image possesses substantially 
vertical side walls and is capable of reproducing submicron features. 
The compositions of the invention are generally prepared following prior 
art procedures for the preparation of photoresists and other photocurable 
compositions with the exception that the polymer binder with acid labile 
groups as described above is substituted for the conventional resins used 
in the formulation of such compositions. The compositions of the invention 
are formulated as a coating composition by dissolving the components of 
the composition in a suitable solvent such as, for example, a glycol ether 
such as 2-methoxyethyl ether (diglyme), ethylene glycol monomethyl ether, 
ethylene glycol monomethyl ether, propylene glycol monomethyl ether; a 
Cellosolve ester such as methyl Cellosolve Acetate; an aromatic 
hydrocarbon such as toluene or xylene; or a ketone such as methylethyl 
ketone. Typically, the solids content of the composition varies between 
about 5 and 35 percent by weight of the total weight of the radiation 
sensitive composition. 
The compositions of the invention are used in accordance with generally 
known procedures though exposure and development conditions may vary as a 
consequence of improved photospeed and altered solubility in developer. 
The liquid coating compositions of the invention are applied to a 
substrate such as by spinning, dipping, roller coating or other 
conventional coating technique. When spin coating, the solids content of 
the coating solution can be adjusted to provide a desired film thickness 
based upon the specific spinning equipment utilized, the viscosity of the 
solution, the speed of the spinner and the amount of time allowed for 
spinning. 
The composition is applied to substrates conventionally used in processes 
involving coating with photoresists. For example, the composition may be 
applied over silicon or silicon dioxide wafers for the production of 
microprocessors and other integrated circuit components. 
Aluminum--aluminum oxide and silicon nitride wafers can also be coated 
with the photocurable compositions of the invention. Another suitable use 
of the composition of the invention is as a planarizing layer or for 
formation of multiple layers in accordance with art recognized procedures. 
Following coating of the resist onto a surface, it is dried by heating to 
remove the solvent until preferably the resist coating is tack free. 
Thereafter, it is imaged through a mask in conventional manner. The 
exposure is sufficient to effectively activate the photoactive component 
of the photoresist system to produce a patterned image in the resist 
coating layer and, more specifically, the exposure energy typically ranges 
from about 10 to 300 mJ/cm.sup.2, dependent upon the exposure tool. 
A wide range of activating radiation can be suitably employed to expose the 
photoacid-generating compositions of the invention, including radiation of 
wavelengths anywhere in the range of from about 248 to 700 nm. As noted 
above, the compositions of the invention are especially suitable for deep 
UV exposure. The spectral response of the compositions of invention can be 
expanded by the addition of suitable radiation sensitizer compounds to a 
composition. 
Following exposure, the film layer of the composition is preferably baked 
at temperatures ranging from about 70.degree. C. to about 140.degree. C. 
Thereafter, the film is developed. The exposed resist film is rendered 
positive working by employing a polar developer, preferably an aqueous 
based developer such as an inorganic alkali exemplified by sodium 
hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, 
sodium silicate, sodium metasilicate, or the like. Alternatively, organic 
developers can be used such as choline based solutions; quaternary 
ammonium hydroxide solutions such as a tetra-alkyl ammonium hydroxide 
solution; various amine solutions such as ethyl amine, n-propyl amine, 
diethyl amine, di-n-propyl amine, triethyl amine or, methyldiethyl amine; 
alcohol amines such as diethanol amine or triethanol amine; cyclic amines 
such as pyrrole, pyridine, etc. The exposed resist film is rendered 
negative working by employing suitable organic developers such as 
methylene chloride or hexanes, or mixtures thereof. In general, 
development is in accordance with art recognized procedures. 
The developed substrate may then be selectively processed on those 
substrates areas bared of resist, for example chemically etching or 
plating substrate areas bared of resist in accordance with procedures 
known in the art. For the manufacture of microelectronic substrates, for 
example the manufacture of silicon dioxide wafers, suitable etchants 
include a plasma gas etch and a hydrofluoric acid etching solution. The 
compositions of the invention are highly resistant to such etchants 
thereby enabling manufacture of highly resolved features, including lines 
with submicron widths. After such processing, resist may be removed from 
the processed substrate using known stripping procedures. 
The following examples are illustrative of the invention. 
GENERAL COMMENTS 
In the examples, the hydrogenated poly(vinylphenol) resins were PHM-C grade 
and obtained from Maruzen Oil of Tokyo, Japan. The degree of hydrogenation 
of these poly(p-vinyl phenols) is expressed as % of aromatic double bonds 
converted to single bonds, or equivalently as % hydroxyphenyl groups 
converted to hydroxycyclohexyl groups. All temperatures throughout this 
disclosure are in degrees Celsius. 
EXAMPLE 1 
Preparation of t-Butylacetate-modified Poly(4-vinylphenol). 
The title compound was prepared as follows. 20 g of poly(4-vinylphenol) at 
10% hydrogenation was dissolved in 200 mL of dry dimethylformamide under 
nitrogen. To this solution was added 0.80 g of NaH (95%) and the reaction 
mixture was allowed to stir for 30 minutes. 5.4 g of tert-butyl 
chloroacetate was then added dropwise to the solution and the mixture was 
heated at 70.degree. C. for 18 hours. After cooling and filtering the 
product was isolated by adding the solution to 3 L of water. The 
precipitate was collected by filtration, re-slurried in water and 
re-filtered. The resulting polymer was then dried at 50.degree. C. under 
vacuum for 24 hours. The degree of substitution (about 20 mole percent of 
available hydroxyl groups) was confirmed by proton and carbon-13 NMR. 
EXAMPLE 2 
Preparation of t-Butylacetate-modified Hydrogenated m-Cresol Novolak. 
The title compound was prepared by procedures similar to those described in 
Example 1. Thus, a 30 g sample of hydrogenated (20%) m-cresol novolak 
(catalytically reduced with Raney nickel under 100 atm) was treated with 
3.0 g of NaH and 18.8 g of tert-butyl chloroacetate. The mixture was 
heated at 70.degree. C. for 12 hours. The reaction mixture was cooled and 
the product isolated by aqueous quench, washed and the final product dried 
at 60.degree. C. for 24 hours. The degree of substitution (about 15 
percent of available hydroxyl groups) was confirmed by proton and 
carbon-13 NMR. 
EXAMPLE 3 
This Example illustrates deblocking of the t-Butylacetate-modified 
Poly(vinylphenol). 
To a 22 weight percent solution of the t-butylacetate-modified 
poly(vinylphenol) prepared in Example 1, in 3:1 (v/v) propylene glycol 
monomethylether acetate/anisole mixture was added 5 weight percent (based 
on weight of the polymer) of tris(mesyl)pyrogallol. The solution was spin 
coated onto silicon wafers (HMDS primed) at 3000 rpm (30 seconds) to form 
a 1 .mu.m film. The films were then softbaked at 90.degree. C. for 60 
seconds on a vacuum hot plate. The films exhibited a dissolution rate of 
170 A/s in 0.21N tetramethylammonium hydroxide (TMAH) developer at 
25.degree. C. After exposing the films to 125 mJ/cm.sup.2 of UV radiation 
(260 nm) and baking at 110.degree. C. (hot plate, 60 seconds) a 
dissolution rate of 10,600 A/s was obtained under the same development 
conditions. The deblocking of the acid labile groups was confirmed by IR 
spectroscopy. 
EXAMPLE 4 
This Example illustrates deblocking of the t-Butylacetate-modified 
Hydrogenated m-Cresol Novolak. 
To a 25 weight percent diglyme solution of the t-butylacetate-modified 
hydogenated m-cresol novolak prepared in Example 2 was added 5% (by weight 
of polymer) of triphenylsulfonium hexafluoroarsenate. The solution was 
spin coated onto silicon wafers primed with hexamethyldisilazane (HMDS) at 
3000 rpm (30 seconds). After softbaking for 60 seconds at 90.degree. C. on 
a hot plate the wafers were exposed to 125 mJ/cm.sup.2 of UV (260 nm) 
radiation and post-exposure baked at 130.degree. C. for 60 seconds. The 
dissolution rate before exposure was zero and after deblocking the rate 
was greater than 20,000 A/s in a 0.21N tetramethylammonium hydroxide 
(TMAH) aqueous developer solution. 
EXAMPLE 5 
A photoresist solution comprised of 23 weight percent of the 
t-butylacetate-modified poly(4-vinylphenol) prepared in Example 1, 2.3 
weight percent of tris(methanesulfonyl)pyrogallol, and about 75 weight 
percent diglyme was spin coated onto HMDS primed silicon wafers (4,000 
rpm, 30 seconds). After baking at 90.degree. C. for 60 seconds (hot plate) 
0.9 micron films were obtained. An array of 4.times.8 mm square regions 
were exposed over a range of energies from 7.2 to 115.2 mJ in steps of 3.6 
mJ on a GCA AWIS Excimer Laser Stepper at 248 nm. The exposed wafers were 
post-exposure baked at 90.degree. C. for 60 seconds and developed by 
single puddle for 60 seconds in 0.14N TMAH aqueous developer solution. 
Scanning electron microscopy analysis revealed that 0.5 .mu.m lines having 
essentially vertical sidewalls were printed. 
EXAMPLE 6 
Preparation of a positive resist composition sensitized with bisphenol-A 
and suitable for deep UV exposure. 
To a 25 weight solution of diglyme and the t-butylacetate-modified 
poly(4-vinylphenol) prepared in Example 1 was added 10% of 
tris(mesyl)pyrogallol and 10% bisphenol-A (based on polymer weight). After 
filtration this resist solution was coated to one micron onto silicon 
substrates on a SVG 86 Wafertrac (3,000 rpm, 60 seconds) and softbaked for 
60 seconds at 90.degree. C. The wafers were exposed on an HTG DUV exposure 
unit, post-exposure baked at 90.degree. C. for 60 seconds (hotplate), and 
developed in 0.14N TMAH. Values for contrast and E.sub.0 were then 
calculated from plots of normalized thickness versus log exposure dose. 
The values for the example described above were E.sub.0 =21 mJ/cm.sup.2 
and a gamma of 20 while those of a resist without any sensitizer were 40 
mJ/cm.sup.2 and 5.9 respectively. 
EXAMPLE 7 
Preparation of a dual blocked polymer. 
The t-butylacetate-modified poly(4-vinylphenol) prepared in Example 1 was 
dissolved in 400 mL of tetrahydrofuran while purging with nitrogen. To 
this solution was added 1.19 g of potassium t-butoxide and the reaction 
was stirred for 15 minutes. A solution of 2.32 g of di-t-butyl dicarbonate 
in 20 mL of tetrahydrofuran was then added dropwise and the mixture was 
allowed to stir for 12 hours at room temperature. The resulting polymer 
was precipitated into water, redissolved in acetone, and re-precipitated. 
The product was then dried at 60.degree. C. for 18 hours under vacuum. 
This reaction yielded a polymer containing 10% t-butoxycarbonyloxy groups. 
EXAMPLE 8 
A dual blocked positive resist suitable for deep UV exposure. 
A resist composition comprised of 25 weight percent of the dual blocked 
polymer prepared in Example 7 and 10 weight percent of 
tris(mesyl)pyrogallol dissolved in diglyme was treated as described in the 
Example 6 with the exception that the post-exposure bake temperature was 
100.degree. C. The contrast curve yielded an E.sub.0 of 33 mJ/cm.sup.2 and 
a gamma value of 6.8. 
The foregoing description of the present invention is merely illustrative 
thereof, and it is understood that variations and modifications can be 
effected without departing from the spirit or scope of the invention as 
set forth in the following claims.