Photoresist composition with aromatic novolak binder having a weight-average molecular weight in excess of 1500 Daltons

A photoresist comprising a light sensitive component and an essentially aromatic alkali soluble novolak resin comprising the product resulting from the acid condensation of an aromatic aldehyde and a phenol where the resin has a molecular weight in excess of 1,500 and a glass transition temperature in excess of 125.degree. C. If desired, the aromatic novolak resin may be blended with a conventional novolak resin to regulate the glass transition temperature of the resin.

BACKGROUND OF THE INVENTION 
1. Introduction 
This invention relates to a photoresist composition comprising a 
light-sensitive component admixed with a binder that is a novel novolak 
resin formed from one or more phenols and one or more aromatic aldehydes 
or a blend of said novolak resin with another resin typically used in a 
photoresist composition including conventional novolak and other phenolic 
resins. 
2. Description of the Prior Art 
Photoresist compositions are well known in the art and described in 
numerous publications including DeForest, Photoresist Materials and 
Processes, McGraw-Hill Book Company, New York, 1975. Photoresists comprise 
coatings produced from solution or applied as a dry film which, when 
exposed to light of the proper wavelength, are chemically altered in their 
solubility to certain solvents (developers). Two types are known. The 
negative-acting resist is initially a mixture which is soluble in its 
developer, but following exposure to activating radiation, becomes 
insoluble in developer thereby defining a latent image. Positive-acting 
resists work in the opposite fashion, light exposure making the resist 
soluble in developer. 
Positive-working photoresists are more expensive than negative-working 
photoresists but are capable of providing superior image resolution. For 
example, the positive-working photoresist described above can be developed 
to yield relief images with a line width as low as one micron or less. In 
addition, considering the cross section of a photoresist image, the 
channels formed in the resist by development have square corners and 
sidewalls with only minimal taper. 
The positive-working resists comprise a light sensitive compound in a 
film-forming polymer binder. The light sensitive compounds, or sensitizers 
as they are often called, most frequently used are esters and amides 
formed from o-quinone diazide sulfonic and carboxylic acids. These esters 
and amides are well known in the art and are described by DeForest, supra, 
pages 47-55, incorporated herein by reference. These light sensitive 
compounds, and the methods used to make the same, are all well documented 
in prior patents including German Pat. No. 865,140 granted Feb. 2, 1953 
and U.S. Pat. Nos. 2,767,092; 3,046,110; 3,046,112; 3,046,119; 3,046,121; 
3,046,122 and 3,106,465, all incorporated herein by reference. Additional 
sulfonic amide sensitizers that have been used in the formulation of 
positive-acting photoresists are shown in U.S. Pat. No. 3,637,384, also 
incorporated herein by reference. These materials are formed by the 
reaction of a suitable diazide of an aromatic sulfonyl chloride with an 
appropriate resin amine. Methods for the manufacture of these sensitizers 
and examples of the same are shown in U.S. Pat. No. 2,797,213, 
incorporated herein by reference. Other positive-working diazo compounds 
have been used for specific purposes. For example, a diazo compound used 
as a positive-working photoresist for deep U.V. lithography is Meldrum's 
diazo and its analogs as described by Clecak et al, Technical Disclosure 
Bulletin, Volume 24, Number 4, September 1981, IBM Corporation, pp. 1907 
and 1908. An o-quinone diazide compound suitable for laser imaging is 
shown in U.S. Pat. No. 4,207,107. The aforesaid references are also 
incorporated herein by reference. 
A class of negative resists comprising a negative-acting sensitizer in a 
polymer binder is described by Iwayanagi et al, IEEE Transactions on 
Electron Devices, Vol. ED-28, No. 11, November, 1981, incorporated herein 
by reference. The resists of this reference comprise an aromatic azide in 
a phenolic binder. It is believed that these resists are first disclosed 
and claimed in U.S. Pat. No. 3,869,292, also incorporated herein by 
reference. Additional aromatic azide sensitizers are disclosed by 
DeForest, supra, and U.S. Pat. Nos. 2,940,853 and 2,852,379, incorporated 
herein by reference. 
The resin binders most frequently used with the o-quinone diazides in 
commercial practice are the alkali soluble phenol formaldehyde resins 
known as the novolak resins. Photoresists using such polymers are 
illustrated in U.K. Pat. No. 1,110,017, incorporated herein by reference. 
These materials are the product of reaction of a phenol with formaldehyde 
under conditions whereby a thermoplastic polymer is formed with a glass 
transition temperature of about 100.degree. C. Novolaks with glass 
transition temperatures in excess of 100.degree. C are known but are not 
generally used in photoresist formulations because they are expensive and 
involve extraction of low molecular weight fractions. 
Another class of binders used with both the negative-acting aromatic azides 
and the positive acting o-quinone diazides are the homopolymers and 
copolymers of vinyl phenol. Photoresists of this nature are disclosed in 
U.S. Pat. No. 3,869,292, supra. It is believed that photoresists using 
binders of polymers formed from vinyl phenols have not found extensive use 
in commerce. 
In the prior art, the above described positive resists using novolak resins 
as a binder are most often used as masks to protect substrates from 
chemical etching in photo-engraving processes. For example, in a 
conventional process for the manufacture of a printed circuit board, a 
copper-clad substrate is coated with a layer of a positive working 
photoresist, exposed to actinic radiation to form a latent circuit image 
in the photoresist coating, developed with a liquid developer to form a 
relief image and etched with a chemical etchant whereby unwanted copper is 
removed and copper protected by the photoresist mask is left behind in a 
circuit pattern. For the manufacture of printed circuit boards, the 
photoresist must possess chemical resistance, must adhere to the circuit 
board substrate, and for high density circuits, must be capable of fine 
line image resolution. 
Similar photoresists are also used in the fabrication of semiconductors. As 
in the manufacture of printed circuits, the photoresist is coated onto the 
surface of a semiconductor wafer and then imaged and developed. Following 
development, the wafer is typically etched with an etchant whereby the 
portions of the wafer bared by the development of the photoresist are 
dissolved while the portions of the wafer coated with photoresist are 
protected, thereby defining a circuit pattern. For use in the manufacture 
of a semiconductor, the photoresist must possess resistance to chemical 
etchants, must adhere to the surface of the semiconductor wafer and must 
be capable of very fine line image resolution. 
Recent developments in photoresist technology involve processes where high 
temperatures are encountered. For example, a recent development in the 
fabrication of semiconductors substitutes dry plasma etching for wet 
chemical etching to define a circuit. Plasma etching provides advantages 
over wet chemical etching in that it offers process simplification and 
improves dimensional resolution and tolerance. However, the demands on the 
resist are significantly greater when using plasma etching. For both wet 
etching and plasma etching, the resist must adhere to the substrate and 
must be capable of fine line image resolution. For plasma etching, in 
addition to these properties, the resist must often be capable of 
withstanding high temperatures without image deformation and without 
eroding as plasma etching generates high temperatures at the wafer 
surface. 
The above described prior art positive-working resists provide good 
resistance to chemical etchants and fine line image resolution. However, 
they soften and begin to flow at temperatures somewhat in excess of about 
120.degree. C. This can result in image distortion and poorer image 
resolution. 
SUMMARY OF THE INVENTION 
The subject invention is directed to photoresist compositions useful for 
the same purposes as prior art photoresists, but also useful for purposes 
where resistance to temperatures in excess of 120.degree. C. is required. 
The photoresist may be positive-acting or negative-acting photoresist, 
dependent upon the selection of the sensitizer. The photoresist comprises 
a sensitizer such as as diazo compound or an azide compound in a resin 
binder comprising the condensation product of a phenol and an aromatic 
aldehyde or a mixture of such a resin with other phenolic resins including 
conventional novolak resins--i.e., those prepared by the reaction of a 
phenol with formaldehyde in the presence of an acid catalyst. 
The new resins used as binders for the photoresist exhibit glass transition 
temperatures in excess of 125.degree. C. and many exhibit glass transition 
temperatures as high as 175.degree. C. or higher. The novel resins are 
compatible with conventional novolak resins and other resins including 
other phenolic resins to provide new polymer mixtures exhibiting excellent 
film forming and thermal properties. Where the glass transition 
temperature of the new resins of the invention and other resins used in 
combination with those of the invention are known, resin blends are 
readily prepared exhibiting any desired intermediate glass transition 
temperature by adjustment of the concentration of each resin in the blend. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As described above, the invention is directed to a photoresist composition 
that comprises an admixture of a light sensitive component and an aromatic 
novolak resin binder. The aromatic novolak resins are acid catalyzed 
condensation products of one or more phenols and an aromatic aldehyde 
formed by the condensation of the reactants in the presence of a strong 
acid and a divalent sulfur compound as a catalyst. The phenol is of the 
type conventionally used in the formation of novolak resins, such as, for 
example, phenol itself, the cresols, xylenols, resorcinols, naphthols and 
bisphenols such as 4,4-isopropylidene diphenol. Preferred phenols for 
purposes of the invention include the cresols and 
2,6-bis(hydroxymethyl)-p-cresol, m-cresol being most preferred. 
The aromatic novolak is one formed by condensation of the phenol with an 
aromatic aldehyde. The aromatic aldehyde is preferably one conforming to 
the following formula: 
##STR1## 
where R is a member selected from the group consisting of halogen, cyano, 
nitro, carboxyl, alkoxy or alkyl having from 1 to 5 carbon atoms; m is an 
integer ranging between 0 and 2 and n is a whole integer ranging between 0 
and 3. Preferred aromatic aldehydes are those where a hydroxyl group is in 
a position ortho to the carbonyl group. Most preferred aromatic aldehydes 
are salicylaldehyde, benzaldehyde and mixtures of the two. Other aromatic 
aldehydes suitable for purposes of the invention include 
2-chlorobenzaldehyde, 3-hydroxy benzaldehyde, 4-hydroxy benzaldehyde, 
2-methoxy benzaldehyde, 3-nitro benzaldehyde, etc. Mixtures of aromatic 
aldehydes may also be used. In a lesser preferred embodiment, the aromatic 
aldehyde may be mixed with formaldehyde or a formaldehyde precursor such 
as paraformaldehyde if desired. However, the aromatic aldehyde preferably 
is in molar excess of formaldehyde, more preferably comprises at least 90% 
by weight and most preferably is the only aldehyde used to form the resin. 
The aromatic novolak resins are formed by condensing the aromatic alcohol 
with the aromatic aldehyde in the presence of a strong acid and a divalent 
sulfur compound as a catalyst. The molar concentration of the aromatic 
aldehyde may be slightly less than that of the aromatic alcohol, but 
unexpectedly, may also be equivalent to or slightly in excess of the 
aromatic alcohol without formation of a cross linked resin. In this 
respect, the ratio of the phenol to the aldehyde may vary between about 
1.1 to 1.0 and 1.0 to 1.1. 
Aromatic aldehydes, compared to formaldehyde, are less reactive towards 
condensation reactions leading to polymerization. However, under more 
vigorous reaction conditions, aromatic aldehydes can condense with a 
reactive phenol in the presence of a strong mineral or organic acid such 
as sulfuric acid or toluene sulfonic acid. Generally, the polymers 
produced by this procedure are of low molecular weight, possess poor 
physical and mechanical properties and are generally unsuitable for 
lithographic properties. However, it has been found that by using 
catalytic amounts of ionizable compounds of divalent sulfur such as sulfur 
dichloride, sodium thiosulfate, hydrogen sulfide, sodium sulfide, thiols, 
thiophenols, thioacetic acid, thioglycolic acid, mercapto alkyl sulfonic 
acid or hydroxyalkyl thiols in conjunction with a strong acid catalyst 
such as sulfuric acid or toluene sulfonic acid, the condensation of the 
aromatic aldehyde with a reactive phenol results in the formation of 
polymers that are of high molecular weight, and therefore, are more 
suitable as resins for coating compositions, especially for photoresist 
coating compositions. 
Whereas in the prior art, aromatic aldehydes could not be reacted with 
phenols to produce resins having weight average molecular weights in 
excess of about 1,000 Daltons, in accordance with the method disclosed 
herein for the formation of aromatic novolak resins, the resins can be 
formed having weight average molecular weights in excess of 1,500 Daltons 
and typically in excess of 2,500 Daltons. Further, with respect to 
molecular weight, it has been found that the molecular weight distribution 
of the resins produced in accordance with the invention generally have a 
narrow molecular weight distribution, especially when m-cresol is used as 
the phenol. In addition to increased molecular weight, the resins of the 
invention have improved glass transition temperatures generally in excess 
of 125.degree. C. and often in excess of 175.degree. C. Though not wishing 
to be bound by theory, it is believed that the improved thermal properties 
of the resin are due to strong hydrogen bonding and a more rigid polymer 
backbone. 
The aromatic novolak resins are formed by mixing the reactants and a 
dehydrating solvent in a reactor and refluxing the mixture at an elevated 
temperature for a period of time sufficient to form a polymer of at least 
the weight average molecular weight given above. The reactor may be any 
conventional condensation reactor equipped with an agitator, means for 
reflux and distillation and conventional heat transfer means as required 
to perform the reaction. In general, a preferred method for carrying out 
the condensation reaction is to dissolve the condensation agent (the 
aromatic aldehyde) and the aromatic alcohol in an appropriate dehydrating 
water miscible solvent and then add the acid catalyst and ionizable 
divalent sulfur compound as described above. The resultant mixture is 
agitated and heated to reflux over a period of time ranging from about 2 
to 24 hours, during which the aromatic alcohol and the aldehyde condense. 
The condensation reaction typically involves the formation of low 
molecular weight intermediates which initially form and then rearrange and 
combine with each other at a later stage to form higher molecular weight 
polymers. 
Following reflux, excess water is removed from the condensate and the 
condensate is then subjected to distillation at a temperature of from 
120.degree. to 180.degree. C. to complete the condensation reaction. The 
resin solution is then typically diluted with more solvent and added to 
excess water to precipitate the resin. The resin is then washed with water 
and dried at elevated temperature under vacuum. The resin will have a 
glass transition temperature of at least 125.degree. C. 
In accordance with the procedure described herein, if desired, the aromatic 
novolak resin may be blended with other phenolic resins such as 
conventional novolak resins, polyvinyl phenol resins, pyrogallol-acetone 
condensates or any other phenolic resins known to the art. The ratio of 
the aromatic novolak to the additional phenolic resin can vary within wide 
limits and is, in part, dependent upon the desired glass transition 
temperature and other desired properties of the resin blend. Preferably, 
the aromatic novolak resin is present in the blend in an amount of at 
least 10 percent by weight, more preferably in predominant proportion, and 
most preferably in an amount that varies from 80 to 100 percent by weight 
of the blend. Other additives may be present in the resin blend as would 
be obvious to those skilled in the art. 
The method of forming a blend of the aromatic novolak with another phenolic 
resin is not critical and is not considered to be a part of the invention. 
The two resins, in finely divided powder form or in solution may be mixed 
with each other using methods known to the art.

The following examples will better illustrate the method for the 
formulation of the novel aromatic resins discussed herein and provides 
comparison of the same with prior art resins and methods for making prior 
art aromatic resins. 
EXAMPLE 1 
A m-Cresol Salicylaldehyde Resin 
A mixture of 183.2 grams salicylaldehyde, 162.2 grams m-cresol, 5.0 grams 
3-mercaptopropionic acid, 1.5 grams of a 50 percent aqueous solution of 
p-toluene sulfonic acid and 200 ml of glacial acetic acid were charged 
into a 1-liter reaction vessel equipped with a paddle stirrer, reflux 
condenser and a nitrogen inlet tube. The mixture was heated to reflux and 
maintained at reflux for 16 hours. The reaction mixture was slowly poured 
into 7 liters of deionized water to precipitate the resin. Once the 
solvent had exchanged with water, the product was collected on a filter, 
slurried once in warm deionized water for about 30 minutes, again 
collected, rinsed with water and dried in a vacuum oven under about 125 mm 
Hg and at about 100.degree. to 105.degree. C. About 286 grams of a brown 
powder was obtained. 
EXAMPLE 2 
A m-Cresol Salicylaldehyde Resin--Additional Example 
A mixture of 184.1 grams of salicylaldehyde, 162.2 grams of m-cresol, 5.0 
grams of 3-mercaptopropionic acid, 1.5 grams of p-toluenesulfonic acid and 
200 ml of glacial acetic acid were charged into a 1-liter reactor vessel 
equipped with a paddle stirrer, reflux condenser and a nitrogen inlet 
tube. The mixture was heated to reflux and maintained at reflux for 7.5 
hours. The reaction mixture was slowly added to a 7-liter flask of 
deionized water to precipitate the resin. Once the solvent had exchanged 
with water, the product was collected on a filter, slurried in warm 
deionzized water for 30 minutes, again collected, rinsed with water and 
dried in a vacuum oven under 125 mm Hg and at about 105.degree. to 
110.degree. C. About 297 grams of a brown powder having a weight average 
molecular weight of 4,138 Daltons and a polydispersity of 2.1 was 
collected. Due to the nature of the primary and secondary structure of the 
resin, its glass transition temperature could not be determined from the 
differential scanning calorimetry melting curve but it can be stated that 
it possessed a glass transition temperature in excess of 150.degree. C. 
EXAMPLE 3 
An o-Cresol Salicylaldehyde Resin 
A mixture of 183.6 grams of salicylaldehyde, 162.2 grams of o-cresol, 3.0 
grams of 3-mercaptopropionic acid, 1.I grams of p-toluenesulfonic acid 
monohydrate and 75 ml of bis(2-methoxyethyl)ether were charged into a 
1-liter reaction vessel equipped with a paddle stirrer, reflux condenser 
and a nitrogen inlet tube. The mixture was heated to reflux and maintained 
at reflux for 4.0 hours. The more volatile components in the reaction 
mixture were then removed by distillation at ambient pressure under a 
constant flow of nitrogen. The mixture temperature was then raised and 
maintained between 170.degree. and 178.degree. C. for 2 hours to complete 
the reaction. Upon cooling, the product mixture was diluted first with 150 
ml of glacial acetic acid followed by 300 ml of methanol. The solution was 
slowly added to 3.2 liters of deionized water to precipitate the resin. 
Once the solvent had exchanged with water, the product was collected on a 
filter, slurried in warm deionized water, rinsed with water and dried in 
vacuum oven under about 125 mm Hg and at about 115.degree. to 120.degree. 
C. About 289 grams of a brown powder having a weight average molecular 
weight of 19,439 Daltons and a polydispersity of 7.32 was obtained. Due to 
the nature of the primary and secondary structure of the resin, its glass 
transition temperature could not be determined from the differential 
scanning calorimetry melting curve but it can be stated that its glass 
transition temperature exceeded 150.degree. C. 
EXAMPLE 4 
A p-Cresol Salicylaldehyde Resin 
A mixture of 183.2 grams of salicylaldehyde, 162.2 grams of p-cresol, 3.0 
grams of 3-mercaptopropionic acid, 1.1 grams of p-toluenesulfonic acid 
monohydrate and 75 ml of bis(2-methoxyethyl)ether were charged into a 
1-liter reactor vessel equipped with a paddle stirrer, reflux condenser 
and a nitrogen inlet tube. The reaction was carried out according to the 
procedure of Example 3 to yield about 272.5 grams of resin having a weight 
average molecular weight of 11,622 Daltons and a polydisperisity of 7.39. 
Due to the nature of the primary and secondary structure of the resin, its 
glass transition temperature could not be determined from the differential 
scanning calorimetry melting curve but it can be stated that its glass 
transition temperature exceeded 150.degree. C. 
EXAMPLE 5 
A m-Cresol Salicylaldehyde-Benzaldehyde Resin 
A mixture of 778.6 grams of salicylaldehyde, 453.1 grams of benzaldehyde, 
357.8 grams of m-cresol, 14.5 grams of 3-mercaptopropionic acid, 9.6 grams 
of p-toluenesulfonic acid monohydrate and 650 ml of propionic acid were 
charged into a 4-liter reaction vessel equipped with a paddle stirrer, 
reflux condenser and a nitrogen inlet tube. The mixture was heated to 
reflux and maintained at reflux for 4.0 hours. The more volatile 
components in the reaction mixture were then removed by distillation at 
ambient pressure under a constant flow of nitrogen. The mixture 
temperature was then raised and maintained between 141.degree. and 
145.degree. C. and allowed to reflux for 4 hours to complete the reaction. 
Upon dilution with 1.6 liters of propionic acid, the resin solution was 
precipitated into 14 liters of deionized water. The product was collected 
on a filter, slurried in 14 liters of deionized water, collected by 
filtration, rinsed with deionized water and dried at 110.degree. to 
115.degree. C. About 1,485 grams of a brown powder having a weight 
average molecular weight of 1,790 Daltons and a polydispersity of 1.95 was 
obtained having a glass transition temperature of about 177.degree. C. 
EXAMPLE 6 
An m-Cresol Salicylaldehyde 2,6-bis(hydroxymethyl)-p-Cresol Resin 
A mixture of 146.0 grams m-cresol, 146.5 grams salicylaldehyde, 25.2 grams 
2,6-bis(hydroxymethyl)-p-cresol, 5.0 grams 3 mercaptoproprionic acid and 
1.5 grams p-toluenesulfonic acid monohydrate in 200 ml glacial acetic acid 
was reacted as described in Example 1 and about 281 grams of resin was 
obtained. The resin had a glass transition temperature of 233.degree. C. 
and a molecular weight of about 4,085 Daltons with a weight average 
molecular weight to a number average molecular weight of 2.77. 
EXAMPLE 7-21 
Misc. Cresol Aromatic Aldehyde Resins 
Following generally the procedures of Examples 1 to 5, additional polymers 
were prepared using various combinations of monomers. The monomers, their 
mole ratio and the glass transition temperature and weight average 
molecular weight of the polymers formed are set forth in the following 
table: 
______________________________________ 
Example Molecular Weight 
No. Monomers Mole % Tg. .degree.C. 
Average 
______________________________________ 
7 m-Cresol 50 152 2,023 
Benzaldehyde 
50 
8 m-Cresol 50 None 4,138 
Salicylaldehyde 
50 obs. 
9 m-Cresol 50 164 3,038 
Benzaldehyde 
45 
Salicylaldehyde 
5 
10 m-Cresol 50 166 2,610 
Banzaldehyde 
40 
Salicylaldehyde 
10 
11 m-Cresol 50 147 1,962 
Benzaldehyde 
38 
Salicylaldehyde 
12 
12 m-Cresol 50 nm 2,001 
Banzaldehyde 
36.6 
Salicylaldehyde 
13.3 
13 m-Cresol 50 nm 2,317 
Benzaldehyde 
36 
Salicylaldehyde 
14 
14 m-Cresol 50 147 1,999 
Benzaldehyde 
35 
Salicylaldehyde 
15 
15 m-Cresol 50 161 2.319 
Benzaldehyde 
25 
Salicylaldehyde 
25 
16 m-Cresol 50 189 2,826 
Benzaldehyde 
17 
Salicylaldehyde 
33 
17 o-Cresol 50 125 4,328 
Banzaldehyde 
30 
Salicylaldehyde 
20 
18 o-Cresol 50 132 4,446 
Benzaldehyde 
25 
Salicylaldehyde 
25 
19 o-Cresol 50 134 6,610 
Benzaldehyde 
20 
Salicylaldehyde 
30 
20 m-Cresol 43.3 133 1,667 
p-Cresol 13.3 
Benzaldehyde 
26 
Salicylaldehyde 
24 
21 m-Cresol 43.3 131 3,041 
o-Cresol 13.3 
Benzaldehyde 
26 
22 m-Cresol 33 138 2,007 
o-Cresol 17 
Benzaldehyde 
30 
Salicylaldehyde 
20 
23 m-Cresol 25 125 2,343 
o-Cresol 25 
Benzaldehyde 
30 
Salicylalehyde 
20 
24 m-Cresol 17 131 2,564 
o-Cresol 33 
Benzaldehyde 
30 
Salicylaldehyde 
20 
25 o-Cresol 50 132 4,446 
Saliclaldehyde 
25 
Benzaldehyde 
25 
26 m-Cresol 33 138 2,007 
o-Cresol 17 
Benzaldehdye 
30 
Salicylaldehyde 
20 
27 m-Cresol 43.3 133 1,667 
p-Cresol 13.3 
Benzaldehyde 
26 
Salicylaldehyde 
24 
28 m-Cresol 50 147 1,671 
3-Hydroxybenz- 
50 
aldehyde 
29 m-Cresol 50 nm 1,451 
4-Hydroxybenz- 
50 
aldehyde 
______________________________________ 
EXAMPLES 30 TO 32 
Aromatic Novolak--Conventional Novolak Blends 
This example exemplifies resin blends using the resin of Example 7 (Resin 
A) with a conventional cresol formaldehyde novolak resin (Resin B) having 
a glass transition temperature of 94.degree. C. 
The resin blends were prepared by adding the appropriate amount of each 
resin to a common flask, dissolving the two resins in methanol and then 
evaporating the solvent under reduced pressure. The resin blend was then 
raised to a temperature of between 70.degree. and 80.degree. C. under 
vacuum to remove remaining solvent. The molar ratio of Resin A to Resin B 
and the resultant glass transition temperature are set forth in the 
following table. 
______________________________________ 
Resin A to Resin B 
Tg. .degree.C. 
______________________________________ 
3 to 1 140 
1 to 1 114 
1 to 3 101 
______________________________________ 
The following examples are comparative examples to better illustrate 
differences between the aromatic novolak resins used as binders herein and 
prior art novolak resins and prior art methods for making aromatic novolak 
resins. 
EXAMPLE 33 
A Mixed Cresol Formaldehyde Novolak [Comparative] 
A 2-L four-neck resin kettle equipped with a stirrer, heating source, 
thermometer, variable reflux ratio distilling head and a nitrogen inlet 
tube was charged with 278.3 g meta-cresol, 335.5 g para-cresol, 34.3 g 
ortho-cresol, 68.3 g of 36.9 percent formaldehyde, 20 mL of deionized 
water and 12.0 g of oxalic acid dihydrate. The mixture was heated to about 
60.degree. C. at which point an exothermic condensation reaction ensued. 
When the reaction mixture temperature reached about 100.degree. C., 273.3 
g of 36.9 percent formaldehyde was added in about 30 minutes. The reaction 
was then allowed to continue for about 4 hours at reflux temperature. The 
more volatile components in the reaction mixture were removed by 
distillation at ambient pressure under a constant flow of nitrogen. When 
the temperature of the reaction mixture reached about 220.degree. C., a 
partial vacuum pressure was applied and was gradually increased until a 
maximum vacuum of 7 mm Hg was achieved and the mixture was at about 
228.degree. C. The liquified resin remaining in the kettle was poured 
into a tray under nitrogen and allowed to cool and solidify. About 516 g 
of novolak resin having a glass transition temperature of about 
100.degree. C. was obtained. 
EXAMPLE 34 
A m-Cresol Benzaldehyde Resin Formed Without A Divalent Sulfur Compound 
A mixture of 159.2 grams of benzaldehyde, 162.2 grams of m-cresol and 1.7 
grams of 50% p-toluenesulfonic acid monohydrate solution were charged into 
a 0.5 liter reaction vessel equipped with paddle stirrer, reflux condenser 
and a nitrogen inlet tube. The mixture was heated to and kept at reflux 
for about 4 hours. The more volatile components in the reaction mixture 
were then removed by distillation at ambient pressure under a constant 
flow of nitrogen. When the reaction mixture temperature reached 
220.degree. C., the system was slowly placed under full vacuum to complete 
the distillation. The resin melt was then decanted from the reactor and 
cooled to yield about 245 grams of a brown solid having a glass transition 
temperature of 124.degree. C. and a weight average molecular weight of 
1,296 Daltons with a polydispersity of 1.45. Repetition of the procedure 
adding 2 grams of 3-mercaptopropionic acid produces 276 grams of resin 
with a molecular weight of 2,023 and a glass transition temperature of 
152.degree. C. 
To formulate a photoresist using an aromatic novolak resin, the light 
sensitive compound is admixed with the resin using art recognized 
procedures. The light sensitive compound used may be any of the various 
light sensitive compounds known to be suitable as sensitizer in 
photoresist comprising an alkali soluble polymer binder. Examples of such 
compounds are described above. The amount of sensitizer used and the 
manner of preparing the photoresist is in accordance with art recognized 
procedures. In this respect, dependent upon the specific sensitizer and 
polymer combination, the sensitizer can vary from 0.1 to 50 weight percent 
of the photoresist composition and preferably varies between about 5 and 
25 percent by weight of the formulation. 
For use as a liquid coating composition, the photoresist components are 
admixed with a solvent together with other additives typically used in the 
prior art. Other phenolic resins are particularly suitable as additives 
such as for example, conventional novolak resins and polyhydroxy-carbonyl 
condensates such as pyrogallol-acetone, polyvinyl phenols, vinyl phenol 
copolymers, etc. The solvent used to form the coating composition is any 
solvent typically used for this purpose including glycol ethers and 
acetates such as the propylene glycol methyl ether acetates and 
monooxymonocarboylic acid esters such as ethyl lactate. A solution having 
a solids content of from 5 to 40 percent by weight is suitable. 
The method of using photoresists of the invention is also in accordance 
with prior art procedures. The most conventional method comprises forming 
a film from solution by whirl coating, dipping, spraying, etc. 
Alternatively, the photoresist can be applied as a dry film in accordance 
with art recognized procedures. 
In addition to the light sensitive constituent, other constituents such as 
dyes, softeners and other resins may be used in a mixture with the novolak 
binder as is known in the art. A particularly useful class of additives is 
the polyvinyl ethers such as those disclosed in U.S. Pat. No. 3,634,082, 
incorporated herein by reference. These polymers may be added in amounts 
varying from 1 to 10 percent by weight of the resist. The preferred 
polyvinyl ether is polyvinyl methyl ether. 
The photoresist compositions of this invention are applied to conventional 
substrates in conventional manner. For example, the photoresist may be 
applied to a copper clad substrate, a semiconductor, a silicon wafer, etc. 
by any of whirl coating, spraying, dipping or the like. Thereafter, the 
substrate is dried, imaged and developed by washing with an aqueous 
alkaline developer. 
The following examples illustrate the preparation and use of photoresists 
in accordance with the invention. 
EXAMPLE 35 
Resist Using Example 1 Novolak 
The following resist formulation was prepared: 
______________________________________ 
Composition: 
Resin of Example 1 21.83 grams 
.sup.(1) 4.16 grams 
Ethyl Lactate 52.88 grams 
Anisole 9.78 grams 
Amyl Acetate 9.78 grams 
Performance: 
Photosensitivity, mJ/cm.sup.2 
21.0 
Contrast 1.57 
Initial Film Thickness 
1.227 um 
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.sup.(1) Oxodiazonaphthalene-sulfonate mixed ester of 
2,3,4trihydroxybenzophenone. 
EXAMPLE 36 
Photoresist Using Example 10 Resin 
A light sensitive composition solution was prepared by dissolving 20.8 g of 
resin of Example 10, 5.2 g of a naphthoquinone-2-diazide-5-sulfonyl ester 
mixture of 2,3,4-trihydroxybenzophenone, in a mixture of 65.6 g of 
propylene monomethyl ether acetate and 6.6 g of butyl acetate. The 
ultraviolet exposure energy necessary for resolving 2 microns equal 
lines/spaces pattern was 98 mJ/cm.sup.2. The hardbake deformation 
temperature was found to be 155.degree. C. 
EXAMPLE 37 
Photoresist Using A Blend of Two Aromatic Aldehyde Resins 
A light sensitive composition solution was prepared by dissolving 17.6 g of 
resin of Example 10, 3.1 g of resin of Example 16, 4.94 g of a 
naphthoquinone-2-diazide-5-sulfonyl ester mixture of 
2,3,4-trihydroxybenzophenone in 73.4 g of a solvent mixture comprising of 
60 percent of ethyl lactate, 30 percent of anisole and 10 percent of amyl 
acetate. The ultraviolet exposure energy necessary for resolving 2 microns 
equal lines/spaces pattern was 105 mJ/cm.sup.2. The hardbake deformation 
temperature was found to be 170.degree. C. 
EXAMPLE 38 
Photoresist Using A Blend of An Aromatic Aldehyde Resin With a Cresylic 
Formaldehyde Resin 
A solution of a photoresist composition was prepared from 17.56 g of the 
resin made by the procedure of Example 33, 3.10 g of a resin prepared by 
the procedure of Example 10, 4.94 g of a 
naphthoquinone-2-diazide-5-sulfonyl ester mixture of 
2,3,4-trihydroxybenzophenone and 73.4 g of a solvent mixture comprising of 
60 percent of ethyl lactate, 30 percent of anisole and 10 percent of amyl 
acetate. The ultraviolet exposure energy necessary for resolving 2 microns 
equal lines-spaces pattern was 65 mJ/cm.sup.2. The hardbake deformation 
temperature was found to be 125.degree. C. 
EXAMPLE 39 
Photoresist Using A Blend of An Aromatic Aldehyde Novolak and A 
Pyrogallol-Acetone Condensate Resin 
A light sensitive composition solution was prepared by dissolving 17.56 g 
of resin of Example 10, 3.1 g of a pyrogallol-acetone condensate resin 
having a mp of 150.degree.-160.degree. C. and a molecular weight of 1250, 
4.94 g of a naphthoquinone-2-diazide-5-sulfonyl ester mixture of 
2,3,4-tri-hydroxybenzophenone in 73.2 g of a solvent mixture comprising of 
60 percent of ethyl lactate, 30 percent of anisole and 10 percent of amyl 
acetate. The ultraviolet exposure energy necessary for resolving 2 microns 
equal lines/spaces pattern was 82 mJ/cm.sup.2. The hot-plate hardbake 
deformation temperature was found to be 165.degree.-175.degree. C. while 
the convection oven hardbake was 180.degree. C. 
EXAMPLE 40 
Photoresist Using A Resin Blend of An Aromatic Aldehyde Cresol Novolak and 
A Pyrogallol-bis-1,4-isopropenylbenzene Condensate 
A light-sensitive composition solution was prepared by dissolving 17.56 g 
of resin of Example 10, 3.1 g of a pyrogallol-bis-1,4-isopropyl benzene 
condensate having a molecular wight of 1354, 4.94 g of a 
naphthoquinone-2-diazide-5-sulfonyl ester mixture of 
2,3,4-trihydroxybenzophenone in 73.2 g of a solvent mixture comprising of 
60 percent of ethyl lactate, 30 percent of anisole and 10 percent of amyl 
acetate. The ultraviolet exposure energy necessary for resolving 2 microns 
equal lines/spaces pattern was 103 mJ/cm.sup.2. The hot-plate hardbake 
deformation temperature was found to be 170.degree. C. 
EXAMPLE 41 
Aromatic Aldehyde Resin Blend With Polyvinylphenol 
A light sensitive composition solution was prepared by dissolving 8.78 g of 
resin of Example 11, 1.55 g of a polyvinylphenol polymer having a 
molecular weight of 1,500-7,000, 2.47 g of a 
naphthoquinone-2-diazide-5-sulfonyl ester mixture of 
2,3,4-trihydroxybenzophenone in 36.6 g of a solvent mixture comprising of 
60 percent of ethyl lactate, 30 percent of anisole and 10 percent of amyl 
acetate. The ultraviolet exposure energy necessary for resolving 2 microns 
equal lines/spaces pattern was 75 mJ/cm.sup.2. The hot-plate hardbake 
deformation temperature was found to be 160.degree.-180.degree. C. 
EXAMPLE 42 
Aromatic Aldehyde Novolak-Cresylic Formaldehyde Novolak Blend Using A 
Other Than A 2,3,4-Trihydroxybenzophenone Based 
A light sensitive composition solution was prepared by dissolving 3.88 g of 
resin of Example 14, 1.67 g of the formaldehyde novolak condensate 
prepared in Example 38, 0.757 g of a naphthoquinone-2-diazide-4-sulfonyl 
ester mixture of 2,6-bis(4-hydroxy-3,5-dimethylbenzyl)-4-methylphenol in 
11.22 g ethyl lactate, 5.61 g anisole and 1.87 g amyl acetate. The 
ultraviolet exposure energy necessary for resolving 1.25 microns equal 
lines/spaces pattern was 425 mJ/cm.sup.2. 
EXAMPLE 43 
Photoresist Using A Resin Blend Where the Aromatic Aldehyde Novolak 
Contains o-Cresol 
A light sensitive composition solution was prepared by dissolving 18.59 g 
of resin of Example 17, 2.07 g of a pyrogallol-acetone condensate having a 
molecular weight of 1,670 and a melting point of 170.degree.-180.degree. 
C., 4.94 g of a naphthoquinone-2-diazide-5-sulfonyl ester mixture of 
2,3,4-trihydroxybenzophenone in 73.8 g of a solvent mixture comprising of 
60 percent of ethyl lactate, 30 percent of anisole and 10 percent of amyl 
acetate. The ultraviolet exposure energy necessary for resolving 2 microns 
equal lines/spaces pattern was 40.1 mJ/cm.sup.2. 
EXAMPLE 44 
Photoresist Using Aromatic Aldehyde Resin Containing m- and o-Cresol 
Monomers 
A light sensitive composition solution was prepared by dissolving 10.33 g 
of resin of Example 24, 2.47 g of a naphthoquinone-2-diazide-5-sulfonyl 
ester mixture of 2,3,4-trihydroxybenzophenone in 36.7 g of a solvent 
mixture comprising of 60 percent of ethyl lactate, 30 percent of anisole 
and 10 percent of amyl acetate. The ultraviolet exposure energy necessary 
for resolving 2 microns equal lines/spaces pattern was 35 mJ/cm.sup.2. 
EXAMPLE 45 
Photoresist Using Aromatic Aldehyde Resin and Novolak Resin Blends 
Radiation sensitive resist compositions containing resin blends and blends 
of naphthoquinone diazide compounds can demonstrate useful lithographic 
performance. Such blends can improve solubility, dissolution rates, 
coating properties, contrast, etch resistance, photospeed, resolution or 
feature profiles. 
A light sensitive composition solution was prepared by dissolving 83.6 g of 
resin of Example 5, 250.8 g of the formaldehyde condensate resin of 
Example 33, 22.8 g of a naphthoquinone-2-diazide-5-sulfonyl ester mixture 
of 2,6-bis(4-hydroxy-3,5-dimethylbenzyl)-4-methylphenol, 22.8 g of a 
naphthoquinone-2-diazide-5-sulfonyl ester mixture of 
4-benzyl-2,3,4-trihydroxybenzene in 612.4 g of a solvent mixture 
comprising of 90 percent ethyl lactate, 5 percent butylacetate and 5 
percent xylene. The ultraviolet exposure energy necessary for resolving 
1.5 microns equal lines/spaces pattern was 180 mJ/cm.sup.2. 
EXAMPLE 46 
Photoresist Using Aromatic Aldehyde Resin 
A light sensitive composition solution was prepared by dissolving 10.39 g 
of resin of Example 6, 2.47 g of a naphthoquinone-2-diazide-5-sulfonyl 
ester mixture of 2,3,4-trihydroxybenzophenone in 36.59 g of a solvent 
mixture comprising of 60 percent of ethyl lactate, 30 percent of anisole 
and 10 percent of amyl acetate. The ultraviolet exposure energy necessary 
for resolving 2 microns equal lines/spaces pattern was 125 mJ/cm.sup.2. 
The hardbake deformation temperature was found to be 180.degree. C.