Anionically polymerizable monomers, polymers thereof and use of such polymers in photoresists

Anionically polymerizable monomers containing at least one silicon or titanium atom form polymeric photoresists having good dry etch resistance for use in microlithography. The monomers are of the formula ##STR1## wherein A is --H or --CH.dbd.CH.sub.2 ; X is a strong electron withdrawing group; PA1 Y is a strong electron withdrawing group containing at least one silicon or titanium atom. Preferably Y is ##STR2## wherein n is 1-5 and R.sup.2, R.sup.3 and R.sup.4 are C.sub.1 -C.sub.10 alkyl. A particularly preferred monomer is 3-trimethylsilylpropyl 2-cyanoacrylate. Methods for applying a resist coating by vapor deposition of these monomers and exposure to radiation are described. A positive or negative tone image can be produced, depending upon the imaging method employed. The imaging layer may be applied over a planarizing layer to form a multilayer photoresist.

CROSS REFERENCE TO RELATED APPLICATIONS 
This Application is related to application Ser. No. 07/542,465, now 
abandoned, entitled "Photoresists formed by Polymerization of 
Di-Unsaturated Monomers" filed on even date herewith claiming priority 
from Irish Patent Application No. 2044/89, now abandoned, a division of 
which has now issued as U.S. Pat. No. 5,200,238, incorporated herein by 
reference, and application Ser. No. 07/542,466 now abandoned, entitled 
"Liquid Crystal Display Devices" filed on even date herewith, now 
abandoned, incorporated herein by reference, a continuation-in-part of 
which has now issued as U.S. Pat. No. 5,187,048. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to anionically polymerizable monomers containing at 
least one silicon or titanium atom, polymers thereof, and use of such 
polymers in photoresists, particularly for the microelectronics industry. 
In one aspect this invention also relates to vapour deposition and 
polymerization of silicon-functionalised cyanoacrylates. 
2. Description of the Related Art 
The use of anionically (or zwitterionically) polymerisable monomers as 
resist materials for microlithography is known in the art, as discussed in 
U.S. Pat. Nos. 4,675,273 Woods et al. and 4,675,270 Woods et. al. both 
assigned to Loctite (Ireland) Limited, the contents of which are 
incorporated herein by reference. Such resist materials are usually 
applied to or formed as a coating on an etchable substrate; the coated 
substrate is then imaged using high energy radiation; the image is 
developed by a development process, normally using a solvent; and the 
image is etched using a suitable plasma or chemical etching process. 
Chemical etching has a significant disadvantage in that it is isotropic, 
i.e. the etching can affect the substrate below the photoresist. To 
achieve anisotropic etching, it is preferred to use dry etching by radio 
frequency glow discharge or large area ion beam methods. The most 
preferred methods are: 
(i) plasma etching, e.g. using oxygen or a halocarbon, particularly a 
fluorocarbon such as CF.sub.4 or CH.sub.2 F.sub.2 with chlorine or argon; 
or 
(ii) reactive ion etching. 
(See "Plasma Etching" by J. A. Mucha and D. W. Hess in "Introduction to 
Microlithography"(L. F. Thompson, C. G. Willson and M. J. Bowden Ed.) ACS 
Symposium Series 219, Am. Chem. Soc. (1983), 216-285; and "Multilayer 
Techniques and Plasma Processing" by A. Reiser in "Photoreactive 
Polymers--the Science and Technology of Resins", John Wiley & Sons (1989), 
359-393). 
However in plasma etching the photoresist itself is vulnerable to being 
etched away. There is a need therefore for polymeric photoresist films 
which have a good dry etch resistance. It is known to increase the plasma 
resistance of a resist material by including silicon in it (see the Reiser 
reference mentioned above, pages 375-381). U.S. Pat. No. 4,551,418 Hult 
et. al. describes a process for generating a negative tone resist image 
comprising the steps of: 
(1) coating a substrate with a film that contains a cationic 
photoinitiator; 
(2) exposing the film in an imagewise fashion to radiation and thereby 
generating cationic initiator in the exposed regions of the film; 
(3) treating the exposed film with a cationic sensitive monomer to form a 
film of polymer resistant to plasma etching; and 
(4) developing the resist image by etching with a plasma. 
The cationic sensitive monomer may be an organometallic monomer wherein the 
organometallic elements include silicon, germanium and tin. Particular 
examples of monomers include an epoxy substituted siloxane or silane or a 
silyl substituted vinyl ether. The monomer may be dissolved in a solvent 
or may be in the vapor state. 
However there is no teaching concerning improving the dry etch resistance 
of anionically polymerizable resist materials. 
SUMMARY OF THE INVENTION 
The present invention provides anionically polymerizable monomers of the 
formula I 
##STR3## 
wherein A is --H or --CH.dbd.CH.sub.2 ; X is a strong electron withdrawing 
group; 
Y is a strong electron withdrawing group containing at least one silicon or 
titanium atom. 
The term "strong electron withdrawing group" refers to groups which are 
more electron withdrawing than halo. 
X may suitably be selected from --CN, --COR, --COOR, --SO.sub.2 R and 
--SO.sub.3 R wherein R is H or a hydrocarbyl group preferably a C.sub.1 
-C.sub.12 hydrocarbyl group. Preferably X is --CN. 
Y may suitably be selected from --COR.sup.1, --COOR.sup.1, SO.sub.2 R.sub.1 
and --SO.sub.3 R.sup.1 wherein R.sup.1 is a group containing Si or Ti, 
preferably a hydrocarbyl, aryl or hydrocarbylaryl group (or a substituted 
derivative thereof) substituted with a group containing Si or Ti. 
The term "hydrocarbyl" as used herein means "aliphatic hydrocarbyl" 
including alkyl, alkenyl and alkynyl. Hydrocarbyl groups shall preferably 
contain from 1 to 10 carbon atoms, more preferably from 1 to 5 carbon 
atoms, and aryl and hydrocarbylaryl groups shall preferably have from 6 to 
20 carbon atoms, more preferably from 6 to 10 carbon atoms. Hydrocarbyl 
groups are preferred, especially alkyl or alkenyl groups. A substituted 
derivative of the foregoing may suitably be substituted with one or more 
halo or alkoxy groups or interrupted by one or more oxygen or nitrogen 
atoms. Halogen may be chlorine, bromine, fluorine or iodine. 
Specific examples of the groups for R.sup.1 are a methyl group, an ethyl 
group, an n-propyl group, an isopropyl group, an n-butyl group, an 
isobutyl group, a pentyl group, a hexyl group, an allyl group, a methallyl 
group, a crotyl group, a propargyl group, a cyclohexyl group, a benzyl 
group, a phenyl group, a phenoxide group, a cresyl group, a 2-phenylethyl 
group, a 2-chloroethyl group, a 3-chloropropyl group, a 2-chlorobutyl 
group, a trifluoroethyl group, a 2-methoxyethyl group, a 3-methoxybutyl 
group or a 2-ethoxyethyl group, substituted with a group containing Si or 
Ti. 
Preferably R.sup.1 comprises or is substituted with at least one group 
consisting of or containing 
##STR4## 
wherein R.sup.2, R.sup.3 and R.sup.4 which may be the same or different 
are selected from H (provided that not more than one of R.sup.2, R.sup.3 
and R.sup.4 is H), C.sub.1 -C.sub.10 alkyl, aryl , C.sub.1 -C.sub.10 
alkoxy and siloxy groups of the formula: 
##STR5## 
wherein R.sup.5, R.sup.6 and R.sup.7 which may be the same or different 
are selected from H, CH.sub.3 or phenyl provided that not more than one of 
R.sup.5, R.sup.6 and R.sup.7 is H; 
and wherein R.sup.2 may also be a group selected from siloxane oligomers or 
polymers of the structure 
##STR6## 
wherein R.sup.5, R.sup.6 and R.sup.7 are defined as above and m is an 
integer from 2 to 100. 
Preferably m is in the range from 2 to 20, and most preferably in the range 
from 2 to 5. In the case of monomers intended for vapour deposition it is 
desirable that m be low, for example not more than 2. 
TABLE I 
______________________________________ 
##STR7## 
A R No. 
______________________________________ 
##STR8## 1. 
H 
##STR9## 2. 
CH.sub.2CH 
##STR10## 3. 
H 
##STR11## 4. 
H 
##STR12## 5. 
CH.sub.2CH 
##STR13## 6. 
H 
##STR14## 7. 
CH.sub.2CH 
##STR15## 8. 
H 
##STR16## 9. 
H CH.sub.2CCSi(CH.sub.3).sub.3 
10. 
CH.sub.2CH 
##STR17## 11. 
CH.sub.2CH Si(CH.sub.3).sub.3 12. 
H 
##STR18## 13. 
H 
##STR19## 14. 
H CH.sub.2Si(CH.sub.3).sub.3 
15. 
CH.sub.2CH 
##STR20## 16. 
H 
##STR21## 17. 
______________________________________ 
Alkyl groups shall preferably contain 1 to 5 carbon atoms and aryl groups 
shall preferably have from 6 to 10 carbon atoms, most preferably being 
phenyl. 
More preferably Y is 
##STR22## 
where n is 1-5 and R.sup.2, R.sup.3 and R.sup.4 are as defined above. 
Preferably n is at least 3. Preferably R.sup.2, R.sup.3 and R.sup.4 are 
C.sub.1 -C.sub.10 alkyl. 
A particularly preferred monomer is 3-trimethylsilylpropyl 2-cyanoacrylate 
of the formula II 
##STR23## 
Other examples of the monomers are the following monomers Nos. 1-17 whose 
formulae are set out in Table 1 below: 
______________________________________ 
No. MONOMER 
______________________________________ 
1. 4'-Trimethylsilylphenyl 2-cyanoacrylate 
2. 3'-Trimethylsilylphenyl 2-cyanoacrylate 
3. 3'-Trimethylsilylphenyl 2-cyanopenta-2,4-dienoate 
4. 3',5'-Bis (Trimethylsilyl)phenyl 2-cyanoacrylate 
5. 4'-(Trimethylsilylmethyl)phenyl 2-cyanoacrylate 
6. 4'-Trimethylsilyloxphenyl 2-cyanopenta-2,4-dienoate 
7. 3'-(Trimethylsilylmethyloxy)phenyl 2-cyanoacrylate 
8. 4'-Trimethylsilylbenzyl 2-cyanopenta-2,4-dienoate 
9. 2,(3"-Trimethylsilylphenyl)ethyl 2-cyanoacrylate 
10. 1'-Trimethylsilylpropargyl 2-cyanoacrylate 
11. 3'-Methyl-2'-Trimethylsilylallyl 2-cyanopenta-2,4-dienoate 
12. Trimethylsilyl 2-cyanopenta-2,4-Dienoate 
13. Phenyldimethylsilyl 2-cyanoacrylate 
14. Dimethylisopropylsilyl 2-cyanoacrylate 
15. Trimethylsilylmethyl 2-cyanoacrylate 
16. Phenyldimethylsilylmethyl 2-cyanopenta-2,4-dienoate 
17. 3-Pentamethyldisiloxypropyl 2-cyanoacrylate 
______________________________________ 
The monomers wherein A is --CH.dbd.CH.sub.2 may be prepared by methods 
analogous to those described in our co-pending application Ser. No. 
07/542,465, now abandoned entitled "Photoresists formed by Polymerization 
of Di-Unsaturated Polymers" claiming priority from Irish Patent 
Application No. 2044/89 e.g. by reaction of acrolein with an appropriately 
substituted alkyl cyanoacetate. 
The present invention also provides polymers formed by anionic 
polymerization of monomers of Formula I as described above. In particular 
the invention provides polymeric photoresists formed by polymerisation of 
monomers of Formula I. The photoresists are preferably formed by 
polymerization from monomer vapour to produce a polymeric film on a 
substrate, in the manner described in U.S. Pat. Nos. 4,675,273 or 
4,675,270. In one aspect therefore, the invention provides a method for 
applying a polymeric resist coating to a substrate which comprises 
exposing the substrate to the vapour of a monomer of formula I as defined 
in claim 1 for sufficient time to deposit a polymerized coating of the 
monomer on the substrate. In a further aspect, the substrate has a 
planarizing layer of etchable polymeric material applied thereto before 
the resist coating of the monomer of formula I is deposited thereon. 
Alternatively the monomer may be polymerized in solution or in the bulk 
state and deposited on the substrate e.g. by spin coating to form a 
photoresist. 
Photoresist films produced from monomers of Formula I may be processed 
similarly to conventional polycyanoacrylates, but they have significantly 
improved dry etch resistance as compared to photoresists formed of 
conventional polycyanoacrylates. They also have improved dry etch 
resistance as compared to other conventional photoresist materials 
exemplified by poly(methylmethacrylate) and Novolac systems. 
Photoresist films produced from monomers of Formula I have been found to 
normally image with negative tone, in contrast with photoresists formed 
from conventional poly(cyanoacrylates) which image with positive tone. By 
"negative tone" is meant that upon exposure to UV radiation through a mask 
followed by solvent treatment, the unexposed areas are dissolved away, 
whereas by "positive tone" is meant that on similar treatment the exposed 
areas are removed by the solvent. 
Alternatively the monomers of Formula I may be used to form photoresists 
with positive tone images by coating the substrate with a compound which 
releases acid upon irradiation, image-wise exposing the coated substrate, 
and then forming the photoresist by deposition from monomer vapour, as 
described in U.S. Pat. No. 4,675,270 for poly(cyanoacrylates). 
In the case of deposition from solution, a polymer is prepared and then 
dissolved in a suitable solvent such as dichloromethane, acetone, 
nitromethane, tetrahydrofuran, acetonitrile, or chloroform. In the case of 
vapour deposition processes, the monomer vapours may be generated from the 
monomers at ambient temperatures and pressures but it is generally 
preferred to heat the monomers and/or reduce the atmospheric pressure 
above the monomer generated in the chamber in order to generate sufficient 
concentrations of vapour to accomplish the polymer deposition on the 
substrate in a reasonable time. 
Virtually any substrate upon which a polymeric image is desired may be 
utilized in the inventive processes. Most advantageously, the substrates 
will be ones which undergo subsequent plasma etching during which the 
polymer coating serves as an etch resist. Suitable substrate materials 
include silicon dioxide, including SiO.sub.2 coated silicon, metallic 
oxides, and glass, all of which may be etched by plasma etching processes. 
The preferred substrate is SiO.sub.2 coated silicon, e.g. the silicon chips 
conventionally used in preparation of semi-conductor devices. Most 
suitably, this substrate is etched by plasma etching process. 
If desired, more particularly where the substrate has a stepped surface, a 
planarizing layer of etchable polymeric material such as 
poly(methylmethacrylate) may be applied to the substrate before the resist 
layer is applied thereon. 
the case of vapour deposition processes, no surface treatment will be 
necessary if the substrate surface is inherently active for inducing 
anionic or zwitterionic polymerization of the monomer. In certain cases, 
however, where the substrate is slightly acidic or neutral it is necessary 
to activate the surface with a basic liquid or vapour which is 
substantially removed before exposing the substrate to the monomer vapour. 
Suitable activators include the known initiators for anionic or 
zwitterionic polymerization of alkyl cyanoacrylates. Especially suitable 
activators are organic amines and phosphines. 
A conventional solvent development process may be used to develop the 
image, e.g. immersion in ethyl acetate, isobutyl methyl ketone, acetone or 
blends of ethyl acetate with either of isobutyl methyl ketone and acetone. 
Compounds which release acid upon irradiation for the process of forming a 
positive tone photoresist include any compounds which release Lewis or 
protonic acids such as those known as photoinitiators for cationically 
polymerizable resins such as epoxies or vinyl ethers. 
Additionally included are compounds which release sulfonic acids upon 
irradiation and are known as photolytically releasable latent thermal 
catalysts for acid curable storing lacquers. 
Suitable radiation sensitive acid precursors useful in the inventive method 
include salts of complex halogenides represented by the formula 
EQU [A].sub.d.sup.+ [MX.sub.e ].sup.-(e-f) 
wherein A is a cation selected from iodonium, iodosyl, Group VIa onium, 
pyrylium, thiopyrylium, sulfonylsulfoxonium, and diazonium, M is a metal 
or metalloid, X is a halogen radical, d=e-f, f=the valence of M and is an 
integer equal to from 2 to 7 inclusive and e is greater than f and is an 
integer having a value up to 8; compounds of the formula 
EQU R.sup.8 [O.SO.sub.2 --CQ.sub.3 ].sub.n' 
wherein R.sup.8 is an organic radical of valency 1 to 4 and Q is hydrogen 
or fluorine and n' is an integer from 1 to 4; and compounds which release 
sulfonic acids when irradiated such as those disclosed in U.S. Pat. Nos. 
4,504,372 and 4,510,290, both incorporated herein by reference. 
The acid generating compound may be applied neat or in a solvent which is 
subsequently evaporated. If a surface activator is also to be applied to 
the substrate, both the activator and the acid generating compound may be 
applied simultaneously in a common solvent. Alternatively, the activator 
may be applied before or after application of the acid generating 
compound. 
Only trace amounts of surface activator and acid generating compound are 
necessary. Mirror finish substrates may be repolished, e.g. with a 
suitable tissue, after application of these compounds and still retain 
sufficient activator and acid generator to give sharply imaged resists 
after irradiation and exposure to monomer vapour.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
EXAMPLE 1 
Preparation of 3-trimethylsilylpropyl cyanoacetate 
Cyanoacetic acid (14.20 g, 0.167 moles), 3-trimethylsilylpropan-1-ol (22.04 
g, 0.167 moles) and p-toluenesulfonic acid monohydrate (0.18g) were 
dissolved in toluene (100 mls) and heated under reflux in a Dean Stark 
apparatus until the quantitative amount of expected water from 
esterification (3.09) was recovered. The reaction mixture was cooled and 
allowed to stand at room temperature for four days during which time small 
quantity of a white crystalline solid separated. The mixture was filtered 
to remove the solid material and the solvent removed from the filtrate by 
distillation under reduced pressure. This process yielded a clear, 
colourless, low viscosity liquid in quantitative yield (34 g) which was 
shown by .sup.1 Hnmr and I.R. analyses to be 3-trimethylsilylpropyl 
cyanoacetate of the structure: 
##STR24## 
.sup.1 Hnmr, 60 mHz (CDCl.sub.3): .tau.10.0 singlet, 9H, (CH.sub.3).sub.3 
--Si 
.tau.9.6, multiplet, 2H, --CH.sub.2 --Si 
.tau.8.4, multiplet, 2H, --CH.sub.2 -- 
.tau.6.7, singlet, 2H, --CH.sub.2 --CN 
.tau.5.9, triplet, 2H, O--CH.sub.2 -- 
I.R. (NaCl, film): 
2950 cm.sup.-1, C-H stretching vibration 
2250 cm.sup.-1, C.tbd.N stretching vibration 
1750 cm.sup.-1, C.dbd.O stretching vibration 
1250 cm.sup.-1, Si--CH.sub.3 symmetric deformating vibration 
EXAMPLE 2 
Preparation of 3-Trimethylsilylpropyl 2-cyanoacrylate 
3-trimethylsilylpropyl 2-cyanoacetate (31.84 g, 0.16 moles) prepared as 
described in Example 1, was added dropwise over 10 minutes to a stirred 
solution of paraformaldehyde (4.8 g, 0.16 moles formaldehyde) and 
piperidine (0.12 g) in n-butylacetate at 70.degree. C. The mixture was 
heated under reflux in a Dean-Stark apparatus until the quantitative 
amount of water expected from formaldehyde condensation had been collected 
(2.8 g). The mixture was allowed to cool and phosphorous pentoxide (0.57 
g), p-toluenesulfonic acid (1.09 g) and 1,4-hydroquinone (2.18g) were 
added. The solvent was removed by distillation under reduced pressure to 
yield a viscous, orange/yellow coloured liquid. The liquid was 
fractionated under reduced pressure to give crude monomer (16.80 g b.p. 
150.degree.-180.degree. C. at 0.7-10 mbar). Vacuum distillation of the 
crude material onto a catalytic quantity of methanesulfonic acid and 
1,4-hydroquinone (10.sup.-4 g) afforded the pure product 
3-trimethylsilylpropyl 2-cyanoacrylate as a slightly yellow coloured 
reactive liquid (12.45 g, 37%). 
Spectral analysis confirmed the structure of the product to be: 
##STR25## 
.sup.1 Hmr, 60MH.sub.z (CDCl.sub.3 ), 
.tau.10.0, singlet, 9H, Si--(CH.sub.3).sub.3 
.tau.9.5, multiplet, 2H, --CH.sub.2 --Si 
.tau.8.3, multiplet, 2H, --CH.sub.2 -- 
.tau.5.8, triplet, 2H, O--CH.sub.2 -- 
.tau.3.2, doublet, 2H, CH.sub.2 .dbd.C, J.sub.H-H =25H.sub.Z 
I.R. (NaCl, film) 
2950 cm.sup.-1 --C--H stretching vibration 
2230 cm.sup.-1 --C.tbd.N stretching vibration 
1740 cm.sup.-1 
##STR26## 
stretching vibration 1615 cm.sup.-1 C.dbd.C conjugated, stretching 
vibration 
EXAMPLE 3 
Vapour Deposition & Polymerization of 3-trimethylsilylpropyl 
2-cyanoacrylate 
Photoresist layers of poly(3-trimethylsilylpropyl 2-cyanoacrylate) were 
prepared by a vapour phase deposition process of the corresponding 
monomer, prepared as described in Example 2, according to the following 
procedure. A polished silicon wafer three inches in diameter was activated 
by pouring a sufficient quantity of a solution of 10% N, N, N, 
N-tetramethylethylenediamine (TMED) in 1,1,1,3,3,3-hexamethyldisilazane 
(HMDS) to cover the surface. The wafer was then spun at 4,000 rpm to 
restore the mirror finish and mounted in the top of closed cylindrical 
chamber 11 cm. in diameter consisting of an aluminium base and plastic 
sides 2 cm in height into which 2.0 grams of monomer 
3-trimethylsilylpropyl 2-cyanoacrylate had been placed. The chamber was 
mounted on thermostatically controlled hot plate and preheated to 
40.degree. C. prior to the introduction of the activated wafer. The wafer 
was mounted such that the treated polished side was located 2 cm directly 
above the heated monomer liquid and in contact with its vapour. A thin 
polymer film was formed on the silicon wafer during its exposure to the 
vapour. 
The process was repeated for different periods of exposure to monomer 
vapour and it was found that the amount of material deposited and hence 
the film thickness was directly related to the vapour exposure as the 
following data indicates: 
______________________________________ 
Wafer Vapour Exposure 
Weight of Re- 
Calculated Film 
Sample No. 
Time (mins) sist Film (mg) 
Thickness (.mu.m) 
______________________________________ 
1 10 0.86 0.19 
2 17 1.04 0.23 
3 30 2.11 0.46 
4 40 3.14 0.69 
______________________________________ 
Assuming a density of 1 g.cm.sup.-3 for the polymer film, the corresponding 
film thickness may be calculated according to the relationship: 
##EQU1## 
where d=film thickness in .mu.m 
m=mass of deposited polymer in mg 
r=radius of the silicon substrate in mm 
The process was repeated with the monomer temperature adjusted to 
50.degree. C. In this case, it was also found that the quantity of polymer 
deposited was directly related to the period of vapour exposure but the 
rate of deposition was greater at the higher temperature. The results at 
50.degree. C. were as follows: 
______________________________________ 
Wafer Vapour Exposure 
Weight of Re- 
Calculated Film 
Sample No. 
Time (Mins) sist Film (Mg.) 
Thickness (.mu.m) 
______________________________________ 
5 15 1.90 0.42 
6 30 3.92 0.86 
______________________________________ 
By plotting the vapour exposure time against the calculated film thickness 
the polymer deposition growth rates were found (from the slopes of the 
lines) to be 0.017 and 0.029 .mu.m min.sup.-1 for 40.degree. and 
50.degree. C. respectively (cf. FIG. 1). 
EXAMPLE 4 
Ultraviolet Light Lithographic Evaluation of Poly(3-methylsilylpropyl 
2-cyanoacrylate) resist 
A silicon wafer, 3 inches in diameter was vapour coated with 2.1 milligrams 
(0.46 .mu.m) of poly (3-trimethylsilylpropyl 2-cyanoacrylate) by the 
procedure described in Example 3. The coated wafer was then imagewise 
exposed to ultraviolet (UV) light from a medium pressure mercury arc lamp 
(operating at 80 Wcm.sup.-1) through a 4 inch (10 cm) square chrom plated 
quartz test mask which had alternate opaque and transmissive elements of 
varying sizes over the range 1000-1 micrometers patterned on the surface. 
To ensure adequate contact between the mask and coated wafer, a copper 
plate 4 inches (10 cm) square and 5/8 inches (1.6 cm) in thickness with a 
2 inch (5 cm) square centralized hole was placed on the perimeter of the 
mask. The weight of the copper plate was 1 kilogram. The coated wafer, 
mask and copper plate assembly was located directly below the arc lamp 
such that the distance between the arc and wafer was 20 cms. The wafer was 
exposed to UV light for 120 seconds, cooled to room temperature and 
immersed for 30 secs. in a bath of developer solvent, prepared by blending 
one part of toluene with 4 parts of petroleum spirit b.p. 
40.degree.-60.degree. C. During this period, a negative tone relief image 
of the mask pattern had formed in the resist layer. A microscopic 
examination of the imaged wafer showed minimum feature sizes of 2.5 .mu.m. 
In all cases unexposed resist was cleanly removed by the developer 
solvent. 
EXAMPLE 5 
Electron Beam Lithographic Evaluation of Poly(3-trimethylsilylpropyl 
2-cycanoacrylate) resist 
A silicon wafer, 3 inches in diameter was vapour coated with 3.55 
milligrams (0.78 .mu.m) of poly(3-trimethylsilylpropyl 2-cyanoacrylate) by 
the method described in Example 3. The coated wafer was scribed and broken 
in small pieces approximately 10.times.10 mm.sup.2 in size. The small 
wafers were mounted in a scanning electron microscope and exposed to an 
electron beam, O.1 .mu.m in diameter, at an accelerating voltage of 25 KV 
for varying current beam densities (radiation dose) over the range 41-205 
.mu.C.cm.sup.-2. A series of 8 lines 10, 5, 2, 1, 0.8, 0.6, 0.4 and 0.3 
.mu.m were irradiated in a vector scan mode. Following irradiation, the 
wafers were developed by immersion in a bath of a toluene/petroleum spirit 
blend (4:96) for 60 secs. followed by rinsing with isopropyl alcohol for 
60 secs. 
In all cases where imaging occurred, a negative tone was observed which 
indicates that the solubility of the resist decreases on exposure to 
electron beams. This may be indicative of an electron beam induced 
crosslinking reaction. The results obtained were as follows: 
______________________________________ 
Sample Current Beam Developed 
No Density (.mu.C.cm.sup.-2) 
Lines (.mu.m) 
______________________________________ 
7-1 41 None 
7-2 82 None 
7-3 123 10 and 5 
7-4 164 10,5 and 2 
7-5 205 10,5 and 2 
______________________________________ 
In all cases, the development solvent removed all resist not exposed to the 
electron beam. 
EXAMPLE 6 
Evaluation of the Plasma Etch Resistance of Poly(3-trimethysilylpropyl 
2-cyanoacrylate) 
A silicon wafer approximately 1 cm.sup.2 was vapour coated with 0.8 um of 
poly (3-trimethylsilylpropyl 2-cyanoacrylate) (PTSCA) according to the 
procedure described in Examples 3 and 5. The resist coated wafer was 
placed in a plasma reactor along with a similar substrate which had been 
sputter coated with 1.0 .mu.m of silicon dioxide (SiO.sub.2) and exposed 
to a plasma of argon and trifluoromethane (Ar/CHF.sub.3) under reactive 
ion etching conditions at 120 watts for sufficient time to allow the 
etching rates to be determined. For comparative purposes, a similar 
substrate was vapour coated with 1.2 .mu.m of poly(ethyl 2-cyanoacrylate) 
(PECA) and the plasma etching rate of this resist relative to SiO.sub.2 
was also measured under similar conditions. The results obtained were as 
follows: 
______________________________________ 
Resist Etch SiO.sub.2 Etch 
Resist/SiO.sub.2 Etch 
Resist Rate .ANG..min.sup.-1 
Rate, .ANG..min.sup.-1 
Rate Ratio 
______________________________________ 
PTSCA 106 312 0.34 
PECA 180 292 0.62 
______________________________________ 
These results demonstrate a significant improvement in the etch resistance 
of the silicon containing cyanoacrylate resist compared to a similar 
photoresist which does not contain silicon. 
The etch rate of PTSCA resist in an oxygen plasma was also determined in a 
related experiment. In this case, the etch resistance was compared not 
only to PECA but also to a number of commercially available photoresist 
products. The results obtained are as follows: 
______________________________________ 
Etch Rate, Relative Etch 
Resist O.sub.2 Plasma, .ANG..min.sup.-1 
Resistance to PECA 
______________________________________ 
PTSCA 162 30.09 
PECA 5000 1 
AZ 4330 (Hoechst) 
2814 1.8 
Microposit 2400 (Shipley) 
2172 2.3 
Photoresist 1400-27 (Shipley) 
2437 2.1 
______________________________________ 
The experiment shows that the silicon containing PTSCA is over 30 times 
more resistant to O.sub.2 plasma than non silicon containing PECA resist 
and approximately 15 times more resistant to a number of popular 
commercial products, 
Poly(3-Trimethylsilylpropyl 2-cyanoacrylate) as contact mask for Plasma and 
Deep Ultra Violet (DUV) Imaging of Planarizing Layers in Multilayer 
Photoresists (FIG. 2) 
Examples 4-6 demonstrate the utility of the new polymer as a solvent 
developed, negative acting, single layer photoresist having outstanding 
resistance to plasma etching. The polymer is, however, also suitable as an 
imaging mask layer in a multilayer photoresist system. Multilayer resists 
are usually designed to separate the imaging function of a photoresist 
from its planarizing function and the technique is particularly useful 
where relief images over stepped features are required. A typical 
multilayer photoresist consists of an underlying relatively thick (1-5 
.mu.m) planarizing layer over which a thin imaging layer (0.1-0.3 .mu.m) 
is deposited. The polymeric materials of the present development are 
particularly suitable for use as the thin imaging layer of multilayer 
resist system and function as a plasma or DUV contact mask ensuring image 
transfer through the planarizing layer to the substrate surface. This 
process is shown schematically in FIG. 2. 
Referring to FIG. 2, the first step involves the application to a substrate 
10 of a relatively thick planarizing layer 12 which may consist of any 
O.sub.2 plasma or DUV sensitive polymeric material such as 
poly(methylmethacrylate) (PMMA). The polymer is applied by conventional 
means for example by spin casting from solution onto a substrate and 
baking to remove solvent. The polymeric solution may optionally contain a 
small quantity of a non-volatile anionic polymerization initiator such as 
an amine or phosphine (e.g. 0.01% piperonylamine). Alternatively, the 
surface of the dry polymer may be activated by a short exposure to vapour 
of a volatile amine (e.g. 2 mins. exposure to a solution of 50% 
hexamethyldisilazane in triethylamine). The planarizing layer 12 is next 
exposed to monomer 3-trimethylsilylpropyl 2-cyanoacrylate and the imaging 
layer 14 is grown (typically 0.1-0.3 .mu.m film thickness). The preferred 
method of growth is by the vapour deposition procedure as outlined in 
Example 3 although the polymer may also be grown by immersion of the 
substrate in a solution of the monomer dissolved in a suitable solvent 
(e.g. two minutes immersion in 5% solution in petroleum spirit) or by spin 
casting from solution. 
The bi-layer photoresist is then imagewise exposed to UV light through a 
mask 16 and the image developed as described in Example 4 (FIG. 2, step 
A). The photoresist is then exposed to an oxygen plasma for sufficient 
time to etch the planarizing layer and expose the substrate (FIG. 2, step 
B). Since the plasma etches anisotropically, relief images with excellent 
aspect ratios are achieved particularly over stepped features. 
Alternatively to plasma imaging, the imaged hi-layer resist may be flood 
exposed to DUV irradiation and the planarizing layer developed by means of 
a suitable solvent. The process described here may be modified to include 
the deposition of an isolation layer to prevent intermixing of the 
planarizing and imaging layer or the deposition of a DUV dye layer between 
the planarizing and imaging layer to enhance the contrast and resolution 
of the photo resist. 
Process for Preparing Positive Relief Images of Poly 
(3-trimethylsilylpropyl 2-cyanoacrylate) (FIG. 3) 
The lithographic examples relating to the above polymer so far described 
have been concerned only with the generation of negative tone images. It 
is however possible to provide positive tone images based on the above 
resist provided that the imaging step is carried out prior to deposition 
of the polymer. 
This process, illustrated schematically in FIG. 3, is achieved by first 
coating a layer 23 of a photosensitive latent acid catalyst (i.e. a 
material capable of producing strong acid on exposure to radiation) over 
the substrate 20. This coating may preferably be a modified planarizing 
layer (e.g. 4 .mu.m PMMA) or alternatively may be placed directly over a 
planarising layer 22. In the latter case, the layer 23 is conveniently 
referred to as an inhibitor layer (e.g. 0.2 .mu.m film of poly 
(4-methoxystyrene) containing 20% by weight of CE 1014, a commercially 
available latent acid catalyst supplied by General Electric Corp. ). The 
layer(s) 22, 23 are deposited by conventional spin coating methods and 
preferably contain a small quantity of cyanoacrylate polymerization 
initiator. Useful latent acid catalysts include triarylsulfonium and 
diaryliodonium salts containing non-nucleophilic counterions and benzene 
sulfonate esters of benzoin and should account for between one and 30% of 
the dry polymer weight. Irradiation of the layer(s) 22, 23 through a mask 
25 at wavelengths corresponding to the absorption characteristics of the 
latent acid, produces a pattern of strong acid in the inhibitor layer 
which corresponds to a positive image of the mask pattern (FIG. 3, Step 
A). 
The patterned resist is next exposed to monomer 3-trimethylsilylpropyl 
2-cyanoacrylate, preferably by vapour deposition as described in Example 3 
although solution methods may also be used to selectively grow the 
corresponding polymer 28 on the unexposed regions of the inhibitor or 
photosensitive layer (FIG. 3, Step B) 
Polymer 28 does not grow on the exposed areas 30 where the photogenerated 
strong acid inhibits the anionic polymerization of the monomer. It is 
important to ensure that concentration of photogenerated acid exceeds the 
concentration of anionic polymerization initiator included in the 
planarization or inhibitor layers. Thus a positive tone relief image of 
the mask is transferred into the photosensitive/inhibitor layer without 
the need for a solvent development step. 
The imaged resist is next exposed to an oxygen plasma for sufficient time 
to transfer the image through the photosensitive/inhibitor and planarizing 
layer (if present) to expose the substrate (FIG. 3, Step C). This step may 
be preceded by flood exposing the coated wafer to DUV light to alter the 
solution characteristics of the plasma mask. 
Alternatively, the image may be transferred by first flood exposure to DUV 
light and developing the image in a suitable solvent. The process is shown 
schematically in FIG. 3.