Photosensitive material having a silicon-containing polymer

A silicon-containing polymer comprising repeating units of silicon-containing cyclic compound, represented by a general formula (I) ##STR1## (wherein m and n are zero or a positive integer, respectively, however m+n>0, and X is any of an alkyl group, alkoxy group, phenyl group, naphthyl group, substituted phenyl group and substituted naphthyl group or a mixture of these, and the substituent of said substituted phenyl group or substituted naphthyl group indicates any of halogen atom, halogenated alkyl group, amino group, aminoalkyl group and nitro group or a mixture of these), and a photosensitive material containing said silicon-containing polymer are disclosed.

BACKGROUND OF THE INVENTION 
The present invention relates to a novel silicon-containing polymer and a 
novel photosensitive material containing siloxane linkages, which is 
useful for resist having photosensitive groups responsive to electrons, 
X-rays, UV light and deep UV light as are used when producing 
semiconductor integrated circuits, and which is also usable as an 
insulation film or a protective film. 
The silicon-containing polymers are used in a variety of fields for the 
reasons that they exhibit excellent heat resistance and cold resistance, 
that the electric characteristics thereof are stable over a wide range of 
temperature, and the like. Moreover, silicon-based polymers provided with 
photosensitive group have been recently developed and their uses are 
spreading out in electronic materials. 
In the electronic field, particularly in the production of semiconductors 
(integrated circuits), the processing of substrates at high levels of 
precision has become more complicated and higher precision has been 
required as the degree of circuit integration has become higher. 
Accompanying this, techniques for performing processing at a sub-micron 
scale on substrates at different levels have been proposed and various 
methods have been tried. As one of them, a two-layer resist technique 
using a silicon-based resist as a top layer has been proposed, and has 
recently received much attention. This technique will now be explained. 
A resin or resist having resistance to halogen gas is spin-coated onto a 
bottom layer, which is subject to soft- or hard-baking. Then, a 
silicon-based resist is spin-coated onto the top layer. Using an exposure 
device, the top layer resist is exposed to light and only the top layer is 
developed. Then, using the patterned area of the top layer resist as a 
mask, the bottom layer resist is etched with O.sub.2 gas plasma. Finally, 
using the bottom layer resist as a mask, the substrate is etched with 
halogen gas. 
The functions needed for the top layer resist are as follows: 
(1) To be excellent in resistance to O.sub.2 plasma. 
(2) To be excellent in flatness. 
(3) To have a high glass transition temperature. 
(4) To have high resolution. 
(5) To have high sensitivity. 
Silicon-containing resist materials are excellent in resistance to O.sub.2 
plasma and some resist materials using them are known. As representatives 
thereof, a method of attaching a silyl group directly or indirectly to the 
benzene rings of Novolak resin or polystyrene, a method utilizing a 
polysilane linkage, and, in particular, recently, a method utilizing a 
ladder polymer (silsesquioxane linkage) have been proposed. 
In the case of the type where a silyl group is attached directly or 
indirectly to the benzene rings, however, the problem that the resistance 
to O.sub.2 plasma is insufficient exists because the content of Si is low 
and Si is introduced into a side chain. Moreover, in the case of the 
polysilane type, poor coating property and stability are generally 
encountered, though the content of Si may be increased depending on the 
kind of compounds. Furthermore, in the case of silsesquioxane type 
polymers, there is a problem that the sensitivity is not enough though the 
resistance to O.sub.2 plasma is excellent. 
As described above, at present resist materials with excellent resistance 
to O.sub.2 plasma and excellent flatness which have a high Tg, high 
resolution and high sensitivity have not been developed. 
The present invention was made to overcome the problems as above and the 
purpose thereof is to provide a novel silicon-containing polymer and a 
photosensitive material using the same which is excellent in resistance to 
O.sub.2 plasma, has excellent flatness and which has high Tg, high 
resolution and high sensitivity. 
As a result of diligent studies against such background, the inventors have 
found that by using a polymer having a single siloxane cyclic compound as 
a repeating unit or a copolymer having various siloxane cyclic compounds 
as repeating units, a resist material which is highly sensitive, highly 
flat and excellent in resistance to O.sub.2 plasma and yet having a high 
Tg can be obtained, leading to the completion of the present invention. 
SUMMARY OF THE INVENTION 
Said silicon-containing polymer comprising repeating units of 
silicon-containing cyclic compound is represented by a general formula 
(I). 
##STR2## 
(wherein m and n are positive integers including 0, respectively, however 
m+n&gt;0, and X can be an alkyl group, alkoxy group, phenyl group, naphthyl 
group, substituted phenyl group and substituted naphthyl group or a 
mixture of these, and the substituent of said substituted phenyl group or 
substituted naphthyl group can be a halogen atom, halogenated alkyl group, 
amino group, aminoalkyl group and nitro group or a mixture of these).

DETAILED DESCRIPTION OF THE INVENTION 
The alkyl group being X in the general formula (I) is not particularly 
restricted. In the case of straight alkyl, however, it is each group of, 
for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, 
dodecyl, vinyl, propenyl, butenyl, pentenyl, hexenyl, octenyl, decenyl, 
dodecenyl, or the like, and, in the case of branched alkyl, it is each 
group of, for example, sec-propyl, sec-butyl, t-butyl, 2-methylpropyl, 
2-methylbutyl, neopentyl, 1-methylpentyl, 2-methylpentyl, 4-methylpentyl, 
2-ethylhexyl or the like. Part of the hydrogens in said alkyl group may be 
substituted by a halogen atom such as F, Cl, Br or I and/or by phenyl, 
naphthyl, substituted phenyl or substituted naphthyl group. As a 
substituent in said substituted phenyl or substituted naphthyl, for 
example, chlorine, fluorine, bromine, nitro group, alkyl group, amino 
group or the like can be mentioned. Moreover, in the case of cyclic alkyl, 
each group of cyclopropyl, cyclopropenyl, cyclobutyl, cyclobutenyl, 
cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, cyclooctyl, 
cyclooctenyl or the like can be mentioned. Moreover, also when X is an 
alkoxy group, this is not particularly restricted and, for example, 
methoxy, ethoxy, propoxy, butoxy, pentoxy, phenoxy or the like can be 
mentioned. 
Since the resist material of the invention has a siloxane structure 
containing an Si group on the main chain of the polymer and the content of 
Si is also high, it is very high in resistance to O.sub.2 plasma and 
further, because of the cyclic ring structure, it has a high Tg. Of 
course, when a higher Tg is desired, such can easily be obtained by 
introducing a phenyl group or naphthyl group to the side chain of the Si 
group. 
As the methods to impart photosensitivity, there is a method where one 
allows an Si group or a side chain of an Si group in the polymer of the 
invention to have introduced a photosensitive group, for example, 
halogenated alkyl group, aminoalkyl group or the like, or a method which 
involves adding a photosensitive agent to the polymer of the invention. 
For the method of producing the siloxane polymer of the invention 
represented by the general formula (I), there are two ways to start from 
the monomer and cyclic ring. For example, when starting from a monomer, 
following the reactions are utilized. 
##STR3## 
Moreover, when starting from a cyclic ring, the rearrangement due to a 
Lewis acid or the dissociation reaction of Si-C is utilized. For example, 
##STR4## 
successively, using the reaction 2SiOH.fwdarw.Si--O--Si, the 
polymerization is contemplated (R: arbitrary substituent). 
Furthermore, when using a cyclic ring containing a phenyl group as a 
starting raw material, the following reaction is utilized. 
##STR5## 
In succession, H.sub.2 O or alcohol is allowed to react to convert to SiOH 
or SiOR' (R': arbitrary substituent). As a halogenating agent to be used 
here, acids such as H-Hal (Hal: halogen atom), Hal.sub.2, alkyl halide, 
thionyl halide, sulfonyl halide or the like can be mentioned. 
By adding the photosensitive agent to or introducing the photosensitive 
group into the polymer of the invention produced utilizing the reactions 
aforementioned, the polymer becomes usable as a photosensitive material. 
For introducing the photosensitive group, there is a method of making a 
cyclic ring using a compound which can become the photosensitive group, 
for example, an Si compound having double bond such as H.sub.2 
C.dbd.CH--CH.sub.2 --Si for the side chain of Si. Or, after produced the 
polymer of the invention, the photosensitive group may be introduced into 
the side chain of an Si compound or the photosensitive agent may be added. 
Further, if necessary, coupling of SiOH or SiOR" (R": alkyl group or 
phenyl group) contained in the polymer of the invention may be conducted 
with a silane coupling agent. Still more, if need be, a crosslinking 
agent, sensitizer or the like as are commonly used may be added. 
In the following, the invention will be illustrated in more detail based on 
examples, but the invention is not confined to these. 
PRODUCTION EXAMPLE 1 
To 100 g of ether cooled with ice were added 10 g of .phi. SiHCl.sub.2. 
Then, a small amount of hydrochloric acid (35% aqueous solution) and 50 g 
of chloromethyl methyl ether were added under stirring and the mixture was 
stirred for about 30 minutes under cooling with ice. After the completion 
of reaction, said reaction product was added dropwise into a large amount 
of methanol solution to produce precipitates. Two peaks were recognized on 
analyzing the precipitates with silicon NMR. When fractionating with GPC 
to analyze, these precipitates were confirmed to be a mixture of two kinds 
of compounds, i.e., trisilylcyclosiloxane and tetrasilylcyclosiloxane. 
Then, 5 g of these precipitates were dissolved into 100 g of THF 
(tetrahydrofuran) solution containing approximately 0.5% by weight of 
water and triethylamine was added in a small amount, and the system 
violently stirred. Thereafter, the reaction liquor was added dropwise into 
benzene to precipitate the cyclosiloxane compound. Upon taking an H-NMR of 
these precipitates, a peak originating from SiOH was identified. 
Successively, for the chloromethylation, 5 g of the precipitates 
previously obtained were added into a solution of 100 g of methylal and 8 
g of thionyl chloride, which was adjusted to -20.degree. C. while 
stirring. Then, a Lewis acid (e.g., FeCl.sub.3) was added in small amount 
to allow the polymerization reaction and the chloromethylating reaction to 
progress concurrently. After reaction for about 20 hours, this reaction 
product was added dropwise into a large amount of solution at 0.degree. 
C. comprising methanol and water (1:1) to precipitate the polymer. Upon 
determining the molecular weight after drying, it was found to be 
MW.apprxeq.10000 (in terms of polystyrene) and the content of Cl was 4.1% 
by weight. 
EXAMPLE 1 
To 45 g of DIBK (dibutyl ketone) were added 5 g of polymer in Production 
example 1, which was sufficiently stirred and completely dissolved. Then, 
this was filtered through a 0.2 .mu.m filter to make up a resist solution. 
Following this, OFPR-800 (photoresist made by Tokyo Oka Co.) was coated 
onto a 3 in. silicon substrate so the thickness become 1 .mu.m, which was 
baked for about 30 minutes at 200.degree. C. in an oven. After baking, 
said resist solution was coated while adjusting the number of revolutions 
of a spin coater so the thickness become 0.2 .mu.m. After baking again for 
20 minutes at 80.degree. C., exposure was done with an electron ray 
exposure device. Next, development was performed with a solution of 
1-methoxy-2-propanol/di-n-butyl ether=5/2. The sensitivity at this time 
was 12 .mu.C/cm.sup.2 at an area where the rate of residual resist film 
was 50%. Successively, etching with O.sub.2 gas was performed by the use 
of dry a etching device (RIE). 
______________________________________ 
Etching conditions: 
Gas flow rate 40 SCCM 
RF power 125 W 
0.sub.2 pressure 40 m Torr 
Etching speed 
Resist of the invention 
30 .ANG./min 
OFPR-800 2000 .ANG./min 
______________________________________ 
As above, the resist of the invention was confirmed to be excellent in 
resistance to O.sub.2 plasma. When measuring the resolution with electron 
an microscope, a gap pattern with a line width of 3 .mu.m and a space 
width of 0.2 .mu.m was resolved distinctly. 
EXAMPLE 2 
The resist prepared in Example 1 was spin-coated onto a silicon wafer while 
adjusting the number of revolutions so the thickness become 0.35 .mu.m. 
Thereafter, this was baked for 20 minutes at 80.degree. C. in an oven and 
drawing and development were made by the same technique as that in Example 
1. Thereafter, when baking for 30 minutes at 80.degree. C. or 160.degree. 
C., the line width of the pattern was not changed at either temperature. 
That is to say, it could be confirmed that the flow of resist did not take 
place even if baking at high temperature. 
PRODUCTION EXAMPLE 2 
To 80 g of methylal were added 6 g of commercial hexaphenylcyclotrisiloxane 
(When determining with silicon NMR, two peaks were detected at 33-34 ppm 
and 43 ppm (see FIG. 1). Upon conducting FD-MS measurement 
(electrolytically eliminated ion-mass spectrum), this was confirmed to be 
a mixture of a compound with a mass of 594 originating from 
hexaphenylcyclotrisiloxane and that with a mass of 792 originating from 
octaphenylcyclotetrasiloxane). Further, after adding 10 g of thionyl 
chloride, the mixture was sufficiently stirred and the temperature of the 
solution was adjusted so as to become -20.degree. C. Next, a small amount 
of FeCl.sub.3 catalyst was added to concurrently cause the polymerization 
and the chloromethylating reaction to proceed over a period of 20 hours. 
After the completion of reaction, this reaction product was added dropwise 
into a solution of methanol:water=1:1 to precipitate the polymer. Upon 
measuring the molecular weight with GPC after drying, this was found to be 
MW=39000 and the content of Cl was 6.8% by weight. 
In this polymerization procedure, sampling was made at 10 minutes after the 
addition of catalyst to conduct FD-MS measurement. Results are shown in 
FIG. 2. Further, results of silicon NMR, .sup.13 C-NMR and elemental 
analysis of a sample after the completion of reaction are shown in FIG. 3, 
FIG. 4 and Table 1, respectively. 
From the results of analysis above, the structure of the present polymer is 
assumed as follows: 
##STR6## 
TABLE 1 
______________________________________ 
Results of elemental analysis 
C H Si Cl 
______________________________________ 
Polymer 42.7% 3.6% 24.7% 6.8% 
______________________________________ 
EXAMPLE 3 
Except that 3.5 g of polymer in Production example 2 were dissolved into 48 
g of DIBK, entirely same procedure was used as in Example 1 and 2. 
Sensitivity 
Very high sensitivity was obtained as proved at a 50% rate of residual 
film=2.8 .mu.C/cm.sup.2. 
Etching speed 
Resist of the invention: 20 .ANG./min 
OFPR-800: 2000 .ANG./min 
Resolution 
Distinct gap pattern of L/S=3 .mu.m/0.2 .mu.m was obtained. 
Test for heat resistance 
Even when post-baking was performed for 30 minutes at 80.degree. C. or 
180.degree. C., the line width of the pattern was not changed. 
EXAMPLE 4 
Into 45 g of DIBK were dissolved 3.5 g of the resin of Production example 2 
and 1.2 g of 4,4'-diazidobenzophenone, which was filtered through a 0.2 
.mu.m filter to obtain a resist solution. 
OFPR-800 was coated onto a wafer (3 in.) so the film thickness became 1.2 
.mu.m, which was baked for 30 minutes at 200.degree. C. Next, the resist 
of the invention was coated at 0.2 .mu.m. Closely contacting exposure was 
conducted using PLA-521F (deep UV light). Thereafter, etching was 
performed under the same conditions as in Example 1. 
Sensitivity 
Very high sensitivity was confirmed also to the deep UV light as proven by 
a 70% rate of residual film=2.2 L. I. 
Etching speed 
Resist of the invention: 25 .ANG./min 
OFPR-800: 2000 .ANG./min 
As above, the resist of the invention was confirmed to have sufficient 
resistance to O.sub.2 even when adding a photocrosslinking agent. 
Resolution 
Distinct pattern of L/S=0.5 .mu.m/0.5 .mu.m was obtained. 
As illustrated above, the photosensitive material using the novel 
silicon-containing polymer having a silicon-containing cyclic compound as 
a repeating unit in accordance with the invention is very highly sensitive 
to electrons, X-rays, deep UV light and UV light. Moreover, it has high 
etching resistance to O.sub.2 because the main chain has a siloxane 
linkage and the content of Si is high, and it is also excellent in the 
heat resistance because of cyclic ring, and further it has high 
resolution. It is therefore suitable for the production of semiconductor 
integrated circuit elements such as super LSI.