Fine pattern forming method

The fine pattern forming method includes the steps of applying an organic polymer film on a semiconductor substrate and heat treating the same; applying a resin solution (including an acid degradation polymer or an acid reactive monomer, an acid generator capable of generating an acid by irradiation with an electric charged beam, and a silicone resin) on the organic polymer layer and heat treating the same; carrying out a heat treatment after a pattern is written, causing the generated acid to react with the acid degradation polymer or the acid reactive monomer and carrying out a development in an alkaline solution to form a resist pattern; and etching the organic polymer layer using the resist pattern as a mask. The use of the resist layer including the silicone resin, the acid generator, and the acid degradation polymer or the acid reactive monomer enables an accurate fine resist pattern to be formed which has a high sensitivity and dry etching resistance, and in which charging is prevented when a pattern is written by a charged beam.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a fine pattern forming material used when 
semiconductor devices and integrated circuits are made by forming a 
pattern thereon using an electron beam, and to a fine pattern forming 
method using such material. 
2. Description of the Prior Art 
Conventionally, in the manufacture of ICs and LSI circuits, patterns are 
formed by photolithography using ultraviolet rays. To cope with a 
requirement to make devices smaller in size, a numerical aperture of a 
stepper lens is increased and a light source having a shorter wavelength 
is used, which results in a drawback in that a focus depth is shortened. 
Further, as a pattern of LSI devices is made finer in size and ASICs are 
put into production, electron beam lithography has been used 
Positive type electron beam resists are indispensable to form a fine 
pattern by electron beam lithography. Polymethyl methacrylate (PMMA) is 
known as a resist having the best resolution among them, but it has a 
drawback of low sensitivity. Thus, recently, there have been numerous 
reports relating to improving the sensitivity of positive type electron 
beam resists, in which reference is made to positive type resists such as 
polybutyl methacrylate, a copolymer of methyl methacrylate and methacrylic 
acid, a copolymer of methacrylic acid and acrylonitrile, a copolymer of 
methyl methacrylate and isobutylene, polybutene-1-sulfon, polyisopropenyl 
ketone, fluoro polymethacrylate, and the like. These resists, which aim at 
an improvement in sensitivity, are arranged such that an electron 
withdrawing group is introduced to the side chain or an easily degradable 
bond is introduced to the principal chain thereby to enable an electron 
beam to easily scissor the principal chain, but they cannot sufficiently 
improve both resolution and sensitivity. Further, since they do not have 
sufficient dry etching resistance and heat resistance, they are difficult 
to be used as a mask for dry etching, and thus a field to which they are 
applicable is limited. 
Negative type electron beam resists using cyclized rubber as a base have 
inferior adhesion to a substrate, thus suffering a drawback in difficulty 
in forming a coated uniform layer of high quality without pin holes on the 
surface of the substrate and inferior heat stability and resolution. 
Therefore, conventionally, various improvements have been made to the 
negative type electron beam resists. For example, negative type electron 
beam resists such as polyglycidyl methacrylate, chloro methyl polystyrene, 
chloro methyl .alpha.- methyl polystyrene, polymethacrylate maleic acid 
ester, polystyrene chrolide, a copolymer of glycidyl methacrylate and 
ethyl acrylate, and the like are reported. These resists, which aim at an 
improvement in sensitivity, are arranged such that an epoxy group easily 
reactive to electrons and chlorine atoms are introduced thereby to enable 
an electron beam to easily produce a radical to cause a cross-linking 
reaction, but do not have sufficient resolution and heat resistance. 
Although an organic solvent is needed to develop these negative type 
resists comprising a rubbery thermoplastic polymer using a cyclized rubber 
or polyisoprene as a base, the resists on which a pattern is written may 
be swelled in the organic solvent developer while they are developed. As a 
result, the resolution of the pattern is lowered, and sometimes the 
pattern is distorted and unable to be used. In addition, the organic 
solvent developer is harmful to the environment and health and further is 
not desirable from the view point of the igniting property thereof. 
Electron beam lithography has such drawbacks as an adverse effect to a 
pattern accuracy caused by the inferior dry etching resistance and heat 
resistance of electron beam resists and a proximity effect due to forward 
and backward scattering of electrons, and an adverse effect to a pattern 
drawing due to charging by incident electrons, and the like. A multi-layer 
resist, the function of which is shared by its pattern forming layer and 
planarizing layer, is very effective to compensate for these drawbacks. 
FIGS. 3A to 3D are diagrams explaining a multi-layer resist process 
applied to the electron beam lithography. To suppress the proximity 
effect, an organic polymer film is applied to a thickness of 2 to 3 
microns as a bottom layer 31 and subject to a heat treatment (FIG. 3A). 
Further, an inorganic film of SiO.sub.2 or the like, or an inorganic 
polymer film of SOG (spin on glass) or the like is applied thereon to a 
thickness of 0.2 micron as an intermediate layer 32, and an electron beam 
resist is applied to a thickness of 0.5 micron as a top layer resist 33. 
An aluminum film 34 of about 100 Angstroms is deposited thereon to prevent 
charging (FIG. 3B). After a pattern is written by an electron beam, the 
aluminum film 34 is removed with an alkaline solution, then a development 
is carried out to obtain a resist pattern 33P (FIG. 3C). Next, the 
intermediate layer 32 is dry etched using the resist pattern 33P as a 
mask, and further the bottom layer 31 is dry etched using the intermediate 
layer 32 as a mask (FIG. 3D). The use of the above multi-layer resist 
process enables a fine pattern to be formed at a high aspect ratio. In the 
multi-layer resist process in which the aluminum film is deposited, 
however, manufacturing processes are more complex and have such problems 
as contamination, an increase in dimensional shift caused when a pattern 
is transferred, and the like, and thus this process is not applicable to 
actual use. 
As described above, although the multi-layer resist process using an 
aluminum film is an effective method, it has the problem of complex 
manufacturing processes, contamination of aluminum, and dimensional 
variation of the resist when the pattern is transferred. 
Further, a multi-layer process not using an aluminum film has a problem of 
charging, which is a phenomenon wherein incident electrons are stored in a 
resist, an intermediate layer or a bottom layer, all being insulators. The 
charging effect causes a serious problem such as deterioration of a field 
butting accuracy and overlay accuracy, and the like in the electron beam 
lithography. In addition, the charging phenomenon is also observed in a 
single layer resist and causes the deterioration of a field butting 
accuracy and overlay accuracy, as in the three-layer resist. More 
specifically, incident electrons scattered in a resist in the electron 
beam lithography stay in a region at a depth of 1 to 1.5 microns from the 
surface of the resist and a charge is stored in this region. It is 
supposed that the stored charge causes an electron beam to be curved 
thereby to deteriorate the field butting accuracy and overlay accuracy. 
When a pattern is written by an electron beam, a thick bottom layer must be 
applied, because a pattern accuracy is greatly affected by the proximity 
effect. Thus, a silicon containing resist, inorganic resist, and the like, 
which not only serve as a mask for the bottom layer but also serve as a 
resist layer, have been developed. They include a resist having a siloxane 
bond coupled to the principal chain thereof, ladder type polysiloxane, a 
chalcogenide glass type inorganic resist and the like, but cannot yet 
sufficiently improve dry etching resistance and also has inferior 
sensitivity and resolution. Thus they are far from achieving practical 
use. Since these resists employ an organic solvent as a developer, they 
have a large variation in sensitivity and dimension, a smaller process 
margin, and a problem of environmental pollution and the like. 
Since a charging phenomenon is also caused in the two-layer resist process, 
as in the three-layer resist process, an aluminum film is deposited on a 
resist to prevent the occurrence of charging. Further, the resist process 
using an aluminum film has a problem in that a novolac type resist using 
an organic alkaline solution as a developer cannot be used, because an 
alkaline solution is used to remove the aluminum film. 
The present inventors have developed highly sensitive conducting electron 
beam resists and a fine pattern forming method using the resists to solve 
these phenomena. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a material capable of 
forming a resist film having high sensitivity and dry etching resistance 
when an electric charged beam direct writing is carried out by an electric 
charged beam such as an electron beam, focused ion beam, or the like using 
multi-layer resists, and a method of forming an accurate fine resist 
pattern without a pattern deformation caused by charging using the 
material. 
To achieve the above object, according to the present invention, an 
arbitrary accurate fine resist pattern without a pattern deformation 
caused by charging while writing is carried out is formed by using a 
material comprising a silicone resin, an acid generator, and an acid 
degradation polymer or an acid reactive monomer. 
A fine pattern forming material according to the present invention 
comprises an acid degradation polymer, an acid generator capable of 
generating an acid when an electron beam is radiated, and a silicone resin 
containing silicon atoms in the principal chain or side chain thereof. 
A conducting polysilane polymer or a conducting polysilicone polymer is 
preferably used as the silicone resin. 
Further, the present invention provides a fine pattern forming method 
comprising the steps of applying an organic polymer film on a 
semiconductor substrate and heat treating the same, applying a resin 
solution comprising an acid degradation polymer, acid generator capable of 
generating an acid by the irradiation with an electric charged beam, and a 
silicone resin on the organic polymer film and heat treating the same, 
carrying out a heat treatment after a pattern is written, causing the 
generated acid to react with the acid degradation polymer and carrying out 
a development in an alkaline solution to form a resist pattern, and 
etching the organic polymer film using the resist pattern as a mask. 
Further, the present invention provides a fine pattern forming material 
comprising an acid reactive monomer, an acid generator capable of 
generating an acid when an electron beam is radiated thereto, and a 
silicone resin having the principle chain or side chain thereof containing 
silicon atoms. 
Further, the present invention provides a fine pattern forming method 
comprising the steps of applying an organic polymer film on a 
semiconductor substrate and heat treating the same, applying a resin 
solution comprising an acid reactive monomer, an acid generator capable of 
generating an acid by the irradiation with an electric charged beam, and a 
silicone resin on the organic polymer film and heat treating the same, 
carrying out a heat treatment after a pattern is written, causing the 
generated acid to react with the acid reactive monomer and carrying out a 
development by an alkaline solution to form a resist pattern, and etching 
the organic polymer film using the resist pattern as a mask. 
According to the present invention, an accurate fine pattern without a 
pattern deformation caused by charging can be easily formed by the above 
conducting silicon containing electron beam resists and the resist process 
using them. In particular, an accurate fine resist pattern can be formed, 
wherein the deposition of an aluminum film does not needed, a problem of 
contamination is not arise, a resist process can be simplified, no 
dimensional shift is caused when a pattern is transferred, a highly 
sensitive alkaline solution can be used as a developer, and charging 
caused by writing electrons is prevented. As a result, an accurate fine 
pattern having high resolution can be formed by the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS 
First, an outline of the present invention will be described. The present 
invention intends to solve the above problems by using a three-component 
type material comprising an acid generator capable of generating an acid 
by the irradiation with an electric charged beam, e.g., an electron beam, 
focused ion beam, etc., a polymer to be degraded by the acid, and a 
silicone resin. Further, a conducting polysilane is used as the silicone 
resin. 
The acid generator capable of generating an acid by irradiation with an 
electric charged beam includes halogenide organic compounds, onium salts, 
and the like. The halogenide organic compounds include, for example, 
1,1-bis[p-chlorophenyl]-2,2,2-trichloroethane, 
1,1-bis[p-methoxyphenyl]-2,2,2-trichloroethane, 
1,1-bis[p-chlorophenyl]-2,2-dichloroethane, 
2-chloro-6-(trichloromethyl)pyridine, and the like. Further, the onium 
salts include the following substances, and the like: 
##STR1## 
These compounds generate a Lewis acid as a strong acid by the irradiation 
with an electric charged beam such as an electron beam. 
The polymer (also referred to herein as acid degradation polymer) to be 
degraded by the acid preferably includes, for example, the following 
compounds which have a C--O--C bond at the principal chain or side chain 
thereof: 
##STR2## 
These compounds allow the following reaction to proceed in the presence of 
an acid, which is converted into a substance having alkaline solubility. 
##STR3## 
Further, the silicone resins used here as a matrix polymer must have 
alkaline solubility, and the following resins, for example, have the 
alkaline solubility. 
##STR4## 
Writing a pattern by an electric charged beam causes the acid generator to 
generate a Lewis acid, by which the polymers having a C--O--C bond are 
degraded and made alkaline-soluble. Since the silicone resins are 
originally alkaline soluble, a region where a pattern is written is 
dissolved in an alkaline developer, and since the acid degradation polymer 
acts as a dissolution inhibitor, a region where a pattern is not written 
is difficult to be dissolved in an alkaline solution, so that a positive 
type pattern can be formed. 
Further, since these silicone resins have a low surface resistance and are 
a conducting polymer, they can prevent the occurrence of charging caused 
when the pattern is written. 
The use of these silicon containing substances as an upper-layer resist of 
a two-layer resist enables a multi-layer resist to be easily formed. This 
multi-layer resist can easily form an accurate positive type fine resist 
pattern, in which no charging is caused, because the multi-layer resist 
has sufficiently high dry etching resistance, sufficiently high 
sensitivity due to chemical amplification, and conductivity, and which is 
not bad for the environment and human bodies, because it can use an 
alkaline solution as the developer. 
Further, the above problems can be also solved by using, as a resist, a 
three-component type material comprising an acid generator capable of 
generating an acid by the irradiation with a charged beam, e.g., an 
electron beam, a monomer to be reacted by the acid, and a silicone resin. 
Conducting polysilane and the like can be used as the silicone resin. 
The acid generator includes halogenide organic compounds, onium salts, and 
the like, as described above. 
The monomer to be reacted by the acid includes melamine, methylol melamine, 
and the like. Methylol melamine is represented by the following formula, 
in which --OH base is eliminated by acid: 
##STR5## 
These compounds cause a cross-linking reaction with the silicone resin as 
a matrix polymer. 
##STR6## 
R:H, CH.sub.2 OH, etc. The above cross-linking reaction proceeds to form 
the three-dimensional cross-linkage in the silicone resins. Writing a 
pattern by an electron beam, for example, causes the acid generator to 
produce a Lewis acid, by which the monomer such as melamine or the like is 
reacted with the silicone resin to form a cross-linking structure Since 
the silicone resins originally have alkaline solubility, a region where a 
pattern is not written is dissolved in an alkaline developer, and a region 
where a pattern is written is difficult to be dissolved in an alkaline 
solution, because it is cross-linked, so that a negative type pattern is 
formed. 
Further, these silicone resins have a low surface resistance and are 
conducting polymers, they can prevent the occurrence of charging caused 
when the pattern is written. 
The use of these silicon containing substances as an upper-layer resist of 
a two-layer resist enables a multi-layer resist to be easily formed. This 
multi-layer resist can easily form an accurate negative type fine resist 
pattern, in which no charging is caused, because the multi-layer resist 
has sufficiently high dry etching resistance, sufficiently high 
sensitivity due to chemical amplification, and conductivity, and which is 
not bad for the environment and human bodies, because it can use an 
alkaline solution as the developer. 
EXAMPLE 1 
FIG. 1 A-D shows an embodiment according to the present invention. An 
organic polymer film was applied on a semiconductor substrate 11 to a 
thickness of 2 microns as a bottom layer 12 and baked at 220.degree. C. 
for 20 minutes (FIG. 1A). A substance obtained in the following Example 2 
was applied thereon to a thickness of 0.5 micron as an upper layer 
electron beam resist 13 and baked at 90.degree. C. for 20 minutes (FIG. 
1B). Next, a pattern was written by an electron beam with an accelerating 
voltage of 20 KV and a dosage of 10 .mu.C/cm.sup.2. Baking was carried out 
at 120.degree. for 20 minutes, and deesterification by the generated acid 
was accelerated. The wafer was developed in an alkaline solution for 6 
minutes, whereby an accurate positive type fine resist pattern 13P could 
be obtained (FIG. 1C). The bottom layer 12 was etched using the resist 
pattern as a mask to obtain an accurate vertical fine resist pattern (FIG. 
1D). As described above, according to the present invention, when a highly 
sensitive silicon containing resist is used as the upper layer resist of a 
two-layer resist, a highly accurate positive type fine resist pattern can 
be formed. 
EXAMPLE 2 
An acid generator consisting of 
1,1-bis[p-chlorphenyl]-2,2,2-trichloroethane in an amount of 1.0 g, ethyl 
polymethacrylate in an amount of 10 g, and poly(p-hydroxyphenylsiloxane) 
in an amount of 15 g were dissolved in an ethyl celosolve acetate solution 
to make a mixture. The mixture was slowly stirred at 25.degree. C. for 5 
minutes and a uniform solution was prepared by filtering out insoluble 
substances therefrom. The solution was dropped onto a semiconductor 
substrate and spin coated at 2000 rpm for 2 minutes. The wafer was baked 
at 90.degree. C. for 20 minutes, whereby a resist film having a thickness 
of 1.0 micron could be obtained. Next, a pattern was written with an 
accelerating voltage of 30 KV and a dosage of 10 .mu.C/cm.sup.2, then the 
wafer was baked at 110.degree. C. for 20 minutes. Then the 
deesterification of ethyl polymethacrylate was accelerated by the 
generated acid. When the wafer was developed in an organic alkaline 
solution for 6 minutes, an accurate positive type fine resist pattern 
could be obtained. 
EXAMPLE 3 
A mixture was prepared by dissolving an acid generator consisting of 
1,1-bis[p-methoxyphenyl]-2,2,2-trichloroethane in an amount of 1.0 g, 
poly(p-vinyl benzoate) in an amount of 10.0 g, and 
poly(p-hydroxyphenylsilane) in an amount of 15 g in a celosolve acetate 
solution, in the same manner as in Example 2. The mixture was slowly 
stirred at 25.degree. C. for 5 minutes and a uniform solution was prepared 
by filtering out insoluble substances therefrom. The solution was dropped 
onto a semiconductor substrate and spin coated at 2000 rpm for 2 minutes. 
The wafer was baked at 90.degree. C. for 20 minutes thereby to obtain a 
resist film having a thickness of 1.0 micron. Next, a pattern was written 
with an accelerating voltage of 30 KV and a dosage of 10 .mu.C/cm.sup.2, 
and the wafer was baked at 100.degree. C. for 20 minutes. Then the 
deesterification of the poly(p-vinyl benzoate) was accelerated by the 
generated acid. When the wafer was developed in an organic alkaline 
solution for 6 minutes, an accurate positive type fine resist pattern 
could be obtained. 
EXAMPLE 4 
FIG. 2A-D shows a fourth embodiment according to the present invention. An 
organic polymer film was applied on a semiconductor substrate 11 to a 
thickness of 2 microns as a bottom layer 21 and baked at 220.degree. C. 
for 20 minutes (FIG. 2A). A substance obtained in the following Example 5 
was applied thereon to a thickness of 0.5 micron as an upper layer 
electron beam resist 22 and baked at 90.degree. C. for 20 minutes (FIG. 
2B). Next, a pattern was written by an electron beam with an accelerating 
voltage of 20 KV and a dosage of 10 .mu.C/cm.sup.2, baking was carried out 
at 120.degree. C. for 20 minutes and cross-linking by the generated acid 
was accelerated The wafer was developed in an alkaline solution for 6 
minutes, whereby an accurate negative type fine resist pattern 22P could 
be obtained (FIG. 2C). The bottom layer 21 was etched using the resist 
pattern as a mask thereby to obtain an accurate vertical fine resist 
pattern (FIG. 2D). As described above, according to the present invention, 
when a highly sensitive silicon containing resist is used as the upper 
layer resist of a two-layer resist, a highly accurate negative type fine 
resist pattern can be formed. 
EXAMPLE 5 
An acid generator consisting of 
1,1-bis[p-chlorophenyl]-2,2,2-trichloroethane in an amount of 1.0 g, 
methylol melamine in an amount of 2.0 g, and poly(p-hydroxyphenylsiloxane) 
in an amount of 15 g were dissolved in an ethyl cellosolve acetate 
solution to make a mixture. The mixture was slowly stirred at 25.degree. 
C. for 5 minutes and a uniform solution was prepared by filtering out 
insoluble substances therefrom. The solution was dropped onto a 
semiconductor substrate and spin coated at 2000 rpm for 2 minutes. The 
wafer was baked at 90.degree. C. for 20 minutes, whereby a resist film 
having a thickness of 1.0 micron was obtained. Next, a pattern was written 
with an accelerating voltage of 30 KV and a dosage of 10 .mu.C/cm.sup.2, 
and then the wafer was baked at 110.degree. C. for 20 minutes. Then the 
cross-linking of the melamine with the polysiloxane was accelerated by the 
generated acid. When the wafer was developed in an organic alkaline 
solution for 6 minutes, an accurate negative type fine resist pattern 
could be obtained. 
EXAMPLE 6 
A mixture was prepared by dissolving an acid generator consisting of 
1,1-bis[p-methoxyphenyl]-2,2,2-trichloroethane in an amount of 1.0 g, 
methylol melamine in an amount of 2.0 g, and poly(p-hydroxyphenylsilane) 
in an amount of 15 g in a cellosolve acetate solution, in the same manner 
as in Example 5. The mixture was slowly stirred at 25.degree. C. for 5 
minutes and a uniform solution was prepared by filtering out insoluble 
substances therefrom The solution was dropped onto a semiconductor 
substrate and spin coated at 2000 rpm for 2 minutes. The wafer was baked 
at 90.degree. C. for 20 minutes, whereby a resist film having a thickness 
of 1.0 micron could be obtained Next, a pattern was written with an 
accelerating voltage of 30 KV and a dosage of 10 .mu.C/cm.sup.2, and then 
the wafer was baked at 110.degree. C. for 20 minutes, and then the 
cross-linking of melamine with polysilane was accelerated by the generated 
acid. When the wafer was developed in an organic alkaline solution for 6 
minutes, an accurate positive type fine resist pattern could be obtained.