JPS6259950A - Ionizing radiation sensitive positive type resist - Google Patents

Abstract

PURPOSE:To obtain a positive type resist having high sensitivity to ionizing radiation as well as excellent developability and high resolving power by usnig a copolymer consisting of two kinds of specific methacrylate structural units. CONSTITUTION:This resist consists of the copolymer formed of the structural units expressed by the formula I and the formula II (n is 5-10, R is an alkyl). The copolymer having 10,000-100,000mol.wt. is used. The molar ratio of the structural units expressed by the formula I and the formula II is 50:50-1:99, more particularly preferably 25:75-5:95. Such copolymer is dissolved in, for example, an arom. solvent, etc. and the soln. is coated on a semiconductor substrate or mask substrate. The coating is subjected to a prebaking treatment to form a resist film. The ionizing radiation is irradiated to the resist film according to the conventional practice to draw a pattern. The resist film is then processed with a developing soln. to obtain a resist pattern. Such copolymer has good adhesiveness to the substrate to permit the formation of the uniform thin film. The film has the high sensitivity to the ionizing radiation and the excellent developability as well. The positive image having high resolving power is thus obtd. and the resist is used for a large-scale integrated circuit, lithography, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is suitable for forming fine patterns used in one step of lithography in the production of high-density integrated circuits such as LSIs and VLSIs, or photomasks used in the production thereof. The present invention relates to a positive resist, and more particularly to a positive resist with high sensitivity and high resolution to ionizing radiation.

Problems to be Solved by the Prior Art and the Invention As is well known, in recent years there has been an increasing demand for higher performance and higher integration of semiconductor integrated circuits and the like. For this reason, instead of photolithography using conventional ultraviolet rays, lithography technology uses ionizing radiation with shorter wavelengths and higher energy, such as electron beams, soft X-rays, ion beams, etc. Efforts are being made to establish pattern processing technology.

On the other hand, in order to enable ultra-fine lithography technology by changing the radiation source, the resist material used must also have corresponding properties, that is, it must be sensitive to ionizing radiation, and It must have properties as a resist.

Generally, resist materials used in ultrafine lithography using high-energy IT ionizing radiation are required to have first-order characteristics.

(a) High sensitivity to ionizing radiation.

(b) High resolution.

(c) Good adhesion to the substrate.

(d) It is possible to form a homogeneous thin shield.

(e) Excellent developability.

Conventionally, many ionizing radiation sensitive resists have been developed for use for the above purpose.

These are divided into positive types, in which a decay reaction occurs upon irradiation with ionizing radiation and the irradiated portions become solubilized, and negative types, in which crosslinking reactions occur upon irradiation with ionizing radiation and the irradiated portions become insolubilized. Among these, when compared in terms of resolution, positive types are generally superior to negative types.

Typical conventionally known positive resists include alkyl methacrylates such as polymethyl methacrylate and derivatives in which the alkyl group is substituted with various halogens, as well as olefin resists such as polybutene-1-sulfone. There are sulfone resists, etc.

However, these conventional positive resists sensitive to ionizing radiation have the following drawbacks, and are not necessarily satisfactory as resists for use in ultrafine lithography.

For example, although polymethyl methacrylate has relatively high resolution, it has low sensitivity to ionizing radiation (e.g., 1 x 10-4 corons/a for electron beams).
There is a problem in that it takes time to form a pattern (requiring a dose of irradiation of j or more). Furthermore, halogenated polyalkyl methacrylate is known to have relatively high sensitivity compared to polymethyl methacrylate, but it has the problem of poor adhesion to substrates, so it is difficult to adhere it to substrates such as silicon. The resist pattern easily peels off during development. Furthermore, although olefin sulfone resists, such as polybutene-1-sulfone, have sensitivity that is one order of magnitude higher than that of polymethyl methacrylate, their resolution is not as high as that of polymethyl methacrylate, and their adhesion and There are problems with thermal stability, etc., and it is extremely difficult to set and control the conditions for one lithography process (e.g., developer composition, temperature, processing time, etc.) in order to obtain patterning accuracy that is better than - There is.

Means for Solving the Problems The present invention has been made in view of the problems of the conventional resists described above, and has high sensitivity and high resolution to ionizing radiation, and has good adhesion to the substrate. The object of the present invention is to provide an ionizing radiation-sensitive positive resist having excellent properties and developability.

As a result of research to obtain a resist material that enables ultra-fine lithography, the present inventor found that a polymer in which a fluoroalkyl methacrylate having a long-chain fluoroalkyl group and an alkyl methacrylate were copolymerized in a specific ratio,
The present invention was achieved by discovering that this resist has extremely excellent properties as a positive resist. That is, the present invention.

General formula below It consists of a copolymer of (1) and (2), and has a molecular weight of to and oo.

The present invention relates to an ionizing radiation-sensitive positive resist material characterized in that the resist composition has the following characteristics: -i, ooo, ooo.

(', +4- (n in the formula is 5 to 10. R represents an alkyl group) The ratio of general formulas I and II in the copolymer related to the present invention is so:so to 1:99.In particular, 25 Near 5-5:95
If the proportion of the general formula (1) in the copolymer is preferably 50 mol % or more, the solubility will be significantly reduced, causing problems in the imaging characteristics and making it difficult to obtain the desired sensitivity.

As the alkyl group of R in general formula (■), methyl group,
Ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, n-amyl group, 3
-pentyl group, 2-methyl-1-butyl group.

3-methyl-1-butyl group, n-hexyl group, 2-methyl-1-pentyl group, 2-ethyl-1-butyl group, 4-
Examples include methyl-2-pentyl group, n-heptyl group, 2-heptyl group, and n-octyl group. If the alkyl group of R is made larger than this, polymerization becomes difficult and it becomes difficult to obtain a polymer with a desired molecular weight.

Compounds of general formula (1) and H include, for example, compounds of general formula I: IH, 1) 1.2) 1.2) 1-tridecafluorooctanyl methacrylate, l) 1. IH, 2H, 2
H-pentadecafluorononanyl methacrylate, 1)
1. IH,2H,2) 1-heptadecafluorodecanyl methacrylate, IH2LH,2H,2H-nonadecafluoroundecanyl methacrylate, IH,IH,2H,2
) 1-eicosafluorododecanyl methacrylate, IH
, IH, 2H, 2H-tricosafluorotridecanyl methacrylate. Compounds of general formula H include methyl methacrylate, ethyl methacrylate, rhopropyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-Butyl methacrylate, low amyl methacrylate, 3-pentyl methacrylate, 2-methyl-1-
Butyl methacrylate, 3-methyl-1-butyl methacrylate, n-hexyl methacrylate, 2-methyl-
Examples include 1-pentyl methacrylate, 2-ethyl-1-butyl methacrylate, 4-methyl-2-pentyl methacrylate, n-heptyl methacrylate, 2-hebutyl methacrylate, and n-octyl methacrylate.

The copolymerization method is not particularly limited,
Copolymerization can be carried out by conventional polymerization methods 1, such as emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization.

Next, a method of performing lithography using the resist of the present invention will be described.

First, the resist of the present invention is prepared using aromatic solvents such as benzene and xylene, ketone solvents such as acetone and methyl ethyl ketone, chlorine solvents such as chloroform and ethylene chloride, and ester solvents such as ethyl acetate and methyl cellosolve acetate. , a resist solution of about 3 to 15% by weight having a viscosity suitable for coating is prepared by dissolving it in a mixed solvent.

Next, this resist solution is uniformly applied onto a semiconductor substrate to be processed or a mask substrate by a conventional method such as a spinner coating method, and a prebaking process is performed to form a resist film with a thickness of about 0.1 to 2 μs. . Prebake conditions depend on the type of solvent used, but generally the temperature is 7.
A temperature of 0°C to 180°C and a time of about 20 to 40 minutes is suitable.

Next, a desired portion of the resist film is exposed to an electron beam using a conventional method.
Patterns are drawn by irradiating ionizing radiation such as soft X-rays,
Furthermore, a resist pattern is formed by processing with a developer to selectively dissolve and remove the resist film in the irradiated areas. As the developer, a mixed solvent of a lower alcohol and the same solvents as those used in preparing the resist solution described above is preferably used. The substrate having the resist pattern after development is further subjected to post-bake treatment and scum removal treatment as required, and then etched to form an etched pattern on the exposed portion of the substrate.

The post-bake treatment is performed, for example, at a temperature of 120 to 180° C. and a time of 20 to 40 minutes, and the scum removal treatment is performed, for example, using oxygen plasma at a pressure of 0.8 to ITorr and an output of 100 W for 1 to 2 minutes. This can be done by

After etching, one cycle of one lithography process is completed by removing the resist pattern using a stripping solution or the like.

Example The present invention will be explained in more detail below using examples.

Example 1 lu, to, 2H, zu where n in general formula I is 5
, -tridecafluorooctanyl methacrylate 17.
3% (0.04 mol) and methyl methacrylate in which R in the general formula H is a methyl group 40. Of (0.4 mol) was added to 100 g of tetrahydrofuran (Tl(F), to which azobisisobutyronitrile (AIBN) 0
．． After adding 0.5 g of the mixture, the mixture was reacted at 55° C. for 40 hours in a nitrogen atmosphere. After the reaction, the mixture was poured into methanol to recover the polymer, and the resulting polymer was purified by reprecipitation twice in a THF-methanol system to obtain a copolymer with a yield of 18.5%.

The proportion of methyl methacrylate in the obtained copolymer is
It is 90 mol% by elemental analysis, and the molecular weight is 264 by gel permeation chromatography (GPC).
It was 000.

The above polymer was dissolved in chlorobenzene and filtered through a 0.2-filter to obtain a resist solution having a concentration of 8% by weight. This resist solution was applied onto a chrome mask substrate by a spinner coating method and prebaked at 90°C for 30 minutes to obtain a uniform resist film with a thickness of 5,000 mm. , acceleration voltage 10k
Electron beam irradiation was performed at V. After irradiating with varying exposure doses, immerse it in methyl isobutyl ketone (MIBK):isopropyl alcohol (IPA) = 1:2 for 40 seconds and rinse with isopropyl alcohol. The sensitivity curve was plotted and the exposure amount at which the residual film rate after development was 0 was defined as the sensitivity. The sensitivity of this resist film was 3×10 −′ coulombs/csl.

Furthermore, using this resist, a resist film with a thickness of 5,000 layers was obtained on a chrome mask substrate in the same manner as above, and using an electron beam with a beam diameter of 0.5 μs and an acceleration voltage of 10 kV,
Pattern drawing was performed by irradiating with a dose of 3×10 −′ clones/d. Furthermore, this resist film is coated with MIBK:IPA
= 1:2 for 40 seconds, developed, and washed with IPA for 30 seconds to obtain a resist pattern.

Next, the substrate with the resist pattern was heated to 140℃ for 3
After post-baking for 0 minutes, the exposed portion of the chromium film was etched for 40 seconds by immersing it in an aqueous ceric ammonium nitrate solution. The resist pattern showed sufficient adhesion to the substrate during the wet etching described above. After etching, the substrate was immersed in a stripping solution consisting of a sulfuric acid-hydrogen peroxide mixture at 70 DEG C. for 5 minutes, and then the resist pattern was stripped off to obtain a photomask having a chrome pattern consisting of single lines and spaces.

Example 2 Similar procedure to Example 1 using 25 g (5,79×10-” mol) of 1H,IH,2H,2H-tridecafluorooctanyl methacrylate and 23.2 t (0,23 mol) of methyl methacrylate. A copolymer was obtained.The proportion of methyl methacrylate in the obtained copolymer was 79 moles.

The molecular weight was 235,000.

The obtained polymer was dissolved in chlorobenzene and 0.2-
A resist solution having a concentration of 8% by weight was obtained.

This resist solution was applied onto a silicon wafer having a silicon oxide film with a thickness of 1,500 mm using a spinner coating method, and prebaked at 90°C for 30 minutes to form a uniform resist film with a thickness of 5 mm. This resist film has a beam diameter of 0.25. .

Electron beam with acceleration voltage 10kV 2X10-''!Coulomb/
After irradiation with d MIBK: IPA = 17: 33
The resist pattern was developed by processing with water for 40 seconds, and was washed with IPA for 30 seconds to form a resist pattern.

Next, after performing the same boss baking treatment as in Example 1,
It was immersed in an etching solution prepared by mixing a 40% ammonium fluoride aqueous solution and a 48% hydrofluoric acid aqueous solution in a ratio of 10=1, and etched for 3 minutes.

After etching, the substrate was heated to 5 Torr using oxygen plasma.
The resist was removed by processing under the conditions of 300W, and the
A silicon oxide film pattern consisting of - lines and spaces was obtained.

Example 3 LH, LH, 28, 2H where n in general formula (■) is 7
-Hebutadecafluorodecanyl methacrylate 20.0
A copolymer was obtained in the same manner as in Example 1 using i (3,76 x 10-" mol) and methyl methacrylate 37.67 (0,376 mol). Methyl methacrylate in the obtained copolymer The proportion was 91 mol%, and the molecular weight was 212,000.

The obtained polymer was dissolved in chlorobenzene and 0.2-
A resist solution having a concentration of 8% by weight was obtained.

This resist solution was applied onto a chrome mask substrate using the Spicin coating method and prebaked at 180° C. for 30 minutes to obtain a uniform resist film with a thickness of 6,000.

Next, apply a beam diameter of 0.25 to this resist film. , accelerating electric 10
Pattern writing was performed by irradiation with an electron beam at kV with a dose of 5XIO-' coulombs/layer. Furthermore, this resist film is
IB: IPA = 2:3, process for 1 minute, develop and IPA
A resist pattern was formed by washing for 30 seconds.

Next, the substrate with the obtained resist pattern was heated at iso℃.
After post-baking for 30 minutes, scum removal treatment was performed for 1 minute using oxygen plasma at a pressure of I Torr and an output of 100 W. Next, apply a pressure of 3X 1O-1 to this substrate.
The exposed portion of the chromium film was etched for 5 minutes by reactive sputter etching using a mixed gas of Ca2 and 0□ at Torr and an output of 300 W.

After etching, the resist was peeled off in the same manner as in Example 1 to obtain a photomask having a chrome pattern consisting of 1- lines and spaces.

Example 4 IH,LH,211,2H-hebutadecafluorodecanyl methacrylate 10.6 molecules (1,99x 10-”)
A copolymer was obtained in the same manner as in Example using 40.0i (0.4 mol) of methyl methacrylate.

The proportion of methyl methacrylate in the obtained copolymer is
It was 95 mol% and the molecular weight was 195,000.

The obtained polymer was dissolved in methyl cellosolve acetate and filtered through a 0.2 μs filter to obtain a resist solution having a concentration of 8% by weight.

After coating and prebaking this resist solution in the same manner as in Example 1, electron beam irradiation was performed to obtain MI
Development with BK:IPA=1:2 for 60 seconds gave a sensitivity of 5×10-' coulombs/layer.

Example 5 IH, LH, 2H, 2H-tridecafluorooctanyl methacrylate-21,6# (0.05 mol) and methyl methacrylate 305F (0.30 mol) were added to 100 benzene and AIBN was added to the mixture. After adding 0.02 i, the mixture was reacted at 55° C. for 60 hours in a nitrogen atmosphere. After the reaction, the copolymer was purified in the same manner as in Example 1 to obtain 90% of the copolymer.
% yield.

The proportion of methyl methacrylate in the obtained copolymer was 8
The molecular weight was 68,000.

Using a resist solution consisting of a 5% by weight methyl cellosolve acetate solution of the above polymer, it was coated and prebaked in the same manner as in Example 1, then irradiated with an electron beam and developed with MIBK:IPA=:2:3 for 30 seconds. , lXl0-@coulomb/d.

Example 6 18.114,2H,2H-hebutadecafluorodecanyl methacrylate 21.3 g (0.04 mol) and general formula ■
A copolymer was obtained in the same manner as in Example 1 using 28.49 (0.20 mol) of n-butyl methacrylate in which R is an n-butyl group.

The proportion of n-butyl methacrylate in the obtained copolymer was 83 mol% and the molecular weight was 420,000.

Using a resist solution consisting of a 6% by weight chlorobenzene solution of the obtained polymer, it was coated and prebaked in the same manner as in Example 3, followed by electron beam irradiation and development with IBK:IPA=2:3 for 60 seconds. It showed a sensitivity of 2×10 −' coulombs/layer.

Example 7 n in general formula I is 9 1)1. IH, 2H, 2
H-eicosafluorododecanyl methacrylate 31.6
g-(0.05 mol) and n-propyl methacrylate 38.4 in which R in the general formula (■) is an n-propyl group
A copolymer was obtained in the same manner as in Example 1 using i (0.30 mol).

The proportion of n-propyl methacrylate in the obtained copolymer was 86 mol% and the molecular weight was 280,000.

Using a resist solution consisting of a 5% by weight chlorobenzene solution of the above polymer, coating and prebaking were performed in the same manner as in Example 1, followed by electron beam irradiation.
:IPA=2:3 when developed for 40 seconds.2.
A sensitivity of I x 10-' coulombs/layer was shown.

1) - LH, IH, where n in the general formula I is lO, 2) 1.
2H-)-licosafluorotridenicyl methacrylate 1
In the same manner as in Example 1 using the 0.23 method (1,5X IP'' mol) and n-octyl methacrylate 29°7@ (0.15 mol) in which R in the general formula H is an n-octyl group. A copolymer was obtained.

The proportion of n-octyl methacrylate in the obtained copolymer was 89 mol% and the molecular weight was 165,000.

After coating and prebaking in the same manner as in Example 3 using a resist solution consisting of an 8% by weight chlorobenzene solution of the above polymer, electron beam irradiation was performed to obtain MIBK:
3.5 when developed for 90 seconds with IPA=1:2
The sensitivity was expressed in X 10-' coulombs/al.

The properties of the resists of Examples 1 to 8 are shown in the table together with commercially available resists.

(Left below) Effects of the Invention The present invention is made of a copolymer of a specific fluorine-containing alkyl methacrylate and an alkyl methacrylate in a specific ratio, and can form a uniform thin film with good adhesion to a substrate, and is resistant to ionizing radiation. It is a positive resist material that has high sensitivity to light, excellent developability, and high resolution, and can be said to be a highly practical invention.

Claims (3)

[Claims] (1) Consisting of a copolymer of the following general formulas I and II, with a molecular weight of 10,000
1,000,000. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(II) (In the formula, n is 5 to 10, R represents an alkyl group) (2) The molar ratio of general formulas (I) and (II) is 50:5
The ionizing radiation-sensitive positive resist material according to claim 1, comprising a copolymer having a ratio of 0 to 1:99. (3) The molar ratio of general formulas (I) and (II) is 25:75
Claim 1 consisting of a copolymer of ~5:97
The ionizing radiation-sensitive positive resist material described in .