Resist compositions and patterning process

Details Resist compositions and patterning process Resist compositions and patterning process

2000-09-15

2002-07-16

Ashton, Rosemary (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Radiation sensitive composition or product or process of making

C430S326000, C430S921000

Reexamination Certificate

active

06420085

ABSTRACT:

This invention relates to a resist composition for use with an ArF excimer laser comprising a specific sulfonium salt as the photoacid generator, and a patterning process using the same.
BACKGROUND OF THE INVENTION
While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using an ArF excimer laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.2 &mgr;m or less.
In the photolithography using an ArF excimer laser (wavelength 193 nm) as the light source, a high sensitivity resist material capable of achieving a high resolution at a small dose of exposure is needed to prevent the degradation of precise and expensive optical system materials. Among several measures for providing a high sensitivity resist material, the most common is to select each component which is highly transparent at the wavelength of 193 nm. For example, polyacrylic acid and derivatives thereof, norbornene-maleic anhydride alternating copolymers, polynorbornene and metathesis ring-opening polymers have been proposed as the base resin. This choice is effective in that the transparency of a resin alone is increased. However, the photoacid generator has the problem that increasing its transparency leads to a drop of acid generation efficiency, resulting in a low sensitivity or the lack of thermal stability and storage stability. There is available no photoacid generator which is practically acceptable.
For example, JP-A 7-25846, JP-A 7-28237 and JP-A 8-27102 disclose alkylsulfonium salts which are highly transparent, but unsatisfactory in acid generation efficiency and thermal stability. JP-A 10-319581 discloses alkylarylsulfonium salts which have a high sensitivity and a good balance of transparency and acid generation efficiency, but lack thermal stability and storage stability. Arylsulfonium salts, which are regarded effective in photolithography using a KrF excimer laser, are good in acid generation efficiency, thermal stability and storage stability, but very low transparent to ArF excimer laser light so that the pattern resulting from exposure and development is noticeably tapered. The lack of transparency can be compensated for by thinning the resist, but such a thin resist film is less resistant to etching. This is inadequate as the pattern forming process.
SUMMARY OF THE INVENTION
An object of the invention is to provide a highly resolvable resist composition comprising a photoacid generator having a high sensitivity to ArF excimer laser light as well as thermal stability and storage stability. Another object is to provide a patterning process using the resist composition.
It has been found that a sulfonium salt of the following general formula (1) has a high sensitivity to ArF excimer laser light as well as satisfactory thermal stability and storage stability and that a resist composition having the sulfonium salt blended therein has a high resolution and is fully suited for precise micropatterning.
The invention provides a resist composition for use with an ArF excimer laser, comprising a base resin, a photoacid generator, and a solvent. The photoacid generator is a sulfonium salt of the following general formula (1).
Herein R
1
is a hydroxyl group, nitro group, or straight, branched or cyclic monovalent hydrocarbon group of 1 to 15 carbon atoms which may contain an oxygen, nitrogen or sulfur atom, and two R
1
groups may form a ring together, the R
1
groups are straight, branched or cyclic divalent hydrocarbon groups of 1 to 15 carbon atoms which may contain an oxygen, nitrogen or sulfur atom when they form a ring, K
−
is a non-nucleophilic counter ion, x is an integer of 1 or 2, and y is an integer of 0 to 3.
In one preferred embodiment, the base resin is a polymer comprising recurring units of the following general formula (2) and having a weight average molecular weight of 1,000 to 500,000.
Herein R
001
is hydrogen, methyl or CH
2
CO
2
R
003
, R
002
is hydrogen, methyl or CO
2
R
003
, wherein R
003
is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, R
004
is hydrogen or a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group; at least one of R
005
to R
008
represents a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group while the remaining R's independently represent hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, or R
005
to R
008
, taken together, may form a ring, and in that event, at least one of R
005
to R
008
is a divalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group, while the remaining R's are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms; R
009
is a monovalent hydrocarbon group of 3 to 15 carbon atoms containing a —CO
2
— partial structure; at least one of R
010
to R
013
is a monovalent hydrocarbon group of 2 to 15 carbon atoms containing a —CO
2
— partial structure, while the remaining R's are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms, or R
010
to R
013
, taken together, may form a ring, and in that event, at least one of R
010
to R
013
is a divalent hydrocarbon group of 1 to 15 carbon atoms containing a —CO
2
— partial structure, while the remaining R's are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms; R
014
is a polycyclic hydrocarbon group having 7 to 15 carbon atoms or an alkyl group containing a polycyclic hydrocarbon group; R
015
is an acid labile group; k is equal to 0 or 1, a1, a2, a3, b1, b2, b3, c1, c2, c3, d1, d2, d3, and e are numbers from 0 to less than 1, satisfying a1+a2+a3+b1+b2+b3+c1+c2+c3+d1+d2+d3+e=1.
In another aspect, the invention provides a process for forming a pattern, comprising the steps of applying the resist composition defined above onto a substrate to form a coating, heat treating the coating and exposing the coating to light having a wavelength of 193 nm through a photo-mask, optionally heat treating the exposed coating, and developing the coating with a developer.
The sulfonium salt of the formula (1) has a very high sensitivity to ArF excimer laser light so that even when blended in a small amount, it can generate a sufficient amount of acid. Then a resist composition having the sulfonium salt blended therein has a high sensitivity and high transparency, forms a pattern having high rectangularity following exposure and development, and is advantageous in etching because of no need for film thinning. The inventive sulfonium salt eliminates the lack of thermal stability and storage stability which is the drawback of prior art alkylsulfonium salts and alkylarylsulfonium salts.
In the sulfonium salt of the formula (1), one or two aryl groups are introduced at the sacrifice of transparency to some extent. However, the introduction of aryl group(s) improves acid generation efficiency outstandingly and as a consequence, enables to enhance sensitivity. When the sensitivity to light of 193 nm wavelength is compared between resist films having the same transmittance, the sulfonium salt of formula (1) improves the sensitivity by a factor of at least 3 over the arylsulfonium salts. The problem of thermal stability and storage stability that the prior art salts suffer from has been overcome by selecting as the alkyl, methyl which is free of an adjacent carbon atom and hydrogen on the carbon atom.
It is noted that the sulfonium salt of formula (1) is highly sensitive to only ArF excimer laser light, and not useful in photolithography using KrF excimer laser light of 248 nm wavelength.
DESCRIPTION OF THE PREFE

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