Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2002-09-12
2004-03-09
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
C430S325000, C430S326000, C526S281000
Reexamination Certificate
active
06703183
ABSTRACT:
This invention relates to (i) a polymer comprising specific recurring units, (ii) a resist composition comprising the polymer as a base resin, and (iii) a patterning process using the resist composition.
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 a KrF or 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 0.3 &mgr;m or less.
For resist materials for use with KrF excimer lasers, polyhydroxystyrene having a practical level of transparency and etching resistance is, in fact, a standard base resin. For resist materials for use with ArF excimer lasers, polyacrylic or polymethacrylic acid derivatives containing an adamantane structure in their side chain are often used as described in JP-A 9-73173 and JP-A 9-90637. Few of these polymers are regarded as exhibiting satisfactory performance.
More particularly, resist compositions using derivatives of polyacrylic or polymethacrylic acid as the base resin exhibit satisfactory sensitivity and resolution upon pattern formation by exposure and development, but have extremely low dry etching resistance. It is possible to improve the dry etching resistance to some extent by introducing many acid-decomposable units having an adamantane structure as typified by 2-alkyl-2-adamantyl groups to increase the carbon density. The introduction of adamantane-containing acid-decomposable units, however, sacrifices resolving power and working convenience owing to their dull reactivity and is thus undesirable. Specifically, such polymers can give rise to many problems including a T-top profile of pattern, serration on pattern side-walls, deposition of foreign matter on the substrate and pattern, and substantial changes of sensitivity with minute shifts of heat treatment temperature. They are thus practically unacceptable. While a finer pattern rule is being demanded, there is a need to have a resist material which exerts satisfactory performance with respect to sensitivity and resolution, has practically acceptable etching resistance, and is convenient to work with due to a wide margin allowed for processing conditions.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide (i) a polymer having a high resolution, practically acceptable etching resistance, and a substantial margin allowed for heat treatment temperature, (ii) a resist composition comprising the polymer as a base resin, and (iii) a patterning process using the resist composition.
It has been found that novel polymers comprising recurring units of the following general formulae (1) and (2) and having a weight average molecular weight of 1,000 to 500,000, which are produced by the method to be described later, have improved properties as the resist base resin; that a resist composition comprising the polymer as the base resin has a high resolution and practically acceptable etching resistance, and is convenient to work with due to a wide margin allowed for heat treatment temperature; and that this resist composition lends itself to precise micropatterning.
In a first aspect, the invention provides a polymer comprising recurring units of the general formula (1) and recurring units of the general formula (2) and having a weight average molecular weight of 1,000 to 500,000.
Herein R
1
and R
3
each are hydrogen or methyl, R
2
and R
4
each are a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, R
5
, R
6
, R
7
and R
8
each are hydrogen, or a pair of R
5
and R
7
and a pair of R
6
and R
8
each stand for a group of atoms to form trimethylene or 1,3-cyclopentylene.
The polymer may further include recurring units of the general formula (3).
Herein R
9
is hydrogen or methyl, R
10
is hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, R
11
is hydrogen or CO
2
R
12
, R
12
is a straight, branched or cyclic alkyl group having 1 to 15 carbon atoms in which at least one oxygen atom may intervene in any carbon-to-carbon bond, and X is methylene or an oxygen atom.
In a second aspect, the invention provides a resist composition comprising the inventive polymer as a base resin.
In a third aspect, the invention provides a process for forming a resist pattern comprising the steps of applying the resist composition onto a substrate to form a coating; heat treating the coating and then exposing it to high-energy radiation or electron beam through a photo mask; and optionally heat treating the exposed coating and developing it with a developer.
As described in the preamble, acid-decomposable units containing an adamantane structure have dull reactivity and adversely affect resolving power and ease of use, despite many advantages including excellent etching resistance and alleviated line density dependence. Based on the presumption that a satisfactory resist material is obtained by enhancing the acid decomposition reactivity of a polymer as a whole while keeping the advantages of adamantane-containing acid-decomposable units, we attempted to use recurring units containing an adamantane structure of formula (1) in combination with recurring units of formula (2) featuring a high acid decomposition reactivity and found that the object is achieved thereby. The recurring units of formula (3) are capable of imparting substrate adhesion, developer affinity and solvent solubility to the base resin, while minimizing any decline of etching resistance associated with the polar structure introduced, and therefore, better results are obtained by using the recurring units of formula (3) in combination with the units of formulae (1) and (2). Therefore, a resist composition using as a base resin the polymer comprising recurring units of formula (1), recurring units of formula (2) and optionally, recurring units of formula (3) according to the invention satisfies the performance factors of sensitivity and resolution, has practically acceptable dry etching resistance, is improved in substrate adhesion, developer affinity and solvent solubility, allows for a wide margin to the heat treatment temperature range, is convenient to use, and is thus very useful in forming micropatterns.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Polymer
Novel polymers or high molecular weight compounds according to the invention are defined as comprising recurring units of the following general formula (1) and recurring units of the following general formula (2). The polymers have a weight average molecular weight of 1,000 to 500,000.
Herein R
1
and R
3
are hydrogen or methyl. R
2
and R
4
are straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, ethylcyclopentyl, butylcyclopentyl, ethylcyclohexyl, butylcyclohexyl, adamantyl, ethyladamantyl, and butyladamantyl. R
5
, R
6
, R
7
and R
8
are hydrogen, or a pair of R
5
and R
7
and a pair of R
6
and R
8
each stand for a group of atoms to form trimethylene or 1,3-cyclopentylene.
The preferred polymers further include recurring units of the general formula (3).
Herein R
9
is hydrogen or methyl. R
10
is hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, examples of which are as enumerated above for R
2
and R
4
. R
11
is hydrogen or CO
2
R
12
wherein R
12
is a straight, branched or cyclic alkyl group having 1 to 15 carbon atoms or a similar alkyl group in which one or more oxygen atoms intervene in any carbon-to-carbon bond. Suitable alkyl groups are as enumerated above for R
2
and R
4
, and examples of the alkyl group in which one or more oxygen atoms intervene in any carbon-to-carbon bond include methoxymethyl, methoxyethoxymethyl, 1-et
Hasegawa Koji
Kinsho Takeshi
Nagura Shigehiro
Nishi Tsunehiro
Watanabe Satoshi
Ashton Rosemary
Birch & Stewart Kolasch & Birch, LLP
Shin-Etsu Chemical Co. , Ltd.
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