Polymer, resist composition and patterning process

Details Polymer, resist composition and patterning process Polymer, resist composition and patterning process

2002-06-14

2004-01-06

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

Reexamination Certificate

active

06673518

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 a 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 polycyclic structures as typified by adamantane structures to increase the carbon density. The resulting polymers, however, become highly hydrophobic as a whole, giving rise to undesired phenomena including pattern separation due to reduced substrate adhesion and development defects due to developer repellency. Still worse, the polymers substantially lose solubility in safe solvents such as propylene glycol monomethyl ether acetate. They are thus practically unacceptable. While a finer pattern rule is being demanded, there is a need to have a base resin for resist material which exerts satisfactory performance with respect to sensitivity and resolution, has practically acceptable etching resistance, and provides good adhesion to substrates, affinity to developers and solubility in solvents.
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, improved substrate adhesion and developer affinity, and a high solubility in safe solvents such as propylene glycol monomethyl ether acetate, (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 formula (1) and recurring units having a carboxylic acid protected with an acid-decomposable protecting group containing an adamantane structure or tetracyclo[4.4.0.1
2,5
.1
7,10
]dodecane structure 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, practically acceptable etching resistance, improved substrate adhesion, developer affinity, and solvent solubility; and that this resist composition lends itself to precise micropatterning.
In a first aspect, the invention provides a polymer comprising recurring units of the following general formula
(1) and recurring units having a carboxylic acid protected with an acid-decomposable protecting group containing an adamantane structure or tetracyclo[4.4.0.1
2,5
.1
7,10
]dodecane structure, the polymer having a weight average molecular weight of 1,000 to 500,000.
Herein R
1
is hydrogen or methyl, R
2
is hydrogen or a straight, branched or cyclic alkyl group having 1 to 8 carbon atoms, R
3
is hydrogen or CO
2
R
4
, and R
4
is a straight, branched or cyclic alkyl group having 1 to 15 carbon atoms.
Preferably, the recurring units having a carboxylic acid protected with an acid-decomposable protecting group containing an adamantane structure or tetracyclo-[4.4.0.1
2,5
.1
7,10
]dodecane structure are units of at least one of the following general formulae (2) to (4).
Herein R
5
, R
7
and R
10
each are hydrogen or methyl, R
6
, R
8
, R
9
and R
11
each are a straight, branched or cyclic alkyl group having 1 to 15 carbon atoms.
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, polyacrylic acid or polymethacrylic acid derivatives generally suffer from very low dry etching resistance. This drawback can be overcome by introducing substantial amounts of units containing an adamantane structure or tetracyclo[4.4.0.1
2,5
.1
7,10
]dodecane structure. However, the resulting polymers as a whole become highly hydrophobic, detracting from substrate adhesion, developer affinity, and solvent solubility. On the other hand, recurring units of formula (1) are rather excessively hydrophilic. Surprisingly, the recurring units of formula (1), combined with the units containing an adamantane structure or tetracyclo[4.4.0.1
2,5
.1
7,10
]dodecane structure, exert an appropriate degree of developer affinity and solvent solubility. The units of formula (1) in which an oxygen functional group is effectively positioned within the cyclic structure are minimized in the reduction of dry etching resistance due to a lowering of carbon density. Therefore, a resist composition using the inventive polymer as a base resin satisfies the performance factors of sensitivity and resolution, has practically acceptable dry etching resistance, is improved in substrate adhesion, developer affinity and solvent solubility, 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 having a carboxylic acid protected with an acid-decomposable protecting group containing an adamantane structure or tetracyclo[4.4.0.1
2,5
.1
7,10
]dodecane structure. The polymers have a weight average molecular weight of 1,000 to 500,000.
Herein R
1
is hydrogen or methyl. R
2
is hydrogen or a straight, branched or cyclic alkyl group having 1 to 8 carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, cyclopentyl-methyl, cyclopentylethyl, cyclohexylmethyl and cyclohexyl-ethyl. R
3
is hydrogen or CO
2
R
4
. R
4
is a straight, branched or cyclic alkyl group having 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.
In the inventive polymers, the recurring units having a carboxylic acid protected with an acid-decomposable protecting group containing an adamantane structure or tetracyclo[4.4.0.1
2,5
.1
7,10
]dodecane structure are preferably units of at least one of the following general formulae (2) to (4):
Herein R
5
, R
7
and R
10
each are hydrogen or methyl. R
6
, R
8
, R
9
and R
11
each are a straight, branched or cyclic alkyl group having 1 to 15 carbon atoms, examples of which are as enumerated fo

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