Polymer, resist composition and patterning process

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

2001-12-03

2003-01-28

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S258000, C526S266000, C526S271000, C526S281000, C526S284000, C430S270100, C430S281100

Reexamination Certificate

active

06512067

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 transmittance and etching resistance is, in fact, a standard base resin. For resist materials for use with ArF excimer lasers, polyacrylic or polymethacrylic acid derivatives and polymers containing aliphatic cyclic compounds in the backbone are under investigation. All these polymers have advantages and disadvantages, and none of them have been established as the standard base resin.
More particularly, resist compositions using derivatives of polyacrylic or polymethacrylic acid have the advantages of high reactivity of acid-decomposable groups and good substrate adhesion and give relatively satisfactory results with respect to sensitivity and resolution, but have extremely low etching resistance and are impractical because the resin backbone is weak. On the other hand, resist compositions using polymers containing alicyclic compounds in their backbone have a practically acceptable level of etching resistance because the resin backbone is robust, but are very low in sensitivity and resolution because the reactivity of acid-decomposable protective groups is extremely low as compared with those on the (meth)acrylic polymers. Since the backbone of the resin is too robust, substrate adhesion is poor. These compositions are thus impractical as well.
Both the (meth)acrylic and alicyclic backbone systems commonly have the problem of pattern disruption due to swelling of resist film. Resist compositions based on these systems have been designed so as to improve their resolution performance by increasing the difference in dissolution rate before and after exposure, and as a consequence, they eventually become highly hydrophobic. Highly hydrophobic resist compositions, when applied as a film and processed with a developer, can maintain the film tenaciously in unexposed regions and allow the film to be instantaneously dissolved in over-exposed regions, while relatively broad exposed regions therebetween allow penetration of the developer, but are kept undissolved, that is, swollen. At the very small pattern size for which ArF excimer laser is actually used, those resist compositions which allow adjacent pattern strips to be joined together and disrupted on account of swelling are rejected. While a finer pattern rule is being demanded, there is a need to have a resist material which is not only satisfactory in sensitivity, resolution, and etching resistance, but fully restrained from swelling.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide (i) a polymer having improved reactivity, robustness and substrate adhesion as well as minimized swell during development, (ii) a resist composition comprising the polymer as a base resin, which has a higher resolution and etching resistance than conventional resist compositions, and (iii) a patterning process using the resist composition.
It has been found that novel polymers comprising recurring units of the following general formula (1-1) or (1-2) 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 reactivity, robustness or rigidity and substrate adhesion as well as an appropriately high solubility and minimized swell in a developer; that a resist composition comprising the polymer as the base resin has a high resolution and etching resistance; 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 (1-1) or (1-2) and having a weight average molecular weight of 1,000 to 500,000.
Herein R
1
, R
2
, R
3
and R
4
each are hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, R
1
and R
2
, and R
3
and R
4
, taken together, may form a ring, wherein each combination of R
1
with R
2
and of R
3
with R
4
is a straight, branched or cyclic alkylene group of 2 to 15 carbon atoms,
R
5
and R
6
each are hydrogen, a straight, branched or cyclic alkyl, acyl or alkylsulfonyl group of 1 to 15 carbon atoms or a straight, branched or cyclic alkoxycarbonyl or alkoxyalkyl group of 2 to 15 carbon atoms, in which some or all of the hydrogen atoms on constituent carbon atoms may be substituted with halogen atoms, and k is 0 or 1.
In one preferred embodiment, the polymer comprises, in addition to the recurring units of formula (1-1), recurring units of the following general formula (2-1).
Herein R
7
is hydrogen, methyl or CH
2
CO
2
R
9
; R
8
is hydrogen, methyl or CO
2
R
9
; R
9
is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms; R
10
is an acid labile group; R
11
is selected from the class consisting of a halogen atom, a hydroxyl group, a straight, branched or cyclic alkoxy, acyloxy or alkylsulfonyloxy group of 1 to 15 carbon atoms, and a straight, branched or cyclic alkoxycarbonyloxy or alkoxyalkoxy group of 2 to 15 carbon atoms, in which some or all of the hydrogen atoms on constituent carbon atoms may be substituted with halogen atoms; Z is a single bond or a straight, branched or cyclic (p+2)-valent hydrocarbon group of 1 to 5 carbon atoms in which at least one methylene may be substituted with oxygen to form a chain-like or cyclic ether or two hydrogen atoms on a common carbon may be substituted with oxygen to form a ketone; k is 0 or 1, and p is 0, 1 or 2.
In another preferred embodiment, the polymer comprises, in addition to the recurring units of formula (1-1), recurring units of the following general formulae (2-1) and (3).
Herein k, p and R
7
to R
11
are as defined above, Y is —O— or —(NR
12
)—, and R
12
is hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms.
In a further preferred embodiment, the polymer comprises, in addition to the recurring units of formula (1-1), recurring units of the following general formula (4) alone or in combination with recurring units of the following general formula (2-1), and recurring units of the following general formula (3).
Herein k, p, R
7
to R
11
and Y are as defined above.
In a still further preferred embodiment, the polymer comprises, in addition to the recurring units of formula (1-2), recurring units of the following general formula (2-2).
Herein k, p and R
7
to R
11
are as defined above.
In a second aspect, the invention provides a resist composition comprising the polymer defined above.
In a third aspect, the invention provides a process for forming a resist pattern comprising the steps of applying the resist composition defined above onto a substrate to form a coating; heat treating the coating and then exposing it to high-energy radiation or electron beams through a photo mask; and optionally heat treating the exposed coating and developing it with a developer.
The polymers comprising recurring units of formula (1-1) or (1-2) have high rigidity since bridged aliphatic rings are incorporated in the backbone. Unlike polar groups introduced at a position spaced from the backbone, highly polar ether sites incorporated within the backbone ensure that transition from penetration of a developer to dissolution of the resin rapidly takes place within a time too short for swelling to occur. Additionally, even a minor proportion of recurring units of formula (1-

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