Polymers, resist materials, and pattern formation method

Details Polymers, resist materials, and pattern formation method Polymers, resist materials, and pattern formation method

2002-01-16

2004-01-13

Baxter, Janet (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

C430S330000, C430S296000, C430S326000, C430S327000, C526S256000

Reexamination Certificate

active

06677101

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to (1) polymers containing specific repeating units, (2) resist materials containing such polymers as base resins, and (3) a pattern formation method using such a resist materials.
2. Description of the Related Art
In recent years, increasingly finer pattern rules are required as the degree of integration and speed of LSIs become higher. Under these circumstances, far ultraviolet lithography is regarded as a promising fine processing technique of the next generation. In particular, photolithography using KrF or ArF excimer laser light as the light source is considered to be a technique indispensable for ultrafine processing to a size of 0.3 &mgr;m or less, and its realization is eagerly desired.
In resist materials for use with a KrF excimer laser, polyhydroxystyrene having a practicable level of transparency and etching resistance has become an actual standard base resin. In resist materials for use with a ArF excimer laser, several materials such as derivatives of polyacrylic acid or polymethacrylic acid and polymers containing an alicyclic compound in the main chain are being investigated. However, both of them have merits and demerits. In the present situation, therefore, no standard base resin has been established as yet.
Specifically, resist materials using a derivative of polyacrylic acid or polymethacrylic acid have advantages such as high reactivity of acid-decomposable groups and excellent adhesion to the substrate, and produce relatively good results with respect to sensitivity and resolving power. However, since the main chain of the resin is soft and weak, these resist materials have very low etching resistance and are hence unsuitable for practical use. On the other hand, resist materials using a polymer containing an alicyclic compound in the main chain have a practicable level of etching resistance owing to the sufficiently rigid main chain of the resin. However, since the reactivity of acid-decomposable groups is much poorer as compared with (meth)acrylic type resist materials, their sensitivity and resolving power are low. Moreover, their adhesion to the substrate is low owing to the excessively rigid main chain of the resin. Consequently, these resist materials are also unsuitable for practical use. As used herein, the term “(meth)acrylic type” means methacrylic type or acrylic type.
A problem common to both the (meth)acrylic type and the alicyclic main chain type is the disintegration of patterns due to swelling of the resist film. In these types of resist materials, their resolving power has been enhanced by increasing the difference between dissolution rates before and after exposure. Consequently, they have come to reach a very high level of hydrophobicity. Highly hydrophobic resist materials can hold the film strongly in unexposed regions and allow the film to be instantaneously dissolved in overexposed regions. However, in the considerably wide exposure range therebetween, they permit infiltration of the developer but fail to dissolve, and hence swell. Actually, for very minute pattern sizes requiring the use of an ArF excimer laser, it is impossible to use a resist material which causes adjacent patterns to be united together or disintegrated as a result of swelling. In the present situation where increasingly finer pattern rules are required, there is a need for a resist material which not only exhibits excellent properties such as sensitivity, resolving power and etching resistance, but also undergoes a well-controlled degree of swelling.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide (1) a polymer which has excellent reactivity, rigidity and adhesion to the substrate, and undergoes a low degree of swelling during development, (2) a resist material which uses this polymer as the base resin and hence exhibits much higher resolving power and etching resistance than conventional resist materials, and (3) a pattern formation method using this resist material.
The present inventors carried out intensive investigations with a view to accomplishing the above object. As a result, it has now been found that a novel polymer containing repeating units represented by the following general formula (1-1) or (1-2) and having a weight-average molecular weight of 1,000 to 500,000, which can be prepared according to a process as will be described later, has excellent reactivity, rigidity and adhesion to the substrate, exhibits suitably high solubility in developers, and undergoes a low degree of swelling, that a resist material using this polymer as the base resin has high resolving power and high etching resistance, and that this resist material is very useful for accurate and fine processing.
Thus, the present invention provides a polymer containing repeating units represented by the following general formula (1-1) or (1-2) and having a weight-average molecular weight of 1,000 to 500,000.
wherein R
1
represents a hydrogen atom, a methyl group or CH
2
CO
2
R
3
; R
2
represents a hydrogen atom, a methyl group or CO
2
R
3
; R
3
represents a straight-chain, branched or cyclic alkyl group having 1 to 15 carbon atoms, and may be common to R
1
and R
2
or different therebetween; W represents a straight-chain or branched divalent hydrocarbon radical having 2 to 10 carbon atoms, which may have one or more ester linkages in its structure and may further be substituted by one or more other atomic groups containing a heteroatom; and k is 0 or 1.
Moreover, the present invention also provides a resist material containing a polymer as described above, as well as a pattern formation method comprising the steps of applying the resist material to a substrate; after a heat treatment, exposing the resist material to high-energy radiation or electron rays through a photomask; and, after an optional heat treatment, developing the resist material with a developer.
Polymers containing repeating units represented by the general formula (1-1) or (1-2) have bridged alicyclic rings in the main chain and hence exhibit high rigidity. Moreover, since they have a very highly polar 7-oxabicyclo[2.2.1]heptane ring in the side chain, they also exhibit excellent adhesion to the substrate and a good affinity for developers which is directly associated with a reduction of swelling. Furthermore, since a spacer having a suitable length is introduced between the 7-oxabicyclo[2.2.1]heptane ring and the rigid main chain, the rigidity which has been excessively high in the prior art is moderately relaxed. In addition, the 7-oxabicyclo[2.2.1]heptane ring moiety is located at a position remote from the main chain, and can hence function more effectively as a polar group. Consequently, these compounds have much better adhesion to the substrate than conventional compounds. Furthermore, the low reactivity which has been a big problem in the prior art is improved by the introduction of a spacer and the ensuing enhanced diffusibility of the acid produced, and a reduction in line edge roughness is achieved at the same time. Accordingly, resist materials using these polymers as base resins have excellent properties from the viewpoint of sensitivity, resolving power and etching resistance, and undergo a well-controlled degree of swelling during development, so that they are very useful for the formation of fine patterns.
Since resist materials using the polymers of the present invention as base resins are sensitive to high-energy radiation and have excellent sensitivity, resolving power and etching resistance, they are useful for fine processing with electron rays or far ultraviolet radiation. In particular, since they exhibit low absorption at the exposure wavelengths of ArF and KrF excimer lasers, they are characterized in that fine patterns perpendicular to the substrate can be easily formed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be more specifically desc

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