Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Utility Patent
1998-03-09
2001-01-02
Chu, John S. (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
C430S905000
Utility Patent
active
06168900
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to chemically amplified resist including a polyhydroxystyrene polymer having a protection group whereof polarity is changed by acid catalyst and a photoacid generator, which is usable as positive resist, for example, to be applied to pattern formation wherein the positive resist is formed on a semiconductor substrate, exposed to KrF excimer laser light projected through a mask or a reticle, processed with PEB (Post Exposure Bake), and developed with a developer.
In conventional photolithograply technique, solubility-suppressed positive resist has been prevalent wherein novolac polymer is used as a base polymer added with naphthoquinonediazido as a photosensitive to be exposed to g-ray (436 nm) or i-ray (365 nm). However, lithography applying far ultraviolet rays such as excimer laser light of 248 nm or 193 nm has become required along with advances of fine integration of semiconductor circuits. As for the excimer laser light, the above conventional resist is not convenient because of its too strong photo-absorption to obtain a good resist pattern together with its too amplified photosensitivity. Hence, chemically amplified resist making use of sensitization of acid catalyst obtained from a photoacid generator (hereafter abbreviated as PAG) is proposed and is being adopted as a resist material for short-wave lithography or electron-beam lithography requiring high sensitivity.
However, the above conventional chemically amplified resist has a problem that acid generated by the exposure may vanish from surface of the resist film or made inactive neutralized by bases in atmosphere. Hence, an insoluble surface layer is generated, wherein solubilization does not proceed in following PEB process, resulting in a T-shaped resist pattern
402
developed on a wafer
401
, as schematically illustrated in FIG.
4
. This phenomenon is often seen in high-resolution resist having a high solution-speed ratio (solubility contrast) between exposed part and unexposed part.
This T-shaped resist pattern is fatal especially for fine pattern configuration, degrading resolution, focusing and size accuracy.
For resolving this problem, in chemically amplified resist disclosed in a Japanese patent application laid open as a Provisional Publication No. 80516/'93, alkali-soluble groups such as a hydroxyl group, a carboxyl group, a methoxy group, or an anhydride group are introduced in the polymer intending to prevent the T-shaped resist pattern by controlling solution speed of the resist material. With this resist material, even though generation of the T-shaped resist pattern may be somewhat restrained, there arises another problem that upper edges of cross-sectional pattern become rounded and rectangularity of the resist pattern is spoiled, resulting also in degradation of the resolution.
SUMMARY OF THE INVENTION
Therefore, primary objects of the present invention is to provide chemically amplified resist which is excellent in resolution, focusing and size accuracy as well, preventing the T-shaped resist pattern by suppressing generation of the surface insoluble layer owing to the acid-intactivation at the resist surface, and to provide the chemically amplified resist giving, at the same time, a sharp gradient to the solubility characteristic (exposure dependence of the solution speed), by resolving the above problems of the prior art.
In order to achieve the object, in chemically amplified resist of the invention comprising a first polyhydroxystyrene polymer having a first protection group whereof polarity is changed by acid catalyst and a photoacid generator; a second polyhydroxystyrene polymer of different average molecular weight, having a second protection group whereof polarity is changed by acid catalyst, is mixed with the first polyhydroxystyrene polymer.
Generally, polymers of low molecular weight give high solution speed. Therefore, by adding the low molecular weight polymers, solution speed of low exposure area can be made high. Making use of this phenomenon, the solution speed is controlled by applying a mixture of protected polyhydroxystyrene polymers of different molecular weight to the base polymer, in the chemically amplified resist of the invention. When the solution speed is made high, the insoluble layer generated on the surface of the resist pattern can be eliminated, film surface being somewhat solved by the developer. Thus, the T-shaped resist pattern can be prevented. Further, making use of the low molecular weight polymer functioning to make the solution reaction uniform in a depth direction, the gradient of solubility characteristic, which is most important for the resist resolution, is reinforced in the invention, realizing still high resolution.
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Chu John S.
Hayes, Soloway, Hennessey, Grossman & Hage
NEC Corporation
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