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
2001-03-07
2003-10-28
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
C430S326000, C430S905000, C430S910000
Reexamination Certificate
active
06638684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensitive laminate, to a process for forming a resist pattern using the photosensitive laminate, and to a positive resist composition.
2. Description of the Related Art
Semiconductor devices are more and more being intensified in the degree of integration in recent years. The mass production of large-scale integrated circuits (LSIs) using 0.20-&mgr;m design rules has been already launched, and the mass production of LSIs using 0.18-&mgr;m design rules was to be launched at the end of 1999.
Various types of chemically amplified resists have been proposed. Today, the dominating chemically amplified resists are binary system resists including a base resin and an acid generator. In these binary system resists, the base resin is composed of polyhydroxystyrene which is highly transparent to KrF laser beam, whose hydroxyl group is substituted with an acid-decomposable alkali-dissolution-inhibiting group, such as a t-boc (tert-butoxycarbonyloxy) group, as proposed in Japanese Examined Patent Application Publication No. 2-27660.
Using the resist proposed in the aforementioned publication, a resist pattern is basically formed in the following mechanism.
The base resin has a t-boc group and therefore has a lower solubility in alkalis than a polyhydroxystyrene having no t-boc group. When this type of base resin is mixed with an acid generator and is selectively exposed to light, the t-boc group in exposed areas is dissociated to yield polyhydroxystyrene by action of an acid generated from the acid generator. Thus, the base resin becomes soluble in alkalis.
The alkali-solubility of the base resin in the above resist is derived from an alkali-solubility which a polyhydroxystyrene inherently possesses, and the dissociation of the t-boc group by action of an acid generated by exposure restores the alkali-solubility of the polyhydroxystyrene. Accordingly, no more alkali-solubility than that the polyhydroxystyrene inherently possesses can be expected.
In contrast, (1) Japanese Patent Laid-Open No. 4-287044, (2) Japanese Patent Laid-Open No. 5-40342, (3) Japanese Patent Laid-Open No. 5-313372, and (4) Japanese Patent Laid-Open No. 6-130670 respectively propose ternary system chemically amplified resist compositions. Each of these resist compositions is composed of (&agr;) a novolak resin as a base resin component, (&bgr;) an acid generator, and (&ggr;) a compound in which an acid-decomposable dissolution-inhibiting group is dissociated by actin of an acid from the acid generator to yield an organic carboxylic acid (a compound whose carboxyl group is substituted with an acid-decomposable dissolution-inhibiting group).
In such ternary system resists, as described in detail in the publications (2) and (3), a carboxylic acid is formed from the ingredient (&ggr;) by action of an acid generated from the ingredient (B) upon exposure, and this carboxylic acid can impart more alkali-solubility to the resist than the alkali solubility which the ingredient (&agr;) inherently possesses. Accordingly, the resulting resist exhibits a satisfactory contrast between exposed areas and unexposed areas.
However, the novolak resins used in the resists have a low transparency to KrF laser beam, and these resists are insufficient in resist pattern profile and definition and cannot be used in practice in the production of semiconductor devices where fine resist pattern sizes of not more than 0.20 &mgr;m are required.
Separately, development of resist materials for F
2
laser (157 nm) or extreme ultraviolet rays (EUV, extreme ultraviolet rays; 13 nm) as next-generation or next-to-next-generation resist materials is urgently necessary for the production of semiconductor devices using 0.15-&mgr;m or less design rules. Such resist compositions must have a higher dry etching resistance and an improved SEM resistance, since the energy of light used is increased in such a short wavelength region. In this connection, the formed resist pattern must be observed with a scanning electron microscope (SEM), but the formed resist pattern is deteriorated by action of an electron beam used in SEM observation. The term “SEM resistance” used herein means the resistance of the resulting resist pattern against such a electron beam in SEM observation.
Some resist compositions for light having a short wavelength equal to or less than that of F
2
laser beam have been proposed, but they are not sufficient solutions to the above problems.
In addition, to provide resist compositions at as low costs as possible has increased in importance in semiconductor industries, because of rapid price cuts in semiconductor devices such as 64-Mbit dynamic random access memory (DRAM) chips.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a photosensitive laminate especially for KrF laser, which is available at low costs, can form resist patterns with good profile, and have a satisfactory dry etching resistance and a high definition, to provide a process for forming a resist pattern using the photosensitive laminate, and to provide a positive resist composition.
Another object of the present invention is to provide a photosensitive laminate for light having a short wavelength equal to or less than that of F
2
laser, which has a higher dry etching resistance and an improved SEM resistance, as well as to provide a process for forming a resist pattern using the photosensitive laminate, and to provide a positive resist pattern.
The present inventors focused attention on the high contrast between exposed areas and unexposed areas of the chemically amplified positive resists described in the publications (1) to (4), and on very low costs of novolak resins as compared with polyhydroxystyrene. They found that the above object can be achieved by applying such a ternary system chemically amplified resist to a process for producing a very thin film resist 500 to 5800 angstroms thick. The present invention has been accomplished based on these findings.
In this connection, the above publications (1) to (4) neither describe nor indicate a process for producing such a very thin film resist as in the present invention.
Specifically, the invention provides, in an aspect, a photosensitive laminate including a substrate and a resist layer 500 to 5800 angstroms thick formed on the substrate. The resist layer is formed from a positive resist composition, and this positive resist composition includes (A) a compound which generates an acid upon irradiation with radioactive ray, (B) an alkali-soluble novolak resin, and (C) a compound having at least one acid-decomposable dissolution-inhibiting group, and the dissolution-inhibiting group is decomposable by action of an acid generated from the ingredient (A) to yield an organic carboxylic acid. In another aspect, the invention provides a process for forming a resist pattern. This process includes the step of sequentially subjecting the photosensitive laminate to selective exposure to KrF excimer laser or with light having a short wavelength equal to or less than that of F
2
laser, post exposure baking, and development with an alkali. In a further aspect, the invention provides the positive resist composition.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments.
DETAILED DESCRIPTION OF THE INVENTION
The invented photosensitive laminate includes a substrate and a resist layer 500 to 5800 angstroms thick formed on the substrate. This very thin resist layer features the invented photosensitive laminate. By this feature, the photosensitive laminate can exhibit more efficient exposure in exposure to KrF laser light or to light having a short wavelength equal to or less than that of F
2
laser. The photosensitive laminate can form resist patterns having markedly improved profiles and having greatly improved definition even in the production of semiconductor devices using KrF laser light where a resist pattern size
Nitta Kazuyuki
Ogata Toshiyuki
Okubo Waki
Sato Kazufumi
Chu John S.
Tokyo Ohka Kogyo Co. Ltd.
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