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
2000-09-13
2002-09-17
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, C525S119000, C526S271000, C526S272000, C526S319000
Reexamination Certificate
active
06451501
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resist composition and, more specifically, it relates to a resist composition for which shorter wavelength light such as excimer laser light can be used as the image-forming radiation, and which can be developed by a basic aqueous solution after exposure. The present invention further relates to a positive resist pattern forming method employing the resist composition. The resist composition of the present invention can be used to form intricate positive patterns that have practical sensitivity, undergo no swelling and exhibit no peeling. The present invention still further relates to an acid sensitive copolymer useful for the preparation of the resist composition.
BACKGROUND ART
As is well known, the recent trend toward higher integration of semiconductor integrated circuits and the feasibility of VLSIs is leading to wiring patterns with wiring widths on the submicron level. This has rendered essential the establishment of microworking techniques, and in the field of lithography the demand has largely been met by shifting the ultraviolet wavelengths of light exposure sources to shorter wavelengths in the far ultraviolet range, and by developing light exposure techniques employing light sources with wavelengths in the deep ultraviolet range. At the same time, rapid development has been progressing with resist materials that exhibit lower light absorption of the aforementioned shorter wavelengths, have satisfactory sensitivity and also exhibit a high dry etching resistance.
In recent years much research has been conducted in the field of photolithography employing krypton fluoride excimer lasers (wavelength: 248 nm, hereunder abbreviated to KrF) as a new light exposure technique for the manufacture of semiconductor devices, and they have been applied to practical use. Also, H. Ito et al. of IBM, U.S.A. have already developed resist compositions based on the concept of “chemical amplification”, as resists with high sensitivity and high resolution that are suitable for such short wavelength light exposure. (See, for example, J. M. J. Frechet et al.,
Proc. Microcircuit Eng.,
260(1982), H. Ito et al., Digest of Technical Papers of 1982 Symposium on VLSI Technology, 86(1983), H. Ito et al., “Polymers in Electronics”, ACS Symposium Series 242, T. Davidson ed., ACS, 11(1984), and U.S. Pat. No. 4,491,628). As is readily understood from these publications, the fundamental concept of chemical amplification resist compositions is based on higher sensitivity through an improved apparent quantum yield achieved by a catalytic reaction in the resist film.
There may be cited the very widely used and researched chemical amplification resist type that comprises t-butoxycarbonyl polyvinylphenol (t-BOCPVP) and further contains a Photo Acid Generator (PAG), which has the function of generating an acid upon exposure; to light “post exposure baking” (PEB) of the exposed sections of the resist results in loss of the t-BOC groups to give isobutene and carbon dioxide. The proton acid produced upon loss of t-BOC serves as a catalyst promoting a deprotection chain reaction, which greatly alters the polarity of the exposed sections. With this type of resist, an appropriate developer can be selected to match the large change in polarity of the exposed sections, to easily form a resist pattern.
Recent years have seen abundant research in the field of lithography using even shorter wavelength argon fluoride excimer lasers (wavelength: 193 nm, hereunder abbreviated to ArF) for the fabrication of devices, such as gigabit class DRAMs. For this wavelength, it has been essential to shift away from the base resins that have conventionally been used, i.e. phenolic resins, because of their strong light absorption. Much research and development has been directed toward chemical amplification resists that can be applied to such short wavelengths.
Most conventional chemical amplification resists employ, as the base resins, methacrylic acid-based resins with polycyclic alicyclic ester groups (for example, adamantane, isobornane, tricyclodecane, etc.). (See, for example, K. Nozaki et al., Chem. Mater., 6, 1492(1994), K. Nakano et al., Proc. SPIE, 2195, 194(1994), R. D. Allen et al., J. Photopolym. Sci. Technol., 7, 507(1994)). These chemical amplification resists include alicyclic ester groups in the resins in order to achieve dry etching resistance which is indispensable for resists, but the presence of the alicyclic groups also presents the risk of peeling of the resist during development. Such resists also have insufficient solubility at the exposed sections, and it has therefore been necessary to take compensating measures such as introducing carboxylic acid units into the resin, using more diluted developers, or adding an alcohol such as isopropyl alcohol (IPA).
DISCLOSURE OF THE INVENTION
It is an object of the present invention to solve the problems of the prior art described above by providing a novel resist composition that allows the use of a basic aqueous solution as the developer (a standard alkali developer), that can form fine patterns with practical sensitivity and no swelling, as well as an acid sensitive copolymer that is useful for its preparation.
It is another object of the invention to provide a novel resist composition that is suitable for exposure to light sources in the deep ultraviolet range, typical of which are KrF and ArF excimer lasers, and that also exhibits excellent dry etching resistance.
It is yet another object of the invention to provide a novel resist composition that exhibits excellent adhesion to substrates and can form fine patterns with high sensitivity, high contrast and high resolution.
It is still another object of the invention to provide a resist pattern forming method employing the novel resist composition.
These and other objects of the invention will become readily apparent from the detailed explanation presented below.
As a result of diligent research aimed at achieving the objects mentioned above, the present inventors have completed the present invention upon discovering that, for chemical amplification resist compositions, it is effective to use a film-forming copolymer, with protecting group-containing carboxyl groups on the side chain of one of the monomer units, as the polymer used for the base resin, where a group with a specific acid anhydride portion with weak alkali solubility is used as the protecting group of the carboxyl group in the copolymer, and to combine this with introduction of an additional acidic functional group with an acid-unstable protecting group onto the side chain of one of the other monomer units.
According to one aspect of the present invention, there is provided an acid sensitive copolymer which is formed by copolymerization of two or more different monomers, the polymer being characterized in that
(1) it is itself insoluble in basic aqueous solutions, but is rendered soluble in basic aqueous solutions when the protecting group of the protected carboxyl group bonded to the side chain of the first monomer unit of the copolymer is removed by the action of the acid,
(2) the protecting group of the carboxyl group comprises an acid anhydride portion represented by the following formula (I):
where
R
1
represents a hydrogen atom or represents one or more substituents selected from the group consisting of alkyl, alkoxy and alkoxycarbonyl groups, and when more than one R
1
substituent is present the substituents may be the same or different,
L is either absent or represents a linking group comprising a linear or branched hydrocarbon group of 1 to 6 carbon atoms, and
n is an integer of 1 to 4;
(3) the second monomer unit of the copolymer further contains, bonded to its side chain, an acidic functional group protected with an acid-unstable protecting group; and
(4) it has a weight average molecular weight of 2,000 to 1,000,000.
According to another aspect of the present invention, there is provided a resist composition capable of being developed in basic aqueous solutions, characterized by compri
Nozaki Koji
Yano Ei
Armstrong Westerman & Hattori, LLP
Ashton Rosemary
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