Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2000-07-27
2002-05-28
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S192000, C430S193000, C430S270100, C430S942000
Reexamination Certificate
active
06395447
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to resist materials for fabricating a fine pattern and fabrication method of a resist material. This application is based on patent applications Nos. Hei 8-166607, Hei 8-242560, and Hei 9-038538 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Pattern fabrication in relation to semiconductor integrated devices represented by ULSI is performed such that a thin film layer of a resist material (often abbreviated as a “resist”, hereinafter), which is sensitive to high energy beams such as Ultra-violet light (often abbreviated as a “UV”, hereinafter), X-ray, or electron beams, is deposited on a semiconductor substrate, and then the resist is irradiated with such high energy beams and is developed.
FIGS. 3A-3B
are diagrams for explaining processes for fabricating a pattern using a conventional resist material. In
FIGS. 3A-3B
, reference numeral
1
indicates a (semiconductor) substrate, reference numeral
2
indicates a resist film, reference numeral
3
indicates high energy beams (such as UV, X-ray, or electron beams), and reference numeral
4
indicates reactive etching species. Accordingly, it is necessary for the resist materials (i) to have high sensitivity to high-energy beams in consideration of quick pattern fabrication, (ii) to be keenly sensitive to the high energy beams so as to obtain high pattern-resolution capability, and (iii) to have high etching resistance in the etching of semiconductor-substrate. Generally, the thinner the resist film is, the smaller the spreading of the high energy beam is in the resist film; thus, pattern resolution is increased. Similarly, due to thinner resist films, etched pattern transfer difference from a resist pattern becomes smaller; thus, fabrication precision in the substrate etching is improved. Therefore, the pattern fabrication has been performed with a resist film as thin as possible. In particular, in the research and development of most-advanced devices such as the next ULSI, or quantum-effect devices, pattern widths will be in a range between 10 nm~150 nm, thus thinning of resist films is much more necessary for realizing miniaturization or nano-fabrication and higher precision.
The resist used for such ultra-fine processing can be generally classified into the following 5 types:
(1) a resist comprising an alkaline soluble resin and a diazonaphthoquinone compound as a photo-sensitizer;
(2) an acrylic type polymer resist which degrades via main chain scission;
(3) a resist material comprising an alkaline soluble resin and an azide as a photo-sensitizer;
(4) a crosslinking type resist containing a chloromethyl group or an epoxy group; and
(5) a chemical amplification resist comprising an alkaline soluble resin, an acid generator, and a dissolution controlling agent having an acid sensitive group.
The resist material of type (1), generally used in LSI processing, is exposed to UV and the diazonaphthoquinone-compound as a sensitizer is subjected to a chemical change during UV exposure, by which solubility of the alkaline soluble resin is enhanced and a pattern is fabricated. As the alkaline soluble resin, a novolac resin, a phenol resin, poly(hydroxy styrene), and the like are used; however, the novolac resin is most commonly used. This type of resist has been used for pattern fabrication with a relatively thick film, approximately up to 200 nm.
The resist material of type (2) has mainly been used in the ultra-fine pattern fabrication of 200 nm or less. In this type, the acrylic main chains are cut by irradiating an electron beam, an X-ray, or UV having a wavelength of 300 nm or less, by which solubility of the resist is enhanced and a pattern is fabricated. (i) Poly(methyl methacrylate) (i.e., PMMA), (ii) ZEP (manufactured by Nippon Zeon Co.) which is a copolymer of &agr;-chloro methacrylate and &agr;-methyl styrene, and (iii) poly 2,2,2-trifluoroethyl &agr;-chloro acrylate (e.g., EBR-9 manufactured by Toray Co.) are representative resist materials of this type. In this type of resist, the difference in solubility rates between exposed and unexposed areas is very large, hence very high resolution can be realized. Therefore, this type of resist is generally used in thin-film form so as to fabricate an ultra-fine pattern of 200 nm or less.
As an example of fabricating a fine pattern of 10-50 nm range by thinning the resist film, it has been reported, in “Fabrication of 5-7 nm wide etched lines in silicon using 100 keV electron-beam lithography and polymethylmethacrylate resist”, Applied Physics Letters, Vol. 62 (13), pp. 1499-1501, Mar. 29, 1993, that a Si substrate is dry-etched through a mixture gas of SiCl
4
and CF
4
by using a 65 nr thick PMMA resist, a representative high-resolution resist. Another article, “Si nanostructures fabricated by electron beam lithography combined with image reversal process using electron cyclotron resonance plasma oxidation”, Journal of Vacuum Science and Technology, Vol. B13 (6), pp. 2170-2174, November/December, 1995, also reported the use of a 50 nm thick ZEP resist, which is known to have resolution as good as PMMA and also to have relatively high etching resistance for oxygen plasma processing of substrate.
On the other hand, in the case of defining a relatively large nanometer pattern of 50-150 nm, necessary resolution can be achieved in the present circumstances by using a relatively thick PMMA or ZEP resist and high energy beams mentioned above. In this range of pattern size, it is rather important to process substrates without forming any defects during dry-etching; then, the resist thickness is increased to ensure necessary dry-etching resistance. Typical resist thickness for this purpose is in a range of 0.1-0.5 &mgr;m.
The resist material of type (3) is normally used for UV or an electron beam exposure. This type of resist comprises the azide as a photo-sensitizer and the alkaline soluble resin, and the chemical change of azide, and the UV or electron beam exposure makes alkaline soluble resin insoluble, resulting in the formation of negative type patterns.
The resist material of type (4) comprises polymer resins containing the chloromethyl group or the epoxy group which has high crosslinking reactivity. In this type, the polymers are crosslinked with each other when they are irradiated by UV, an electron beam, or an X-ray, and the polymers become insoluble and a pattern is fabricated. This type of the resist is mainly used in negative-type pattern fabrication in which exposed areas remain.
The resist material of type (5) comprises the alkaline soluble resin, the acid generator, and the dissolution controlling agent (it may also be called a dissolution inhibitor) having the acid sensitive group. In this type, an acid is generated from the acid generator through irradiation of UV, electron beam, or X-ray, then, the acid reacts with the acid sensitive group of the dissolution controlling agent, by which the solubility of the alkaline soluble resin is changed and a pattern is fabricated. Since the reaction between the acid and the dissolution controlling agent proceeds via chain reaction scheme, very high sensitivity can be achieved in this type of resist. As the alkaline soluble resin, a novolac resin, a phenol resin, poly(hydroxy styrene), and the like are used. Additionally, in the chemical amplification type, there are some variations such that (i) the alkaline soluble resin functions as a dissolution controlling agent having an acid sensitive group, or (ii) a resin having an acid sensitive group reacts with an acid, making the resin alkaline soluble. However, in this type of resist, the acid becomes inactive due to water, ammonia, and the like included in the air, hence the resist sensitivity is considerably varied with the time between exposure and development. In order to stabilized the sensitivity, another polymer film to prevent the deactivators from penetrating in the resist film are overcoated on the resist.
Hereinbelow, common prob
Ishii Tetsuyoshi
Kurihara Kenji
Nozawa Hiroshi
Tamamura Toshiaki
Chu John S.
Finnegan Henderson Farabow Garrett & Dunner LLP
Nippon Telegraph and Telephone Corporation
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