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
1996-09-09
2004-03-09
Weiner, Laura (Department: 1745)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S325000, C522S015000, C522S031000
Reexamination Certificate
active
06703181
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensitive composition and a pattern formation method for use in micropatterning of semiconductor devices, specifically, large-scale integrated circuits (LSIs).
2. Description of the Related Art
The manufacture of semiconductor devices such as LSIs makes use of a micropatterning technique performed by photolithography. This technique is done in accordance with the following processes. That is, a photo-resist film is first formed on a substrate, such as a silicon single-crystal wafer, by, e.g., spin coating and then the film is exposed. Thereafter, treatments such as developing and rinsing are performed for the resist film, thereby forming a resist pattern. Subsequently, the exposed wafer surface is etched by using the resist pattern as an anti-etching mask to form lines and windows with small widths, thereby forming a desired pattern.
In the manufacture of LSIs, as the packing density of LSIs has increased, a processing technique capable of forming finer patterns has been required in lithography. To meet this requirement, it has been conventionally attempted to shorten the wavelength of the exposure light source. As one such attempt, a lithography technique using as its light source deep UV, such as a KrF excimer laser (wavelength 248 nm) or an ArF excimer laser (wavelength 193 nm), has been examined.
Conventional resist materials, however, have an excessively large absorbance for deep UV. Therefore, it is impossible to make UV light sufficiently reach a portion apart from the surface of a resist film (e.g., an interface region between a resist film and a substrate) during exposure. Consequently, the chemical change which is due to the exposure does not occur satisfactorily throughout the total film thickness in the exposed portion of the resist film. The result is a nonuniform solubility in the direction of thickness with respect to a developing solution. The solubility especially in the portion apart from the surface of the resist film as described above is poor, and so the sectional shape of a resist pattern formed after development becomes triangular in that portion. This brings about a problem when the resultant resist pattern is to be used as an anti-etching mask; i.e., it is impossible to transfer a fine pattern of interest onto a substrate or the like.
As a resist material by which the above problem can be solved, a resist called a chemical amplification type resist has been proposed. The chemical amplification type resist is a photosensitive composition containing a compound which generates a strong acid upon being irradiated with light, i.e., a photo-acid generator, and a compound which changes into a hydrophilic substance if its hydrophobic group is decomposed by the acid generated. As a practical example of such resist material, U.S. Pat. No. 4,491,628 (1985) to H. Ito, C. G. Wilson, and J. M. J. Frechet discloses a positive resist containing a polymer which is obtained by blocking a hydroxyl group of poly(p-hydroxystyrene) by a butoxycarbonyl group, and an onium salt as the photo-acid generator. In addition, M. J. O'Brien, J. V. Crivello, SPIE, Vol. 920, Advances in Resist Technology and Processing, p. 42 (1988) discloses a positive resist containing an m-cresol novolak resin, a naphthalene-2carboxylic acid-tert-butylester, and a triphenylsulfonium salt as the photo-acid generator. Also, H. Ito, SPIE, Vol. 920, Advances in Resist Technology and Processing, p. 33 (1988) discloses a positive resist containing 2,2-bis(4-tert-butoxycarbonyloxyphenyl)propane or polyphthalaldehyde, and an onium salt as the photo-acid generator.
In each of these chemical amplification type resists, the acid generated by the photo-acid generator functions as a catalyst to bring about a chemical change efficiently inside the resist even with a small amount. When the resist film is exposed, therefore, the reaction proceeds sufficiently even in the interior of the film to which it is difficult to make a radiation reach compared with the film surface. This consequently makes it possible to form, after development is performed, a resist pattern having a rectangular sectional shape, particularly, a resist pattern in which the side surface of a line portion is steep and vertical.
In the above chemical amplification type resists, however, the amount of the acid generated in the exposed portion of the resist film is very small. Therefore, the resist is readily affected by the surrounding environment, especially the atmospheric oxygen and moisture and other atmospheric trace components on the surface of the resist film. This makes it difficult to stably form fine patterns. More specifically, a slight amount of dimethylaniline contained in the atmosphere deactivates an acid generated near the surface of the resist film upon irradiation of light. As a result, a so-called sparingly soluble layer whose rate of dissolution with respect to a developing solution is very low is formed on the surface of the resist film. It is reported that this sparingly soluble layer remains as an overhang on the surface of the resist pattern after exposure and development (S. A. MacDonald, N. J. Cleark, H. R. Werdt, C. G. Willson, C. D. Snyder, C. J. Knors, N. B. Deyoe, J. G. Maltabes, J. R. Morrow, A. E. MacGuire, and S. J. Hplmes, Proc. SPIE, Vol. 1466, 2 (1991)).
This sparingly soluble layer reduces the resolution of the resist, and an overhang formed on the resist pattern by the sparingly soluble layer adversely affects the etching accuracy of a semiconductor substrate region. To prevent the formation of this overhang-like sparingly soluble layer, as shown in
FIG. 3A
, exposure is performed after the atmospheric influence is reduced by forming a protective layer
8
on a resist film (Jpn. Pat. Appln. KOKAI Publication No. 4-2040848). Even by this method, however, an overhang cannot be completely removed, and an overhang-like sparingly soluble layer
9
as shown in
FIG. 3B
is formed on the side walls of a resist pattern
6
. This method of forming a protective layer has problems in addition to the above problem; i.e., the method requires an additional coating device and degrades the workability because the number of processes is increased.
On the other hand, it is known that the resolution can be increased by adding to a chemical amplification type resist composition any of aniline-type, imidazole-type, pyridine-type, and ammonia-type derivatives each of which acts as a base with respect to the acid generated upon irradiation of light (Jpn. Pat. Appln. KOKAI Publication No. 5-127369). However, the miscibility of these amine-type compounds with respect to a low-molecular compound (to be described later) has not been reported yet.
In addition, in the formation of a pattern using the above chemical amplification type resist, when a resist film is formed, i.e., when a resist solution is coated on a substrate, a phase separation is sometimes caused in the film by the difference in molecular weight between components, resulting in a nonuniform concentration distribution of each component. As a result, the chemical change does not proceed uniformly in the exposed portion of the film, so a fine resist pattern with a rectangular sectional shape cannot be obtained stably.
The phase separation is described more specifically in H. Ito, J. Polymer. Sci.: Part A 24, 2971 (1986) which reports that in the synthesis of polyvinyl phenol, which is used as one component of a resist material, and in which phenolic hydroxyl groups are partially protected by tert-butoxycarbonyl, the phase separation occurs depending on the introduction rate of the protective groups of that polymer. The concentration distribution of a component in a resist film is described more specifically in M. Toriumi, M. Yanagimachi, and H. Masuhara, Proc. SPIE, Vol. 1466, 458 (1991).
It is also known that in the pattern formation using the chemical amplification type resist, the line width changes in correspondence with the baking temperature after exposure, and this de
Chiba Kenji
Hayashi Takao
Miyamura Masataka
Onishi Yasunobu
Sato Kazuo
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Weiner Laura
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