Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-08-29
2002-12-03
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S311000, C430S318000, C430S322000, C430S325000, C430S945000
Reexamination Certificate
active
06489082
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a microlithographic process using a photosensitive composition, a micromachining technique for preparing a semiconductor device, or the like, and a process for preparing the semiconductor device, or the like, including the microlithographic process. More particularly, the present invention relates to a method for forming a negative pattern suitable for a photolithographic process using a far ultraviolet radiation having a wavelength of not more than 220 nm, such as an ArF excimer laser, which is a radiation source for wavelengths shorter than those in currently used UV sources including high pressure mercury lamps and KrF excimer lasers.
BACKGROUND OF THE INVENTION
A photolithographic technique for fabricating micro-order or submicron-order fine patterns within an electronic device, such as a semiconductor, has been at the core of micromachining techniques for mass production. A demand for an increase in integration and an increase in density of semiconductor devices in recent years has led to many improvements in micromachining techniques. In particular, as the minimum possible machining dimension approaches the exposure wavelength, photolithographic techniques using light sources for shorter wavelengths ranging from g-line (436 nm) and i-line (365 nm) in a high pressure mercury lamp to a KrF excimer laser (248 nm), have been developed. A change in exposure wavelength has led to the development of photoresists made from materials suitable for the wavelength being used. In any of the photoresists suitable for the above wavelengths, aqueous alkali development utilizing the solubility of resins having a phenol structure or polymeric materials in an aqueous alkali has been adopted on a commercial scale, although they are different from each other in photoactive compound and photoactivating mechanism. These resins and polymeric materials necessarily contain many aromatic rings which are also chemical structural elements for enhancing the etching resistance in the step of dry etching after the formation of the resist pattern.
Negative resists prepared from resins having the above-mentioned phenol structure are classified into ones of a crosslinking type as disclosed in Japanese Patent Laid-Open No. 164045/1987 and ones of a dissolution inhibition type as disclosed in Japanese Patent Laid-Open No. 165359/1992. In any type, submicron-order fine patterns can be formed without causing swelling.
Photolithography using an ArF excimer laser (193 nm) as a light source has become more and more commonplace for photolithography which can provide a minimum possible machining dimension of less than 0.25 &mgr;m. This wavelength corresponds to the absorption maximum of an aromatic ring. Therefore, in the photoresist material composed mainly of a phenol structure, which has been used on a commercial scale, the formation of a latent image in response to the exposure is limited to a portion which is very near the surface of the photoresist film, making it difficult to form a fine resist pattern by aqueous alkali development.
On the other hand, various resist materials have been proposed which have high transmittances in the above-mentioned wavelength region while possessing high dry-etching resistance. Utilization of an adamantane structure (Japanese Patent Laid-Open Nos. 39665/1992 and 265212/1993) and utilization of a norbornane structure (Japanese Patent Laid-Open Nos. 80515/1993 and 257284/1993) have been proposed as chemical structures which are transparent in the far ultraviolet region including the wavelength 193 nm of the ArF excimer laser and, instead of the aromatic ring, can impart dry-etching resistance to the resist material. Japanese Patent Laid-Open Nos. 28237/1995 and 259626/1996 disclose that, in addition to these structures, general alicyclic structures, such as a tricyclodecanyl group, are also useful.
Regarding resist materials which have been rendered developable with an aqueous alkali by using a polymer having a chemical structure transparent in the far ultraviolet region including the wavelength 193 nm of the ArF excimer laser and, utilization of the carboxylic acid structure of acrylic acid or methacrylic acid, has been attempted in Japanese Patent Laid-Open Nos. 39665/1992, 184345/1992, 226461/1992, and 80515/1993. In these publications, the aqueous alkali solubility of a portion dissolved in a developing solution in the aqueous alkali development depends upon the carboxylic acid structure of acrylic acid or methacrylic acid. Furthermore, Japanese Patent Laid-Open No. 8-259626 discloses a polymeric compound in which a carboxylic acid group has been provided in an alicyclic structure introduced into the side chain of a methacrylic acid ester.
SUMMARY OF THE INVENTION
The phenol structure which has so far been used as an alkali-soluble group has a pKa of 10.0 (phenol), whereas the above carboxylic acid structure has a pKa of as low as 4.8 (acetic acid), indicating that its acidity is high. Therefore, when they are used as the alkali-soluble group of the base resin, the results is that with the same molar fraction the resin having a carboxylic acid structure has a higher dissolution rate in an aqueous alkali and in addition can be dissolved in an alkali developing solution having such a low concentration that it will not dissolve the resin having a phenol structure.
Use of the resin having a carboxylic acid structure in combination with a cross-linking agent as described in Japanese Patent Laid-Open No. 164045/1987 is disadvantageous because it causes the carboxylic acid having high acidity to remain in the crosslinked portion and an alkali developing solution infiltrates into this portion and swells, which makes it impossible to form a fine pattern. On the other hand, when use is made of a material described in Japanese Patent-Laid Open No. 165359/1992, wherein the acid formed upon exposure produces a compound having a dissolution inhibitory activity, no contrast in dissolution is created if the resin has a carboxylic acid structure, thereby making it impossible to provide a negative resist disadvantageously.
The fact that an acid-catalyzed reaction of a carboxylic acid with an alcohol in a solution results in conversion of the carboxylic acid to a carboxylic acid ester is generally known in the art, and this reaction is one useful method for synthesizing a carboxylic acid ester. Since, however, this reaction is an equilibrium reaction, it is necessary for the reaction to proceed toward the ester side. Thus, alcohol should be used in large excess and, in addition, water as a by-product should be discharged outside the system. When the application of this reaction to a radiation-sensitive composition is contemplated, the alcohol cannot be added in large excess while maintaining the solubility of the coating in an alkali. Further, in this case, it is difficult to discharge water produced in the reaction outside the system. For this reason, in general, the esterification proceeds to an extent of only several percent. A reduction in the amount of the carboxylic acid to this extent is unsatisfactory for creating contrast of dissolution high enough to form a pattern.
A first object of the present invention is to provide a method for negative pattern formation which enables development using an aqueous alkali developing solution without causing swelling of a fine pattern, utilizes esterification of a resin having a carboxylic acid structure, and provides a fine pattern with excellent resolution.
A second object of the present invention is to provide a process for preparing a semiconductor device using the method for pattern formation according to the first object of the present invention.
The first object of the present invention can be attained by a method for pattern formation, including the following steps: forming a coating having a photosensitive composition containing at least a carboxylic acid structure on a predetermined substrate; irradiating the coating with an actinic radiation in a predetermined pattern form to form
Hattori Takashi
Shiraishi Hiroshi
Tsuchiya Yuko
Barreca Nicole
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
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