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
1998-03-06
2001-09-11
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
C430S910000
Reexamination Certificate
active
06287746
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a chemically amplified resists and, more particularly, to a chemically amplified resist sensitive to ultra violet light, far ultra violet light, an electron beam, an ion beam and an x-ray and a process of forming a mask from the chemically amplified resist.
DESCRIPTION OF THE RELATED ART
The integration density of a semiconductor integrated circuit device such as a dynamic random access memory device is getting higher and higher, and, accordingly, a lithography is expected to transfer a miniature pattern to a photo-sensitive compound layer spread over a thin layer to be patterned.
One of the approaches to the miniature pattern is to use exposure light with a shorter wavelength. 256 mega-bit dynamic random access memory devices are scheduled in near feature, and are designed to have the minimum pattern width equal to or less than 0.25 micron. In order to achieve the minimum pattern width, KrF excimer laser would be used for the pattern transfer rather than i-ray, because the KrF excimer laser has the wavelength of 248 nanometers shorter than i-ray's wavelength of 365 nanometers.
The dynamic random access memory device of the next generation, i.e., 1 giga-bit dynamic random access memory device would have the minimum pattern width equal to or less than 0.2 micron, and such a miniature pattern requires a shorter wavelength. In fact, research and development efforts are made on a lithography using ArF excimer laser of 193 nanometers wavelength.
The lithography for the ultra large-scale integration requires high-sensitive high-resolution resist material. The high sensitivity is desirable, because an image is transferred to the resist layer through a small amount of exposure light. The small amount of exposure light reduces damage to the optical component such as a lens incorporated in the aligner. Moreover, the pattern transfer through the small amount of exposure light less deteriorates the laser source gas sealed in the excimer laser light source. The laser source gas is so expensive that the pattern transfer through the small amount of exposure light reduces the production cost of ultra large-scale integration.
A chemically amplified resist achieves high sensitivity. The chemically amplified resist contains photoacid generator such as cationic generator, which provides photochemically generated acid in exposure to active light. Japanese Patent Publication of Examined Application No. 2-27660 discloses chemically amplified resist composed of triphenylsulfonium-hexafluoroace-nato and poly(t-butoxycarbonyloxy-&agr;-methylstyrene. The chemically amplified resist is featured by the components. When the chemically amplified resist is exposed to photo radiation, the photochemical acid-generator generates protonic acid. The protonic acid is moved through the solid-state resist during the post heat treatment, and serves as a thermally driven catalyst so as to increase the reaction hundred times to thousand times. If we define an efficiency of photochemical reaction as the rate of chemical reaction per photon, the efficiency of photochemical reaction of conventional resist is less than 1. However, the chemically amplified resist drastically increases the efficiency of photochemical reaction, and enhances the sensitivity to the photo radiation. Most of the resist material is of the chemically amplified type, and the chemically amplified function is indispensable for new resist material.
The prior art photo-sensitive synthetic resin compound is hardly available for the lithography using excimer laser light equal to or less than 220 nanometer wavelength, because the resin component is poor in transparency and resistance against etchant.
The prior art lithography uses the exposure light longer in wavelength than KrF excimer laser light, which has the wavelength of 248 nanometers, and the photo-sensitive synthetic resin contains resin component such as Novolak resin or poly (p-vinylphenyl). The resin available for the resist has aromatic ring in the structural unit, and the aromatic ring imparts the dry etching resistance to the resist. However, the aromatic ring is strong in light absorption to the light equal to or less than 220 nanometer wavelength, and the prior art resin is hardly used for the resist, because a surface portion of the resist absorbs most of the exposure light. In other words, the exposure light does reach the boundary between the resist and the substrate, and miniature pattern is hardly transferred to the resist mask. This phenomenon is reported by Sasago et. al. in “ArF Excimer Laser Lithography (3)—Evaluation of Resist—”, proceedings of Joint Lectures of 35 Meeting of Applied Physics Society, 1p-K-4, 1989. For this reason, the lithography of the next generation requires resin achieving large dry etching resistance without the aromatic ring.
Several high-molecular compounds which have large dry etching resistance and good transparency to 193 nanometer wavelength light has been proposed. Followings are the prior art high-molecular compounds already known.
Takechi et. al. discloses copolymer of adamantylmethacrylate and tert-butylmethacrylate in “Alicyclic Polymer for ArF and KrF Excimer Resist Based on Chemical Amplification”, Journal of photopolymer Science and Technology, volume 5, Number 3 (1992), pages 439 to 446. Adamantylmethacrylate forms a unit of the copolymer, and is a kind of alicyclic high-molecular compound.
Japanese Patent Publication of Unexamined Application (JPA) No. 5-265212 discloses high-molecular compound similar to that proposed by Takechi et. al.
Endo et. al. discloses poly (norbonyl methacrylate) in “Challenges in Excimer Laser Lithography for 256 DRAM and beyond”, proceedings of IEDM, CA14-18, San Francisco, 1992.
G. M. Wallraff et. al. discloses copolymer with poly (isobornyl methacrylate) unit in “Single-layer chemically amplified photoresists for 193-nm lithography”, Journal of Vacuum Science and Technology, B11, volume 6, pages 2783 to 2788.
Japanese Patent Publication of Unexamined Application No. 8-82925 teaches poly (menthyl-methacrylate) unit.
Alicyclic group such as adamantyl group, norbornyl group, isobornyl group or menthyl group imparts good dry etching resistance to these prior art high-molecular compounds. However, there is no residual unit in the group for changing the solubility between an exposed portion and a non-exposed portion. For this reason, the high-molecular compounds are barely available for resin component when they form copolymer together with comonomer, in which carboxyl group of methacryl acid unit is protected, such as tertial methacrylate or tetrahydropyranyl methacrylate. In order to achieve the difference in solubility between the exposed portion and the non-exposed portion, the prior art resist requires the comonomer between 30 molecular percent and 50 molecular percent. The comonomer is small in dry etching resistance so that the prior art resist is also poor in the dry etching resistance. This means that the prior art resin component is hardly available for the actual lithography.
Moreover, alicyclic group and polar converting group are hydrophobic, and, accordingly, polymer with the hydrophobic group is poor in adhesion to a silicon substrate. For this reason, a miniature pattern is less reproducible by using the prior art resist. Another drawback inherent in the prior art resist is scum or residue left in alkaline developing solution, and the residue deteriorates the developing solution.
In order to overcome the drawbacks, the present inventors proposed improved polymer and photo-sensitive resin compound in Japanese Patent Publication of Unexamined Application No. 8-259626. The polymer was well transparent to the exposure light having the wavelength equal to or less than 220 nanometer wavelength, good in dry etching resistance and large in solubility between an exposed portion and non-exposed portion.
In detail, the alicyclic group imparts good dry etching resistance to the polymer, and carboxyl group is large in polarity. The present inventors bonded the a
Hasegawa Etsuo
Iwasa Shigeyuki
Maeda Katsumi
Nakano Kaichiro
Chu John S.
NEC Corporation
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