Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-06-13
2003-10-28
Solola, Taofiq (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C430S270100, C338S015000, C252S511000
Reexamination Certificate
active
06639084
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compounds used in photoresist and, more particularly, to chemically amplified photoresist sensitive to far-ultraviolet light equal in wavelength to or less than 220 nanometers, polymer used for producing the chemically amplified resist, monomer for producing the polymer and a method for transferring a pattern to a chemically amplified resist layer.
DESCRIPTION OF THE RELATED ART
Pattern images are sequentially transferred to semiconductor wafers in processes for fabricating semiconductor devices, and design rules have been renewed in the fabrication process. Now, semiconductor devices are designed under sub-micron rules, and requirements for the photolithography get sever and sever.
Manufacturers require 0.13 micron patterns for 1 giga-bit DRAMs (Dynamic Random Access Memory), and research and development efforts are being made for the photolithography used in the ultra large scale integration. 193-nanometer wavelength ArF excimer laser lithography is disclosed by Donald C. Hofer et. al. in “193 nm Photoresist R & D: The Risk & Challenge”, Journal of Photopolymer Science and Technology, vol. 9, No. 3, pages 387-397, 1996. The ArF excimer laser lithography requires new photo-resist. The ArF excimer laser system is expensive, and the gaseous mixture used therein is short in-lifetime. In these circumstances, the new photoresist is expected to be highly sensitive to the ArF excimer laser light as well as the high resolution from the viewpoint of the cost performance.
The chemically amplified photoresist is attractive. The chemically amplified photoresist contains photo-acid generator, which accelerates the chemical reaction in the photoresist. A typical example of the chemically amplified photoresist is disclosed in Japanese Patent Application laid-open No. 2-27660. The prior art chemically amplified photoresist contains triphenylsulfonium hexafluoroarsenate and poly (p-tert-butoxycarbonyloxy-a-methylstyrene). The prior art chemically amplified photoresist is presently used in KrF excimer laser lithography as taught by Hiroshi Itoh and C. Grantwillson, American Chemical Society Symposium Series, vol. 242, pages 11-23, 1984.
When the chemically amplified photoresist is exposed to the light, proton acid is generated from the photo-acid generator. The proton acid reacts with the copolymer in the heat treatment after the exposure to the light. The amount of reaction per photon, i.e., photoreaction efficiency is enhanced through the acid-catalyzed reaction. Although the photoreaction efficiency is less than 1 in the conventional photoresist, the chemically amplified photoresist achieves the photoreaction efficiency greater than 1, and most of new products of photoresist presently developed are of the type chemically amplified.
The ArF excimer laser is an example of the short-wavelength band equal to or less than 220 nanometers. The photoresist available for the photolithography in the short-wavelength band is expected to be transparent to the exposure light and large in resistance against dry etching. The prior art products of photoresist, which are responsive to g-line with 438 nanometer wavelength, i-line with 365 nanometer wavelength or KrF excimer laser light with 248 nanometer wavelength, contain copolymer having the structural unit with the aromatic ring such as novolak resin or poly (p-vinylphenol), and the aromatic ring makes the copolymer resistive against the dry etching.
Although the copolymer with the aromatic ring is preferable for the KrF excimer laser light or the long wavelength rays, the copolymer exhibits strong light absorption to the light in the short wavelength band equal to or greater than 220 nanometer wavelength. In fact, when the prior art photoresist based on the copolymer is exposed,to the ArF excimer laser light, most of the ArF excimer laser light is absorbed in the surface portion of the prior art photoresist layer, and hardly reaches the substrate. This means that any fine pattern is not obtained from the prior art photoresist layer.
As described hereinbefore, the prior art products of photoresist are not available for the ArF excimer laser lithography, and the semiconductor manufacturers desire a new product of photoresist available for the ArF excimer laser lithography. The structural unit of the photoresist is expected to exhibit large resistance against dry etching without the aromatic ring, because the photoresist would exhibit the transparency to the ArF excimer laser light.
The prior art photoresist available for 193 nm ArF excimer laser lithography is taught by Takechi et. al., Journal of Photopolymer Science and Technology, vol. 5, No. 3, pages 439 to 446, 1992. The photoresist is based on copolymer having adamantyl methacrylate units which are alicylic polymer. Another prior art photoresist is based on copolymer having isobornyl methacrylate units as disclosed by R. D. Allen et. al, Journal of Photopolymer Science and Technology, vol. 8, No. 4, pages 623 to 636, 1995 and vol. 9, No. 3, pages 465-474, 1996. Yet another prior art photoresist is based on copolymer having the structural unit of alternating copolymerization between norbornene and maleic anhidride as taught by F. M. Houlihan et. al, Macromolecules, vol. 30, pages 6517-6524, 1997.
Carboxy group and hydroxy group are categorized in the polar groups. The polar group makes the photoresist strongly held in contact with substrates, and are preferable to the photoresist. However, the aforementioned monomer, which has the alicylic group, does not have any polar group. The prior art photoresist is hydrophobic, and the photoresist layer is liable to peel off from the substrates such as silicon substrates. Thus, the first drawback inherent in the prior art photoresist is the weak adhesion to substrates.
The second drawback inherent in the photoresist containing the polymer having an alicylic group is poor uniformity of film formation. When the prior art photoresist is spread over substrates, the prior art photoresist layers are irregular in thickness. This phenomenon is also derived from the hydrophobic property due to the lack of the polar group.
The third drawback is a small difference in solubility between the pre-exposure to light and the post-exposure. Adamantyl—containing residue, isobornyl—containing residue and menthyl—containing residue give the strong resistance against dry etching to the photoresist. However, the prior art photoresist does not have any residue which makes the photoresist widely different in solubility between the pre-exposure to light and the post-exposure. This means that the photoresist layer has a dull edge.
It is possible to overcome those drawbacks by employing copolymerization with certain comonomers for improving the difference in solubility and/or comonomers for enhancing the adhesion to substrates. t-butyl methacrylate and tetrahydropyranyl methacrylate are examples of the comonomer for improving the difference in solubility, and methacrylic acid is an example of the comonomer for enhancing the adhesion to substrates. However, the comonomer is required at least 50 mole %. The comonomer is less resistive against dry etching. Thus, the manufacturers desire new photoresist which exhibits high transparency to the exposure light, large difference in the solubility and strong adhesion to substrates without sacrifice of the resistance against dry etching.
The other sorts of photoresist, which contain the alternating copolymerization between norbornene and maleic anhydride, have the norbornane ring. The norbornane ring also does not have any polar group, and the photoresist exhibits poor adhesion. When copolymer with acrylic acid is introduced into the resin based on the alternating copolymer between norbornene and maleic anhydride, the adhesion is improved. However, the resultant photoresist is less resistive against dry etching. The manufacturers also desire new photoresist exhibiting strong adhesion to substrates without sacrifice of the resistance against dry etching.
SUMMARY OF THE INVENTION
It is therefore an i
Maeda Katsumi
Nakano Kaichiro
NEC Corporation
Solola Taofiq
Sughrue Mion LLP
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