Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
2000-10-16
2002-04-30
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S270100
Reexamination Certificate
active
06379874
ABSTRACT:
TECHNICAL FIELD
This invention is directed to generating negative tone resist images in a lithographic process for use, for example, in the manufacture of microelectronics.
BACKGROUND OF THE INVENTION
A lithographic process used to pattern integrated circuits and other microelectronics is as follows: A polymeric material is spun onto a substrate such as a silicon wafer to form a uniform coating. Then, the polymer is exposed to a source of photons, electrons, or X-rays through a mask based on the pattern information to be transferred. The mask allows the radiation to pass through previously selected areas. The polymer exposed to radiation undergoes a chemical change (e.g., cross-linking, chain-scission, or polarity change). The next step is the use of a solvent to selectively remove the exposed or the unexposed regions to transfer the pattern onto the polymer layer. The use of the solvent is called development, and the solvent is called a developer. The polymer is called a positive-tone resist if the exposed regions become more soluble in the solvent, and the polymer is called a negative-tone resist if the exposed regions become less soluble in the solvent.
The trend in the electronics industry towards miniaturization and increased complexity has set up a need for decrease in resolvable feature size. This has been achieved by decreasing the wavelength of the exposing radiation but for further diminished feature size, the selectivity of the solvent becomes increasingly important. However, the use of liquid developers in the mainstream production environment generates enormous amounts of waste, causing great environmental concern. In view of this, supercritical fluids have been considered for use as environmentally friendly, nontoxic, nonflammable and very low cost lithographic developers.
Allen et al. U.S. Pat. No. 5,665,527 is directed to generating a negative tone resist image in a process comprising the steps of (1) coating a substrate with a film of a polymeric composition comprising a polymer, a photosensitive acid generator and acid labile groups; imagewise exposing the film to generate free acid; and developing the image with critical fluid. In the sole working example, the polymer is a 75/25 (mole percent) random copolymer of pentafluoropropyl methacrylate and t-butyl methacrylate and the critical fluid developer is carbon dioxide critical fluid. This process does not enable resolution of sub 0.3 &mgr;m features.
SUMMARY OF THE INVENTION
It has been discovered that block copolymers allow development at lower pressures and temperatures to entirely dissolve the unexposed regions to form a negative tone resist image than where random copolymer with the same volume percentages of the same monomers is used.
Moreover, it has been discovered in a preferred embodiment of the invention that block copolymers with acid cleavable tetrahydropyranyl groups and supercritical CO
2
soluble fluoro side-chain containing methacrylate groups chemically amplified to effect the polarity change leading to the solubility change in supercritical CO
2
enables sub 0.3 &mgr;m features to be resolved.
The invention herein is directed to a process for generating a negative tone resist image, comprising the steps of:
(a) coating a substrate with a film comprising block copolymer comprising: (i) block having pendant fluoro-containing groups and (ii) block having pendant hydrolyzable ester containing groups, the volume percent of block (i) being great enough to provide complete solubility in regions of the film to be removed in step (c) but not so great that sub 0.3 &mgr;m features cannot be resolved in step (c);
(b) hydrolyzing hydrolyzable ester to polar functionality insoluble in the supercritical fluid used in step (c) to form a pattern defined by supercritical fluid soluble and supercritical fluid insoluble regions of the film; and
(c) developing a negative tone resist image from the pattern by using supercritical fluid to dissolve the supercritical fluid soluble regions of the film.
The block copolymer has a weight average molecular weight, for example, ranging from 2,000 to 20,000.
Typically, the supercritical fluid is supercritical CO
2
(which is selective to polarity changes).
In the preferred embodiment referred to above, the blocks (ii) are formed by polymerizing 2-tetrahydropyranyl methacrylate and the blocks (i) are formed by polymerizing fluorinated alkyl methacrylate. In an embodiment herein, the block copolymer contains more than 50% by volume blocks (i). In an embodiment herein, the block copolymer contains at least 20% by volume blocks (ii). Working examples are presented hereinafter wherein the blocks (i) are formed by polymerizing 1H, 1H-perfluoro-n-butyl methacrylate (Example I) and by polymerizing 1H, 1H-perfluorooctyl methacrylate (Examples II and III).
The molecular weights herein including weight average molecular weights M
w
, number average molecular weights M
n
and polydispersities M
w
/M
n
are determined by gel permeation chromatography using poly(methyl methacrylate) standards.
The volume percentages of the block copolymers are calculated from
1
HNMR by comparing the integrated area of the methine proton in the tetrahydropyranyl methacrylate or of the methylene protons in the tetrahydropyranyl methacrylate ring to the integrated area of the methylene protons in the fluorinated alkyl methacrylate.
The term “supercritical fluid” is used herein to mean substance heated to a temperature above its critical temperature and compressed to a pressure above its critical pressure to achieve miscibility without phase separation. For a supercritical fluid consisting of one substance, there is miscibility between the liquid and gas phase of such substance. For critical fluids consisting of two or more substances, there is miscibility between the two liquids and the two gases of such substances.
DETAILED DESCRIPTION
As indicated above, the invention is directed to a process for generating a negative tone resist image comprising the steps of: (a) coating a substrate with a film comprising block copolymer comprising: (i) block having pendant fluoro-containing groups and (ii) block having pendant hydrolyzable ester containing groups (i.e., which are hydrolyzable to supercritical fluid insoluble functionality in step (b)), the volume percent of block (i) being great enough to provide complete solubility in regions of the film to be removed in step (c) at pressures less than 7,000 psi and temperature less than 80° C. in step (c), but not so great that sub 0.3 &mgr;m features cannot be resolved in step (c); (b) hydrolyzing hydrolyzable ester to polar functionality insoluble in the supercritical fluid used in step (c) to form a pattern defined by supercritical fluid soluble and supercritical fluid insoluble regions of the film; and (c) developing a negative tone image resist from the pattern by using supercritical fluids to dissolve the supercritical fluid soluble regions of the film. The block copolymer has, for example, a weight average molecular weight ranging from 2,000 to 20,000, for example, 4,000 to 15,000, for example, 4,500 to 12,000, a number average molecular weight ranging from 1,500 to 18,000, for example, from 4,000 to 12,000 and a polydispersity ranging, for example, from 1.05 to 1.20. Suitable substances for use as the supercritical fluid include carbon dioxide, ammonia, difluorodichloromethane, methane, ethane and propane; other suitable substances will be known to those skilled ill the art.
We turn now to the preferred case where the block (ii) is formed by polymerizing 2-tetrahydropyranyl methacrylate and the block (i) is formed by polymerizing fluorinated alkyl methacrylate. For this preferred case, the supercritical fluid is preferably supercritical CO
2
.
The polymers for this preferred case have, for example, the structure
where the molecular weight ranges are as set forth above in the general case and p is 1 to 6, preferably 1, and q is 1 to 12, preferably 3 to 7, and n and m−1 are such as to provide said molecular weight and a volume percent of more than 50%
Ober Christopher K.
Wang Jianguo
Cornell Research Foundation Inc.
Duda Kathleen
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