Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1994-11-28
2001-08-21
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S270100, C430S327000, C430S330000
Reexamination Certificate
active
06277546
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved lithographic imaging process for use in the manufacture of integrated circuits.
BACKGROUND OF THE INVENTION
Presently there is a desire in the industry for higher circuit density in microelectronic devices which are made using lithographic techniques. One method of increasing the number of components per chip is to decrease the minimum feature size on the chip, which requires higher lithographic resolution. There is a goal in industry to reduce feature size to 0.25 microns. The use of shorter wavelength radiation (e.g. deep UV e.g. 190 to 315 nm) than the currently employed mid-UV spectral range (e.g. 350 nm to 450 nm) offers the potential for this higher resolution. However, with deep UV radiation, fewer photons are transferred for the same energy dose and higher exposure doses are required to achieve the same desired photochemical response. Further, current lithographic tools have greatly attenuated output in the deep UV spectral region.
In order to improve resolution, Deckman et al. U.S. Pat. No. 4,608,281 (issued Aug. 26, 1986discloses the use of an electron beam exposure tool. Poly(methyl methacrylate) (PMMA) which undergoes main chain scission upon e-beam exposure is used as the resist material. After exposure the degraded polymer is removed with solvent to develop the image. Deckman teaches pre-exposure baking of the polymeric resist above its glass transition temperature (Tg) to remove solvent and improve resolution. Brault et al. U.S. Pat. No. 4,777,119 (issued Oct. 11, 1988also discloses pre-exposure baking of PMMA resist above its Tg to crosslink the polymer to improve its lithographic performance. Unfortunately, the lithographic mechanism of Deckman and Brault of main chain scission polymer degradation requires high exposure doses of radiation and is not suitable for manufacturing processes.
In order to improve the sensitivity of a resist for use in the deep UV, Ito et al. developed an acid catalyzed chemically amplified resist which is disclosed in U.S. Pat. No. 4,491,628 (Jan. 1, 1985). The resist comprises a photosensitive acid generator and an acid sensitive polymer. The polymer comprises side chain (pendant) groups which are bonded to the polymer backbone and are reactive towards a proton. Upon imagewise exposure to radiation, the photoacid generator produces a proton. The resist film is heated and, the proton causes catalytic cleavage of the pendant group from the polymer backbone. The proton is not consumed in the cleavage reaction and catalyzes additional cleavage reactions thereby chemically amplifying the photochemical response of the resist. The cleaved polymer is soluble in polar developers such as alcohol and aqueous base while the unexposed polymer is soluble in nonpolar organic solvents such as anisole. Thus the resist can produce positive or negative images of the mask depending of the selection of the developer solvent.
Nalamasu et al., “An Overview of Resist Processing for Deep-UV Lithography”, J. Photopolym. Sci. Technol. 4, 299 (1991) also discloses a chemically amplified resist composition comprising a photoacid generator and poly(t-butoxycarbonyloxystyrene sulfone).
Schlegel et al., “Determination of Acid Diffusion in Chemical Amplification Positive Deep Ultraviolet Resist”, J. Vac. Sci. Technol. 278 March/April 1991 discloses a chemically amplified resist comprising a photoacid generator and a chemically amplified dissolution inhibitor p-tetrahydropyranyl protected polyvinylphenol disposed in novolac resin. Schlegel teaches using a high pre-exposure bake temperature in combination with a low post-exposure bake temperature. However, due to the high absorbance of the novolac resin in the deep UV, such a composition is unsuitable for use in semiconductor manufacturing in the deep UV.
Further, because of the catalytic nature of the imaging mechanisms, these chemically amplified resist systems are sensitive toward minute amounts of airborne chemical contaminants such as basic organic substances. These substances degrade the resulting developed image in the resist film and cause a loss of the linewidth control of the developed image. This problem is exaggerated in a manufacturing process where there is an extended and variable period of time between applying the film to the substrate and development of the image. In order to protect the resist from such airborne contaminants, the air surrounding the coated film is carefully filtered to remove such substances. Alternatively, the resist film is overcoated with a protective polymer layer. However, these are cumbersome processes. There still is a need in the art for a process for imaging chemically amplified resists for use in semiconductor manufacturing.
It is therefore an object of the present invention to provide an improved process for imaging of photoresist.
Other objects and advantages will become apparent from the following disclosure.
SUMMARY OF THE INVENTION
The present invention relates to a process for generating a resist image on substrate comprising five steps. The first step involves coating the substrate with (i) a vinyl polymer (ii) a photosensitive acid generator, and (iii) acid labile groups. In one embodiment, the acid labile groups are pendant from the polymer backbone. In another embodiment, the acid labile groups are on a molecule disposed in the polymer. Upon exposure to acid, the acid labile groups undergo a polarity change which results in dissolution differentiation. The second step involves heating the film to an elevated temperature which is preferably at or above the glass transition temperature of the polymer and below the temperature which causes thermally activated polarity change in the acid labile group. The third step involves imagewise exposing the film to radiation to generate free acid. In the fourth step, the film is heated to an elevated temperature preferably at least above about 110° C. The acid generated from the photosensitive acid generator converts the acid labile groups to polar groups which alter the solubility of the polymer in the exposed area of the film. The last step of the process involves developing the image with standard techniques such as solvent development.
The key features of the process of the present invention are the second and fourth steps. The second step involves post apply, pre-exposure heating to an elevated temperature preferably to a temperature which is at or above the glass transition temperature (Tg) of the polymer and below the temperature which causes thermally activated polarity change of the acid labile group. The fourth step involves post-exposure heating of the film to a high temperature. The combination of the pre-exposure heating step and the post-exposure heating step provides unexpected protection of the resist film from airborne chemical contaminants during the process for generating a resist image on the substrate and also provides developed images with high constrast and high resolution.
Preferably, in the process of the present invention, the polymer is a copolymer comprised of a hydroxystyrene monomer and a monomer having an acid labile group. Preferably, the acid labile group is an acid cleavable group, preferably an acid cleavable ester group.
The present invention also relates to an integrated circuit formed using the process of the present invention.
A more thorough disclosure of the present invention is presented in the detailed description which follows and from in accompanying drawings in which
FIGS. 1-3
are scanning electron micrographs of resist images.
REFERENCES:
patent: 4430419 (1984-02-01), Harada
patent: 4476217 (1984-10-01), Douglas et al.
patent: 4491628 (1985-01-01), Ito et al.
patent: 4608281 (1986-08-01), Deckman et al.
patent: 4618564 (1986-10-01), Demmer et al.
patent: 4777119 (1988-10-01), Brault et al.
patent: 4824763 (1989-04-01), Lee
patent: 4840876 (1989-06-01), Arai
patent: 4842992 (1989-06-01), Arai
patent: 4845143 (1989-07-01), Ito et al.
patent: 4869996 (1989-09-01), McCartin et al.
patent: 4897337 (1990-01-01), K
Breyta Gregory
Clecak Nicholas Jeffries
Hinsberg, III William Dinan
Hofer Donald Clifford
Ito Hiroshi
Duda Kathleen
International Business Machines - Corporation
Martin Robert B.
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