Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-04-19
2004-07-06
Zalukaeva, Tatyana (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S333300, C525S344000, C525S346000, C526S319000, C526S219600, C526S323200, C526S329700, C526S346000, C526S347100
Reexamination Certificate
active
06759483
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the production of homo-, co- and ter-polymers of substituted styrenes such as p-acetoxystyrene (ASM), and/or alkyl acrylates and/or other monomers that are useful in photoresists and optical applications.
2. Description of the Prior Art
There is a desire in the industry for higher circuit density in microelectronic devices that 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 resolutions. The use of shorter wavelength radiation (e.g., deep UV e.g. 190 to 315 am) than the currently employed mid-UV spectral range (e.g. 350 am to 450 am) offers the potential for 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 sensitivity, several acid catalyzed chemically amplified resist compositions have been developed such as those disclosed in U.S. Pat. No. 4,491,628 (Jan. 1, 1985) and Nalamasu et al, “An Overview of Resist Processing for Deep UV Lithography”, J. Photopolymer Sci. Technol. 4, 299 (1991). The resist compositions generally comprise a photosensitive acid generator and an acid sensitive polymer. The polymer has acid sensitive side chain (pendant) groups that 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 non-polar 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. Although chemically amplified resist compositions generally have suitable lithographic sensitivity, in certain applications, their performance can be improved by (i) increasing their thermal stability in terms of thermal decomposition and plastic flow and (ii) increasing their stability in the presence of airborne chemical contaminants. For example, in some semiconductor manufacturing processes, post image development temperatures (e.g. etching, implantation etc.) can reach 200° C. Brunsvold et al., U.S. Pat. Nos. 4,939,070 (issued Jul. 3, 1990) and U.S. Pat. No. 4,931,379 (issued Jun. 5, 1990) disclose chemically amplified, acid sensitive resist compositions having increased thermal stability in the post image development stage. Brunsvold's resist compositions form a hydrogen bonding network after cleavage of the acid sensitive side chain group to increase the thermal stability of the polymer. Brunsvold avoids hydrogen-bonding moieties prior to the cleavage reaction because such hydrogen bonding is known to unacceptably destabilize the acid sensitive side chain. Although Brunsvold resists have suitable thermal stability, they also have lower sensitivity and therefore are unsuitable in certain applications.
With respect to chemical contamination, MacDonald et al. SPIE 14662. (1991) reported that due to the catalytic nature of the imaging mechanisms, 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 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.
Therefore, there was a need in the art for an acid sensitive, chemically amplified photoresist composition having high thermal stability and stability in the presence of airborne chemical contaminants for use in semiconductor manufacturing. Apparently, this was accomplished in the invention outlined in U.S. Pat. No. 5,625,020 which relates to a photosensitive resist composition comprising (i) a photosensitive acid generator and (ii) a polymer comprising hydroxystyrene and acrylate, methacrylate or a mixture of acrylate and methacrylate. The resist has high lithographic sensitivity and high thermal stability. The resist also exhibits surprising stability in the presence of airborne chemical contaminants. However, one of the problems with this composition was that the process of preparing the polymer as outlined in column 3, lines 10-30 and in Example 1 (of U.S. Pat. No. 5,625,020) results in poor conversion rates and chemical cleavage of some groups in the repeat units. Thus, one of the objects of the present invention is an improved process for preparing the polymers used in the photoresist compositions.
The processes of the present invention provide methods which are fast, clean, anhydrous, and render the analysis of catalyst used therein in an easy manner. Furthermore, the polymer in solution, if desired can be further treated to provide a photoresist composition which can be directly used without isolating the polymer beforehand.
Prior Art
The following references are disclosed as general background information.
1. U.S. Pat. No. 4,898,916 discloses a process for the preparation of poly(vinylphenol) from poly(acetoxystyrene by acid catalyzed transesterification.
2. U.S. Pat. No. 5,239,015 discloses a process for preparing low optical density polymers and co-polymers for photoresists and optical applications.
3. U.S. Pat. No. 5,625,007 discloses a process for making low optical polymers and co-polymers for photoresists and optical applications.
4. U.S. Pat. No. 5,625,020 discloses a process for making a photoresist composition containing a photosensitive acid generator and a polymer comprising the reaction product of hydroxystyrene with acrylate, methacrylate or a mixture of acrylate and methacrylate.
5. EP 0 813113 A1, Barclay, discloses an aqueous transesterification to deprotect the protected polymer.
6. WO 94 14858 A discloses polymerizing hydroxystyrene without the protecting group.
Other patents of interest are U.S. Pat. Nos. 4,679,843; 4,822,862; 4,912,173; 4,962,147, 5,087,772; and 5,304,610.
All of the references described herein are incorporated herein by reference in their entirety.
SUMMARY OF THE INVENTION
This invention relates to a novel, one-pot, cost efficient process for the preparation of homopolymers and copolymers such as terpolymers and tetrapolymers of p-hydroxystyrene or substituted p-hydroxystyrene and/or alkyl acrylates and/or other monomers. The process involves polymerization of esters of p-hydroxystyrene (or its substituted analogs), alkyl acrylate monomers and/or one or more of ethylenically unsaturated monomers in an alcohol solvent in the presence of a free radical initiator. The anhydrous reaction mixture containing the so formed polymer is then subjected to transesterification conditions using a catalytic amounts of catalyst to result in co- and/or terpolymers of p-hydroxystyrene without cleavage of the alkyl ester in the acrylate repeat unit. Preferred embodiments include homopolymers of p-hydroxystyrene; copolymers of p-hydroxystyrene, and tert-butyl acrylate; and terpolymer of p-hydroxystyrene, tert-butyl acrylate and styrene. These polymers have a wide variety of applications including as photoresists in microelectronics industry.
DETAILE
Sheehan Michael T.
Sounik James R.
Chemfirst Electronic Materials L.P.
Mullen James J.
Zalukaeva Tatyana
LandOfFree
Preparation of homo-, co- and terpolymers of substituted... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preparation of homo-, co- and terpolymers of substituted..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation of homo-, co- and terpolymers of substituted... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3225688