Methacrylamide Copolymer Resists for Electron Beam Lithography

摘要

Polymethacrylamide (PMAAm) and copolymers of MAAm with methyl methacrylate were synthesized and evaluated for their applicability to electron beam lithography. The sensitivity of PMAAm has previously been reported as less than 1 microcurie/sq cm, with thermal stability at temperatures up to 330 C. Despite these claims, further lithographic evaluation of this resist system is apparently absent from the literature. This research was conducted to further investigate the lithographic performance of these resists and to determine their sensitivity using current definitions. Using PMAAm homopolymer with a 15 minute prebake at 200 C, the lithographic results were much poorer than expected. Patterns exposed to doses of 10 microcuries/sq cm or lower could not be developed using water was the developing solvent. Forced developing with Na2SiO3 solution (pH = 10) developed lower doses than water, but much greater thinning as observed. An unexposed thinning of 10% occurred when developing exposures of 15 microcuries/sq cm with water, and 40 microcuires/sq cm with Na2SiO3 solution (20 KV). Swelling of the unexposed polymer and some adhesion problems were observed. Because of the problems encountered with the PMAAm homopolymer during lithography, a series of MMA-MAAm copolymers were synthesized and evaluated as potential resists. These copolymers eliminated the problems of swelling and poor solubility of the homopolymer, but sensitivity enhancement over that of PMMA was minimal.