Photo-degradation and electron beam-induced degradation of poly(pentamethyldisilylstyrene sulfone)s.

Abstract

Positive tone polysulfone resists have been studied extensively because they have weak C-S bond in the main chain upon UV light exposure. However, poly(olefin sulfone)s do not have UV absorption longer than 200 nm. The sensitivity of polysulfones as deep-UV resists can be endowed by incorporation of pendant aromatic ring into their structure. Organometallic polymers, primarily silicon-containing polymers are significantly interested in bilayer lithography because of the high oxygen plasma etch resistance. Poly(pentamethyldisilylstyrene sulfone)s have two functional groups, phenyl group and disilyl group in the polymer side chain. Phenyl group in the side chain increases the absorption in UV region and the high content of silicon atom enhances the oxygen plasma resistance. The incorporation of pentamethyldisilyl group also enhances the solubility of the polysulfone. Alternating poly(styrene sulfone) is insoluble in usual solvents whereas alternating poly(pentamethyldisilystyrene sulfone) is highly soluble to usual organic solvents. These features of poly(pentamethyldisilylstyrene sulfone)s are to be expected for a high performance photo-resist. Polysulfones are also applicable as positive tone electron beam resist owing to the high sensitivity of the C-S bond upon electron beam. O'Donnell et al. [ l ] and Bowden et al. [2] have investigated the radiation-induced degradation of poly(olefin sulfone)s extensively.Although there are many papers reporting the resist characterization, few papers discuss the mechanism of the degradation on the basis of the direct observation of transient intermediates.One of the reasons is the complication of the degradation in solid state because the rapid reaction among the unstable intermediates easily occurs in the dense system and the proceeding complicated reactions prevent the observation of transient intermediates produced in the first stage of the degradation. The degradation in solution is somewhat different from that in solid state, however, it simplifies the reaction and affords useful information about the assignment of transient intermediates. In this paper we