RADIATION DEGRADATION OF POLY(METHYL METHACRYLATE) IN THE SOFT-X-RAY REGION

The molecular weight distribution change has been measured for the pho toresist poly(methyl methacrylate) [PMMA] after in-vacuo exposure to m onochromatic soft x-rays from the Canadian Synchrotron Radiation Facil ity [CSRF]. The experimental changes in the molecular weight distribut ions derived from gel permeation chromatography [GPC], were compared t o a simple Monte Carlo simulation model that assumes random main chain scission. Using this model a scission radiation chemical yield of G(x -ray)vacuo(S) = 1.28 +/- 0.10 at room temperature was found to give th e best fit at a photon energy of 621 eV. This value is similar to valu es reported previously in the literature using electron beam and gamma -ray sources, but significantly larger than those reported for fast ne utrons, alpha-particles, or energetically charged particles. It was fo und that in this soft x-ray energy regime, that degradation of PMMA in volves primarily a random scission process of the main chain. The resu lts of a least-squares fit of this soft x-ray G(S) data and all availa ble literature values from other radiation sources, to the linear ener gy transfer [LET] dE/dx are discussed. (C) 1993 John Wiley & Sons, Inc .