Electron beam induced conductivity in poly(methylmethacrylate) and SiO2 thin films

Abstract

Electron beam charging and discharging of insulating samples is greatly influenced by electron beam induced conductivity (EBIC). Most prior studies on EBIC focused on inorganic materials; measuring EBIC in organic resist was hampered by high extrinsic leakage and low induced conductivity. We describe here EBIC in thin (1 μm) films of poly(methylmethacrylate) (PMMA) and thermal SiO2. The measurements were made using the external bias method, with the insulating thin film sandwiched between a metal electrode and a highly doped silicon substrate. Under the same exposure conditions, we found the induced conductivity in PMMA to be almost two orders of magnitude less than that in SiO2. The induced current in PMMA responds linearly to the bias, regardless of the polarity, but the induced current in SiO2 is surprisingly dependent on not only electron beam energy, but also on bias polarity. When the top metal electrode is biased positively and the electron beam has high enough energy to penetrate the electrode and the oxide, the results indicate that an internal emission of electrons from the silicon substrate into the oxide contributes substantially to the total measured current.