HIGH-FREQUENCY ELECTRON-GAS SECONDARY NEUTRAL MASS-SPECTROMETRY - EVALUATION OF TRANSIENT EFFECTS

In electron-gas secondary neutral mass spectrometry (SNMS), a low-pres sure plasma serves both as an ion source for sputter depth profiling t he target and for post-ionizing the sputtered neutrals. In its high-fr equency mode, a rectangular RF bias is applied to the target. We inves tigate by PIC/MC kinetic simulation the processes occurring in the vic inity of the substrate as a consequence of the voltage jumps: sheath e xpansion and contraction, as well as flux and energy of the ions impin ging onto the substrate. In particular, we determine the enhancement o f the ion current shortly after negatively charging the substrate; thi s enhancement is due to the acceleration of the large ion population i n the expanding sheath. Our results indicate that already at a switch frequency of only 1 MHz the surface treatment by rectangularly shaped RF potentials is dominated by transient effects.