Ions in RF-Discharges with Si-Organic Admixtures

Results of mass spectrometric measurements in capacitively coupled asymmetric Ar rf discharges with small admixtures of the Si-organic compounds TMS, TEOS, and HMDSO are presented. The relative ion currents to the wall were determined using a plasma monitor and integrating the measured kinetic energy distribution of the ions over the energy range. The contribution of the fragment ions of the parent molecules to the total current is small, whereas hydrogen and light hydrocarbon ions are dominant. We also present partial and total electron -impact ionization cross sections of the parent molecules measured in a high resolution double-focussing mass spectrometer. The measured ion spectra are compared to the calculated ion populations derived from the rate coefficients for electron-impact ionization using various electron temperatures. The observed dominance of lighter fragment ions in the plasma indicates the important role of decomposition processes and secondary reactions in the plasma.