DETERMINATION OF MASS AND ENERGY-DISTRIBUTION OF IONS IN GLOW-DISCHARGES

Equipment was designed for the study of energy and mass distribution of particles hitting the cathode of a glow discharge. Energy and mass analysis were performed using a two-stage differentially pumped plasma monitor. The plasma monitor consisted of a quadrupole mass spectrometer and a modified cylindrical mirror analyser that can measure parallel ion beams. D.c. and pulsed discharges were investigated under conditions typical for plasma assisted chemical vapour deposition and plasma diffusion treatment. Gas atmospheres containing nitrogen, hydrogen, argon and tetramethylsilane (TeMS) were studied at pressures of some millibars. Ions prevailing at the cathode are formed by electron impact ionization of species having low ionization potential. The appearance of ArH+ and N2H+ ions can be explained by ion-molecule reactions. The addition of nitrogen to a TeMS-H-2-Ar discharge caused a higher degree of fragmentation of the organometallic precursor and an increase in ion energy. Even in the case of d.c. excitation the energy of nearly all the ions exceeds the sputtering threshold of materials (10-30 eV for metals).