Characterization of a magnetron radiofrequency glow discharge with a glass cathode using experimental design and mass spectrometry

Abstract

A magnetron radiofrequency-powered glow discharge with a borosilicate glass cathode has been interfaced to a quadrupole mass spectrometer and an energy analyser. The influence of the electrical discharge parameters on the ion energies of Ar and Si and on the intensity of the signals has been studied, as well as the influence of the position of the extraction orifice (along or perpendicular to the discharge axis). This study was carried out via an ‘experimental design’ procedure. For both orifice positions, the ions entering the mass filter have minimum energy at 60 mTorr (1 Torr = 133.322 Pa), when the pressure is increased from 10 to 450 mTorr. The ion energy does not depend significantly on the power. When the orifice position is along the discharge axis, the ion energy doubles when the orifice–cathode distance is decreased from 5 to 2.5 cm; above 5 cm, the distance does not influence the energy. In the lateral position, the ion intensity increases when the pressure goes from 10 to 130 mTorr; above this pressure, the intensity remains constant. Maximum intensity is observed at 100 mTorr, when the quadrupole is positioned along the discharge axis. For both positions, the intensity rises by less than one order of magnitude with an increase in power of from 20 to 70 W. An important relationship between the parameters has been found: in the axial position, an increase in the pressure leads to a rise in the ion intensity for a small orifice–cathode distance whereas, for a larger distance, maximum intensity is observed at 60 mTorr.