A mass spectrometric diagnostic of C2F6 and CHF 3 plasmas during etching of SiO2 and Si

Abstract
A mass spectrometric analysis of the neutral products and the positive ions extracted from discharges in C2F6 and CHF 3, sustained at 25 kHz with pressures between 0.2 and 0.8 torr (1 torr = 133 Pa) was performed. The apparatus calibration and the calculation of the partial pressures from mass spectra at 70 eV are described The formation reactions of the many detected products : CF4, C2F 2, C2F4, C3F6, C3F 8, C4F8, C2HF5 and HF are discussed. Variations in the neutral composition of these plasmas, induced by etching of SiO2 and Si were observed These variations are explained by the consumption of CFn radicals (n = 1 to 3) at the etched surface. The main positive ions produced are CF+ 3, CF+, CF+2 and CHF+ 2. Their formation is explained by the ionization of neutral molecules and molecular radicals