\bfiIn situ Monitoring of Product Species in Plasma Etching by Fourier Transform Infrared Absorption Spectroscopy

Abstract

In situ Fourier transform infrared (FTIR) absorption spectroscopy has been used to detect reaction products resulting from the etching of Si in Cl2 plasmas. Silicon tetrachloride SiCl4 was the only gas-phase product species detected during etching. Unsaturated silicon chlorides SiCl x (x=1–3) were not observed in the plasma within the present level of detection. By comparing the absorbances of SiCl4 in Cl2 plasma etching of Si and in pure SiCl4 gases, it is suggested that the concentrations of SiCl4 or product species during etching are comparable to the feedstock Cl2 gas densities, e.g., [SiCl4] ∼1 ×1013 cm-3 at a pressure of 0.5 mTorr. In contrast, on the surface-etched Si, unsaturated silicon chlorides SiCl x (x=1–3) as well as SiCl4 were found to occur by FTIR reflection absorption spectroscopy (RAS). Moreover, absorption features of silicon oxides were observed both in the gas phase and on the surface, presumably arising from reactions between Si produced from etching and oxygen included in the reactor chamber owing to a small leak.