\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.