IN-SITU MONITORING OF PRODUCT SPECIES IN PLASMA-ETCHING BY FOURIER-TRANSFORM INFRARED-ABSORPTION SPECTROSCOPY

In situ. Fourier transform infrared (FTIR) absorption spectroscopy has been used to detect reaction products resulting from the etching of S i in Cl-2 plasmas. Silicon tetrachloride SICl4 was the only gas-phase product species detected during etching. Unsaturated silicon chlorides SiClx (x=1-3) were not observed in the plasma within the present leve l of detection. By comparing the absorbances of SiCl4 in Cl-2 plasma e tching of Si and in pure SiCl4 gases, it is suggested that the concent rations of SiCl4 or product species during etching are comparable to t he feedstock Cl-2 gas densities, e.g., [SiCl4] similar to 1 x 10(13) c m(-3) at a pressure of 0.5 mTorr. In contrast, on the surface-etched S i, unsaturated silicon chlorides SIClx (x=1-3) as well as SiCl4 were f ound to occur by FTIR reflection absorption spectroscopy (RAS). Moreov er, absorption features of silicon oxides were observed both in the ga s phase and on the surface, presumably arising from reactions between Si produced from etching and oxygen included in the reactor chamber ow ing to a small leak.