In Situ Fourier Transform Infrared Measurements of Si Surface and Bulk Plasmas in Cl₂/O₂ and HBr/O₂ Electron Cyclotron Resonance Plasma Etching: Influence of Oxygen on Reaction Products

Abstract

In situ Fourier transform infrared (FTIR) absorption spectroscopy, electrostatic probe measurements and optical emission spectroscopy have been used to investigate reaction products during Si etching in HBr/O 2 electron cyclotron resonance plasmas, in comparison with the results obtained in Cl 2 /O 2 plasmas. In HBr/O 2 plasmas, the plasma parameters were found to be almost constant within the range of the percentage of O 2 gas flow rate to total gas flow rate of 0–10% by electrostatic probe measurements. The ratio of emission intensity of O atom to that of Br atom during Si etching was almost the same as that during SiO 2 etching, while the ratio of emission intensity of O atom to that of Cl atom during Si etching was much lower than that during SiO 2 etching. In FTIR absorption spectra, silicon bromides SiBr x ( x =1–4) were not detected in the gas phase during Si etching in HBr/O 2 plasmas at the present level of detection. A chemical shift of the position of a peak related to silicon oxides was observed, indicating the existence of silicon oxybromides on the Si surface. On the Si surface, FTIR absorption spectra revealed asymmetric Si–O stretching vibrational mode after Si etching even in pure HBr plasmas. Thus, Si etching mechanisms in HBr/O 2 plasmas were considered to be different from those in Cl 2 /O 2 plasmas.