BEHAVIOR OF REACTION-PRODUCTS OF POLY-SI IN ELECTRON-CYCLOTRON RESONANCE ION STREAM ETCHING AND ITS APPLICATION TO STABLE AND HIGH-SELECTIVITY ETCHING

Effects of reaction products (SiClx) are investigated in electron cyclotron resonance (ECR) ion stream etching of poly-Si metal-oxide-semiconductor (MOS) gates in which Cl2 is employed as a main etching gas. Experiments using a gas mixture of Cl2-SiCl4 confirm that SiCl4 gas (i) promotes SiO2 etching to some extent, (ii) reduces the effect of added O2 which is utilized to lower SiO2 etch rate, and (iii) is approximately equivalent to the reaction products in etching characteristics. In Cl2 with proper amounts of SiCl4 and O2, the above results prove that the SiCl4 can control the change in etching characteristics caused by a decrease in the amount of the reaction products during overetching to proceed in a self-regulating manner toward the cessation of SiO2 etching. This results in stable etching conditions with high selectivity (poly-Si/SiO2) over 100.