Negative Ion Transfer Model of Low-Temperature Oxidation of Silicon Surface by High-Density Microwave Plasma

摘要

High-quality thin SiO_2 layer is rapidly formed at low temperature (～400℃) by oxidation of silicon wafer using high-density microwave plasma in argon containing a few % O_2. The oxidation rate is proportional to the square root of electron density but hardly correlates with the measured O radical density. Secondary ion mass spectrometry (SIMS) depth analysis of SiO_2 layer with ~(18)O as an isotope tracer suggests that predominant mobile species in the oxide layer is not neutral oxygen atom but oxygen negative ion, possibly O~(2-), as proposed by Jorgensen and Mott. The time evolution of oxidation process calculated in a negative ion transfer model well explains the experimental observation and accounts for the square root dependence on the electron density.