LOW-TEMPERATURE VOLTAGE ENHANCED UV-ASSISTED OXIDATION OF SILICON

The use of ultra-violet (UV) irradiation as a way to assist the thermal oxidation of silicon in a dry O-2 ambient has been previously studied. A new low temperature (similar to 650 degrees C) oxidation method is presented here which uses the basic UV assisted process in addition to a voltage, applied to the silicon wafer, and reduced processing pressure. This combination results in a greatly improved oxidation rate. The applied voltage has several purposes: firstly it helps to remove the build-up of negative charge at the Si-SiO2 interface which occurs by the diffusion of negative oxygen ions (O-) through the growing oxide. The second purpose of the voltage is to improve the kinetics of the O- supply and diffusion to the interface. A reduced processing pressure allows effective electrical breakdown of the oxidizing ambient to occur, thus concentrating the voltage drop in the system across the growing oxide. Results of experiments to optimize the oxidation rate are described.