Effect of rapid thermal annealing on the structural and electrical properties of a silicon-silicon oxide system

Abstract

An investigation of the electrical and structural properties of rapid thermal annealed Czochralski silicon wafers has been carried out. The electrical properties examined here are the minority carrier lifetime, measured using the laser microwave photoconductance technique, and the donor concentration (N d), determined by the four-point probe method. Thermal donors were intentionally introduced into the silicon and were found to be completely annihilated by the rapid thermal annealing (RTA) process. The minority carrier lifetime was found to increase significantly for wafers annealed at 900 and 1000 °C. It was concluded that due to the very short annealing time used in this work, a denuded zone was unlikely to form in silicon and be responsible for the increase in the lifetime. Infrared, x-ray photoelectron (XPS) and Auger electron spectroscopies were used for the structural analysis. Auger results showed that higher oxygen concentration could be found in a thicker layer of silicon in annealed wafers, as compared to the as-received, virgin sample. The XPS data showed that the SiO2:Si ratio increased from 0.28 for the virgin sample to 3.5 for wafers annealed at 1000 °C. It is suggested that the Auger and XPS data could be explained by considering oxygen outdiffused from the bulk of the silicon to the native oxide and the silicon next to the native oxide. We believe this is the first investigation of the effect of RTA on the behavior of oxygen and thermal donors, and its influence on the minority carrier lifetime of Czochralski silicon. © 1995 American Institute of Physics.