Sensitivity enhanced FTIR investigation of defects introduced by RTA pre-treatment in Czochralski silicon wafers

Abstract

The investigation of vacancy oxygen complexes in silicon wafers by FTIR is not easy because their concentration is close to the detection limit. In order to enhance the sensitivity of the FTIR measurement we investigated stacked samples of about 1 cm thickness at temperature close to liquid helium temperature. This method was applied to study the absorption bands of defects in as-grown silicon wafers, rapid thermal annealing (RTA) pre-treated wafers, and in RTA pre-treated wafers with subsequent anneals at 800 °C for short periods. We found that the RTA pre-treatment at 1250 °C could not fully annihilate the thermal double donors which were present in the as-grown wafer. By RTA at 1100 °C annihilation was possible. In the wafer pre-treated by RTA at 1250 °C we found the absorption bands of VO4 at 985 cm−1 and 991 cm−1 in the measurements carried out at room temperature and at 6 K, respectively. In this wafer we also detected an unknown band at 1030 cm−1. The VO4 band and the unknown band at 1030 cm−1 disappeared immediately after annealing at 800 °C for 10 min. Instead, the bands at 1096 and 1099 cm−1, both assigned to VO5,6, appeared. These bands are already present in the as-grown sample but their absorption coefficient decreases during RTA at 1100 °C. In samples annealed at 800 °C for 30 min or longer a new absorption band at 1053 cm−1 appears which can be also assigned to VO5,6 complexes.