Oxygen Precipitation Properties of Nitrogen-Doped Czochralski Silicon Single Crystals with Low Oxygen Concentration

摘要

Oxygen precipitation properties in the as-grown defect-free region of nitrogen-doped Czochralski silicon (Cz-Si) single crystals with very low oxygen concentrations ([Oi]) are investigated. At [Oi] values of 4.6-5.9 x 10(17) atoms cm(-3), oxide precipitates with a high density of 10(9) cm(-3) are generated owing to the enhancement in oxygen precipitation by nitrogen-doping. In contrast, at [Oi] values of 1.3-2.6 x 10(17) atoms cm(-3), no oxide precipitates are observed even though the crystals are nitrogen-doped. Oxygen precipitation in the as-grown defect-free region is analyzed based on a thermodynamic model, in which some embryos are assumed to exist in nitrogen-doped Cz-Si crystals at high temperatures of crystal growth, and they grow as oxide precipitates during a subsequent cooling process. The analysis of oxygen precipitation indicates that, at [Oi] values below 3 x 10(17) atoms cm(-3), the radii of oxide precipitates included in the as-grown Cz-Si crystals remain small owing to a low growth onset temperature; therefore, oxide precipitates cannot be detected after heat treatment for wafer evaluation. These findings suggest that nitrogen-doped Cz-Si crystals with [Oi] values below 3 x 10(17) atoms cm(-3) are potential materials for power devices, such as insulated gate bipolar transistors.