Tsutomu Kawamura

Precipitation and redistribution of oxygen in Czochralski‐grown silicon

Thermally induced oxygen precipitation and redistribution phenomena in Czochralski‐grown silicon crystals are investigated by means of transmission electron microscopy and differential‐infrared absorption (DIR). In order to investigate the role of thermal history and the oxygen supersaturated condition for oxygen precipitation, a two‐step annealing process is adopted. Evident existence of SiO2 (crystobalite) is observed in as‐grown crystals by DIR at 1225 cm−1. As a result, it is ascertained that oxygen precipitation does not occur by homogeneous nucleation depending on the ratio of supersaturated oxygen but occurs by heterogeneous nucleation. A model of a grown‐in nucleus for oxygen precipitation by heat treatment is also proposed.

Surface‐ and inner‐microdefects in annealed silicon wafer containing oxygen

Surface‐ and inner‐microdefects examined after a two‐step annealing process are compared and related to the intrinsic gettering phenomenon. After the defects are characterized by means of transmission electron microscopy, the defect types (dislocations, precipitates, and stacking faults) and defect structures as well as nature are correlated with the annealing temperature. It is found from the observations that a surface‐microdefect is a stacking fault extrinsic in nature possibly caused by a process‐induced ’’heavy metal contamination’’ such as copper and that the type of Si‐O complex precipitates generated strongly depends on annealing temperatures: <1050°C⋅⋅⋅ platelike cristobalite, 1100°C<⋅⋅⋅ regular octahedral amorphous SiO2. In addition, the mechanism for the formation of these defects is discussed based on electron microscope observations.