Copper precipitation in large-diameter Czochralski silicon

Abstract

The behavior of the copper precipitation in the large-diameter Czochralski silicon (Cz–Si) annealed at 1100°C followed by air cooling or slow cooling was studied by means of scanning infrared microscopy (SIRM), optical microscopy, and surface photovoltage. For the air-cooled specimen, a high density of copper-precipitate colonies with strong contrast could be easily found in the A-defect zone, while in the D-defect zone of the same specimen almost no colonies could be observed through SIRM. However, optical images showed that the higher density of the etching pits induced by the copper-precipitate colonies occurred in the D-defect zone, which indicates that the copper-precipitate colonies in the D-defect zone was below the detection limitation of SIRM. This suggestion was confirmed by minority-carrier diffusion-length mapping, which revealed that the diffusion length of the minority carriers in the D-defect zone was noticeably lower than that in the A-defect zone. As for the slow-cooled specimen, big star-like colonies formed both in the D-defect zone and A-defect zone, but the diffusion length of the minority carriers in the D-defect zone was also lower than that in the A-defect zone. On the basis of experiments, it is suggested that the as-grown vacancies or their related defects in the D-defect zone enhance the nucleation of copper precipitation either under air cooling or under slow cooling, resulting in the lower diffusion length of minority carriers.