Tadami Tanaka

Formation of Grown-in Defects during Czochralski Silicon Crystal Growth.

The formation behavior of grown-in defects in Czochralski silicon (CZ-Si) crystals was investigated using two crystals that were quenched during growth but in one case after crystal growth had been halted for 5 h. The distributions of grown-in defect density and size, and their micro-structures were analyzed as a function of temperature during crystal growth just before quenching by means of an optical precipitate profiler (OPP) and an atomic force microscope (AFM) coupled with a laser particle counter. The formation of grown-in defects, which are considered to be octahedral voids, was found to consist of two dominant processes. The first step involves rapid void growth in a narrow temperature range of about 30° C below 1100° C and the subsequent step consists of an oxide film growth on the inner surface of the void during the cooling process to about 900° C after void formation. It was also found that the growth of the oxide film in the voids is rate-limited by the diffusion rate of oxygen atoms in silicon. In addition, it is strongly suggested that void formation in such a narrow temperature range is due to a rapid agglomeration of vacancies.

Nitrogen effect on grown-in defects in Czochralski silicon crystals

The formation behavior of grown-in voids during crystal growth was investigated for nitrogen-doped Czochralski silicon crystals by means of a new quantitative defect evaluation method using a bright-field infrared-laser interferometer. Crystal quenching techniques were employed to study void formation and it was found that in crystals grown without nitrogen doping, the total amount of vacancies composing the voids did not change during the crystal growth halt. In nitrogen-doped crystals, however, the total amount of vacancies composing the voids increased during the crystal growth halt. These results indicate that nitrogen makes excess vacancies remain after void formation in crystals grown without a growth halt.