LATTICE DEFECTS IN SILICON RAPIDLY SOLIDIFIED FROM THE MELT

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In order to study defect behaviors of silicon at high temperatures, two kinds of experiments have been performed. (1) A rapid heating and cooling apparatus with infrared rays was prepared, and small FZ-Si particles were vacuum-melted and quenched. The as-quenched specimens were investigated by transmission electron microscopy (TEM). (2) In situ high-resolution transmission electron microscopy (HRTEM) has been carried out to observe melting and solidification of silicon using a specially designed heating specimen holder. FZ-Si specimens with lower oxygen content have been mainly used, but CZ-Si specimens widely used in the semiconductor device technology were also examined in some cases. The results are summarized as follows.A variety of lattice defects were found to be formed in the as-quenched specimens ; {111} micro-twins, extrinsic type {111} stacking faults, stacking fault tetrahedra, 60 degree dislocations, interstitial type dislocation loops and unidentified fine defect clusters. … More HRTEM suggested clustering of vacancies. In situ high temperature HRTEM observations showed most liquid-solid interface planes became {111}, and the interface went forth or back by lateral motion of a pair of atomic steps along the interface with slight temperature change. The interface motion was frequently interrupted by several tiny silicate with impurities diffusing on the specimen surfaces. It was also shown that {111} micro-twins were formed by shear motion of successive {111} planes in the vicinity of liquid-solid interface. Formation of a transient layer with a thickness of about 1 nm is suggested to exist between solid and liquid phases. A number of {113} defect clusters possibly associated with interstitial atom clustering were observed at high temperatures. It is concluded from the present experiments that both interstitial atoms and vacancies are certainly produced at high temperatures near the melting temperature of silicon, and they are correlated with introduced impurities to form various lattice defects. Less