The Origin and Structures of the Anomalous Defects Observed in Silicon Crystals

Abstract

The structure of defects in silicon crystals, which cause anomalous etching phenomenon and X-ray double images, is studied in detail by X-ray diffraction topography and etching technique. If one uses a particular etching method, the etching phenomenon is a sensitive reflection of the defect structure. Generation of these defects is related to the content of hydrogen gas flow used as the ambient and not to the thermal gradient in the crystal during growth. The images of the defects resemble to those of inclusions with spherical symmetry. When a specimen was annealed in the range from 1000°C to 1200°C, the anomalous etching phenomenon diminishes considerably and the double image changes to various structures such as disc, pair of dot arrays, and concentric multi-loops. A model is proposed to explain the observed experimental results. The differences in the images between the floating zoned crystals and the pulled crystals and between the prismatic loops and the concentric loops are explained in terms of the cooling rates and the vacancy concentration, respectively.