Structural Improvement of Seeds for Bulk Crystal Growth by Using Hot-Wall CVD of 4H-SiC

Abstract

Growth of 4H-SiC epitaxial layers has been performed in a horizontal hot-wall CVD (chemical vapor deposition) reactor using the silane-propane-hydrogen system. Two inch 4H-SiC, C-face wafers with an off-cut angle of about 7° towards <11 2 0> direction have been used as substrates. Micropipe dissociation has been investigated by varying the carbon-silicon (C/Si) ratio in the source gas atmosphere. Depending on the C/Si ratio the micropipes propagate into the layer without changing their image (C/Si > 1) or they dissociate in separate dislocations leaving a scar like formed surface region (C/Si £ 1). The substrates including epitaxial layers of reduced micropipe density were used as seeds for bulk crystal growth. If a micropipe is once closed in an epilayer grown at a low C/Si ratio, it is not opened in the subsequent growth process at high temperature.