Anisotropy of dissolution and defect revealing on SiC surfaces

Micropipes and dislocations in silicon carbide single crystals are revealed by chemical etching. Micropipes are shown to be interconnected with other structural defects and the reason for this is discussed. The Si and C faces are attacked by molten KOH preferentially and isotropically, respectively. The mechanism is discussed in relation to the different surface free energies on the Si and C faces. The revealing of micropipes is more pronounced on the Si face. The hexagonal pattern of micropipes are revealed by rapid etching provided by a large undersaturation at the surface. It is shown that etching from a melt gives a disintegration of the SiC crystal at the micropipe via spiral dissolution which is due to etching near equilibrium conditions. The temperature dependence of the etch rate follows an Arrhenius dependence with an apparent activation energy of about 12-15 kcal mol-1 derived from measuring etch rate and weight loss.