The relationship between seed mounting and the formation of thermal decompo
sition cavities in physical vapor transport grown silicon carbide was inves
tigated. Scanning electron microscopy, energy dispersive x-ray spectroscopy
, Auger electron spectroscopy, and optical microscopy were used to characte
rize thermal decomposition cavities at various stages of their development.
The observations indicate that the attachment layer that holds the seed to
the graphite crucible lid frequently contains voids. The seed locally deco
mposes at void locations and Si-bearing species are transported through the
void. The decomposition produces a cavity in the seed; the silicon is depo
sited on and diffuses into the graphite lid. The formation of thermal decom
position cavities can be suppressed by the application of a diffusion barri
er on the seed crystal backside.