Reduction of morphological defects in 4H-SiC epitaxial layers

Correlation between morphological defects and device yield in the 4H-SiC epitaxial layers were investigated with overlapped morphological defect mapping and device yield mapping figures. The results show the harmful level of various morphological defects for device yield should be triangular > downfall > carrot > particle. Origins of the triangular defects were traced by a multiple cycle of polishing and molten KOH etching process, revealing that the triangular defects are mainly formed at initially epitaxial stage and caused by threading screw dislocations (TSDs) in substrates or spontaneous nucleation. Etching temperature and time of the hydrogen surface etching process and C/Si ratio in buffer layer growth process were also systematically optimized. The density of triangular defects can be reduced to 0.1 cm−2. Meanwhile, an additional buffer layer with a step-bunching surface was applied and can effectively restrain the extending of triangular defect along 〈1 −1 0 0〉 direction.