Study on the Relaxation Process in 4H-SiC Homoepitaxy Growth

BPD half loops arrays (HLAs) present in the homoepitaxial layers of 4H-SiC are responsible for introducing an increase in the forward voltage drop via the electron-hole Recombination Enhanced Dislocation Glide (REDG) and therefore are harmful to the device operation. Different sources are observed to form HLAs and interfacial dislocations (IDs) including surface, scratch, micropipe, 3C inclusion. Recent observation was made in a 100mm 4H-SiC wafer where a short edge-oriented BPD segment in the substrate was drawn towards the interface during the epitaxy growth producing screw-oriented segments intersecting the growth surface. These screw segments of BPDs subsequently glide under the mismatch stress when the critical thickness is reached. HLAs and IDs are subsequently formed. We believe that the formation of HLAs and IDs is driven by the mismatch stress brought by the doping concentration difference between the substrate and the epilayer. To verify this, we first estimate the amount of mismatch strain caused by the epi/substrate doping concentration difference according to Sasaki’s work ^[1]. Then Matthews-Blakeslee’s model ^{[2, 3]} is used to predict the value for critical thickness corresponded to such amount of mismatch strain. The predict value is then compared to the critical thickness that we measured via Synchrotron X-ray study and they are found to have a good agreement with each other. This indicates that mismatch strain brought by the doping concentration is sufficient for relaxation process to occur.

[1] S. Sasaki, J. Suda, and T. Kimoto, Materials Science Forum 717-720, 481 (2012).

[2] J. W. Matthews, Journal of Vacuum Science and Technology 12(1), 126 (1975).

[3] J. Matthews and A. Blakeslee, Journal of Crystal Growth 27, 118 (1974).