Carrier Concentrations in Implanted and Epitaxial 4H-SiC by Scanning Spreading Resistance Microscopy

Free carrier distributions in 4H-SiC have been studied by scanning spreading resistance microscopy (SSRM). The SSRM signal is discussed in relation to the chemical impurity concentration measured by secondary ion mass spectrometry (SIMS). The method is demonstrated on a p-type Al epi-layer staircase structure with doping concentration ranging from 2x10(16)cm(-3) to 2x10(20) cm(-3) and an implanted acceptor dopant profile of shallow Al and deep B. The results of the epi-layer investigation are in good agreement with the macroscopic spreading resistance model R=rho/4r, and show a much higher dynamic range in 4H-SiC than conventional spreading resistance profiling. Measurements of the implantation profile reveal a resistance in the highly doped region (> 10(18) cm(-3)) of more than two orders of magnitude larger than that measured in the epi-layer with similar concentration. The observation may be attributed to remaining implantation-induced defects. The SSRM measurements also show a diffusion of B consistent with SIMS data. The investigation clearly demonstrates that the technique is a valuable method to determine high gradient carrier concentrations in p-type SiC, although the detailed mechanism of the spreading resistance current is presently not completely understood.