Etch rates near hot-wall CVD growth temperature for Si-face 4H-SiC using H2 and C3H8

During the growth of silicon carbide (SiC) by hot-wall chemical vapor deposition, there is a competition between etching and growth processes due to hydrogen etching of the SiC surface, which is a function of temperature and the etching atmosphere. The interplay of the etch rates and growth rates and the influence of the doping level of the growing layer on these rates must be taken into account when growing device structures with stringent thickness constraints. In this work, a comparison of secondary ion mass spectrometry data with etch rates for a variety of individual epilayers is used to differentiate the contribution of etching processes from that of site competition effects between precursor and incorporated dopant species on the net growth rate. It is found that the presence of nitrogen at the growing surface decreases the net growth rate by competing with carbon species for incorporation into surface lattice sites at a level far beyond what would be expected for most dopant atoms. This is a result of the high nitrogen flux required at the surface due to the inefficiency of nitrogen incorporation at growth temperatures. Furthermore, etch rates of SiC epilayers were found to increase with increasing carrier concentrations for both p- and n-type 4H-SiC. Finally, small additions of propane to the hydrogen atmosphere suppresses the etch rate of SiC; however, too much propane leads to degradation of the surface morphology. The activation energy for the hydrogen–propane etching mechanism is determined to be 120.5 kcal mol−1, in good agreement with values reported in the literature.