We have investigated the effect of the thermal field on interface step structures during PVT growth of (0001)Si-face 6H-SiC. It is shown that the SiC growth interface exhibits the whole range of growth modes varying from atomically smooth (faceted) to atomically rough growth depending on the inclination cc of the interface in respect to the (0001) plane. Within faceted areas more impurities are incorporated but crystal quality is better in terms of hollow defects. It is shown that interface follows the thermal field geometry only for alpha higher than a critical value. By proper control of the thermal field the mechanism of growth could be chosen depending on crystal application.