Etching of 4° and 8° 4H-SiC using various hydrogen-propane mixtures in a commercial hot-wall CVD reactor

Hydrogen etching of 4H-SiC has been performed in a hot-wall chemical vapor deposition reactor to reduce surface damage and to create a bilayer-stepped surface morphology, optimal for initiation of growth on 4H-SiC substrates offcut 4 degrees and 8 degrees towards the < 11-20 > direction. To understand how step bunching evolves during the ramp to growth temperature, samples were etched ending at temperatures from 1400 to 1580 degrees C under 0, 2 or 10 sccm of propane (C3H8) addition to hydrogen. Initial exploratory growth of 5 mu m thick epilayers on the 4 degrees etched surfaces are also discussed. Atomic force microscopy (AFM) and Nomarski microscopy were employed to investigate changes in the surface morphology. The 8 degrees substrates subjected to H-2-C3H8 etching up to growth temperature routinely exhibited bilayer steps. However, when the 4 degrees substrates were etched with a 10 SCCM C3H8 flow, considerable step bunching was observed. At 14500 degrees C, with a 10 SCCM Of C3H8 flow (partial pressure is 1.25x 10(-5) bar), step bunching started with the formation of ribbon-like steps. Progression to higher temperature etches have shown the coalescence of the ribbons into larger macro-steps up to 30 nm in height. Etching 4 degrees substrates under 2 SCCM Of C3H8 (partial pressure is 2.5x10(-6) bar) or in pure H-2 up to 1500 degrees C results in minimal step bunching.