Basal plane dislocation conversion near the epilayer/substrate interface in epitaxial growth of 4° off-axis 4H–SiC

The conversion of basal plane dislocations (BPDs) is investigated in the epitaxial growth of 4° off-axis SiC by three approaches: (1) regular growth on untreated substrates, (2) growth on pre-etched substrates and (3) growth-etch-regrowth approach. In the regular growth, ∼99.0% of the substrate BPDs are converted to threading edge dislocations (TEDs) in the vicinity of the epilayer/substrate interface and the rest ∼1.0% BPDs are converted throughout the ∼20 μm thick epilayer. A modified KOH–NaOH–MgO eutectic mixture is developed to mildly etch the substrate in approach (2) or a grown buffer-layer in approach (3) to enhance BPD conversion rate. In the subsequent epitaxial growth, the BPD conversion rate near the interface is enhanced up to 99.9% in approach (2) and to 100% in approach (3). Using the modified KOH–NaOH–MgO eutectic mixture, very mild etching of the surfaces (substrate or buffer-layer) for a short duration (2–3 min) will generate very small etch pits, and will not degrade the morphology of the etched surfaces and also that of the subsequently grown epilayer surfaces, but very high (∼100%) BPD conversion rate is still preserved. Post-polishing process is no longer needed for future device fabrication. It is proposed that the opening of a sector plane in the BPD etch pit, which enables lateral epitaxial growth to pinch off the step-flow growth inside the etch pit, is responsible for the high BPD conversion rate near the interface. The degree of anisotropic etching in the 〈11–20〉 directions versus the 〈1–100〉 directions determines the sector open angle of the BPD etch pits. The degree of anisotropic etching is studied for different KOH formulations—pure KOH, regular KOH–NaOH eutectic and the modified KOH–NaOH–MgO eutectic mixture.

► BPD conversion rate >99.9% is achieved close to the epilayer/substrate interface.
► High BPD conversion is achieved by KOH–NaOH–MgO mild etching of SiC substrates.
► When the mild etching is employed on a buffer-layer, BPD-free is always achieved.
► Small sector angle BPD pit due to anisotropic etch is key for high BPD conversion.
► Very mild etching (3 min) is non-destructive to the etched surfaces.