Method of forming a silicon-carbide device with a shielded gate

A method of forming a semiconductor device from a first conductivity type silicon-carbide semiconductor substrate having a main surface, the method comprising:

• forming a plurality of buried second conductivity type regions beneath the main surface and laterally spaced apart from one another;
• forming a first conductivity type source region and a second conductivity type body region in the substrate, the source region extending from the main surface to the body region, the body region being arranged above the buried regions;
• forming second conductivity type contact regions in the substrate extending from the main surface to the buried second conductivity type regions;
• annealing the substrate so as to activate dopant atoms in the source, body and contact regions;
• forming a gate trench that extends through the source and body regions and has a bottom that is arranged over a portion of the buried regions;
• applying a high-temperature step in a non-oxide and non-nitride forming atmosphere so as to realign silicon-carbide atoms along sidewalls of the gate trench and to form rounded corners between the bottom and sidewalls of the gate trench;
• and
• removing a surface layer that forms along the sidewalls of the gate trench during the high-temperature step from the substrate.