Semiconductor devices having a mesa structure and method of fabrication for improved surface voltage breakdown characteristics

A semiconductor rectifier having a mesa structure provided by a process comprising providing a generally rectangular etch mask on a <100>

• surface of a monocrystalline silicon wafer, said mask having straight sides meeting at curved corners, each of said corners being symmetrical about an axis passing through a point on the periphery of the corner, said mask straight sides being disposed at an angle of 45 degrees to <111>
• directions on said surface, and the periphery of each of said corners comprising, starting from said point, a pair of oppositely extending straight first lines forming an angle therebetween of about 150 degrees, each of said straight lines terminating in a curved line connecting said each straight line to its corresponding mask straight side, and anisotropically etching said wafer for providing a mesa structure underlying said mask.

A semiconductor rectifier comprising a monocrystalline silicon wafer having a major surface lying in the <100>

• crystal plane, a generally rectangular mesa structure extending upwardly from said surface, said mesa structure having spaced apart top and bottom surfaces interconnected by four side walls meeting at corner walls, horizontal edges of said side walls being disposed at an angle of 45 degrees to <111>
• directions on said major surface, each of said corner walls comprising a centrally positioned first triangular facet lying in the <111>
• crystal plane, and a plurality of planar second facets extending between each side of said triangular facet and a pair of said side walls, the planes of adjoining second facets being angularly off-set from one another, and the slopes of said second facets, with respect to said mesa structure bottom surface, being 45 degrees.