Abstract: A surface layer (10), for example oxide, is provided on a first major surface (2) of a semiconductor body (1). A masking layer (11) having at least one window (12) is defined on the surface layer (10). The surface layer (10) and the semiconductor body (1) are etched through the window (12) to define an opening (13in the surface layer (10) and a recess (14) within the semiconductor body (1) extending beneath the surface layer (10) so that a rim portion (10a) of the surface layer (10) overhangs the recess (14). The rim portion (10a) of the surface layer (10) is removed by causing a settable flowable material (15) to flow onto the surface layer (10) and into the recess (14) and then causing the flowable material to set and thereby change volume to apply a force for causing the rim portion (10a) to break away from the remainder ( 10b) of the surface layer (10). The set flowable material (150) and thus the rim portion (10a) of the surface layer (10) are then removed.

Abstract: Diffusion of aluminium into a silicon semiconductor wafer from an annular or grid pattern of deposited metallic aluminium to form a p-type annular zone at least 75 microns deep. The diffusion is performed in an oxidizing atmosphere to inhibit aluminium contamination of the wafer portion bounded by the p-type annular zone and in which for instance a thyristor may subsequently be formed. The aluminium may be diffused through the whole thickness of the wafer to form a peripheral zone of the thyristor body.