PROCESS FOR MAKING A SEMICONDUCTOR ELEMENT

1,140,139. Semi-conductor devices. BROWN, BOVERI & CO. Ltd. 6 Sept., 1966 [8 Sept., 1965], No. 39743/66. Heading H1K. A rectifier is produced by diffusing aluminium into the surface of a weakly doped (less than 1016 atoms/cm.3) N-type silicon wafer to produce a weakly doped (less than 1016 atoms/cm.3) P-type surface layer, Fig. 1 (not shown), which is then removed from the sides and upper surface by lapping, Fig. 2 (not shown). A goldantimony disc (2) is alloyed to the upper surface to produce a heavily doped (greater than 1016 atoms/cm.3) N+type region, Fig. 4 (not shown), and an aluminium disc (3) is alloyed to the lower surface to produce a heavily doped (greater than 1016 atoms/cm.3) P+type region, Fig. 5 (not shown). A molybdenum or tungsten carrier plate 4 is then soldered to the alloyed aluminium disc 3 and the edge of the wafer is ultrasonically machined to produce a conical frustum surface 5 and a portion 6 which is said to strengthen the edge of the wafer, Fig. 6. The impurity concentration gradient and the field strengths at the junctions are quoted and it is stated that the device can dissipate as much power under avalanche conditions in the reverse direction as in the forward direction.