Method of producing a broad area low resistance contact to a silicon semiconductor body

Abstract

Abstract 916,953. Semi-conductor devices. PACIFIC SEMICONDUCTORS Inc. Feb. 2, 1961 [April 25, 1960], No. 3992/61. Class 37. A broad area low resistance contact to a Si semi-conductor body is produced by heating the body in pressure contact with Au and Ni to a temperature between the lowest melting-point of the ternary Au-Ni-Si system and the melting- point of Si. As shown, Fig. 1, a Ni-clad Mo disc 20 is brazed to a Cu stud 15 with the aid of a thin wafer 25 of Ag-Cu-P by being heated at 700‹ C. for 2-3 minutes. A Si wafer 10, having an N-P-N " comb " structure, is placed on Ni-clad disc 20 with an Au foil 30 between them and a weighted quartz flat 32 on top of the Si wafer. An axial recess 16 in stud 15, which in operation provides access for cooling water, is placed over a carbon heating element 42, Fig. 4, connected in series with resistance heating elements 40, 41 in a bell-jar 52, and the assembly for is heated to a temperature between 400‹ C. and 475‹ C., preferably 425‹ C., 30 seconds in a vacuum of 10<SP>-4</SP> mm. Hg, to produce a molten Au-Ni-Si alloy zone. The heating is discontinued and the assembly is quenched with He to reduce the temperature from 425‹ to 200‹ C. in about 3 minutes, after which the cooling is completed in open air, room temperature being attained in about 10 minutes. In an alternative arrangement, Fig. 7, a plurality of assemblies to be alloyed are placed in recesses in a boat 67 in a furnace 60, a predetermined pressure being exerted by the flexure of a bi-metallic strip 72, which acts on a quartz flat 70 common to all the assemblies, at the alloying temperature. Forming gas (15% H 2 : 85% N 2 ) or A is flowed through the furnace, or a vacuum is maintained therein, while the temperature is kept at 400-550‹ C., preferably 500‹ C., for 5 minutes, by resistance heating element 65. The boat is then maintained at 200‹ C. for 15 minutes, the gas flow being continued, after which the assemblies are removed from the furnace. Interdigitated base and emitter electrodes (not shown) are secured to the upper surface of wafer 10. The Ni content of the alloy should be from 0.5 to 10% by weight relative to the Au content, and may alternatively be supplied by plating, from a Ni foil, or in an Au-Ni amalgam. The invention is applicable to the formation of contacts to Si rectifiers, photo-cells, point contact devices &c.

Inventors

• 👤 Pighini Gerald Pio

Bibliographic Details