Patent GB-1006807-A (GB)
Title: Improvements in or relating to methods of manufacturing semiconductor devices
IPC: H01L21/322
Filed: 1963-07-31
Abstract: 1,006,807. Semi-conductor devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. July 31, 1963 [Aug. 28, 1962], No. 30321/63. Heading H1K. Reduction of the minority carrier lifetime in a body of semi-conductor material is effected by coating part of the surface of the body with a material of such a nature that when the body coating is heated above the plastic flow temperature of the body, but below its melting- point, and subsequently cooled, the mechanical stresses produced at the body-coating interface produce corresponding strains in the body which effect the necessary reduction in carrier lifetime. In one embodiment (Fig. 2C) a germanium wafer 20 is provided with an apertured silicon monoxide coating by evaporation over a patch of sodium chloride which is subsequently washed away. An impurity material of the opposite conductivity producing type is then diffused over the aperture in the masking coating and provides the regions 26 and 27. After heating and cooling of the wafer to. produce the dislocations in the crystal lattice the mask is washed off and metal contacts, are evaporated on the regions 27 and 28 and alloyed thereto, followed by the provision of leads on the contacts fixed by thermo compression bonding. Several hundred diodes could be formed on a single wafer which is subsequently severed into individual coinponents. A further embodiment (Fig. 3E) involves the production of a mesa diode structure. An N or P-type wafer of silicon or germanium 30 has a layer 31 of opposite conductivity type formed in its upper portion by diffusion and is provided with a thin elongate metal contact 32, e.g. by vacuum evaporation of silver through an apertured mask. A mask of silicon monoxide or dioxide is then provided over the top surface of the wafer and the heating step follows which produces the recombination centres 34 after which the coating is washed off. A wax coating is then applied and etching effected to remove the shoulders of the device and produce the mesa structure of Fig. 3E. Another embodiment relates to the formation of an N-P-N germanium mesa transistor. An N-type region 40, Fig. 4I, has a P-type diffused region 41 established therein, followed by the provision of a silicon oxide mask over the whole top surface except for a rectangular region defined by the " salt patch" " technique as already described. N- type impurity is then diffused through the aperture in the mask to form the emitter region. The coating is then removed and metal contacts 46, 47 of silver-indium and silver-arsenic alloys respectively are evaporated through masks on the respective emitter and base regions. A coating of silicon oxide is again provided over the surface of the device at this stage and heating effected as before. The lifetime of carriers in the collector region being the predominant factor in the choice of coating thickness. The coating has the added effect of preventing the " balling " of the contact materials during the alloying and recombination centre forming steps. The mask is then washed off and the shoulders removed, as before, before a collector terminal 48 is soldered to the semi-conductor, after which the device is encapsulated. Reference is made to prior methods of reduction of carrier lifetimes in semi-conductors by the diffusion therein from a surface layer of copper, iron, gold or nickel and by electron bombardment or mechanical damage to the semi-conductor surface.