| abstract |
Superposed layers of gold and silver (or predominantly silver) are deposited on germanium or silicon bodies in the following manner to provide ohmic contacts thereto. A silicon body comprising zones of different conductivity types so disposed as to make it suitable as a transistor (see Group XXXVI) is masked, enclosed in a vacuum chamber provided with heater filaments loaded with silver and a gold antimony alloy (0.1% by weight antimony) respectively and heated to 500 DEG C. The gold loaded filament is first energised to evaporate gold on to the wafer through the mask to provide a series of groups of three parallel elongated gold layers. When the layers are about 200 thick the silver loaded filament is energized and the other switched off as soon as silver begins to deposit. The amount of silver is limited so that its complete evaporation results in layers 5 m thick. A further layer of gold is provided by re-energizing the gold loaded filament. In an alternative method, after deposition of the first gold layer the silver and gold are evaporated simultaneously, the evaporation of the measured amount of silver being so much more rapid that while it lasts the layer is essentially of silver. When the silver is exhausted the gold continues to evaporate to provide the outer layer. When germanium is used instead of silicon it is maintained at a temperature of only 390-400 DEG C. during the deposition process. Specifications 809,642, 809,643, 821,832 and 821,834 are referred to. |