Metallic coating on an insulating substrate

摘要

1,023,531. Semi-conductor devices. STANDARD TELEPHONES & CABLES Ltd. Oct. 18, 1963 [Oct. 19, 1962], No. 39650/62. Addition to 1,010,111. Heading H1K. Contacts to zones of a planar diffused junction device exposed through apertures in a surface oxide layer comprise bi-metallic films extending over the layer into the apertures. The upper surface of each film consists of a solderable metal and the lower surface of a different metal which adheres well to the oxide. A typical device, a silicon transistor, Fig. 6 (not shown), is formed by successive diffusions through an oxide mask to form base and emitter zones in a high resistivity N-type layer epitaxially grown on a heavily doped N-wafer. After selectively etching to expose areas of these zones contacts are made thereto by vapour depositing aluminium over the entire surface and then etching it from the coated areas. After heating to alloy the aluminium to the silicon a layer grading from chromium or chromium-copper below to gold above, or from manganese to silver is evaporated over the entire surface as described in the parent Specification and then selectively etched to leave strips 11, 12 extending to the emitter and base contacts respectively. Alternatively the strips are obtained directly by evaporation through a mask. The graded layer can also be applied without the intermediary of aluminium if the exposed surface of the base zone is heavily doped beforehand by acceptor diffusion. The back face of the wafer may be friction alloyed to a header, or coated with a graded chromiumgold film and soldered to a header constituting the collector electrode or to a similar graded film on a glass substrate. Alternatively the collector electrode may be formed in the same way as the emitter and base electrodes on the oxide coated surface. The invention is also applicable to planar diodes and solid circuits and to germanium planar devices with silicon oxide masking layers.