Patent GB-908593-A (GB)
Title: Semiconductor device fabrication
IPC: H01L23/29
Filed: 1961-07-05
Abstract: 908,593. Semi-conductor devices. HUGHES AIRCRAFT CO. July 5, 1961 [Oct. 27, 1960 (2)], No. 24355/61. Class 37. In processing semi-conductor devices a silicon oxide masking pattern is produced on a semiconductor body by forming a film of silicon oxide on a surface of the body, covering the film with a metal film, coating the metal film with photosensitive polymerizable material and exposing this to a light pattern so that illuminated areas are polymerized, developing the partly polymerized film to uncover those parts of the metal film under unpolymerized material, selectively removing the uncovered parts of the metal film and then selectively removing those parts of the silicon oxide film thus uncovered. Germanium and chromium are preferred metals for the process, chromium being used when germanium semi-conductor bodies are treated, but nickel, cadmium, and their alloys with chromium may also be used. In the embodiment described a surface of a slab of P-type silicon is exposed to an argon/arsenious oxide atmosphere so that arsenic diffuses into the crystal and forms an N-type layer 31 on the surface of the remaining P-type material 32. A silicon oxide film 33 also forms in this atmosphere, the effect being enhanced by humidifying the atmosphere or adding oxygen before the end of the diffusion step. A germanium film 34 is then vacuum deposited on the silicon oxide film and the process continued as outlined above (full details being given in the Specification) to leave the semiconductor body, as shown in Fig. 8, with a pattern of silica oxide on its surface overlayed with germanium 34 and polymerized photosensitive material. Then the polymerized material is softened with suitable solvents and mechanically removed and the remaining germanium etched away to leave only the silicon oxide pattern on the semi-conductor body which contains a PN junction between layers 31 and 32. The Specification describes in detail how mesatype transistors are made from such a slab having a striped silicon oxide pattern. A further P-type layer 38 is formed between the oxide stripes by exposure to a boron oxide atmosphere and a further silicon oxide layer 33A is grown over the entire surface in a moist argon atmosphere, the original stripes of oxide being removed before the oxide layer is regrown only if they were thick. A layer 39 of chromium is evaporated on to the oxide layer and covered with a layer 40 of photo-sensitive material which is illuminated so as to polymerize squares of material 41 bridging the P and N regions of the crystal surface. Various selective etching steps and selective removal of the polymerized and unpolymerized portions of the photosensitive material lead to the stage shown in Fig. 19. An ohmic aluminium electrode 42 is then fused to the base of the slab which is diced to provide the bodies shown in Fig. 21, having P-type regions 32 and 39 separated by N-type region 31. The mesa transistors are completed by the removal of the remaining silicon oxide 33A, the provision of leads, and encapsulation. Mesa diodes may be produced by starting the second stage of the process with a block of uniform N-type conductivity having masking stripes of silicon oxide.