Patent GB-1300768-A (GB)
Title: Improvements in or relating to semiconductor structures
IPC: H01L27/06
Filed: 1970-05-07
Abstract: 1300768 Semi-conductor devices FAIRCHILD CAMERA & INSTRUMENT CORP 7 May 1970 [29 July 1969] 22082/70 Heading H1K A layer of silicon oxide 12 in grid form, P or N doped with Bo, P, As, is deposited on a substrate 11 of, e.g. mono-crystal silicon, spinel, or sapphire lightly doped with a similar impurity; to define a pattern of isolation regions for an integrated circuit wafer; the silicon oxide being deposited as a layer and thereafter photolithographically etched. Thereafter Si is epitaxially deposited by pyrolysis of silane on the surface to form a wafer 10 of single crystal Si 13 on the substrate and polycrystal Si 14 on the grid. During growth a selected dopant of opposite conductivity to that of the grid is added to the Si, and diffusion of dopant from the oxide into the polysilicon reverses the conductivity of the latter since diffusivity of dopant into polysilicon exceeds that into mono crystal silicon A sharp boundary between 13 and 14 is formed perpendicular to the substrate surface. Active and passive semi-conductor elements are now diffused by planar techniques into each island of monocrystal silicon surrounded by polycrystal silicon, and during diffusion into an island of an impurity of opposite type to that already contained in the island to form a base region, the impurities in the polycrystal silicon diffuse laterally at the same rate into the adjacent monocrystal silicon, and during diffusion into an island of an impurity of opposite type to that already contained in the island to form a base region the impurities in the polycrystal silicon diffuse laterally at the same rate into the adjacent monocrystal silicon, and during diffusion of an emitter region into such base region the impurity in polycrystal 14 continues to diffuse into monocrystal 13, and on completion of the diffusion the impurity in polycrystal 14 has migrated into monocrystal 13 to form PN junctions 15, 16, 17 which are sharply defined perpendicularly to the substrate (Fig. 2c). Since impurity in grid 12 diffuses both into polycrystal 14 and into adjacent monocrystal 13, regions 15a, 16a, 17a of the junctions contact substrate 11, which may be doped with impurity of similar conductivity type to the grid. Thus the monocrystal islands 13 surrounded by polycrystal 14 and substrate 11 are isolated from adjacent islands on backbiasing of the separating PN junctions. In a modification (Fig. 4c), a substrate 11 of, e.g. monocrystal silicon is formed with a silicon oxide grid 12, and region 21 is formed by diffusing dopant of opposite conductivity type to that of the grid to a selected depth of the substrate, and a region 20 of silicon oxide doped with the same conductivity type as region 21 is formed over one edge thereof. The wafer 10 is epitaxially deposited with monocrystal Si over surface 11, while polycrystal Si 14, 23 forms over grid 12 and oxide region 20. The dopant in region 21 diffuses into region 13 to form region 22, while dopants in grid 12 and region 20 diffuse rapidly into the newly grown polycrystal regions 14, 23. Polycrystal region 14 is doped with an opposite conductivity type to that of polycrystal region 23. Active and/or passive elements are diffused into the islands 13; e.g. an emitter 26 of the same conductivity type as monocrystal region 13 but with higher dopant concentration is diffused into base 25 of same conductivity type as polycrystal region 14. The collector comprises adjacent monocryatal 13 contacted by underlying buried layer 21, 22 of same conductivity as monocrystal 13 but more heavily doped; connected to the surface of wafer 10 through low resistance polycrystal pipe 23 overlying oxide region 20 which is bypassed by region 24a. Examples of practical fabrication are given.