Patent GB-1154891-A (GB)
Title: Semiconductor Devices and Methods of Manufacture
IPC: H01L29/47
Filed: 1966-07-06
Abstract: 1,154,891. Semi-conductor devices. TEXAS INSTRUMENTS Inc. 6 July, 1966 [8 July, 1965], No. 30365/66. Heading H1K. A semi-conductor device comprises a monocrystalline substrate with an epitaxially deposited mesa extending from a plane surface, the mesa being edge isolated by insulating material which leaves part of its top exposed and having an electrical contact to the exposed part and extending on to the insulating material. As shown, Fig. 1, a Schottky barrier diode is produced by thermally oxidizing an N<SP>+</SP>type silicon substrate 16, the thickness of the oxide being equal to that of the desired epitaxial layer and being measured by optical methods, photomasking and etching to leave a ring 20 of oxide surrounding the device area, epitaxially growing high resistivity material on the exposed parts of the substrate to form a "plug" 14 and a surrounding region 26, determining the thickness of the epitaxial layer by means of a profile indicating machine using the known thickness of the oxide layer as a reference, depositing a further oxide layer 22 using a low temperature process, photomasking and etching to expose a portion of the top of the epitaxial "plug" 14, depositing a layer of molybdenum followed by a layer of gold, and patterning to leave electrode 12. Electrode 12 forms a rectifying contact with epitaxial region 14 and a second metallized layer 18 on the lower face of the substrate provides an ohmic contact to the region 14. In a known form of hybrid X-band mixer Fig. 3 (not shown), comprising strip lines deposited on a high resistivity silicon or intrinsic gallium arsenide substrate with a metallized ground plane on the opposite surface and including a pair of diodes (60), each of the diodes may be produced according to the invention by diffusing-in a low resistivity strip region (68), thermally growing an oxide film (70) over the region, photomasking and etching a slot (72) in the oxide along part of the length of the region, epitaxially depositing a high resistivity layer (74a) within the slot depositing a further layer (76) of oxide, etching a slot (78) in the second oxide layer at right angles to the first slot to expose a small area (84) of the epitaxial plug, and depositing the strip lines on the wafer. One line (61b) contacts the exposed area of the epitaxial region to form a Schottky barrier and a second line (61a) forms an ohmic contact to the two ends of the diffused region through windows (80, 82) in the oxide layers, Figs. 4 and 5 (not shown). An integrated circuit, Fig. 6 (not shown), comprising an NPN transistor with a Schottky diode connected to its base region may be produced by diffusing an N type collector region (104), a P type base region (108), and an N<SP>+</SP>type emitter region (110) into a P type substrate 106 to form the transistor, the diode being formed by simultaneously diffusing-in an N-type region (112) and an N <SP>+</SP> type contact region (114) and subsequently growing a small epitaxial region (120a) on the N type region. The surface is covered with a deposited oxide layer (122), windows are formed and a layer of metal is deposited and etched to provide interconnections, one (124) of which forms a Schottky barrier with the top of the epitaxial region (120a) and another (125) of which joins the diode N<SP>+</SP> type contact region (114) to the P type base transistor base region (108). A PNP transistor, Fig. 7 (not shown), may be produced by depositing a P type epitaxial layer (156) on a P<SP>+</SP>type substrate (152) to form the collector region, masking (158) and growing an N type epitaxial layer (162a) to form the base region, diffusing-in a P type emitter region (166), and providing metallic connections (154, 168, 170). The emitter region may also be produced by an epitaxial process. An integrated circuit comprising a PNP transistor with a Schottky diode connected in parallel with its collector-base junction is described, Fig. 8 (not shown), and also forms part of the subject-matter of Specification 1,154,892.