Patent GB-1360130-A (GB)
Title: Semiconductor devices
IPC: H01L21/331
Filed: 1972-05-24
Abstract: 1360130 Semi-conductor devices INTERNATIONAL BUSINESS MACHINES CORP 24 May 1972 [18 June 1971] 24380/72 Heading H1K A method of making a semi-conductor device comprises forming a dielectric layer on a monocrystalline substrate, opening a window in the layer, growing an epitaxial layer in the window and continuing the growth over the dielectric layer surrounding the window thus forming monocrystalline material within and above the window and polycrystalline material above the dielectric, forming a component in the monocrystalline material and applying a contact for the component to the polycrystalline material, the lateral extent of the polycrystalline material being bounded by a second dielectric layer formed on the first layer. In a first embodiment, Figs. 1 to 4, a bi-polar transistor is produced by diffusing P, As or Sb through a mask to form an N<SP>+</SP>-type subcollector region 24 in a P--type substrate 20, removing the mask and oxidizing to form a thin protective layer on which a first thick SiO 2  layer 23 is applied by sputtering. A thin layer 25 of Si 3 N 4  is deposited and covered with a second thick SiO 2  layer 26. Apertures 28, 30, 32 are selectively etched through the insulating layers and P-type Si is epitaxially deposited in the apertures to the thickness of the first SiO 2  layer 23. These deposits are monocrystalline and in the apertures 30, 32 above the subcollector region the P-type material is converted to N-type due to redistribution of impurities. The part of the top SiO 2  layer surrounding the aperture 32 is removed by selective etching to define the device area 34, the Si 3 N 4  layer 25 preventing removal of the lower SiO 2  layer. P-type Si is then epitaxially deposited to fill the apertures. The material in the device region 34 is monocrystalline above the aperture 32 and is surrounded with polycrystalline material over the exposed Si 3 N 4  layer. The material deposited in the upper part of the aperture 30 is converted to N-type by diffusion to form a collector reach-through and an N<SP>+</SP>-type emitter region 36 is diffused into the monocrystalline part of the device region which forms the base of the transistor. A layer of metal is deposited and patterned to form contacts, the base connection being made via the polycrystalline material. The device may be modified to produce an inverse transistor so that region 36 forms the collector. In a second embodiment, Figs. 5 to 8 (not shown), a P--type Si wafer (20) with an N<SP>+</SP>-type sub-collector region (24) is provided with an insulating layer (26) by sputtering a thick layer SiO 2  and covering with a thin layer of Si 3 N 4 . Two apertures (40, 42) are formed above the sub-collector region and one aperture (44) which defines a resistor region is formed above the substrate. Si is epitaxially deposited in the openings and over the top of the insulating layer, the material being undoped or N--type until the apertures are filled and the dopant then being changed to P-type. The deposited material is monocrystalline within and above the apertures (40, 42, 44) but polycrystalline above the insulating layer. The surface is oxidized and unwanted portions of the epitaxial layer are etched away to leave the monocrystalline region surrounded by polycrystalline material over one of the apertures to form the device region and to leave the monocrystalline deposits within the other apertures. The surface is re-oxidized and P or As is selectively diffused into the reach-through and resistor areas, and As, P or Sb is selectively diffused-in to form the N<SP>+</SP>-type emitter region in the monocrystalline part of the base region and to heavily dope the collector and resistor contact regions. Al electrodes are then applied. In a modification, Fig. 9 (not shown), instead of removing parts of the deposited P-type layer, isolation is achieved by selective thermal oxidation of the polycrystalline Si. In another embodiment, Figs. 10 to 12 (not shown) an N<SP>+</SP>-type sub-collector region (24) is formed in a P-type substrate (20), the surface is oxidized (62) and covered with Si 3 N 4  (64) and two windows (66, 68) are opened above the sub-collector region. A thick layer (70) of SiO 2  is pyrolytically deposited and windows (72, 74) are opened aligned with those in the underlayers but one being of larger area. An undoped layer (76) is epitaxially grown in the windows, the deposit in the smaller windows being monocrystalline and that in the other window having a monocrystalline cone surrounded by polycrystalline material. P or As is selectively diffused onto the collector reach-through region (80), a P-type impurity is diffused onto the monocrystalline and polycrystalline base region and finally P or As is selectively diffused to form the emitter region (81) in the monocrystalline part of the base region and to form the collector contact region. Contacts are applied as before. In a further embodiment, Figs. 13 to 15 (not shown), an MOS transistor is produced by thermally oxidizing the surface of a P--type layer (82), depositing a layer (86) of Si 3 N 4 , opening a window (88) in the Si 3 N 4  layer, depositing a thick layer (90) of SiO 2  pyrolytically or by sputtering, and opening a larger window (92) in the thick SiO 2  layer. P-type material is epitaxially deposited to fill the windows and forms a monocrystalline core (94) flanked by polycrystalline material. The surface is oxidized and P or As is selectively diffused into the polycrystalline material to form the source and drain regions (98, 100), the edges of the monocrystalline region also being doped to form the active parts of these regions. The device is then completed by conventional processing.