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Recent United Kingdom patents in microelectronics
Microelectronics and Reliability
Pergamon Press 1970. Vol. 9, pp. 211-214.
Printed in Great Britain
RECENT U N I T E D K I N G D O M P A T E N T S IN MICROELECTRONICS N.B. Where a patent appears to describe some significant new fact or technique, or some noteworthy modification, this has been summarized. Some U.K. patents are filed as a safeguard for a particular design which a manufacturer has decided to adopt, or involve a combination of minor details or present a complex combination of details, which are of interest to comparatively few readers. These are merely listed to allow readers to judge whether they are relevant to their interest. The U.K. patent number and patentee is quoted in each case. Copies are available from Patents Office, 25 Southampton Buildings, Chancery Lane, London, W.C.2, or from the Sales Branch at Orpington, Kent, BR5 3RD.
1,157,719 (Westinghouse) A controllable semiconductor rectifier with a turn-off capability is formed from two complementary transistor sections in a single package. 1,157,989 (IBM) In an improved process for cleaning semiconductor surfaces or substrates, the area to be cleared is surrounded by a conductive mask, of aluminium, molybdenum, or chromium, for instance. 1,158,091 (Danfoss A]S) A heat- and oxidation-resistant resistor is formed of silicon carbide with silicon nitride and possibly silicon oxynitride as binding agents. 1,158,120 (Danfoss A/S) A semiconductor diode, for use as a voltage-dependent resistor or as a double Zener diode, is formed by Schottky barrier contacts with metallic electrodes mechanically pressed against a semiconductor material. Graphite, silver and molybdenum are suggested as electrodes with silicon, gallium arsenide, or indium phosphide as the semiconductor. Several diodes of this type may be used in a series-connected pile, and graphite is the preferred material for at least the intermediate electrodes in the pile. 1,158,218 (Seimens AG) A locally-doped inorganic insulating layer is formed on a semiconductor by first depositing dopants on selected areas, forming an insulating layer (silicon dioxide or nitride) on top, and then diffusing the dopants outwards into the insulating layer. This technique can be used to make improved field-effect transistors. Selenium, sulphur or tellurium may be used as alternatives to conventional dopants. It is also useful where the insulating layer is required to be luminescent (in which case it may be zinc sulphide, zinc oxide, or potassium chloride). This is said to indicate a new way to make screens for colour television, comprising semiconductor diodes which may be used to energize the phosphor to produce different colours in different areas, with copper, silver or thallium dopant. 1,158,585 (J. Lucas Ltd.) Improved gate-controllable switches are made by diffusing the gate layer in a reducing atmosphere, to make the p-type impurity concentration as high as possible at the p--n gate-cathode junction. 1,158,897 (Hughes Aircraft Co.) A space-charge-limited semiconductor triode suitable for use in integrated circuits. 1,158,900 (IBM) Light-sensitive and field-sensitive Gunn-effect oscillators and circuits. 211
212
R E C E N T U N I T E D K I N G D O M P A T E N T S IN M I C R O E L E C T R O N I C S
1,158,922 (Philips) Radiation detectors or solar cells having an electrode which is partly transparent and partly of a material more conductive than any transparent material, are formed by vapourdepositing a porous highly-conductive layer over photosensitive grains, etching the highlyconductive layer and then depositing a transparent electrode over it. A surface pretreatment or a photo-resist masking process may also be used. Gold 0"1 micron thick and copper 100 A thick are suggested for the highly-conductive layer and the transparent electrode. 1,158,923 (Philips) Radiation detectors or solar cells are formed of photosensitive grains embedded in photoresist. The photoresist is exposed from one side of the layer, and photoresist material from the shadowed (unexposed) side of the grains is washed away. 1,158,924 (Philips) To make radiation detectors or solar cells, photosensitive grains are temporarily stuck on an adhesive layer from which they protrude. A binder is applied and hardened, then the adhesive is dissolved away and an electrode deposited in place of the adhesive. Polystyrene, polymethylmethacrylate, or a mixture of saccharose and glucose are suitable readily-soluble adhesives. 1,158,994 (Texas) A header structure for high-power transistors in which the thermal expansion of a metal of high thermal conductivity is restrained by an embedded grid of stronger, lower conductivity metal (e.g. a kovar grid in copper). 1,159,393 (Telefunken) Regions in a semiconductor substrate are etched away and then filled with conductive polycrystalline semiconductor material for use as through-connection terminals. 1,159,539 (Westinghouse Corp., U.S.A.) A process for making pnpn thyristors by diffusion without oxide layers and without the thermal cycling in oxygen conventionally used to form oxide masks. A photoresist mask is used, and a selective deposition of aluminium is required. 1,159,553 (Texas) A method of making integrated circuits in which a semiconductor wafer is etched to form mesas, and then covered firstly with an insulating layer of silicon carbide and secondly with a polycrystalline semiconductor material. The wafer is then inverted, the polycrystalline layer serving as a supporting substrate while the original underside is ground down to the carbide layer so that it now appears with the original mesas of monocrystalline semiconductor filling isolated pockets in the carbide layer. Devices or circuits are formed in the isolated monocrystalline semiconductor pockets, and interconnections between the devices are deposited over the ground (carbide) surface. This method is used to make a thermal printing head of the kind described in U.K. patent 1,151,848. 1,159,637 (Siemens AG) A method for making transistors using two masks of different materials (e.g. silicon dioxide and silicon nitride) simultaneously, with one dopant which can pass through one of the mask materials but not through both of them, and another dopant which cannot pass through either mask material. 1,159,704 (CSF, France) An electrolytic method for preparing semiconductor surfaces for metallization, which oxidizes silicon and then removes all the silicon dioxide formed. Metal can then be electrolytically deposited on the prepared surfaces, to form Schottky diodes. 1,159,937 (IBM) Transistors formed by a single diffusion of a collector region and an emitter region, 1000-3000 A apart in a base region substrate. 1,159,979 (IBM) Flip-chip contacts of aluminium covered with chromium, copper and gold, are connected to a conductive pattern by a controlled soldering process. 1,160,058 (Motorola Inc.) Integrated circuits having semiconductor regions of different carrier lifetimes may be made by providing impurity gettering regions near regions where comparatively long lifetimes are required. Phosphorus dopant and a phospho-silicate glass can be used as getting materials for gold dopant in silicon.
R E C E N T U N I T E D K I N G D O M P A T E N T S IN M I C R O E L E C T R O N I C S
213
1,160,086 (Western Electric) Semiconductor diodes are formed under very small holes in oxide and wire contacts made to them. 1,160,267 (Plessey) Low-capacitance junctions can be formed in thin films deposited on a (112) plane surface of an insulating crystal, doped to form a junction at right angles to the (112) plane surface. 1,160,301 (RCA) A monocrystalline layer of silicon can be deposited on an alumina substrate by heating the alumina to about 1150°C in a silane-containing atmosphere and then heating the substrate preferable to 1335-1400°C for 60 rain in a non-reactive atmosphere. The alumina is preferably monocrystaUine, cut and highly polished at 60 ° to its C axis, so as to expose a 2243 crystal face in which the atomic spacing is believed to be close to that of silicon. The deposited layer may be made either n-type or p-type by having a few parts per million of phosphine or diborane respectively in the silane-hydrogen mixture used for the original deposition. 1,160,429 (Philco-Ford Corp.) An epitaxial transistor construction intended to reduce fringing effects. 1,160,744 (Plessey) Areas on a substrate separated by oxide spacers are covered with films, n-type and p-type in alternate areas, on which complementary pairs of transistors can be formed without unwanted stray interconnections. 1,160,911 (STC) Leads to a semiconductor device are anchored by a bead of plastics material separate from the device. 1,160,931 (Sylvania Inc., U.S.A.) An array of semiconductor devices is formed integrally with a supporting grid, each device having a beam lead connection to the grid and having several contacts areas in a predetermined relationship with the grid. The contact areas are bonded to contact areas on an array of header parts before, or just after, the devices are separated from the grid and before the header parts are separated from each other. 1,160,932 (Sylvania Inc.) Transistor or device mounting by bonding the device to groups of leads temporarily attached to a carrier strip. 1,160,947 (IBM) An image scanning circuit for use with an array of photodiodes. 1,161,049 (S. Teszner, France) Grid structures for field-effect transistors. 1,161,174 (STC) Photocells having translucent metal electrodes are improved by a matching dielectric layer (e.g. silicon nitride or a three-layer structure of ZnS, MgF~ and ZnS) of a thickness related to the cell's most sensitive wavelength. 1,161,248 (Brown Boveri) Controllable rectifier devices including pnpn structures with segmented and layers and electrodes contacting the inner layers. One such structure may be combined with a diode, or two such structures may be connected back-to-back, to form rectifier devices. 1,161,269 (Westinghouse) Optically gated semiconductor controlled rectifiers which can be triggered by light transmitted through the cathode-emitter region. The light is preferably infra-red direct to the rectifier from a gallium arsenide diode through a light guide. 1,161,309 (Teledyne Inc.) A resistor with improved isolation formed in an integrated circuit. 1,161,340 (Matsushita) Solar cells with an electrochemically formed thin layer, 1-100 microns thick, of p-type cadmium, copper and sulphur. Best results are from cells formed with a current density of 0.1-1.0 mA/cm z in copper sulphate with no added acid. 1,161,343 (Texas) Techniques utilizing the effects of crystalline orientation on epitaxial growth rates to form shaped deposits. 1,161,351 (IBM) Carrier lifetime reducing impurities (e.g. gold) are preferably injected into a semiconductor device in a non-oxidizing atmosphere after a final oxide layer has been formed on its surface, to avoid short-circuits which tend to occur when such impurities are injected under other conditions.
214
RECENT U N I T E D K I N G D O M PATENTS IN M I C R O E L E C T R O N I C S
1,161,354 (RCA) Semiconductor devices made by epitaxial growth and etching processes, avoiding impurity diffusions. 1,161,367 (Brown Boveri) Perforated molybdenum discs are embedded in solder-alloy contacts on devices (apparently thyristors or the like). 1,161,517 (Matsushita) Silicon junction devices are better if made in material of high etch pit density, which gives more well-defined junction areas. Preferred dopant and contact alloys and production processes are detailed. 1,161,647 (RCA) Thin-film field-effect devices of improved stability are made by plasma-anodizing an aluminium-film gate electrode to provide the gate insulation. 1,161,656 (I.T.T. Industries) Terminal members, a semiconductor device and a beryllia insulator are shaped to locate on each other, forming a self-aligning stacked assembly or mount suitable for high-power, high-frequency transistors. 1,161,730 (National Cash Register Co.) A pressure-sensitive switch for use in miniaturized circuits is formed of a fluoro-silicone elastomer uniformly loaded with a conductive filler. 1,161,782 (Associated Semiconductor Manufacturers) Gunn-effect devices which have their two ohmic contacts on the same plane surface.
Pergamon Press 1970. Vol. 9, pp. 211-214.
Printed in Great Britain
RECENT U N I T E D K I N G D O M P A T E N T S IN MICROELECTRONICS N.B. Where a patent appears to describe some significant new fact or technique, or some noteworthy modification, this has been summarized. Some U.K. patents are filed as a safeguard for a particular design which a manufacturer has decided to adopt, or involve a combination of minor details or present a complex combination of details, which are of interest to comparatively few readers. These are merely listed to allow readers to judge whether they are relevant to their interest. The U.K. patent number and patentee is quoted in each case. Copies are available from Patents Office, 25 Southampton Buildings, Chancery Lane, London, W.C.2, or from the Sales Branch at Orpington, Kent, BR5 3RD.
1,157,719 (Westinghouse) A controllable semiconductor rectifier with a turn-off capability is formed from two complementary transistor sections in a single package. 1,157,989 (IBM) In an improved process for cleaning semiconductor surfaces or substrates, the area to be cleared is surrounded by a conductive mask, of aluminium, molybdenum, or chromium, for instance. 1,158,091 (Danfoss A]S) A heat- and oxidation-resistant resistor is formed of silicon carbide with silicon nitride and possibly silicon oxynitride as binding agents. 1,158,120 (Danfoss A/S) A semiconductor diode, for use as a voltage-dependent resistor or as a double Zener diode, is formed by Schottky barrier contacts with metallic electrodes mechanically pressed against a semiconductor material. Graphite, silver and molybdenum are suggested as electrodes with silicon, gallium arsenide, or indium phosphide as the semiconductor. Several diodes of this type may be used in a series-connected pile, and graphite is the preferred material for at least the intermediate electrodes in the pile. 1,158,218 (Seimens AG) A locally-doped inorganic insulating layer is formed on a semiconductor by first depositing dopants on selected areas, forming an insulating layer (silicon dioxide or nitride) on top, and then diffusing the dopants outwards into the insulating layer. This technique can be used to make improved field-effect transistors. Selenium, sulphur or tellurium may be used as alternatives to conventional dopants. It is also useful where the insulating layer is required to be luminescent (in which case it may be zinc sulphide, zinc oxide, or potassium chloride). This is said to indicate a new way to make screens for colour television, comprising semiconductor diodes which may be used to energize the phosphor to produce different colours in different areas, with copper, silver or thallium dopant. 1,158,585 (J. Lucas Ltd.) Improved gate-controllable switches are made by diffusing the gate layer in a reducing atmosphere, to make the p-type impurity concentration as high as possible at the p--n gate-cathode junction. 1,158,897 (Hughes Aircraft Co.) A space-charge-limited semiconductor triode suitable for use in integrated circuits. 1,158,900 (IBM) Light-sensitive and field-sensitive Gunn-effect oscillators and circuits. 211
212
R E C E N T U N I T E D K I N G D O M P A T E N T S IN M I C R O E L E C T R O N I C S
1,158,922 (Philips) Radiation detectors or solar cells having an electrode which is partly transparent and partly of a material more conductive than any transparent material, are formed by vapourdepositing a porous highly-conductive layer over photosensitive grains, etching the highlyconductive layer and then depositing a transparent electrode over it. A surface pretreatment or a photo-resist masking process may also be used. Gold 0"1 micron thick and copper 100 A thick are suggested for the highly-conductive layer and the transparent electrode. 1,158,923 (Philips) Radiation detectors or solar cells are formed of photosensitive grains embedded in photoresist. The photoresist is exposed from one side of the layer, and photoresist material from the shadowed (unexposed) side of the grains is washed away. 1,158,924 (Philips) To make radiation detectors or solar cells, photosensitive grains are temporarily stuck on an adhesive layer from which they protrude. A binder is applied and hardened, then the adhesive is dissolved away and an electrode deposited in place of the adhesive. Polystyrene, polymethylmethacrylate, or a mixture of saccharose and glucose are suitable readily-soluble adhesives. 1,158,994 (Texas) A header structure for high-power transistors in which the thermal expansion of a metal of high thermal conductivity is restrained by an embedded grid of stronger, lower conductivity metal (e.g. a kovar grid in copper). 1,159,393 (Telefunken) Regions in a semiconductor substrate are etched away and then filled with conductive polycrystalline semiconductor material for use as through-connection terminals. 1,159,539 (Westinghouse Corp., U.S.A.) A process for making pnpn thyristors by diffusion without oxide layers and without the thermal cycling in oxygen conventionally used to form oxide masks. A photoresist mask is used, and a selective deposition of aluminium is required. 1,159,553 (Texas) A method of making integrated circuits in which a semiconductor wafer is etched to form mesas, and then covered firstly with an insulating layer of silicon carbide and secondly with a polycrystalline semiconductor material. The wafer is then inverted, the polycrystalline layer serving as a supporting substrate while the original underside is ground down to the carbide layer so that it now appears with the original mesas of monocrystalline semiconductor filling isolated pockets in the carbide layer. Devices or circuits are formed in the isolated monocrystalline semiconductor pockets, and interconnections between the devices are deposited over the ground (carbide) surface. This method is used to make a thermal printing head of the kind described in U.K. patent 1,151,848. 1,159,637 (Siemens AG) A method for making transistors using two masks of different materials (e.g. silicon dioxide and silicon nitride) simultaneously, with one dopant which can pass through one of the mask materials but not through both of them, and another dopant which cannot pass through either mask material. 1,159,704 (CSF, France) An electrolytic method for preparing semiconductor surfaces for metallization, which oxidizes silicon and then removes all the silicon dioxide formed. Metal can then be electrolytically deposited on the prepared surfaces, to form Schottky diodes. 1,159,937 (IBM) Transistors formed by a single diffusion of a collector region and an emitter region, 1000-3000 A apart in a base region substrate. 1,159,979 (IBM) Flip-chip contacts of aluminium covered with chromium, copper and gold, are connected to a conductive pattern by a controlled soldering process. 1,160,058 (Motorola Inc.) Integrated circuits having semiconductor regions of different carrier lifetimes may be made by providing impurity gettering regions near regions where comparatively long lifetimes are required. Phosphorus dopant and a phospho-silicate glass can be used as getting materials for gold dopant in silicon.
R E C E N T U N I T E D K I N G D O M P A T E N T S IN M I C R O E L E C T R O N I C S
213
1,160,086 (Western Electric) Semiconductor diodes are formed under very small holes in oxide and wire contacts made to them. 1,160,267 (Plessey) Low-capacitance junctions can be formed in thin films deposited on a (112) plane surface of an insulating crystal, doped to form a junction at right angles to the (112) plane surface. 1,160,301 (RCA) A monocrystalline layer of silicon can be deposited on an alumina substrate by heating the alumina to about 1150°C in a silane-containing atmosphere and then heating the substrate preferable to 1335-1400°C for 60 rain in a non-reactive atmosphere. The alumina is preferably monocrystaUine, cut and highly polished at 60 ° to its C axis, so as to expose a 2243 crystal face in which the atomic spacing is believed to be close to that of silicon. The deposited layer may be made either n-type or p-type by having a few parts per million of phosphine or diborane respectively in the silane-hydrogen mixture used for the original deposition. 1,160,429 (Philco-Ford Corp.) An epitaxial transistor construction intended to reduce fringing effects. 1,160,744 (Plessey) Areas on a substrate separated by oxide spacers are covered with films, n-type and p-type in alternate areas, on which complementary pairs of transistors can be formed without unwanted stray interconnections. 1,160,911 (STC) Leads to a semiconductor device are anchored by a bead of plastics material separate from the device. 1,160,931 (Sylvania Inc., U.S.A.) An array of semiconductor devices is formed integrally with a supporting grid, each device having a beam lead connection to the grid and having several contacts areas in a predetermined relationship with the grid. The contact areas are bonded to contact areas on an array of header parts before, or just after, the devices are separated from the grid and before the header parts are separated from each other. 1,160,932 (Sylvania Inc.) Transistor or device mounting by bonding the device to groups of leads temporarily attached to a carrier strip. 1,160,947 (IBM) An image scanning circuit for use with an array of photodiodes. 1,161,049 (S. Teszner, France) Grid structures for field-effect transistors. 1,161,174 (STC) Photocells having translucent metal electrodes are improved by a matching dielectric layer (e.g. silicon nitride or a three-layer structure of ZnS, MgF~ and ZnS) of a thickness related to the cell's most sensitive wavelength. 1,161,248 (Brown Boveri) Controllable rectifier devices including pnpn structures with segmented and layers and electrodes contacting the inner layers. One such structure may be combined with a diode, or two such structures may be connected back-to-back, to form rectifier devices. 1,161,269 (Westinghouse) Optically gated semiconductor controlled rectifiers which can be triggered by light transmitted through the cathode-emitter region. The light is preferably infra-red direct to the rectifier from a gallium arsenide diode through a light guide. 1,161,309 (Teledyne Inc.) A resistor with improved isolation formed in an integrated circuit. 1,161,340 (Matsushita) Solar cells with an electrochemically formed thin layer, 1-100 microns thick, of p-type cadmium, copper and sulphur. Best results are from cells formed with a current density of 0.1-1.0 mA/cm z in copper sulphate with no added acid. 1,161,343 (Texas) Techniques utilizing the effects of crystalline orientation on epitaxial growth rates to form shaped deposits. 1,161,351 (IBM) Carrier lifetime reducing impurities (e.g. gold) are preferably injected into a semiconductor device in a non-oxidizing atmosphere after a final oxide layer has been formed on its surface, to avoid short-circuits which tend to occur when such impurities are injected under other conditions.
214
RECENT U N I T E D K I N G D O M PATENTS IN M I C R O E L E C T R O N I C S
1,161,354 (RCA) Semiconductor devices made by epitaxial growth and etching processes, avoiding impurity diffusions. 1,161,367 (Brown Boveri) Perforated molybdenum discs are embedded in solder-alloy contacts on devices (apparently thyristors or the like). 1,161,517 (Matsushita) Silicon junction devices are better if made in material of high etch pit density, which gives more well-defined junction areas. Preferred dopant and contact alloys and production processes are detailed. 1,161,647 (RCA) Thin-film field-effect devices of improved stability are made by plasma-anodizing an aluminium-film gate electrode to provide the gate insulation. 1,161,656 (I.T.T. Industries) Terminal members, a semiconductor device and a beryllia insulator are shaped to locate on each other, forming a self-aligning stacked assembly or mount suitable for high-power, high-frequency transistors. 1,161,730 (National Cash Register Co.) A pressure-sensitive switch for use in miniaturized circuits is formed of a fluoro-silicone elastomer uniformly loaded with a conductive filler. 1,161,782 (Associated Semiconductor Manufacturers) Gunn-effect devices which have their two ohmic contacts on the same plane surface.