Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
  • H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
  • H01L29/417—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions carrying the current to be rectified, amplified or switched

Definitions

• This invention relates to electrical crystal contact devices of the type comprising a semi-conducting crystal of which silicon is a, main constituent and a metallic contact member in contact with it, the contact member commonly taking the form of a fine wire having one end pointed and biased into contact with the crystal; the invention relates also to methods of preparing the crystal of such contact devices.
• contact devices of. the type specified are as mixers of electric oscillations of very high frequency, for example 3000 mc./s. Their efficiency for this purpose at this high frequency, and even more at still higher frequencies, increases as the capacity of the contact decreases.
• the object of this invention is to provide crystals that yield contact devices of smaller capacity than those prepared according to the methods particularly described in the said application, or rathersince crystals resulting from apparently the same process often yield contact devices differing widely in capacity-to provide a method of making the crystals that produces a larger proportion of crystals yielding contact devices having very small capacity.
• Chromium is generally preferable to molybdenum, because it usually enables the contact device to Withstand larger values of wavesignal power than does molybdenum.
• the addition of chromium or molybdenum, or a mixture thereof is introduced in accordance with the invention into the silicon, which is first freed from its usual impurities, at the same time that a small quantity of beryllium or aluminium or both isintroduced into the silicon.
• the proportion of chromium or molybdenum to silicon is one not much less, and possibly greater, than 10% by weight.
• the additive characteristic of the invention is chromium. Little or no other change would be required if it were molybdenum or a mixture of chromium and molybdenum.
• the additive metals are preferably introduced by melting a mixture of the pure silicon and the additive. During this process, care must be taken not to introduce undesired impurities. Those that might be derived from the air (a small quantity of oxygen is not necessarily deleterious) can be avoided by melting in. a suitable atmosphere; the most suitable we have found is a vacuum, that is to say, residual gas at a pressure of not more than 0.001 mm. of mercury. But it is difiicult or perhaps impossible to find any crucible to contain a melt that does not react slightly with the melted silicon.
• the eutectic temperature of the aluminium-berylliumsilicon appears not to be known. It has been found that when the additive is one-quarter per cent. of aluminium, heating at 575 C. to 580 C. for several hours will produce the desired result. But if the amount of the additive is less than that corresponding to the eutectic, which will certainly be the case when the additive is beryllium, the minimum temperature may be much below the eutectic temperature; moreover there is no reason Why temperatures approaching the minimum should be used. Accordingly, these theoretical considerations are of little value as a guide to practice. Whether the additive is aluminium or beryllium or a mixture of the two (We have found one-quarter per cent. aluminium and one-half per cent.
• a fragment of the cooled melt has a plane part of its surface highly polished by any of the processes customary among metallurgists, for example grinding with emery of increasing fineness and finally polishing with alumina-or magnesia or both.
• the whole surface of the fragment is then dipped for 5 minutes into commercially pure 40% hydrogen fluoride diluted with an equal quantity of water.
• the main purpose of this treatment with hydrofluoric acid is to prepare the polished surface for the subsequent oxidation; accordingly it is not necessary, though it is usually convenient, that the unpohshed part of the surface should be dipped.
• step (5) the necessary surface oxidation is performed.
• body resulting from step (4) is placed on a fiat silica tray (together possibly with other bodies at the same stage of preparation) and introduced into a silica tube furnace filled with air at a region thereof maintained at 1050" C.
• a fiat silica tray together possibly with other bodies at the same stage of preparation
• a silica tube furnace filled with air at a region thereof maintained at 1050" C.
• the body is maintained in the said region for 2 hours and then allowed to cool.
• An atmosphere of oxygen at a controlled pressure may be substituted for the air in the furnace; then the time of heating will depend on the pressure of oxygen.
• step (6) the treatment given in step (4) is repeated.
• step (7) the unpolished part must be dipped.
• the dipping of the polished part is equally necessary, in
• step (5) the 4 order that part of the oxide layer formed in step (5) should be removed. After the dipping, the body is washed with water.
• a metallic layer is deposited on some or all of the unpolished surfaces.
• the layer must not be deposited on the polished surface; accordingly this is first protected .by
• a layer of adhesive which may be the material known as monostyrene, and pressing the polished surface against this layer.
• the exposed unpolished surface is then coated with copper by a method described by Bedel in Comptes Rendus, vol. 192 (1931), page 802. It consists merely in dipping the surface for 5 to 10 seconds into a solution of cuprous oxide in 20% hydrofluoric acid; the copper layer deposited may be subsequently thickened by electrolysis. Copper is not deposited in tungsten or molybdenum by this process; accordingly the said rod may be conveniently of tungsten or molybdenum.
• the coated surface is then washed and dried.
• the body can then be mounted in a suitable metal capsule by means of solder or some other suitable low-melting alloy intervening between the metal layer and the cap sule.
• the rod is then detached from the body and the polished surface of the body cleaned from the adhesive by washing with a suitable solvent, such as benzene or ethyl acetate.
• the production of said silicon contact element by a process which includes the step of introducing into the silicon a determinate quantity of at least one of the two metals chromium and molybdenum, the quantity of such additive being at least of the order of 10% of the silicon.
• the production of said silicon contact element by a process which includes the step of introducing into silicon that is substantially freed from the metallic impurities common in commercial silicon a determinate quantity of at least one of the two metals chromium and molybdenum, the quantity of such additive being at least of the order of 10% of the silicon, and a determinate relatively small quantity of at least one of the two metals aluminium and beryllium,which form a solid solution with the silicon.
• the production of'said silicon contact element by a process which includes the step of introducing into silicon that is substantially freed from the metallic impurities common in commercial silicon a determinate quantity of at -least one of the two metals chromium and molybdenum, the quantity of such additive being at least of the order of 10% of the silicon, and a determinate quantity of at least one of the two metals aluminium and beryllium, which form a solid solution with the silicon, the quantity of such latter additive bein of the order of between /2% and 1% of the silicon.
• an electrical crystal contact device of the kind in which the semiconducting. crystal contact element is mainly silicon
• the production of said silicon contact element by a process which includes the steps of purifying commercial silicon so as to eliminate therefrom substantially all its common metallic impurities, and thereafter melting the purified silicon in vacuo in a crucible at least the interior surfaces of the walls of which are composed of pure beryllia, with between and of its weight of at least one of the two metals chromium and molybdenum and with enough of at least one of the two metals aluminium and beryllium to give a content of substantially /2% of the latter additive in the final product;
• an electrical crystal contact device oi' the kind in which the semiconducting crystal contact element is mainly silicon
• the production of said silicon contact element by a process which includes the steps of purifying commercial silicon so as to eliminate therefrom substantially all its common metallic impurities, and thereafter melting the purified silicon in vacuo in a crucible, at least the interior surfaces of the walls of which are composed of pure beryllia, with substantially 20% of chromium and with enough aluminium and beryllium to give a content of substantially 4% of each of said last two metals in the final prodnot.
• the production of said silicon contact equent by a process which includes the steps of introducing into silicon that is substantially freed from the metallic impurities common in commercial silicon a determinate quantity of at least one of the two metals chromium and molybdenum, the quantity of such additive being at least of the order of 10% of the silicon, and a determinate quantity of at least one of the two metals aluminium and beryllium, which form a solid solution with the silicon, the quantity of such latter additive being of the order of between /2% and 1% of the silicon, polishing a plane part of the surface of a fragment of the resulting product, thereafter treating saidfragment with hydrofluoric acid, thereafter heating said fragment in an oxidising atmosphere, thereafter treating said fragment with hydrofluoric acid so as to remove some but not all of the oxide layer formed during said heating, and finally depositing a metallic layer on at least part of the unpolished surface of said fragment
• An electrical crystal contact device including a semi-conducting crystal contact element comprised of silicon which contains a quantity, of the order of at least 10% of the silicon, of at least one of the two metals chromium and molybdenum, said element having a polished and oxidised surface, and a metallic contact element cooperating with said surface of said crystal element.
• An electrical crystal contact device including a semi-conducting crystal contact element comprised of silicon which contains a quantity, of the order of at least 10% of the silicon, of at least one of the two metals chromium and molybdenum, together with a determinate relatively small quantity of at least one of the two metals aluminium and beryllium, said element having a polished and oxidised surface, and a metallic contact element cooperating with said surface of said crystal element.
• An electrical crystal contact device including a semi-conducting crystal contact element comprised of silicon which is substantially free from the metallic impurities common in commercial silicon but which contains a quantity,- between substantially 10% and 20% of the weight of silicon, of at least one of the two metals chromium and molybdenum, together with a quantity, between substantially and 1% cf the weight of silicon, of at least one of the two metals aluminium and beryllium, said element having a polished and oxidised, surface, and a metallic contact element co-operating with said surface of said crystal element.
• An electrical crystal contact device inc1uding a semi-conducting crystal contact element comprised of silicon which is substantially free from the metallic impurities common in commercial silicon but which contains substantially 20% of chromium, of aluminium and of beryllium, these percentages being of the weight of silicon, said element having a partially etched-away oxidised and polished surface, and a metallic contact element co-operating with said surface of said crystal.
• An electrical crystal contact element comprising silicon and a quantity, of the order of at least ten per cent by weight of the silicon, of at least one of the 'tWo metals chromium and molybdenum.
• An electrical crystal contact element comprising silicon, a quantity of the order of at least ten per cent by weight of the silicon of at least one of the two metals chromium and molybdenum, and a determinate relatively small quantity of at least one of the two metals aluminium and beryllium.
• An electrical crystal contact element comprising silicon, a quantity between substantially ten per cent and twenty per cent by weight of the silicon of at least one of the two metals chromium and molybdenum, and a quantity between substantially one-half per cent and one per cent by weight of the silicon of at least one of the two metals aluminium and beryllium.
• An electrical crystal contact element comprising silicon which is substantially free from the metallic impurities common in commercial silicon, twenty per cent of chromium by weight of the silicon, and one-quarter per cent of aluminium and one-quarter per cent of beryllium by weight of the silicon.
• An electrical crystal contact element comprising silicon and a quantity of the order of at least ten per cent by weight of the silicon of at least one of the two metals chromium and molybdenum, said element having at least one polished and oxidised surface area.
• An electrical crystal contact device comprising silicon, between substantially ten per cent and twenty per cent by weight of the silicon of at least one of the two metals chromium and molybdenum, and between substantially one-half per cent and one per cent by weight of the silicon of at least one of the two metals aluminium and beryllium, said element having at least one polished and oxidised surface area.

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• Manufacturing & Machinery (AREA)
• Ceramic Engineering (AREA)
• Contacts (AREA)
• Conductive Materials (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)

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Cited By (5)

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Citations (1)

• 0
  • NL NL64663D patent/NL64663C/xx active
  • BE BE467418D patent/BE467418A/xx unknown
• 1943
  • 1943-03-22 GB GB4676/43A patent/GB578013A/en not_active Expired
• 1944
  • 1944-02-24 US US523748A patent/US2438944A/en not_active Expired - Lifetime
• 1946
  • 1946-06-11 FR FR927778D patent/FR927778A/fr not_active Expired
  • 1946-08-21 CH CH265647D patent/CH265647A/de unknown

Patent Citations (1)

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