US2864729A - Semi-conducting crystals for rectifiers and transistors and its method of preparation - Google Patents

Semi-conducting crystals for rectifiers and transistors and its method of preparation Download PDF

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US2864729A
US2864729A US490606A US49060655A US2864729A US 2864729 A US2864729 A US 2864729A US 490606 A US490606 A US 490606A US 49060655 A US49060655 A US 49060655A US 2864729 A US2864729 A US 2864729A
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crystal
impurities
crystals
layers
transition zone
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US490606A
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Karl O Seiler
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International Standard Electric Corp
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International Standard Electric Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/28—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection
    • H01L23/29—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection characterised by the material, e.g. carbon
    • 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
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/24—Alloying of impurity materials, e.g. doping materials, electrode materials, with a semiconductor body
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D99/00—Subject matter not provided for in other groups of this subclass
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

  • n semiconductors While those having a deficiency of electrons (or excess of holes) are termed p semiconductors.
  • Semiconducting crystals having 2 or more layers of different types of conductivity are termed pn crystals and are used for making rectifiers or transistors. Such crystals are also referred to as junction type crystals.
  • the pn crys tals have the advantage over corresponding arrangements using point contacts in that they may be used with higher current intensities.
  • the intensity of this field is determined by the distribution of the impurities in the transition zone between the areas of the different conductivity types. If this zone is made wide enough, it is possible to achieve high cut-off voltages in the blocking direction while employing material of good conductivity on both sides of the transition zone. However, there is a limit to the width of this zone since if it is too wide, recombination of the current carriers in this zone will occur. Thus for example, the transition zone may be made of the order of some tenth of a millimeter thick, thus reducing the intensity of the field in the transition zone and causing a substantial increase of the resistance or dielectric strength in the blocking direction.
  • An object of the present invention is the provision of a method of producing pn crystals, and the provision of such crystals, in which these surface influences are avoided or diminished and in which the blocking voltage is increased towards the theoretically possible limit.
  • pn crystals are built up in such a way that the gradation of impurities in, or adjacent the transition zone is substantially flatter on the surface of the crystal than in the inside thereof.
  • the density of impurities decreases from the center of the transition zone towards the ends of the crystal.
  • One method of obtaining the desired widening of the transition zone at the surface layers thereof is by the use of a suitable heat treatment.
  • widening of the transition zone we refer to spreading the impurities which areclosely packed or densest at the transition zone over a wider area at the surface of the crystal so that the impurity density becomes less.
  • density curve of the impurities is flattened at the surface layers of the transition zone. This will become clearer as described hereinafter.
  • the desired degree of flattening of this curve determines the temperature and the duration of the heat treatment. It is known that the diffusion velocity of the impurities in the surface layers of semi-conducting crystals is much greater than in the inside.
  • the impurities will spread more rapidly in the surface layers when heat is applied. Heating of the crystal is performed in such a way that chiefly only the surface layers are heated. Thus the crystal may be intensely heated for a short time from the outside and then quickly cooled before the heat can spread into the inside of the crystal. Another method of heating the surface of the crystal without similarly heating the interior thereof consists of using skin effect of high frequency heating.
  • the desired flattening of the distribution curve of the impurities in the surface of the crystal can also be effected by the addition of an impurity of the type effecting conductivity, to the surface of the crystal at or near the transition zone and by heating the same to cause diffusion of this impurity into or near the Zone as will be described hereinafter.
  • Fig. 1 is a schematic cross sectional view of a bar shaped semi-conducting crystal of the pn type according to the prior art while Fig. 2 is a similar view according to the present invention.
  • the crystal there shown has 2 areas of different conductivity designated by the letters P and N respectively.
  • the transition zone between the 2 areas is denoted by 1.
  • the density of the lines 2 serves to illustrate the distribution of field intensity along the length or greatest dimension of the crystal. Within the area of the pn transition at 1, the density of the lines of equal potential is a very great one, but rapidly decreases within a short distance in the transition zone, while remaining nearly constant or uniform within the rest of the crystal.
  • the lines 2 likewise serve to indicate the field strength in the crystal.
  • Fig. 2 shows the distribution of the lines of equal potential according to the present invention.
  • the distribution of the lines of equal potential is almost equal to that in Fig. 1 whereas at the surface of the crystal the distribution curveof the density of the lines of equal potential in the transitionzone is much flatter, as -may-be -scen from the greater width of zone 1.
  • This likewise applies to the field intensity inside the crystal in which the intensity is substantially lower at the'surfacesof the-crystal in Fig. 2 while in the center or interior of'the crystal it is closer to that indicated in the transitionzone ofF ig. l.
  • onemethod of producing the flattening of the gradient of the-impurity density is by a heattreatment.
  • the crystal to be sotreated is a'g'rown crystaljiroduced from a melt
  • the melt for example surrounding the growing crystal may 'be first doped with indium and the pn transition produced by the addition of arsenic.
  • the effective impurity density at both sides shallbe for example approximately cm. This expresses the number of atoms of the impurity per cubic centimeter.
  • frequencies higher than mc./s., especially 10 and 100 mc./s., may be of particular advantage because of the better skin effect.
  • the flattening of the surface profile with the aid of subsequently diffused impurities differs according to impurity or annealing temperature.
  • the impurity must be of such condition that 'it reduc'es the effective impurity difference at thesurface, which means that if n-substance is to be weakened the subsequently diffused substance must be of p-type. 'Howevenonly such quantity of p-substance may be subsequently diffused that the n-substanceat the surface willnot be converted. When a conversion takes place it is sufficient to subsequently reduce the crystal by'etching.
  • the crystal is either embedded in a most-finely distributed aluminum oxide, titanium dioxide or a similar substance, or is coated with a layer thereof. It is'necessary that the size of granulation of the powder into which the crystal is embedded or with which the crystal is coated, is small as compared with the thickness of the transition zone.
  • the transition zone as is well known, may range in the size of some hundredth part of a millimetre, but it is also possible that it exhibits thicknesses down to ill. From this it will be evident'that with such slight thicknessesof the transition zone there have to be employed extremely fine powders for the embedding or surface coating of the crystal respectively. In some cases it will be sufficient to only provide the coating in-the surroundings of the transition zone.
  • germanium pn crystals can be coated advantageously with a coating of silicon dioxide. This can be effected by, for example, evaporating silicon monoxide on the surface, particularly adjacent the transition zone and then changing it into silicon dioxide.
  • the invention can be employed with all types of semiconductor pn crystals in which there exists a solitary or reiterated change of the conductivity character.
  • the invention is in no way limited to the exemplified methods and substances mentioned hereinbefore.
  • a junction type semiconductor crystal comprising two layers of semiconductor material of different electrical properties joined together by a junction layer constituting a region of transition between said semiconductor layers, the electrical properties of said layers being determined by the nature of impurities in said layers, and the impurity density being greatest in said junction layer, characterized in that the density of impurities is greatest towards the center of said junction layer and decreases towards the peripheral surface area thereof.
  • a method of altering the distribution of impurities in a transition layer intermediate two layers of difierent References Cited in the file of this Palmt conductivities in a semiconductor crystal comprising sub- UNITED STATES PA jecting the surface of the crystal to a temperature of approximately 900 C. for a time sufiicient to cause greater 2415841 Ohl 1947 diifusion of the impurities at the surface of the crystal 2437269 Ohl 1948 2,485,069 Scafi' et al Oct. 18, 1949 than towards the center thereof, and cooling said crystal 10 to maintain such impurity distribution.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
US490606A 1954-03-03 1955-02-25 Semi-conducting crystals for rectifiers and transistors and its method of preparation Expired - Lifetime US2864729A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3100730A (en) * 1960-12-29 1963-08-13 Richard F Post Method for reducing the impurity resistivity of sodium
US3208887A (en) * 1961-06-23 1965-09-28 Ibm Fast switching diodes
US3388000A (en) * 1964-09-18 1968-06-11 Texas Instruments Inc Method of forming a metal contact on a semiconductor device

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1207012B (de) * 1955-12-24 1965-12-16 Telefunken Patent Halbleiterbauelement mit einer injizierenden und einer sammelnden Elektrode
DE1116824B (de) * 1956-06-07 1961-11-09 Licentia Gmbh Verfahren zum Herstellen einer elektrischen Halbleiteranordnung mit mindestens einemp-n-UEbergang

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2415841A (en) * 1944-12-14 1947-02-18 Bell Telephone Labor Inc Conducting material and device and method of making them
US2437269A (en) * 1944-04-10 1948-03-09 Bell Telephone Labor Inc Translating device and method of making it
US2485069A (en) * 1944-07-20 1949-10-18 Bell Telephone Labor Inc Translating material of silicon base

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2437269A (en) * 1944-04-10 1948-03-09 Bell Telephone Labor Inc Translating device and method of making it
US2485069A (en) * 1944-07-20 1949-10-18 Bell Telephone Labor Inc Translating material of silicon base
US2415841A (en) * 1944-12-14 1947-02-18 Bell Telephone Labor Inc Conducting material and device and method of making them

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3100730A (en) * 1960-12-29 1963-08-13 Richard F Post Method for reducing the impurity resistivity of sodium
US3208887A (en) * 1961-06-23 1965-09-28 Ibm Fast switching diodes
US3388000A (en) * 1964-09-18 1968-06-11 Texas Instruments Inc Method of forming a metal contact on a semiconductor device

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