US3563810A - Method for reducing the cross section of semiconductor rods by molten-zone stretching - Google Patents

Method for reducing the cross section of semiconductor rods by molten-zone stretching Download PDF

Info

Publication number
US3563810A
US3563810A US840105A US3563810DA US3563810A US 3563810 A US3563810 A US 3563810A US 840105 A US840105 A US 840105A US 3563810D A US3563810D A US 3563810DA US 3563810 A US3563810 A US 3563810A
Authority
US
United States
Prior art keywords
coil
rod
zone
diameter
turns
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US840105A
Inventor
Wolfgang Keller
Herbert Kramer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Application granted granted Critical
Publication of US3563810A publication Critical patent/US3563810A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C30B15/08—Downward pulling
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C30B13/16—Heating of the molten zone
    • C30B13/20—Heating of the molten zone by induction, e.g. hot wire technique
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
    • Y10S117/91—Downward pulling
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
    • Y10T117/10—Apparatus
    • Y10T117/1024—Apparatus for crystallization from liquid or supercritical state
    • Y10T117/1032—Seed pulling
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
    • Y10T117/10—Apparatus
    • Y10T117/1024—Apparatus for crystallization from liquid or supercritical state
    • Y10T117/1032—Seed pulling
    • Y10T117/1072—Seed pulling including details of means providing product movement [e.g., shaft guides, servo means]

Definitions

  • Our invention relates to a method and means for reducing the cross section of semiconductor rods by subjecting them to floating zone melting and simultaneously stretching the molten zone by moving one end of the rod away from the other.
  • This method and suitable apparatus for its performance are known from Pats. 3,030,194.
  • a vertically mounted semiconductor rod secured at both ends in respective holders, is surrounded by a heater which produces an axially narrow molten zone in the rod while the rod holders are being moved away from each other thus stretching the molten zone and reducing the cross section of the recrystallizing rod.
  • the ultimate rod can be sliced into semiconductor plates of the size required for the production of electronic semiconductor devices, thus eliminating the time consuming and wasteful subdivision of slices whose cross section is larger than needed.
  • the heating of the molten zone is effected by means of an annular strip of tungsten traversed by electrical current to assume a temperature of about 2000 C.
  • the transfer of heat from the heater to the semiconductor rod is by radiation.
  • the attainable maximum reduction in cross section is mm.
  • the induction coil has the shape of a flat spiral.
  • semiconductor rods having a diameter of more than 25 mm. can readily be processed into thinner rods of monocrystalline constitution.
  • FIGS. 1, 2 and 3 respectively different embodiments of the invention by way of example.
  • an induction heater coil 2 surrounds the bottom portion of a molten zone 3 between an upper, thick rod portion 4 and a lower, thin rod portion 5.
  • the upper end of portion 4 is secured in a holder, and the lower end of portion 5 is likewise secured in a holder (both holders not shown) which are being moved apart during the zone-melting operation.
  • the coil 2 is designed as a flat spiral.
  • the inner winding turns of coil 2 are located vertically beneath the thick rod portion 4 and thus impose a levitating action upon the molten zone 3 by means of the magnetic field of the coil.
  • the molten zone is thus sustained in its position and much better prevented from dripping off than is the case in the apparatus previously known.
  • the thick rod 4 processed according to FIG. 1 may have a diameter of 40 mm. and the thin rod portion 5 recrystallizing from the molten zone 3 may have a diameter of 20 mm. With an inner coil diameter of about 25 mm., the levitating action of the magnetic field is ample for securing a stable zone-stretching operation.
  • the operation can be performed in known manner in vacuum or in a protective gas. Preferably applied is a vacuum.
  • the travel of the molten zone relative to the semiconductor rod is produced by moving the heater coil, or by moving the rod holders with respect to the heater coil which then may remain fixed.
  • the two rod portions 4 and 5 must move at respectively different speeds. That is, with a fixed heater coil 2, the thick rod portion 4 is to be moved downward at relatively low speed toward the coil 2, while simultaneously the thin rod portion 5 is pulled downwardly at a correspondingly higher speed. For example, with a reduction from 40 to 20 mm. in diameter, the thin rod portion must move at four times the speed of the thick portion relative to the heater coil.
  • the method can be performed also by maintaining the upper rod portion 4 at rest and moving only the lower portion, in which case the heater coil 2 must also be moved.
  • FIG. 2 shows a funnel-shaped heater coil 2 whose levitating efiect has likewise been found to be excellent.
  • FIG. 3 shows the lower end of the thick rod 4 which has been given a frustoconical or somewhat pointed shape by grinding or other suitable mechanical machining.
  • the thick rod 4 consists for example of polycrystalline silicon or other semiconductor material produced by pyrolytic precipitation from the gaseous phase.
  • a thin crystal seed 5a which is monocrystalline and which is to be fused to the lower end of the thick rod 4 when commencing the above-described zone-stretching operation.
  • the improvement which comprises placing around the top of a thin crystal seed an induction heater coil having turns of a diameter larger than the thickness of the thin crystal seed, forming the lower end of a thick rod having a diameter greater than 25 mm. and greater than the diameter of a plurality of inner turns of the coil but smaller than the diameter of at least one of the outer turns of the coil approximately into the shape of the molten zone to be produced by the coil, contacting the lower end of the thick rod with the top of the seed and heating the junction thereof with the coil so that the turns of the coil are positioned vertically beneath the thick portion, and thereafter commencing the zone melting and stretching operation.
  • Method according to claim 1 which comprises sharpening the lower end of the thick rod to a substantially conical shape before commencing the zone melting and stretching operation.

Abstract

METHOD OF FLOATING ZONE MELTING A VERTICALLY MOUNTED ROD AND SIMULTANEOUSLY STRETCHING THE MOLTEN ZONE FOR REDUCING THE ROD IN CROSS SECTION INCLUDES PLACING AROUND THE TOP OF A THIN CRYSTAL SEED AN INDUCTION HEATER COIL HAVING TURNS OF A DIAMETER LARGER THAN THE THICKNESS OF THE THIN CRYSTAL SEED, FORMING THE LOWER END OF A THICK ROD HAVING A DIAMETER GREATER THAN 25 MM. A GREATER THAN THE DIAMETER OF A PLURALITY OF INNER TURNS OF THE COIL BUT SMALLER THAN THE DIAMETER OF AT LEAST ONE OF THE OUTER TURNS OF THE COIL APPROXIMATELY INTO THE SHAPE OF THE MOLTEN ZONE TO BE PRODUCED BY THE COIL, CONTACTING THE LOWER END OF THE THICK ROD WITH THE TOP OF THE SEED AND HEATING THE JUNCTION THEREOF WTH THE COIL SO THAT THE TURNS OF THE COIL ARE POSITIONED VERTICALLY BENEATH THE THICK PORTION, AND THEREAFTER COMMENCING THE ZONE MELTING AND STRETCHING OPERATIONS.

Description

Feb. 16, 1971 w. KELLER ETAL 3,563,810
METHOD FOR REDUCING THE CROSS SECTION OF SEMICONDUCTOR RODS BY MOLTEN-ZONE STRETCHING Original Filed July 10, 1964 Int. Cl. B613 17/10 US. Cl. 1481.6 2 Claims ABSTRACT OF THE DISCLOSURE Method of floating zone melting a vertically mounted rod and simultaneously stretching the molten zone for reducing the rod in cross section includes placing around the top of a thin crystal seed an induction heater coil having turns of a diameter larger than the thickness of the thin crystal seed, forming the lower end of a thick rod having a diameter greater than 25 mm. and greater than the diameter of a plurality of inner turns of the coil but smaller than the diameter of at least one of the outer turns of the coil approximately into the shape of the molten zone to be produced by the coil, contacting the lower end of the thick rod with the top of the seed and heating the junction thereof with the coil so that the turns of the coil are positioned verticall beneath the thick portion, and thereafter commencing the zone melting and stretching operations.
This application is a divisional of Ser. No. 757,217, filed Aug. 28, 1968, now abandoned, which is a continuation of Ser. No. 381,744, filed July 10, 1964, now abandoned.
Our invention relates to a method and means for reducing the cross section of semiconductor rods by subjecting them to floating zone melting and simultaneously stretching the molten zone by moving one end of the rod away from the other. This method and suitable apparatus for its performance are known from Pats. 3,030,194.
According to the apparatus described in the patent, a vertically mounted semiconductor rod, secured at both ends in respective holders, is surrounded by a heater which produces an axially narrow molten zone in the rod while the rod holders are being moved away from each other thus stretching the molten zone and reducing the cross section of the recrystallizing rod. As a result, for example, the ultimate rod can be sliced into semiconductor plates of the size required for the production of electronic semiconductor devices, thus eliminating the time consuming and wasteful subdivision of slices whose cross section is larger than needed.
The heating of the molten zone is effected by means of an annular strip of tungsten traversed by electrical current to assume a temperature of about 2000 C. The transfer of heat from the heater to the semiconductor rod is by radiation. The attainable maximum reduction in cross section is mm.
In cases where to be reduced in the cross section of the original rod diameter is rather large or where a greater than the above-mentioned reduction in cross section is desired, considerable difficulties have been encountered because under such conditions the molten zone is no longer sufficiently stable and can drip off since the thin portion of the rod can no longer sustain the molten zone.
United States Patent 0 3,563,810 Patented Feb. 16, 1971 It is an object of the invention to minimize these difficulties and to afford or improve the drawing-thin of rods having a considerably larger cross section than permissible in the above-mentioned known apparatus.
To this end, and in accordance with the invention, we perform the floating-zone stretching process fundamentally in the above-described manner with the rod portion of reduced cross section located vertically below the thick portion, and we employ as zone heater an induction winding and have it surround the top of the thin rod portion so closely that one or more turns of the induction coil are situated vertically beneath the thick rod portion. Preferably the induction coil has the shape of a flat spiral.
By virtue of the invention, semiconductor rods having a diameter of more than 25 mm. can readily be processed into thinner rods of monocrystalline constitution.
The drawing shows schematically in FIGS. 1, 2 and 3 respectively different embodiments of the invention by way of example.
It should be understood that the illustrated rod portions and induction heater coils form part of an apparatus which may be identical with the one illustrated in FIGS. 1 to 3 of Pat. 3,030,194 so that reference may be had to the patent for a detailed description of components not essential to the present invention proper.
According to FIG. 1 of the present disclosure, an induction heater coil 2 surrounds the bottom portion of a molten zone 3 between an upper, thick rod portion 4 and a lower, thin rod portion 5. The upper end of portion 4 is secured in a holder, and the lower end of portion 5 is likewise secured in a holder (both holders not shown) which are being moved apart during the zone-melting operation. The coil 2 is designed as a flat spiral. The inner winding turns of coil 2 are located vertically beneath the thick rod portion 4 and thus impose a levitating action upon the molten zone 3 by means of the magnetic field of the coil. The molten zone is thus sustained in its position and much better prevented from dripping off than is the case in the apparatus previously known.
For example, the thick rod 4 processed according to FIG. 1 may have a diameter of 40 mm. and the thin rod portion 5 recrystallizing from the molten zone 3 may have a diameter of 20 mm. With an inner coil diameter of about 25 mm., the levitating action of the magnetic field is ample for securing a stable zone-stretching operation.
The operation can be performed in known manner in vacuum or in a protective gas. Preferably applied is a vacuum. The travel of the molten zone relative to the semiconductor rod is produced by moving the heater coil, or by moving the rod holders with respect to the heater coil which then may remain fixed. In the latter case, since the cross section of the semiconductor rod is very greatly reduced, the two rod portions 4 and 5 must move at respectively different speeds. That is, with a fixed heater coil 2, the thick rod portion 4 is to be moved downward at relatively low speed toward the coil 2, while simultaneously the thin rod portion 5 is pulled downwardly at a correspondingly higher speed. For example, with a reduction from 40 to 20 mm. in diameter, the thin rod portion must move at four times the speed of the thick portion relative to the heater coil.
The method, of course, can be performed also by maintaining the upper rod portion 4 at rest and moving only the lower portion, in which case the heater coil 2 must also be moved.
It has been found advantageous to move the thin rod portion at highest feasible speed with respect to the heater winding 2; i.e. at a speed which, if possible, should be higher than 3 mm. per minute. For example, this speed may be 4 mm./min. or may be increased up to 6 mm./ min. Increasing the speed of the thin rod portion improves the crystal quality because the lower boundary 6 of the molten zone 3 is nearly planar under these conditions. Hence, the crystal growing out of the melt exhibits only slight crystalline disturbances at the solid-toliquid boundary because the tensions are substantially equalized.
The shape of the heater coil can be adapted to any particular requirements. Thus FIG. 2 shows a funnel-shaped heater coil 2 whose levitating efiect has likewise been found to be excellent.
We have found it advisable to approximately adapt the shape of the thicker rod portion, prior to commencing the zone melting, to the expected shape of the molten zone. Otherwise it may happen that some semiconductor material can drip off at the beginning of the zone-melting operation and may short-circuit the turns of the heater coil or cause damage in the zone-melting equipment. FIG. 3 shows the lower end of the thick rod 4 which has been given a frustoconical or somewhat pointed shape by grinding or other suitable mechanical machining. The thick rod 4 consists for example of polycrystalline silicon or other semiconductor material produced by pyrolytic precipitation from the gaseous phase. Also shown in FIG. 3 is a thin crystal seed 5a which is monocrystalline and which is to be fused to the lower end of the thick rod 4 when commencing the above-described zone-stretching operation.
We claim:
1. In the method of floating zone melting a vertically mounted rod and simultaneously stretching the molten zone for reducing the rod in cross section, the improvement which comprises placing around the top of a thin crystal seed an induction heater coil having turns of a diameter larger than the thickness of the thin crystal seed, forming the lower end of a thick rod having a diameter greater than 25 mm. and greater than the diameter of a plurality of inner turns of the coil but smaller than the diameter of at least one of the outer turns of the coil approximately into the shape of the molten zone to be produced by the coil, contacting the lower end of the thick rod with the top of the seed and heating the junction thereof with the coil so that the turns of the coil are positioned vertically beneath the thick portion, and thereafter commencing the zone melting and stretching operation.
2. Method according to claim 1, which comprises sharpening the lower end of the thick rod to a substantially conical shape before commencing the zone melting and stretching operation.
References Cited UNITED STATES PATENTS 2,981,687 4/1961 Parmee 252-623 2,992,311 7/1961 Keller 219-10.77 3,030,189 4/1962 Schweikert et a1. 232235 3,030,194 4/1962 Emeis 23301 3,113,841 12/1963 Reuschel 23223.5 3,121,619 2/1964 Scholte 23301 3,136,876 6/1964 Crosthwait 21910.77 3,232,716 2/1966 Quast et al. 23273 3,351,433 11/1967 Keller 23301 L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R. 23273, 301
US840105A 1963-07-13 1969-06-12 Method for reducing the cross section of semiconductor rods by molten-zone stretching Expired - Lifetime US3563810A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DES0086157 1963-07-13
DES0099116 1965-08-28

Publications (1)

Publication Number Publication Date
US3563810A true US3563810A (en) 1971-02-16

Family

ID=25997302

Family Applications (1)

Application Number Title Priority Date Filing Date
US840105A Expired - Lifetime US3563810A (en) 1963-07-13 1969-06-12 Method for reducing the cross section of semiconductor rods by molten-zone stretching

Country Status (6)

Country Link
US (1) US3563810A (en)
BE (2) BE650386A (en)
CH (1) CH407959A (en)
DE (2) DE1719021B1 (en)
DK (1) DK112794B (en)
GB (2) GB1012998A (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS59190300A (en) * 1983-04-08 1984-10-29 Hitachi Ltd Method and apparatus for production of semiconductor
DE3433458A1 (en) * 1984-09-12 1986-03-20 Leybold-Heraeus GmbH, 5000 Köln METHOD AND DEVICE FOR MELTING ROD-SHAPED MATERIAL BY MEANS OF AN INDUCTION COIL

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE975158C (en) * 1953-12-30 1961-09-14 Siemens Ag Method and device for crucible-free zone melting of an elongated rod-shaped body
AT194444B (en) * 1953-02-26 1958-01-10 Siemens Ag Method and device for treating an elongated semiconductor crystal arrangement
NL108958C (en) * 1959-05-29

Also Published As

Publication number Publication date
BE685925A (en) 1967-02-24
DE1519879B2 (en) 1973-08-16
CH407959A (en) 1966-02-28
DK112794B (en) 1969-01-20
GB1012998A (en) 1965-12-15
DE1719021B1 (en) 1969-09-11
BE650386A (en) 1965-01-11
GB1084930A (en) 1967-09-27
DE1519879C3 (en) 1974-05-09
DE1519879A1 (en) 1970-02-26

Similar Documents

Publication Publication Date Title
US3002824A (en) Method and apparatus for the manufacture of crystalline semiconductors
US2961305A (en) Method of growing semiconductor crystals
JPS6046998A (en) Pulling up of single crystal and its device
US3129061A (en) Process for producing an elongated unitary body of semiconductor material crystallizing in the diamond cubic lattice structure and the product so produced
US2793103A (en) Method for producing rod-shaped bodies of crystalline material
US3173765A (en) Method of making crystalline silicon semiconductor material
US3108169A (en) Device for floating zone-melting of semiconductor rods
US2855335A (en) Method of purifying semiconductor material
US3135585A (en) Method of growing dislocation-free semiconductor crystals
US3563810A (en) Method for reducing the cross section of semiconductor rods by molten-zone stretching
US3351433A (en) Method of producing monocrystalline semiconductor rods
US3159459A (en) Method for producing semiconductor crystals
US3271115A (en) Apparatus for crucible-free zone melting of semiconductor material
US3658598A (en) Method of crucible-free zone melting crystalline rods, especially of semiconductor material
US3939035A (en) Method of producing monocrystalline semiconductor material, particularly silicon, with adjustable dislocation density
US3261722A (en) Process for preparing semiconductor ingots within a depression
US3494742A (en) Apparatus for float zone melting fusible material
US3935059A (en) Method of producing single crystals of semiconductor material by floating-zone melting
US3124633A (en) Certificate of correction
US3060123A (en) Method of processing semiconductive materials
US3397042A (en) Production of dislocation-free silicon single crystals
US3134700A (en) Dislocation removal by a last pass starting at a location displaced from the original seed into the grown crystal
US3936346A (en) Crystal growth combining float zone technique with the water cooled RF container method
US3179593A (en) Method for producing monocrystalline semiconductor material
US3454367A (en) Method of crucible-free zone melting of semiconductor material,particularly silicon