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US3685973A - Method for crucible-free zone melting using a displaced heater - Google Patents

Method for crucible-free zone melting using a displaced heater Download PDF

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Publication number
US3685973A
US3685973A US72878A US3685973DA US3685973A US 3685973 A US3685973 A US 3685973A US 72878 A US72878 A US 72878A US 3685973D A US3685973D A US 3685973DA US 3685973 A US3685973 A US 3685973A
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US
United States
Prior art keywords
rod
heating device
heating coil
zone
seed crystal
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Expired - Lifetime
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US72878A
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English (en)
Inventor
Wolfgang Keller
Konrad Reuschel
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Siemens AG
Siemens Corp
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Siemens Corp
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Filing date
Publication date
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    • 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
    • C30B13/28—Controlling or regulating

Definitions

  • the rod is substantially vertically supported at one end by a first end holder located in the substantially vertical axis of the rod, a seed crystal being attached to the other end of the rod and having a free end supported by a second end holder, and a molten Zone is formed in the rod by an annular heating device surrounding the rod and dividing it into two rod portions, the annular heating device and the rod being moved relative to one another in the axial direction of the rod from the seed crystal to the first end holder so that one of the portions of the rod is supplied to the melt and the other portion thereof crystallizes out of the melt.
  • the improvement in the method includes laterally displacing the annular heating device to a position eccentric to the axis of the rod but nevertheless still surrounding the rod, and maintaining the eccentric relationship of the annular heating device to the rod for at least part of the molten zone pass along the rod.
  • Our invention is a method of crucible-free zone melt- This method is to be carried out by zone melting apparatus of the general type illustrated and described in US. Pat. Nos. 2,972,525, 2,992,311 and 3,030,194, for example.
  • the crystals When performing a crucible-free zone melting process to produce crystalline rods, especially semiconductor rods having large cross sections, such as silicon rods for example of more than 25 mm. diameter, by employing an annular heating device, such as an induction heating coil, the crystals tend at times to travel or stray laterally or transversely to the axis of the rod during the growth thereof so that, after completion of the zone melting operation, the rods have a substantially corkscrew shape. This undesired deformation is observable especially when the crystallizing rod portion is set into relatively rapid rotation or is after-heated so that the liquid-solid boundary surface constituting the solidifying front is substantially planar.
  • an annular heating device such as an induction heating coil
  • the rate of displacement of the rod or the end holders thereof and the heating device or heating coil relative to one another can be predetermined so that the diameter of the rod portion resolidifying from the melt has a predetermined value which may be greater than the inner diameter of the annular heating device.
  • the diameter of the rod portion supplied to the melt can be greater than the inner diameter of the heating coil so that the melting zone is strangled or necked down in the vicinity of the coil and consequently has particular stability against dripping of the melt.
  • the rod portion recrystallizing from the melt can be selectively disposed above or below the heating device and concentric or eccentric to the rod portion supplying the melt.
  • the heating device can be laterally displaced with respect to the rod before the seed crystal is fused to an end of the rod; for example it can be laterally displaced up to an eccentricity of 5 mm. when employing an induction heating coil having an inner diameter of between 15 and 40 mm. This eccentricity can then be maintained during the entire zone melting process.
  • the heating coil in the shape of a flat coil with an inner diameter of 31 mm. and an outer diameter of 56 mm. is laterally displaced about 3 mm. or previously installed with such an eccentricity.
  • FIGS. 1 and 2 are elevational views partly broken away and partly in section showing two phases during the practice of one mode of the method of our invention, wherein the relative displacement of the heating device to the rod is in an upward direction;
  • FIG. 2a is a diagrammatic plan view, partly in section, showing various phases during the practice of a mode of the method of our invention wherein the heating coil is rotated;
  • FIGS. 3 to 5 are elevational views partly broken away and partly in section showing three phases during the practice of another mode of the method of our invention wherein the relative displacement of the heating device to the rod is in a downward direction.
  • FIG. 1 there is shown a silicon rod 2 having a diameter D to which there is fused at the lower end thereof as shown in FIGS. 1 and 2, a seed crystal 3 having a diameter D corresponding to a cross section that may be one tenth or less than that of the rod cross section.
  • an annular heating device or flat heating coil 4 energized by a high frequency alternating current for example, there is produced a melting zone in the rod 2 which can be passed through the rod 2 along the length thereof by maintaining stationary the holders 6 at the ends of the rod and seed crystal respectively while moving the heating coil 4 upwardly as shown in FIGS.
  • the seed crystal 3 can be monocrystalline for effecting monocrystalline growth.
  • the seed crystal 3 and the resolidified rod portion 2a therewith are rotated about their longitudinal axis.
  • the melting zone is located at the transition boundary between the seed crystal 3 and a rod 2 of relatively greater thickness.
  • the ensuing method steps are represented by the arrows in FIG. 1.
  • the heating coil 4 is displaced not only upwardly with respect to the stationary rod 2, but also simultaneously laterally or transversely thereto, for example toward the left-hand side of FIG. 1, so that the melting zone 5 is also forced toward the left-hand side of FIG.
  • FIG. 2 there is shown a phase of one mode of the method of the invention in which a predetermined nominal diameter D of the recrystallizing rod portion 2a is attained.
  • the heating coil 4 is no longer moved transversely to the axis of the rod but is only moved upwardly as shown in FIG. 2.
  • the upper end holder 6 FIG. 1 for the supply rod portion 2b is continually moved closer to the melting zone with suitable velocity in the axial direction of the rod.
  • the heating coil 4 can again be moved back during the zone-melting process to a position in which it is less eccentric to the rod or can be moved back altogether to its original position in which it is coaxial with the rod or can be moved back and forth repeatedly between this position and positions at which it has predetermined eccentricity relative to the rod or between positions in which it has predetermined maximum and minimum eccentricities relative to the rod.
  • the speed of the back-and-forth or reciprocatory motion of the heating coil 4 is advantageously great relative to the speed at which the melting zone 5 is passed through the rod 2.
  • a coil 4 can be reciprocated transversely to the rod 2 at a rate of nine (9) alternations per minute between the maximum and minimum eccentricity of the coil 4 relative to the rod 2 at the same time that the rod is being pulled in the direction of its longitudinal axis at a rate of about two (2) millimeters per minute. If the rotational speed of the recrystallizing rod portion 2a is revolutions per minute, the phase relationship of the rod portion 2a and the coil 4, starting from the position of maximum eccentricity therebetween, is altered by the passage sequentially of the recrystallized rod portion 2a through various angular positions, and the original phase relationship of maximum eccentricity between coil 4 and rod portion 2a is attained only when the coil is making its 9th alternation as it is being laterally reciprocated.
  • the heating coil 4 can be forced to carry out a substantially sinusoidal course with the air of an eccentric drive mechanism, vibration or shock to the zone-melting apparatus can be greatly avoided.
  • The can be achieved even better as shown in the plan view of FIG. 2a, by having the heating coil 4 effect a circular movement about an axis IV lying outside the axis II of the recrystallized rod portion 2a and extending parallel thereto, at constant peripheral or tangential velocity on the circular path described by each point of the coil 4.
  • This can be achieved for example by a parallel guide with the aid of a second eccentric having the same eccentricity and the same peripheral velocity as the drive eccentric, and having an angular position conforming therewith.
  • the circle K represents the rotary path of the coil axis III about the axis IV.
  • FIGS. 3 to 5 those members corresponding to the members shown in FIGS. 1 and 2 are provided with the same reference numerals as in FIGS. 1 and 2.
  • the arrows indicate the respective directions of movement.
  • the rod portion 2b supplied to the melt 5 has a diameter of 26 millimeters
  • the crystallized rod portion 2a has a nominal diameter of 33 millimeters.
  • the respective axes of the rod portions 2a and 2b are parallel and are displaced from one another a distance of about five (5) millimeters.
  • a heating coil 4 of the flatly wound type having an inner diameter of about 30 millimeters and an outer diameter of about 55 millimeters, are located so that the axis thereof extends in substantially the same vertical plane in which the axes of the two rod portions 2a and 2b extend, and the eccentricity of the coil 4 relative to the two rod portions is substantially the same, namely about 2.5 millimeters respectively.
  • the heating coil 4 is gradually displaced laterally or transversely to the axis of the rod portions, as shown in FIG.
  • FIG. 4 represents an instant or phase in which the nominal diameter of the crystallized rod portion 2a, and, simultaneously, the outermost limit of the lateral displacement of the heating coil 4 is achieved.
  • FIGS. 4 and 5 represent both reversing points of the lateral reciprocatory motion of the coil 4.
  • the circular path described by the center of the coil does not surround the axis of the crystal lized rod portion 2a, as shown in FIGS. 4 and 5.
  • semi-conductor rods are in fact produced having specific resistance determined over the rod cross section with maximum deviations or tolerances of less than 10% and with an etch-pit density of less than 50,000 per square centimeter.
  • a method of zone melting a semiconductor rod wherein the rod is substantially vertically supported at one end by a first end holder, a seed crystal is attached to the other end of the rod and has a free end supported by a second end holder, and a molten zone is formed in the rod by an induction heating coil surrounding the rod and divides the rod into two rod portions, the induction heating coil and the rod being moved relative to one another in the axial direction of the rod from the seed crystal to the first end holder so that the molten zone passes axially through the rod, one of the portions of the rod being supplied to the molten zone and the other portion thereof being crystallized out of the molten zone, the improvement therein which comprises laterally displacing the induction heating coil in a direction transverse to the axial direction of the rod to a position in which it is eccentric to the rod though still surrounding the rod, and maintaining the eccentric position of the induction heating coil relative to the rod for at least part of the molten zone pass along the rod.
  • both rod portions have longitudinal axes laterally offset from one another, and which includes displacing the induction heating coil to a position in which the axis thereof is eccentric to the axes of the rod portions and is spaced a greater distance from the axis of the crystallizing rod portion and a smaller distance from the axis of the supply rod portion than the distance between the respective axes of both rod portions.
  • Method according to claim 1 which includes fusing the seed crystal to the other end of the rod, the seed crystal having a cross section smaller than the cross section of the rod, and moving the rod end holder relative to one another as the molten zone is being passed along the rod so that the crystallizing rod portion, beginning at the end of the rod fused with the seed crystal, is steadily increased in thickness to a nominal diameter and is maintained at that nominal diameter.
  • Method according to claim 3 which includes fusing the seed crystal to the other end of the rod with the induction heating coil surrounding the rod, and laterally displacing the heating coil for a period until the nominal diameter of the rod portion crystallizing from the molten zone is attained.
  • Method according to claim 2 which includes laterally displacing the induction heating coil before fusing the seed crystal to the rod.
  • Method according to claim 3 which includes imparting a periodic movement to the induction heating coil in said transverse direction, after the nominal diameter of the rod is attained, for repeatedly displacing it between two limiting positions in which the heating coil is eccentric to the rod.
  • Method according to claim 3 which includes setting the induction heating coil in rotary motion about an axis located outside the axis of the recrystallized rod portion and parallel thereto.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Liquid Deposition Of Substances Of Which Semiconductor Devices Are Composed (AREA)
US72878A 1966-06-15 1970-09-16 Method for crucible-free zone melting using a displaced heater Expired - Lifetime US3685973A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DES0104290 1966-06-15

Publications (1)

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US3685973A true US3685973A (en) 1972-08-22

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US (1) US3685973A (da)
BE (1) BE699651A (da)
DK (1) DK138779B (da)
GB (1) GB1175449A (da)
NL (1) NL143435B (da)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4002523A (en) * 1973-09-12 1977-01-11 Texas Instruments Incorporated Dislocation-free growth of silicon semiconductor crystals with <110> orientation
US4092124A (en) * 1975-07-29 1978-05-30 Siemens Aktiengesellschaft Apparatus for floating melt zone processing of a semiconductor rod
US4110586A (en) * 1975-09-01 1978-08-29 Wacker-Chemitronic Gesellschaft Fur Elektronik-Grundstoffe Mbh Manufacture of doped semiconductor rods
US5009860A (en) * 1987-05-25 1991-04-23 Shin-Etsu Handotai Co., Ltd. Semiconductor rod zone melting apparatus
US5319670A (en) * 1992-07-24 1994-06-07 The United States Of America As Represented By The United States Department Of Energy Velocity damper for electromagnetically levitated materials

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4002523A (en) * 1973-09-12 1977-01-11 Texas Instruments Incorporated Dislocation-free growth of silicon semiconductor crystals with <110> orientation
US4092124A (en) * 1975-07-29 1978-05-30 Siemens Aktiengesellschaft Apparatus for floating melt zone processing of a semiconductor rod
US4110586A (en) * 1975-09-01 1978-08-29 Wacker-Chemitronic Gesellschaft Fur Elektronik-Grundstoffe Mbh Manufacture of doped semiconductor rods
US5009860A (en) * 1987-05-25 1991-04-23 Shin-Etsu Handotai Co., Ltd. Semiconductor rod zone melting apparatus
US5319670A (en) * 1992-07-24 1994-06-07 The United States Of America As Represented By The United States Department Of Energy Velocity damper for electromagnetically levitated materials

Also Published As

Publication number Publication date
GB1175449A (en) 1969-12-23
DE1519894A1 (de) 1971-01-21
NL143435B (nl) 1974-10-15
BE699651A (da) 1967-12-08
DE1519894B2 (de) 1975-10-09
DK138779B (da) 1978-10-30
NL6708321A (da) 1967-12-18
DK138779C (da) 1979-04-09

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