US3915660A - Preparing oriented semiconductor monocrystalline rods - Google Patents

Preparing oriented semiconductor monocrystalline rods Download PDF

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Publication number
US3915660A
US3915660A US378943A US37894373A US3915660A US 3915660 A US3915660 A US 3915660A US 378943 A US378943 A US 378943A US 37894373 A US37894373 A US 37894373A US 3915660 A US3915660 A US 3915660A
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Prior art keywords
rod
starting
resolidified
zone
monocrystalline
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Expired - Lifetime
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US378943A
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English (en)
Inventor
Wolfgang Keller
Alfred Muehlbauer
Konrad Reuschel
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Siemens AG
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Siemens AG
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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
    • C30B13/30—Stabilisation or shape controlling of the molten zone, e.g. by concentrators, by electromagnetic fields; Controlling the section of the crystal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
    • B01J3/004—Sight-glasses therefor
    • 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
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
    • 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
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
    • Y10T428/2913—Rod, strand, filament or fiber

Definitions

  • ABSTRACT A process for preparing oriented semiconductor monocrystalline rods with a specific resistance which drops towards the center of the rod. The process utilizes rapid non-crucible moving zone melting of a preformed vertically positioned semiconductor rod using an inductive heating device which annularly surrounds the rod.
  • Monocrystalline rods have been produced by noncrucible zone melting with the aid of seed crystals by heating preformed, doped polycrystalline semiconductor rods, in particular silicon rods.
  • a molten zone is made to travel longitudinally and circumferentially from one end of a preformed polycrystalline semiconductor feed rod section where a seed crystal is applied to the other end thereof.
  • the semiconductor rod is generally fixed vertically between two holders, and at least one holder is set in rotation about the rod axis during such zone melting, thus ensuring a symmetrical growth within the solidifying material.
  • the semiconductor basic material (111)-orientated silicon crystalline wafers which each possess a deliberate break or change in the specific electric resistance (p) in their center.
  • p specific electric resistance
  • wafers are conveniently and conventionally formed by transversely slicing a suitable preformed semiconductor monocrystalline rod.
  • the present invention has as a primary aim the provision of a resistance profile in a semiconductor monocrystalline rod which varies radially from therod central region outwardly, or vice versa.
  • a resistance profile is produced by non-crucible zone melting of a preformed, doped semiconductor monocrystalline rod, preferably comprising non-dislocated, (111)-orientated silicon monocrystals.
  • the present invention realizes this aim by providing a process in which a feed or starting monocrystalline cylindrical rod is selectively heated under controlled conditions to produce a monocrystalline rod of smaller diameter which has a desired such resistance profile. A melt zone rapidly moving through a rod is used.
  • FIG. 2 shows the resistance profile associated with a high power diode
  • FIG. 3 is a partial, vertical sectional view through a silicon rod being zone heated and rotated in accordance with the teachings of this invention but not subjected to a moving zone of heat, this FIG. illustrating a characteristic solid-fluid phase boundary profile so produced in such rod, which profile, in a product semiconductor wafer member, results in a resistance profile as illustrated in FIG. 1;
  • FIG. 4 is a vertical sectional view through another silicon rod, but of the type shown in FIG. 3, which not only is being heated and rotated as in FIG. 3, but also is being subjected to an axially rapidly moving zone of heat, this FIG. illustrating the desired solid-fluid phase boundary profile so produced in such rod, achievable in the practice of the present invention, which profile, in a product semiconductor wafer member, results in a resistance profile as illustrated in FIG. 2; and
  • FIG. 5 illustrates an embodiment of one form of apparatus suitable for use in the practice of the present invention.
  • the present invention is directed to a process for the production of (111)-orientated semiconductor monocrystalline rods with a specific resistance which drops towards the center of the rod.
  • This process employs non-crucible zone melting of a preformed, initially polycrystalline, starting or feed semiconductor rod held vertically at its opposite ends.
  • Such a zone melting is achieved by using a zone of heat annularly surrounding such rod, such zone being produced by an inductive heating device or the like which surrounds a portion of the rod circumferentially and concentrically and which produces within the adjacent encircled rod portion the desired melt zone.
  • the movement of the melt zone through the rod is termed pulling or drawing, and, in the present invention pulling is carried out at a relatively rapid speed.
  • a constantly concavely curved boundary area is produced at the solid-fluid phase boundary in the rod undergoing such zone melting to which boundary a (11 1)- tangent can be applied only in the center of the rod.
  • the drawing (or pulling) speed of the melt zone is at least about 3.5 mm/min, and preferably a drawing (pulling) speed of about 5.5 mm/min is used.
  • the axial displacement of rod material is set to be less than about 10 percent of the diameter of the semiconductor monocrystalline rod which is to be produced.
  • the ratio of the diameter of the feed rod to the diameter of the product monocrystalline rod is adjusted to be not less than about 1:1, and preferably is greater than about 1:1.
  • FIG. 2 shows resistance profiles which are used for overhead-ignition-resistant thyristors (FIG. 1) and for high power diodes (FIG. 2).
  • the specific electric resistance p is plotted in Ohm. cm. as ordinate, and the radius of the crystalline wafer is plotted as abscissa.
  • the broken line which runs in parallel to the ordinate indicates the center of the wafer.
  • the facet is particularly noticeable in the case of a non-dislocated silicon crystal due to the fact that, in the case of the crystal which exhibits non-dislocated growth, the degree of undercooling necessary for the formation of a crystallization seed on the facet is greater than in the case of dislocated silicon.
  • the dislocations affect the (111)-facet almost in the manner of crystallization seeds before the drastic degree of undercooling characteristic of rods exhibiting non-dislocated growth has been reached.
  • dislocated silicon the atom layer begins to advance laterally (horizontally) prematurely; in this case the facet is small.
  • the dopant conventionally and characteristically in a starting rod is incorporated into the monocrystal of the product in a greater concentration in the region of the facet than outside the facet region which concentration gradient causes a break in the specific resistance of the rod in the region of this (1 l l )-facet. Since, for example, thyristor silicon is mainly produced in non-dislocated form, the facet, and thus also the specific resistance break occuring in the facet region is particularly deep and of wide expanse.
  • a growing silicon monocrystal 1 is formed as the moving melt zone 2 solidifies.
  • the line 3 indicates the course of the melt isotherms, and the line 4 indicates the solid-fluid phase boundary.
  • the arrow 5 represents the direction of growth of the crystal in the (lll)-direction.
  • a faceted inner region 6 which is convexly curved, relative to the boundary area, is accompanied at the edge by a ring-shaped concave region 7.
  • This concave region 7 is termed, in accordance with the main minimum in the p-profile occuring in the center of the rod, the secondary minimum p in the profile. It has been established that here, too, there is a dopant maximum concentration in the semiconductor material along the ring 7.
  • An aim of the present invention is to displace this dopant maximum located in the secondary minimum, and thus the concave region itself, into the center region of the rod, by influencing the form of the boundary area of the solidfluid phase.
  • FIG. 4 shows the form of the solid-fluid phase boundary which is achieved by the practice of the process of the present invention.
  • the recrystallized, monocrystalline silicon rod 1 is continuously formed from the moving melt zone 2.
  • the line 8 shows the course of the boundary of the solid-fluid phase
  • the horizontal line 9 represents the (11 l )-tangent which can be applied only in the center of the rod.
  • the arrow indicates the growth direction of the crystal in the (111)- direction, that is to say, when the seed crystal is arranged towards the bottom, the monocrystalline rod grows from below in the upwards direction.
  • vessel 21 which has defined therewithin an elongated, vertically oriented chamber, is provided in its top and bottom portions with passages equiped with respective annular seals 22 and 23 which ensure vacuumtight passage therethrough of coaxial, longitudinally spaced drive shafts 24 and 25.
  • the shafts 24 and 25 can be axially reciprocated and also rotated about their respective axes.
  • a molten zone 29 is produced in the rod 26 by means of an electric induction heating coil 30 which is preferably an annular coil comprising a single winding.
  • the induction heating coil 30 is fixed relative to vessel 21 and is passed in vacuum-tight fashion through a side wall of the vessel 21 by means of a mounting assembly 31.
  • the mounting assembly 31 can take the form of a coaxial mounting which is used both to supply the current and a coolant for the coil, preferably water.
  • an inspection window 32 is provided in the side wall of the vessel 21 generally opposite the mounting assembly 21, an inspection window 32 is provided. Hydrogen, argon, or other suitable inert gas is fed from a reservoir 33 through a piping system 34 into the vessel 21.
  • a reducing valve 35, a shutoff valve 36, and a pressure gauge 37 In the piping system 34 there is provided a reducing valve 35, a shutoff valve 36, and a pressure gauge
  • the rod undergoing zone melting is rotated, for example, in the vessel 21 of the apparatus shown in FIG. 5.
  • Shaft 25, when it holds the starting or feed rod portion, is revolved at a substantially uniform rate of from about 5 to 100 revolutions per minute (r.p.m.), preferably about 20 r.p.m.
  • shaft 24, when it holds the recrystallized monocrystalline product rod is revolved at a substantially uniform rate of from about 0 to r.p.m., preferably about 5 r.p.m.
  • the shafts 24 and 25 are preferably rotated in the same direction but these shafts may also counterrotate with respect to one another if desired.
  • the melt zone 29 moves vertically, preferably upwardly, at a substantially uniform rate of at least about 3.5 mm/min., and this speed may be as rapid as desired, consistent with the need to achieve the indicated desired other process conditions. Pulling speeds for this melt zone 29 may range up to about 10 mm/min., though smaller and larger upper range values may be employed, if desired, as those skilled in the art will appreciate, depending on equipment, process considerations, rod being processed, and the like.
  • Silicon monocrystalline rods produced by the process of the present invention typically exhibit p-breaks in the rod center in a range of from about to 40 percent.
  • Product monocrystalline rods with closely bounded, drastic fluctuations in resistance radially measured can be conventionally sliced into wafers which are suitable for usage in thyristors of the typewhich may be ignited in overhead fashion.
  • such product rods are tempered in a separate step, preferably in a separate apparatus (conventional) while being maintained in a solid state at a temperature approaching the melting point of the rod semiconductor material in an inert shield gas atmosphere (e.g. hydrogen, argon, or the like), or in air, to improve their crystalline quality.
  • an inert shield gas atmosphere e.g. hydrogen, argon, or the like
  • such a tempering can be carried out at temperatures in a range of from about 1,300 to 1,400C for a time of at least about five hours, in, for instance a silicon tube, or the like, and the desired wide break in resistance in the center region of such rods so tempered is characteristically substantially retained.
  • a narrow break in resistance is characteristically levelled out in rods during such a tempering.
  • the present invention is directed to a process for preparing an oriented semiconductor monocrystalline rod having a specific resistance which drops towards the center thereof and to aa rod so prepared.
  • the ratio of the diameter of said starting rod to said recrystallized rod to be at least about 1:1
  • the axial displacement of said semi-conductor material is not more than about 10 percent of the diameter of said recrystallized rod.
  • the deviation from the (111)- orientation is most preferably under about 15 for silicon rods.
  • the ratio of the axial length (or height) of said so melted portion relative to the diameter of said recrystallized rod said moving ranges from about 1:1 to 05:1.
  • a monocrystalline silicon rod diameter of about 30 mm one preferably selects a molten zone height of about 25 mm, and, for another example, in the case of a rod diameter of about 45 mm, one preferably selects a molten zone height of about 26 mm, and, for yet another example, with a rod diameter of about mm, one preferably selects a molten zone height of from about 28 to 30 mm.
  • a preformed, doped polycrystalline silicon rod having a di ameter of about 45 mm is mounted vertically between mountings 27 and 28.
  • a seed crystal contacts the bottom end of the rod.
  • the vessel 21 is purged and charged with hydrogen gas of 99.999 weight percent purity to a pressure of about mm Hg.
  • the induction coil 30 annularly surrounds the bottom end region of the rod concentrically and radially symmetrically. The coil 30 is energized and the temperature transversely across and within the region of the coil 30 is adjusted so that the temperature of the molten or melt zone 29 therewithin is maintained uniformly.
  • the coil 30 is moved upwardly axially relative to the rod from the bottom portion of the rod at a uniform rate of about 5.5. mm/min. Simultaneously, the bottom end of the rod in mounting 28 is rotated clockwise (when viewed from above) by shaft 25 at a uniform rate of about 20 r.p.m. while the top end of the rod in mounting 24 is rotated likewise clockwise by shaft 24 at a uniform rate of about 5 r.p.m. As the melt zone 29 moves upwards, the molten rod material solidifies substantially in a monocrystalline form, and the diameter of this so solidified, monocrystalline rod is found to be about 35 mm.
  • a constantly concavely curved boundary area is produced at the solid-fluid phase boundary in the rod to which a (111)-tangent can be applied only in the center of the rod.
  • the axial displacement of the diameter of the semi-conductor monocrystalline rod is about 8 percent.
  • the resulting product rod is removed from vessel 21, placed in a silicon tube in an air shield gas atmosphere, and tempered in a solid state at a temperature ranging from about l,325 to 1,375 C for about five hours.
  • the crystalline structure of the tempered rod is found to be improved and the desired break in p valves near the rod center is substantially maintained after this tempering.
  • the product silicon rod produced exhibits a specific resistance p break in the center of the rod of about 30 percent which is closely bounded.
  • the wafers are found to be useful in thyristers which can be ignited in overhead fashion.
  • a process for preparing an oriented semiconductor monocrystalline rod having a specific resistance which drops towards the center thereof com prisinng the steps of simultaneously and continuously
  • the ratio of the diameter of said starting rod to said recrystallized rod to be at least about 1:1

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Liquid Deposition Of Substances Of Which Semiconductor Devices Are Composed (AREA)
  • Silicon Compounds (AREA)
US378943A 1972-07-13 1973-07-13 Preparing oriented semiconductor monocrystalline rods Expired - Lifetime US3915660A (en)

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Application Number Priority Date Filing Date Title
DE2234512A DE2234512C3 (de) 1972-07-13 1972-07-13 Verfahren zum Herstellen von (Umorientierten Halbleitereinkristallstäben mit zur Stabmitte abtauendem spezifischem Widerstand

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US (1) US3915660A (de)
JP (1) JPS4953372A (de)
BE (1) BE802326A (de)
CA (1) CA1016847A (de)
DE (1) DE2234512C3 (de)
DK (1) DK143457C (de)
FR (1) FR2192870B1 (de)
GB (1) GB1375132A (de)
IT (1) IT992613B (de)
NL (1) NL7305060A (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4126509A (en) * 1975-11-14 1978-11-21 Siemens Aktiengesellschaft Process for producing phosophorous-doped silicon monocrystals having a select peripheral dopant concentration along a radial cross-section of such monocrystal
US4634630A (en) * 1984-11-13 1987-01-06 Alps Electric Co., Ltd. Tellurium oxide whiskers and a method of producing the same
US6452211B1 (en) * 1997-06-10 2002-09-17 Semiconductor Energy Laboratory Co., Ltd. Semiconductor thin film and semiconductor device

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS50159967A (de) * 1974-06-17 1975-12-24

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3121619A (en) * 1959-10-19 1964-02-18 Philips Corp Zone-melting method and apparatus
US3268301A (en) * 1962-12-03 1966-08-23 Siemens Ag Method of pulling a semiconductor crystal from a melt
US3441385A (en) * 1965-08-05 1969-04-29 Siemens Ag Reducing dislocation defects of silicon semiconductor monocrystals by heat treatment
US3477811A (en) * 1964-02-01 1969-11-11 Siemens Ag Method of crucible-free zone melting crystalline rods,especially of semiconductive material

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL243511A (de) * 1959-09-18

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3121619A (en) * 1959-10-19 1964-02-18 Philips Corp Zone-melting method and apparatus
US3268301A (en) * 1962-12-03 1966-08-23 Siemens Ag Method of pulling a semiconductor crystal from a melt
US3477811A (en) * 1964-02-01 1969-11-11 Siemens Ag Method of crucible-free zone melting crystalline rods,especially of semiconductive material
US3441385A (en) * 1965-08-05 1969-04-29 Siemens Ag Reducing dislocation defects of silicon semiconductor monocrystals by heat treatment

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4126509A (en) * 1975-11-14 1978-11-21 Siemens Aktiengesellschaft Process for producing phosophorous-doped silicon monocrystals having a select peripheral dopant concentration along a radial cross-section of such monocrystal
US4634630A (en) * 1984-11-13 1987-01-06 Alps Electric Co., Ltd. Tellurium oxide whiskers and a method of producing the same
US6452211B1 (en) * 1997-06-10 2002-09-17 Semiconductor Energy Laboratory Co., Ltd. Semiconductor thin film and semiconductor device
US6693300B2 (en) 1997-06-10 2004-02-17 Semiconductor Energy Laboratory Co., Ltd. Semiconductor thin film and semiconductor device

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Publication number Publication date
JPS4953372A (de) 1974-05-23
FR2192870A1 (de) 1974-02-15
DK143457B (da) 1981-08-24
DE2234512A1 (de) 1974-01-24
NL7305060A (de) 1974-01-15
IT992613B (it) 1975-09-30
DE2234512B2 (de) 1978-08-24
BE802326A (fr) 1973-11-05
DK143457C (da) 1981-12-28
CA1016847A (en) 1977-09-06
FR2192870B1 (de) 1977-12-23
DE2234512C3 (de) 1979-04-19
GB1375132A (de) 1974-11-27

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