US3223493A - Method of crucible-free zone-melting of semiconductor material - Google Patents

Method of crucible-free zone-melting of semiconductor material Download PDF

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Publication number
US3223493A
US3223493A US115974A US11597461A US3223493A US 3223493 A US3223493 A US 3223493A US 115974 A US115974 A US 115974A US 11597461 A US11597461 A US 11597461A US 3223493 A US3223493 A US 3223493A
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Prior art keywords
zone
melting
vessel
rod
pass
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US115974A
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English (en)
Inventor
Keller Wolfgang
Kramer Herbert
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Siemens Schuckertwerke AG
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
    • 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
    • Y10S117/906—Special atmosphere other than vacuum or inert

Definitions

  • Our invention relates to a method of producing or processing hyperpure semiconductor material by a crucible-free or floating zone-melting method, such hyperpure simiconductor material being applicable in the production of rectifiers, transistors, photo-diodes, four-layer devices and other electronic semiconductor components.
  • the crucible-free zone-melting is performed by mounting a rod of the semiconductor material, preferably vertically, between two holders which engage the respective ends of the rod.
  • a ring-shaped heating device in most cases an induction coil, surrounds the semiconduction rod and, during zone-melting operation, travels axially along and over the entire exposed length of the rod while melting an axially narrow zone of the rod located within, and travelling with, the heater coil. In the travelling direction of the molten zone, new semiconductor material is continuously melted at the leading side of the zone, whereas previously melted semiconductor material solidifies at the lagging side.
  • the progressing melting and recrystallizing has a purifying effect which eliminates impurities from the rod material and causes it to migrate toward one end of the rod where it can subsequently be romoved by cutting a piece of the rod.
  • the rod is thereafter sliced into Wafers for use in respective semiconductor devices.
  • crucible-free zone-melting methods are growing of monocrystals.
  • a monocrystalline seed is fused to one end of a polycrystalline semiconductor rod, and a melting zone, starting from the fusion point, is passed through the entire length of the semiconductor rod toward the other end, this method being repeated several times if desired.
  • the crucible-free zone-melting is also applicable for zone levelling.
  • the molten zone is repeatedly passed through the entire length of the rod in both directions so that the concentration of certain impurities, contained in the semiconductor material or added thereto, is uniformly distributed over the entire rod length.
  • FIG. 1 shows apparatus for crucible-free zone-meltmg.
  • the crucible-free zone-melting is performed within a protective gas atmosphere or in an evacuated vessel.
  • the above-described phenomena are accompanied by an additional purifying effect due to evaporation of foreign impurities from the rod into the vacuum.
  • apparatus for crucible-free zone-melting comprises a vessel composed of hell 31 of relatively great Width which is vacuum-tightly seated upon a bottom plate 32.
  • the bell 31 may consist of steel or other sheet metal and is preferably provided with an observation window 31a of glass.
  • the processing space within the vessel can be evacuated through a nipple 31b to be connected to a vacuum pump.
  • water vapor containing gas may also be supplied through the nipple, or through a separate inlet (not shown) to the vessel.
  • a frame structure 21 which carries a holder 22 vertically above another holder 23 that is mounted on the bottom plate 32 and may be fastened to a shaft 25 passing through a seal 33 in the bottom plate in order to permit imparting rotation to the semiconductor material 24 during the zone-melting operation, as is desirable for some purposes.
  • the semiconductor rod 24, for example of silicon, is held in and between the two holders 22 and 23 and is surrounded by an inductive heating coil 26.
  • the coil 26 is energized by electric current and causes a narrow horizontal zone of the rod 24 to melt, while being slowly shifted upwardly or downwardly along the rod thus gradually passing the melted zone through the entire body for the purpose of purifying it, levelling it and/or converting it to monocrystalline condition.
  • Coolant such as water
  • the entrance and exit of the flowing coolant are indicated in FIG. 1 by arrows 39.
  • a water-containing gas for example air from the environment or steam, prior to commencing the last pass of the melting zone.
  • the resulting semiconductor material exhibits greatly improved properties, due to the fact that the lifetime of the minority carriers in the product is considerably increased. We have been unable to fully explain this phenomenon. However, We consider it reasonable to assume that a slight amount of oxygen is built into the resulting crystal lattice and thereby eliminates lattice disturbances, particularly dislocations.
  • the silicon product when operating with high vacuum, for example of about 10" mm. Hg with a total of 10 passes of the molten zone along a silicon rod, the silicon product can be obtained with a specific resistance of 1000 ohm cm. and an eifective charge-carrier lifetime T (tau of about 300 to 500 seconds.
  • T eifective charge-carrier lifetime
  • Patented Dec. 14, 1965 and all phases terminate at the opposite end. Whereafter the heating is reduced to a low temperature at which the semiconductor material can solidify, but the material is still. in glowing condition, and the glowing zone is then passed in reverse direction back to the starting point of the next pass.
  • the processing is interrupted and the vacuum vessel filled for a short interval of time with water-containing gas, for example atmospheric air, then the material resulting after completion ofthe subsequent last melting-zone pass exhibits a lifetime T about five timesgreater than otherwise obtained, all other essential properties being not discernibly afiected.
  • water-containing gas for example atmospheric air
  • the process can be carried out for example as follows. After the ninth pass of the melting zone, the heating of the melting zone is completely discontinued, for example by de-energizingthe electric induction coil. Then the vacuum vessel is permitted to cool for a short period of time and rinsed with air. Thereafter the vacuum vessel is again closed, sealed'and evacuated. Thereafter the tenth and last pass of the melting zone is performed. Whenever the vacuum vessel is opened'in the course of the process, that is for the purpose of supplying air or upon completing the last pass, it is preferable to provide for a sufficient cooling time of the semiconductor material to prevent the formation of oxide skins.
  • the process can be carriedout in a similar manner. That is, after the melting zone has been passed through the rod the desired number of times, the melting zone is permitted to cool, steam is admitted into the vacuum vessel, whereafter the vessel is again evacuated, and ultimately a melting zone is again produced and is passed once through the entire length of the rod.
  • the latter modification is sometimes preferable and simpler in performance because water can readily be produced in the high degree of purity suitable for semicondutor techniques.
  • the number of zone passes is not critical and can be adapted to the other requirements or desiderata of the process; Critical only is the temporary admission of water-containing gas prior'to the last zonemelting pass. It is of course possible to repeat the justmentioned processing step by opening the vacuum vessel and admitting air or steam.
  • the vacuum vessel could be supplied with water-containing gas after each individual zone-melting pass.
  • arod-shaped semiconductor body is mounted within a vacuum vessel, said vessel being evacuated, and a heater within said' vessel serves to cause a molten zone to pass repeatedly through and along the length of said body being within said vessel, the improvement which comprises the steps of introducing humid air into said vessel after the penultimate zone-melting pass, re-evacuating the vessel and performing the last zone-melting'pass.

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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)
  • Silicon Compounds (AREA)
  • Liquid Deposition Of Substances Of Which Semiconductor Devices Are Composed (AREA)
US115974A 1960-06-11 1961-06-09 Method of crucible-free zone-melting of semiconductor material Expired - Lifetime US3223493A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DES68896A DE1207341B (de) 1960-06-11 1960-06-11 Verfahren zum tiegelfreien Zonenschmelzen von Germanium- oder Siliciumstaeben
DES71088A DE1209102B (de) 1960-06-11 1960-11-02 Verfahren zum tiegelfreien Zonenschmelzen von Germanium- oder Siliciumstaeben

Publications (1)

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US3223493A true US3223493A (en) 1965-12-14

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US115974A Expired - Lifetime US3223493A (en) 1960-06-11 1961-06-09 Method of crucible-free zone-melting of semiconductor material

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US (1) US3223493A (fr)
BE (1) BE604423A (fr)
CH (1) CH391305A (fr)
DE (2) DE1207341B (fr)
GB (1) GB946064A (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3660062A (en) * 1968-02-29 1972-05-02 Siemens Ag Method for crucible-free floating zone melting a crystalline rod, especially of semi-crystalline material

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2901325A (en) * 1955-07-22 1959-08-25 Bell Telephone Labor Inc Method of preparing silicon

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL168491B (fr) * 1951-11-16 Roussel-Uclaf, Societe Anonyme Te Parijs.

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2901325A (en) * 1955-07-22 1959-08-25 Bell Telephone Labor Inc Method of preparing silicon

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3660062A (en) * 1968-02-29 1972-05-02 Siemens Ag Method for crucible-free floating zone melting a crystalline rod, especially of semi-crystalline material

Also Published As

Publication number Publication date
DE1209102B (de) 1966-01-20
BE604423A (fr) 1961-11-30
GB946064A (en) 1964-01-08
DE1207341B (de) 1965-12-23
CH391305A (de) 1965-04-30

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