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Combination Heater-Magnetic Solenoid Coil(s) for Suppressing Melt Convection in Crystal Growth

IP.com Disclosure Number: IPCOM000041608D
Original Publication Date: 1984-Feb-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Giess, EA: AUTHOR [+3]

Abstract

A helical coil or "coaxial" nest of coils with cylindrical symmetry is provided to supply both heat and an axial magnetic field to a Czochralski crystal puller. The axial magnetic field reduces convection in the melt, resulting in decreased oxygen content in Si crystals. The coil material is a refractory metal, such as Ta, W, Mo or Pt, that can be used in a vacuum at elevated temperatures (around 1500ŒC). Turbulent thermal convection induced by thermal gradients in a crystal growth melt can produce crystals with striations from cyclic-dopant segregation. In the case of Si melts, there is also an increase in oxygen dissolution by erosion from the silica (SiO2) crucible. There is a need to control the amount of oxygen in the melt to regulate the oxygen impurity level in crystals.

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Combination Heater-Magnetic Solenoid Coil(s) for Suppressing Melt Convection in Crystal Growth

A helical coil or "coaxial" nest of coils with cylindrical symmetry is provided to supply both heat and an axial magnetic field to a Czochralski crystal puller. The axial magnetic field reduces convection in the melt, resulting in decreased oxygen content in Si crystals. The coil material is a refractory metal, such as Ta, W, Mo or Pt, that can be used in a vacuum at elevated temperatures (around 1500OEC). Turbulent thermal convection induced by thermal gradients in a crystal growth melt can produce crystals with striations from cyclic-dopant segregation. In the case of Si melts, there is also an increase in oxygen dissolution by erosion from the silica (SiO2) crucible. There is a need to control the amount of oxygen in the melt to regulate the oxygen impurity level in crystals. Melt convection is suppressed by a magnetic field by known principles. Providing heat and a magnetic field from separate coils can be done, but this is inefficient because the magnetic field coil has to be thermally insulated and the heat generated is lost to cooling water. Both the heat and field functions can be provided by a single coil (or a coaxial series of coils) energized by direct current no greater than those projected for use in scaled-up conventional-type crystal growth furnaces. A Ta wire coil 23 cm. in diameter with 25 turns in its 25 cm. axial height (with a wire cross-sectional a...