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Process and apparatus for controlling the melt level while pulling single crystals

  • US 5,437,242 A
  • Filed: 08/18/1993
  • Issued: 08/01/1995
  • Est. Priority Date: 09/17/1992
  • Status: Expired due to Term
First Claim
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1. A process for controlling the melt level of molten material in a crucible covered by a crucible cover while pulling a single crystal according to the Czochralski process, comprising:

  • a) providing said crucible cover with at least one characteristic shaped portion in a distance S to the melt surface, said shaped portion causing a reflection from the melt surface;

    b) recording an image of an evaluation area from the melt surface, said evaluation area, at least in part, containing said reflection;

    c) determining with the aid of the recorded image said distance S and generating an actual signal proportional to this distance;

    d) comparing the actual signal with a set point signal and, if a difference is observed, generating a control signal to change the melt level.

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