Diameter and melt measurement method used in automatically controlled crystal growth
AssigneeSEH America, Inc.
InventorsBarton V. White, David J. Vickrey
Life of this patent
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Abstract
A CCD camera is used to measure the diameter of a growing crystal through optical recognition of the luminous ring at a crystal-melt interface. The result is an optical diameter control method and apparatus that eliminates the negative effects of orbit, melt-level and incorrect camera angle. The CCD camera is positioned such that it focuses on a full half of the circumference of the crystal as it is being grown. An automatic control system uses two points diametrically opposed on the crystal to measure the diameter, and a third point on the crystal closest to the camera to compute the melt level error. The automatic control system controls a crucible height and a crystal pull rate to optimize crystal diameter.
Claims18
A method for automatically controlling growth of a crystal being pulled from a crucible, the method comprising the steps of:
- detecting first, second and center areas on a circumference of the crystal;
- computing an actual crystal diameter based on a distance between first and second detected areas;
- comparing the actual crystal diameter with a target crystal diameter;
- adjusting a pull rate of the crystal based on the comparison between the actual crystal diameter and the target crystal diameter;
- determining a melt level error based on a center detected area between the first and second areas;
- and
- adjusting a melt level based on the melt level error.
A method for automatically controlling growth of a crystal being pulled from a crucible, the method comprising the steps of:
- computing a first crystal diameter;
- comparing the first crystal diameter to a target crystal diameter;
- adjusting a crystal pull rate based on the comparison of the first crystal diameter to the target crystal diameter;
- computing a diameter error based on at least the first crystal diameter;
- computing a melt level error based on the diameter error;
- and
- adjusting a melt level by adjusting a height of the crucible based on the melt level error.
Dependencies are inferred from the claim text.