Method for controlling growth of a silicon crystal

• US 5,653,799 A
• Filed: 06/02/1995
• Issued: 08/05/1997
• Est. Priority Date: 06/02/1995
• Status: Expired due to Term

• Current Assignee: SunEdison, Inc.
• Original Assignee: MEMC Electronic Materials, Inc. (SunEdison, Inc.)
• Inventors: Fuerhoff, Robert H.
• Primary Examiner(s): HITESHEW, FELISA CARLA
• Application Number:
  US08/459,765
• Time in Patent Office: 795 Days
• Field of Search: 117/13, 117/14, 117/15, 117/20, 117/201, 117/202, 250/559.24
• US Class Current: 117/14
• CPC Class Codes: C30B 15/26 using television detectors; using photo or X-ray detectors
• CPC Class Codes: G01B 11/105 using photoelectric detection means
• CPC Class Codes: Y10T 117/1004 with means for measuring, testing, or sensing
• CPC Class Codes: Y10T 117/1008 with responsive control means

Abstract

System and method for determining the diameter of a silicon crystal being pulled from a silicon melt for controlling a silicon crystal growing apparatus. The melt has a surface with a meniscus which is visible as a bright ring adjacent the crystal. A camera generates an image pattern of a portion of the bright ring adjacent the crystal. Image processing circuitry detects a characteristic of the image pattern and defines an edge of the bright ring as a function of the detected characteristic. The image processing circuitry further defines a generally circular shape including the defined edge of the bright ring. The diameter of the crystal is then determined based on the diameter of the defined shape for use in controlling the crystal growing apparatus.

Claims

1. A method for use in combination with an apparatus for growing a silicon crystal from a silicon melt, said method for determining a diameter of the silicon crystal being pulled from the silicon melt, said silicon melt having a surface with a meniscus which is visible as a bright area adjacent the silicon crystal, said method comprising the steps of:

generating an image pattern of a portion of the bright area adjacent the silicon crystal with a camera;

detecting an optical characteristic of the image pattern;

defining edges in the image pattern as a function of the detected optical characteristic, said defined edges corresponding to an edge of the bright area;

defining a curve corresponding to the shape of the meniscus, said defined curve representing a circle that fits the defined edges in the image pattern corresponding to the edge of the bright area;

determining a dimension of the defined curve; and

determining the diameter of the silicon crystal as a function of the determined dimension of the defined curve.

2. The method of claim 1 further comprising the step of defining window regions of the image pattern adjacent the portion of the bright area wherein the optical characteristic of the image pattern is detected within the window regions for defining the edges in the image pattern corresponding to the edge of the bright area.

3. The method of claim 2 wherein the optical characteristic of the image pattern is an intensity gradient and wherein the step of detecting an optical characteristic of the image pattern includes determining the intensity gradient of the image pattern within the window regions.

4. The method of claim 2 wherein the silicon crystal is generally cylindrical and the bright area is generally ring-shaped and wherein the step of defining the curve includes defining a circle that includes the edge of the ring-shaped bright area defined within at least three of the window regions of the image pattern.

5. The method of claim 4 further comprising the step of determining the center of the defined circle with respect to a reference x-y coordinate system wherein the y coordinate of the center is indicative of melt level.

6. The method of claim 5 wherein a crucible contains the silicon melt from which the silicon crystal is pulled and the crystal growing apparatus provides for relative movement between the silicon crystal and the crucible and further comprising the step of controlling the vertical position of the crucible as a function of the y coordinate of the center of the defined circle thereby to control the crystal growing apparatus.

7. The method of claim 1 further comprising the step of searching the image pattern for the portion of the bright area as a function of the intensity of the image pattern thereby to detect the bright area.

8. The method of claim 1 wherein a crucible contains the silicon melt from which the silicon crystal is pulled and the crystal growing apparatus provides for relative movement between the silicon crystal and the crucible and further comprising the steps of controlling the rates at which the crucible, the silicon crystal, or both, are rotated in response to the determined diameter of the silicon crystal thereby to control the crystal growing apparatus.

9. The method of claim 1 wherein aa crucible contains the silicon melt from which the silicon crystal is pulled and the crystal growing apparatus provides for relative movement between the silicon crystal and the crucible and further comprising the step of controlling the rate at which the silicon crystal is pulled from the silicon melt in response to the determined diameter of the silicon crystal thereby to control the crystal growing apparatus.

10. The method of claim 1 wherein a crucible contains the silicon melt from which the silicon crystal is pulled and the crystal growing apparatus provides for relative movement between the silicon crystal and the crucible and further comprising the step of controlling the temperature of the silicon melt in response to the determined diameter of the silicon crystal thereby to control the crystal growing apparatus.

11. A method for use in combination with an apparatus for growing a silicon crystal from a silicon melt, said method for determining a diameter of the silicon crystal being pulled from the silicon melt, said silicon melt having a surface with a meniscus which is visible as a bright area adjacent the silicon crystal, said method comprising the steps of:

generating an image pattern of a portion of the bright area adjacent the silicon crystal with a camera;

detecting an optical characteristic of the image pattern;

defining an edge of the bright area as a function of the detected optical characteristic;

defining window regions of the image pattern adjacent the portion of the bright area wherein the optical characteristic of the image pattern is detected within the window regions for defining the edge of the bright area;

moving the window regions as a function of the detected optical characteristic of the image pattern within the window regions in response to the bright area varying during pulling;

defining a curve including the defined edge of the bright area, said defined curve corresponding to the shape of the meniscus;

determining a dimension of the defined curve; and

determining the diameter of the silicon crystal as a function of the determined dimension of the defined curve.

12. A method for use in combination with an apparatus for growing a silicon crystal from a silicon melt, said method for determining a diameter of the silicon crystal being pulled from the silicon melt, said silicon melt having a surface with a meniscus which is visible as a bright area adjacent the silicon crystal, said method comprising the steps of:

generating an image pattern of a portion of the bright area adjacent the silicon crystal with a camera;

detecting an optical characteristic of the image pattern;

defining an edge of the bright area as a function of the detected optical characteristic;

defining window regions of the image pattern adjacent the portion of the bright area wherein the optical characteristic of the image pattern is detected within the window regions for defining the edge of the bright area;

defining a center point on the image pattern, wherein the window regions are defined at preselected positions on the image pattern which are located radially with respect to the defined center point;

searching the image pattern for the portion of the bright area as a function of the intensity of the image pattern thereby to detect the bright area if the edge of the portion of the bright area is not defined within the window regions at the preselected positions;

defining a curve including the defined edge of the bright area, said defined curve corresponding to the shape of the meniscus;

determining a dimension of the defined curve; and

determining the diameter of the silicon crystal as a function of the determined dimension of the defined curve.

13. A method for use in combination with an apparatus for growing a silicon crystal from a silicon melt, said method for determining a diameter of the silicon crystal being pulled from the silicon melt, said silicon melt having a surface with a meniscus which is visible as a bright area adjacent the silicon crystal, said crystal growth apparatus providing for rotation of the silicon crystal at a reference rate, said method comprising the steps of:

generating an image pattern of a portion of the bright area adjacent the silicon crystal with a camera;

detecting an optical characteristic of the image pattern;

defining an edge of the bright area as a function of the detected optical characteristic;

defining a curve including the defined edge of the bright area, said defined curve corresponding to the shape of the meniscus;

determining a dimension of the defined curve;

determining the diameter of the silicon crystal as function of the determined dimension of the defined curve; and

detecting periodic deviations in the determined dimension of the defined curve relative to the reference rate thereby indicating zero dislocation growth of the silicon crystal.

14. A method for use in combination with an apparatus for growing a silicon crystal from a silicon melt, said method for determining a diameter of the silicon crystal being pulled from the silicon melt, said silicon melt having a surface with a meniscus which is visible as a bright area adjacent the silicon crystal, said silicon crystal being pulled from the silicon melt along a longitudinal axis which is substantially perpendicular to the silicon melt surface, said method comprising the steps of:

generating an image pattern of a portion of the bright area adjacent the silicon crystal with a camera, said camera having an optical axis which is at an acute angle with respect to the longitudinal axis;

compensating for distortion of the image pattern caused by the camera angle;

detecting an optical characteristic of the image pattern;

defining an edge of the bright area as a function of the detected optical characteristic;

defining a curve including the defined edge of the bright area, said defined curve corresponding to the shape of the meniscus;

determining a dimension of the defined curve; and

determining the diameter of the silicon crystal as a function of the determined dimension of the defined curve.

15. A method for use in combination with an apparatus for growing a silicon crystal from a silicon melt, said method for determining a diameter of the silicon crystal being pulled from the silicon melt, said silicon melt having a surface with a meniscus which is visible as a bright area adjacent the silicon crystal, said silicon crystal being generally cylindrical and said bright area being generally ring-shaped, said method comprising the steps of:

generating an image pattern of a portion of the bright area adjacent the silicon crystal with a camera;

detecting an optical characteristic of the image pattern;

defining an edge of the bright area as a function of the detected optical characteristic;

defining window regions of the image pattern adjacent the portion of the bright area wherein the optical characteristic of the image pattern is detected within the window regions for defining the edge of the bright area;

defining an ellipse that includes the edge of the ring-shaped bright area defined within at least three of the window regions of the image pattern, said defined ellipse corresponding to the shape of the meniscus;

determining a dimension of the defined ellipse; and

determining the diameter of the silicon crystal as a function of the determined dimension of the defined ellipse.