Method and apparatus for measuring the monocrystal diameter and the melt level during crucible drawing in the Czochralski process

• US 4,832,496 A
• Filed: 10/29/1986
• Issued: 05/23/1989
• Est. Priority Date: 06/08/1979
• Status: Expired due to Term

• Current Assignee: Balzers und Leybold Deutschland Holding AG (Balzers & Leybold Group)
• Original Assignee: Leybold-Heraeus GmbH (Leybold Aktiengesellschaft)
• Inventors: Thomas, Friedrich W.
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US06/925,485
• Time in Patent Office: 937 Days
• Field of Search: 356/384, 356/385, 356/386, 356/387, 356/72, 356/73, 356/375, 73/291, 73/293
• US Class Current: 356/635
• 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

Abstract

A method and apparatus for measuring the diameter of a monocrystal during crucible drawing determines the brightness profile at the melt/monocrystal change-over point. The spacial position of maxima in the brightness profile in relation to a reference point indicates the diameter. The brightness profile is obtained by optically scanning the melt/monocrystal change-over point with a mirror rotating about a horizontal axis, applying the optical beam reflected by the rotating mirror to a row of photosensitive elements in parallel with the axis, and analyzing the outputs corresponding to the brightness profile for determining the diameter.

Claims

1. A method of measuring the diameter of monocrystals and controlling the melt level during crucible drawing of the Czochralski type wherein the brightness profile at the melt/monocrystal change-over point is determined by an optical system having an observation axis under an acute angle to an axis of the monocrystal and the spatial position of the brightness profile in relation to a reference point on a display device is indicated, said method comprising the steps of:

optically scanning the melt-monocrystal change-over point by rotating a mirror about a horizontal axis;

applying the optical beam reflected by the rotating mirror to a row of photo-sensitive elements in parallel with the horizontal axis;

periodically retrieving the measured values from the row of photo-sensitive elements in synchronism with the rotation of the mirror thereby to produce a plurality of scan lines;

analyzing the outputs corresponding to the brightness profile in each scan line to determine intensity maxima of the scan line that corresponds to the direction of view onto a diameter of the monocrystal that passes through the melt-monocrystal change-over point, the distance between said intensity maxima in the selected scan line representing the said crystal diameter;

applying the analyzed output signals for at least said selected scan line to the display device; and

controlling the level of the molten material in the crucible by comparing the position of the selected scan line with a predetermined position and providing a signal proportional to the difference to a crucible-lifting mechanism for reducing said difference.

2. A method of controlling the melt level and measuring the diameter of the monocrystal being drawn vertically from the melt in a Czochralski type crystal drawing process in a crucible wherein the brightness profile at the melt/monocrystal change-over point is observed, the position of the melt/monocrystal change-over point changing as the monocrystal is drawn from the melt, and the spatial position of maxima in the brightness profile is determined in relation to a reference point for measuring the diameter of the monocrystal indicated thereby, said method comprising the steps of:

optically scanning at least one of the monocrystal and melt at least to the melt/monocrystal change-over points;

positioning only one row of photo-sensitive elements horizontally to receive the optical scanning;

intermittently obtaining the response of the row of photo-sensitive elements to the optical scanning, thereby producing a plurality of scan lines;

processing the responses of the row of photo-sensitive elements in each scan line to identify a scan line corresponding to the direction of view onto a diameter of the monocrystal that passes through the melt/monocrystal change-over point, and the responses of the individual photo-sensitive elements in the identified scan line of the row to identify maxima therein; and

controlling the level of the molten material in the crucible by comparing the position of the selected scan line with a predetermined position and providing a signal proportional to the difference to a crucible-lifting mechanism for reducing said difference;

whereby the spatial position of the individual photo-sensitive elements producing the maxima in the identified scan line indicates the diameter at the melt/monocrystal change-over point without variation from the position of melt/monocrystal change-over point and whereby the position of the selected scan line indicates the level of the molten material.

3. The method of claim 2, wherein the optically scanning comprises rotating a mirror about a horizontal axis, positioning the row of photo-sensitive elements comprises fixedly positioning the same to receive optically-scanning reflections from the mirror, and intermittently obtaining the responses of the row of photo-sensitive elements comprises intermittently obtaining the response of the same to the reflections.

4. The method of claim 3, wherein the optically scanning comprises rotating a mirror having at least one planar reflection surface.

5. The method of claim 4, wherein the optically scanning comprises rotating a mirror having prismatically-arranged planar reflection surfaces.

6. The method of claim 4, wherein intermittently obtaining the responses of the row of photo-sensitive elements comprises identifying each rotation of the planar reflection surface and obtaining sufficient intermittant responses from the row of photo-sensitive elements after each rotation that one of the responses from the reflection from the mirror onto the row of photo-sensitive elements corresponds to the brightness profile.

7. The method of claim 6, wherein intermittently obtaining the responses of the row of photo-sensitive elements comprises periodically obtaining the same number of responses after each identified rotation of the planar reflection surface for synchronism therewith and processing the responses comprises displaying each of the periodic, synchronized responses of the row of photo-sensitive elements as successive lines of a picture of the scan thus obtained, whereby the brightness of the brightness profile identifies the same in the picture and the position thereof in the picture corresponds to the position of the melt/monocrystal change-over point.

8. The method of claim 6, wherein processing the responses comprises selecting those intermittent responses which exceed a preselected level.

9. The method of claim 8, wherein processing the responses additionally comprises preselecting individual ones of the intermittent responses, whereby the one corresponding to the brightness profile may be selected.

10. The method of claim 9, wherein processing the responses additionally comprises preselecting the individual photo-sensitive elements of the row from which responses are obtained, whereby the position of the maxima of the brightness profile is obtained from the response maxima of the corresponding individual photo-sensitive elements.

11. Apparatus for controlling the melt level and measuring the diameter of a monocrystal being drawn vertically from the melt in a crucible using the Czochralski process, wherein the brightness profile at the melt/monocrystal change-over point is observed, the position of the melt/monocrystal change-over point changing as the monocrystal is drawn from the melt, and wherein the spatial position of maxima in the brightness profile is determined for measuring the diameter of the monocrystal indicated thereby, said apparatus comprising:

only one horizontal row of photo-sensitive elements;

means for directing an optical scan of at least the monocrystal change-over point onto the row of photo-sensitive elements;

means for intermittently obtaining the responses of the row of photo-sensitive elements to the optical scan, thereby producing a plurality of scan lines;

means for processing the response of the row of photo-sensitive elements to identify a scan line corresponding to the direction of view onto a diameter of the monocrystal that passes through the melt/monocrystal change-over point and the responses of the individual photo-sensitive elements in the identified scan line of the row to identify intensity maxima therein; and

means for controlling the level of the molten material in the crucible by comparing the position of the identified scan line with a predetermined position and providing a signal proportional to the difference to a crucible-lifting mechanism for reducing said difference;

whereby the spatial position of the individual photo-sensitive elements producing the maxima in the identified scan line indicates the diameter at the melt-monocrystal change-over point without variation from the position of melt/monocrystal change-over point and whereby the position of the selected scan line indicates the level of the molten material.

12. Apparatus as in claim 11, wherein the row of photo-sensitive elements is fixedly positioned, and the means for directing the optical scan comprises at least one planar mirror and means rotating it about a horizontal axis for reflecting the optical scan onto the row of photo-sensitive elements.

13. Apparatus as in claim 12, wherein the means for processing the responses comprises means for displaying the response of at least preselected ones of the individual photo-sensitive elements in at least a preselected one of the intermittent responses,

whereby the intermittent response corresponding to the brightness profile may be identified from the response signal level and the spatial position of maxima therein may be identified from the individual photo-sensitive elements corresponding to the response-maxima.

14. Apparatus as in claim 13, additionally comprising means for synchronizing the means for intermittently obtaining the responses to the means for rotating the mirror and wherein the means for processing the responses comprises means for displaying each intermittent response in vertical progression and horizontal spatial positions corresponding to the individual photo-sensitive elements producing the same, whereby a steady line-by-line picture of the optical scan is obtained from which the position of the brightness profile and its maxima are obtained.