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

• Current Assignee: Siltronic AG (Dr. Alexander Wacker Familiengesellschaft Mit Beschrã¤Nkter Haftung)
• Original Assignee: Wacker-Chemitronic Gesellschaft Fur Elektronik-Grundstoffe MbH
• Inventors: Bauer, Werner, Berger, Walter, Hofstetter, Christian, Mittelbach, Bernd
• Primary Examiner(s): KUNEMUND, ROBERT M
• Application Number:
  US08/108,897
• Time in Patent Office: 713 Days
• Field of Search: 117/14, 117/15, 117/30, 117/201, 117/208, 117/217
• US Class Current: 117/14
• CPC Class Codes: C30B 15/26 using television detectors; using photo or X-ray detectors
• CPC Class Codes: G01B 11/14 for measuring distance or clearance between spaced objects or spaced apertures G01B11/26 takes precedence; rangefinders G01C3/00
• CPC Class Codes: Y10T 117/1004 with means for measuring, testing, or sensing
• CPC Class Codes: Y10T 117/1032 Seed pulling
• CPC Class Codes: Y10T 117/1068 including heating or cooling details [e.g., shield configuration]

Abstract

A process and an apparatus for carrying out the process provides for the accurate and simple control of the melt level when pulling single crystals according to the Czochralski process. The process comprises disposing a mechanical reference mark above the melt in such a way that it causes a reflection from the melt surface. An image of the metal surface is then recorded, and with the aid of the recorded image the distance of the mechanical reference mark from the melt surface is determined. An actual signal proportional to this distance is then generated and is compared with a set point signal, and the melt level is changed as a function of any difference observed.

Claims

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.

2. The process as claimed in claim 1, comprising generating a control signal by means of which the melt level is changed by raising or lowering of the crucible.

3. The process as claimed in claim 1, comprising generating a control signal by means of which the melt level is changed by feeding of material to be melted or already molten into the crucible.

4. An apparatus 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) said crucible cover having 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) an optical recording device which records an image of an evaluation area from the melt surface, said evaluation area, at least in part, containing said reflection;

c) an electronic image-processing device which determines with the aid of said recorded image the distance S and generates an actual signal proportional to said distance S;

d) a set point generator which generates a set point signal proportional to a predetermined value; and

(e) a control device which compares the actual signal with the set point signal and, if a difference is observed, generates a control signal to change the melt level.

5. The apparatus as claimed in claim 4, wherein the optical recording device is a CCD camera.