Patent ID: 7172656

Claim:
A method for measuring the position of a liquid surface of a melt from which a single crystal is pulled by a Czochralski method, the method comprising: capturing an image of a fusion ring at a boundary between the single crystal and the melt; setting a first measuring line across the captured image below a central reference point in the captured image; setting a second measuring line across the captured image spaced below and parallel to the first measuring line; detecting the positions in the captured image of intersections of the respective measuring lines and the fusion ring defined on opposite sides of the fusion ring and determining the interval between the intersections on each measuring line; calculating the center of the fusion circle based on the detected positions of the intersections of the respective measuring lines and the determined intervals between the intersections for each measuring line; and determining the position of the liquid surface of the melt based on the calculated center of the fusion circle.