Patent ID: 8130386

Claim:
A position measuring method for measuring a surface level of melt in a CZ furnace based on a principle of triangulation, in which a light source and a photo detector are provided; light emitted from the light source is applied to a surface of the melt; and the light reflected by the surface of the melt is received by the photo detector, wherein the method is a position measuring method for measuring the surface level of the melt between a member in the CZ furnace and a single crystal, and the method comprises: arranging a heat shield outside a single crystal inside the CZ furnace, causing the emitted light to be reflected by a side surface of an inner circumference of a lower end portion of the heat shield, and applying the reflected light to the melt surface, and causing the reflected light reflected by the surface of the melt to be received by the photo detector; or applying the emitted light to the surface of the melt, causing the light reflected by the surface of the melt to be reflected by the side surface of the inner circumference of the lower end portion of the heat shield, and causing the reflected light to be received by the photo detector, the emitted light reflecting off the surface of the melt only once before reaching the photo detector.