Patent ID: 7264674

Claim:
A method for pulling a single crystal with an apparatus having an apparatus body, a crucible in the apparatus body for holding a melt, a lifting device for lifting the crucible, a reference reflector located inside the apparatus body, and an optical device located outside of the apparatus body, said method comprising: forming a melt of a material for the single crystal; partially melting a front portion of a seed crystal in the melt; forming a neck; forming a shoulder; forming a main body of the single crystal having a uniform diameter and a prescribed length; measuring a diameter of the main body of the single crystal while forming the main body; calculating a decrease in volume of the melt in the crucible based on the diameter of the main body of the single crystal and a pulled crystal length of the single crystal; calculating an ascent speed of the crucible based on the decrease in volume of the melt; measuring an actual level position of the melt by detecting a mirror image position of the reference reflector reflected by a surface of the melt using the optical device; calculating an adjustment value of the ascent speed of the crucible based on the actual level position; judging whether criteria are satisfied for adding the adjustment value to the ascent speed, wherein the criteria are the diameter of the main body of the single crystal, the actual level position, a distance between the main body of the single crystal and the reference reflector, and a crucible rotation speed; and controlling a level position of the crucible based on the ascent speed to which the adjustment value was added when the criteria are satisfied, and controlling the level position of the crucible based on just the ascent speed when the criteria are not satisfied.