Method for pulling single crystals

Claim 1

In an improved method for pulling a single crystal, comprising the steps of preparing a double crucible assembly having an outer crucible and an inner crucible which communicate with each other; feeding raw material to said double crucible assembly to provide molten raw material therein; and pulling the single crystal from the surface of the molten raw material within said inner crucible in such a manner that during the steady state, the pulled single crystal has a dopant concentration of about kC, where k is the segregation coefficient and C the dopant concentration of the molten raw material in said inner crucible at the steady state; the improvement comprising: raising the dopant concentration of the molten raw material in said inner crucible prior to the pulling, to a value higher than the dopant concentration C of the molten raw material in said inner crucible at the steady state; and at the initial stage of the pulling, introducing the raw material having a dopant content ratio of less than kC into said outer crucible at a rate greater than the rate of decrease of the molten raw material within said inner crucible during the pulling, to achieve a concentration ratio of dopant between said inner and outer crucibles at such a target value that the ratio of the dopant concentration in the outer crucible to the dopant concentration in the inner crucible is k; and subsequently, introducing the raws material having kC as the dopant content ratio into said outer crucible, at a rate equal to the rate of decrease of the molten raw material during the pulling.