Method and apparatus for pulling a single crystal by the FZ method

A method for pulling a single crystal by the FZ method, in which a polycrystal having a conical section at its lower end is melted by means of an electromagnetic melting apparatus and then recrystallized, comprising:

• a) in a first phase (P1) melting a lower end of the polycrystal by means of the melting apparatus;
• b) in a second phase (P2) attaching a monocrystalline seed to the lower end of the polycrystal and melting the monocrystalline seed beginning from an upper end of the seed;
• c) in a third phase (P3) forming a thin neck section between a lower section of the seed and the polycrystal, the diameter (dD) of the thin neck section being smaller than that (dI) of the seed;
• and
• d) in a fourth phase (P4) forming a conical section of the single crystal between the thin neck section and the polycrystal, and
• e) before the fourth phase (P4) is reached, determining a switchover position (h′) of the polycrystal, the switchover position being a position, at which a rate with which the polycrystal is moved relative to the melting apparatus is to be reduced in amount, the switchover position (h′) determined by either
• e)i) measuring a distance (d) of a location (PS) characteristic of the polycrystal and situated at the lower end of a conical section of the polycrystal relative to a fixed reference point (PB), the switchover position (h′) determined from the distance (d), or
• e)ii) determining an intermediate position (h) of the polycrystal, at which a location (PS) characteristic of the polycrystal and situated at the lower end of a conical section of the polycrystal reaches or exceeds a predetermined distance (d) relative to a fixed reference point (PB) during movement of the polycrystal, the switchover position (h′) determined from the intermediate position (h);
• and
• f) in the fourth phase (P4) reducing the rate at which the polycrystal is moved relative to the melting apparatus, when the switchover position (h′) is reached.