Method for pulling a single crystal by the FZ method comprising dynamically adapting the power of a melting apparatus based on a position of lower and upper phase boundaries
A single crystal is pulled by the FZ method, in which in a first phase, a lower end of the polycrystal is melted by the melting apparatus, in a second phase, a monocrystalline seed is attached to the lower end of the polycrystal, and in a third phase, between a lower section of the seed and the polycrystal, a thin neck section is formed whose diameter is smaller than that of the seed, where the power of the melting apparatus before the third phase is dynamically adapted in dependence on a position of a lower phase boundary (P U ) between liquid material and solid material on the part of the seed, and where the power of the melting apparatus during the third phase is dynamically adapted in dependence on the position of an upper phase boundary (P O ) between liquid material and solid material on the part of the polycrystal plant.
1. A method for pulling a single crystal by the FZ method in which a polycrystal is melted by means of an electromagnetic melting apparatus and then recrystallized, comprising:
in a first phase (P 1 ), melting a lower end of the polycrystal by means of the melting apparatus,
in a second phase (P 2 ), attaching a monocrystalline seed to a lower end of the polycrystal, and
in a third phase (P 3 ), forming a thin neck section between a lower section of the seed and the polycrystal, where the diameter (d D ) of the thin neck section is smaller than the diameter (d 1 ) of the seed,
dynamically adapting a power of the melting apparatus before the third phase (P 3 ) at least temporarily in dependence on a position of a lower phase boundary (P U ) between liquid material and solid material on the seed,
dynamically adapting the power of the melting apparatus during the third phase (P 3 ) at least temporarily in dependence on a position of an upper phase boundary (P O ) between liquid material and solid material on the part of the polycrystal, and
directly performing a change in the dependence of the power of the melting apparatus from the position of the lower phase boundary (P U ) to dependence on the position of the upper phase boundary (P O ).
2. The method of claim 1 , where the change in the dependence on the position of the lower phase boundary (P U ) to the dependence on the position of the upper phase boundary (P O ) takes place before an increase in a rate at which the seed and/or the polycrystal are moved in the vertical direction.
3. The method of claim 1 , further comprising in a fourth phase (P 4 ), forming a conical section between the thin neck section and the polycrystal, and dynamically adapting the power of the melting apparatus during the fourth phase (P 4 ) at least temporarily in dependence on a characteristic variable from which it is possible to deduce an angle (φ) of inclination of the conical section.
4. The method of claim 2 , further comprising in a fourth phase (P 4 ), forming a conical section between the thin neck section and the polycrystal, and dynamically adapting the power of the melting apparatus during the fourth phase (P 4 ) at least temporarily in dependence on a characteristic variable from which it is possible to deduce an angle (φ) of inclination of the conical section.
5. The method of claim 3 , where the characteristic variable used is one or more of the angle of inclination of the conical section of crystallized material, an angle of inclination of the conical section at a triple point between solid material, liquid material and surroundings, a change in a diameter of the conical section, or the diameter of the conical section at the lower phase boundary.
6. The method of claim 3 , further comprising, during the adaptation of the power of the melting apparatus, performing a change in the dependence on the position of the upper phase boundary (P O ) directly to the dependence on the characteristic variable, or temporarily adapting the power of the melting apparatus at the same time in dependence on the position of the upper phase boundary (P O ) and in dependence on the characteristic variable.
7. The method of claim 3 , where the change in the dependence on the position of the upper phase boundary (P O ) to the dependence on the characteristic variable takes place as soon as a recognition of the position of the upper phase boundary (P O ) is subsequently possible only with less than a predetermined accuracy.
8. The method of claim 3 , further comprising determining the characteristic variable for the angle (φ) of inclination of the conical section by using a camera which is disposed below the melting apparatus.
9. The method of claim 1 , further comprising taking into account the positions of the lower phase boundary (P U ) and/or of the upper phase boundary (P O ) each as the distance (h U , h O ) of the respective phase boundary to a fixed reference point (P B ) on the melting apparatus.
10. The method of claim 1 , further comprising taking into account the position of the lower phase boundary (P U ) by using a camera which is disposed below the melting apparatus.
11. The method of claim 1 , further comprising taking into account the position of the upper phase boundary (P O ) by using a camera which is disposed above the melting apparatus.