Method for producing semiconductor wafers composed of silicon with reduced pinholes
View Patent ↗Silicon semiconductor wafers are produced by pulling a single crystal at a seed crystal from a melt heated in a crucible; supplying heat to the center of the crucible bottom with a heating power which, in the course of the growth of a cylindrical section of the single crystal, is increased at least once to not less than 2 kW and is then decreased again; and slicing semiconductor wafers from the pulled single crystal.
1. A method for producing silicon semiconductor wafers, comprising
pulling a single crystal at a seed crystal from a melt having a free surface heated in a crucible by means of a side heater embodied as a resistance heater;
during the pulling of a cylindrical section of the single crystal, supplying heat to the center of the crucible bottom by means of a heating device adjacent to the crucible bottom which can be lifted and lowered with the crucible, wherein the heat is supplied with a heating power which is increased at least once to not less than 2 kW and in a manner following a ramp within a time period which is ≧90 min and <900 min such that the highest temperature in the crucible bottom migrates from a position at the edge of the crucible bottom as far as the center of the crucible bottom, and the heating power is then decreased again; and
slicing silicon semiconductor wafers from the pulled single crystal.
2. The method of claim 1 , further comprising exposing the melt to the influence of a horizontal magnetic field or a CUSP magnetic field with a magnetic flux density of not less than 50 mT at an edge of the crucible bottom.
3. The method of claim 1 , further comprising exposing the melt to the influence of a CUSP magnetic field whose neutral surface intersects a central longitudinal axis of the single crystal at a distance from the plane of the free surface of the melt of not less than 90 mm.
4. The method of claim 2 , further comprising exposing the melt to the influence of a CUSP magnetic field whose neutral surface intersects a central longitudinal axis of the single crystal at a distance from the plane of the free surface of the melt of not less than 90 mm.
5. The method of claim 1 , further comprising rotating the crucible at a speed of not more than 2 revolutions per minute and rotating the single crystal at a speed of not less than 6 revolutions per minute.
6. The method of claim 2 , further comprising rotating the crucible at a speed of not more than 2 revolutions per minute and rotating the single crystal at a speed of not less than 6 revolutions per minute.
7. The method of claim 3 , further comprising rotating the crucible at a speed of not more than 2 revolutions per minute and rotating the single crystal at a speed of not less than 6 revolutions per minute.
8. The method of claim 1 , further comprising conducting inert gas to the free surface of the melt at a volumetric flow rate of 600-12,000 l/h at a pressure of 1100-8000Pa.
9. The method of claim 1 , wherein the ramp comprises a portion with a substantially linearly increasing heating power and a portion with a decreasing heating power.
10. The method of claim 1 , wherein the ramp comprises a portion with a substantially linearly increasing heating power, a portion with a substantially constant heating power, and a portion with a decreasing heating power.
11. The method of claim 1 , wherein the heating power is increased and decreased a plurality of times during growth of the cylindrical section of the single crystal.
12. The method of claim 11 , wherein the heating power is increased and decreased from 2 to 10 times during growth of the cylindrical section of the single crystal.
13. The method of claim 1 , wherein the heating power is increased to from not less than 2 kW to 5 kW.