Controlling a Melt-Solid Interface Shape of a Growing Silicon Crystal Using an Unbalanced Magnetic Field and Iso-Rotation

• US 20090320743A1
• Filed: 06/29/2009
• Published: 12/31/2009
• Est. Priority Date: 06/30/2008
• Status: Active Grant

• Current Assignee: GlobalWafers Co., Ltd. (Sino-American Silicon Products Incorporated)
• Original Assignee: SunEdison, Inc.
• Inventors: Holzer, Joseph C., Kulkarni, Milind S., Korb, Harold W., Schrenker, Richard G., Sreedharamurthy, Hariprasad
• Granted Patent: US 8,398,765 B2
• Time in Patent Office: Days
• US Class Current: 117/32
• CPC Class Codes: C30B 15/305 Stirring of the melt
• CPC Class Codes: C30B 29/06 Silicon
• CPC Class Codes: C30B 30/04 using magnetic fields
• CPC Class Codes: Y10T 117/1032 Seed pulling

Abstract

A system for growing silicon crystals that facilitates controlling a shape of a melt-solid interface is described. The crystal growing system includes a heated crucible including a semiconductor melt from which a monocrystalline ingot is grown according to a Czochralski process. The ingot is grown on a seed crystal pulled from the melt. The method includes applying an unbalanced cusped magnetic field to the melt, and rotating the ingot and the crucible in the same direction while the ingot is being pulled from the melt.

Claims

1. A method of controlling crystal growth in a crystal growing system, the crystal growing system having a heated crucible including a semiconductor melt from which a monocrystalline ingot is grown according to a Czochralski process, the ingot being grown on a seed crystal pulled from the melt, said method comprising:

applying an unbalanced cusped magnetic field to the melt; and

rotating the ingot and the crucible in the same direction while the ingot is being pulled from the melt.

2. A method in accordance with claim 1, wherein applying an unbalanced cusped magnetic field comprises applying a first magnetic field above a melt-solid interface and a second magnetic field below the melt-solid interface, wherein a field strength of the first magnetic field is weaker than a field strength of the second magnetic field.

3. A method in accordance with claim 2, wherein a ratio of the field strength of the first magnetic field to the field strength of the second magnetic field is between 0.10 and 0.90.

4. A method in accordance with claim 1, wherein applying an unbalanced cusped magnetic field comprises applying a first magnetic field above a melt-solid interface and a second magnetic field below a melt-solid interface such that an axial component of the applied magnetic field is greater than a radial component of the applied magnetic field at the melt-solid interface.

5. A method in accordance with claim 4, wherein applying the first magnetic field above the melt-solid interface and the second magnetic field below the melt-solid interface comprises applying a constant first magnetic field and a constant second magnetic field to facilitate maintaining the axial component of the applied magnetic field at the melt-solid interface.

6. A method in accordance with claim 4, wherein applying the first magnetic field above the melt-solid interface and the second magnetic field below the melt-solid interface comprises varying the strength of at least one of the first magnetic field and the second magnetic field to facilitate maintaining a predetermined strength of the axial component of the applied magnetic field at the melt-solid interface.

7. A method in accordance with claim 1, wherein controlling crystal growth in a crystal growing system comprises controlling a shape of the melt-solid interface of the ingot.

8. A method in accordance with claim 7, wherein controlling a shape of the melt-solid interface comprises facilitating production of an ingot having a substantially concave melt-solid interface shape relative to the ingot.

9. A system for growing silicon crystals that facilitates controlling a shape of a melt-solid interface, said crystal growing system having a heated crucible including a semiconductor melt from which a monocrystalline ingot is grown according to a Czochralski process, said ingot being grown on a seed crystal pulled from the melt, said melt and said ingot forming said melt-solid interface therebetween, said system comprising:

a first set of coils and a second set of coils positioned adjacent to an exterior of the crucible for generating an unbalanced cusped magnetic field; and

a crucible drive unit and a crystal drive unit configured to rotate the crucible and the crystal in the same direction.

10. A system in accordance with claim 9, wherein said first set of coils are positioned above the melt-solid interface and said second set of coils are positioned below the melt-solid interface, wherein said first set of coils are configured to generate a first magnetic field and said second set of coils are configured to generate a second magnetic field.

11. A system in accordance with claim 10, wherein said first set of coils and said second set of coils are configured to generate a magnetic field having an axial component that is greater than a radial component at the melt-solid interface.

12. A system in accordance with claim 10, wherein a field strength of the first magnetic field is weaker than a field strength of the second magnetic field.

13. A system in accordance with claim 10, wherein a ratio of the field strength of the first magnetic field to the field strength of the second magnetic field is between 0.10 and 0.90.

14. A system in accordance with claim 10, wherein a ratio of the field strength of the first magnetic field to the field strength of the second magnetic field is between 0.40 and 0.70.

15. A system in accordance with claim 9, wherein said first set of coils is powered by a first level of current and said second set of coils is powered by a second level of current.

16. A system in accordance with claim 15, wherein said first level of current is lower than said second level of current.

17. A system in accordance with claim 9, wherein said unbalanced cusped magnetic field generated by said first and second set of coils, in combination with said rotation in the same direction of the crucible and the crystal by said crucible drive unit and said crystal drive unit, respectively, facilitates controlling a shape of the melt-solid interface of the ingot.

18. A system in accordance with claim 17, wherein said shape of the melt-solid interface of the ingot comprises a substantially concave melt-solid interface shape relative to the ingot.

19. A system in accordance with claim 9, wherein said unbalanced cusped magnetic field generated by said first and second set of coils, in combination with said rotation in the same direction of the crucible and the crystal by said crucible drive unit and said crystal drive unit, respectively, facilitates producing an ingot having a desired process window and defect transition.

20. A system in accordance with claim 9, wherein said unbalanced cusped magnetic field generated by said first and second set of coils, in combination with said rotation in the same direction of the crucible and the crystal by said crucible drive unit and said crystal drive unit, respectively, facilitates strengthening a Karman cell formed during the crystal growth.