Seed crystals for pulling single crystal silicon
View Patent ↗The present invention provides for a process for preparing a single crystal silicon ingot by the Czochralski method. The process comprises selecting a seed crystal for Czochralski growth wherein the seed crystal comprises vacancy dominated single crystal silicon.
1. A process for preparing a single crystal silicon ingot, grown in accordance with the Czochralski method, the process comprising:
heating polycrystalline silicon in a crucible to form a silicon melt;
selecting a seed crystal for contacting the crystal melt, said seed crystal having crystal lattice vacancies as the predominant intrinsic point defect therein;
contacting said seed crystal to the silicon melt until the seed crystal begins to melt, forming dislocations therein;
withdrawing the seed crystal from the melt to grow a neck portion of the ingot, wherein during the withdrawal dislocations are eliminated from the neck;
growing an outwardly flaring seed-cone adjacent the neck portion of the ingot; and,
growing a main body adjacent the outwardly flaring seed-cone, the body having a nominal diameter of at least about 150 mm.
2. A process as set forth in claim 1 wherein said seed crystal comprises vacancy dominated silicon substantially free of agglomerated defects.
3. A process as set forth in claim 1 wherein said seed crystal comprises vacancy dominated silicon comprising voids or D-defects.
4. A process as set forth in claim 1 wherein the body has a nominal diameter of at least about 200 mm.
5. A process as set forth in claim 1 wherein the body has a nominal diameter of at least about 300 mm.
6. A process as set forth in claim 1 wherein the body has a weight of at least about 100 kilograms.
7. A process as set forth in claim 1 wherein the body has a weight of at least about 200 kilograms.
8. A process as set forth in claim 1 wherein dislocations are eliminated in the neck within an axial length of less than about 175 mm.
9. A process as set forth in claim 1 wherein dislocations are eliminated in the neck within an axial length of less than about 100 mm.
10. A process as set forth in claim 1 wherein the neck has a nominal diameter of at least about 5 mm.
11. A process as set forth in claim 1 wherein the neck has a nominal diameter of from about 6 mm to about 8 mm.
12. A process as set forth in claim 1 wherein the neck has a nominal diameter of at least about 10 mm.
13. A process as set forth in claim 1 wherein said seed crystal has a critical resolved shear stress of at least about 950 psi.
14. A process as set forth in claim 1 wherein said seed crystal has a critical resolved shear stress of at least about 1000 psi.