Weir method for improved single crystal growth in a continuous Czochralski process
View Patent ↗A method is disclosed for continuous CZ crystal growing wherein one or more crystal ingots are pulled into a growth chamber from a crystal/melt interface defined in a crucible containing molten crystalline material that is continuously replenished by crystalline feedstock. The method includes separating the molten crystalline material, controlling the flow of the molten crystalline material and defining an annular space with respect to sidewalls of a heat shield in the chamber.
1. A method for continuous CZ crystal growing wherein one or more crystal ingots are pulled into a growth chamber from a crystal/melt interface defined in a crucible containing molten crystalline material that is continuously replenished by crystalline feedstock, the method comprising:
separating the molten crystalline material into an inner growth region surrounding the crystal/melt interface and an outer region for receiving the crystalline feedstock, wherein separating the molten crystalline material includes providing a weir supported on the base of the crucible;
controlling the flow of the molten crystalline material by increasing path distance and time for crystalline feedstock to travel between the outer region and the inner growth region, wherein controlling the flow of the molten crystalline material includes providing an inner weir within the weir such that the inner weir defines an interconnecting region between the inner growth region and the outer region; and
defining an annular space with respect to sidewalls of a heat shield in the growth chamber such that the annular space substantially restricts entry of dust into the growth region.
2. The method of claim 1 further comprising circulating a purge gas about the growing ingot in the growth chamber such that the purge gas flows over the surface of the melt and exits through the annular space to sweep away silicon oxides from the melt.
3. The method of claim 1 further comprising receiving the crystalline feedstock in the outer region.
4. The method of claim 1 wherein the heat shield is a conical heat shield including a base with downwardly depending walls extending into the growth chamber at an angle with respect to the ingot, the walls tapering to a cone shape having a peripheral end, the peripheral end having a smaller diameter than the base and defining an annular opening dimensioned for receiving the ingot drawn from the melt/crystal interface.
5. The method of claim 1 wherein the weir comprises cylindrical sidewalls extending vertically to a first height closely spaced apart from the heat shield, and the sidewalls having a portion extending further outwardly in substantially parallel concentric alignment with the adjacent heat shield to a second height, wherein the outwardly extending sidewalls define a closely spaced parallel concentric annular gap with respect to the heat shield.
6. The method of claim 5 further comprising directing a flow of purge gas away from the growing ingot and into the annular gap at a velocity sufficient to overcome entry of dust particles into the growth region.
7. The method of claim 6 further comprising dimensioning the annular gap to increase an outflow purge gas pressure to substantially restrict the entry of dust into the growth region.
8. The method of claim 7 including dimensioning the annular gap between 5 mm to 20 mm in length.
9. The method of claim 8 further comprising activating a vacuum to draw a stream of the purge gas through the annular gap from the inner growth region to the outer region.
10. The method of claim 9 further comprising providing a plurality of heaters beneath the crucible.
11. The method of claim 9 further comprising providing a plurality of heaters beneath the crucible in a radial pattern.
12. The method of claim 1 wherein the inner weir has a lower height than the weir.
13. The method of claim 12 wherein the weir and the inner weir each comprise a passageway configured to allow the molten crystalline material to flow therethrough.
14. The method of claim 13 wherein the passageway of the weir and the passageway of the inner weir are offset with respect to one another.
15. The method of claim 12 wherein the heat shield further comprises second downwardly depending walls disposed substantially parallel with the weir.
16. The method of claim 12 wherein the weir includes a devitrification promoter.
17. The method of claim 12 wherein the crucible has a wider aspect ratio than the weir.