Weir design providing optimal purge gas flow, melt control, and temperature stabilization for improved single crystal growth in a continuous Czochralski process
View Patent ↗A weir is extended vertically to define an optimal annular gap between the top of the weir and the underside of a super-adjacent heat shield. The annular gap provides a high velocity stream of argon gas to be directed from the growth region to the melt region to substantially eliminate the transport of airborne particles from the melt region to the growth region. The tall weir may be configured as a modular, reusable weir extension supportably engaged with an outer (and/or inner) weir.
1. An apparatus for growing ingots by the Czochralski method, the ingots being drawn from a melt/crystal interface in a quantity of molten silicon replenished by crystalline feedstock, the apparatus comprising:
a growth chamber defining an enclosure configured to circulate a purge gas about the growing ingot;
a crucible provided in the growth chamber configured to hold the molten silicon,
a heat shield comprising a conical body having a base and downwardly depending sidewalls extending into the growth chamber and tapering conically to define an annular opening configured to receive the ingot drawn from the melt/crystal interface;
a weir supported in the crucible, and configured to separate the molten silicon into an inner growth region surrounding the crystal/melt interface from an outer region configured to receive the crystalline feedstock, the weir comprising sidewalls extending vertically and terminating in a peripheral edge adjacent to the sidewalls of the heat shield to define an annular space with respect to the sidewalls of the heat shield, wherein the annular space is sized to restrict entry of dust into the growth region; and
an inner weir disposed within the weir, the inner weir defining a middle interconnecting region between the inner growth region and the outer region.
2. An apparatus as in claim 1 , further comprising a vacuum pump configured to direct the 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 zone.
3. An apparatus for growing of ingots by the Czochralski method, the ingots being drawn from a melt/crystal interface in a quantity of molten silicon replenished by crystalline feedstock, the apparatus comprising:
a growth chamber defining an enclosure for circulating a purge gas about the growing ingot;
a crucible provided in the growth chamber configured to hold the molten silicon;
a heat shield comprising a conical body having a base and downwardly depending sidewalls extending into the growth chamber and tapering conically to define an annular opening configured to receive the ingot drawn from the melt/crystal interface; and
a modular weir comprising a first cylindrical portion supported in the crucible configured to separate the molten silicon into an inner growth region surrounding the crystal/melt interface from an outer region configured to receive the crystalline feedstock, and a second coextensive cylindrical portion comprising sidewalls configured to be engageably mounted on the first portion above the molten silicon, the sidewalls of the second coextensive cylindrical portion extending vertically and terminating in a peripheral edge adjacent to the heat shield to define an annular space with respect to the adjacent heat shield, wherein the annular space is sized to restrict entry of dust particles into the growth region.
4. A Czochralski (CZ) grower for preventing transport of dust and particles into a crystal growth region and a growing crystal, the CZ grower comprising:
a crucible containing a melt portion defining a central growth region from which a crystal ingot is pulled;
a heat shield provided above the crucible having sidewalls depending downward to define an annular opening substantially coextensive with the central growth region, the annular opening configured to receive the ingot pulled from the melt portion;
a base weir provided in the crucible and extending above a height of a melt in the melt portion, the base weir configured to provide a path length for molten silicon feedstock to travel between an outer melting region and the central growth region for melting of solid particles of feedstock,
a modular weir provided on the base weir comprising sidewalls extending vertically to define an annular passageway with adjacent downwardly depending sidewalls of the heat shield, wherein the annular passageway is configured to substantially block transport of dust particles to the crystal growth region.
5. A CZ grower according to claim 4 wherein the modular weir further comprises a base supporting the sidewalls, the base having an engagement portion configured for removable locking engagement with the base weir.
6. An apparatus according to claim 1 wherein the annular gap is dimensioned to increase an outflow purge gas pressure to substantially restrict the entry of dust into the growth region.
7. An apparatus according to claim 1 further comprising a vacuum configured to draw a stream of the purge gas through the annular gap from the inner growth region to the outer region.
8. An apparatus according to claim 1 wherein the annular space is approximately 5 mm to 20 mm in length.
9. An apparatus according to claim 1 , further comprising a plurality of heaters disposed beneath the crucible.
10. An apparatus according to claim 9 wherein the plurality of heaters are disposed in a radial pattern.
11. An apparatus according to claim 1 , further comprising the inner weir having a lower height than the weir.
12. An apparatus according to claim 11 wherein the weir and the inner weir each comprise a passageway configured to allow the molten silicon to flow therethrough.
13. An apparatus according to claim 12 wherein the passageway of the weir and the passageway of the inner weir are offset with respect to one another.
14. An apparatus according to claim 1 wherein the heat shield further comprises second downwardly depending walls disposed substantially parallel with the weir.
15. An apparatus according to claim 1 wherein the weir comprises a devitrification promoter.
16. An apparatus according to claim 1 wherein the crucible has a wider aspect ratio than the weir.
17. An apparatus according to claim 16 wherein a diameter of the weir is approximately 50% to 75% of a diameter of the crucible.
18. An apparatus according to claim 1 wherein the sidewalls have a portion extending further outwardly and having a length of approximately 10 mm to 100 mm.
19. An apparatus according to claim 13 wherein the passageway of the weir and the passageway of the inner weir are offset 180°.