Methods for reducing the erosion rate of a crucible during crystal pulling
View Patent ↗Production of silicon ingots in a crystal puller that involve reduction of the erosion rate at the crucible contact point are disclosed.
1. A method for reducing the erosion rate of a crucible during preparation of a silicon ingot, the ingot being formed by pulling the silicon ingot from a melt of silicon within the crucible, the crucible being positioned within a housing having an atmosphere therein, the melt and atmosphere forming a melt-gas interface, the method comprising:
introducing a first dopant into the silicon melt to achieve a desired silicon ingot resistivity, the first dopant being selected from the group consisting of boron and phosphorous;
introducing a second dopant selected from the group consisting of indium, gallium, thallium, arsenic, antimony and combinations thereof into the silicon melt to alter the oxygen evaporation profile of the melt, the second dopant being different from the first dopant; and
withdrawing a silicon ingot from the doped melt within the crucible, the melt, crucible and atmosphere forming an interface at which the crucible is eroded, the atmosphere being at a pressure of at least about 5 kPa while withdrawing the silicon ingot, the crucible being made of quartz with quartz contacting the silicon melt, the second dopant reducing erosion at the interface between the melt, crucible and atmosphere.
2. The method as set forth in claim 1 comprising replenishing the silicon melt by adding silicon to the crucible.
3. The method as set forth in claim 2 wherein the second dopant is added intermittently or continuously to the melt to replenish the second dopant in the melt.
4. The method as set forth in claim 1 wherein the atmosphere is at a pressure of at least about 7 kPa while withdrawing the silicon ingot.
5. The method as set forth in claim 1 further comprising:
establishing a baseline pressure for withdrawing the silicon ingot from the melt without second dopant being introduced into the melt;
commencing addition of second dopant into the melt to alter the oxygen evaporation profile of the melt; and
increasing the pressure of the atmosphere above the baseline pressure to offset an increase in oxygen evaporation from the melt caused by addition of second dopant into the melt.
6. The method as set forth in claim 5 wherein increasing the pressure of the atmosphere above the baseline pressure reduces the rate of erosion at an interface between the crucible, the melt and the atmosphere.
7. The method as set forth in claim 1 wherein second dopant is added to the melt separately from the addition of silicon.
8. The method as set forth in claim 1 wherein second dopant is added with silicon.
9. The method as set forth in claim 1 wherein the second dopant is added at a rate to achieve a concentration of 1×10 15 atoms per cm 3 to about 1×10 20 atoms/cm 3 in the melt.
10. The method as set forth in claim 1 wherein the first and/or second dopant is added at a rate to produce a silicon ingot with a resistivity of about 0.01 ohm-cm to about 6 ohm-cm.
11. The method as set forth in claim 1 wherein the atmosphere is at the recited pressure during at least about 80% of the crystal growth process.
12. The method as set forth in claim 1 wherein the atmosphere is at a pressure of at least about 13 kPa while withdrawing the silicon ingot.
13. The method as set forth in claim 1 wherein the first and/or second dopant is added at a rate to produce a silicon ingot with a resistivity of about 0.5 ohm-cm to about 6 ohm-cm.
14. The method as set forth in claim 1 wherein the quartz crucible contains at least about 90 wt % silica.
15. The method as set forth in claim 1 wherein the quartz crucible contains at least about 99 wt % silica.
16. The method as set forth in claim 1 wherein the atmosphere is at the recited pressure during at least about 95% of the crystal growth process.
17. The method as set forth in claim 1 wherein the atmosphere is at the recited pressure during the entire crystal growth process.
18. The method as set forth in claim 1 wherein the first dopant is boron to achieve P-type growth.
19. The method as set forth in claim 18 wherein the second dopant is selected from the group consisting of indium, gallium and thallium.
20. The method as set forth in claim 1 wherein the first dopant is phosphorous to achieve N-type growth.
21. The method as set forth in claim 20 wherein the second dopant is selected from arsenic and antimony.
22. The method as set forth in claim 1 wherein the atmosphere is controlled to be the same pressure while withdrawing the silicon ingot.