Methods for reducing deposits in ingot puller exhaust systems
View Patent ↗Production of silicon ingots in a crystal puller that involve reduction in the formation of silicon deposits on the puller exhaust system are disclosed.
1. A method for reducing the rate at which deposits form within the exhaust of an ingot puller, the ingot puller comprising a crucible having a silicon melt therein, a housing disposed around the crucible, the housing having an atmosphere therein, 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, phosphorous, arsenic and antimony;
introducing a second dopant selected from the group consisting of indium and thallium into the silicon melt to reduce silicon oxide formation, the second dopant being different from the first dopant; and
withdrawing a silicon ingot from the doped melt within the crucible, 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 such that oxygen dissolves from the quartz and enters the silicon melt, wherein, when the second dopant is indium, indium reacts with oxygen dissolved from the quartz crucible to form one or more indium oxides to reduce silica oxide formation and, when the second dopant is thallium, thallium reacts with oxygen dissolved from the quartz crucible to form one or more thallium oxides to reduce silica oxide formation.
2. The method as set forth in claim 1 further comprising:
introducing a process gas into the housing; and
withdrawing a spent process gas from the housing, the spent process gas passing through an exhaust system of the ingot puller during withdrawal.
3. The method as set forth in claim 1 wherein the second dopant reacts with oxygen to form an oxide 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 reduce silicon oxide formation; 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 1 wherein silicon is not added to the melt after the melt is formed.
7. The method as set forth in claim 1 further comprising replenishing the silicon melt by adding silicon to the crucible.
8. 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.
9. 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.
10. 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.
11. 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.
12. The method as set forth in claim 1 wherein the quartz crucible contains at least about 90 wt % silica.
13. The method as set forth in claim 1 wherein the quartz crucible contains at least about 99 wt % silica.
14. 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.
15. The method as set forth in claim 1 wherein the atmosphere is at the recited pressure during the entire crystal growth process.
16. The method as set forth in claim 1 wherein the first dopant is boron to achieve P-type growth.
17. The method as set forth in claim 1 wherein the atmosphere is controlled to be the same pressure while withdrawing the silicon ingot.
18. The method as set forth in claim 1 wherein, when the second dopant is indium, the indium oxide is In 2 O 3 and, when the second dopant is thallium, the thallium oxides are selected from the group consisting of Tl 2 O, Tl 2 O 3 , TlO 2 and Tl 4 O 3 .
19. The method as set forth in claim 1 wherein the second dopant is indium.
20. The method as set forth in claim 1 wherein the second dopant is thallium.