Methods for producing a single crystal silicon ingot using boric acid as a dopant
Methods for producing a single crystal silicon ingot are disclosed. The ingot is doped with boron using solid-phase boric acid as the source of boron. Boric acid may be used to counter-dope the ingot during ingot growth. Ingot puller apparatus that use a solid-phase dopant are also disclosed. The solid-phase dopant may be disposed in a receptacle that is moved closer to the surface of the melt or a vaporization unit may be used to produce a dopant gas from the solid-phase dopant.
1. A method for producing a single crystal silicon ingot from a silicon melt held within a crucible in an ingot puller apparatus, the ingot puller apparatus having an outer housing, the method comprising:
adding polycrystalline silicon to the crucible, the crucible being disposed within an ingot puller inner chamber;
heating the polycrystalline silicon to cause the silicon melt to form in the crucible;
pulling the single crystal silicon ingot from the silicon melt;
providing a source of solid-phase boric acid;
producing a boron-containing gas from the solid-phase boric acid, wherein:
the boron-containing gas is produced from the solid-phase boric acid while the solid-phase boric acid is disposed exterior to the ingot puller outer housing; or
the boron-containing gas is produced from the solid-phase boric acid while the solid-phase boric acid is supported by a dopant receptacle disposed within a feed tube, wherein the source of solid-phase boric acid is added to the dopant receptacle when the dopant receptacle is in a loading position in which the dopant receptacle is disposed exterior to the ingot puller outer housing, the dopant receptacle being moved relative to the feed tube from the loading position to a feed position in which the dopant receptacle is disposed within the ingot puller inner chamber, the boron-containing gas being produced from the solid-phase boric acid while the dopant receptacle is in the feed position; and
contacting the boron-containing gas with a surface of the melt to cause boron to enter the melt as a dopant while pulling the single crystal silicon ingot from the melt.
2. The method as set forth in claim 1 comprising adding an n-type dopant to the crucible prior to pulling the single crystal silicon ingot from the melt.
3. The method as set forth in claim 2 wherein the n-type dopant is phosphorous.
4. The method as set forth in claim 1 wherein the boron-containing gas is produced by:
liquefying the solid-phase boric acid to produce a boric acid liquid; and
evaporating the boric acid liquid to produce the boron-containing gas.
5. The method as set forth in claim 1 wherein the boron-containing gas is produced from the solid-phase boric acid while the solid-phase boric acid is supported by the dopant receptacle disposed within the feed tube, wherein the source of solid-phase boric acid is added to the dopant receptacle when the dopant receptacle is in the loading position in which the dopant receptacle is disposed exterior to the ingot puller outer housing, the dopant receptacle being moved relative to the feed tube from the loading position to the feed position in which the dopant receptacle is disposed within the ingot puller inner chamber, the boron-containing gas being produced from the solid-phase boric acid while the dopant receptacle is in the feed position.
6. The method as set forth in claim 5 wherein the dopant receptacle is a capsule.
7. The method as set forth in claim 5 wherein the feed tube is an outer feed tube that is at least partially disposed exterior to the ingot puller outer housing, the outer feed tube defining an outer feed tube chamber and having a distal end, a proximal end and an outer feed tube axis that extends through the distal end and the proximal end, the ingot puller apparatus comprising an elongate member that is moveable within the outer feed tube chamber along the outer feed tube axis, the method further comprising:
adding the source of solid-phase boric acid to the dopant receptacle, the dopant receptacle being coupled to the elongate member; and
moving the elongate member from the loading position to the feed position, the boron-containing gas discharging from the dopant receptacle and contacting the surface of the melt to cause boron to enter the melt as the dopant while pulling the single crystal silicon ingot from the melt.
8. The method as set forth in claim 7 wherein the dopant receptacle is a capsule that is separable from the elongate member.
9. The method as set forth in claim 8 wherein the capsule comprises:
an outer capsule housing; and
a weir disposed within the outer capsule housing, the weir forming a channel for the boron-containing gas to pass through, the weir having an upper end and a lower end, the upper end and lower end being open, an annular chamber disposed between the weir and the ingot puller outer housing for holding the solid-phase boric acid.
10. The method as set forth in claim 7 wherein the ingot puller apparatus comprises a tube disposed below the dopant receptacle to direct the boron-containing gas to the surface of the melt.
11. The method as set forth in claim 7 wherein the elongate member is a tube.
12. The method as set forth in claim 7 wherein the ingot puller apparatus further comprises a valve for sealing the ingot puller inner chamber when the elongate member is withdrawn from the ingot puller inner chamber.
13. The method as set forth in claim 7 comprising operating a translation device to move the dopant receptacle between the loading position and the feed position.
14. The method as set forth in claim 13 wherein the translation device is a magnetically coupled through-wall translation unit.
15. The method as set forth in claim 13 wherein the translation device comprises bellows.
16. The method as set forth in claim 1 wherein the solid-phase boric acid is disposed exterior to the ingot puller outer housing of the ingot puller apparatus.
17. The method as set forth in claim 16 wherein the solid-phase boric acid is within a vaporization unit, the vaporization unit comprising a chamber for holding solid-phase boric acid.
18. The method as set forth in claim 16 wherein the ingot puller apparatus comprises a dopant conduit having a gas inlet disposed exterior to the ingot puller inner chamber and a gas outlet disposed in the ingot puller inner chamber, and a dopant vaporization unit disposed exterior to the ingot puller inner chamber, the method further comprising:
adding the source of solid-phase boric acid to a dopant chamber of the dopant vaporization unit;
operating a heating device of the dopant vaporization unit to heat the solid-phase boric acid and produce the boron-containing gas; and
passing the boron-containing gas through an outlet of the dopant vaporization unit and into the dopant conduit.
19. The method as set forth in claim 18 comprising introducing a process gas through an inlet that is in fluid communication with the dopant chamber, the process gas passing through the dopant chamber and through the outlet.