1. A string for use in a string ribbon crystal comprising a crystal material, the crystal material being one of silicon, silicon-germanium, gallium arsenide and indium phosphide, the string comprising:
a substrate;
a refractory layer supported on the substrate; and
an externally exposed layer having a contact angle with the crystal material of between about 15 and 120 degrees, the externally exposed layer being radially outward of the refractory layer.
2. The string as defined by claim 1 further comprising a handling layer radially outward of the refractory layer, the handling layer applying a generally radially inward force to the refractory layer.
3. The string as defined by claim 2 wherein the handling layer includes the externally exposed layer.
4. The string as defined by claim 2 wherein the externally exposed layer is radially outward of the handling layer.
5. The string as defined by claim 1 wherein the externally exposed layer comprises at least one of pyrolytic carbon, oxide, and nitride.
6. The string as defined by claim 1 wherein the externally exposed layer has a contact angle with the crystal material of greater than about 25 degrees.
7. The string as defined by claim 1 wherein the substrate comprises carbon, the refractory layer comprising silicon carbide.
8. The string as defined by claim 1 wherein the crystal material has a material coefficient of thermal expansion, the substrate, refractory layer, and exposed layer having a combined coefficient of thermal expansion that is substantially matched to the material coefficient of thermal expansion.
9. The string as defined by claim 1 wherein the exposed layer is thinner than the refractory layer.
10. The string as defined by claim 1 wherein the string has a coefficient of thermal expansion that is generally matched to the coefficient of thermal expansion of polysilicon.
11. A string for use in a string ribbon crystal, the string comprising:
a base portion comprising a refractory material; and
an externally exposed layer radially outward of the refractory material, the base portion having a coefficient of thermal expansion that is generally matched with the coefficient of thermal expansion for silicon, the externally exposed layer having a contact angle with silicon of between about 15 and 120 degrees.
12. The string as defined by claim 11 wherein the base portion comprises a carbon-based substrate supporting a silicon carbide refractory layer.
13. The string as defined by claim 11 wherein the externally exposed layer comprises a handling layer.
14. The string as defined by claim 11 wherein the externally exposed layer comprises a least one of carbon, carbide, oxide, and nitride.
15. A ribbon crystal comprising:
a string having a string coefficient of thermal expansion and an outer surface; and
a body comprising a body material having a body coefficient of thermal expansion that is generally matched to the string coefficient of thermal expansion,
the string outer surface being partially exposed.
16. The ribbon crystal as defined by claim 15 wherein the exposed portion of the string is free of body material.
17. The ribbon crystal as defined by claim 15 wherein the string outer surface has a contact angle with the body material of between about 15 and 120 degrees.
18. The ribbon crystal as defined by claim 15 wherein the body material comprises polysilicon.
19. The ribbon crystal as defined by claim 15 wherein the string comprises a refractory material supported on and substantially entirely covering a substrate.
20. The ribbon crystal as defined by claim 15 wherein the string comprises a substrate supporting a refractory layer, the string further comprising a handling layer radially outward of the refractory layer, the handling layer applying a generally radially inward force to the refractory layer.
21. The ribbon crystal as defined by claim 20 wherein the handling layer includes the string outer surface.
22. The ribbon crystal as defined by claim 20 wherein the string outer surface is radially outward of the handling layer.
23. The ribbon crystal as defined by claim 15 wherein the string outer surface comprises at least one of pyrolytic carbon, oxide, and nitride.
24. The ribbon crystal as defined by claim 15 wherein the string outer surface has a contact angle with the body material of greater than about 25 degrees.
25. A method of forming a string for use with a ribbon crystal, the method comprising:
forming a refractory layer on a substrate; and
applying a reduced wetting material radially outward of the refractory layer, the reduced wetting material having a contact angle with silicon of between about 15 and 120 degrees.
26. The method as defined by claim 25 further comprising adding a handling layer radially outward of the refractory layer.
27. The method as defined by claim 26 wherein the handling layer comprises the reduced wetting material.
28. The method as defined by claim 26 wherein the reduced wetting material is radially outward of the handling layer.
29. The method as defined by claim 25 wherein forming comprises extruding refractory material on the substrate.
30. The method as defined by claim 25 wherein the refractory layer, substrate, and reduced wetting material have a combined coefficient of thermal expansion that substantially matches polysilicon.
31. A method of forming a ribbon crystal, the method comprising:
providing molten material having a material coefficient of thermal expansion;
providing a string having an outer surface with a contact angle with the molten material of between about 15 and 120 degrees, the string also having a string coefficient of thermal expansion that is substantially matched to the material coefficient of thermal expansion; and
passing the string through molten material to form a sheet.
32. The method as defined by claim 31 wherein the string comprises a refractory layer supported on a substrate.
33. The method as defined by claim 32 wherein the string comprises a handling layer radially outward of the refractory layer.
34. The method as defined by claim 33 wherein the outer surface of the string comprises the handling layer.
35. The method as defined by claim 33 wherein the string comprises a reduced wetting layer radially outward of the handling layer, the reduced wetting layer comprising the outer surface of the string.
36. The method as defined by claim 31 wherein the material comprises a silicon based material.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method, comprising:
introducing a cleaning gas to a processing chamber;
applying an electrical bias to a gas distribution showerhead that is coupled to the processing chamber while a substrate support disposed opposite the showerhead is electrically floating or grounded, the showerhead having a showerhead body comprising stainless steel having a roughened surface with a ceramic coating thereover facing the substrate support, the ceramic coating deposited on the roughened surface while controlling deposition pressure to form a desired roughness, the showerhead body having a plurality of first gas passages and a plurality of second gas passages extending therethrough, the electrical bias igniting the cleaning gas into a plasma containing cleaning gas radicals and ions;
reacting the cleaning gas radicals with deposits formed on the ceramic coating by bombarding the ceramic coating with the cleaning gas radicals to form a byproduct and expose the ceramic coating, the exposed ceramic coating having an emissivity within 2 percent of the emissivity of the ceramic coating prior to formation of the deposits thereon; and
exhausting the byproduct from the processing chamber.
2. The method of claim 1, wherein the cleaning gas comprises a chlorine containing gas.
3. The method of claim 2, wherein the chlorine containing gas is selected from the group consisting of Cl2, ICl, HCl, BCl3, CCl4, CH3Cl and combinations thereof.
4. The method of claim 3, wherein the electrical bias is a negative electrical bias.
5. The method of claim 4, wherein the pressure within the chamber during the cleaning is less than about 300 mTorr.
6. The method of claim 5, wherein the electrical bias is between about 2.23 Win2 to about 16 Win2.
7. A method, comprising:
performing a deposition process on one or more substrates in a processing chamber while changing the emissivity of a gas distribution showerhead from a first emissivity level to a second emissivity level;
removing the substrates from the processing chamber;
introducing a cleaning gas to a processing chamber;
applying an electrical bias to the gas distribution showerhead that is coupled to the processing chamber while a substrate support disposed opposite the showerhead is electrically floated or grounded, the showerhead having a showerhead body comprising stainless steel having a roughened surface and a ceramic coating thereover facing the substrate support, the ceramic coating deposited on the roughened surface while controlling deposition pressure to form a desired roughness, the showerhead body having a plurality of first gas passages and a plurality of second gas passages extending therethrough, the electrical bias igniting the cleaning gas into a plasma containing cleaning gas radicals and ions;
reacting the cleaning gas radicals with deposits formed on the ceramic coating by bombarding the ceramic coating with the cleaning gas radicals to form a byproduct and expose the ceramic coating, the exposed ceramic coating having a third emissivity level that is within 2 percent of the first emissivity level; and
exhausting the byproduct from the processing chamber.
8. The method of claim 7, wherein the cleaning gas comprises a chlorine containing gas.
9. The method of claim 8, wherein the chlorine containing gas is selected from the group consisting of Cl2, ICl, HCl, BCl3, CCl4, CH3Cl and combinations thereof.
10. The method of claim 9, wherein the electrical bias is a negative electrical bias.
11. The method of claim 10, wherein the deposition process is a MOCVD process.
12. The method of claim 11, further comprising performing another deposition process on one or more additional substrates after exhausting the byproduct.
13. The method of claim 1, wherein the cleaning occurs in-situ.