Dry etch method for texturing silicon and device

1. A method for texturing silicon, comprising:

loading a silicon wafer into a vacuum chamber;

heating the silicon wafer;

thermal cracking a gas to generate cracked sulfur species, the thermal cracking including passing the gas through a first zone at a first temperature and subsequently through a second zone at a second temperature, the first and second temperatures being different from each other; and

exposing the silicon wafer to the cracked sulfur species for a time duration in accordance with a texture characteristic needed for a surface of the silicon wafer.

2. The method as recited in claim 1 , wherein heating includes heating the silicon wafer to a temperature greater than 350 degrees C.

3. The method as recited in claim 1 , wherein the first temperature is approximately between 100-200 degrees C. and the second temperature is greater than about 400 degrees C.

4. The method as recited in claim 1 , wherein exposing the silicon wafer to the cracked sulfur species includes exposing a (100) silicon wafer to the cracked sulfur species to etch the wafer to expose (111) silicon surfaces.

5. The method as recited in claim 1 , wherein the texture characteristic includes pyramidal recesses formed in the wafer having a depth of between about 10 nm and about 300 nm.

6. The method as recited in claim 1 , further comprising exhausting volatile Si—S specifies generated by etching the silicon wafer.

7. The method as recited in claim 1 , wherein the cracked sulfur species include one or more of S n where n=8, 7, 6, 5, 3, 2.

8. The method as recited in claim 1 , further comprising forming a junction layer, a first electrode layer and a second electrode layer on the surface of the silicon wafer to form a photovoltaic device.

9. A method for texturing silicon, comprising:

cleaning a silicon wafer to remove oxide;

loading the silicon wafer into a vacuum chamber;

degassing the wafer to expose a clean Si surface;

heating the silicon wafer in the vacuum chamber to a temperature greater than about 350 degrees C.;

flowing thermally cracked sulfur species into the vacuum chamber by passing the gas through a first zone at a first temperature and subsequently through a second zone at a second temperature, the first and second temperatures being different from each other;

anisotropically etching the silicon wafer with the cracked sulfur species for a time duration in accordance with a texture characteristic needed for a surface of the silicon wafer; and

exhausting volatile Si—S specifies generated by etching the silicon wafer.

10. The method as recited in claim 9 , wherein the first temperature is approximately between 100-200 degrees C. and the second temperature is greater than about 400 degrees C.

11. The method as recited in claim 9 , wherein anisotropically etching the silicon wafer includes exposing a (100) silicon wafer to the cracked sulfur species to etch the wafer to expose (111) silicon surfaces.

12. The method as recited in claim 9 , wherein the texture characteristic includes pyramidal recesses formed in the wafer having a depth of between about 10 nm and about 300 nm.

13. The method as recited in claim 9 , wherein the cracked sulfur species include one or more of S n where n=8, 7, 6, 5, 3, 2.

14. The method as recited in claim 9 , further comprising forming a first electrode layer, a junction layer and a second electrode layer on the surface of the silicon wafer to form a photovoltaic device.

15. The method as recited in claim 1 , wherein the first zone is a bulk zone and the second zone is a cracking zone.

16. The method as recited in claim 9 , wherein the first zone is a bulk zone and the second zone is a cracking zone.