Surface processing method of silicon substrate for solar cell, and manufacturing method of solar cell

1. A surface processing method of a crystalline silicon substrate for a solar cell, the method comprising:

a crystalline silicon substrate providing step for providing a substrate which comprises crystalline silicon;

a first surface processing step for forming a plurality of first protrusions on surfaces of the substrate by etching the substrate by using an aqueous solution;

a second surface processing step for forming a plurality of second protrusions smaller than the first protrusions by adhering etching residues onto an upper surface, a light receiving surface among the surfaces of the substrate, by using a first etching gas; and

a residue removing step for removing the etching residues adhered onto the upper surface of the substrate having undergone the second surface processing step,

wherein in an assumption that an area of a surface in a completely flat state where an anti-reflection film is to be formed, among the surfaces of the substrate having undergone the first surface processing step, is an ideal surface area, a ratio between a substantial surface area etched in the first surface processing step and the ideal surface area is in the range of 1.2˜3.2.

2. The method of claim 1 , wherein the aqueous solution used in the first surface processing step includes HF and HNO3.

3. The method of claim 1 , further comprising a substrate damage removing step for removing damages formed on the surfaces of the crystalline silicon substrate sliced from a crystalline silicon ingot, by using an acid aqueous solution or alkali aqueous solution, before the first surface processing step.

4. The method of claim 1 , wherein the crystalline silicon substrate is a monocrystalline silicon substrate or a multicrystalline silicon substrate.

5. The method of claim 1 , wherein in the residue removing step, the etching residues are removed by dipping the substrate in a wet station containing residue removing liquid, or by transferring the substrate by roller.

6. The method of claim 5 , wherein the residue removing liquid is hydrofluoric acid aqueous solution.

7. The method of claim 5 , wherein the residue removing liquid includes water or hydrofluoric acid aqueous solution, and ultrasonic waves are applied to the residue removing liquid when performing the residue removing step.

8. The method of claim 1 , wherein in the residue removing step, the etching residues remaining on an upper surface of the substrate are removed by plasmarizing a second etching gas.

9. The method of claim 8 , wherein the second etching gas includes fluorine or chlorine.

10. The method of claim 8 , wherein the second etching gas includes one of HCl , ClF3, NF, CF4, C3F8, NF3, C2F6, F2, CHF3, SF6 and Cl2.

11. The method of claim 8 , wherein the second etching gas has a lower reactivity with the substrate than the first etching gas.

12. The method of claim 8 , wherein the first etching gas is gas including elements which belong to Group VII, and the second etching gas is gas including at least one of elements rather than the elements which belong to Group VII.

13. The method of claim 8 , wherein the second etching gas includes at least one of inert gas and oxygen.

14. The method of claim 5 , further comprising a hydrofluoric acid dipping step of dipping the substrate in hydrofluoric acid aqueous solution, after the residue removing step.

15. A method for manufacturing a solar cell including the surface processing method of a substrate for a solar cell according to claim 1 .

16. The method of 15 , further comprising a hydrofluoric acid dipping step of dipping the substrate in hydrofluoric acid aqueous solution, after the residue removing step.

17. A method for manufacturing a solar cell including the surface processing method of a substrate for a solar cell according claim 4 .

18. A method for manufacturing a solar cell including the surface processing method of a substrate for a solar cell according claim 1 .