We are trying to etch unpolished silicon surface (back side) using SF6 plasma by Reactive Ion Etching (RIE) technique. we observed that the etching rate falls one order in magnitude on unpolished to polished surface. I would like to know why the etching rate differ on unpolished side of silicon. Is it because of roughness ? Are there some other issues ?
Yes, I think the roughness is the main reason. You have a higher surface area in this case (the rough sample), as a consequence, a higher number of radical (F*) can interact with surface atoms at the same time.
The difference due to higher surface area and it will need more time to be etched.
yes, I agree with your points. As the roughness increases, the surface area increases. But, F* radicals will concentrate more on the hills rather than on valleys. It means the hills are etched quite fast than valleys. so, after some time, the roughness should get decreased and therefore, the etching rate should get enhanced. Isn't it?
I etched rough silicon for a couple of hours and there is no enhancement in etching rate.
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