My query is whether the helium plasma can etch the surface of deposited film and damage the film more in comparison to hydrogen plasma?
The gap between my plasma zone and substrate at present is ~50mm. If the previous damage is imminent, can increasing the gap between plasma zone and substrate is a good solution?
Kindly suggest.
With plasmas, you can have two etching processes:
1) A physical sputtering process that is just caused by highly accelerated ions of the chamber gas impinging on the substrate. This process works both with He and H, but usually you don't want this to happen in PECVD since it can generate defects so most chamber setups will be optimized to avoid it.
2) A chemical etching process in which the reaction gas, either as an activated molecule or in atomized form, forms volatile species with the substrate that desorb, e.g. SiH4 if you etch Si. This process can behave geometrically different since surfaces with many dangling are more affected. This effect should not make significant contributions in a He plasma since there are no stable neutral He compounds.
In conclusion, I dare to say that using He for the etching process would not so much be harmful with respect to defect generation but primarily be brutally ineffective in most PECVD setups.
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