Initial silicon film density affects porosity
For the last three weeks, we have increased the substrate bias power from 25 W to 32 W (for both oxide and a-Si) to adress some film quality issues. I have found that it is “harder” to open pores in a film deposited at higher bias. Below are micrographs showing the difference in porosity for two 15 nm pnc-Si samples annealed at 1000 C @ 100 C/s w/o susceptor.
This confirms the point raised about initial a-Si density affecting pore formation. It seems that a denser film yields a less porous film. Can we make the argument that higher density creates more of an energy barrier during the void formation?
I think this experiment should be put at the top of the queue, maybe next week. Substrate bias has been shown to be one of the most sensitive knobs that we have to turn, and it’s also not monotonic. I suspect there is a clear optimal point for pore formation that could give us an important piece of information. Maybe in the experiment we could run oxide at 25W, and Si over 0, 10, 20, 30, and 40W? Although, this requires some ellipsometry to establish a dep rate for each bias, so it may not be possible next week….