Substrate bias
We wanted to test the effects of changing the substrate bias during the Si deposition step similar to what Dave Fang had done so many years ago. Attached is a couple of plots showing the effect of varying substrate bias on pore size and porosity. He used 15 nm thick a-Si and an anneal at 1000 C, 100 C/s, 60 s.
The second plot contains effects on both pore size and porosity for 3, 5, 7 and 10 W biases. We used a 25/30/25 stack with a final anneal of 1050 C, 100 C/s for 60 s. (It’s not a perfect comparison, but we can sell the final TEM samples. Also, we are really just trying to see if 5 W is still providing us with the largest pores and highest porosity possible)
It looks like 5 W remains an optimal substrate bias. 3 and 7 W produce very similar pore sizes and porosities, while 10 W decreases the porosity by a couple percent.
In short, we plan to continue using 5 W substrate bias.
