Polymer deposition updates
The 20nm deposited polymer film permeability is approximately 1e6 barrers, while bulk polyimide permeability is less then 100. So the experimental value is too high.
There are two possibilities to explain it:
First, the pores are partially open and 20 nm thick layer is too thin to cover big pores. I will try AFM this Wednesday to see if the openings can be recognized. Also this is a good possibility to test porosity determination method in work. Results: wafer398 (0.9% before deposition, 0.05% after); wafer213 (1.2%before, less then 0.2% after).
Second, the person that is helping me with deposition said that they have some strange peak shift in measured FTIR spectrum of the polymer we are depositing. This can mean that the deposited polyimide is not dense enough and that’s why the permeability is high. I certainly hope this is the case and we can cover the pores with such thin layer.
The permeability is not the value that should be high in our case, the flux is.
Prof. Anthamatten’ group has problems with their tool very often and they mostly work on figuring out how it works. So I am looking for a more stable source to make the depositions. I will tell more about it tomorrow at the meeting.
What is a “barrer”, I’m not familiar with this unit. Also, TEM would be a better method to measure porosity…