Membranes deposited with 'dirty' targets
The AJA sputtering system has 2 oxide targets and 1 silicon target that are focused with stainless steel chimneys. During our process, films inevitably deposit on the chimney and shutters and after a while start cracking causing flakes of material to fall on the targets.
I have noticed that our thinner amorphous films (5 nm, 7 nm) have different morphologies depending on if it was deposited on a week that parts were recently cleaned or if it was deposited with a dirty target (> 2 wks w/o cleaning).
Below are images of films that was deposited with a dirty target.
TEM 054 – 5 nm amorphous
TEM 082 – 7 nm amorphous
Here’s a film that was deposited on a week following a clean.
TEM 061 – 5 nm amorphous
The ‘dirty’ films have tears while the clean film looks continuous. The 7 nm “amorphous” film also has what appears to be copper nanoparticles (dark, spherical objects). The week that TEM 082 was deposited, I discovered that one of the oxide targets was worn out to the copper backing plate. It is very possible that some metal was incorporated into the silicon layer, as well.
The target has been cleaned, but all depositions performed on the week of 1/21 are now suspect. Here’s a film that was made post-cleaning:
It doesn’t seem like there’s any copper, but we’ll have to confirm after all the wafers have been etched and imaged.
The SepCon thickness series was done the week of 1/21. Is that study lost?
Those wafers have not been etched yet. We may have to repeat the study due to the possibility of a contamination… With the new sandblaster arriving next week, we’ll institute a bi-weekly cleaning of the system now that it is getting regular usage.