I am curious if the surface roughness of a target is considered an important factor for sputter deposition, because if my target is rough I think there is a higher chance of contaminants becoming trapped in small pores, for instance organic contaminants like carbon.
If the surface roughness of the target is minimal and very smooth there is less areas/pores where these could become trapped.
For example, I had an EDX analysis done on a LiNBO3 off cut which I clean in acetone, it had a polished smooth side, and an unpolished rough side.
The smooth side came back without any other additional elements listed, but the rough side showed traces of C, K, Cl, in some of the points that were taken.
And I am curious for sputtering, if my target surface, for a new target, is not a polished surface, and I see other elements from the EDX analysis for this target, I expect I run the risk of deposited films of compositions other than what my target is supposed to be.
I understand pre-sputtering is used to clean a target surface before deposition, and some people suggest plasma cleaning in O2 for some time also to minimise contaminants.
But do people also polish their targets surface so that it is smooth to minimise pores where contaminants could become trapped?
If you prepare the target yourself, it should imply a high temperature during preparation depending on the elements you use to obtain the target. So this automatically "cleans" the target from any organic elements like carbon, water, ethanol and so on and it should make it durable after the thermal treatment (it should't have visible pores). However, by pre-sputtering you actually clean the target from impurities and if you have any doubts take more time for pre-sputtering. I think that polishing the target will cause more impurities..
Best of luck!
Normally people don't bother the samples bother sputtering. Acetone or IPA cleaning is good enough. The K and Cl signals might be the noise or from some unknown sources. As long as the signals from your target elements are clear, you could simply ignore other peaks in EDX spectra. EDX always picks up some "strange" elements, whose spectra might overlap with those of your signals.
Surface roughness should not affect your EDX, unless the surface RMS is much smaller than the thickness of sputtered Au (or other metal). I guess the Au layer is only tens of nm in your case?
I agree with the Dr. m. Toma, because presputtering time will decide the concentration of contamination on the target surface. The self made targets are rougher than the paid targets.
Thank you for your replies everyone.
I do not prepare the targets myself, an outside manufacturer did using a vacuum melting process. I am working with an FeGa target, galfenol with a 81:19 ratio %at.
When I got a target, I sent it for analysis (EDX) to confirm the composition and it came back with the correct ratio of Fe:Ga but with a C content of ~30 %at.
This may just be a surface contamination, as I have been informed that C can come for a variety of different sources. And a decent pre-sputter before deposition may resolve it for my films.
I have a Ti target which I looked at also and it came back as 100 %at. Ti, I compared the roughness Ra of the two targets with the FeGa being 1.6um and the Ti as 0.3 um. I looked at this as it was suggested that FeGa target appeared rougher with more pores for contaminates to be trapped, and I was curious.
I am not sure what is considered normal or regular for sputtering targets, their composition and surface contaminants. I had thought that if I got a target produced to be Fe 81 : Ga 19 that is what I would see with minimal traces of other elements, but seeing something in the region of ~Fe 60 : Ga 10 : C 30 gave me some pause, as a C content can change the properties of the films I am interested in.
Smooth target Surfaces are important to avoid arcing. Arcing is a main cause of pinholes in thin films. If you start with a new, rough target, you will need much longer sputter-in time (before you can actually use the target for depositons) before you get a stable plasma (read: arc-free). For very rough targets, the plasma never really gets stable and you get thin films with a lot of pinholes.
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