Greatings everyone, we've been troubled by the phenomena stated in the topic. Our goal is to co-deposited CZTSe thin film, by the means
of thermal PVD, each element has thier own crucible, heating coil and temperature monitor. After the deposition rate of zinc stabilizes,
we open the shutter shielding the substrate, deposition starts; then, deposition rate of zinc decrease rapidly, often from 20 A/sec down to
5~6 A/sec. However, this only happens to zinc, other elements have no such problem. We'd appreciate a clear answer, advises also
greatly welcomed. Thank you!
*parameters: multi-source chamber, background vacuum 2×10^-6 torr, zinc temperature 170C, stabilizing time after target temperature 30min.
---------------2015/11/21 reply-----------------
Thank you so much for your replies!
to Stephan Harrer:
We check our crucibles along with ingredients they contained every time we take them down from the chamber, everything looks right, no
contamination; we've not yet measure film thickness, for the reason that we don't thick measuring it under unstable deposition rate is meaningful.
to Joel De Jesus:
This instability of deposition rate occurred to zinc exclusively, other elements all have stable deposition rate, and film thickness are as
calculated. We've not remove the substrate shutter yet, not before we figured out what really cause it.
However, I think there might be a possibility that the monitor was overwhelmed by overflowing particles. We'll look into that.
to Ata H Khalid:
We didn't apply boat or quartz tube design in our experiments, but like Mr.Jesus stated, there is a chance that thickness monitor reporting
incorrectly can be the reason. Thank you!
Have you had a look on your crucibal? I had a similar problem with some organics condesing on the top of the crucibal instead of our sample. Have you checked if the thinckness of your layer corresponds to the depostition rate?
It should also happen with the other elements. How do you measure your growth rates? What is your substrate temperature?
Seems you have achieved full coverage of zinc of your substrate surface. Excess zinc just bounce off, not sticking to the surface. If you wish to keep accumulating zinc, then lower the substrate temperature.
This seems to me very strange because I have evaporated Zinc for p-type contact to HBTs and we always had trouble to control the Zinc evaporation because as soon as it starts evaporating, it gets increased rapidly and if the user was not careful we would get 1000nm instead of 100nm. So on this background I would suggest following investigations to find out what really going on:
1. Have you measured the thickness of Zinc alone and compared it with the value you get on the thickness monitor?
2. Is there a possibility that after you have opened the shutter the thickness monitor becomes overwhelmed with the rapid increase of the rate and thickness monitor reporting incorrectly and in fact the real rate is not gone down instead it has gone out of control leading to no Zinc left in the boat.
3. What type of the boat you are using for evaporating Zinc, may be all Zinc creep under the boat and hence no evaporation take place towards the sample.
I think if you can investigate these areas you would find your answer. In my opinion, in your case all of the zinc evaporated before even you open the shutter that is why rate goes down.
I agree with Ata. You have a cloud of Zinc underneath the shutter that would keep on re evaporating before you open the shutter along with a thermal buildup that then the plume ( density) changes once the shutter is opened and then you go from 2nm to .5nm/sec.
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