[labnetwork] ZnS sputtering
Pramod C Karulkar
pkarulkar9 at gmail.com
Fri May 10 18:36:07 EDT 2013
Depositing ZnS and CdS (as you mentioned in the earlier e-mail) are
both difficult tasks particularly for the equipment person. There are
several issues (1) health hazard, (2) deterioration of the vacuum system
including the pumping station (2) equipment and process area
contamination, (3) cross contamination for all other depositions done in
the same system, and (4) process and quality control for ZnS and CdS
and, more importantly, for other materials deposited in the same
system. The contamination issue itself is quite serious.
These materials will contaminate the chamber permanently particularly
with all the non-stoichiometric material that will be produced during
the deposition. It will reach every surface including locations that
are not in the line of sight from the source. Removing the material
completely from the chamber is virtually impossible. Then you end up
having perpetual cross contamination, out-gassing, and corrosion
problems. You shouldn't use the vacuum system for these materials if it
is critical to other processes involving device quality materials (pure
metals, silicides, nitrides, photoconductors, superconductors, optical
films etc). The contamination will remain in the system for ever and
you will see traces of it in subsequent runs. Materials analysis
techniques may not show it but it will manifest as bad films (e.g.
quenched superconducting transition temperature or deterioration of
similar other properties that are affected by extremely low level trace
contamination).
Sometimes you can risk making a run for an extremely important project
if the user shares in the risk. "Somehow managing one or two runs"
will depend on the system design and how you maintain it. The runs can
be scheduled just before you take apart the system for a major wet
chemical clean up and rebuilding with new vacuum components. I would
install deposition shields all over the chamber and also try to use a
chimney (metallic tube or duct) if possible to restrict the material in
the target-to-substrate region only. I have done this a number of times
but it is extremely disruptive and time consuming. It creates a
precedence too.
See Zn vapor pressure on chart 14 of this presentation:
http://www.cockcroft.ac.uk/education/PG_courses_2006-7/RR_vacuum_2007/Reid_Lecture_5.ppt
There are some references to sputtering similar solar cell materials
that would allow you to contact the authors directly or send samples out
for deposition.
http://www.hindawi.com/journals/ijp/2011/801292/
Propose alternate techniques. Here is info on SILAS. This would
involve safety precautions/systems for use of exotic vapors/gases.
http://www.sciencedirect.com/science/article/pii/S0169433297002481
Good luck....
Pramod C Karulkar Ph. D.
Home 2*5*3* 3*0*3 0*4*1*8
6024 33rd Street Ct NW
Gig Harbor WA 98335
5/9/2013 10:53 PM, raghavan wrote:
>
> Dear all
>
> We have a request from a tool user to sputter ZnS in our sputter tool.
> Our sputter tool is a share tool used by many users. I would like to
> know from experienced users if ZnS sputtering needs any extra
> precautions to be taken? Does it contaminate the chamber?
>
> Thank you
>
> Best wishes
>
> Raghavan
>
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>
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>
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