[labnetwork] ZnS sputtering

[Pramod C Karulkar]

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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