[labnetwork] Discolouration on evaporated Mg

[Pramod C Karulkar]

I hope you have eliminated the evaporation source and process themselves 
as the sources of problem.  Mg deposition is very tricky because it is 
very reactive.

The particles are probably contaminants that are present on the 
substrate/wafer before evaporation.   Two possibilities for the rings:  
The rings are present around the particle before deposition and are from 
the same source of contamination.  They manifest vividly after 
deposition.   Other origin for the rings is out-gassing or decomposition 
of the particle.  Shadowing by the particle can also cause some rings.  
The substrate (elemental such as silicon or oxide such as SiO2 or Al2O3) 
can play a role in this too.  Varying thermal treatment without breaking 
the vacuum may help to understand this.  Look up literature on reactions 
with substrate and condensation phenomena in ultra-thin films in JVST 
and APL. Substate processes can modify film structure (Very interesting 
effect is described here: 
http://apl.aip.org/resource/1/applab/v93/i21/p213304_s1?view=fulltext&display=print&bypassSSO=1 
) But the "rings"  strongly suggest contamination.

There is one way to be perfect and infinite ways to be imperfect. 
Contamination is an imperfection in the process.  It is not something 
that happens universally.   Hence it is difficult to explain what is 
happening based on your brief comment.   Someone has to audit your 
complete process (not just the evaporation) thoroughly.  You will also 
have to do some experimentation and analytical work to resolve this.

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

On 7/16/2013 3:33 PM, Iyer, Nandini wrote:
> Hi,
>
> Recently, we have noticed some unusual spots on our evaporated Mg film 
> (~10um).  It consists of a contaminating particle and a ring shaped 
> discolouration around the particle. We suspect that the contaminant 
> may be Mg particles deposited during evaporation but we are not 
> certain about this. Does anyone have any theories about what could be 
> happening?
>
> Thank you.
>
> Nandini
>
>
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-- 


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

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