[mems-talk] Damaging of boats during nickel evaporation

[Kagan Topalli]

Dear all,

I am trying to coat nickel in a thermal evaporator. I have a problem 
related with the (Alumina coated) Tungsten boats where the nickel 
pellets are placed in. I have observed that nickel pellets melted as I 
increased the current to ~250 Amperes. After 60-70 seconds (while the 
deposition was continuing without any problem), suddenly the boat has 
been damaged (There occurred a hole at the mid of the boat). I have 
tried the experiment with reduced number of pellets. But the result is 
same. Please note that the boats can withstand even a current of 350 
Amperes during gold deposition. Is there anyone that can identify the 
problem? Is there any solution for that?

Thanks in advance,

Regards,

-- 
Kagan TOPALLI, Ph. D.
Senior Research Engineer
MEMS-VLSI and EMT Group
Middle East Technical University
Dept. of Electrical & Electronics Eng.
TR-06531 Ankara Turkey
Phone: +90 312 210 44 09 or +90 312 210 23 40
Fax: +90 312 210 23 04
http://www.mems.eee.metu.edu.tr/~topalli/
--