[labnetwork] Ag-Bi-Zn films in high vacuum

[Aaron Hryciw]

Dear colleagues,

I'm hoping you can offer some advice on the wisdom of allowing substrates
coated with a Zn-containing thin film into some of our open-access
facility's shared high vacuum systems.

The material in question is a Ag-Bi-Zn alloy (98.9 at% Ag, 0.1 at% Bi, 1.0
at% Zn), which one of our user groups wants to deposit as a cathode layer
for an OLED process.  A 50 nm thick film of this material is being
deposited elsewhere (not in our shared equipment).  However, they would
like to continue processing this film in our equipment, which includes two
vacuum deposition steps (thermal evaporation for organics, then sputtering
for the anode layer, patterned via lift-off).  Both of these deposition
processes nominally have the substrate at room temperature, although there
is no active substrate cooling to offset heating from the process itself.
The maximum exposed area of the Ag-Bi-Zn would be ~20 cm² (i.e., equivalent
of a quarter of a 4" wafer).

I understand that due to its high vapour pressure, having metallic Zn is
generally a bad idea in shared systems if you want Zn-free films
thereafter, but I wanted to discuss how likely we'd be to see Zn
contamination in either the organics evaporator or the sputtering tool,
given the relatively low (?) total volume of exposed Zn that would be
involved.  I am mostly concerned about the organics evaporator, as the
Ag-Bi-Zn film would be exposed to high vacuum; in the sputtering tool, the
Ag-Bi-Zn would already be coated by several layers of organics.

Could contamination risk be mitigated by copious foiling/shielding of the
chamber?  Does anyone have any recommendations for a (non-destructive) test
that could be done to determine the extent of Zn contamination during the
organics evaporation step?  Any advice would be greatly appreciated.  Many
thanks.

Cheers,

 – Aaron




Aaron Hryciw, PhD, PEng

Fabrication Group Manager

University of Alberta - nanoFAB

W1-060 ECERF Building

9107 - 116 Street

Edmonton, Alberta

Canada T6G 2V4 Ph: 780-940-7938
www.nanofab.ualberta.ca
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