[labnetwork] Blistering of metal film stack on PMMA

[Mark K Mondol]

Mary, Norman and Nathan all have good points. Here are my two paise's 
worth of advice:

It would be nice to have the substrate farther away from the source. It 
would also be nice to have a second shutter (close to the substrate and 
not blocking the deposition sensor) so the substrate is not getting 
heated during the warming of the source. You probably don't have the 
ability to change those things though.

Norman is correct that a magnet can deflect stray electrons and might be 
the solution for you.

In the NanoStructures Lab we don't use crucibles except for Cu and SiOx, 
thereby eliminating Carbon contamination.

Anecdotally, it seems that some evaporators generate enough Xrays to 
expose PMMA and some don't, well the Xrays are probably generated but 
aren't emitted in a direction that exposes PMMA. Any wavelength shorter 
than 220nm will expose PMMA, we use an old UV aligner to flood expose 
PMMA for a variety of processes.

I guess I would try to see if it is heat that is the problem by 
evaporating 10nm of Au to find out if it works with shorter 
evaporations. If heating is the problem see the two solutions at the 
top, or try to install a cooler behind your substrate. You might also 
find an evaporation recipe that uses a shorter or less powerful soak 
step to reduce heat. Possibly a different position on your holder might 
help, but anything that is not directly above the source will make for 
more difficult liftoff.

Regards,

Mark K Mondol



-- 
Mark K Mondol
Assistant Director NanoStructures Laboratory
And
Facility Manager
Scanning Electron Beam Lithography Facility
Bldg 36  Room 229
www.rle.mit.edu/sebl
mondol at mit.edu
office - 617-253-9617
cell - 617-224-8756