Hi,

We use a thin layer of aluminium 7 nm on all our ebeam runs (Sapphirre
substrate, Niobium photolith, PMMA thicknesses ranging from 60 nm to 1
micron mostly in P(MMA/MMA) / PMMA double layers ). After exposure, they
are removed with a dilute solution of NaOH (1%, 15s). So far we have not
had any issues, single pixels lines go down to 8 nm on a 30 kV system,
with spacing of 20-30 nm... The only thing to be careful with is the
concentration of the NaOH, a too large concentration will lead to large
tension in the film, possibly leading to "delamination" (which took all
the photolith gold with it on a recent test chip).

Best,

Gabriel

Quantum Device Lab
Solid State Laboratory
ETH Zurich

Am 8/12/2011 11:54 PM, schrieb Jaroslaw Syzdek:
> Hi everybody,
>
> I want to use PMMA (with underlayer of copolymer) for E-beam writing over an
> insulating substrate (most probably glass). In order to make it possible I'm
> going to deposit copper on top of PMMA. After exposure I'm going to get rid
> of copper prior to development, by immersing the thing in FeCl3 solution in
> water. It dissolves copper really quickly. However I'm wondering if that
> will affect PMMA (both exposed and non-exposed). I'm not concerned with Fe
> or Cl - I'll wash them away with water.
>
> If anybody knows something about PMMA-FeCl3 interactions, I'll appreciate an
> answer.
>
> Jarek