Jie Zou

You didn't mention where the delamination is occuring or details about your
deposition technique. If you break vacuum between the first Cr layer and the Au
deposition, the adhesion could be severely impaired. Gold sticks well to most
metals but not too well to oxides. Normally I would say look at the remaining
layer and tell us the colour, but with 3nm this amount of Cr could be readily
oxidized and be transparent, so I would look at the underside of the peeled
metal and see if it's gold in colour or not.

Even if you don't break vacuum, if there is a combination of long time between
depositions, higher than normal pressure in vacuo or higher than normal
outgassing of your gold target you could cause some semblance of the oxidation
required (or other contamination).
A lot of these same issues exist if the delamination can be shown to be under
the bottom layer of Cr. But in this case the most common candidate is the
lithography process, it may be inadequate and may have to be redeveloped. A thin
organic layer of resist could be left if you have the wrong combination of
either expired resist, improperly stored resist, uncalibrated or inadequate
exposure, unclean or incorrect mask material, expired or improperly stored
developer, chemicals, DI water, etc. or the part is left too long in air or
inadequate storage after developing and before deposition.

As you can see, there are lots of ways to go wrong so you have to make sure all
of the logical candidates are ruled out and if you find any areas for
improvement, then correct them and try again. A good start would be to consult
the resist supplier and they can tell you what needs to be done correctly for
their material to work properly. They are particularly sensitive to this as they
frequently get blamed for a lot of process miscues so they have to have the
answers ready.

Good Luck,
Rick Williston

>
> Jie Zou wrote:
> > Hey everyone,
> >
> > Using a Photoresist S1813 - LOR3A bilayer, I evaporated about 3nm Cr (as
> > adhesion) 120nm gold and 130nm Cr (from bottom to top). Then I lifted it
> > off. So far so good. I need to do a e-beam lithography after that. Thus I
> > spinned PMMA A4 and baked it @ 180 C (30mins in oven). After I lift-off or
> > just washed away the PMMA, I found parts of the metal layer detached and it
> > coiled itself. I ran a test that without the PMMA, I directly baked the
> > sample with the metal layer on the hot-plate, and the detachment happened
> > again. I also tried a sample with only 120nm gold or only Cr layer (and the
> > 3nm Cr adhesion layer) baking under the same condition. It is fine.
> >
> > I think this detachment and coiling is due to the stress difference between
> > the Cr and Au, since I don't have any problem with only gold or only Cr..
> > When I heated my sample, the two metals extended and release its stress in
> > different ways.
> >
> > Sometimes the first evaporation also failed. I think it was also due to the
> > high temperature in the evaporation chamber.
> >
> > Anyone had the same experience and any suggestion? Is there some annealing
> > process I could try?