Hi Lando

To add a little bit to the discussion, I usually bake my PMMA at 120 for
1-3 hours, but in the past have baked at 180 for 1 hour and have never
observed cracking except for seriously thick resists (2-3um from
memory).  There's a bit of degradation of normal (sub-micron) films
after 12-16 hours at 180C.  Of course, one hotplate's 180C might be
another oven's 200C..?  However, I have not seen any noticeable
difference in performance across those ranges.

But that's a bit of a red herring if I'm following this correctly -
Lando, your resist is not cracked after the plasma descum, and not
cracked when you load into the e-beam evaporator, but cracked when you
unload?  If so, forget resist bake temperature/time.  Cracking says it's
been thoroughly roasted in the evaporator to me, and presumably (well)
above 200C.  Insolubility says the same (but could also be massive UV or
e-beam exposure, though both seem implausible).

I'm finding it hard to resist the temptation to type this in the style
of Hercule Poirot for some reason.  Anyway...

You say "most of my colleagues are using photoresist" - do your
colleagues do the exactly same process apart from a different resist?  I
don't have experience of all the photoresists in the world, but I'd
generally expect PMMA to cope with higher temperatures than the average
photoresist.  Something doesn't quite add up.  Are your colleagues doing
*exactly* the same, or is there some subtle difference you can think of?

As others have said, you can usually lift off a sputtered layer way more
easily than you'd expect, particularly if it's just 20nm thick.  I'd
give that a go, and then we can think some more.

But in summary, my bet (in agreement with some other contributors) is
that it looks like you're cooking your sample during the e-beam
evaporation, even if your temperature monitor tells you otherwise.

Andy

p.s. I'm still etching MnAs badly, but it's improving... ideas still
welcomed!

On 02/06/2010 23:16, D.Grimm@ifw-dresden.de wrote:
> Your process seems ok.
>
> I would bake a little bit lower Temps at 150°C for 5min. Higher
> temperatures usually gives you a measurable roughness in AFM.
> I don't use the stripper step and still obtain low Ohmic contacts. So,
> give it a try.
>
> In your ebeam evaporator it should be absolutely no problem. I deposit
> in a Auto500 as well as Auto300 easily over 100nm.
>
> Try to repeat the process and see what happens (sometimes, it just goes
> wrong on the wrong day)
>
> Best
> Daniel