Hi,

Hard to discuss your question without knowing more details:

* Does your substrate have a blanket SiO2 surface, or are you trying for bare
Si?  I'm assuming SiO2 since you're only doing a piranha clean and not a full
RCA clean (or even an HF dip).

* How thick is your SU-8 coating?

* Which SU-8 series are you using (original, 2000, or 3000)?

* Are you allowing any delay between your O2 plasma treatment (which will
function as a dehydration bake), spinning the adhesion promoter, and spinning
the SU-8?  Keep in mind that any delay may allow rehydration of the wafer
surface, negating the effect of the HMDS.

* What is the ambient humidity in your facility, and is it well controlled?

I've seen some suggestions that the softbake time/ramp/temperature can also
affect adhesion, primarily by the mechanism of differential thermal stress as
compared with Si/SiO2, but without more knowledge, I'd tend to look more closely
at the surface priming process first.

In general, SU-8 has poor adhesion to SiO2.  HMDS priming (such as MCC primer)
can improve that, but I've read lots of mixed results with it.  After talking to
MicroChem's SU-8 support experts, I switched to MicroChem's "OmniCoat", which is
a combination adhesion and lift-off layer.  It requires some extra processing
steps (bake and develop) and requires you to account for its thickness in your
final structure, but has the advantage of allowing one to lift off even hard-
baked SU-8 in solvent.

There are also some tips on SU-8 adhesion on this web page (including notes on
using an HMDS primer):
        http://memscyclopedia.org/su8.html

Good luck,
Mike

On Apr 4, 2011, at 23:10, 첸로 wrote:

> I am using su-8 in photolithography technique. I'm having difficulty when
handling it.
>
> The adhesion strength of su-8 and silicon is not very even.  I clean the
silicon wafer in piranha solution, give it a oxygen plasma treatment and use the
Mcc primer (microchem).
> After 1.5 minutes developing some patterns will peel off.   M mask dimension
is only 10microns.
>
> Has anybody encountered this problem?
>
> Is the adhesion strength decided by the softbake time or post bake time or
both?
> Should I increase the baking time for both?