Hi, Shah,

I have had many people recommend me to do lift-off by "overnight soak
in acetone" however, in my experience it results in very poor
lift-off.  I always do liftoff in an ultrasonic bath at moderate
power, and achieve complete liftoff in a matter of minutes, with no
damage to the pattern (if film adhesion is good).  I've done 0.5
micron features without any noticeable damage due to sonication.

Also, about the film thickness/resist thickness ratio - I routinely do
lift-off with a 0.5 um gold film over a 2 um-thick S1818, without any
problems (without using PMGI or any other undercut layer) so an long
as the resist is 2-3 times thicker than the film, you should be OK.
In this case the film is also sputtered at an angle (with rotation),
but that does not cause problems.

One factor which I may affect liftoff is the quality of resist edges.
I find that if the mask makes good contact to the resist - so that the
shadow edges are sharper - the liftoff is more reliable.  Therefore I
recommend removing edge beads even when doing low resolution
lithography.

I have never worked with SPR 220-3, I have done liftoff with PMMA,
SU-8 2000.5 and S18xx series resists:

For Shipley 18xx series it is best to use resist stripper 1165,
acetone does not do very well.

For PMMA/MMA acetone works well.

For SU-8 2000.5, even without any underlayer  (e.g. Omnicoat) Remover
PG works very well, as long as it is heated to above 60C.

Hope this helps,

-Mikas.

On Tue, Jul 14, 2009 at 11:06 AM, Shah, Forum N wrote:
> Hello everyone,
>
> I am trying to do the lift-off process for the first time but am not able to
achieve it. Its
> been over 24 hrs that the wafer is immersed in acetone but the gold film is
not leaving
> the Si substrate.
>
> Details of the process are:
> I have spun SPR 220-3 on a SI wafer near 3 micron of a thickness. After
exposing and
> developing it, I sputtered 100 angstrom gold film.
>
> Please guide me on how to do a lift off process. And if acetone is sufficient
for doing
> lift-off or do I need any other solvent or chemical?
>
> Thanks
> Forum