Thank you to all who have replied so far to my questions

I shall state a few other relevant points:

1. The Al is e-beam evaporated at a base pressure of ~ 1x10-7 mbar.
Sputtering deposition tools are also available.
2. Deposition rate is 0.3 nm/s
3. The bi-layer resist thickness is 1.3 um while the metal thickness is
1um. Now I know one should always have a resist thickness at least two
time greater than the metal thickness however I can add the caveat that
one of the groups here at Glasgow Uni have successfully lifted off 1.2
microns Au using the same resist thickness (1.3 microns) - and they say
their process is very repeatable! The problem my colleague has is he is
already using the thickest e-beam resist he has available. He could
probably sneak another 200 nm from spinning the resist at lower rpm
which may of course aid lift-off.
4. I told him to try sonication which he has done for around 10 minutes.
No joy.
5. All processing was completed within 2 days (i.e. substrate clean,
resist spinning, bake, exposure, development, ashing, HF dip, Al
evaporation)
6. He has not attempted to deposit thin Al

I had a look at his sample for him and the metal in large areas has
lifted off however in the fine feature areas (~1 um feature size) the
metal has not even begun to lift-off.

His next step will be to deposit 500 nm instead of 1um. I hope lift-off
is more successful this time.

Thanks for all your helpful comments,

James

Edward Sebesta wrote:
> Are you using evaporation for the metal deposition? What type of metal
> deposition equipment are you using. If not using evaporation for metal
> deposition set parameters for poor step coverage which would be to have
> the substrate cold for starters. However, given you are attempting lift
> off I am assuming the substrate is unheated already.
>
> Also, what is the height of the bi-layer relative to the metal
> thickness?
>
> Edward H. Sebesta
> Independent Process Engineer

Dr. James Paul Grant
Postdoctoral Research Associate
Microsystems Technology Group
76 Oakfield Avenue Room 3
University of Glasgow
Glasgow
Scotland
G12 8LS
Telephone: +44(0)141 330 3374