Are you sure that that your sample is properly developed and there is
no more photoresist left on the bottom of the windows?

Try some descumming in oxigen plasma.

Make sure that your metal isn't thicker than 1/3 of your photoresist film.

I hope this will help.

Cristian
On 7/8/05, ahajjiah  wrote:
>
> I am currently working on depositing (300A)Ti/1000A(Al) metals on GaN. I am
> using S1813 as my photoresist. i am spinning the photoresist at 3000rpm for
> 30s. My deposition rate on the e-beam is 7-10 A/s for both metals.The vacuum
> pressure inside the chamber of the e-beam is 9e-7 before doing my deposition.
> i use Acetone for the lift-off process. For some reason when i stick the
> sample in acetone without ultrasonic agitation, the lift-off process does not
> happen, basically the sample just sets there and nothing happens. On the other
> hand, when i use the ultrasonic agitation, all the metals on my sample will
> lift-off and the lift-off process fails!! it seems that the metals are not
> sticking very well to the sample for some reason??
>
> Keep in mind that i cleaned the GaN sample with (HCL:HNO3 3:1) for 15 min then
> used Acetone and methanol and finally DI water and blow dry with N before
> doing lithography. I believe this is enough to clean the sample.
>
> Any suggestions on how to deal with this problem???