I have had similar problems. The last step that you need to do is pirranha
clean (after acetone and ISO) and close couple it with a dehydration bake.
We do a bake at 200C and also the layer that the resist is adhering to could
be non-uniform or could have some pin holes, causing improper adhesion.

Hope this helps.

On Tue, Jan 25, 2011 at 12:55 AM, hui yan  wrote:
>
> i m using positive photoresist AZP4620 for photolithography. However,
> during the development step, the resist layer peels off when washed with DI
> water; though i have tried numerous times and have shorten the development
> time to 20s.
>
> I have cleaned my wafer using piranha solution, followed by DI water rinse,
> then rinsing with acetone, IPA, DI water. And then dehydrate my wafer at 120
> C for 30 min.
>
> Does HMDS primer helps? if so, what is the recipe for spin coating it?
>
> Regards,
> Hui Yan
> Mechanical Engineering
> National University of Singapore