I have seen this before, and I think it may have to do with inadequate
rehydration of the photoresist. You need to let the resist relax for 30
minutes or more depending on the thickness and ambient humidity. Thicker
films and lower ambient humidity will need longer relaxation times. If it
is not rehydrated properly, the bottom parts of the resist will not develop
regardless of the dose.

On the other hand, I don't know why this is happening only when you use
HMDS. One possibility could be that the untreated surface is holding on to
some surface moisture which is helping to rehydrate the resist.



On Mon, Sep 21, 2015 at 5:24 AM, Mehmet Yilmaz 
wrote:

> Dear mems-talk community,
> If I use HMDS as adhesion layer, I am having a problem with the development
> of a photoresist called AZ4562 (about 10 micron thickness). In addition, I
> am having the same development problem with AZ5214E (about 1.4 micron
> thickness).
>
> If I do not use HMDS, the development time is usually about 60 seconds, or
> even less. However, if I use HMDS, the development time goes up to 45
> minutes (not seconds...) and still the development is not successful, but
> the resist is completely removed from some parts of the patterned areas on
> the wafer.
>
> Also, I have seen this problem with different substrates such as Silicon,
> Quartz, and Pyrex.
>
> I am wondering what would be the reason for that? Is it possible that HMDS
> is old, and out of date? Could that explain the problem? Or, do you have
> any other comments based on your own experience? Could you please comment?
>
> I am looking forward to your replies.
>
> Thanks in advance,
>
> Mehmet
>
> Mechanical Engineer
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