Are your sure the print of your mask pattern is facing the wafer? If not
this will introduce a gap the thickness of the mylar film which is
enough to affect it.
I have also just noticed your exposure dose of 700mJ/cm^2 is rather high
for a 25um film. About 200mJ/cm^2 is recommended (more if you are using
a filter).


Abhishek Jain wrote:
> I am using EVG 624 for exposure. the power wattage of the bulb is
> 12mW/cm^2.
>
>
> On 3/30/07, Gareth Jenkins  wrote:
>>
>> What are you using for the exposure?
>> I would guess either your source isn't well collimated or your mask is
>> not well contacted with the wafer.
>>
>> Abhishek Jain wrote:
>> > I am making SU-8 2025 masters on Si for PDMS replica molding. I use a
>> > mylar mask and the structures are ~25um tall. I have a problem that I
>> > do not get good vertical walls of SU-8. A 15um feature comes out as a
>> > flat length of ~30um and then a linearly decaying thickness that makes
>> > a total feature size of ~60um.
>