What missing from your process flow is a final hard baking step before casting
PDMS. Try baking your mold at 200C for a couple of hours. Also, there's no need
to cure PDMS at that high of a temp, 60 to 70C is good enough. As for the
Alignment keys, to completely eliminate the prob, use front to back alignment.
To improve the visibility of the alignment keys, you need to generate the keys
out of oxide or metal or silicon first, you can  do it by using one of the masks
that you already have.

  Cheers,

  H.




Date: Fri, 23 Feb 2007 10:33:41 -0600
From: Vishwa 
Subject: Re: [mems-talk] Problem with PDMS removal from the SU-8 mold
To: General MEMS discussion 

Thanks a bunch for the response. I do have negative slope. When I tried to
make just the array structure on the wafer, I exposed it by 10, 20 under and
10,20,30,40,50 percent over the recommended values. All them peeled out,
when I cast the PDMS. Also, I observed the there is negative slope like
Gareth mentioned.

If i try to spin the second layer, I dont see any alignment markers to align
the second layer. Is there any way of achieving this. Right now, when I do
PEB, I see the alignment marker from the first layer and then align it to
the second.