Dear Vishwa,

You should consider the two layers as independent when you calculate spin speeds
and exposure dosages. I.e. for your second layer you need to find a spin recipe
that will produce a 50 µm thick layer and bake + expose accordingly. Otherwise,
I think you will end up with a 350 µm thick structure...

Regards,

Maria


-----Original Message-----
From:   Vishwa [mailto:dagarshali@gmail.com]
Sent:   Sun 10/29/2006 5:07 PM
To:     General MEMS discussion
Cc:
Subject:        [mems-talk] coating a second layer of Su8...
Hi Guys,

I am trying to make two layers of Su8-2100 on a  Si-Wafer.

The first layer is the base structure for the microchannel the
dimensions being 2.5mm x 150um x 5cm (W x H x L).

The second layer is of same width and length, the difference being the
height of microstructures, which is 50um.

The procedure that I currently follow is outlined below :-

- First spin the SU8 on the wafer and coat a 150um layer. Then do the
soft bake, expose, then do the post exposure bake and finally develop.

- Now spin the second layer of SU8 for a thickness of 200um. This is
done assuming that the first layer structure is 150um and I need 50um
structure on top of that layer. So am spinning as if I am making a
200um layer.

-The Soft bake, exposure and the post exposure bake are all calculated
for 200um thickness.

I just want to know if the procedure that I am following is correct?.
If not, what is the better way of achieving the same task.