Abishek,

Another item you need to keep in mind regarding films of AZP4620 at the
thickness you are mentioning (50-75 µm) is the absorptivity of the film. The
overall transparency of AZP4620 is fairly low; exposing that thick a layer can
definitely provide difficulties.

If you have issues with the exposure dose, you may want to look into higher-
transparency materials.  Best would probably be AZ9260, which has nearly
identical coating capabilities to AZP4620, but has greater transparency to allow
for higher aspect-ratio exposures.

As a side note, it is possible to get a 50µm thick film in a single coat with
both AZP4620 and AZ9260 - but it dose depend a bit on the coating system you are
using - a high capability spinner motor (accurate at low-end spin speeds with
high acceleration capability) plus a very precise control system is critical.  I
used an EVG150 system to get a 55µm for both of these materials in a single
coat.

Best Regards,
Chad Brubaker

EV Group       invent * innovate * implement
Technology - Tel:  480.727.9635, Fax:  480.727.9700  e-mail:
[email protected], www.EVGroup.com

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Saravana P. Natarajan
Sent: Thursday, September 28, 2006 9:30 AM
To: [email protected]
Subject: [mems-talk] Multiple coats of AZ P4620

Hi Abishek,
                     I have done two coats of AZ4620. Use HMDS before the
first coat only. Spin the resist at the desired RPM and bake for 90 secs at
110 deg. Let it to cool and spin the second coat and bake for 2 mins and the
subsequent coat for about 4 to 5 mins. Prolonged bakes causes the resist to
harden quite a bit and may need extended exposure and develop times. A 20 um
thick layer took me about 2 min 30 secs to develop in AZ 400K (1:3)

Saravana P. Natarajan
Grad. Research Assistant - RF Microsystems Group
University of South Florida,Tampa, FL,
Ph: 813-974-4851
Fax: 813-974-5250