Hi MEMS group
We are involved in fabication of silicon piezoresistive MEMs accelerometer.
The problem we are facing during processing is as follows
The wafer front surface was selectively etched to a depth of 50 micron
followed by lithography on the same surface for further processing. While
spinning the negative photoresist (HNR120, Arch chemical) it was observed that
photoresist thickness was not uniform on the surface. Particularly photoresist
was piled up at the edges of the etched corners and so the developing was very
poor. However, if aluminium is deposited on the wafer and then do the
lithography using positive photoresist (S1813, Shipley Co.) this problem did
not arise. So what is the reason of nonuniform thickness of negative
photoresist.
Can anyone tell me what is the maximum limit of unevenness on the wafer after
etching so that lithography can be done smoothly on that surface.
Thanks in advance.

Dr. Soumen Das
Sr. Scientific Officer
Microelectronics Centre
Dept. of Electronics & ECE
Indian Institute of Technology
Kharagpur 721 302, India
email: [email protected]
Phone: +91-3222-81914 (O)
            +91-3222-81475 (Lab)
            +91-3222-81915 (R)
Fax: +91-3222-755303/777190