Hi Xiaochuan Zhou,

it is certainly difficult to apply resist onto a wafer with deep structures.
Even if you succeed with this (spray resist, resist lamination) the structures
may become less accurate. There is a trick though which works with some
structures:
Do all the lithos one after the other BEFORE deep etching. Then, after each deep
etching step, remove one layer of resist with dry etching. This resist stripping
must be quite accurate, of course.
Please let me know about your solution and results.

Thank you,
Ralf G. Longwitz.

Research Assistant
Microsystems integration group
Swiss Fed. Inst. of Technology
_______________________________

EPFL-DMT-IMS  BM 3.125
http://dmtwww.epfl.ch/~rlongwit
Tel: +41.21-693 6727
Fax: +41.21-693 5950
_______________________________


> Dear colleagues:
>
> I would like to get suggestions on fabrication processes.  I am designing a
> process for fabricating a device containing three levels of etched features
> on a silicon wafer.  The features include basins of about 10 micron deep,
> trenches of about 50 micron wide and 50 micron deep, and narrow
> through-holes (etched all-the-way through the silicon wafers of 300 to 450
> micron thick).  I am considering the use of Si(110) substrates and KOH wet
> etching for achieving the arrow through-holes.  It seems that I have to go
> through at least three etching steps in order to achieve three levels of
> depth.  My difficulty is at the photoresist coating between the steps.  Any
> one of my device features would cause sufficient corrugations on the
> substrate surface and make uniform photoresist coating impossible.  I would
> like to hear any suggestions on the overall process design, suitable etching
> processes (wet or dry), and any tricks and/or materials that may make the
> fabrication easier.
>
> Thank you very much.
>
>
>
> Xiaochuan Zhou, Ph.D.
> Xeotron Corporation
> E-mail xczhou@xeotron.com