Hi Manjula,

under-etching of the hard mask is a typical problem with long KOH
etching processes as the adhesion of the masking material on the
bevelled wafer edges is poor. We have also seen the problem with
HF-etching of glass wafers with a polysilicon hard mask. We use a
mechanical wafer holder (from AMMT, www.ammt.de) that protects the
edge of the wafer to avoid this as we have not found any deposition
technique suitable for edge protection.

Best regards,

Jan

*******************************

Dr. Jan Lichtenberg
Team Leader Biosensor and Microfluidics Group

Physical Electronics Laboratory
ETH Zurich
Hoenggerberg, HPT H4.2
CH-8093 Zurich, Switzerland

Phone:  +41-1-633 2187
Fax:    +41-1-633 1054
E-mail: lichtenb@iqe.phys.ethz.ch

*******************************

Tuesday, April 27, 2004, 5:36:23 PM, you wrote:

mr>   I need some information of some etch mask other than
mr> silicon dioxide for KOH etching.I am doing a long duration
mr> etching(atleast 5 hrs)and using a thick thermally grown oxide
mr> mask.But, the sides of my wafer start etching out.I have tried
mr> PECVD Nitride as mask but that does not help.Is there any resist i
mr> can apply to the edges of my wafer during the last 1-1.5hrs of my
mr> etching
mr> Manjula