> Dear colleagues, > > I am trying to isotropically etch glass wafers. I want to etch the mask > directly, but after etch in 1:1 BOE/HF, I found that the Cr was lift off > and etched away, and the lateral etch rate is much higher than vertical. > I don't understand why is that, maybe because the etching of Cr, but accord- > ing to CRC hand book, Cr should be able to stand for HF. Is there anyone did > the similar process? How can I get good isotropic etching of glass wafer? > Any suggestions and explanations are highly appreciated. Thanks a lot. > > Ingrid Y. Xu > Microfabrication and Application Lab > The University of Illinois at Chicago > TEL: (312)-413-7576 > ******************************************************************************** Dear Colleagues, We have also worked on this problem at the Institute of Microtechnology, University of Neuchatel Switzerland. Effectively Cr layers have a relatively poor adhesion on glass. Former work by us where using a Cr/Au layer to etch glass. But this technique requires to etch gold and to etch the chrome layer in two different solutions and a lot of pin holes were present limiting thus the etch to 20 microns. We decided to change our masking material and made sevral tests until we found that an amorphous silicon can be used for such a purpose. We also found some works made at the TU Deft in the Netherland reporting the use of LPCVD Polysilicon to etch pyrex glass as well as work at the MIT Cambridge USA where poly masks were used to etch quartz. As the polysilicon can be batch deposited, we usually used it now to etch pyrex #7740 glass wafers. Nevertheless, both (amorphous silicon and polysilicon) are etched in a plasma etcher to define the mask. And with such layers it has been possible to etch through pyrex #7740 glass wafers of 0.5 mm. It means an etch depth of 500 microns without any problems. It is clear that this etching technique is completely isotropic due to the use of the HF solution. This work will be presented in Eurosensor '96 at Leuven Belgium and in micro-TAS in Basel switzerland, applied to the realisation of micr capillary tubes. Marc-Alexis Gretillat Institute of Microtechnology University of Neuchatel Rue Jaquet-Droz 1 P.O. Box 3 CH-2007 Neuchatel Switzerland E-mail: marc.gretillat@imt.unine.ch present E-mail adress until August 24 1996: gretilla@mtl.mit.edu ******************************************************************************** **