Hi, James,

Try the following two references:

Deep reactive ion etching of Pyrex glass using SF6 plasma
Xinghua Li, Takashi Abe and Masayoshi Esashi
Sensors and Actuators A: Physical
Volume 87, Issue 3, 5 January 2001, Pages 139-145

Fabrication of high-density electrical feed-throughs by deep-reactive-ion
etching of Pyrex glass
Li X., Abe T., Liu Y., Esashi M., Journal of Microelectromechanical Systems,

Volume: 11,  Issue: 6 pp: 625- 630,Dec 2002

Hope they help,

Best regards,

Fei Wang
Postdoctoral researcher, Dr
MIC - Department of Micro and Nanotechnology
Technical University of Denmark (DTU)
Building 344, 1st floor, Room no. 130
DK-2800, Kgs. Lyngby
Denmark
Tel:  +45 4525 6311
Fax:  +45 4588 7762
Email: fei.wang@nanotech.dtu.dk
         http://www.nanotech.dtu.dk


2009/2/4 James Paul Grant 

> Thanks to all who have contriubuted to this topic.
>
> Yes I'd love to use a thicker resist such as AZ9260 however I do not have
> this available to me. The thickest resist we have is AZ4562. Normally if I
> spin AZ4562 on a 3 inch wafer at low spin speeds (e.g. 1500 rpm) I can
> obtain a resist thickness of ~ 10 microns. I know I create other problems
> for myself with such a low spin speed (non-uniformity, more edge bead etc.)
> however these are not show stopping problems. Unfortunately my substrate is
> a CMOS chip of 5 mm by 5 mm and if I try to spin AZ4562 at 1500 rpm the
> resist essentially does not spin and I got a very non-uniform coating. The
> resist does spin nicely at spin speeds greater than 4000 rpm. So essentially
> I have 6.2 microns of photoresist to play with and have to etch 10 microns
> SiO2. Up until now I cannot get the selectivity required for my process
> (~2:1). I can achieve 1.5:1 however the etch rate is incredibly slow (~20
> nm/min). Note I only have RIE processes available to me for etching SiO2
> (there is also one ICP process for deep silicon etching).
>
> I contacted Surface Technology Systems (STS) for details about their
> Advanced Oxide Etch (AOE). This is an ICP based process and from the paper
> released by STS using this process selectivities of up to 12:1 can be
> achieved using photoresist. The gas chemistry is C4F8/H2 by the way. I was
> also told if a metal mask is used selectivities of up to 200:1 are possible.
> I will try and convince my line manager we should try this AOE however it is
> all dependent on cost!
>
> Thanks to Morten as well for sharing his process.
>
> James