By using concentrated HF, I was just trying to confirm the strength of
my photoresist soft mask. Thanks a lot for your suggestion. I shall
try it out.

On 3/3/06, Gareth Jenkins  wrote:
> Is there any reason why you use concentrated HF? My experience is that
> less aggressive solutions allow greater depths - you just have to wait
> longer. As Roger Shile suggests, use a chromium layer if possible and
> BOE. I have also had good results with 2% HF + 2% HNO4 with soda-lime glass.
> Without chrome I have achieved around 20microns with Shipley S1818
> resist (2um layer). If I remember correctly S1818 has it's own adhesion
> promoter so no need for HMDS. Do a thorough solvent wash followed by
> dehydration of the glass (~300 deg for 30mins) immediately before coating.