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.

Gareth

Rupesh Sawant wrote:

>I am using a positive photoressit AZ P4620 for making a soft mask on glass
>slide. Usage of HMDS is not assuring me a good adhesion of photoresist on
>glass surface. The photoresist is getting etched in 5 min after I keep the
>slide in concentrated HF. My main aim is to get 20u microchannel in the
>glass slide. Which procedure will guarantee me a strong adhesion which can
>make the photoresist soft mask to withstand concentrated HF for 30 min?. The
>thickness of my photoresist soft mask if 6.5u.