[mems-talk] Etching SiO2

[Huy]

You should usealready made 6:1 BOE to do the etching, but if you like playing 
with chemistry, try this money back guarantee recipe 296 g NH4F: 425 ml 
of DI water: 106 ml 49%HF. It removes 1000A of oxide per minute without 
destroying your resist mask.   
   
  Cheers,
   
  H.
    
  
Dear all

For one of my projects, I need to pattern thick thermal oxide of
1.5um. I used 49%HF:DI = 1:6 as the etchant and 20um AZ9260 as a mask
(the reason of using this thick resist is that I need to do a through
wafer Deep RIE after patterning the SiO2).

The etching of the oxide takes more than half an hour in the etchant.
My problem is that the photoresist can not stand the HF solution and
start to peel off (especially the smaller features) after about 20min.
HF also attacks the photoresist reducing the overall thickness of the
photoresist, which can impact my later DRIE process.

Could anybody illuminate me with a better method to etch the oxide
layer without destroying the photoresist?