Dear Mr.Xiaoguang "Leo" Liu,
For etching the thick oxide, BOE 6:1 would work better compared to the dil HF.
You may use dry etch with CF4 and CHF3 chemistry also for the oxide etch.
Bhat
alsoQuoting "Xiaoguang \\Leo\\ Liu" :

> 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?