Hi,

It depends on how much you want to underetch. I'll guess around 10um
should be fine. Sacrifial layer thickness should work also. But be
aware, that etching rate is rather slow (~2um\min laterally in the
case of thermal oxide) and HF will attack slowly your metal.
By the way, we are working a lot with strained layers which are to
released. So, perhaps you want to read something about our controlled
wrinkling and rolling processes: http://www.ifw-dresden.de/institutes/iin

Best wishes
Daniel

Zitat von "xiaohui.lin" :

> Hi, all. We are having a sandwich structure- bottom substrate is Si,
> middle is SiO2(10nm), top is Cr/Au(200nm).
>
> we would like to etch away the middle SiO2 layer. Is it possible if
> we dip it in HF or BOE? Since the solution can only touch the side
> (10nm, very thin), I am afraid it will not separate the sandwich
> completely.
>
> Any suggestion is appreciated!
>
> Thanks.