Hi Shane,

CHF3 plasma tends to polymerize more and that's generally good for
achieving better selectivity over Si and straighter sidewall angles (CF4
can be used for very straight, striation-free etches as well but that
requires very low pressure and a lot more tweaking) whereas CF4 attacks
a broader range of materials.  Sounds like in your situation, etching of
the electrode is undesirable and therefore the metal will act as an etch
stop and you'd need careful characterization of your etch rate to
prevent lateral attack on SiO2 after reaching the metal surface.  I
think the best approach would be to stick with CHF3 for straighter
sidewall angle and choose a slower etch recipe so that you can time your
etch more precisely.

Hope that helps.
Trent


liuxf wrote:
> Hi all,
>
> My SiO2 film thickness is about 200nm, and I want to open a hole with diameter
3um so that to pass through my electrode. I wonder when I etch it with CF4
plasma, will this have a bad aspect ratio? I mean probably only the center of
the hole is opened but the other area still has some SiO2 left?
>
> BTW: how about CHF3 compared with CF4?
>
> thank you in advance
> shane