I'm trying to etch SiO2 Buried oxide layer Isotropically using RIE with CHF3 + Oxygen plasma. I have problems to etch underneath of top silicon (Device layer) and i think it is due to polymerization of side walls on SiO2 that hinder lateral etching. How to overcome it using Dry etching if possible.
I also tried at different pressures from 0.04 Torr to 0.2 Torr and at different RF Power.
It seems to me a difficult task for plasma etching. SiO2 etching in fluorocarbon pasma is an ion stimulated process, so it will go mainly at the bottom of the trench rather than on the walls which are almost not hit by ions. Even in SF6 with no polymer. The isotropic etching with no bias will likely involve F atoms that will etch Si much faster than SiO2. If you want an isotropic etching may be it's better to consider wet etching in HF solution? It's isotropic and selectivity to Si is rather good.
I think also that it's not the right to etch SiO2 and having Silicon as mask. You will never get an isotropic etching with CHF3/O2 for SiO2 because it's assited by ion energy which are rather directional. increasing the température might help a little but it will be difficult to get selectivity vs silicon. If you use SF6 you will etch more Silicon than SiO2. I recomend also the wet etching.
Dear all,
After multiple experiments by varying pressure, RF power, Oxygen percentage, i always got only anisotropic etching of SiO2 by RIE.
As per your suggestion, we are now using vapor HF for further etch process.
Thanks
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