I am trying to get the structures obtained in the figure I attached. Basically I need an isotropic plqsmq etch of SiO2 with CF4. Ive only been able to obtain quite vertical sidewalls so far for some reason. I'm using a home build sputtering/etching system with DC-pulsed power source. Ive tried ranging from pressures of 5e-3mbar to 0.5mbar and powers of 150W to 50W and still seem to be getting vertical sidewalls. Any suggestions as to how else I can get an isotropic etch with plasma etching?
I have also tried HF etching already, however it seems my layer underneath has some pinholes and seems to peel off if I use HF.
Hi Matthew:
some suggestions:
- why not do an etch with longer duration, finally, you will get enough 'underetching' to also remove the SiO2 underneath the cap.
- If you refer to HF, do you mean a kHz plasma ? I would go for a RF (13.56 MHz) plasma which will be less oriented.
- Did you try to change the etchant ? Maybe you should try with SF6. Please check if you can pump that gas in your system or if it is safe to use in your lab.
Thanks Paul, with HF I meant hydrofluoric acid wet etch. It is kHz plasma. Unfortunately we don't have the possibility for RF power source at our institute, nor do we have any other fluorine based gases available. I have done quite long etching and it seems to start etching my structure away before I get under etching
I think you have to set the pressure at the few hundreds Pa. At second, heating of the wafer may be useful. And negative potential at the wafer to reduce the ion bombardment is required.
Any way, the ICP system and SF6 gas are prefereable.
You would have to etch the SiO2 chemically, using excessive fluorine. This is normally done at high pressure around 1 Torr and somewhat elevated temperature around 90 oC. The rate will strongly depend on the density of the material, so thermal oxide will etch very slowly whereas PECVD oxide will etch with reasonable rate. You can achieve a rate up to 300 nm/min. Selectivity to resist will be just below 10:1 using O2/N2/CF4 chemistry. I do not know if this is what you’re looking for.
Depending on your hardmark, you could use dHF wet etch to get you higher selectivity.
Hi Matthew,
It is old question but i would like to know more about it.
Did you succeed in lateral etching of SiO2 using Dry etching?
I'm facing the similar problem to underetch the buried SiO2 layer on SOI substrates using RIE. I am using CHF3+Oxygen plasma. I think that the side walls are polymerized and it hinder lateral SiO2 etching.
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