Is it OK to etch the wet oxidation deposited SiO2 in BHF solution? Will that have effects on the device performance? I am planning to fabricate FETs based on 2D layered materials (Mos2, WS2). The desired thickness of SiO2 was 300 nm, but the obtained thickness is about 330 nm. If anyone has done so, what could be the roughness difference in the as deposited and the etched SiO2? Please suggest me on this.
Hello, wet oxidation of a Silicon Substrate produces a a oxide of a good Quality. The selectivity of the BHF etching of SiO2 to Si is very high. If you etch away the whole oxide, the surface of the Silicon wouldn´t change at all. The etching in the oxide is isotropic. That wouldn´t be the case, if you would use a stack of a second oxide, for example a CVD oxide made of TEOS. But as you have that high Quality oxide, you should not introduce much roughness.
@ Thomas Popp, thank you very much.
Any idea on how much would be the roughness of the etched SiO2?
Hello,
Below is a article, that deals with the roughness of the Silicon after 24 h Immersion in BHF. Although that is somewhat different to your question, I would estimate, that the additional roughness introduced by etching 10 % of the thickness of your oxide is less than a Nanometer. Maybe you get some nonuniformity introduced by rinsing and drying.
regards
Thomas
http://jes.ecsdl.org/content/141/10/2899.abstract?sid=a2ab69bf-5722-4c92-a3e2-36a822f52aea
Thomass Popp you are right! SiO2 exposed to BHF is really smooth. As far as I remember there are tho commonly used concentration of BHF (7:1 and 10:1). Check this out. The only thing you should consider during fabrication of FET is very gentle slope of etched SiO2 layer (which was previously masked). I etched layers with total thickness of 230nm and obtained very long slope (about 800 nm long) while thickness was only 230 nm.
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