Hello, Why don't you use the HF vapour etching? The etching rate is about 5 microns/hour. You can find more information in the following link. http://www.idonus.com/ Good luck Selon Jeff chen: > Dear all, > > When I checked the references and found the etching rate of BHF is > 100nm/min, if I wanna etch out 5 nm SiO2, just need 3 sec. That's too > short to operate. > Can I dilute the BHF to 1:10 concentration? Just using water to dilute it? > How can I check the etching rate for the diluted BHF?