NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
HF based solutions (Dilute HF or BOE) etch silicon dioxide with a rate dependent on the concentration of HF in the solution.
The actual etchant in more concentrated fluoride solutions is HF2, which is a result of the equilibria:
No attack on silicon or silicon nitride
However, photoresist or thin polysilicon are not always adequate masks.