Reaction mechanism for fluorine etching of silicon

A reaction mechanism is proposed for etching of Si surfaces by F atoms in which SiF4 is formed. We proposed that in the rate-determining step the F atom attacks the back side of a SiF3 moiety with simultaneous SiF bond formation and SiSi bond rupture (as in an SN2 process). The transition state for this process involves charge transfer from the rupturing SiSi bond to the attacking F atom and is consistent with recent observations that the etch rate is greater for n-type than for p-type silicon.