We investigated the effects of fluorine on boron diffusion in thin silicon oxides used for metal‐oxide‐semiconductor structures, including silicon dioxide and oxynitride. We used secondary ion mass spectroscopy to measure the boron penetration depth fromp+‐polycrystalline silicon to the silicon substrate through the silicon oxides for various fluorine doses. We compared experimental and simulated results and determined the boron diffusion coefficients in the silicon oxides. The diffusion coefficients have an Arrhenius relationship for each fluorine dose. The diffusion coefficients at a fluorine dose of 1×1016cm−2were 30 times larger than with no fluorine dose, and at a fluorine dose of 1×1015cm−2, diffusion coefficients were 5 times larger. With oxynitride, fluorine has the same enhancing effect. With no fluorine, the diffusion coefficients were independent of oxide thickness. When fluorine is implanted into polycrystalline silicon, especially with a high dose, the diffusion coefficient is larger for thinner oxides because of the higher fluorine concentration. ©1995 American Institute of Physics.