Wet etching of various silicon oxide films using BHF solution was studied as a means of post-RIE wet cleaning to form small contact holes with the designed shape. Measurements show a dependence of etching rate on HF concentration for thermal and CVD oxide films. Thermal and ECR-CVD oxide films showed lower etching rates than doped/nondoped APCVD, LPCVD, and PCVD oxide films showed. The etching rate dependence on HF concentration was linear for the lower etching rate films but nonlinear for the higher etching rate films. This suggests that, for BHF etching of the higher etching rate films, the dominant etching species is HF, while HF2- plays only a small role.