In this study, the characterizations of oxide contact hole etching are investigated with C4F8/O2/Ar and CH2F2/C4F8/O2/ Ar plasma. As the percent composition of C4F8 in a C4F8/O2/Ar mixture increases, the amount of polymer deposited on the etched surface also increases because the CxFy polymer layer retards the reaction of oxygen atoms with PR. Adding CH2F2 into the C4F8/O2/Ar plasma increases the etch rate of the oxide and the selectivity of oxide to PR. The profile of contact holes was close to 90°, and no visible residue was seen in the SEM image at a C4F8/(C4F8+O2) ratio of 58%. The changes of chemical composition in the chamber were analyzed using optical emission spectroscopy, and the chemical reaction on the etched surface was investigated using X-ray photoelectron spectroscopy.