The effect of fluorocarbon polymer buildup on oxide etching was investigated by monitoring the reactor chamber under an O-2/Ar plasma. Its effect on contact etching was also investigated by employing a CF4/CHF3/Ar plasma. It was determined that the O-2/Ar plasma was very useful for confirming polymer buildup on the inner chamber surface. This is because of arm increased oxide etch rate by fluorine radicals, formed by the dissociation of the fluorocarbon polymer. Meanwhile, contact etching in a CF4/CHF3/Ar plasma with a high CHF4/CE4 ratio caused a reduction in etch rate near the edge of the wafer (in some-cases even an etch stop), a considerable loss of critical dimension, and higher etch selectivity to polysilicon. These various etch behaviors are attributed to the polymer buildup on the inner surface of the chamber.