Bottom anti-reflective coatings (BARCs) are now used in applications such as gate patterning that requires the tight critical dimension (CD) control. BARC removal must be accomplished before the film (e.g. poly and dielectric) is etched. BARC etch is a critical step that can affect the final line width of the etched features. In general, an oxygen plasma with additives is used to etch BARC, in which photoresist has been trimmed simultaneously. In this work, the effect of O@sub 2@/N@sub 2@ and O@sub 2@/He plasmas on etching of photoresist is investigated on Lam TCP 9400PTX system. The self-bias voltage on the wafer has been measured for a variety of conditions with different top source powers, bottom bias powers, gas mixtures and gas flow rates. The results show that compared to O@sub 2@/N@sub 2@ plasma, the self-bias voltage is lower and the etching rate of resist is higher for O@sub 2@/He. Our measurements indicate that the etched products can lead to an increase of self-bias voltage with a fixed bias power. The influence of etched products is due to the decrease of the ion flux to wafers, which is shown through the use of plasma simulator, the Hybrid Plasma Equipment Model (HPEM).