A method is described for detecting the initial exposure of the stop layer underlying a patterned dielectric film. The bias compensation signal from the power supply of the ceramic electrostatic chuck displays a step increase when the etch front reaches the underlayer. The end-point signal strength is essentially independent of exposed oxide area over the range similar to0.01 to 1%. End point is detected just as the underlayer is exposed, significantly earlier than that for optical emission end point. The proposed origin of the bias compensation end-point signal is the change in resistance between wafer substrate and plasma as holes are etched through the dielectric film. This model correctly predicts which etch applications will produce an end-point signal, including standard via etch and contact etch. Dual damascene via etch also produces a useful end-point signal, apparently due to lowered resistance of the silicon nitride stop layer during etch. The use of bias compensation end point in a commercial wafer production facility is described. (C) 2001 The Electrochemical Society.