Abstract: A method of etching a variable thickness material on a substrate through an opening or openings is disclosed. The method includes a first etch step in which the material is isotropically etched until the substrate material is first exposed defining a first end point. Thereafter, a second anisotropic etch is performed until all of the remaining material at the opening or openings is removed.Preferably the etching is by dry plasma etching and the first end point is detected by monitoring the change in concentration of a reactive species. The change is sharply defined by taking a second derivative of the curve of the change in intensity of the peak of the sensed species.