Real time measurement of etch rate during a chemical etching process

A contactless method and apparatus for real-time in-situ monitoring of a chemical etching process during etching of at least one wafer in a wet chemical etchant bath are disclosed. The method comprises the steps of providing two conductive electrodes in the wet chemical bath, wherein the two electrodes are proximate to but not in contact with a wafer; monitoring an electrical characteristic, e.g the resistance between the two electrodes as a function of time in the etchant bath of the at least one wafer, wherein a prescribed change in the electrical characteristic is indicative of a prescribed condition of the etching process; and recording a plurality of values of the electrical characteristic as a function of time during etching. From the plurality of recorded values and corresponding times, instantaneous etch rates, average etch rates, and etching end points may be determined with reference to the attached drawings, starting point (102) corresponds to the start of the etching process. Intermediate region (103) of the curve corresponds to thinning of the film during the etch process. Inflexion point (108) corresponds approximately to a point in time at which all features are etched to nominal size in an essentially uniform film. Flat region (110) of the curve corresponds to the period during which more than the nominal or desired amount of material to be removed by etching is being removed from the substrate, for example, by an undercutting process. Such a method and the apparatus therefor are particularly useful in a wet chemical etch station.