Method and apparatus for optical endpoint detection during chemical mechanical polishing

摘要

A method for detecting during a planarization process the removal of a first layer of material overlying a workpiece is provided. Relative motion is effected between the first layer and a working surface to remove the first layer. A light having a spectrum of wavelengths is transmitted to the workpiece. The intensity for each of a plurality of reflected wavelengths of a reflected light reflected from the workpiece is measured to obtain a spectrum. The spectrum is a function of the plurality of reflective wavelengths. A spectrum reference value is calculated and a plurality of spectrum difference values are calculated by subtracting the spectrum reference value from the spectrum. An absolute value for each of the plurality of spectrum difference values that is a function of one of the plurality of reflected wavelengths that falls within a selected range of wavelengths is summed together to obtain a delta value. An endpoint parameter is calculated from the delta value.