Patent ID: 7399711

Claim:
A method of controlling a recess etch process, comprising: for a multilayered substrate having a trench therein and a column of material deposited in the trench, determining a first dimension from a surface of the substrate to a reference point in the substrate by: obtaining a measured net reflectance spectrum of at least a portion of the substrate including the trench; computing a modeled net reflectance spectrum of the portion of the substrate as a weighted incoherent sum of reflectances from n ≧1 different regions constituting the portion of the substrate; determining a set of parameters that provides a close match between the measured net reflectance spectrum and the modeled net reflectance spectrum; and extracting the first dimension from the set of parameters; computing an endpoint of the recess etch process as a function of the first dimension and a desired recess depth measured from the reference point; and etching down from a surface of the column of material until the endpoint is reached.