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Abstract

A method and apparatus for measuring etch depth during the etching of a device pattern into a nontransparent substrate, is disclosed. The method makes use of the finding that the device patterns etched into substrates produce diffraction patterns when illuminated. Thus, according to the method, a beam of light is directed onto a region of a substrate, into which region a portion of a device pattern is being etched. The light reflected from this region forms a diffraction pattern and, according to the inventive method, the intensity of a diffraction order is detected and recorded as a function of time during the etching procedure. The intensity of the diffraction order varies with time. The etch rate of the substrate is inversely proportional to the period of the oscillations in the recorded intensity-time curve.

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First Claim