Two-wavelength phase-shifting interferometry is applied to an interference phase-measuring microscope enabling the measurement of step features. The surface is effectively tested at a synthesized equivalent wavelength λeq = λaλb/|λa − λb| by subtracting phase measurements made at visible wavelengths λa and λb. The rms repeatability of the technique is λ/1000 at the equivalent wavelength. To improve the precision of the data, the phase ambiguities in the single-wavelength data are removed using the equivalent wavelength results to determine fringe orders. When this correction is made, a measurement dynamic range (feature height/rms repeatability) of 104 is obtainable. Results using this technique are shown for the measurement of an optical waveguide and a deeply modulated grating.
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