Abstract: A photomask/wafer alignment apparatus for achieving a high precision alignment of the wafer alignment mark and the photomask window at all stages of photomask patterning employs a variable wavelength light source the optical output frequency of which is selectively controllable, so as to optimize the signal-to-noise ratio of the wafer alignment mark and the photomask alignment window, either under operator control, or through an automatic feedback arrangement. The system also includes a two-dimensional variable aperture plate inserted between the variable wavelength light source and the projection optics for the photomask. This variable aperture plate provides the capability of control both bandwidth and coherence of the variable wavelength light beam emitted from the multi-color light source, thereby optimizing the signal-to-noise ratio of the imaged alignment mark.