A lithographic alignment vernier based on low-magnification imaging of line-space patterns has been developed. Its resolution is limited only by the lithographic process used; a vernier that can be interpolated to 1/16 µm is demonstrated, using step-and-repeat optical lithography. This vernier can be read quickly and easily because it is read at low magnification, where there are no problems with depth of focus, even for multilevel resists. The vernier is tolerant to variations in linewidth, resist thickness, and edge profile. A machine-readable version of this vernier is also described.
Peter A. Heimann,
"The Color-Box alignment vernier: a sensitive lithographic alignment vernier read at low magnification," Optical Engineering 29(7), (1 July 1990). https://doi.org/10.1117/12.55649