A semiconductor wafer vacuum chuck used as part of a photographic wafer-alignment machine for performing contactless photolithography has integral spacer means disposed on a substantially planar surface thereof for mechanically maintaining a fixed distance between portions of a wafer positioned adjacent the spacer means and the surface of the wafer chuck, whereby a controlled separation is provided between a surface of the wafer and a photographic mask overlying the surface of the wafer upon the application of a vacuum to the surface of the wafer chuck.
A calibration method suitable for highly precise and highly accurate surface metrology measurements is described. In preferred embodiments, an optical inspection tool including a movable optics system is characterized in terms of position and wavelength dependent quantities over a range of motion. Once the position-dependant quantities are determined at various wavelengths and positions, they are stored and used to interpret data from test wafers having an unknown metrology. Free of position-dependent variations and other information pertaining to the measurement system, the accuracy of the resulting wafer measurement more closely matches the precision of the tool than existing techniques. In particular embodiments, a portion of the characterization of the optical system is accomplished by using tilted black glass to provide a non-reflective reference.
