Abstract: The focus and overlay alignment of photolithographic exposure tools of the type wherein the location of the wafer is accurately tracked with respect to a baseline position, such as in step and repeat cameras, are evaluated by monitoring the output signal generated by a photodetector in response to the light radiated from one or more periodic test patterns carried by a re-useable calibration wafer while such a test pattern is being exposed to an aerial image of a matching calibration mask. Overlay alignment suitably is evaluated by stepping the pattern on the wafer from side-to-side and fore and aft of the aerial image while monitoring the photodetector for a peak output signal, whereby overlay alignment errors along the x-axis and y-axis of the exposure tool are determined by the displacement of the wafer positions at which such peak signals are detected from the positions at which such peak signals ae expected.

Abstract: The present invention is directed to new and improved apparatus for measuring overlay error between a wafer pattern and a mask pattern projected onto the wafer pattern by a lithographic exposure instrument, which includes a grating mask; a grating wafer having reflective lines alternating with non-reflective spaces patterned like the mask pattern; the lithographic instrument having projection optics mounted to project an image of the mask on the wafer, and a mechanism for moving the grating mask and grating wafer relative to the projection optics; the grating on the wafer being offset from the grating on the mask forming Moire fringes corresponding to the overlay error between the wafer pattern and a mask pattern projected onto the wafer; a photodiode array wherein each photodiode corresponds to a pixel on the grating wafer; viewing optics mounted to project the Moire fringes onto the photodiode.

Abstract: This invention relates to overlay test measurement systems which are useful for testing lithographic instruments used in making microcircuits, which includes a single second-level pattern set in the middle of a checkerboard-like arrangement of first level patterns alternating with opaque patterns, the patterns being constructed and arranged so that if a second substantially identical cluster is imaged on the first cluster with the second level pattern of the second cluster aligned with any one of the first level patterns on the first cluster then the opaque patterns of the second cluster would be aligned with the other first level patterns on the first cluster thereby protecting them from exposure.According to a feature of the invention there is provided a method of making a test wafer of the type described as well as a method of testing the alignment of lithographic tools using the aforesaid test mask and test wafer.