| 摘要 |
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. Focus, on the other hand, suitably is evaluated by incrementally defocusing the imaging optics of the exposure tool while monitoring the rms width of the output signal generated by the photodetector as the wafer pattern is stepped through the aerial image of the calibration mask at each focal setting. The best focal setting minimizes the rms width of the output signal.
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