초록 ▼

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 t

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.

대표청구항 ▼

In combination with a photolithographic exposure tool having a reticle platen, a wafer stage, a light source for illuminating said platen, and imaging optics disposed between said reticle platen and said wafer stage; the improvement comprising a calibration wafer mounted on said wafer stage, said wa

In combination with a photolithographic exposure tool having a reticle platen, a wafer stage, a light source for illuminating said platen, and imaging optics disposed between said reticle platen and said wafer stage; the improvement comprising a calibration wafer mounted on said wafer stage, said wafer having a plurality of test dies positioned at different locations thereon, each of said test dies being patterned to have a checkerboard-like array of periodic, mutually orthogonal gratings oriented to align along an x-axis and a y-axis of said exposure tool, the gratings on said test dies having a predetermined spatial frequency and a predetermined duty ratio; a calibration mask mounted on said reticle platen, said mask being imaged onto said calibration wafer by said imaging optics to produce an aerial image of said mask, said mask being patterned to have a checkerboard-like array of periodic, mutually orthogonal gratings oriented to aling along the x-axis and the y-axis of said exposure tool, the aerial image of said mask gratings having a spatial frequency and a duty ratio which are essentially equal to and substantially greater than said predetermined spatial frequency and said predetermined duty ratio, respectively; a single photodetector positioned to produce an electrical output signal in response to light angularly radiated from said test dies; and means for scanning one after another of said test dies transversely with respect to the aerial image of said mask gratings, first along one of said axis and then along the other of said axis; whereby the output signal of said photodetector varies over time to provide an x-y scanned representation of the aerial image of said mask gratings at each of said test die locations.