| 摘要 |
The invention features interferometry systems that characterize cyclic errors. In many embodiments, the systems include a phase-shifting component (e.g., a phase or frequency shifter) for introducing a variable and controlled phase between the reference and measurement beams of an interferometer. By analyzing the distance measurements of the interferometer as a function of the introduced phase, an analyzer in the interferometry system can characterize the cyclic errors in the interferometer. Once the cyclic errors are characterized, the analyzer can directly correct the distance measurements to remove contributions from cyclic errors. Alternatively, or in addition, to including the phase shifting component, the interferometry systems can perform dispersion measurements of the gas in the measurement arm at multiple positions of the measurement object and the analyzer can determine cyclic errors in the system based on the dispersion measurements. The invention also features lithography systems for making integrated circuits, wherein the lithography systems include at least one of the interferometry systems described above.
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