LITHOGRAPHIC APPARATUS AND DEVICE MANUFACTURING METHOD

摘要

Measurements of an interferometric measurement system are corrected for variations of atmospheric conditions such as pressure, temperature and turbulence using measurements from a second harmonic interferometer (10). A ramp, representing the dependence of the SHI data on path length, is removed before use of the SHI data. The SHI may use a passive Q-switched laser (11) as a light source and Brewster prisms (142,144) in the receiver module. Optical fibers may be used to conduct light to the detectors (145-147). A mirror reflecting the measurement beams has a coating of a thickness selected to minimize the sensitivity of the SHI data to changes in coating thickness.