Interferometry system error compensation in twin stage lithography tools

A method for using a lithography tool including an exposure apparatus and first and second stages, wherein the first and second stages are transposable between an exposure position proximate to the exposure apparatus and another position remote from the exposure position, the method comprising:

• exposing a first wafer on a first stage to radiation from the exposure apparatus while the first stage is in the exposure position;
• interferometrically monitoring the location of the first wafer with respect to a reference position for the first wafer during the exposure, wherein the monitoring comprises compensating a measured interference phase based on a first predetermined representation indicative of systematic errors of the interferometry system for the first stage in the exposure position;
• exchanging the first stage with the second stage at the exposure position;
• and
• exposing a second wafer on the second stage to radiation from the exposure apparatus while the second stage is in the exposure position.

A twin stage lithography tool, comprising:

• an exposure system;
• first and second stages each capable of supporting and positioning a wafer, wherein the first and second stages are transposable between first and second positions, the first position being proximate to the exposure system;
• an interferometry system comprising one or more interferometers configured to monitor the location of the first and second stages in the first and second positions;
• and
• an electronic storage medium providing a first predetermined representation indicative of systematic errors for the first stage in the first position and a second predetermined representation indicative of systematic errors for the second stage in the first position.

A method, comprising:

• providing an interferometry system comprising an interferometer and first and second measurement objects;
• alternately monitoring a degree of freedom of the first and second measurement objects with respect to the interferometer, wherein during the monitoring the interferometer directs two beams along different paths and then combines them to produce an output beam, wherein the output beam comprises information about an optical path length difference between the two beams and one of the beams contacts the monitored measurement object, and wherein imperfections in the interferometry system cause a measurable interferometric phase derived from the output beam to deviate from the expression Φ=pknL, where p is an integer, k is the wavenumber of the output beam, and nL corresponds to the optical path length difference;
• compensating a measured interference phase based on a first predetermined representation indicative of systematic errors of the interferometry system while monitoring the first measurement object;
• compensating the measured interference phase based on a second predetermined representation indicative of systematic errors of the interferometry system while monitoring the second measurement object.