Interferometric servo control system for stage metrology

An electronic processing system for use with a servo-system for positioning a measurement object, the electronic processing system comprising:

• an input port configured to receive a position signal from an interferometry system indicative of a position for the measurement object;
• a memory storing a representation of non-linear errors in the interferometry system;
• a processor which during operation generates a compensated position signal based on the position signal from the interferometry system and the stored representation;
• and
• an output port configured to direct the compensated position signal to a servo-controllers
• wherein the stored representation of non-linear errors can be expressed as a sum of one or more corrections terms each having a sinusoidal dependence on a distance to the measurement object.

A method for determining non-linear cyclic errors in a metrology system that positions a measurement object under servo-control based on an interferometrically derived position signal, the method comprising:

• translating the measurement object under servo-control at a fixed speed;
• identifying frequencies of any oscillations in the position of measurement object as it is translated at the fixed speed;
• and
• determining amplitude and phase coefficients for a sinusoidal correction term at least at one of the identified frequencies which when combined with the position signal suppress the oscillations at the at least one identified frequency.

A method for positioning a measurement object under servo-control based on an interferometrically derived position signal indicative of a position for the measurement object, the method comprising:

• generating a compensated position signal based on the interferometrically derived position signal and at least one correction term that has a sinusoidal dependence on the position of the measurement object;
• and
• repositioning the measurement object based on the compensated position signal and a desired position for the measurement object,
• wherein the generation of the compensated position signal includes:
• determining a speed for the measurement object based on the interferometrically derived position signal, and
• selecting parameters for the at least one sinusoidal correction term based on the determined speed.

A method for positioning a measurement object under servo-control based on an interferometrically derived position signal indicative of a position for the measurement object, the method comprising:

• generating a compensated position signal based on the interferometrically derived position signal and at least one correction term that has a sinusoidal dependence on the position of the measurement object;
• and
• repositioning the measurement object based on the compensated position signal and a desired position for the measurement object,
• wherein the at least one sinusoidal correction term comprises multiple sinusoidal correction terms and each of the multiple sinusoidal correction terms corresponds to a cyclic error in the interferometrically derived position signal.

An electronic processing system for use with a servo-system for positioning a measurement object, the electronic processing system comprising:

• an input port configured to receive a position signal from an interferometry system indicative of a position for the measurement object;
• a memory storing a representation of non-linear errors in the interferometry system;
• a processor which during operation generates a compensated position signal based on the position signal from the interferometry system and the stored representation;
• and
• an output port configured to direct the compensated position signal to a servo-controller,
• wherein the stored representation of non-linear errors can be expressed as a sum of multiple correction terms each having a sinusoidal dependence on the position of the measurement object.

An electronic processing system for use with a servo-system for positioning a measurement object, the electronic processing system comprising:

• an input port configured to receive a position signal from an interferometry system indicative of a position for the measurement object;
• a memory storing a representation of non-linear errors in the interferometry system;
• a processor which during operation generates a compensated position signal based on the position signal from the interferometry system and the stored representation;
• and
• an output port configured to direct the compensated position signal to a servo-controller,
• wherein the stored representation of non-linear errors is parameterized by a speed of the measurement object.