Projection system

A projection system for a lithographic apparatus, the projection system comprising:

• an optical path that is operable to receive an input radiation beam and to project an output radiation beam onto a substrate to form an image, the optical path comprising a plurality of optical elements, the plurality of optical elements comprising a first set of at least two optical elements and a second set of at least one optical element;
• a plurality of sensors, each sensor being associated with one of the plurality of optical elements and operable to determine a position of that optical element;
• a first set of actuators, each actuator in the first set of actuators being associated with one of the second set of optical elements and operable to adjust that optical element;
• and
• a controller, wherein the controller is operable to use the first set of actuators to adjust the second set of optical elements in dependence on the determined position of the first set of optical elements so as to at least partially compensate for optical aberrations and/or line-of-sight errors caused by the positions of the first set of optical elements.

A lithographic apparatus comprising:

• an illumination system configured to condition a radiation beam;
• a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
• a substrate table constructed to hold a substrate;
• and
• a projection system comprising:
• an optical path that is operable to receive the patterned radiation beam and to project an output radiation beam onto the substrate to form an image, the optical path comprising a plurality of optical elements, the plurality of optical elements comprising a first set of at least two optical elements and a second set of at least one optical element;
• a plurality of sensors, each sensor being associated with one of the plurality of optical elements and operable to determine a position of that optical element;
• a first set of actuators, each actuator in the first set of actuators being associated with one of the second set of optical elements and operable to adjust that optical element;
• and
• a controller, wherein the controller is operable to use the first set of actuators to adjust the second set of optical elements in dependence on the determined position of the first set of optical elements so as to at least partially compensate for optical aberrations and/or line-of-sight errors caused by the positions of the first set of optical elements.

A method for controlling a projection system comprising a plurality of optical elements, the method comprising:

• determining a position of each of the plurality of optical elements;
• using a model to determine an optical aberration and/or line-of-sight error caused by the positions of a first set of at least two of the plurality of optical elements;
• using a model to determine an adjustment for each of a second set of the plurality of optical elements that at least partially compensates for the determined optical aberration and/or line-of-sight error;
• and
• applying the determined adjustment to each of the second set of the plurality of optical elements.

A method for controlling a lithographic apparatus comprising a patterning device support structure, a projection system comprising a plurality of optical elements, and a substrate table, the method comprising:

• determining a position of each optical element in the plurality of optical elements;
• using a model to determine a line-of-sight error and/or optical aberration caused by the positions of a first set of at least two of the plurality of optical elements;
• using a model to determine an adjustment for each of a second set of the plurality of optical elements and to determine an adjustment to a position of the patterning device support structure and/or the substrate table that at least partially compensates for the determined line-of-sight error and/or the optical aberration;
• applying the determined adjustment to each of the second set of the plurality of optical elements;
• and
• applying the determined adjustment to the position of the patterning device support structure and/or the substrate table.