METHOD OF DETERMINING A PARASITIC FORCE OF AN ACTUATOR OF AN OPTICAL COMPONENT, CONTROL METHOD FOR AN ACTUATOR, OPTICAL SYSTEM, PROJECTION SYSTEM AND LITHOGRAPHIC APPARATUS

摘要

It is an object of the present invention to enable a more accurate positioning of optical components in a lithographic apparatus, in particular optical components arranged in an optical path between the patterning device and the substrate.According to an aspect of the invention, there is provided a method of determining a parasitic force of an actuator of an optical component, the actuator being mounted to a first frame and being configured to control a position of the optical component relative to a second frame, the method comprising: 1.obtaining a first position signal representing a position of Ihe optical component relative to the first frame; 2.performing a low-pass filtering to the first position signal; 3.obtaining a second position signal representing a position of the optical component relative to the second frame: 4.performing a high-pass filtering to the second position signal, the high-pass tillering being complementary to the low-pass filtering; 5.determining the parasitic force of the actuator, based on the combined Low-pass filtered first position signal and the high-pass filtered second position signal. According to another aspect of the invention there is provided another method of determining a parasitic force of an actuator of an optical component, the actuator being mounted lo a frame and configured lo control a position of the optical component relative to the frame, the method comprising: 1.obtaining a position signal representing a position of the optical component relative lo the frame; 2.performing a low-pass filtering to the position signal; 3.obtaining a reference signal representing a desired posilion of the optical component relative to the frame; 4.performing a high-pass filtering to the reference signal, the high-pass filtering being complementary to the low-pass filtering; 5.determining a parasitic force of the actuator, based on the combined low-pass filtered position signal and the high-pass filtered reference signal. According to yet another aspect of the invention, there is provided a method of controlling an actuator. the actuator being mounted lo a first frame and being configured lo control a position of an optical component relative lo a second frame, the method comprising: 1.obtaining a reference signal representing a desired position of Ihe optical component relative to the second frame and an oplical component position signal representing a measured position of the oplical component relative to the second frame; 2.determining a parasitic force of the actuator using the method according to the invention. 3.determining, based on the reference signal, the optical component position signal and the determined parasitic force, a control signal for controlling the actuator. According to yet another aspect of the invention, there is provided an optical system comprising; 1.an oplical component such as a mirror; 2.an actuator mounted to a first frame of the apparatus, the actuator being configured to control a position of the optical component relative to a second frame of the apparatus; 3.a control unit. the control unit being configured to: 1.1 obtaining a reference signal representing a desired position of the optical component relative to the second frame and an oplical component position signal representing a measured posilion of the oplical component relative to the second frame; 1.2 determining a parasitic force of ihe actuator by: 1.2.1 obtaining a first position signal representing a posilion of the optical component relative to the first frame; 1.2.2 performing a low-pass filtering to the first position signal to ohlain a low-pass filtered signal; 1.2.3 performing a high-pass filtering to the optical component posilion signal or the reference signal to obtain a high-pass filtered signal, the high-pass fihering being complementary to the low-pass filtering; 1.2.4 determining the parasitic force of the actuator, based on the combined low-pass filtered signal and the high-pass filtered