Lithographic apparatus and method
A lithographic apparatus includes an illumination system configured to condition a radiation beam and a support constructed to support a patterning device. The patterning device is configured to form a patterned radiation beam. A substrate table is constructed to hold a substrate, and a projection system is configured to project the patterned radiation beam onto a target portion of the substrate. The apparatus includes a heater arrangement that includes an electron beam generator configured to generate an electron beam, and an electron beam guide arrangement configured to guide the electron beam onto an optical element of the lithographic apparatus. The optical element forms a part of the illumination system or the projection system which, in use, is traversed by the radiation beam. The heater arrangement is controllable to provide a distribution of heat on the optical element by deflection of the electron beam.
1. A lithographic apparatus comprising:
an illumination system configured to condition a radiation beam;
a support constructed to support a patterning device, the patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
a substrate table constructed to hold a substrate;
a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and
a heater arrangement comprising an electron beam generator configured to generate an electron beam, and an electron beam guide arrangement configured to guide the electron beam onto an optical element of the lithographic apparatus,
the optical element forming a part of the illumination system or the projection system of the lithographic apparatus which, in use, is traversed by the radiation beam,
the heater arrangement being controllable to provide a distribution of heat on the optical element by deflection of the electron beam.
2. The lithographic apparatus of claim 1 , wherein the heater arrangement comprises a monitor configured to monitor a deformity characteristic of the optical element, and wherein the heater arrangement further comprises a heater controller configured to estimate the distribution of heat to be provided on the optical element based on an output of the monitor.
3. The lithographic apparatus of claim 2 , wherein the distribution of heat on the optical element is, at least in part, pre-determined.
4. The lithographic apparatus of claim 2 , wherein the deformity characteristic is an interaction between the radiation beam and the optical element.
5. The lithographic apparatus of claim 2 , wherein the deformity characteristic is a detected temperature profile or a distortion profile across a surface of the optical element.
6. The lithographic apparatus of claim 2 , wherein the monitor is a sensor configured to detect a temperature profile or a distortion profile across a surface of the optical element.
7. The lithographic apparatus of claim 6 , wherein the sensor comprises a camera, or a photodiode.
8. The lithographic apparatus of claim 1 , further comprising a shield configured to shield a cathode of the electron beam generator from positively charged entities.
9. The lithographic apparatus of claim 1 , wherein the electron beam guide arrangement comprises a magnetic based deflection arrangement, or an electrostatic based deflection arrangement, or both a magnetic based deflection arrangement and an electrostatic based deflection arrangement.
10. The lithographic apparatus of claim 1 , wherein the illumination system is a reflective illumination system, and/or the projection system is a reflective projection system, and wherein the optical element comprises a mirror.
11. The lithographic apparatus of claim 1 , wherein the electron beam has a beam path between the electron beam generator and the optical element, and wherein the lithographic apparatus, or a part thereof, is constructed and arranged such that:
the beam path is in substantial vacuum; and/or
the beam path is through a gas having a pressure of less than about 100 Pa.
12. The lithographic apparatus according to claim 11 , wherein the radiation beam comprises radiation having a wavelength in the EUV part of the electromagnetic spectrum, the wavelength being in the range of 5-20 nm.
13. A lithographic method for use with a lithographic apparatus, the lithographic apparatus comprising
an illumination system configured to condition a radiation beam;
a support constructed to support a patterning device, the patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
a substrate table constructed to hold a substrate;
a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and
a heater arrangement comprising an electron beam generator configured to generate an electron beam, and an electron beam guide arrangement configured to guide the electron beam onto an optical element of the lithographic apparatus,
the optical element forming a part of the illumination system or the projection system of the lithographic apparatus which, in use, is traversed by the radiation beam,
the heater arrangement being controllable to provide a distribution of heat on the optical element by deflection of the electron beam,
the method comprising:
using the heater arrangement to provide the optical element with the distribution of heat in order to reduce a deformity of the optical element that is caused by, or would be caused by, the radiation beam traversing that optical element.
14. The lithographic method of claim 13 , wherein the distribution of heat on the optical element is, at least in part, pre-determined.
15. The lithographic method of claim 14 , wherein the distribution of heat on the optical element is, at least in part, pre-determined from prior knowledge of an interaction between the radiation beam and the optical element.