Method and apparatus for angular-resolved spectroscopic lithography characterization
An apparatus and method to determine overlay of a target on a substrate ( 6 ) by measuring, in the pupil plane ( 40 ) of a high numerical aperture len (L 1 ), an angle-resolved spectrum as a result of radiation being reflected off the substrate. The overlay is determined from the anti-symmetric component of the spectrum, which is formed by subtracting the measured spectrum and a mirror image of the measured spectrum. The measured spectrum may contain only zeroth order reflected radiation from the target.
1. An inspection apparatus, comprising:
a detector configured to detect an angle-resolved spectrum of radiation reflected from a target formed on a substrate; and
a control system coupled to the detector, the control system being configured to:
compute a mirror image of the angle-resolved spectrum,
generate anti-symmetric components of the angle-resolved spectrum by subtracting the angle-resolved spectrum and the computed mirror image of the angle-resolved spectrum, and
determine an overlay error of the target based on the anti-symmetric components of the angle-resolved spectrum.
2. The inspection apparatus of claim 1 , wherein the control system is configured to determine the overlay error by reference to parts of the anti-symmetric components of the angle-resolved spectrum that are not on an axis of the angle-resolved spectrum.
3. The inspection apparatus of claim 1 , wherein the angle-resolved spectrum of the reflected radiation is one of a transverse magnetic spectrum of the reflected radiation or a transverse electric spectrum of the reflected radiation.
4. The inspection apparatus of claim 1 , wherein the angle-resolved spectrum comprises substantially only a zeroth order of the radiation reflected from the substrate.
5. The inspection apparatus of claim 1 , wherein the target comprises a grating and wherein a pitch of the grating is smaller than a wavelength of the radiation.
6. The inspection apparatus of claim 1 , further comprising:
a high numerical aperture lens configured to collect the reflected radiation;
wherein the detector is configured to measure the angle-resolved spectrum of the reflected radiation in a pupil plane of the high numerical aperture lens.
7. The inspection apparatus of claim 6 , wherein a numerical aperture of the high numerical aperture lens is at least 0.9.
8. The inspection apparatus of claim 1 , wherein the overlay error is related to an extent of a misalignment of two misaligned periodic structures that form the target.
9. An inspection method, comprising:
measuring an angle-resolved spectrum of radiation reflected from a target on a substrate;
computing a mirror image of the angle-resolved spectrum;
subtracting the angle-resolved reflected spectrum and the mirror image of the angle-resolved reflected spectrum to generate anti-symmetric components of the angle-resolved spectrum; and
determining, based on the anti-symmetric components of the angular-resolved reflected spectrum, an overlay error of the target.
10. The method of claim 9 , wherein the determining is performed by reference to parts of the anti-symmetric components of the angle-resolved spectrum that are not on an axis of the angle-resolved spectrum.
11. The method of claim 9 , wherein the measuring comprises measuring one of a transverse magnetic spectrum of the reflected radiation or a transverse electric spectrum of the reflected radiation.
12. The method of claim 9 , wherein the angle-resolved spectrum comprises substantially only a zeroth order of the radiation reflected from the substrate.
13. The method of claim 9 , wherein the target comprises a grating and wherein a pitch of the grating is smaller than a wavelength of the radiation reflected from the substrate.
14. The method of claim 9 , wherein:
the measuring comprises measuring, in a pupil plane of a high numerical aperture lens, the angle-resolved spectrum of the reflected radiation, and
a numerical aperture of the high numerical aperture lens is at least 0.9.
15. The method of claim 9 , wherein the overlay error is related to an extent of a misalignment of two misaligned periodic structures that form the target.
16. A device manufacturing method, comprising:
projecting radiation onto a target portion of a substrate;
measuring an angle-resolved spectrum of the radiation reflected from the target;
computing a mirror image of the angle-resolved spectrum;
subtracting the angle resolved spectrum and the mirror image of the angle-resolved spectrum to generate anti-symmetric components of the angle-resolved spectrum; and
determining, based on the anti-symmetric components of the angle-resolved spectrum, an overlay error of the target.