Inspection apparatus and method for measuring a property of a substrate
An inspection apparatus measures a property of a substrate including a periodic structure. An illumination system provides a beam of radiation with an illumination profile including a plurality of illuminated portions. A radiation projector projects the beam of radiation onto the substrate. A detector detects radiation scattered from the periodic structure and separately detects first order diffracted radiation and at least one higher order of diffracted radiation of each of the illuminated portions. A processor determines the property of the substrate from the detected radiation. The plurality of illuminated portions are arranged such that first order diffracted radiation arising from one or more of the illuminated portions are not overlapped by zeroth order or first order diffracted radiation arising from any other of the illuminated portions. Furthermore, the plurality of illuminated portions are arranged such that first order diffracted radiation arising from the one or more of the illuminated portions are overlapped by at least one of the higher orders of diffracted radiation arising from any other of the illuminated portions.
1. An inspection apparatus comprising:
an illumination system configured to provide a beam of radiation forming a cross-shaped illuminated area on a periodic structure on a substrate;
a detector configured to:
detect radiation scattered from the periodic structure, and
separately detect zeroth order diffracted radiation, first order diffracted radiation, and a higher order of diffracted radiation arising from the illuminated area on the periodic structure, wherein the zeroth order, the first order, and the higher order diffracted radiation are non-overlapping with each other at the detector; and
a processor configured to determine a property of the substrate from the detected radiation.
2. The inspection apparatus according to claim 1 , wherein the zeroth order and the first order diffracted radiation are non-overlapping with second order diffracted radiation arising from the illuminated area.
3. The inspection apparatus according to claim 1 , wherein the zeroth order and the first order diffracted radiation are non-overlapping with third order diffracted radiation arising from the illuminated area.
4. The inspection apparatus according to claim 1 , wherein the zeroth order and the first order diffracted radiation are non-overlapping with fourth order diffracted radiation arising from the illuminated area.
5. The inspection apparatus according to claim 1 , wherein the detector is configured to separately detect the first order diffracted radiation and the higher order of diffracted radiation distributed in a diffraction direction corresponding to a direction of periodicity of the periodic structure.
6. The inspection apparatus according to claim 1 , wherein the cross-shaped illuminated area comprises:
a first illuminated area; and
a second illuminated area overlapping a portion of the first illuminated area.
7. The inspection apparatus according to claim 1 , wherein the cross-shaped illuminated area comprises rectangular illuminated areas.
8. The inspection apparatus according to claim 1 , wherein the cross-shaped illuminated area comprises:
a first illuminated area; and
a second illuminated area perpendicular to the first illuminated area.
9. A lithographic apparatus comprising:
an illumination optical system arranged to illuminate a pattern;
a projection optical system arranged to project an image of the pattern on to a substrate; and
an inspection apparatus comprising:
an illumination system configured to provide a beam of radiation forming a cross-shaped illuminated area on a periodic structure on the substrate;
a detector configured to:
detect radiation scattered from the periodic structure, and
separately detect zeroth order diffracted radiation, first order diffracted radiation, and a higher order of diffracted radiation arising from the illuminated area on the periodic structure, wherein the zeroth order, the first order, and the higher order diffracted radiation are non-overlapping with each other at the detector; and
a processor configured to determine a property of the substrate from the detected radiation.
10. A lithographic cell comprising:
a coater arranged to coat a substrate with a radiation sensitive layer:
a lithographic apparatus arranged to expose images onto the radiation sensitive layer of the substrate coated by the coater;
a developer arranged to develop images exposed by the lithographic apparatus; and
an inspection apparatus comprising:
an illumination system configured to provide a beam of radiation forming a cross-shaped illuminated area on a periodic structure on the substrate;
a detector configured to:
detect radiation scattered from the periodic structure, and
separately detect zeroth order diffracted radiation, first order diffracted radiation, and a higher order of diffracted radiation arising from the illuminated area on the periodic structure, wherein the zeroth order, the first order, and the higher order diffracted radiation are non-overlapping with each other at the detector; and
a processor configured to determine a property of the substrate from the detected radiation.
11. A method comprising:
providing a first beam of radiation that forms a cross-shaped illuminated area on a periodic structure;
detecting radiation scattered from the periodic structure comprising a single grating; and
determining an asymmetry of the single grating from a difference between detected positive and negative first order diffracted radiation arising from the illuminated area.
12. The method according to claim 11 , further comprising:
providing a second beam of radiation;
projecting the second beam of radiation onto an overlay target comprising a pair of overlaid gratings, one of the pair of overlaid gratings being the single grating,
detecting radiation scattered from the overlay target;
determining an overlay error of the overlay target from a difference between detected positive and negative first order diffracted radiation arising from the projection of the second beam of radiation; and
correcting the overlay error based on the determined asymmetry.
13. The inspection apparatus according to claim 11 , wherein the cross-shaped illuminated area comprises rectangular illuminated areas.
14. The inspection apparatus according to claim 11 , wherein the cross-shaped illuminated area comprises:
a first illuminated area; and
a second illuminated area perpendicular to the first illuminated area.
15. The inspection apparatus according to claim 11 , wherein the cross-shaped illuminated area comprises:
a first illuminated area; and
a second illuminated area overlapping a portion of the first illuminated area.