Inspection method for lithography

Patent metadata

Field	Value
Publication number	US-9494872-B2
Application number	US-200913060390-A
Country	US
Kind code	B2
Filing date	Sep 8, 2009
Priority date	Sep 16, 2008
Publication date	Nov 15, 2016
Grant date	Nov 15, 2016

Abstract

The present invention relates to an inspection apparatus and method which include projecting a measurement radiation beam onto a target on a substrate in order to measure the radiation reflected from the target and obtain information related to properties of the substrate. In the present embodiments, the measurement spot, which is the focused beam on the substrate, is larger than the target. Information regarding the radiation reflected from the target is kept and information regarding the radiation reflected from the surface around the target is eliminated. This is done either by having no reflecting (or no specularly reflecting) surfaces around the target or by having known structures around the target, the information from which may be recognized and removed from the total reflected beam. The reflected beam is measured in the pupil plane of the projector such that the information obtained is related to diffraction orders of the reflected beam and profile, critical dimension or overlay of structures on the substrate may be determined.

First claim

The invention claimed is:

1. An inspection apparatus comprising:
an optical system configured to focus a radiation beam into a measurement spot onto a substrate, the measurement spot comprising:
a target area comprising a periodic structure on the substrate, and
an area surrounding the target area:

a detector, positioned in a pupil plane of a high numerical aperture lens of the optical system, configured to detect a signal, wherein:
a first portion of the signal corresponds to a first portion of the radiation beam reflected from the target area, and
a second portion of the signal corresponds to a second portion of the radiation beam reflected only from the area surrounding the target area, the second portion of the signal being different from the first portion of the signal; and

a processor configured to:
derive a property of the substrate using the first portion of the signal; and
eliminate the second portion of the signal.

2. The inspection apparatus according to claim 1 , wherein;
the first portion of the signal corresponds to a first diffraction pattern; and
the second portion of the signal corresponds to a second diffraction pattern when the area surrounding the target area comprises a plurality of patterned areas.

3. The inspection apparatus according to claim 1 , wherein the target area is smaller than 15 by 15 microns.

4. The inspection apparatus according to claim 1 , wherein the processor is configured to derive a dimension of the periodic structure within the target area based on the first portion of the signal.

5. The inspection apparatus according to claim 1 , wherein the target area is within a product die on the substrate.

6. The inspection apparatus according to claim 1 , wherein the measurement spot is larger than the target area in at least one dimension.

7. A method of measuring a parameter of a lithographic process, the method comprising:
focusing, using an optical system, a radiation beam into a measurement spot on a substrate, the measurement spot comprising:
a target area comprising a periodic structure on the substrate, and
an area surrounding the target area;

detecting, using a detector positioned in a pupil plane of a high numerical aperture lens of the optical system, a signal wherein:
a first portion of the signal corresponds to a first portion of the radiation beam reflected from the target area, and
a second portion of the signal corresponds to a second portion of the radiation beam reflected only from the area surrounding the target area, the second portion of the signal being different from the first portion of the signal;

deriving, using a processor, a property of the substrate based on the first portion of the signal; and
eliminating, using the processor, the second portion of the signal.

8. The method according to claim 7 , wherein:
the first portion of the signal corresponds to a first diffraction pattern; and
the second portion of the signal corresponds to a second diffraction pattern when the area surrounding the target area comprises a plurality of patterned areas.

9. The method according to claim 7 , comprising:
deriving, using the processor, a dimension of the periodic structure within the target area based on the first portion of the signal.

10. The method according to claim 7 , comprising:
deriving, using the processor, a thickness of a layer on the substrate based on the first portion of the signal.

11. The method according to claim 7 , comprising:
deriving, using the processor, a profile of a structure within the target area or a dimension of the structure within the target area based on the first portion of the signal.

12. The method according to claim 7 , further comprising determining an error in overlay of a first grating superimposed on a second grating within the target area.

13. The method according to claim 7 , further comprising selecting a portion of the radiation beam using an aperture at an intermediate image plane of the optical system in order to reduce a dimension of the measurement spot.

14. The method according to claim 7 , further comprising mathematically differentiating a first diffraction spectrum from a second diffraction spectrum, wherein:
the first diffraction spectrum corresponds to the first portion of the signal; and
the second diffraction spectrum corresponds to the second portion of the signal, the second diffraction spectrum being different from the first diffraction spectrum.

15. The method according to claim 7 , further comprising selecting a wavelength of the radiation, wherein the wavelength is scattered by the target area and is unscattered by the area surrounding the target area.

16. The method according to claim 7 , further comprising using an area smaller than 15 by 15 microns as the target area.

17. The method according to claim 7 , further comprising using an area within a product die on the substrate as the target area.

18. A lithographic apparatus comprising:
an illumination system configured to illuminate a pattern comprising a sub-pattern of a periodic structure;
a projection system configured to project an image of the pattern on to a substrate; and
an inspection apparatus configured to derive a property of the substrate by measuring a target area on the substrate, the inspection apparatus comprising:
an optical system configured to focus a radiation beam into a measurement spot onto the substrate, the measurement spot comprising:
the target area comprising the periodic structure on the substrate, and
an area surrounding the target area;

a detector, positioned in a pupil plane of a high numerical aperture lens of the optical system, configured to detect a signal, wherein:
a first portion of the signal corresponds to a first portion of the radiation beam reflected from the target area, and
a second portion of the signal corresponds to a second portion of the radiation beam reflected only from the area surrounding the target area, the second portion of the signal being different from the first portion of the signal; and

a processor configured to:
derive a property of the substrate using the first portion of the signal; and
eliminate the second portion of the signal.

19. A lithographic cell comprising:
a coater configured to coat a substrate with a radiation sensitive layer;
a lithographic apparatus configured to expose images onto the radiation sensitive layer;
a developer configured to develop images exposed by the lithographic apparatus; and
an inspection apparatus configured to derive a property of the substrate by measuring a target area on the substrate, the inspection apparatus comprising:
an optical system configured to focus a radiation beam into a measurement spot onto the substrate, the measurement spot comprising:
the target area comprising a periodic structure on the substrate, and
an area surrounding the target area;

a detector, positioned in a pupil plane of a high numerical aperture lens of the optical s stem configured to detect a signal, wherein:
a first portion of the signal corresponds to a first portion of the radiation beam reflected from the target area, and
a second portion of the signal corresponds to a second portion of the radiation beam reflected only from the area surrounding the target area, the second portion of the signal being different from the first portion of the signal; and

a processor configured to:
derive a property of the substrate using the first portion of the signal; and
eliminate the second portion of the signal.

Assignees

• Bhattacharyya Kaustuve
• Den Boef Arie Jeffrey
• Van De Kerkhof Marcus Adrianus
• Van Der Schaar Maurits
• Asml Netherlands Bv

Inventors

• Bhattacharyya Kaustuve
• Den Boef Arie Jeffrey
• Van De Kerkhof Marcus Adrianus
• Van Der Schaar Maurits

Classifications

• G03F7/70625

  Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness · CPC title

• G03F7/70633 Primary

  Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching · CPC title