System and method for lateral shearing interferometry in an inspection tool

Patent metadata

Field	Value
Publication number	US-11609506-B2
Application number	US-202217723240-A
Country	US
Kind code	B2
Filing date	Apr 18, 2022
Priority date	Apr 21, 2021
Publication date	Mar 21, 2023
Grant date	Mar 21, 2023

Abstract

A method for in-situ wave front detection within an inspection system is disclosed. The method includes generating light with a light source and directing the light to a stage-level reflective mask grating structure disposed on a mask stage. The method includes directing light reflected from the stage-level reflective structure to a detector-level mask structure disposed in a plane of a detector and then collecting, with an optical element, light reflected from the detector-level mask structure. The method includes forming a pupil image on the detector and laterally shifting the stage-level reflective mask, with the mask stage, across a grating period of the stage-level reflective mask grating structure to provide phase reconstruction for lateral shearing interferometry. The method includes selectively impinging light reflected from the optical element on the one or more sensors of the detector.

First claim

What is claimed:

1. An inspection system with in-situ wavefront metrology of light of the inspection system comprising:
an imaging sub-system comprising a light source, a set of imaging optics, and a detector including one or more imaging sensors;
a stage;
a stage-level reflective mask grating structure disposed in a plane of a mask secured by the stage, wherein the light source is configured to illuminate the stage-level reflective mask grating structure with incident light;
a detector-level reflective mask grating structure disposed in a plane of the detector, wherein the set of imaging optics is configured to direct light reflected from the stage-level reflective structure to the detector-level mask structure;
an optical element configured to collect light from the detector-level mask structure, wherein the detector-level mask structure is oriented to direct light from the detector-level mask structure to the optical element, wherein the optical element is configured to form a pupil image on the one or more sensors of the detector,
wherein the stage is configured to provide lateral shifting motion across a grating period of the stage-level reflective mask grating structure to provide phase reconstruction for lateral shearing interferometry to identify changes of the wave front of light of the imaging system; and
an actuator configured to selectively impinge light reflected from the optical element on the one or more sensors of the detector.

2. The system of claim 1 , wherein the light source is configured to generate extreme ultraviolet (EUV) light.

3. The system of claim 2 , wherein the inspection system comprises an EUV photomask inspection system.

4. The system of claim 3 , wherein the stage comprises a mask stage.

5. The system of claim 1 , wherein the light source is configured to generate deep ultraviolet (DUV) light.

6. The system of claim 5 , wherein the inspection system comprises a DUV wafer inspection system.

7. The system of claim 6 , wherein the stage comprises a wafer stage.

8. The system of claim 1 , wherein the light source is configured to illuminate the stage- level reflective mask grating with incident light having full NA of the imaging sub-system.

9. The system of claim 1 , wherein the stage-level reflective mask grating structure is configured to generate a set of coherent diffracted copies of incoherent light NA.

10. The system of claim 1 , wherein the detector-level reflective mask grating structure includes more grating elements than the stage-level reflective mask grating structure.

11. The system of claim 1 , wherein the grating pitch of the detector-level reflective mask grating structure is upscaled by the magnification ratio of the imaging optics.

12. The system of claim 1 , wherein the detector-level reflective mask grating structure is disposed within a free area of the detector plane.

13. The system of claim 1 , wherein the one or more sensors comprise one or more charge coupled devices.

14. The system of claim 13 , wherein a projection of the pupil image on the one or more charged coupled devices extends across two or more pixels of the one or more charge coupled devices.

15. The system of claim 1 , wherein the optical element comprises a mirror.

16. The system of claim 15 , wherein the mirror comprises a spherical mirror.

17. The system of claim 16 , wherein the spherical mirror has a focal length corresponding to a track length of the imaging sub-system.

18. The system of claim 1 , wherein the actuator comprises a shutter positioned between the detector-level reflective mask grating structure and the one or more sensors of the detector to block a reflected pattern from a beam path during normal inspection mode and pass through light during wave front detection mode.

19. The system of claim 1 , wherein the actuator comprises a tilt actuator configured to tilt the mirror such that light reflected from the mirror impinges on the one or more sensors of the detector during wave front detection mode and tilt the mirror such that light reflected from the mirror fails to impinge on the one or more sensors of the detector during normal inspection mode.

20. A method of in-situ wavefront metrology of extreme ultraviolet (EUV) light of a photomask inspection system comprising:
generating EUV light;
directing the EUV light to a stage-level reflective mask grating disposed on a mask stage;
directing EUV light reflected from the stage-level reflective structure through an optical imaging system to a detector-level mask structure disposed in a plane of one or more sensors of a detector;
collecting, with an optical element, EUV light reflected from the detector-level mask structure,
forming a pupil image on the one or more sensors of the detector;
laterally shifting the stage-level reflective mask, with the mask stage, across a grating period of the stage-level reflective mask grating structure to provide phase reconstruction for lateral shearing interferometry to identify changes of the wave front of the EUV light of the photomask inspection system; and
selectively impinging EUV light reflected from the optical element on the one or more sensors of the detector.

21. A method of in-situ wavefront metrology of light of a deep ultraviolet (DUV) wafer inspection comprising:
generating DUV light;
directing the DUV light to a stage-level reflective mask grating structure disposed on a wafer stage;
directing DUV light reflected from the stage-level reflective structure through an optical imaging system to a detector-level mask grating structure disposed in a plane of one or more sensors of a detector;
collecting, with an optical element, DUV light reflected from the detector-level mask structure,
forming a pupil image on the one or more sensors of the detector;
laterally shifting the stage-level reflective mask, with the wafer stage, across a grating period of the stage-level reflective mask grating structure to provide phase reconstruction for lateral shearing interferometry to identify changes of the wave front of the DUV light of the wafer inspection system; and
selectively impinging DUV light reflected from the optical element on the one or more sensors of the detector.

Assignees

• Kla Corp

Inventors

• Mengel Markus

Classifications

• G03F1/84 Primary

  Inspecting · CPC title

• G01B9/02098 Primary

  Shearing interferometers · CPC title

• G03F9/7049 Primary

  Technique, e.g. interferometric · CPC title

• G03F7/70033

  by plasma extreme ultraviolet [EUV] sources · CPC title

• G03F7/7065

  Defects, e.g. optical inspection of patterned layer for defects · CPC title