Reflective Waveplates for Pupil Polarization Filtering

Patent metadata

Field	Value
Publication number	US-2023187242-A1
Application number	US-202217829296-A
Country	US
Kind code	A1
Filing date	May 31, 2022
Priority date	Dec 14, 2021
Publication date	Jun 15, 2023
Grant date	—

Abstract

An optical inspection system includes one or more gratings to convert the polarization of light scattered from a target from an elliptical polarization that varies spatially across a collection pupil to a linear polarization that is uniformly oriented across the collection pupil. The one or more gratings have phase retardation that varies spatially across the collection pupil in accordance with the elliptical polarization. The one or more gratings include at least one grating on a reflective substrate. The optical inspection system also includes a linear polarizer to filter out the linearly polarized light.

First claim

What is claimed is:

1 . An optical inspection system, comprising:
one or more gratings to convert the polarization of light scattered from a target from an elliptical polarization that varies spatially across a collection pupil to a linear polarization that is uniformly oriented across the collection pupil, wherein:
the one or more gratings have phase retardation that varies spatially across the collection pupil in accordance with the elliptical polarization, and
the one or more gratings comprise at least one grating on a reflective substrate; and
a linear polarizer to filter out the linearly polarized light.

2 . The system of claim 1 , wherein the target is a semiconductor wafer.

3 . The system of claim 2 , wherein the semiconductor wafer is unpatterned.

4 . The system of claim 3 , wherein the unpatterned semiconductor wafer is polished.

5 . The system of claim 1 , wherein the light is ultraviolet.

6 . The system of claim 1 , wherein:
the one or more gratings comprise a first grating and a second grating; the first and second gratings are one-dimensional; the first grating is on a first reflective substrate; and the second grating is on a second reflective substrate.

7 . The system of claim 6 , wherein:
the first grating has a duty cycle that varies spatially across the collection pupil and an orientation that varies spatially across the collection pupil; and the second grating has a duty cycle that varies spatially across the collection pupil and an orientation that varies spatially across the collection pupil.

8 . The system of claim 7 , wherein:
the first grating has a depth that is constant across the collection pupil; and the second grating has a depth that is constant across the collection pupil.

9 . The system of claim 6 , wherein:
the first grating has a uniform duty cycle and an orientation that varies spatially across the collection pupil; and the second grating has a duty cycle that varies spatially across the collection pupil and a uniform orientation.

10 . The system of claim 6 , wherein the first grating and the second grating have identical layouts.

11 . The system of claim 6 , wherein:
the first grating and the second grating have distinct orientations that vary spatially across the collection pupil; and the first grating and the second grating have substantially equal phase retardation.

12 . The system of claim 6 , further comprising a uniform waveplate to provide uniform phase retardation for the light scattered from the target.

13 . The system of claim 12 , wherein the first grating and the second grating are disposed between the uniform waveplate and the linear polarizer.

14 . The system of claim 1 , wherein the one or more gratings comprise a two-dimensional grating on a reflective substrate.

15 . A method, comprising:
illuminating a target; collecting light scattered from the illuminated target, wherein the collected light scattered from the illuminated target has an elliptical polarization that varies spatially across a collection pupil; using one or more gratings, converting the polarization of the collected light from the elliptical polarization that varies spatially across the collection pupil to a linear polarization that is uniformly oriented across the collection pupil, wherein:
the one or more gratings have phase retardation that varies spatially across the collection pupil in accordance with the elliptical polarization, and
the one or more gratings comprise at least one grating on a reflective substrate; and
using a linear polarizer, filtering out the light having the linear polarization that is uniformly oriented across the collection pupil.

16 . The method of claim 15 , wherein the target is a semiconductor wafer.

17 . The method of claim 16 , wherein the semiconductor wafer is unpatterned.

18 . The method of claim 17 , wherein the unpatterned semiconductor wafer is polished.

19 . The method of claim 15 , wherein the light is ultraviolet.

20 . The method of claim 15 , wherein:
the one or more gratings comprise a first grating and a second grating; the first and second gratings are one-dimensional; the first grating is on a first reflective substrate; and the second grating is on a second reflective substrate.

21 . The method of claim 15 , wherein the one or more gratings comprise a two-dimensional grating on a reflective substrate.

Assignees

• Kla Corp

Inventors

• Shen Chong
• Zhao Guoheng
• Whiteside Bret

Classifications

• H10P72/0616 Primary

  Monitoring of warpages, curvatures, damages, defects or the like · CPC title

• G02B5/3083

  Birefringent or phase retarding elements (G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001) · CPC title

• G02B5/1814

  structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings (G02B5/189 takes precedence) · CPC title

• G01N21/8806 Primary

  Specially adapted optical and illumination features · CPC title

• G02B5/1819

  Plural gratings positioned on the same surface, e.g. array of gratings (plural diffractive elements positioned sequentially along the optical path G02B27/4272) · CPC title