Nano-structured non-polarizing beamsplitter

Patent metadata

Field	Value
Publication number	US-10976562-B2
Application number	US-201816138092-A
Country	US
Kind code	B2
Filing date	Sep 21, 2018
Priority date	Oct 10, 2017
Publication date	Apr 13, 2021
Grant date	Apr 13, 2021

Abstract

A beamsplitter includes a substrate formed from a material transparent to wavelengths of light at least above a selected cutoff wavelength and reflective structures distributed across a surface of the substrate. The reflective structures split incident light having wavelengths above the selected cutoff wavelength into a reflected beam formed from portions of the incident light reflected from the reflective structures and a transmitted beam formed from portions of the incident light transmitted through the substrate. A splitting ratio of a power of the reflected beam to a power of the transmitted beam is based on a ratio of surface area of the reflective surfaces to an area of the incident light on the substrate. Separation distances between neighboring reflective structures are smaller than the cutoff wavelength such that diffracted power of the incident light having wavelengths above the selected cutoff wavelength is maintained below a selected tolerance.

First claim

What is claimed:

1. A metrology system comprising:
an illumination source configured to generate an illumination beam having wavelengths above a selected cutoff wavelength;
an objective lens;
a detector; and
a beamsplitter, wherein the beamsplitter splits the illumination beam into a first illumination beam and a second illumination beam, wherein the objective lens directs the first illumination beam to a sample, wherein the objective lens collects radiation emanating from the sample in response to the first illumination beam, wherein the beamsplitter splits the radiation emanating from the sample from the objective lens into a first detected beam and a second detected beam, wherein the detector receives the first detected beam, wherein the beamsplitter comprises:
a substrate formed from a material transparent to wavelengths of light at least above the selected cutoff wavelength; and
a plurality of reflective structures distributed across a surface of the substrate to form a non-polarizing beamsplitter, wherein the plurality of reflective structures are configured to split incident light having wavelengths above the selected cutoff wavelength into a reflected beam formed from portions of the incident light reflected from the plurality of reflective structures and a transmitted beam formed from portions of the incident light transmitted through the substrate, wherein separation distances between neighboring reflective structures of the plurality of reflective structures are smaller than the selected cutoff wavelength to prevent diffraction of illumination from the illumination source into non-zero diffraction orders.

2. The metrology system of claim 1 , wherein the plurality of reflective structures comprises:
metallic films on the surface of the substrate.

3. The metrology system of claim 1 , wherein the plurality of reflective structures includes planar surfaces parallel to the surface of the substrate.

4. The metrology system of claim 1 , wherein the plurality of reflective structures is distributed in a square lattice pattern having a common pitch in a first direction and a second direction perpendicular to the first direction.

5. The metrology system of claim 1 , wherein the plurality of reflective structures is distributed in at least one of a hexagonal lattice pattern, an oblique lattice pattern, or an equilateral triangle lattice pattern.

6. The metrology system of claim 1 , wherein the substrate comprises:
at least one of fused silica, Suprasil, Heralux, CaF 2 , MgF 2 , LiF, quartz, or sapphire.

7. The metrology system of claim 1 , wherein the selected cutoff wavelength comprises:
a wavelength in the range of approximately 120 nm to approximately 200 nm.

8. The metrology system of claim 1 , wherein the selected cutoff wavelength comprises:
at least one of an ultraviolet wavelength, a deep ultraviolet wavelength, a vacuum ultraviolet wavelength, or an extreme ultraviolet wavelength.

9. The metrology system of claim 1 , wherein the sizes of the plurality of reflective structures are less than 1 micrometer.

10. The metrology system of claim 1 , wherein the separation distances between neighboring reflective structures are less than 1 micrometer.

11. The metrology system of claim 1 , wherein the substrate and the plurality of reflective structures are configured as a plate beamsplitter.

12. The metrology system of claim 1 , further comprising:
an additional substrate disposed on the plurality of reflective structures, wherein the second substrate is transparent to wavelengths at least above the selected cutoff wavelength.

13. The metrology system of claim 12 , wherein the substrate, the plurality of reflective structures, and the additional substrate are configured as a cubic beamsplitter.

14. The metrology system of claim 1 , wherein the surface of the substrate is a planar surface.

15. The metrology system of claim 1 , wherein the surface of the substrate is a curved surface.

16. The metrology system of claim 15 , wherein the curved surface provides a selected focal power.

17. A method for splitting light comprising:
generating illumination having wavelengths above a selected cutoff wavelength;
directing the illumination to a non-polarizing beamsplitter, wherein the beamsplitter comprises:
a substrate formed from a material transparent to wavelengths of light at least above the selected cutoff wavelength; and
a plurality of reflective structures distributed across a surface of the substrate to form a non-polarizing beamsplitter, wherein the plurality of reflective structures are configured to split incident light having wavelengths above the selected cutoff wavelength into a reflected beam formed from portions of the incident light reflected from the plurality of reflective structures and a transmitted beam formed from portions of the incident light transmitted through the substrate, wherein separation distances between neighboring reflective structures of the plurality of reflective structures are smaller than the selected cutoff wavelength to prevent diffraction of light above the cutoff wavelength into non-zero diffraction orders;

splitting, with the beamsplitter, the illumination into a first illumination beam and a second illumination beam;
directing, with an objective lens, the first illumination beam to a sample;
collecting, with the objective lens, radiation emanating from the sample in response to the first illumination beam;
splitting, with the beamsplitter, the radiation emanating from the sample from the objective lens into a first detected beam and a second detected beam; and
receiving the first detected beam with a detector.

18. The method of claim 17 , wherein the substrate and the plurality of reflective structures are configured as a plate beamsplitter.

19. The method of claim 17 , further comprising:
an additional substrate disposed on the plurality of reflective structures, wherein the additional substrate is transparent to wavelengths at least above the selected cutoff wavelength.

20. The method of claim 19 , wherein the substrate, the plurality of reflective structures, and the additional substrate are configured as a cubic beamsplitter.

Assignees

• Kla Tencor Corp
• Kla Corp

Inventors

• Gorelik Dmitry
• Hill Andrew V
• Bachar Ohad
• Manassen Amnon
• Negri Daria

Classifications

• G03F7/7015

  Details of optical elements · CPC title

• G03F7/70208

  Multiple illumination paths, e.g. radiation distribution devices, microlens illumination systems, multiplexers or demultiplexers for single or multiple projection systems · CPC title

• G03F7/706851

  Detection branch, e.g. detector arrangements, polarisation control, wavelength control or dark/bright field detection · CPC title

• G03F7/70583

  Speckle reduction, e.g. coherence control or amplitude/wavefront splitting · CPC title

• G03F7/706849 Primary

  Irradiation branch, e.g. optical system details, illumination mode or polarisation control · CPC title