Two-dimensional position encoder

Patent metadata

Field	Value
Publication number	US-10921718-B2
Application number	US-201816220624-A
Country	US
Kind code	B2
Filing date	Dec 14, 2018
Priority date	Dec 15, 2017
Publication date	Feb 16, 2021
Grant date	Feb 16, 2021

Abstract

A position encoder for monitoring relative movement between a first object and a second object includes a grating that is coupled to the first object, and an image sensor assembly that is coupled to the second object. The image sensor includes a first image sensor; a second image sensor that is spaced apart from the first image sensor; an optical element that includes a first optical surface and a second optical surface that is spaced apart from the first optical surface; and an illumination system. The illumination system directs an illumination beam at the optical element to create (i) a first reference beam that is reflected by the first optical surface and directed at the first image sensor, (ii) a second reference beam that is reflected by the second optical surface and directed at the second image sensor, and (iii) a transmitted beam that is transmitted through the optical element and is directed at and impinges on the grating to create a first measurement beam that is diffracted by the grating and directed at the first image sensor, and a second measurement beam that is diffracted by the grating and directed at the second image sensor.

First claim

What is claimed is:

1. A position encoder for monitoring relative movement between a first object and a second object, the position encoder comprising:
a grating that is coupled to the first object; and
an image sensor assembly that is coupled to the second object, the image sensor assembly including a first image sensor; a second image sensor that is spaced apart from the first image sensor; an optical element that includes a first optical surface and a second optical surface that is spaced apart from the first optical surface; and an illumination system that directs an illumination beam at the first optical surface of the optical element to create (i) a first reference beam that is a first portion of the illumination beam that is reflected by the first optical surface and directed at the first image sensor, (ii) a first transmitted beam that is a second portion of the illumination beam that is transmitted through the first optical surface and directed at the second optical surface, (iii) a second reference beam that is a first portion of the first transmitted beam that is reflected by the second optical surface and directed at the second image sensor, and (iv) a second transmitted beam that is a second portion of the first transmitted beam that is transmitted through the second optical surface of the optical element and is directed at and impinges on the grating to create a first measurement beam that is diffracted by the grating and directed at the first image sensor, and a second measurement beam that is diffracted by the grating and directed at the second image sensor.

2. The position encoder of claim 1 wherein the grating is a one-dimensional diffraction grating such that the first measurement beam is a +1 order first measurement beam, and the second measurement beam is a −1 order second measurement beam.

3. The position encoder of claim 1 wherein the first reference beam and the first measurement beam are interfered at the first image sensor to generate a first measurement signal; and wherein the second reference beam and the second measurement beam are interfered at the second image sensor to generate a second measurement signal.

4. The position encoder of claim 3 further comprising a control system that receives the first measurement signal and the second measurement signal, the control system monitoring the relative movement between the first object and the second object based at least in part on the first measurement signal and the second measurement signal.

5. The position encoder of claim 4 wherein the control system applies a drift compensation algorithm to the first measurement signal to compensate for position drift of the first image sensor, and applies the drift compensation algorithm to the second measurement signal to compensate for position drift of the second image sensor.

6. The position encoder of claim 1 wherein the illumination system includes a laser diode that launches the illumination beam into free space toward the optical element.

7. The position encoder of claim 1 wherein the transmitted beam impinging on the grating is approximately normally incident on the grating.

8. The position encoder of claim 1 wherein each of the first image sensor and the second image sensor includes a one-dimensional array of detector elements.

9. A stage assembly including a stage that retains a device, a base that supports the stage, and the position encoder of claim 1 that monitors movement of the device relative to the base.

10. The position encoder of claim 1 wherein the first measurement beam that is diffracted by the grating is transmitted back though the second optical surface and the first optical surface of the optical element and is then directed toward the first image sensor; and wherein the second measurement beam that is diffracted by the grating is transmitted back through the second optical surface and the first optical surface of the optical element and is then directed toward the second image sensor.

11. The position encoder of claim 1 wherein the illumination system includes a single illumination source fiber that directs the illumination beam at the optical element.

12. The position encoder of claim 1 wherein the illumination system directs the illumination beam having a substantially spherical wavefront to the first optical surface of the optical element.

13. The position encoder of claim 1 wherein the optical element is substantially wedge-shaped.

14. The position encoder of claim 1 wherein at least one of the first optical surface and the second optical surface is a substantially curved surface.

15. The position encoder of claim 1 wherein at least one of the first optical surface and the second optical surface is a substantially planar surface.

16. The position encoder of claim 1 wherein the second transmitted beam is directed at and impinges on the grating in a single pass to create the first measurement beam and the second measurement beam.

17. A position encoder for monitoring relative movement between a first object and a second object, the position encoder comprising:
a grating that is coupled to the first object; and
an image sensor assembly that is coupled to the second object, the image sensor assembly including a first image sensor; a second image sensor that is spaced apart from the first image sensor; an optical element that includes a first optical surface and a second optical surface that is spaced apart from the first optical surface; and an illumination system that directs an illumination beam at the optical element to create (i) a first reference beam that is reflected by the first optical surface and directed at the first image sensor, (ii) a second reference beam that is reflected by the second optical surface and directed at the second image sensor, and (iii) a transmitted beam that is transmitted through the optical element and is directed at and impinges on the grating to create a first measurement beam that is diffracted by the grating and directed at the first image sensor, and a second measurement beam that is diffracted by the grating and directed at the second image sensor;
wherein the optical element is substantially wedge-shaped; and
wherein the first optical surface is at a wedge angle relative to the second optical surface of between approximately five degrees and thirty degrees.

18. The position encoder of claim 17 wherein the first optical surface of the optical element is positioned at a position angle of between approximately zero degrees and fifteen degrees relative to a horizontal plane that is substantially parallel to a plane of the grating.

19. A position encoder for monitoring relative movement between a first object and a second object, the position encoder comprising:
a grating that is coupled to the first object; and
an image sensor assembly that is coupled to the second object, the image sensor assembly including a first image sensor; a second image sensor that is spaced apart from the first image sensor; an optical element that includes a first optical surface and a second optical surface that is spaced apart from the first optical surface; and an illumination system that directs an illumination beam at the optical element to create (i) a first reference beam that is reflected by the first optical surface and directed at the first image sensor, (ii) a second reference beam that is reflected by the second optical surface and directed at the second image sensor, and (iii) a transmitted beam that is transmitted through the optical element and is directed at and

Assignees

• Nikon Corp

Inventors

• Liu Zhiqiang
• Goodwin Eric
• Goldstein Goldie

Classifications

• G01D5/38 Primary

  by diffraction gratings · CPC title

• G03F7/70516

  Calibration of components of the microlithographic apparatus, e.g. light sources, addressable masks or detectors · CPC title

• G03F7/70775 Primary

  Position control, e.g. interferometers or encoders for determining the stage position · CPC title

• G01B11/002

  for measuring two or more coordinates · CPC title