Two-dimensional position encoder

Patent metadata

Field	Value
Publication number	US-11467506-B2
Application number	US-202117160094-A
Country	US
Kind code	B2
Filing date	Jan 27, 2021
Priority date	Dec 15, 2017
Publication date	Oct 11, 2022
Grant date	Oct 11, 2022

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 having a grating, and a second object whose positional relationship with the first object can be changed at least in a first direction, the position encoder comprising:
an image sensor assembly that is coupled to the second object, the image sensor assembly including (i) a first image sensor having a plurality of pixels that are aligned in a second direction that is different than the first direction; (ii) an optical element; and (iii) an illumination system that generates an illumination beam having a first portion that is diffracted by the grating to create a first measurement beam that is directed by the optical element at the first image sensor, and a second portion that forms a first reference beam that is directed at the first image sensor;
wherein the illumination beam is directed at the optical element;
wherein the optical element includes a first optical surface that reflects the second portion as the first reference beam that is directed at the first image sensor;
wherein the first measurement beam that is diffracted by the grating passes through the first optical surface before being directed at the first image sensor; and
wherein the first measurement beam and the first reference beam are interfered with one another to generate an interference fringe pattern having a pitch in the second direction; and wherein at least a part of the interference fringe pattern is sensed by the first image sensor to monitor the relative movement between the first object and the second object in the first direction.

2. The position encoder of claim 1 wherein the first portion of the illumination beam passes through the first optical surface as a transmitted beam before being diffracted by the grating to create the first measurement beam; and wherein the first measurement beam that is diffracted by the grating passes back through the first optical surface before being directed at the first image sensor.

3. The position encoder of claim 1 wherein the optical element further includes a second optical surface that is spaced apart from the first optical surface; and wherein the first measurement beam that has been diffracted by the grating passes through the second optical surface and the first optical surface before being directed at the first image sensor.

4. The position encoder of claim 3 wherein the first portion passes through the first optical surface and the second optical surface as a transmitted beam before being diffracted by the grating to create the first measurement beam.

5. The position encoder of claim 1 wherein the optical element further includes a second optical surface that is spaced apart from the first optical surface, the second portion passing through the second optical surface and being reflected by the first optical surface as the first reference beam that is directed at the first image sensor; and wherein the first measurement beam that has been diffracted by the grating passes through the second optical surface and the first optical surface before being directed at the first image sensor.

6. The position encoder of claim 5 wherein the first portion passes through the first optical surface and the second optical surface as a transmitted beam before being diffracted by the grating to create the first measurement beam.

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

8. The position encoder of claim 1 wherein the optical element further includes a second optical surface that is spaced apart from the first optical surface, 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.

9. The position encoder of claim 8 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.

10. 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 position encoder further comprises a control system that receives the first measurement signal and monitors the relative movement between the first object and the second object based at least in part on the first measurement signal.

11. The position encoder of claim 10 wherein the control system applies a drift compensation algorithm to the first measurement signal to compensate for position drift of the first image sensor.

12. The position encoder of claim 1 wherein the illumination system includes a single illumination source fiber that launches the illumination beam toward the optical element, and wherein the illumination source fiber launches the illumination beam toward the optical element at an initial beam angle of between approximately two degrees and fifteen degrees relative to an axis that is orthogonal to a plane of the grating.

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

14. 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.

15. The position encoder of claim 1 wherein the first portion is directed at the grating at approximately normal incident on the grating.

16. The position encoder of claim 1 wherein the image sensor assembly further includes a second image sensor having a plurality of pixels that are aligned in a third direction that is different than the first direction and the second direction; wherein the first portion diffracted by the grating further creates a second measurement beam that is directed by the optical element at the second image sensor; wherein the illumination beam includes a third portion that forms a second reference beam that is directed at the second image sensor; and wherein the second measurement beam and the second reference beam are interfered with one another to generate a second interference fringe pattern having a pitch in the third direction, the second interference fringe pattern being sensed by the second image sensor to monitor the relative movement between the first object and the second object in the first direction.

17. The position encoder of claim 16 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.

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

19. 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.

20. A method for monitoring relative movement between a first object having a grating, and a second object whose positional relationship with the first object can be changed at least in a first direction, the method comprising the steps of:
coupling an image sensor assembly to the second object, the image sensor assembly including a first image sensor having a plurality of pixels that are aligned

Assignees

• Nikon Corp

Inventors

• Liu Zhiqiang
• Goodwin Eric
• Goldstein Goldie

Classifications

• G01D5/38 Primary

  by diffraction gratings · CPC title

• G01B11/002

  for measuring two or more coordinates · CPC title

• G03F7/70775 Primary

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

• G03F7/70516

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