Two-dimensional position encoder

Patent metadata

Field	Value
Publication number	US-2019187572-A1
Application number	US-201816220624-A
Country	US
Kind code	A1
Filing date	Dec 14, 2018
Priority date	Dec 15, 2017
Publication date	Jun 20, 2019
Grant date	—

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 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.

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 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.

7 . The position encoder of claim 6 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.

8 . 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.

9 . 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.

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

11 . 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.

12 . 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.

13 . A method for monitoring relative movement between a first object and a second object, the method comprising the steps of:
coupling a grating to the first object; coupling an image sensor assembly 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; and directing an illumination beam at the optical element with the illumination system 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.

14 . The method of claim 13 wherein the step of coupling the grating includes the grating being a one-dimensional diffraction grating; and wherein the step of directing includes the first measurement beam being a +1 order first measurement beam, and the second measurement beam being a −1 order second measurement beam.

15 . The method of claim 13 further comprising the steps of interfering the first reference beam and the first measurement beam at the first image sensor to generate a first measurement signal; and interfering the second reference beam and the second measurement beam at the second image sensor to generate a second measurement signal.

16 . The method of claim 15 further comprising the steps of receiving the first measurement signal and the second measurement signal with a control system; and monitoring the relative movement between the first object and the second object with the control system based at least in part on the first measurement signal and the second measurement signal.

17 . The method of claim 16 further comprising the steps of applying a drift compensation algorithm to the first measurement with the control system to compensate for position drift of the first image sensor; and applying the drift compensation algorithm to the second measurement signal with the control system to compensate for position drift of the second image sensor.

18 . The method of claim 13 wherein the step of coupling the image sensor assembly includes the optical element being substantially wedge-shaped, with the first optical surface being at a wedge angle relative to the second optical surface of between approximately five degrees and thirty degrees.

19 . The method of claim 18 wherein the step of coupling the image sensor assembly includes the first optical surface of the optical element being 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.

20 . The method of claim 13 wherein the step of coupling the image sensor assembly includes the illumination system including a single illumination source fiber; wherein the step of directing includes launching the illumination beam toward the optical element with th

Assignees

• Nikon Corp

Inventors

• Liu Zhiqiang
• Goodwin Eric
• Goldstein Goldie

Classifications

• 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

• G01D5/38 Primary

  by diffraction gratings · CPC title