Minimization of Abbe error caused by tip or tilt between an encoder head and a wafer stage for arbitrary location of a center of rotation

Patent metadata

Field	Value
Publication number	US-9605948-B2
Application number	US-201514736118-A
Country	US
Kind code	B2
Filing date	Jun 10, 2015
Priority date	Mar 12, 2013
Publication date	Mar 28, 2017
Grant date	Mar 28, 2017

Abstract

Methodology of measuring a position of a wafer with an encoder directing measurement beam(s) of light towards a wafer area that is being contemporaneously patterned in an exposure apparatus. The Abbe error of such measurement is minimized or even negated by combining the data from first and second measurement signals, one of which is defined as complementary, Abbe-error correcting measurement signal for which the induced Abbe error is either opposite to or at least different from the Abbe error corresponding to another, main measurement signal. The combination of the main and Abbe-error correcting signals is performed with a heterodyne interferometer employing a two-dimensional diffraction grating diffracting each of the measurement beams twice.

First claim

The invention claimed is:

1. A measurement system for measuring a position of a workpiece, the system comprising:
a diffraction grating mechanically coupled to the workpiece;
an encoder unit facing said diffraction grating, the encoder unit having first and second encoder heads, said heads configured to produce respectively-corresponding first and second measurement beams incident onto a grating at a respectively corresponding first and second points of incidence and to form first and second first.-order diffraction beams at said first and second points of incidence,
said encoder unit positioned
to reduce first and second separations to a point when an overall Abbe error, calculated based on first and second Abbe errors, is smaller than a first Abbe error and a second Abbe error, wherein
the first separation defined between i) a first point of intersection of a first vector, bisecting an angle formed by the first measurement beam and the corresponding first first-order diffraction beam and ii) a center-of rotation of the workpiece;
the second separation defined between second point of intersection of a second vector, bisecting an angle formed by the second measurement beam and the corresponding second first-order diffraction beam and iv) the center-of rotation; and
the first Abbe error corresponds to measurement data acquired based on a first measurement associated, with the first separation,
the second Abbe error corresponds to measurement data acquired based on a second measurement associated with the first separation.

2. A system according to claim 1 ,
wherein each of the first and second first-order diffraction beams includes first and second wavelengths to define first and second points of intersection of said first and second first-order diffraction beams formed with light at said first and second wavelengths, and
wherein the first and second points of intersection and the center-of-rotation are different points.

3. A system according to claim 2 , wherein the first and second points of intersection are located on the opposite sides of the center-of-rotation.

4. A system according to claim 1 , further comprising
an optical detector, and
programmable processor in operable cooperation with tangible non-transitory storage medium and said encoder unit, said processor programmed to acquire optical data, representing interference of light from the first and second measurement beams after said beams have diffracted twice at the diffraction grating, and to reposition at least one of the first and second encoder heads with respect to the diffraction grating such as to minimize a linear combination of first and second Abbe-errors,
wherein the first Abbe-error is defined by a measurement of the e position with the first measurement beam, and the second Abbe-error is defined by a measurement of the position with the second measurement beam.

5. A system according to claim 1 , wherein said diffraction grating is disposed in a plane located between the workpiece and the encoder unit.

6. A system according to claim 1 , wherein said diffraction grating is a two-dimensional (2D) diffraction grating.

7. An exposure apparatus comprising a system according to claim 6 , said exposure apparatus containing an optical system separated from the encoder unit by the workpiece.

8. An exposure apparatus according to claim 6 , wherein the first and second points of intersection and the center-of-rotation are positioned on an optical axis of said optical system.

9. An exposure system according to claim 7 , wherein the workpiece carrying the diffraction grating on a first side thereof has a wafer on a second side thereof, the first and second sides being opposite to one another.

10. A measurement system for measuring a position of a workpiece, the system comprising:
a stage including a holding surface in contact with the workpiece;
a diffraction grating positioned on an opposite side of the stage with respect to the workpiece; and
an encoder unit facing the diffraction grating, the encoder unit including:
a first encoder head, configured to produce and direct a first measurement beam of light towards a first point on the diffraction grating to form a first diffracted beam of light at said first point,
wherein a first angle, formed by said first measurement beam of light and said first diffracted beam of light at said first point, has a first bisector;

a second encoder head, configured to produce and direct a second measurement beam of light towards a second point on the diffraction grating to form a second diffracted beam of light at said second point,
wherein a second angle, formed by said first measurement beam of light and said second diffracted beam of light at said second point, has a second bisector,

wherein the first and second bisectors cross each other at an intersection point, and
wherein a first separation between the diffraction grating and the intersection point along a direction perpendicular to the diffraction grating is larger than a second separation between the intersection point and the holding surface along said direction.

Assignees

• Nikon Corp

Inventors

• Goodwin Eric Peter
• Liu Zhiqiang

Classifications

• G01B11/14 Primary

  for measuring distance or clearance between spaced objects or spaced apertures (G01B11/26 takes precedence; rangefinders G01C3/00) · CPC title

• G01D5/34

  the beams of light being detected by photocells · CPC title

• G03F7/70775 Primary

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