Interferometer system, method of determining a mode hop of a laser source of an interferometer system, method of determining a position of a movable object, and lithographic apparatus

Patent metadata

Field	Value
Publication number	US-11719529-B2
Application number	US-202017613124-A
Country	US
Kind code	B2
Filing date	May 11, 2020
Priority date	Jun 11, 2019
Publication date	Aug 8, 2023
Grant date	Aug 8, 2023

Abstract

An interferometer system including: an optical system arranged to split a radiation beam from a laser source into a first beam along a first optical path and a second beam along a second optical path, and recombine the first beam and the second beam to a recombined beam, a detector to receive the recombined beam and to provide a detector signal based on the received recombined beam, and a processing unit, wherein a first optical path length of the first optical path and a second optical path length of the second optical path have an optical path length difference, and wherein the processing unit is arranged to determine a mode hop of the laser source on the basis of a phase shift in the detector signal.

First claim

The invention claimed is:

1. A heterodyne interferometer system to determine a position of a movable object, the interferometer system comprising:
an optical system arranged to split a radiation beam from a laser source into a first beam along a first optical path and a second beam along a second optical path, wherein the optical system is arranged to recombine the first beam and the second beam to a recombined beam,
a detector to receive the recombined beam and to provide a detector signal on the basis of the received recombined beam, and
a processing unit to process the detector signal,
wherein a first optical path length of the first optical path and a second optical path length of the second optical path have an optical path length difference,
wherein the first beam and/or second beam is guided through a frequency shift device to create a frequency difference between a first frequency of the first beam and a second frequency of the second beam,
wherein the processing unit is configured to determine a mode hop of the laser source on the basis of a phase shift in the detector signal resulting from such mode hop.

2. The interferometer system of claim 1 , wherein the optical path difference is selected such that a phase shift resulting from a mode hop is unequal to 2 TT.

3. The interferometer system of claim 1 , wherein the optical path length difference is unequal to k*c/Δf, wherein k is an integer, c is the speed of light and Δf is a frequency difference caused by a mode hop.

4. The interferometer system of claim 1 , wherein the optical path length difference is equal to (r+k)* c/Δf, wherein r is in the range of 0.1 to 0.9, k is an integer, c is the speed of light and Δf is a frequency difference caused by a mode hop.

5. The interferometer system of claim 4 , wherein k is 0, 1 or 2.

6. The interferometer system of claim 1 , wherein the processing unit is configured to observe changes in a derivative of the phase shift in the detector signal in order to determine the mode hop of the laser source.

7. The interferometer system of claim 1 , wherein the recombined beam is used as a reference beam and the detector is a reference detector.

8. The interferometer system of claim 1 , further comprising:
a tunable laser source arranged to provide the radiation beam with a tunable light frequency, and
a fixed frequency laser source to provide a further radiation beam with a fixed light frequency,
wherein the interferometer system is arranged to determine an absolute position of the movable object.

9. A method of determining a position of a movable object using the interferometer system of claim 1 , the method comprising:
measuring a position of the movable object,
determining whether a mode hop of the laser source of the interferometer system occurred during measuring of the position of the movable object,
if no mode hop occurred, using the measured position, and
if a mode hop occurred, ignoring the measurement results associated with the mode hop and/or repeating the measuring the position of the movable object and determining whether a mode hop occurred during measuring.

10. A non-transitory computer-readable medium having instructions therein, the instructions, when executed by a computer system, configured to cause the computer system to cause carrying out of the method as claimed in claim 9 .

11. A lithographic apparatus comprising:
a mask support constructed to support a patterning device having a pattern;
a substrate support constructed to support a substrate;
a projection system arranged to project the pattern onto the substrate, wherein the mask support, substrate support or projection system comprises a movable object; and,
the interferometer system as claimed in claim 1 to determine the position of the movable object.

12. A lithographic apparatus, comprising:
a mask support constructed to support a patterning device having a pattern;
a substrate support constructed to support a substrate having a marker;
a projection system arranged to project the pattern onto the substrate;
an alignment system arranged to measure a position of the marker; and
the interferometer system as claimed in claim 1 ,
wherein the recombined beam is used as a measurement beam and the detector is a measurement detector, and
wherein the measurement beam is reflected on a reflective measurement surface arranged or connected to the projection system or the alignment system before being received by the measurement detector.

13. A lithographic apparatus comprising:
a mask support constructed to support a patterning device having a pattern;
a substrate support constructed to support a substrate;
a projection system arranged to project the pattern onto the substrate, wherein the mask support, substrate support or projection system comprises an object of interest; and
the interferometer system as claimed in claim 1 to determine the position of the object of interest.

14. A method of determining a mode hop of a laser source of an interferometer system, the method comprising:
splitting a radiation beam from the laser source into a first beam which is guided along a first optical path and a second beam which is guided along a second optical path, wherein a first optical path length of the first optical path and a second optical path length of the second optical path have an optical path length difference,
guiding the first beam and/or second beam through a frequency shift device to create a frequency difference between a first frequency of the first beam and a second frequency of the second beam,
recombining the first beam and the second beam into a recombined beam,
providing a detector signal on the basis of the recombined beam, and
processing the detector signal to determine the mode hop of the laser source on the basis of a phase shift in the detector signal resulting from such mode hop.

15. The method of claim 14 , further comprising observing changes in a derivative of the phase shift in the detector signal in order to determine the mode hop of the laser source.

Assignees

• Asml Netherlands Bv

Inventors

• Jansen Maarten Jozef
• Mridha Manoj Kumar
• Van Der Pasch Engelbertus Antonius Fransiscus

Classifications

• G01B9/02057

  by using common path configuration, i.e. reference and object path almost entirely overlapping · CPC title

• G01B9/0205

  of probe head · CPC title

• G01B9/02002 Primary

  using two or more frequencies · CPC title

• G01B9/0207

  Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer · CPC title

• G01J9/02

  by interferometric methods (using interferometers for measuring optically the linear dimensions of objects G01B9/02) · CPC title