Interferometer system and lithographic apparatus

Patent metadata

Field	Value
Publication number	US-12305979-B2
Application number	US-202118027851-A
Country	US
Kind code	B2
Filing date	Aug 20, 2021
Priority date	Oct 12, 2020
Publication date	May 20, 2025
Grant date	May 20, 2025

Abstract

Interferometer system including a first detector for receiving a first measurement beam travelling to a reference surface; a second detector for receiving a second measurement beam travelling to the target surface; a reference variable delay path and/or measurement variable delay path and a delay path controller for adapting a delay length. A reference spectral coherence pulse occurs at the first detector, at a reference coherence arrangement and a measurement spectral coherence pulse at the second detector at a measurement coherence arrangement. A control unit receives a reference coherence signal from the first detector, and a measurement coherence signal from the second detector, and determines a zero-position of the target surface based on the reference coherence signal and the measurement coherence signal, and based on the reference coherence arrangement and the measurement coherence arrangement and/or a delay path difference between the reference coherence arrangement and the measurement coherence arrangement.

First claim

The invention claimed is:

1. An interferometer system for determining a position of a target surface, wherein the interferometer system comprises:
a first detector configured to receive a first reference beam that is adapted to travel a first reference beam path including a reference beam path, and receive a first measurement beam that is adapted to travel a first measurement beam path including a measurement beam path and a reference axis path determined by a reference surface;
a second detector configured to receive a second reference beam that is adapted to travel a second reference beam path including the reference beam path, and receive a second measurement beam that is adapted to travel a second measurement beam path including the measurement beam path and a measurement axis path determined by the target surface; and
a delay path controller configured to adapt a delay length of: a reference variable delay path which is part of the reference beam path, or a measurement variable delay path which is part of the measurement beam path, or both the reference variable delay path and measurement variable delay path,
wherein during operational use:
a reference spectral coherence pulse of the first reference beam and the first measurement beam occurs at the first detector for the delay length that corresponds to a reference coherence arrangement, and
a measurement spectral coherence pulse of the second reference beam and the second measurement beam occurs at the second detector for the delay length that corresponds to a measurement coherence arrangement; and

a control unit configured to:
receive a reference coherence signal from the first detector, and a measurement coherence signal from the second detector; and
determine a zero-position of the target surface based:
on the reference coherence signal and the measurement coherence signal; and
on the reference coherence arrangement and the measurement coherence arrangement, or a delay path difference between the reference coherence arrangement and the measurement coherence arrangement, or the reference coherence arrangement, the measurement coherence arrangement and the delay path difference.

2. The interferometer system according to claim 1 , further comprising a reference beam path delay for increasing or decreasing a length of the reference beam path relative to a length of the measurement beam path.

3. The interferometer system according to claim 1 , further comprising a broadband radiation source configured to emit broadband radiation forming at least a part of the first and second measurement beam and the first and second reference beam,
wherein, during operational use, the broadband radiation emitted by the broadband radiation source is adapted to cause the reference spectral coherence pulse and the measurement spectral coherence pulse.

4. The interferometer system according to claim 1 , further comprising a narrowband radiation source configured to emit narrowband radiation forming at least a part of the first and second measurement beam and the first and second reference beam.

5. The interferometer system according to claim 4 ,
wherein the delay path controller is configured to, during operational use, adapt the delay length at least until the reference spectral coherence pulse and the measurement spectral coherence pulse have occurred; and
wherein the control unit is configured to determine the zero-position of the target surface based on the narrowband radiation received by:
the first detector, or
the second detector, or
a first reference detector between a reference coherence time and a measurement coherence time, or
any combination selected from: the first detector, the second detector or the first reference detector between the reference coherence time and the measurement coherence time.

6. The interferometer system according to claim 4 , further comprising a narrowband modulator configured to modulate the narrowband radiation forming part of the first and second measurement beam to be at a shifted frequency or phase relative to the narrowband radiation forming part of the first and second reference beam.

7. The interferometer system according to claim 6 , wherein the delay path controller is configured to maintain the delay length at the reference coherence arrangement, and
wherein the control unit is configured to determine the zero-position of the target surface based on the length of the measurement axis path being equal to a length of the reference axis path when the measurement spectral coherence pulse is detected.

8. The interferometer system according to claim 6 , wherein the narrowband light source is configured to add the narrowband radiation to:
the reference beam path downstream of the reference variable delay path, or
the measurement beam path downstream of the measurement variable delay path, or
both the reference beam path downstream of the reference variable delay path and the measurement beam path downstream of the measurement variable delay path.

9. The interferometer system according to claim 3 , further comprising a broadband modulator configured to modulate the broadband radiation forming part of the first and second measurement beam to be at a shifted frequency or phase relative to the broadband radiation forming part of the first and second reference beam.

10. The interferometer system according to claim 1 , further comprising a first reference detector configured to receive:
the first measurement beam, or the second measurement beam, or both the first measurement beam and second measurement beam; and
the first reference beam, or the second reference beam, or both the first reference beam and the second reference beam,

wherein the first reference detector is arranged downstream of:
the reference variable delay path, or
the measurement variable delay path, or
both the reference variable delay path and measurement variable delay path.

11. The interferometer system according to claim 10 , further comprising a second reference detector configured to receive:
the first measurement beam, or the second measurement beam, or both the first measurement beam and second measurement beam; and
the first reference beam, or the second reference beam, or both the first reference beam and second reference beam,

wherein the second reference detector is arranged upstream of:
the reference variable delay path, or
the measurement variable delay path, or
both the reference variable delay path and measurement variable delay path; and

wherein the control unit is configured to:
receive a first reference detector signal from the first reference detector;
receive a second reference detector signal from the second reference detector; and
determine the delay length based on the first reference detector signal and the second reference detector signal.

12. The interferometer system according to claim 11 , wherein the reference beam path comprises a longer delayed beam path configured to guide a longer delayed beam, and a shorter delayed beam path configured to guide a shorter delayed beam, and
wherein the longer delayed beam path has a length that is greater than a length of the shorter delayed beam path.

13. The interferometer system according to claim 1 , further comprising one or more further detectors, each configured to receive:
a respective further reference beam that is adapted to travel a respective further reference beam path including the reference beam path, and
a respective further measurement beam that is adapted to travel a respective further measurement beam path including the measurement beam path and a respecti

Assignees

• Asml Netherlands Bv

Inventors

• Jansen Maarten Jozef

Classifications

• G01B2290/45

  Multiple detectors for detecting interferometer signals · CPC title

• G01B9/02091

  Tomographic interferometers, e.g. based on optical coherence · CPC title

• G01B2290/60

  Reference interferometer, i.e. additional interferometer not interacting with object · CPC title

• G01B9/02065

  using a second interferometer before or after measuring interferometer · CPC title

• G01B9/02028 Primary

  Two or more reference or object arms in one interferometer · CPC title