# US 2021/0344157 A1 · Pulse Stretcher and Method

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- Number: US 2021/0344157 A1
- Document ID: US20210344157A1
- Status: Published application
- Kind: A1
- Application number: 17/268,778
- Filed: 2019-08-05
- Published: 2021-11-04
- Earliest claimed: 2018-08-22
- Assignees: ASML Netherlands B.V.
- Applicants: ASML Netherlands B.V.
- Inventors: Herman Philip GODFRIED; Wilhelmus Patrick Elisabeth Maria OP 'T ROOT
- Web page: https://patentgrep.com/patent/US20210344157A1

## CPC

- H01S 3/0057: {Temporal shaping, e.g. pulse compression, frequency chirping (soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108)}
- G02B 27/144: {using partially transparent surfaces without spectral selectivity (G02B27/147 takes precedence)}
- G02B 27/48: Laser speckle optics
- G02F 1/0102: {Constructional details, not otherwise provided for in this subclass}
- G03F 7/7015: {Details of optical elements}
- G03F 7/70583: {Speckle reduction, e.g. coherence control or amplitude/wavefront splitting}
- G02F 2203/50: Phase-only modulation
- G03F 7/70041: {by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control}
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

An apparatus (10) for increasing a pulse length of a pulsed radiation beam, the apparatus comprising: a beam splitter (16) configured to split an input radiation beam (18) into a first beam (24) and a second beam (22); an optical arrangement (12,14), wherein the beam splitter and the optical arrangement are configured such that at least a portion of the first beam is recombined with the second beam into a modified beam after an optical delay of the first beam caused by the optical arrangement; and at least one optical element (30) in an optical path of the first beam, the at least one optical element configured such that the phase of different parts of a wavefront of the first beam is varied to reduce coherence between the first beam and the second beam.

## Claims

### Claim at position 1

-15. (canceled)

### Claim 16

An apparatus for increasing a pulse length of a pulsed radiation beam, the apparatus comprising:
a beam splitter configured to split an input radiation beam into a first beam and a second beam;
an optical arrangement, wherein the beam splitter and the optical arrangement are configured such that at least a portion of the first beam is recombined with the second beam into a modified beam after an optical delay of the first beam caused by the optical arrangement; and
at least one optical element in an optical path of the first beam, the at least one optical element comprises phase regions across a surface of the at least one optical element configured such that the phase of different parts of a wavefront of the first beam is varied to reduce coherence between the first beam and the second beam,
wherein the at least one optical element is configured such that the angle at which the radiation is diffracted from the at least one optical element is less than a fraction of the acceptance angle of the radiation in an optical column, the fraction being the reciprocal of the number of first beams that substantially contribute to the transmitted intensity of the modified beam.

### Claim 17 (depends on 16)

The apparatus of claim 16, wherein the phase regions have heights that vary across the surface of the at least one optical element to provide the phase variation to the different parts of the wavefront of the first beam.

### Claim 18 (depends on 16)

The apparatus of claim 16, wherein the at least one optical element is configured such that the pitch of the at least one optical element is less than the spatial coherence length of the input radiation beam.

### Claim 19 (depends on 16)

The apparatus of claim 16, wherein the at least one optical element is configured such that the pitch of the at least one optical element is non-commensurate with the spatial coherence length of the input radiation beam.

### Claim 20 (depends on 16)

The apparatus of claim 16, wherein the at least one optical element is configured such that the phase regions are actively modifiable to change the phase variation to the different parts of the wavefront of the first beam.

### Claim 21 (depends on 16)

The apparatus of claim 16, wherein the at least one optical element is a transmissive optical element that is configured such that the phase of the different parts of the wavefront of the first beam is varied after transmission through the transmissive optical element.

### Claim 22 (depends on 21)

The apparatus of claim 21, wherein the at least one optical element comprises at least one of an electrooptic material and a magnetooptical material.

### Claim 23 (depends on 16)

The apparatus of claim 16, wherein the at least one optical element is a reflective optical element that is configured such that the phase of the different parts of the wavefront of the first beam is varied after reflection from the reflective optical element.

### Claim 24 (depends on 23)

The apparatus of claim 23, wherein the beam splitter comprises the reflective optical element.

### Claim 25 (depends on 16)

The apparatus of claim 16, wherein the optical arrangement is a con-focal resonator including a first con-focal mirror and a second con-focal mirror.

### Claim 26 (depends on 16)

The apparatus of claim 16, wherein the apparatus is located in or at the exit of at least one of a laser, an excimer laser, a solid state laser, a solid state oscillator, a master oscillator, a power amplifier, a master oscillator power amplifier, a power oscillator, a master oscillator power oscillator, and a hybrid laser.

### Claim 27 (depends on 26)

The apparatus of claim 26, wherein the apparatus is located between at least one of the master oscillator and the power amplifier, the master oscillator and the power oscillator, the solid state oscillator and the power amplifier, and the solid state oscillator and the power oscillator.

### Claim 28 (depends on 16)

A lithographic apparatus comprising the apparatus of claim 16.

### Claim 29

A method for increasing a pulse length of a pulsed radiation beam using an apparatus, the method comprising:
passing an input radiation beam through a beam splitter of the apparatus to split the input radiation beam into a first beam and a second beam;
passing the first beam through an optical arrangement of the apparatus, wherein the beam splitter and the optical arrangement are configured such that at least a portion of the first beam is recombined with the second beam into a modified beam after an optical delay of the first beam caused by the optical arrangement; and
varying the phase of different parts of a wavefront of the first beam using at least one optical element in an optical path of the first beam to reduce coherence between the first beam and the second beam.

### Claim 30 (depends on 29)

The method of claim 29, wherein the at least one optical element comprises phase regions across a surface of the at least one optical element, the phase regions configured to provide the phase variation to the different parts of the wavefront of the first beam.