# US 10,481,498 B2 · Droplet generator for lithographic apparatus, EUV source and lithographic apparatus

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- Number: US 10,481,498 B2
- Document ID: US10481498B2
- Status: Granted
- Kind: B2
- Application number: 16/061,847
- Filed: 2016-12-15
- Published: 2018-12-20
- Granted: 2019-11-19
- Earliest claimed: 2015-12-17
- Assignees: ASML Netherlands B.V.
- Applicants: ASML Netherlands B.V.
- Inventors: Johan Frederik Dijksman; Bastiaan Lambertus Wilhelmus Marinus van de Ven; Koen Gerhardus Winkels; Theodorus Wilhelmus Driessen; Georgiy O. Vaschenko; Peter Michael Baumgart; Wilhelmus Henricus Theodorus Maria Aangenent; Jan Okke Nieuwenkamp; Wim Ronald Kampinga; Jari Ruotsalainen
- Web page: https://patentgrep.com/patent/US10481498B2

## CPC

- G03F 7/70033: {by plasma extreme ultraviolet [EUV] sources}
- H05G 2/0023: {Constructional details of the ejection system}
- 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)
- H05G: X-RAY TECHNIQUE (investigating or analysing materials by the use of X-rays G01N23/00; apparatus for X-ray photography G03B42/02; X-ray tubes H01J35/00; TV systems having X-ray input H04N5/321)

## Abstract

Droplet generators, such as used in an EUV radiation source, and associated EUV radiation sources and lithographic apparatuses. A droplet generator can include a nozzle assembly to emit the fuel as droplets, the nozzle assembly being within a pressurized environment at substantially the same pressure as the fuel pressure within the droplet generator. A droplet generator can include an actuator in contact with and biased against a pump chamber by means of a biasing mechanism having an actuator support biased against the actuator. The actuator acts on the fuel within the pump chamber to create droplets. The actuator support has a material with a greater coefficient of thermal expansion than its surrounding structure, such that it is moveable within the surrounding structure at ambient temperature, but expands against the surrounding structure at an operating temperature, so as to clamp the actuator support against the surrounding structure at the operating temperature.

## Claims

### Claim 1

A droplet generator configured for use in a laser-produced plasma radiation source and configured for providing a stream of droplets of a liquid fuel at an exit, wherein:
the droplet generator comprises:
a nozzle assembly;
an actuator; and
a pump chamber;
the pump chamber is configured to receive the liquid fuel under an input pressure higher than an exit pressure at the exit;
the pump chamber is located between the actuator and the nozzle assembly;
the actuator is configured to establish a pressure change in the liquid fuel held in the pump chamber;
the nozzle assembly comprises:
an inlet at the pump chamber;
a nozzle structure at the exit of the droplet generator;
a duct configured for establishing a path of the liquid fuel between the inlet and the exit;
the droplet generator has a first chamber configured for accommodating the nozzle assembly;
the first chamber has a first inlet for receipt of a gas under a further pressure that is substantially the same as the input pressure.

### Claim 2 (depends on 1)

The droplet generator of claim 1, wherein:
the droplet generator has a second chamber configured to accommodate the actuator; and
the second chamber has a second inlet for receipt of the gas under the further pressure.

### Claim 3 (depends on 1)

The droplet generator of claim 1, wherein
the nozzle structure comprises a nozzle plate having an orifice being in fluid communication with the duct; and
the orifice is configured to have the fuel exit the droplet generator to form the stream of the droplets.

### Claim 4 (depends on 3)

The droplet generator of claim 3, wherein the nozzle structure comprises of one of: silicon, a compound of silicon, tungsten, molybdenum, rhenium, diamond, tantalum, or titanium.

### Claim 5 (depends on 1)

The droplet generator of claim 1, wherein:
the actuator is configured to establish the pressure change via a wall of the pump chamber; and
the droplet generator comprises a spring configured to bias the actuator against the wall.

### Claim 6 (depends on 2)

The droplet generator of claim 2, wherein:
the actuator is configured to establish the pressure change via a wall of the pump chamber; and
the droplet generator comprises a spring configured to bias the actuator against the wall.

### Claim 7 (depends on 1)

The droplet generator of claim 1, wherein:
the droplet generator comprises an actuator support configured to support the actuator;
the actuator support includes a first part and a second part that form an articulated joint allowing rotational movement between the first part and the second part so as to enable alignment of the actuator support and the actuator.

### Claim 8 (depends on 2)

The droplet generator of claim 2, wherein:
the droplet generator comprises an actuator support configured to support the actuator;
the actuator support includes a first part and a second part that form an articulated joint allowing rotational movement between the first part and the second part so as to enable alignment of the actuator support and the actuator.

### Claim 9 (depends on 1)

The droplet generator of claim 1, wherein:
the actuator is configured to establish the pressure change via a wall of the pump chamber;
the droplet generator comprises a spring configured to bias the actuator against the wall;
the droplet generator comprises an actuator support configured to support the actuator; and
the actuator support includes a first part and a second part that form an articulated joint allowing rotational movement between the first part and the second part so as to enable alignment of the actuator support and the actuator.

### Claim 10 (depends on 2)

The droplet generator of claim 2, wherein:
the actuator is configured to establish the pressure change via a wall of the pump chamber;
the droplet generator comprises a spring configured to bias the actuator against the wall;
the droplet generator comprises an actuator support configured to support the actuator; and
the actuator support comprises a first part and a second part that form an articulated joint allowing rotational movement between the first part and the second part so as to enable alignment of the actuator support and the actuator.

### Claim 11 (depends on 1)

The droplet generator of claim 1, wherein:
the droplet generator comprises an actuator support configured to support the actuator;
the actuator support comprises a first part and a second part that form an articulated joint allowing rotational movement between the first part and the second part so as to enable alignment of the actuator support and the actuator;
the droplet generator comprises a housing configured to accommodate the actuator support and made of a first material having a first coefficient of thermal expansion;
the actuator support comprises a material that has a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion, such that the actuator support is moveable within the housing at ambient temperature, and expands against the housing at an operating temperature of the droplet generator, so as to clamp the actuator support against the housing at the operating temperature.

### Claim 12 (depends on 2)

The droplet generator of claim 2, wherein:
the droplet generator comprises an actuator support configured to support the actuator;
the actuator support includes a first part and a second part that form an articulated joint allowing rotational movement between the first part and the second part so as to enable alignment of the actuator support and the actuator;
the droplet generator comprises a housing configured to accommodate the actuator support and made of a first material having a first coefficient of thermal expansion;
the actuator support comprises a material that has a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion, such that the actuator support is moveable within the housing at ambient temperature, and expands against the housing at an operating temperature of the droplet generator, so as to clamp the actuator support against the housing at the operating temperature.

### Claim 13 (depends on 1)

The droplet generator of claim 1, wherein:
the droplet generator comprises an actuator support configured to support the actuator;
the actuator is configured to establish the pressure change via a wall of the pump chamber;
the droplet generator comprises a spring configured to bias the actuator against the wall; and
the droplet generator comprises a housing configured to accommodate the actuator support and made of a first material having a first coefficient of thermal expansion;
the actuator support comprises a material that has a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion, such that the actuator support is moveable within the housing at ambient temperature, and expands against the housing at an operating temperature of the droplet generator, so as to clamp the actuator support against the housing at the operating temperature.

### Claim 14 (depends on 2)

The droplet generator of claim 2, wherein:
the droplet generator comprises an actuator support configured to support the actuator;
the actuator is configured to establish the pressure change via a wall of the pump chamber;
the droplet generator comprises a spring configured to bias the actuator against the wall; and
the droplet generator comprises a housing configured to accommodate the actuator support and made of a first material having a first coefficient of thermal expansion;
the actuator support comprises a material that has a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion, such that the actuator support is moveable within the housing at ambient temperature, and expands against the housing at an operating temperature of the droplet generator, so as to clamp the actuator support against the housing at the operating temperature.

### Claim 15

A laser-produced plasma radiation source comprising a droplet generator configured for providing a stream of droplets of a liquid fuel at an exit, wherein:
the droplet generator comprises:
a nozzle assembly;
an actuator; and
a pump chamber;
the pump chamber is configured to receive the liquid fuel under an input pressure higher than an exit pressure at the exit;
the pump chamber is located between the actuator and the nozzle assembly;
the actuator is configured to establish a pressure change in the liquid fuel held in the pump chamber;
the nozzle assembly comprises:
an inlet at the pump chamber;
a nozzle structure at the exit of the droplet generator;
a duct configured for establishing a path of the liquid fuel between the inlet and the exit;
the droplet generator has a first chamber configured for accommodating the nozzle assembly;
the first chamber has a first inlet for receipt of a gas under a further pressure that is substantially the same as the input pressure.

### Claim 16 (depends on 15)

The laser-produced plasma radiation source of claim 15, wherein:
the droplet generator has a second chamber configured to accommodate the actuator; and
the second chamber has a second inlet for receipt of the gas under the further pressure.

### Claim 17 (depends on 15)

The laser-produced plasma radiation source of claim 15, wherein
the nozzle structure comprises a nozzle plate having an orifice being in fluid communication with the duct; and
the orifice is configured to have the fuel exit the droplet generator to form the stream of the droplets.

### Claim 18 (depends on 17)

The laser-produced plasma radiation source of claim 17, wherein the nozzle structure comprises one of: silicon, a compound of silicon, tungsten, molybdenum, rhenium, diamond, tantalum, or titanium.

### Claim 19 (depends on 15)

The laser-produced plasma radiation source of claim 15, wherein:
the actuator is configured to establish the pressure change via a wall of the pump chamber; and
the droplet generator comprises a spring configured to bias the actuator against the wall.

### Claim 20 (depends on 15)

The laser-produced plasma radiation source of claim 15, wherein:
the droplet generator comprises an actuator support configured to support the actuator;
the actuator support includes a first part and a second part that form an articulated joint allowing rotational movement between the first part and the second part so as to enable alignment of the actuator support and the actuator.

### Claim 21 (depends on 15)

The laser-produced plasma radiation source of claim 15, wherein:
the droplet generator comprises an actuator support configured to support the actuator; and
the droplet generator comprises a housing configured to accommodate the actuator support and made of a first material having a first coefficient of thermal expansion;
the actuator support comprises a material that has a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion, such that the actuator support is moveable within the housing at ambient temperature, and expands against the housing at an operating temperature of the droplet generator, so as to clamp the actuator support against the housing at the operating temperature.