EP-4741923-A1 - RADIATION SOURCE, EUV UTILIZATION APPARATUS, AND METHOD

EP4741923A1EP 4741923 A1EP4741923 A1EP 4741923A1EP-4741923-A1

Abstract

There is provided a radiation source comprising a laser system, wherein the laser system is arranged to transport a laser beam from a source to a target region along a beam path, the beam path including at least one optical element in thermal communication with a vapour chamber arranged to distribute thermal energy provided by the laser beam and to cool the optical element in combination with a heat sink. Also provided is an EUV utilization apparatus including the radiation as well as a method of operating the radiation. Also described is the use of such a radiation source, EUV utilization apparatus or method in an EUV utilization method or apparatus.

Inventors

JANSSEN, Toni, Wil, Mathijs

Assignees

ASML Netherlands B.V.

Dates

Publication Date: 20260513
Application Date: 20241112

Claims (15)

A radiation source comprising a laser system, wherein the laser system is arranged to transport a laser beam from a source to a target region along a beam path, the beam path including at least one optical element in thermal communication with a vapour chamber arranged to distribute thermal energy provided by the laser beam and to cool the optical element in combination with a heat sink.
The radiation source according to claim 1, wherein the optical element comprises a reflective surface configured to reflect incident laser light and the reflective surface comprises a wall of the vapour chamber.
The radiation source according to claim 2, wherein the reflective surface is a copper reflective surface or a coated surface configured to reflect incident carbon dioxide laser light.
The radiation source according to any preceding claim, wherein the heat sink is an actively or passively cooled heat sink.
The radiation source according to any preceding claim, wherein the optical element is directly or indirectly cooled.
The radiation source according to any preceding claim, wherein the laser system is a carbon dioxide laser system.
The radiation source according any preceding claim, wherein the radiation source includes at least two optical elements, wherein a first optical element is a beam transport system mirror or a final focus assembly mirror, and a second optical element is a high power drive laser mirror, and wherein the first and second optical elements are cooled by respective heat sinks in thermal communication with a common conditioning fluid.
The radiation source according to claim 7, wherein the common conditioning fluid comprises water.
The radiation source according to any preceding claim, wherein the optical element is a mirror or an aperture.
An EUV utilization apparatus including the radiation source according to any of claims 1 to 9.
The EUV utilization apparatus according to claim 10, wherein the EUV utilization apparatus is a lithographic apparatus, an inspection apparatus, or a metrology apparatus.
A method of operating a radiation source, the method including: i) generating a laser beam; ii) illuminating an optical element with the laser beam, the optical element configured to reflect the laser beam; iii) providing a vapour chamber comprising a first face configured to reflect the laser beam and a second face configured to cool vapour within the chamber; iv) providing a conditioning fluid to the vapour chamber to condition vapour therein and consequently condition the optical element.
The method according to claim 12, wherein the method includes providing the conditioning fluid to the vapour chamber and to another optical element.
The use of the radiation source according to any of claims 1 to 9, the EUV utilization apparatus according to claim 10 or 11, or the method according to claim 12 or 13 in an EUV utilisation method or apparatus.
The use according to claim 14, wherein the EUV utilization method or apparatus is a lithographic apparatus or method, an inspection apparatus or method, or a metrology apparatus or method.

Description

FIELD The present invention relates to a radiation source. The radiation may have particular, but not exclusive, relevance to an EUV utilization apparatus, such as a lithographic apparatus or a metrology apparatus. The present invention also therefore relates to an EUV utilization apparatus, such as a lithographic apparatus or a metrology apparatus. In addition, the present invention relates to a method of operating a radiation source as well as the use of such a source, apparatus or method in an EUV utilization method or apparatus. The present invention has particular, but not exclusive application, to a drive laser of an EUV utilization apparatus. BACKGROUND Light generated by means of a radiation source can be used by exposure apparatuses for semiconductor manufacturing processes. Examples of such exposure apparatuses are a lithographic apparatus, a metrology, or an inspection apparatus, such as a mask inspection apparatus or an actinic mask inspection apparatus. A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (e.g., a photoresist or resist) provided on a substrate. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses EUV radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm. EUV radiation may be produced by a laser produced plasma (LPP) radiation source. Within an LPP radiation source, a laser beam may be used to irradiate fuel droplets so as to produce a plasma which will emit EUV radiation. The laser beam may be provided from a radiation source, such as a carbon dioxide laser. A problem associated with existing radiation sources is that optical elements within the radiation sources are exposed to high-powered laser light, which causes the optical elements to heat up. Such heating can cause deformation or damage to the optical elements, and so it is necessary to provide cooling to the optical elements. The requirement to provide cooling to the optical elements requires the addition of additional cooling lines and associated cooling equipment It may be desirable to provide a radiation source in which optical elements are cooled more efficiently and more simply that disclosed or suggested by the prior art. SUMMARY According to a first aspect of the invention, there is provided a radiation source comprising a laser system, wherein the laser system is arranged to transport a laser beam from a source to a target region along a beam path, the beam path including at least one optical element in thermal communication with a vapour chamber arranged to distribute thermal energy provided by the laser beam and to cool the optical element in combination with a heat sink. In a radiation source, a laser beam is transported along a beam path via optical elements. Although the optical elements are configured to reduce the amount of energy absorbed from the laser beam, it is inevitable that when the laser beam illuminates the optical element some energy is absorbed causing the optical element to heat up. Heating up of the optical element can cause deformation or even damage to the optical element and so cooling is utilized to control the temperature of the optical element. In existing cooling systems, the cooling is effected by either direct cooling or indirect cooling. In direct cooling, there are channels, passages, pipes, or similar through which a cooling fluid, such as water, is passed and which thereby cools an optical element comprising the cooling channels, passages, pipes or similar. Examples of such direct cooled optical elements include mirrors of a beam transport system and final focus assembly. The cooling fluid thereby directly cools a slab under the optical element. As such, the cooling channels are integrated into the optical element. In indirect cooling, the cooling fluid, such as water, is used to cool an optical element holder rather than the optical element itself, and heat is transferred through the optical element to the optical element holder. Since the optical elements are generally made of copper and the optical elements are generally made of a different material, such as aluminium, there are two separate cooling fluid circuits, each requiring its own pipework, control mechanism, and cooling units. By providing an optical element with a vapour chamber arranged to distribute thermal energy provided by the laser beam and to cool the optical element