EP-4741922-A1 - WAVELENGTH SELECTION SYSTEM

EP4741922A1EP 4741922 A1EP4741922 A1EP 4741922A1EP-4741922-A1

Abstract

A wavelength selection system comprising an actuatable reflector configured to reflect a radiation beam, and an optical filter configured to receive the reflected radiation beam, wherein the actuatable reflector is moveable between different orientations which direct the radiation beam to different positions on the optical filter, or at different angles of incidence on the optical filter, such that the optical filter selectively filters different wavelengths of the radiation beam, and wherein the wavelength selection system further comprises a dispersive element configured to apply wavelength dispersion to the radiation beam before the radiation beam is incident upon the optical filter.

Inventors

ASSENDELFT, Joep
ÖZTÜRK, Fahri Emre
ZHOU, Zili

Assignees

ASML Netherlands B.V.

Dates

Publication Date: 20260513
Application Date: 20241106

Claims (15)

A wavelength selection system comprising: an actuatable reflector configured to reflect a radiation beam, and an optical filter configured to receive the reflected radiation beam; wherein the actuatable reflector is moveable between different orientations which direct the radiation beam to different positions on the optical filter, or at different angles of incidence on the optical filter, such that the optical filter selectively filters different wavelengths of the radiation beam; and wherein the wavelength selection system further comprises a dispersive element configured to apply wavelength dispersion to the radiation beam before the radiation beam is incident upon the optical filter.
The wavelength selection system of claim 1, wherein the optical filter is a continuously variable optical filter having a wavelength transmission which varies continuously as a function of position on the optical filter.
The wavelength selection system of claim 2, wherein the dispersive element is configured to provide the radiation beam with a wavelength distribution which increases in an opposite direction to a direction in which a filter transition wavelength of the continuously variable optical filter increases.
The wavelength selection system of claim 2 or claim 3, wherein the continuously variable optical filter is one of a pair of continuously variable optical filters that are provided in series.
The wavelength selection system of claim 4, wherein at least one of the continuously variable optical filters is actuatable in a direction which is generally perpendicular to an optical axis of the wavelength selection system.
The wavelength selection system of any preceding claim, wherein the actuatable reflector is configured to move the radiation beam in two dimensions.
The wavelength selection system of claim 6, wherein the optical filter is one of a plurality of optical filters selectable through movement of the radiation beam by the actuatable reflector.
The wavelength selection system of any preceding claim, wherein the dispersive element is located upstream of the actuatable reflector.
The wavelength selection system of any preceding claim, wherein the dispersive element is a prism.
The wavelength selection system of claim 9, wherein the prism is actuatable.
The wavelength selection system of any preceding claim, wherein the wavelength selection system further comprises a second actuatable reflector located downstream of the optical filter, the second actuatable reflector being configured to direct a filtered radiation beam received from the optical filter to an output location.
The wavelength selection system of any preceding claim, wherein the wavelength selection system further comprises a second dispersive element located downstream of the optical filter, the second dispersive element being configured to remove or reduce any wavelength dispersion present in the filtered radiation beam received from the optical filter.
A metrology tool comprising the wavelength selection system of any preceding claim.
A lithographic apparatus comprising the wavelength selection system of claim 12 or the metrology tool of claim 13.
A method comprising using an actuatable reflector to direct a radiation beam onto an optical filter, the radiation beam being incident on the optical filter at a position or with an angle of incidence that is selected via an orientation of the actuatable reflector, such that the optical filter selectively filters different wavelengths of the radiation beam; wherein the method further comprises applying a wavelength dispersion to the radiation beam before the radiation beam is incident upon the optical filter.

Description

FIELD The present invention relates to a wavelength selection system. The wavelength selection system may form part of a metrology tool. The wavelength selection system may form part of a lithographic apparatus. BACKGROUND 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 (also often referred to as "design layout" or "design") at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer). Metrology tools, such as a scatterometer, topography measurement system, or position measurement system are used to measure properties of substrates. The measurements may be performed after exposure of a substrate. The measurements may be used to adjust operation of the lithographic apparatus that exposed the substrate to improve pattern reproduction. Adjustments may include modifying the illumination scheme and/or, adjusting the projection optics. The properties of the radiation used by a metrology tool may affect the type and quality of measurements that may be performed. For some applications, it may be advantageous to use multiple radiation wavelengths to measure a substrate. Multiple different wavelengths may be able to propagate, irradiate, and scatter off a metrology target with no or minimal interference with other wavelengths. Therefore different wavelengths may for example be used to obtain more metrology data. The different wavelengths may for example be provided as a sequence of different wavelengths (i.e. a series of wavelengths). Different radiation wavelengths may also be able to interrogate and discover different properties of a metrology target. A broadband radiation source may provide a broadband radiation beam. A wavelength selection system may be used to select a wavelength from the broadband radiation beam to illuminate a substrate for a measurement, and may then be used to select another wavelength to illuminate the substrate for a subsequent measurement. It may be difficult and/or expensive to generate radiation with desired wavelengths. SUMMARY According to a first aspect of the invention there is provided a wavelength selection system comprising an actuatable reflector configured to reflect a radiation beam, and an optical filter configured to receive the reflected radiation beam, wherein the actuatable reflector is moveable between different orientations which direct the radiation beam to different positions on the optical filter, or at different angles of incidence on the optical filter, such that the optical filter selectively filters different wavelengths of the radiation beam, and wherein the wavelength selection system further comprises a dispersive element configured to apply wavelength dispersion to the radiation beam before the radiation beam is incident upon the optical filter. Because the radiation beam is wavelength dispersed when it is incident upon the optical filter, the intensity of radiation at the optical filter is reduced. This advantageously reduces a risk of damage being caused to the optical filter. For a given position or angle of the radiation beam on the optical filter the selectively filtered wavelengths may comprise a central wavelength and an associated bandwidth. Different positions of the radiation beam on the optical filter may provide an output radiation beam having different central wavelengths. The optical filter may be a continuously variable optical filter having a wavelength transmission which varies continuously as a function of position on the optical filter. The dispersive element may be configured to provide the radiation beam with a wavelength distribution which increases in an opposite direction to a direction in which a filter transition wavelength of the continuously variable optical filter increases. The continuously variable optical filter may be one of a pair of continuously variable optical filters that are provided in series. At least one of the continuously variable optical filters may be actuatable in a direction which is generally perpendicular to an optical axis of the wavelength selection system. The optical filter may provide filtering determined by an angle of incidence of the radiation beam, and wherein a pair of focusing lenses are provided between the actuatable reflector an the optical filter. The pair of focusing lenses may be configured to form a demagnified image of the radiation beam at the actuatable reflector. The actuatable reflector may be configured to move the radiation beam in two dimensions. The optical filter may be one of a plurality of optical filters selectable through movement of the radiation beam by the actuatable reflector. The dispersive element may be located upstream of the actuatable reflector. The dispersive element may be a prism. The prism m