TW202349129A - Method and apparatus for reflecting pulsed radiation - Google Patents

Abstract

Disclosed is an optical arrangement for reflecting pulsed radiation, comprising: an optical retarder and optical reflector. The optical retarder comprises a first axis coinciding with a first linear polarization state and a second axis, orthogonal to the first axis, coinciding with a second linear polarization state. The optical retarder decomposes each pulse of the pulsed radiation into a first pulse component having the first linear polarization state and a second pulse component having the second polarization state and imposes a temporal delay between the first pulse component and the second pulse component of each pulse. The optical reflector comprises an axis of rotation at an angle having a magnitude of substantially 45 degrees with respect to each of the first axis and second axis of the optical retarder, the optical reflector being configured to at least partially reflect the first pulse component and the second pulse component of each pulse.

Description

Methods and devices for reflecting pulsed radiation

The present invention relates to a method and apparatus for reflecting pulsed radiation, particularly when the pulsed radiation is generated from a broadband radiation generator based on a hollow-core photonic crystal fiber.

A lithography device is a machine constructed to apply a desired pattern to a substrate. Lithography devices may be used, for example, in integrated circuit (IC) manufacturing. A lithography apparatus may, for example, project a pattern (also often referred to as a "design layout" or "design") at a patterned device (e.g., a reticle) onto a radiation-sensitive material (e.g., a wafer) provided on a substrate (e.g., a wafer) photoresist) layer.

To project a pattern onto a substrate, a lithography device may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm. Compared to lithography devices that use radiation with a wavelength of, for example, 193 nm, use a lithography device with extreme ultraviolet (EUV) radiation with a wavelength in the range of 4 nm to 20 nm, such as 6.7 nm or 13.5 nm. Can be used to form smaller features on a substrate.

Low-k ₁ lithography can be used to process features that are smaller than the typical resolution limitations of the lithography device. In this program, the resolution formula can be expressed as CD=k ₁ ×λ/NA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics in the lithography device, and CD is the "critical dimension" (usually the smallest printed feature size, but in this case half pitch) and k ₁ is the empirical resolution factor. Generally speaking, the smaller k ₁ is, the more difficult it becomes to reproduce a pattern on a substrate that resembles the shape and size planned by the circuit designer to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection device and/or design layout. These steps include, for example, but are not limited to: optimization of NA, custom illumination schemes, use of phase-shift patterning devices, various optimizations of design layout, such as optical proximity correction (OPC, and sometimes also Referred to as "optical and process correction"), or other methods commonly defined as "Resolution Enhancement Technology" (RET). Alternatively, tight control loops for controlling the stability of the lithography apparatus can be used to improve reproduction of patterns at low k1.

Metrology tools are used in many aspects of the IC manufacturing process, such as as alignment tools to properly position the substrate before exposure, as leveling tools to measure the surface topology of the substrate, for inspection/gauge in process control, for example. Tools based on focus control and scatterometry for measuring exposed and/or etched products. In each case, a radiation source is required. Broadband or white light radiation sources are increasingly used in these metrology applications for a variety of reasons, including measurement robustness and accuracy. Modifications of existing devices for broadband radiation generation will be required.

In a first aspect of the invention there is provided an optical arrangement for reflecting pulsed radiation, comprising an optical retarder comprising a first axis coincident with a first linear polarization state and a third axis coincident with a second linear polarization state. two axes, the first axis and the second axis being orthogonal to each other; the optical retarder configured to receive the pulsed radiation and decompose each pulse of the pulsed radiation into a first pulse component having a first linear polarization state and a second pulse component having a second polarization state; the optical retarder further configured to apply a time delay between the first pulse component and the second pulse component of each pulse; and an optical reflector including an axis of rotation, the The axis of rotation is perpendicular to the plane of incidence of the first pulse component and the second first pulse component on the optical reflector and has a magnitude of substantially 45 degrees relative to each of the first axis and the second axis of the optical retarder. , the optical reflector is configured to at least partially reflect the first pulse component and the second pulse component of each pulse.

In a second aspect of the present invention, a method of setting an optical configuration as in any one of the preceding claims is provided, which includes: identifying the first axis and the second axis of the optical retarder; identifying the rotation axis of the optical reflector ; and rotating one or both of the following: an optical retarder in a first plane defined by the first axis and a second axis and an optical reflector in a plane parallel to the first plane such that the optical The first and second axes of the retarder are each oriented at an angle with the axis of rotation of the optical reflector, the angle having a magnitude of substantially 45 degrees.

Other aspects of the invention include: a radiation source including an optical arrangement according to the first aspect; and a metrology device including such a radiation source.

In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultraviolet (EUV) radiation, e.g. , with wavelengths in the range of 5 to 100 nm).

As used herein, the terms "reticle," "reticle," or "patterned device" may be broadly construed to refer to a general patterned device that can be used to impart a patterned cross-section to an incident radiation beam. The patterned cross-section corresponds to the pattern to be produced in the target portion of the substrate. The term "light valve" may also be used in this context. In addition to classic masks (transmissive or reflective, binary, phase-shifted, hybrid, etc.), other examples of such patterned devices include programmable mirror arrays and programmable LCD arrays.

Figure 1 schematically depicts a lithography apparatus LA. The lithography apparatus LA includes: an illumination system (also called an illuminator) IL configured to regulate a radiation beam B (eg, UV radiation, DUV radiation, or EUV radiation); a mask support (eg, a mask table ) MT, which is constructed to support the patterned device (e.g., photomask) MA and is connected to a first positioner PM configured to accurately position the patterned device MA according to certain parameters; a substrate support (e.g., wafer a truncated table) WT constructed to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection A system (eg, refractive projection lens system) PS configured to project the pattern imparted by the patterned device MA to the radiation beam B onto a target portion C of the substrate W (eg, containing one or more dies).

In operation, the illumination system IL receives a radiation beam from the radiation source SO, eg via the beam delivery system BD. The illumination system IL may include various types of optical components for directing, shaping and/or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and/or other types of optical components or any combination thereof. The illuminator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in the cross-section of the radiation beam at the plane of the patterned device MA.

The term "projection system" PS as used herein should be interpreted broadly to encompass various types of projection systems, including refraction, suitable for the exposure radiation used and/or suitable for other factors such as the use of immersion liquids or the use of vacuum. , reflective, catadioptric, synthetic, magnetic, electromagnetic and/or electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein may be considered to be synonymous with the more general term "projection system" PS.

The lithography device LA may be of the type in which at least part of the substrate may be covered by a liquid with a relatively high refractive index, such as water, in order to fill the space between the projection system PS and the substrate W - this is also called an immersion micro film. More information on infiltration techniques is given in US6952253, which is incorporated herein by reference.

The lithography apparatus LA may also be of the type having two or more substrate supports WT (also known as "double stages"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and/or the step of preparing the substrate W for subsequent exposure may be performed on a substrate W located on one of the substrate supports WT, while Another substrate W on another substrate support WT is used to expose a pattern on the other substrate W.

In addition to the substrate support WT, the lithography apparatus LA may also include a measurement stage. The measurement stage is configured to hold the sensor and/or cleaning device. The sensor may be configured to measure properties of the projection system PS or properties of the radiation beam B. The measurement stage can hold multiple sensors. The cleaning device may be configured to clean portions of the lithography apparatus, such as portions of the projection system PS or portions of the system providing the infiltration liquid. The measurement stage can move under the projection system PS when the substrate support WT is away from the projection system PS.

In operation, the radiation beam B is incident on a patterned device (eg, reticle) MA held on the reticle support MT and is patterned by the pattern (design layout) present on the patterned device MA. Having traversed the reticle MA, the radiation beam B passes through the projection system PS, which focuses the beam on a target portion C of the substrate W. By means of the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, for example, to position different target portions C in the path of the radiation beam B at focused and aligned positions. Similarly, a first positioner PM and possibly another position sensor (not explicitly depicted in FIG. 1 ) may be used to accurately position the patterned device MA relative to the path of the radiation beam B. The patterned device MA and the substrate W may be aligned using the mask alignment marks M1 and M2 and the substrate alignment marks P1 and P2. Although the substrate alignment marks P1, P2 occupy dedicated target portions as shown, they may be located in the spaces between the target portions. When the substrate alignment mark P1 and the substrate alignment mark P2 are located between the target portion C, these substrate alignment marks are called scribe lane alignment marks.

As shown in FIG. 2 , the lithography apparatus LA may form part of a lithography cell LC (sometimes also referred to as a lithocell or (lithography) cluster), which typically also includes performing operations on a substrate W. Equipment for pre-exposure and post-exposure processes. Conventionally, such devices include a spin coater SC for depositing the resist layer, a developer DE for developing the exposed resist, a cooling plate CH and a baking plate BK (e.g. for conditioning the substrate W). temperature, e.g. to regulate the solvent in the resist layer). The substrate handler or robot RO picks up the substrate W from the input/output ports I/O1 and I/O2, moves it between different process devices, and delivers the substrate W to the loading magazine LB of the lithography device LA. The devices in the lithography manufacturing unit that are often collectively referred to as the coating and development system are usually under the control of the coating and development system control unit TCU. The coating and development system control unit TCU itself can be controlled by the supervisory control system SCS. The supervisory control system The system may also control the lithography device LA, for example via the lithography control unit LACU.

In order to correctly and consistently expose the substrate W exposed by the lithography apparatus LA, the substrate needs to be inspected to measure the properties of the patterned structure, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), etc. For this purpose, an inspection tool (not shown in the figure) may be included in the lithography unit LC. If an error is detected, adjustments may be made, for example, to the exposure of subsequent substrates or other processing steps to be performed on the substrate W, especially if other substrates W of the same lot or lot still need to be inspected before being exposed or processed.

Detection devices, which may also be referred to as metrological devices, are used to determine properties of a substrate W, and in particular how properties of different substrates W vary or how properties associated with different layers of the same substrate W vary from layer to layer. The detection device may alternatively be constructed to identify defects on the substrate W, and may for example be part of the lithography unit LC, or may be integrated into the lithography apparatus LA, or may even be a stand-alone device. The detection device can measure the properties of the latent image (the image in the resist layer after exposure), or the properties of the semi-latent image (the image in the resist layer after the post-exposure bake step PEB), or by Properties on a developed resist image (where the exposed or unexposed portions of the resist have been removed), or even on an etched image (after a pattern transfer step such as etching).

Typically, the patterning process in the lithography apparatus LA is one of the most critical steps in a process that requires high accuracy in sizing and placement of structures on the substrate W. To ensure this high accuracy, the three systems can be combined in a so-called "holistic" control environment, as schematically depicted in Figure 3. One of these systems is the lithography device LA, which is (actually) connected to the metrology tool MT (second system) and to the computer system CL (third system). The key to this "holistic" environment is to optimize the cooperation between these three systems to enhance the overall process window and provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA remains within the process window. A process window defines a range of process parameters (e.g., dose, focus, overlap) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device)—generally within that result, allowable Changes in process parameters during the lithography process or patterning process.

The computer system CL can use (part of) the design layout to be patterned to predict which resolution enhancement technology to use and perform computational lithography simulations and calculations to determine which mask layout and lithography device settings achieve the maximum performance of the patterning process. The overall process window (depicted in Figure 3 by the double arrow in the first scale SC1). Typically, the resolution enhancement technology is configured to match the patterning possibilities of the lithography device LA. The computer system CL may also be used to detect where within the process window the lithography apparatus LA is currently operating (e.g., using input from the metrology tool MT) to predict whether defects may be present due to, for example, suboptimal processing (in Figure 3 by The arrow pointing to "0" in the second scale SC2 is depicted).

The metrology tool MT may provide input to the computer system CL to enable accurate simulations and predictions, and may provide feedback to the lithography apparatus LA to identify, for example, possible drifts in the calibration status of the lithography apparatus LA (indicated by the third party in FIG. 3 Depicted by multiple arrows in scale SC3).

During the lithography process, the resulting structures need to be measured frequently, for example for program control and verification. The tools used to make such measurements are often called metrology tools MT. Different types of metrology tools MT are known for making such measurements, including scanning electron microscopes or various forms of scatterometric metrology tools MT. Scatterometers are multifunctional instruments that allow the measurement of parameters of the lithography process by having a sensor in the pupil or in a plane conjugate to the pupil of the objective lens of the scatterometer (measurements are often referred to as light-based pupil-based measurement), or by having a sensor in the image plane or a plane conjugate to the image plane to measure parameters of the lithography process, in which case the measurement is often referred to as image- or field-based measurement. as a basis for measurement. Such scatterometers and associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, which are incorporated by reference in their entirety. The aforementioned scatterometer can measure gratings using light from soft x-rays and visible to near-IR wavelength ranges.

In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In this scatterometer, reconstruction methods can be applied to the measured signals to reconstruct or calculate the properties of the grating. This reconstruction may be caused, for example, by simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulated results with those of measurements. The parameters of the mathematical model are adjusted until the simulated interactions produce a diffraction pattern similar to that observed from a real target.

In a second embodiment, the scatterometer MT is a spectral scatterometer MT. In this spectroscopic scatterometer MT, the radiation emitted by the radiation source is directed onto the target and the reflected or scattered radiation from the target is directed onto a spectrometer detector, which measures the spectrum of the specularly reflected radiation ( That is, a measurement of intensity as a function of wavelength). From this data, the structure or profile of the object producing the detected spectrum can be reconstructed, for example by rigorous coupled wave analysis and nonlinear regression or by comparison with a library of simulated spectra.

In a third embodiment, the scatterometer MT is an ellipsometry scatterometer. Ellipsometry scatterometers allow the determination of lithography process parameters by measuring scattered radiation for each polarization state. The metrology device emits polarized light (such as linear, circular or elliptical) by using, for example, appropriate polarizing filters in the illumination section of the metrology device. Sources suitable for metrology equipment may also provide polarized radiation. Various embodiments of existing ellipsometric scatterometers are described in U.S. Patent Application Nos. 11/451,599, 11/708,678, 12/256,780, 12/486,449, 12/920,968, 12/922,587, which are incorporated by reference in their entirety. 13/000,229, 13/033,135, 13/533,110 and 13/891,410.

In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure two by measuring the reflectance spectrum and/or detecting asymmetries in the configuration related to the extent of overlay. Misalignment of gratings or periodic structures. Two (usually overlapping) grating structures can be applied in two different layers (not necessarily consecutive layers), and the two grating structures can be formed at substantially the same location on the wafer. The scatterometer may have a symmetric detection configuration as described, for example, in commonly owned patent application EP 1,628,164A, so that any asymmetry is clearly identifiable. This provides a direct way to measure misalignment in the grating. Quantities between two layers containing the targeted periodic structure can be found in PCT Patent Application Publication No. WO 2011/012624 or United States Patent Application No. US 20160161863, which are incorporated herein by reference in their entirety. Other examples where measurement overlay error is measured via the asymmetry of these periodic structures.

Other parameters of interest may be focus and dose. The focus and dose can be determined simultaneously by scattering (or alternatively by scanning electron microscopy) as described in US Patent Application US2011-0249244, which is incorporated by reference in its entirety. A single structure with a unique combination of critical dimensions and sidewall angle measurements for each point in the focal energy matrix (FEM, also known as the focal exposure matrix) can be used. If these unique combinations of critical dimensions and sidewall angles can be obtained, focus point and dose values can be uniquely determined from these measurements.

The metrology target may be a collection of composite gratings formed primarily in resist by a lithography process and also formed after, for example, an etching process. Typically, the spacing and line width of the structures in the grating are highly dependent on the measurement optics (especially the NA of the optics) to be able to capture the diffraction orders from the metrology target. As indicated earlier, the diffraction signal can be used to determine the shift between two layers (also known as "overlay") or can be used to reconstruct at least part of the original grating as produced by the lithography process. This reconstruction structure can be used to provide guidance on the quality of the lithography process and can be used to control at least part of the lithography process. The target may have smaller sub-segments configured to mimic the size of functional portions of the design layout in the target. Due to this sub-segmentation, the target will behave more like the functional part of the design layout, so that the overall process parameter measurements better resemble the functional part of the design layout. Targets can be measured in underfill mode or in overfill mode. In underfill mode, the measurement beam produces a spot smaller than the overall target. In overfill mode, the measurement beam produces a spot larger than the target. In this overfill mode, it is also possible to measure different targets at the same time, thereby determining different processing parameters at the same time.

The overall quality of a measurement of a lithography parameter using a particular target is determined at least in part by the measurement recipe used to measure the lithography parameter. The term "substrate measurement recipe" may include measuring one or more parameters of itself, measuring one or more parameters of one or more patterns, or both. For example, if the measurement used in the substrate measurement recipe is a diffraction-based optical measurement, then one or more of the measured parameters may include the wavelength of the radiation, the polarization of the radiation, the intensity of the radiation relative to the substrate. Angle of incidence, orientation of the radiation relative to the pattern on the substrate, etc. One of the criteria used to select a measurement recipe may, for example, be the sensitivity of one of the measurement parameters to process changes. Further examples are described in US Patent Application US2016-0161863 and US Published Patent Application US2016/0370717A, which are incorporated by reference in their entirety.

A metrology device, such as a scatterometer, is depicted in Figure 4 . The metrology device includes a broadband (white light) radiation projector 2 that projects radiation onto a substrate 6 . The reflected or scattered radiation is passed to a spectrometer detector 4 which measures the spectrum 10 of the specularly reflected radiation (ie, a measurement of intensity as a function of wavelength). From this data, the resulting detected spectrum can be reconstructed by the processing unit PU, for example, by strictly coupled wave analysis and nonlinear regression, or by comparison with the simulated spectral library shown at the bottom of Figure 3 Structure or outline. In general, for reconstruction, the general form of the structure is known, and some parameters are assumed from knowledge of the process by which the structure is made, leaving only a few parameters of the structure to be determined from self-scattering measurement data. This scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

The overall quality of the lithography parameter measured by measuring the target is determined at least in part by the measurement recipe used to measure the lithography parameter. The term "substrate measurement recipe" may include measuring one or more parameters of itself, measuring one or more parameters of one or more patterns, or both. For example, if the measurement used in the substrate measurement recipe is a diffraction-based optical measurement, one or more of the measured parameters may include the wavelength of the radiation, the polarization of the radiation, the relative angle of the radiation to The angle of incidence of the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. One of the criteria used to select a measurement recipe may, for example, be the sensitivity of one of the measurement parameters to process changes. Further examples are described in US Patent Application US2016/0161863 and US Published Patent Application US2016/0370717A1, which are incorporated by reference in their entirety.

Another type of metrology tool used in IC manufacturing is a form metrology system, level sensor, or height sensor. Such tools can be integrated into lithography equipment and used to measure the top surface topography of a substrate (or wafer). A map of the configuration of a substrate, also called a height map, can be produced by such measurements indicating the height of the substrate as a function of position on the substrate. This height map can then be used to correct the position of the substrate during transfer of the pattern onto the substrate to provide an aerial image of the patterned device in the proper focused position on the substrate. It should be understood that "height" in the context of this content refers to the dimension generally out of plane to the substrate (also referred to as the Z-axis). Typically, a level or height sensor performs measurements at a fixed position (relative to its own optical system), and relative movement between the substrate and the optical system of the level or height sensor results in a height at a location across the substrate. Measurement.

An example of a level or height sensor LS known in the art is schematically shown in Figure 5, which only illustrates the principle of operation. In this example, the level sensor includes an optical system including a projection unit LSP and a detection unit LSD. The projection unit LSP contains a radiation source LSO providing a radiation beam LSB imparted by the projection grating PGR of the projection unit LSP. The radiation source LSO may be, for example, a narrowband or broadband light source, such as a polarized or unpolarized, pulsed or continuous supercontinuum light source, such as a polarized or unpolarized laser beam. The radiation source LSO may include a plurality of radiation sources with different colors or wavelength ranges, such as a plurality of LEDs. The radiation source LSO of the level sensor LS is not limited to visible radiation, but may additionally or alternatively cover UV and/or IR radiation and any wavelength range suitable for reflection from the surface of the substrate.

The projection grating PGR is a periodic grating, which contains a periodic structure that generates a radiation beam BE1 with periodically varying intensity. A radiation beam BE1 with periodically varying intensity is directed towards a measurement position MLO on the substrate W, with an angle between 0 and 90 degrees relative to an axis perpendicular to the incident substrate surface (Z-axis), typically at Angle of incidence ANG between 70 degrees and 80 degrees. At the measurement position MLO, the patterned radiation beam BE1 is reflected from the substrate W (indicated by arrow BE2) and directed towards the detection unit LSD.

In order to determine the height level at the measurement position MLO, the level sensor further includes a detection system, which includes a detection grating DGR, a detector DET and a processing unit for processing the output signal of the detector DET ( (not shown in the picture). The detection grating DGR can be the same as the projection grating PGR. The detector DET generates a detector output signal indicative of received light, for example indicative of an intensity of received light, such as a light detector, or indicative of a spatial distribution of received intensity, such as a camera . A detector DET may contain any combination of one or more detector types.

With the help of triangulation technology, the height level at the measurement position MLO can be determined. The detected height level is usually related to the signal strength as measured by the detector DET, which signal strength has a periodicity that depends inter alia on the design of the projection grating PGR and the (tilt) angle of incidence ANG.

The projection unit LSP and/or the detection unit LSD may include other optical elements, such as lenses and/or mirrors, along the path (not shown) of the patterned radiation beam between the projection grating PGR and the detection grating DGR.

In one embodiment, the detection grating DGR can be omitted, and the detector DET can be placed at the location where the detection grating DGR is located. This configuration provides more direct detection of the image of the projected grating PGR.

In order to effectively cover the surface of the substrate W, the level sensor LS can be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating a measurement area MLO or light covering a larger measurement range. Array of points.

Various height sensors of general type are disclosed, for example, in US7265364 and US7646471, both of which are incorporated by reference. A height sensor that uses UV radiation instead of visible or infrared radiation is disclosed in US2010233600A1, which is incorporated by reference. In WO2016102127A1, incorporated by reference, a compact height sensor is described that uses a multi-element detector to detect and identify the position of a raster image without detecting the raster.

Another type of metrology tool used in IC manufacturing is alignment sensors. Therefore, a key aspect of the performance of a lithography device is the ability to correctly and accurately place an applied pattern relative to features placed in previous layers (either by the same device or a different lithography device). For this purpose, the substrate is provided with one or more sets of alignment marks. Each mark is a structure whose position can later be measured using a position sensor (usually an optical position sensor). The position sensor may be called an "alignment sensor" and the mark may be called an "alignment mark".

The lithography apparatus may include one or more (eg, a plurality of) alignment sensors by which the positions of alignment marks provided on the substrate can be accurately measured. Alignment (or position) sensors may use optical phenomena such as diffraction and interference to obtain position information from alignment marks formed on a substrate. One example of an alignment sensor used in current lithography apparatus is based on a self-referencing interferometer as described in US6961116. Various enhancements and modifications of position sensors have been developed, such as disclosed in US2015261097A1. The contents of all such publications are incorporated herein by reference.

Figure 6 is a schematic block diagram of an embodiment of a known alignment sensor AS such as that described in US6961116, for example and incorporated by reference. The radiation source RSO provides a radiation beam RB having one or more wavelengths, which is directed by steering optics onto a mark (such as a mark AM located on the substrate W) as an illumination spot SP. In this example, the turning optical element includes the spot mirror SM and the objective lens OL. The diameter of the illumination spot SP by which the mark AM is illuminated may be slightly smaller than the width of the mark itself.

The radiation diffracted by the alignment mark AM (in this example via the objective lens OL) is collimated into the information-carrying beam IB. The term "diffraction" is intended to include zero-order diffraction from the mark (which may be referred to as reflection). A self-referencing interferometer SRI of the type disclosed in US Pat. No. 6,961,116 mentioned above interferes with the beam IB with itself, after which the beam is received by the photodetector PD. Additional optics (not shown) may be included to provide separate beams in the event that more than one wavelength is produced by the radiation source RSO. The light detector can be a single element, or it can contain several pixels if desired. The light detector may include a sensor array.

The steering optics including the spot mirror SM in this example can also be used to block the zeroth order radiation reflected from the mark, so that the information-carrying beam IB contains only the higher order diffracted radiation from the mark AM (this is not necessary for the measurement, but improves the signal-to-noise ratio).

The intensity signal SI is supplied to the processing unit PU. The values of the X position and Y position of the substrate relative to the reference frame are output by a combination of optical processing in the block SRI and computational processing in the unit PU.

A single measurement of the type shown only fixes the position of the mark within a certain range corresponding to one spacing of the mark. Coarse measurement techniques are used in conjunction with this to identify which cycles of the sine wave contain marked locations. The same process at coarser and/or finer levels can be repeated at different wavelengths for improved accuracy and/or for robust detection of marks, regardless of the materials from which the marks are made and the marks provided above and/or the materials below. Wavelengths may be optically multiplexed and demultiplexed for synchronization, and/or the wavelengths may be time-division or frequency-division multiplexed.

In this example, the alignment sensor and light spot SP remain stationary while the substrate W moves. Therefore, the alignment sensor can be rigidly and accurately mounted to the reference frame while effectively scanning the mark AM in a direction opposite to the direction of movement of the substrate W. The movement of the substrate W is controlled by a substrate positioning system installed on the substrate support and controlling the movement of the substrate support. A substrate support position sensor (eg, an interferometer) measures the position of the substrate support (not shown). In one embodiment, one or more (alignment) marks are provided on the substrate support. Measuring the position of the markings provided on the substrate support allows calibration of the position of the substrate support as determined by the position sensor (eg, relative to the frame to which the alignment system is connected). Measurement of the position of the alignment marks provided on the substrate allows determination of the position of the substrate relative to the substrate support.

The metrology tools MT mentioned above, such as scatterometers, configuration measurement systems or position measurement systems, may use radiation originating from a radiation source to perform measurements. The properties of radiation used by metrology tools can affect the type and quality of measurements that can be performed. For some applications, it may be advantageous to use multiple radiation frequencies to measure a substrate, for example, broadband radiation may be used. Multiple different frequencies may be able to propagate, irradiate, and scatter open metrology targets without interfering with other frequencies or with minimal interference with other frequencies. Thus, more metrological information can be obtained simultaneously, for example using different frequencies. Different radiation frequencies may also enable interrogation and discovery of different properties of metrological objects. Broadband radiation can be used in metrology systems MT such as level sensors, alignment mark measurement systems, scatter measurement tools or inspection tools. The broadband radiation source may be a supercontinuum source.

High-quality broadband radiation such as supercontinuum radiation may be difficult to generate. One method for generating broadband radiation may be, for example, to use nonlinear higher order effects to broaden high power narrowband or single frequency input radiation or pump radiation. The input radiation (which may be generated using a laser) may be referred to as pump radiation. Alternatively, the input radiation may be called seed radiation. In order to obtain high power radiation for the broadening effect, the radiation can be restricted to a small area such that strongly localized high intensity radiation is achieved. In these regions, the radiation can interact with the broadening structure and/or the material forming the nonlinear medium to produce broadband output radiation. In regions of high intensity radiation, different materials and/or structures can be used to achieve and/or improve radiation broadening by providing suitable nonlinear media.

In some embodiments, broadband output radiation is generated in a photonic crystal fiber (PCF). In several embodiments, the photonic crystal fiber has microstructure around its fiber core to help confine radiation traveling through the fiber in the fiber core. The fiber core can be made from a solid material that has nonlinear properties and is capable of producing broad-band radiation when high-intensity pump radiation is transmitted through the fiber core. Although it is feasible to generate broadband radiation in solid-core photonic crystal fibers, there can be a few drawbacks to using solid materials. For example, if UV radiation is generated in a solid core, this radiation may not be present in the output spectrum of the fiber because the radiation is absorbed by most solid materials.

In some embodiments, as discussed further below with reference to Figure 8, methods and apparatus for broadening input radiation may use optical fibers for limiting the input radiation and for broadening the input radiation to output broadband radiation. The optical fiber may be a hollow core fiber and may contain internal structures to achieve efficient guidance and confinement of radiation within the fiber. The optical fiber may be, for example, a solid core photonic crystal fiber (SC-PCF) or a hollow core photonic crystal fiber (HC-PCF).

For example, HC-PCF is particularly suitable for strong radiation confinement, mainly inside the hollow core of the fiber, thereby achieving high radiation intensity. The hollow core of an optical fiber can be filled with a gas, which acts as a broadening medium for broadening the input radiation. This fiber and gas configuration can be used to generate a supercontinuum radiation source. The radiation input into the optical fiber may be electromagnetic radiation, such as radiation in one or more of the infrared, visible, UV, and extreme UV spectra. The output radiation may consist of or include broadband radiation, which may be referred to herein as white light.

Some embodiments relate to new designs of such broadband radiation sources including optical fibers. The optical fiber is a hollow core photonic crystal fiber (HC-PCF). In particular, the optical fiber may be a hollow-core photonic crystal optical fiber of the type including anti-resonant structures for confining radiation. Such fibers containing antiresonant structures are known in the art as antiresonant fibers, tubular fibers, single ring fibers, negative curvature fibers, or suppressed coupling fibers. Various designs of such optical fibers are known in the art. Alternatively, the fiber may be a photonic bandgap fiber (HC-PBF, such as a Kagome fiber).

Several types of HC-PCF can be engineered, each based on a different physical guidance mechanism. Two types of HC-PCF include: hollow-core photonic bandgap fiber (HC-PBF) and hollow-core antiresonant reflective fiber (HC-ARF). Details on the design and manufacturing of HC-PCF can be found in U.S. Patent US2004/015085A1 (for HC-PBF) and International PCT Patent Application WO2017/032454A1 (for hollow-core antiresonant reflective fiber), which are incorporated herein by reference. middle. Figure 9(a) shows a Kagome fiber containing a Kagome lattice structure.

An example of an optical fiber used in a radiation source will now be described with reference to Figure 7, which is a schematic cross-section of an optical fiber OF in a transverse plane. Other embodiments similar to the practical example of optical fiber of Figure 7 are disclosed in WO2017/032454A1.

The optical fiber OF includes an elongated body that is longer in one dimension than the other two dimensions of the optical fiber OF. This longer dimension may be referred to as an axial direction and may define the axis of the optical fiber OF. Two other dimensions define a plane that may be called a transverse plane. Figure 7 shows a cross-section of the optical fiber OF in this transverse plane (ie, perpendicular to the axis) labeled x-y plane. The transverse cross-section of the optical fiber OF may be substantially constant along the fiber axis.

It will be appreciated that the optical fiber OF has a certain degree of flexibility, and therefore, generally speaking, the axis will be non-uniform along the length of the optical fiber OF. Terms such as optical axis, transverse section and the like should be understood to mean local optical axis, local transverse section and the like. Furthermore, where components are described as being cylindrical or tubular, these terms should be understood to cover such shapes that may have deformed when the optical fiber OF is bent.

The optical fiber OF can be of any length and it should be understood that the length of the optical fiber OF can depend on the application. The optical fiber OF may have a length between 1 cm and 10 m, for example, the optical fiber OF may have a length between 10 cm and 100 cm.

The optical fiber OF includes: a hollow core HC; a cladding portion surrounding the hollow core HC; and a supporting portion SP surrounding and supporting the cladding portion. The optical fiber OF can be regarded as including a body (including a cladding part and a supporting part SP) with a hollow core HC. The cladding portion contains a plurality of anti-resonant elements for guiding radiation through the hollow core HC. In particular, the plurality of anti-resonant elements are configured to confine radiation propagating through the optical fiber OF primarily within the hollow core HC, and to direct the radiation along the optical fiber OF. The hollow core HC of the optical fiber OF may be positioned substantially in the central region of the optical fiber OF, such that the axis of the optical fiber OF also defines the axis of the hollow core HC of the optical fiber OF.

The cladding portion contains a plurality of anti-resonant elements used to guide radiation through the optical fiber OF. Specifically, in this example, the cladding portion contains a single ring of six tubular capillary CAPs. Each of the tubular capillary CAPs acts as an antiresonant element.

Capillary CAP may also be called a tube. The capillary CAP may be circular in cross-section, or may have another shape. Each capillary CAP includes a generally cylindrical wall portion WP that at least partially defines the hollow core HC of the optical fiber OF and separates the hollow core HC from the capillary cavity CC. It will be appreciated that the wall portion WP can act as an anti-reflective Fabry-Perot resonator for radiation that propagates through the hollow core HC (and that this radiation can be incident on the wall portion WP at a grazing incidence angle ). The thickness of the wall portion WP may be suitable so as to ensure that reflection back into the hollow core HC is substantially enhanced, while transmission into the capillary cavity CC is substantially suppressed. In some embodiments, capillary wall portion WP may have a thickness between 0.01 µm and 10.0 µm.

It should be understood that, as used herein, the term cladding portion is intended to mean that portion of the optical fiber OF used to guide radiation propagating through the optical fiber OF (ie, confine the radiation to the capillary CAP within the hollow core HC). Radiation can be confined in the form of transverse modes, propagating along the fiber axis.

The support portion is generally tubular and supports the six capillary tubes CAP of the cladding portion. The six capillary tubes CAP are evenly distributed around the inner surface of the inner support part SP. The six capillary CAPs can be described as being arranged in a generally hexagonal pattern.

The capillary CAPs are configured so that each capillary does not come into contact with any of the other capillary CAPs. Each of the capillary tubes CAP is in contact with the inner support portion SP and is spaced apart from adjacent capillary tubes CAP in the ring structure. This configuration may be beneficial as it may increase the transmission bandwidth of the optical fiber OF (relative to, for example, a configuration where the capillaries are in contact with each other). Alternatively, in some embodiments, each of the capillary CAPs may be in contact with an adjacent capillary CAP in a ring structure.

The six capillary tubes CAP of the cladding part are arranged in a ring structure around the hollow core HC. The inner surface of the ring structure of the capillary CAP at least partially defines the hollow core HC of the optical fiber OF. The diameter d of the hollow core HC (which can be defined as the smallest dimension between opposing capillaries, indicated by arrow d) can be between 10 µm and 1000 µm. The diameter d of the hollow core HC can affect the mode field diameter of the hollow core HC fiber OF, affecting loss, dispersion, modal multiplicity and nonlinear properties.

In this embodiment, the cladding portion contains a single ring configuration of capillary CAPs (which act as anti-resonant elements). Therefore, a line in any radial direction from the center of the hollow core HC to the outside of the optical fiber OF passes through no more than one capillary CAP.

It should be understood that other embodiments may have different configurations of anti-resonant elements. Such configurations may include configurations with multiple rings of anti-resonant elements and configurations with nested anti-resonant elements. Figure 9(a) shows an embodiment of an HC-PCF with three rings of capillary CAP stacked on top of each other in the radial direction. In this embodiment, each capillary CAP is in contact with other capillaries both in the same ring and in different rings. Additionally, while the embodiment shown in Figure 7 includes six rings of capillaries, in other embodiments, any number of anti-resonant elements may be included (e.g., 4, 5, 6, 7, 8, 9, 10, 11, or One or more loops of 12 capillaries) may be provided in the cladding portion.

Figure 9(b) shows a modified embodiment of the HC-PCF with a single ring of tubular capillaries discussed above. In the example of Figure 9(b), there are two coaxial rings of tubular capillary 21. In order to hold the inner and outer rings of the tubular capillary tube 21, the support tube ST may be included in the HC-PCF. The support tube can be made of silica.

The tubular capillary tubes of the examples of FIG. 7 and FIG. 9 (a) and (b) may have a circular cross-sectional shape. For tubular capillaries, other shapes are also possible, such as elliptical or polygonal cross-sections. In addition, the solid material of the tubular capillary of the examples of FIG. 7 and FIG. 9 (a) and (b) may include plastic materials such as PMA, glass such as silica, or soft glass.

Figure 8 depicts a radiation source RDS for providing broadband output radiation. The radiation source RDS consists of: a pulsed pump radiation source PRS or any other type of source capable of generating short pulses of the required length and energy level; an optical fiber OF with a hollow core HC (such as the type shown in Figure 7); and placement The working medium WM (such as gas) in the hollow core HC. Although in Figure 8 the radiation source RDS includes the fiber OF shown in Figure 7, in alternative embodiments other types of hollow core HC fiber OF may be used.

The pulsed pump radiation source PRS is configured to provide the input radiation IRD. The hollow core HC of the optical fiber OF is configured to receive the input radiation IRD from the pulsed pump radiation source PRS and broaden it to provide the output radiation ORD. The working medium WM can broaden the frequency range of the received input radiation IRD to provide a wide-band output radiation ORD.

The radiation source RDS further contains a reservoir RSV. The optical fiber OF is placed inside the reservoir RSV. The reservoir RSV may also be called a housing, container or cell. The reservoir RSV is configured to contain the working medium WM. The reservoir RSV may comprise one or more features known in the art for controlling, regulating and/or monitoring the composition of the working medium WM (which may be a gas) inside the reservoir RSV. The reservoir RSV may include a first transparent window TW1. In use, the optical fiber OF is positioned inside the reservoir RSV such that the first transparent window TW1 is located close to the input end IE of the optical fiber OF. The first transparent window TW1 may form part of the wall of the reservoir RSV. The first transparent window TW1 may be transparent at least for the received input radiation frequency, so that the received input radiation IRD (or at least a major part thereof) may be coupled into the optical fiber OF located inside the reservoir RSV. It will be appreciated that optics (not shown) may be provided for coupling the input radiation IRD into the optical fiber OF.

The reservoir RSV includes a second transparent window TW2 forming part of the wall of the reservoir RSV. In use, when the optical fiber OF is positioned inside the reservoir RSV, the second transparent window TW2 is located close to the output end OE of the optical fiber OF. The second transparent window TW2 may be transparent at least for the frequencies of the broadband output radiation ORD of the device 120 .

Alternatively, in another embodiment, the two opposing ends of the optical fiber OF may be placed inside different reservoirs. The optical fiber OF may include a first end section configured to receive an input radiation IRD, and a second end section configured to output a broadband output radiation ORD. The first end section can be placed inside the first reservoir containing the working medium WM. The second end section can be placed inside the second reservoir, wherein the second reservoir can also contain the working medium WM. The operation of the reservoir may be as described above with respect to FIG. 8 . The first reservoir may include a first transparent window configured to be transparent to the input radiation IRD. The second reservoir may include a second transparent window configured to be transparent to the broadband output broadband radiation ORD. The first reservoir and the second reservoir may also include sealable openings to allow the optical fiber OF to be placed partially inside the reservoir and partially outside the reservoir such that the gas may be sealed to the reservoir interior. The optical fiber OF may further include an intermediate section that is not contained inside the reservoir. This configuration using two separate gas reservoirs may be particularly convenient for embodiments where the fiber OF is relatively long (eg when the length exceeds 1 m). It will be appreciated that for such a configuration using two separate gas reservoirs, the two reservoirs (which may contain gas pressure sensors known in the art for controlling, regulating and/or monitoring the interior of the two reservoirs) may be One or more characteristics of the composition of the gas) are considered to provide means for providing the working medium WM within the hollow core HC of the optical fiber OF.

In this context, a window may be transparent for that frequency if at least 50%, 75%, 85%, 90%, 95%, or 99% of the incident radiation at that frequency is transmitted through the window.

Both the first TW1 and the second TW2 transparent windows may form a gas-tight seal within the wall of the reservoir RSV, so that the working medium WM (which may be a gas) may be contained within the reservoir RSV. It will be appreciated that the gas WM may be contained within the reservoir RSV at a pressure different from the ambient pressure of the reservoir RSV.

The working medium WM may include: inert gases such as argon, krypton and xenon; Raman active gases such as hydrogen, deuterium and nitrogen; or such as argon/hydrogen mixture, xenon/deuterium mixture, krypton/nitrogen mixture or nitrogen/hydrogen mixture. gas mixture. Depending on the type of filling gas, nonlinear optical processes can include modulation instability (MI), photosolid self-squeezing, photosolid splitting, Kerr effect, Raman effect and dispersive wave generation (DWG). Details are described in WO2018/127266A1 and US9160137B1 (both of which are hereby incorporated by reference). Since the dispersion of the filling gas can be tuned by changing the working medium WM pressure (i.e., gas cell pressure) in the reservoir RSR, the resulting broadband pulse dynamics and associated spectral broadening characteristics can be adjusted to optimize Optimized frequency conversion.

In one embodiment, the working medium WM may be disposed within the hollow core HC at least during the reception of the input radiation IRD for generating the broadband output radiation ORD. It will be appreciated that the gas WM may be wholly or partially absent in the hollow core HC when the fiber OF does not receive the input radiation IRD used to generate the broadband output radiation.

To achieve frequency broadening, high intensity radiation may be required. The advantage of having a hollow core HC fiber OF is that it can achieve high intensity radiation through strong spatial confinement of the radiation propagating through the fiber OF, thereby achieving high localized radiation intensity. The radiation intensity inside the fiber OF may be higher, for example due to high received input radiation intensity and/or due to strong spatial confinement of the radiation inside the fiber OF. An advantage of hollow core fibers is that they can guide radiation over a wider range of wavelengths than solid core fibers, and in particular, hollow core fibers can guide radiation in both the ultraviolet and infrared ranges.

An advantage of using hollow core HC fiber OF may be that most of the radiation guided inside the fiber OF is confined to the hollow core HC. Therefore, most of the interaction of the radiation inside the optical fiber OF is with the working medium WM, which is provided inside the hollow core HC of the optical fiber OF. Therefore, the broadening effect of the working medium WM on radiation can be increased.

The received input radiation IRD may be electromagnetic radiation. The input radiation IRD can be received as pulsed radiation. For example, the input radiation IRD may comprise ultrafast pulses generated by, for example, a laser.

The input radiation IRD may be coherent radiation. The input radiation IRD may be collimated radiation, and this may have the advantage of facilitating and improving the efficiency of coupling the input radiation IRD into the optical fiber OF. The input radiation IRD can contain a single frequency or a narrow range of frequencies. Input radiation IRD can be generated by lasers. Similarly, the output radiation ORD may be collimated and/or may be coherent.

The broad frequency range of the output radiation ORD may be a continuous range, which includes a range of continuous radiation frequencies. The output radiation ORD may comprise supercontinuum radiation. Continuous radiation can be beneficially used in numerous applications, such as in metrology applications. For example, a continuous range of frequencies can be used to interrogate a large number of attributes. A continuous range of frequencies may be used, for example, to determine and/or eliminate frequency dependence of measured properties. The supercontinuum output radiation ORD may comprise, for example, electromagnetic radiation in the wavelength range of 100 nm to 4000 nm. The broadband output radiation ORD frequency range may be, for example, 400 nm to 900 nm, 500 nm to 900 nm, or 200 nm to 2000 nm. The supercontinuum output radiation ORD may include white light.

The input radiation IRD provided by the pulsed pump radiation source PRS may be pulsed. The input radiation IRD may contain electromagnetic radiation at one or more frequencies between 200 nm and 2 µm. The input radiation IRD may, for example, comprise electromagnetic radiation with a wavelength of 1.03 μm. The repetition rate of pulsed radiation IRD can be on the order of 1 kHz to 100 MHz. Pulse energy may be on the order of 0.1 µJ to 100 µJ, for example 1 to 10 µJ. The pulse duration of the input radiation IRD can be between 10 fs and 10 ps, for example 300 fs. The average power of the input radiated IRD can range from 100 mW to several 100 W. The average power of the input radiation IRD may be, for example, 20 W to 50 W.

The pulsed pump radiation source PRS can be a laser. The spatiotemporal transmission characteristics (e.g., its spectral amplitude and phase) of this laser pulse transmitted along the fiber OF can be changed and tuned through (pump) laser parameters, working component WM changes, and fiber OF parameters. The spatiotemporal transmission characteristics may include one or more of the following: output power, output mode profile, output time profile, output time profile width (or output pulse width), output spectral profile, and output spectral profile bandwidth. (or output spectral bandwidth). The PRS parameters of the pulse pump radiation source may include one or more of the following: pump wavelength, pump pulse energy, pump pulse width, and pump pulse repetition rate. The fiber OF parameters may include one or more of the following: fiber length; size and shape of the hollow core HC; size and shape of the capillary; and thickness of the wall of the capillary surrounding the hollow core HC. The working component WM (eg, fill gas) parameters may include one or more of: gas type, gas pressure, and gas temperature.

The broadband output radiation ORD provided by the radiation source RDS may have an average output power of at least 1 W. The average output power can be at least 5 W. The average output power can be at least 10 W. The wide-band output radiation ORD may be a pulse-type wide-band output radiation ORD. The broadband output radiation ORD may have a power spectral density of at least 0.01 mW/nm across the entire wavelength band of the output radiation. The power spectral density of the broadband output radiation may be at least 3 mW/nm throughout the wavelength band.

Radiation source RDS (e.g., as shown in Figure 8) typically requires free-space coupling of the input radiation IRD provided by a pulsed pump radiation source PRS into a hollow-core HC fiber OF (e.g., HC-PCF); broadband output The properties of the radiation ORD are therefore alignment sensitive. Small deviations from optimal incoupling alignment can cause considerable changes in the characteristics (eg, spectrum, power, temporal profile, spatial profile) of the broadband output radiation ORD. Therefore, the radiation source RDS is often equipped with one or more diagnostic tools configured to measure the input radiation IRD and the output light from the hollow HC fiber OF (eg, HC-PCF), and provide feedback to the radiation if necessary. The source RDS is used for corrective actions (eg, making some adjustment to the coupling alignment within the input radiation IRD to compensate for changes in the broadband output radiation).

The initial alignment of the input radiation IRD relative to the HC-PCF may include two main steps, namely coarse alignment and fine alignment. Coarse alignment is performed with sufficiently low pump pulse energy or pump power to prevent damage to the HC-PCF. This step will ensure that the pump beam is properly coupled into the hollow core of the HC-PCF and excites the transverse core mode at the front (or input) facet of the HC-PCF. Without rough alignment, damage can occur when the center of a high-power pump laser beam strikes the cladding wall of an HC-PCF. Once the transverse core mode is excited and transmission efficiency (defined as the ratio between fiber output power and fiber input power) is maximized at low power levels, fine alignment at high power levels begins. Likewise, the purpose of fine alignment is to further maximize transmission efficiency.

However, in this optimization approach, the maximized transmission efficiency (i.e., the maximized output power at a given input power) does not necessarily correspond to the highest mode purity, which is defined as the fundamental transverse mode The ratio between the power below and the total output power. In other words, higher order mode (HOM) content may still be present in the output of the broadband radiation source RDS even after the transmission efficiency is optimized. In order to obtain a good balance between the transmission efficiency of the input radiation IRD and the mode purity of the output radiation ORD, it will be necessary to actively monitor the power and mode of the light emitted from the HC-PCF by, for example, power measurement devices and mode measurement devices, respectively. Space outline.

Once initial alignment optimization is completed, long-term operation of the radiation source RDS can begin. To maintain stable performance, broadband output radiation ORD can be actively monitored via one or more diagnostic tools. In the event of performance degradation identified by the diagnostic tool, the radiation source RDS may take corrective action (e.g., via one or more of: adjusting the pulsed pump radiation source PRS, adjusting the in-coupling alignment of the input radiation , adjust the parameters of the working medium WM) to compensate for performance changes and thereby restore optimal performance. Such diagnostic tools may include, for example, one or more of the following: a power measurement device for measuring the power of the output radiation ORD, a mode measurement device for measuring the spatial profile of the output radiation ORD, A pulse measuring device for measuring the time profile of the output radiation ORD and a spectral measuring device for measuring the spectral profile of the output radiation ORD. One or more of such diagnostic tools may require at least a portion of the output radiation ORD to be split from the main beam of the output radiation ORD.

Figure 10 schematically depicts another example radiation source RDS. In this example, an alignment unit AU is employed to control the alignment of the input radiation IRD relative to the hollow core HC fiber OF. The alignment unit AU may include one or more free space optics (eg, a pair of highly reflective mirrors) configured to adjust the beam direction of the input radiation IRD. At the output end of the radiation source RDS, two conventional beam splitters BS1, BS2 are placed in the beam path of the output radiation ORD. The two beam splitters BS1, BS2 are configured to reflect a portion of the output radiation ORD DB1, DB2 and direct it into the two diagnostic tools DIG1, DIG2 respectively. In the event of performance degradation, one or both of the two diagnostic tools DIG1, DIG2 can generate error signals ER1, ER2 and transmit these error signals to the reservoir RSV, the alignment unit AU and the pulsed pump radiation One or more of the sources PRS, after receiving the error signals ER1 and ER2, one or more of the reservoir RSV, the alignment unit AU and the pulsed pump radiation source PRS can be appropriately adjusted (for example, re-optimized Optimize the coupling of the input radiation IRD into the fiber OF to compensate for performance degradation.

Conventionally, each of the beam splitters BS1, BS2 is a plane-to-plane optical window (with or without optical coating). Figure 11A schematically depicts the operating principle of a beam splitter based on a planar-to-planar optical window (or an optical substrate made of a specific optical material (eg, fused silica)). The refractive index of air , and the refractive index of the optical window is . Non-polarized beam IB to AOI Incident on the first surface FS of the optical window OW, the AOI It is formed between the propagation direction of the incident light beam IB and the normal vector NV of the first surface FS. The AOI can be adjusted by rotating the optical window OW about a rotation axis perpendicular to the plane of incidence (POI). The POI is formed by the propagation direction of the incident light beam IB and the normal vector NV perpendicular to the interface plane (eg, the first surface FS of the optical window OW). According to the coordinate reference system shown in FIG. 11A , the rotation axis of the optical window OW coincides with the Z axis and the POI overlaps with the XY plane. A part RB of the beam IB is reflected from the first surface FS and follows an angle with the normal vector NV direction. The transmitted part TB of the light beam IB has a refraction angle Refraction (relative to the normal vector NV) passes through the optical window OW. After illuminating the second surface SS of the optical window OW, a part (not shown in the figure) of the transmission part TB is reflected from the second surface SS, while the other part is transmitted through the second surface SS and forms the output beam OB.

One disadvantage of using this optical window OW is that the reflectivity (or reflectivity) for p polarization and S polarization for s polarization will vary in different ways with the AOI. Different changes in reflectivity have the effect of inducing polarization splitting into the incident beam IB, and thus create uncertainty in the properties of the reflected (and transmitted) beam RB. The polarization splitting effect causes the ratio of the power of the S-polarization component and the power of the P-polarization component of the reflected beam RB (or the transmitted beam TB) to the power of the S-polarization component and the power of the P-polarization component of the incident beam IB to change. Referring back to FIG. 11A , the p-polarized P-polarized and s-polarized S-polarized states are orthogonal to each other and are both perpendicular to the propagation direction of the incident light beam IB. The polarization states are defined relative to the plane of incidence POI: the P polarization state is parallel to the POI, and the S polarization state is perpendicular to the POI. Fresnel equations [1] and [2] can be used to calculate reflectivity (or reflection coefficient) for both p-polarized P-polarized and s-polarized S-polarized states. , [1] . [2]

Figure 11B is a graph showing two reflectances at an optical interface (eg, the first surface FS of the optical window OW shown in Figure 10) calculated for light waves in the p-polarization state and for light waves in the s-polarization state, respectively. An example of a curve graph. As can be seen in the figure, when the AOI is 0 degrees, the reflectivity of the light wave in the p-polarization state is the same as the reflectivity of the light wave in the s-polarization state. The two reflectance curves maintain substantial overlap until the AOI reaches approximately 10 degrees, where the two reflectance curves begin to diverge and follow two separate trends. S-polarized reflectance continues to increase with increasing AOI, while P-polarized reflectance first decreases to a minimum before increasing again (for example, when the AOI is approximately 56 degrees, this angle is also known as the Brewster angle) . When the AOI is 90 degrees, the S polarization reflectance coincides with the P polarization reflectance again. Therefore, when the AOI is 45 degrees, reflectance (e.g., 0.083 in Figure 11B) than The reflectance (eg, 0.007 in Figure 11B) is more than an order of magnitude greater.

Referring to Figure 11A, when the incident beam IB is unpolarized, the intensity of the P polarization component of the beam IB Essentially the intensity of the S-polarized component of beam IB are the same and the intensity ratio between the two polarization components is 1. After reflection at the surface FS in front of the optical window OW, the two polarization components can experience different reflectivities , , and therefore the reflected beam RB can become partially polarized (where the intensity of the reflected S-polarized component The intensity of the P polarization component 10 times higher). Correspondingly, the transmitted light beam TB may also become partially polarized (where the power of the P polarization component is more than 10 times higher than the power of the S polarization component). In contrast, in the case where the incident beam IB is linearly polarized, the two polarization components of the incident beam may not have the same intensity, but may instead have an angle relative to the polarization direction of the S-polarization or P-polarization direction via the following equation: And changes: ; and [3] ; [4] Among them indicates the intensity of the incident beam IB, and Indicates the angle of the polarization direction of the incident beam IB relative to the P polarization direction. The intensity ratio between two polarization components It depends on the angle of the polarization direction relative to the S-polarization direction or the P-polarization direction. Thus, the intensity of the reflected beam RB (or transmitted beam TB) depends not only on the reflectivity values for the S-polarized and P-polarized states at a given AOI, but also on the S-polarized polarization component and the P-polarized polarization of the incident beam IB The ratio between the intensities of components. If the incident beam IB is linearly polarized along the P polarization direction, the P polarization component will have 100% of the intensity of the beam IB, and the S polarization component will not exist. However, due to the extremely small reflectivity value at the AOI of 45 degrees (For example, as shown in Figure 11B), only a small portion of the P polarization component will be reflected at the front surface FS.

If the above-mentioned optical windows OW are used as beam splitters BS1, BS2 in the setup shown in Figure 10, then the reflectivity of the beam splitters BS1, BS2 (e.g., , ) will be highly dependent on the polarization state of the output radiation ORD. Since the polarization state of the broadband output radiation ORD is generally undefined, changes in the characteristics of the reflected beams DB1, DB2 (e.g. spectral profile, spatial profile, power) caused by the difference in reflectivity for the two polarization states can therefore Varies significantly for different input polarization states. The lack of certainty about the characteristics of the reflected beams DB1, DB2 will in turn lead to inaccurate error signals ER1, ER2, which are generated by the diagnostic tools DIG1, DIG2 and incorrect actions taken by the radiation source RDS. The current method used to avoid the pulse splitting problem is to use an AOI that is small enough so that the reflectance values for the P and S polarization states are the same or substantially close to each other. Referring back to Figure 11B, the desired AOI should be no more than 10 degrees, or preferably no more than 5 degrees. A smaller AOI results in a smaller angular separation between the incident beam IB and the reflected beam RB. Therefore, extremely large path lengths would be required to be able to spatially separate the two beams. Using large path lengths is undesirable because it results in bulky optical setups that tend to suffer from more stability issues than compact setups.

In order to alleviate the aforementioned problems, the present disclosure proposes an optical arrangement capable of reflecting beams of pulsed radiation in a more defined and compact manner. This is accomplished by decomposing each pulse of pulsed radiation into two pulse components with two orthogonal polarizations, applying a time delay to the two pulse components, and specifying each pulse with a well-defined reflectivity (or effective reflectance) R _{e ff} This is achieved by reflecting two pulse components from the ground. The reflectivity can be expressed as: . [5]

Figure 12 schematically depicts an optical configuration for reflecting an incident beam IB of pulsed radiation (eg, the output radiation ORD from the radiation source RDS shown in Figure 10) according to one embodiment. The optical configuration OA includes an optical retarder OT and an optical reflector OR. The optical arrangement OA may be configured to allow the beam of pulsed radiation IB to first pass through the optical retarder OT at a substantially normal angle of incidence and then be at least partially reflected by the optical reflector OR.

The optical retarder OT includes a first axis FA coincident with the first linear polarization FPOL and a second axis SA coincident with the second linear polarization SPOL. The first axis FA and the second axis SA are orthogonal to each other; and therefore the first linear polarization FPOL and the second linear polarization SPOL are orthogonal to each other. The optical retarder OT is configured to decompose each pulse of the incident light beam IB into a first pulse component FC having a first linear polarization FPOL and a second pulse component SC having a second linear polarization SPOL. The optical retarder OT is configured to further impose a time delay TD between the first pulse component FC and the second pulse component SC of each pulse of the incident light beam IB after having traversed the optical retarder OT.

The optical reflector OR contains an axis of rotation RA perpendicular to the plane of incidence POI. The optical reflector OR is configured to at least partially reflect the first pulse component FC and the second pulse component SC of each pulse of the incident light beam IB. The optical arrangement is configured such that the first axis FA and the second axis SA of the optical retarder OT are each at an angle that differs substantially 45 degrees from the axis of rotation RA of the optical reflector OR (e.g., around the angle formed by the incident light beam IB axis defined by the direction of propagation).

In one embodiment, the optical retarder OT may include a birefringent crystal BRC. The birefringent crystal BRC can be configured to decompose each pulse of the incident light beam IB into an ordinary wave (o wave) and an abnormal wave (e wave) respectively corresponding to the first pulse component FC and the second pulse component SC. The o-wave may have a first linear polarization FPOL, and the e-wave may have a second linear polarization SPOL. Birefringent crystal BRC may contain one or more anisotropic optical materials such as crystalline quartz, calcite and sapphire. In one embodiment, the first axis and the second axis of the birefringent crystal BRC may be perpendicular to the propagation direction of the incident light beam IB. In one embodiment, one of the first axis and the second axis may be the optical axis of the birefringent crystal BRC.

Figure 15 illustrates the effectiveness of the embodiment depicted in Figure 12. The polarization direction of the radiation beam IB is varied by rotating a half-wave plate (HWP) through 360 degrees while monitoring the signal (voltage) from the photodiode, which is positioned so that it is in the optical The intensity of the radiation beam RB is monitored after reflection by the reflector (OR). The experiment was completed with the optical retarder OT (solid line in the figure) and without the optical retarder OT (dashed line in the figure) in the optical path. In this case, the optical retarder was chosen to be a birefringent crystal BRC (α-BBO). From Figure 15, it is evident that the presence of the birefringent crystal BRC almost completely removes any polarization dependence of the measured intensity of the radiation beam RB.

Figure 13 schematically depicts the operating principle of an example birefringent crystal BRC. In this example, the birefringent crystal BRC includes a first axis FA along the Y direction and a second axis SA along the X direction, the X and Y directions being indicated by the coordinate reference system shown in FIG. 13 . Both the first axis FA and the second axis SA are perpendicular to the propagation direction of the incident light beam IB. The first axis coincides with the optical axis OA of the birefringent crystal BRC. Birefringent crystal BRC has length , which is the same as the ordinary refractive index and abnormal refractive index Together, the amount of time delay TD between the o-wave and the e-wave is determined after the entire length of the birefringent crystal BRC has been traversed. The relationship between the time delay TD and the refractive index of the birefringent crystal BRC can be expressed by the following formula: , in the case of negative birefringence ( ), or [6] , in the case of positive birefringence ( ), [7] where Represents the speed of light, ordinary refractive index and abnormal refractive index are the refractive index experienced by o-wave and e-wave respectively. The values of the two refractive indexes depend on the material of the birefringent crystal BRC. In the case where the optical axis OA is not perpendicular to the propagation direction of the incident beam IB, the anomalous wave experiences propagation direction-dependent refractive index ,in Indicates the angle formed between the propagation direction and the optical axis OA. For more details about birefringence and how to calculate the refractive index for o-wave and e-wave in birefringent crystal BRC, please refer to Amnon Yariv's work by Holt and Rinehart. and Winston's Optical Electronics, third edition (January 1, 1984), which is incorporated herein by reference.

Preferably, the birefringent crystal BRC is configured such that the time delay TD between the o-wave and the e-wave is at least 50% of the pulse length of the incident beam IB. In one embodiment, the time delay TD is at least 50 fs, at least 100 fs, at least 200 fs, at least 400 fs, or at least 600 fs.

As an alternative, the optical retarder OT may comprise a liquid crystal polymer. Liquid crystal polymers have a much lower damage threshold. Furthermore, retardation is more wavelength dependent.

In one embodiment, the optical reflector OR may include an optical window OW (eg, as shown in Figure 11A). The optical window OW is operable to reflect the time-delayed first and second pulse components FC and SC of each pulse at any given AOI. The AOI may be, for example, at least 10 degrees, at least 20 degrees, at least 30 degrees, at least 40 degrees, or about 45 degrees. The AOI can be adjusted by rotating the optical window OW about an axis of rotation perpendicular to the POI (eg, along the Z-axis shown in Figure 11A). In embodiments, the first pulse component FC and the second pulse component SC of each pulse may be delayed in time by a birefringent crystal BRC (eg, as shown in Figure 13). Accordingly, the first pulse component FC may be an o-wave having a first linearly polarized FPOL along the second axis SA (eg, as shown in FIG. 13 ), and the second pulse component SC may be an o-wave having a first linearly polarized FPOL along the second axis SA (eg, as shown in FIG. 13 ). The e-wave of the second linearly polarized SPOL of axis FA or optical axis OA (eg, as shown in Figure 13). The birefringent crystal BRC can be oriented in a certain manner such that the first linear polarization FPOL of the o-wave and the second linear polarization SPOL of the e-wave form an angle of substantially 45 degrees with respect to the rotation axis RA of the optical window OW. Referring back to FIG. 11A , since the rotation axis is perpendicular to the POI, the S polarization and P polarization directions are defined relative to the POI, so the first linear polarization FPOL of the o wave and the second linear polarization SPOL of the e wave are also correspondingly relative to the S The polarization polarization (perpendicular to the POI) or the P polarization (parallel to the POI) forms an angle of substantially 45 degrees.

Therefore, as described above and according to equations [3] and [4], for an incident beam IB with a linear polarization oriented at 45 degrees relative to the P polarization direction or the S polarization direction, its S polarization component and P polarization component will have The same intensity, that is, 50% of the intensity of the incident beam IB. Therefore, for o-wave or e-wave, its S-polarized component and P-polarized component will have the same intensity. Therefore, for a given AOI, the effective reflectivity of o-wave and e-wave can be determined according to equation [5]. As shown in Figure 12, upon reflection, the first pulse component FC and the second pulse component SC of each pulse of the reflected beam RB may substantially retain their respective linear polarizations.

Referring back to Figure 10, if any of the previous embodiments of the optical configuration OA were used to replace each of the beam splitters BS1, BS2, then these embodiments would provide a well-defined reflectivity for the pulsed radiation ORD, and Certainty of the properties of the reflected beams DB1, DB2 is thus provided, which in turn leads to more accurate error signals ER1, ER2 produced by the diagnostic tools DIG1, DIG2 and to more correct actions taken by the radiation source RDS.

In one embodiment, the optical reflector OR may include an optical substrate or window OW (eg, as shown in FIG. 11A ) having a front reflective surface FS and a back reflective surface SS on the back reflective surface. SS is previously interacted with pulsed radiation, wherein the front reflective surface FS contains a first pulse component of each pulse configured to partially reflect pulsed radiation (eg, output radiation ORD from radiation source RDS shown in Figure 10) The first optical coating of FC and the second pulse component SC.

In one embodiment, the first optical coating can be configured to be highly reflective in a first wavelength range while being highly transmissive in a second wavelength range of pulsed radiation. The first wavelength range may be, for example, between 100 nm and 400 nm, between 150 nm and 400 nm, between 150 nm and 350 nm, or between 350 nm and 400 nm. The second wavelength range may be, for example, between 400 nm and 2000 nm, between 400 nm and 1600 nm, between 400 nm and 1200 nm, or between 400 nm and 700 nm. The reflectivity of the first optical coating in the first wavelength range (eg, any of the first ranges of the examples above) can be, for example, greater than 80%, greater than 85%, greater than 90%, greater than 95 % or higher than 99%. The reflectivity of the first optical coating in the second wavelength range (eg, any of the second ranges of the examples above) can be, for example, less than 20%, less than 15%, less than 10%, or less than 5 %. In one embodiment, the first optical coating can be configured to be partially reflective and partially transmissive over the entire wavelength range of pulsed radiation (eg, 100 nm to 4000 nm). The partial reflectivity of the first optical coating may be, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%. Optionally or in addition, the back-reflective surface SS may include a second optical coating configured to at least partially reflect portions of the first pulse component FC and the second pulse component SC of each pulse of pulsed radiation. (eg, in the second wavelength range), this portion has reached the back-reflecting surface SS after traversing the optical window OW.

In one embodiment, the optical arrangement OA may further include one or more polarization preserving optical elements (eg, total internal reflection (TIR) optical elements) operable to convert the first pulse component of each pulse to The second pulse component is directed to one or more locations (eg, to one or more sensors of interest).

In one embodiment, operation of the optical arrangement may include, for example, the following steps: directing pulsed radiation into the optical arrangement such that the pulsed radiation first passes through the optical retarder and is subsequently reflected by the optical reflector to the target location; identifying the location of the optical retarder the first axis and the second axis; identifying the axis of rotation of the optical reflector; and rotating the optical retarder in the plane of the first axis and the second axis so that the first axis and the second axis of the optical retarder are aligned with the optical reflector The axis of rotation forms an angle of essentially 45 degrees.

Figure 14 is a block diagram illustrating a computer system 1400 that may assist in implementing the methods and processes disclosed herein. Computer system 1400 includes a bus 1402 or other communications mechanism for communicating information, and a processor 1404 (or processors 1404 and 1405) coupled to bus 1402 for processing information. Computer system 1400 also includes main memory 1406, such as random access memory (RAM) or other dynamic storage devices, coupled to bus 1402 for storing information and instructions to be executed by processor 1404. Main memory 1406 may also be used to store temporary variables or other intermediate information during execution of instructions to be executed by processor 1404. Computer system 1400 further includes read-only memory (ROM) 1408 or other static storage device coupled to bus 1402 for storing static information and instructions for processor 1404 . A storage device 1410, such as a magnetic disk or optical disk, is provided and coupled to bus 1402 for storing information and instructions.

Computer system 1400 may be coupled via bus 1402 to a display 1412 for displaying information to a computer user, such as a cathode ray tube (CRT) or a flat panel display or a touch panel display. Input devices 1414 including alphanumeric and other keys are coupled to bus 1402 for communicating information and command selections to processor 1404 . Another type of user input device is a cursor control 1414 for communicating directional information and command selections to the processor 1404 and for controlling cursor movement on the display 1412, such as a mouse, trackball, or cursor direction buttons. The input device typically has two degrees of freedom in two axes, a first axis (eg, x) and a second axis (eg, y), allowing the device to specify a position in a plane. Touch panel (screen) displays can also be used as input devices.

One or more methods as described herein may be performed by computer system 1400 in response to processor 1404 executing one or more sequences of one or more instructions contained in main memory 1406 . These instructions may be read into main memory 1406 from another computer-readable medium, such as storage device 1410 . Execution of the sequences of instructions contained in main memory 1406 causes processor 1404 to perform the program steps described herein. One or more processors in a multi-processing configuration may also be used to execute sequences of instructions contained in main memory 1406. In an alternative embodiment, hardwired circuitry may be used instead of or in combination with software instructions. Therefore, the description herein is not limited to any specific combination of hardware circuitry and software.

The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to processor 1404 for execution. This media can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device 1410 . Volatile media includes dynamic memory, such as main memory 1406 . Transmission media include coaxial cable, copper wire, and fiber optics, including the wires including bus 1402. Transmission media may also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer readable media include, for example, floppy disks, floppy disks, hard disks, tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punched cards, paper tape, any other media with a hole pattern Physical media, RAM, PROM and EPROM, FLASH-EPROM, any other memory chip or cartridge, carrier wave as described below, or any other media that can be read by a computer.

Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to processor 1404 for execution. For example, the instructions may initially be hosted on a disk on the remote computer. The remote computer can load the instructions into its dynamic memory and use a modem to send the instructions over the phone line. The modem on the local side of computer system 1400 can receive data on the telephone line and use an infrared transmitter to convert the data into infrared signals. An infrared detector coupled to bus 1402 can receive the data carried in the infrared signal and place the data on bus 1402 . Bus 1402 carries data to main memory 1406, from which processor 1404 retrieves instructions and executes the instructions. Instructions received from main memory 1406 may be stored on storage device 1410 before or after execution by processor 1404, as appropriate.

Computer system 1400 also preferably includes a communication interface 1418 coupled to bus 1402. Communication interface 1418 provides a two-way data communication coupling to network link 1420, which is connected to local area network 1422. For example, the communication interface 1418 may be an Integrated Services Digital Network (ISDN) card or modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface 1418 may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links can also be implemented. In any such implementation, communication interface 1418 sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.

Network link 1420 typically provides data communications to other data devices via one or more networks. For example, network link 1420 may provide a connection to a host computer 1424 via a local area network 1422 or to a data device operated by an Internet service provider (ISP) 1426. ISP 1426 in turn provides data communications services via the global packet data communications network (now commonly referred to as the "Internet" 1428). Both local area network 1422 and Internet 1428 use electrical, electromagnetic, or optical signals that carry digital data streams. Signals through various networks and signals on network link 1420 and through communication interface 1418 are illustrative forms of carrier waves that carry information, which signals carry digital data to and from computer system 1400 Digital data.

Computer system 1400 can send messages and receive data, including program code, via the network, network link 1420, and communication interface 1418. In the Internet example, server 1430 may transmit the requested code for the application via Internet 1428, ISP 1426, local area network 1422, and communication interface 1418. For example, one such downloaded application may provide one or more of the techniques described herein. The received code may be executed by processor 1404 as it is received, and/or stored in storage device 1410 or other non-volatile storage for later execution. In this manner, computer system 1400 can obtain the application code in the form of a carrier wave.

Other embodiments of the invention are disclosed in the following numbered list: 1. An optical arrangement for reflecting pulsed radiation, comprising: An optical retarder comprising a first axis coincident with a first linear polarization state and a second axis coincident with a second linear polarization state, the first axis and the second axis being orthogonal to each other; the an optical retarder configured to receive the pulsed radiation and decompose each pulse of the pulsed radiation into a first pulse component having the first linear polarization state and a second pulse component having the second polarization state; the optical a retarder further configured to apply a time delay between the first pulse component and the second pulse component of each pulse; and an optical reflector including an axis of rotation perpendicular to the optical reflector A plane of incidence of the first pulse component and the second first pulse component on and having a magnitude of substantially 45 degrees relative to each of the first axis and the second axis of the optical retarder At an angle, the optical reflector is configured to at least partially reflect the first pulse component and the second pulse component of each pulse. 2. The optical configuration of clause 1, wherein the optical retarder includes a birefringent crystal or a liquid crystal polymer configured to decompose the pulsed radiation into components corresponding to the first pulse. component and the second pulse component is an ordinary wave (o wave) and an abnormal wave (e wave). 3. The optical configuration of item 2, wherein the optical retarder includes a birefringent crystal, and the birefringent crystal includes one or more of crystalline quartz, calcite and sapphire. 4. The optical configuration of any one of clauses 1 to 3, configured such that the first axis and the second axis of the optical retarder are each perpendicular to the propagation direction of the pulsed radiation. 5. The optical configuration according to any one of items 1 to 4, wherein one of the first axis and the second axis is the optical axis of the optical retarder. 6. An optical arrangement as in any preceding clause, wherein the time delay is at least 50% of the pulse length of one of the pulsed radiations. 7. The optical configuration of clause 6, wherein the time delay is at least 50 fs. 8. The optical configuration of clause 6, wherein the time delay is at least 100 fs. 9. The optical configuration of clause 6, wherein the time delay is at least 200 fs. 10. The optical configuration of any of the preceding clauses, wherein the angle of incidence of the first pulse component and the second pulse component of each pulse on the optical reflector is at least 10 degrees. 11. The optical configuration of any one of clauses 1 to 9, wherein the incident angle of the first pulse component and the second pulse component of each pulse on the optical reflector is at least 30 degrees. 12. The optical configuration of any one of items 1 to 9, wherein the incident angle of the first pulse component and the second pulse component of each pulse on the optical reflector is between 40 degrees and 50 degrees. between. 13. The optical arrangement of any of the preceding clauses, wherein the optical reflector includes an optical substrate having a front reflective surface and a back reflective surface, the front reflective surface interacting with the pulsed radiation in front of the back reflective surface; wherein the front reflective surface includes a first optical coating configured to partially reflect the first component and the second component of each pulse of the pulsed radiation. 14. The optical configuration of clause 13, wherein the first optical coating is configured to have a first reflectivity in a first wavelength range and a second reflectivity in a second wavelength range, the Each of the first wavelength range and the second wavelength range is a sub-range of the pulsed radiation. 15. The optical configuration of clause 14, wherein the first reflectivity is higher than 80% and the first wavelength range is between 100 nm and 400 nm; and wherein the second reflectivity is lower than 20% and the second The wavelength range is between 400 nm and 2000 nm. 16. The optical arrangement of clause 13, wherein the first optical coating is configured to be partially reflective throughout the entire wavelength range of the pulsed radiation. 17. The optical arrangement of any one of clauses 13 to 16, wherein the back-reflective surface includes a second optical coating configured to partially reflect the first component of the pulsed radiation and the portion of the second component that has reached the back-reflective surface after traversing the optical substrate. 18. If the optical arrangement of any of the preceding clauses further includes polarization preserving optical elements operable to direct the reflected first component and the second component of each pulse of the pulsed radiation to a or multiple locations. 19. A method of setting up an optical configuration as in any of the preceding clauses, which includes: identifying a first axis and a second axis of an optical retarder; identifying an axis of rotation of the optical reflector; and rotating one or both of the following: defined by the first axis and the second axis The optical retarder in a first plane and the optical reflector in a plane parallel to the first plane, such that the first axis and the second axis of the optical retarder are each aligned with the optical reflector The axis of rotation is oriented at an angle having a magnitude of substantially 45 degrees. 20. A radiation source comprising: an optical fiber for generating broadband output radiation; and At least one optical arrangement as in any one of clauses 1 to 18, configured to reflect a portion of the output radiation of the radiation source. 21. The radiation source of clause 20, further comprising at least one diagnostic sensor or tool configured to receive and measure that portion of the output radiation. 22. The radiation source of clause 21, further comprising an alignment module for aligning a pump radiation beam into one of the input facets of the optical fiber; and a control arrangement operable to act based on the At least one diagnostic sensor or one of the tool outputs controls the alignment module. 23. The radiation source of Item 20, 21 or 22, wherein the optical fiber is a solid core or hollow core photonic crystal fiber. 24. A metrological device comprising a radiation source as defined in any one of clauses 20 to 23. 25. A weights and measures device as described in clause 24, wherein the weights and measures device is operable as a scatterometer weights and measures device. 26. A metrological device as in clause 24, wherein the metrological device can operate as a first-order sensor or an alignment sensor. 27. A lithography apparatus comprising at least one of the metrology devices of clause 26 for performing alignment and/or balancing of metrology. 28. A lithography manufacturing unit, which includes a lithography device as in Item 27 and a weight and measurement device as in Item 25.

Although specific reference may be made herein to the use of lithography devices in IC fabrication, it will be understood that the lithography devices described herein may have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

Although specific reference may be made herein to embodiments of the invention in the context of lithography apparatus, embodiments of the invention may be used in other apparatuses. Embodiments of the invention may form part of a reticle inspection device, a metrology device, or any device that measures or processes an object such as a wafer (or other substrate) or reticle (or other patterned device). Such devices may be generally referred to as lithography tools. Such lithography tools may use either vacuum conditions or ambient (non-vacuum) conditions.

Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be understood that where the context permits, the invention is not limited to optical lithography and may be used in other applications, such as embossing. Printed in micro-shadow. While specific embodiments of the invention have been described above, it should be understood that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not restrictive. Accordingly, it will be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims as set forth below.

2: Broadband (white light) radiation projector 4: Spectrometer detector 6: Substrate 1400: Computer system 1402: Bus 1404: Processor 1405: Processor 1406: Main memory 1408: Read-only memory 1410: Storage device 1412: Monitor 1414: Input device/cursor control 1418: Communication interface 1420: Network link 1422: Local area network 1424: Host computer 1426: Internet service provider 1428: Internet 1430: Server ANG: Incident angle AM: Mark AS: Alignment sensor AU: Alignment unit B: Radiation beam BD: Beam delivery system BE1: Patterned radiation beam/measurement beam BE2: Arrow BK: Baking plate BS1: Beam splitter BS2: Beam splitter C: target part CC: capillary cavity CAP: capillary CH: cooling plate CL: computer system DB1: part of the reflected beam/output radiation DB2: part of the reflected beam/output radiation DE: developer DET: detector DGR: detection grating DIG1: diagnostic tool DIG2: diagnostic tool ER1: error signal ER2: error signal FA: first axis FC: first pulse component FPOL: first linear polarization FS: first surface/front surface HC: empty Core IB: incident beam/information carrying beam IE: input end IF: position measurement system IL: lighting system/illuminator IRD: input radiation I/O1: input/output port I/O2: input/output port LA: micro shadow device LACU: lithography control unit LB: loading box LC: lithography manufacturing unit LS: level or height sensor LSB: radiation beam LSD: detection unit LSO: radiation source LSP: projection unit M1: mask alignment mark M2: Mask alignment mark MA: Patterned device/mask MLO: Measurement position/Measurement area MT: Mask support/Metric tool/Spectral scatterometer/Metric system NV: Normal vector n1: Refraction of air Rate n2: Refractive index of optical window OA: Optical configuration/optical axis OB: Output beam OE: Output end OF: Optical fiber OL: Objective lens OR: Optical reflector ORD: Output radiation OT: Optical retarder OW: Optical window P1: Substrate Alignment mark P2: Substrate alignment mark PD: Photodetector PGR: Projection grating PM: First positioner POI: Incident plane PRS: Pulse pump radiation source PS: Projection system PU: Processing unit PW: Second positioning RA: rotation axis RB: radiation beam/reflected beam RDS: radiation source RO: robot RSO: radiation source RSV: reservoir SA: second axis SC: spin coater/second pulse component SC1: first scale SC2 : Second scale SC3: Third scale SCS: Supervisory control system SI: Intensity signal SM: Spot mirror SO: Radiation source SP: Illumination spot/support part SPOL: Second linear polarization SRI: Self-reference interferometer SS : Second surface/back reflective surface ST: Support tube TB: Transmissive part of light beam/transmitted light beam TCU coating and development system control unit TD: Time delay TW1: First transparent window TW2: Second transparent window W: Substrate WM: Work Medium WP: Capillary wall part WT: Substrate support θ _i : Angle θ _t : Refraction angle

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: - Figure 1 depicts a schematic overview of the lithography apparatus; - Figure 2 depicts a schematic overview of the lithography manufacturing unit; - Figure 3 depicts a schematic representation of overall lithography, which represents the cooperation between three key technologies for optimizing semiconductor manufacturing; - Figure 4 depicts a schematic overview of a scatterometry device for use as a metrology device, which may include a radiation source, according to an embodiment of the invention; - Figure 5 depicts a schematic overview of a level sensor device that may include a radiation source according to an embodiment of the invention; - Figure 6 depicts a schematic overview of an alignment sensor device that may include a radiation source according to an embodiment of the invention; - Figure 7 is a schematic cross-sectional view of a hollow core optical fiber that may form part of a radiation source according to an embodiment in a transverse plane (i.e., perpendicular to the axis of the optical fiber); - Figure 8 depicts a schematic representation of an example radiation source for providing broadband output radiation; - Figures 9(a) and 9(b) schematically depict transverse sections of an example of a hollow core photonic crystal fiber (HC-PCF) design for supercontinuum generation; - Figure 10 schematically depicts another example radiation source for providing broadband output radiation; - Figure 11A schematically depicts the operating principle of a beam splitter based on a plano-plano optical window; - Figure 11B is an example graph of two reflectivity curves at the optical interface calculated respectively for the light wave in the p-polarization state and for the light wave in the s-polarization state; - Figure 12 schematically depicts an optical arrangement for reflecting an incident beam of pulsed radiation according to an embodiment; - Figure 13 schematically depicts the principle of operation of an example birefringent crystal; and - Figure 14 is a block diagram illustrating a computer system that may assist in implementing the methods and processes disclosed herein. - Figure 15 experimentally depicts the results obtained demonstrating the effectiveness of an embodiment depicted in Figure 12.

FA: first axis

FC: first pulse component

FPOL: first linear polarization

IB: incident beam/information carrying beam

OA: Optical configuration/optical axis

OB: output beam

OR: optical reflector

OT: Optical retarder

POI: plane of incidence

RA: axis of rotation

RB: Radiation beam/reflected beam

SA: Second axis

SC: spin coater/second pulse component

SPOL: second linear polarization

TD: time delay

Claims (15)

An optical arrangement for reflecting pulsed radiation, comprising: An optical retarder comprising a first axis coincident with a first linear polarization state and a second axis coincident with a second linear polarization state, the first axis and the second axis being orthogonal to each other; the an optical retarder configured to receive the pulsed radiation and decompose each pulse of the pulsed radiation into a first pulse component having the first linear polarization state and a second pulse component having the second polarization state; the The optical retarder is further configured to apply a time delay between the first pulse component and the second pulse component of each pulse; and An optical reflector comprising an axis of rotation perpendicular to an incident plane of the first pulse component and the second first pulse component on the optical reflector and relative to the first plane of the optical retarder Each of the axis and the second axis forms an angle having a magnitude of substantially 45 degrees, and the optical reflector is configured to at least partially reflect the first pulse component and the second pulse component of each pulse. . The optical configuration of claim 1, wherein the optical retarder includes a birefringent crystal or a liquid crystal polymer configured to decompose the pulse radiation into components corresponding to the first pulse component and the liquid crystal polymer respectively. The second pulse component consists of an ordinary wave (o wave) and an abnormal wave (e wave). The optical configuration of claim 2, wherein the optical retarder includes a birefringent crystal, and the birefringent crystal includes one or more of crystalline quartz, calcite and sapphire. The optical configuration of claim 1 is configured such that the first axis and the second axis of the optical retarder are each perpendicular to the propagation direction of the pulsed radiation. The optical configuration of claim 1, wherein one of the first axis and the second axis is the optical axis of the optical retarder. The optical arrangement of claim 1, wherein the time delay is at least 50% of a pulse length of the pulsed radiation. The optical configuration of claim 6, wherein the time delay is at least 50 fs. The optical arrangement of claim 1, wherein the incident angle of the first pulse component and the second pulse component of each pulse on the optical reflector is at least 10 degrees. The optical configuration of claim 1, wherein the incident angle of the first pulse component and the second pulse component of each pulse on the optical reflector is between 40 degrees and 50 degrees. The optical arrangement of claim 1, wherein the optical reflector includes an optical substrate having a front reflective surface and a back reflective surface, the front reflective surface interacting with the pulsed radiation in front of the back reflective surface; wherein the front reflective surface The surface includes a first optical coating configured to partially reflect the first component and the second component of each pulse of the pulsed radiation. The optical configuration of claim 10, wherein the first optical coating is configured to have a first reflectivity in a first wavelength range and a second reflectivity in a second wavelength range, the first Each of the wavelength range and the second wavelength range is a sub-range of the pulsed radiation. A radiation source containing: an optical fiber for generating broadband output radiation; and At least one optical arrangement according to any one of claims 1 to 11 configured to reflect a portion of the output radiation of the radiation source. The radiation source of claim 12, further comprising at least one diagnostic sensor or tool configured to receive and measure the portion of the output radiation. The radiation source of claim 13, further comprising an alignment module for aligning a pump radiation beam into one of the input facets of the optical fiber; and A control arrangement operable to control the alignment module based on an output of the at least one diagnostic sensor or tool. A weight and measurement device comprising a radiation source as claimed in claim 12.