Photonic integrated circuits for generating broadband radiation

Abstract

The photonic integrated circuit includes an optical input configured to receive pump radiation and a number of nonlinear elements coupled to the optical input, the number of nonlinear elements configured to generate broadband radiation upon receiving the pump radiation, and at least two of the number of nonlinear elements differing in at least material and / or dimension.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. 22209252.0, filed November 24, 2022, which is incorporated herein by reference in its entirety.

[0002]

[0002] The present invention relates to generating broadband radiation in photonic integrated circuits, and in particular to generating broadband radiation in photonic integrated circuits having multiple nonlinear elements, at least two of the nonlinear elements having different characteristics. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern (often called a "design layout" or "design") in a patterning device (e.g., mask) onto a layer of radiation-sensitive material (resist) provided on the substrate (e.g., wafer).

[0004]

[0004] Lithographic apparatus may use electromagnetic radiation to project a pattern onto a substrate. 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. Lithographic apparatus using extreme ultraviolet (EUV) radiation with wavelengths in the range 4-20 nm, for example 6.7 nm or 13.5 nm, can form smaller features on a substrate than lithographic apparatus using radiation with a wavelength of, for example, 193 nm.

[0005]

[0005] Low k1 lithography can be used to process features with dimensions smaller than the classical resolution limit of a lithographic apparatus. In such processes, the resolution equation can be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics of the lithographic apparatus, CD is the "critical dimension" (generally the smallest feature size to be printed, in this case the half pitch), and k1 is an empirical resolution factor. In general, the smaller k1 is, the more difficult it is to reproduce on a substrate a pattern that resembles the shape and dimensions planned by a circuit designer to achieve a particular electrical functionality and performance. To overcome such difficulties, advanced fine-tuning steps can be applied to the lithographic projection apparatus and / or the design layout. Such steps include, but are not limited to, optimization of the NA, customization of the illumination scheme, use of phase-shift patterning devices, various optimizations of the design layout, such as optical proximity correction (OPC, sometimes also called "optical and process correction") in the design layout or other methods commonly defined as "resolution enhancement techniques" (RET). Alternatively, a strict control loop can be used to manage the stability of the lithographic apparatus to improve pattern replication at low k1.

[0006]

[0006] In the field of lithography, many measurement systems may be used, both within the lithographic apparatus and external to the lithographic apparatus. Generally, such measurement systems may use a radiation source for irradiating a target with radiation and a detection system operable to measure at least one property of a portion of the incident radiation scattered from the target. An example of a measurement system external to the lithographic apparatus is an inspection apparatus or metrology apparatus, which may be used to determine properties of a pattern previously projected onto a substrate by the lithographic apparatus. Such an external inspection apparatus may include, for example, a scatterometer. Examples of measurement systems that may be provided within the lithographic apparatus include topography measurement systems (also known as level sensors), position measurement systems (e.g., interferometric devices) for determining the position of a reticle or wafer stage, and alignment sensors for determining the position of alignment marks. These measurement devices may perform the measurements using electromagnetic radiation.

[0007]

[0007] Some measurement systems may use radiation in different wavelength ranges to make one or more measurements. This may be possible, for example, by providing a broadband radiation source, such as a supercontinuum radiation source. Such radiation sources may be complex and expensive to manufacture, and it is an object of the present disclosure to ameliorate at least some of the existing challenges in broadband radiation generation. Summary of the Invention

[0008] According to a first aspect of the present disclosure, there is provided a photonic integrated circuit including an optical input configured to receive pump radiation and a number of nonlinear elements coupled to the optical input, the number of nonlinear elements configured to generate broadband radiation upon receiving the pump radiation, at least two of the number of nonlinear elements differing in at least material and / or dimension.

[0009] Optionally, the nonlinear element may be a waveguide.

[0010] Optionally, at least one nonlinear element of the number of nonlinear elements comprises aluminum nitride AlN.

[0011] Optionally, the material of the multiple nonlinear elements may include one or more of diamond, silicon nitride, aluminum nitride, lithium niobate, and gallium arsenide.

[0012] Optionally, at least two of the multiple nonlinear elements may have different dimensions, the dimensions including cross-sectional thickness in a plane perpendicular to the direction of propagation of radiation in the nonlinear element.

[0013] Optionally, the thickness varies along a portion of the length of the nonlinear element, which portion is less than the entire length of the waveguide.

[0014] Optionally, at least two of the multiple nonlinear elements may have different dimensions, the dimensions including lengths along the direction of propagation of the nonlinear elements.

[0015] Optionally, multiple nonlinear elements may be located in the same plane of the substrate of the photonic integrated circuit.

[0016] Optionally, one or more of the multiple nonlinear elements may include a stacked arrangement made up of layers of material, and at least two of the multiple nonlinear elements may have layers of material of different compositions.

[0017]

[0017] Optionally, the photonic integrated circuit may further include a merging element configured to receive the broadband radiation generated in each of the multiple nonlinear elements and merge it into a single broadband radiation beam.

[0018] Optionally, the number of nonlinear elements may include 3 to 50 nonlinear elements, or 15 to 50 nonlinear elements.

[0019]

[0019] Optionally, the broadband radiation may include supercontinuum radiation.

[0020] Optionally, the supercontinuum radiation may comprise radiation having a wavelength in the range of 100 nm to 2000 nm, in the range of 200 nm to 2000 nm, or in the range of 200 nm to 1600 nm.

[0021] Optionally, the pump radiation may comprise a pulsed pump radiation beam.

[0022] Optionally, the pump radiation may comprise one or more wavelengths in the range of 400 nm to 2000 nm, or 1000 to 1500 nm.

[0023] Optionally, the pump radiation may comprise a single pump radiation beam.

[0024] Optionally, the optical input may include a single optical input connected to all of the multiple nonlinear elements.

[0025]

[0025] Optionally, the single optical input may include a star coupler.

[0026] According to another aspect of the present disclosure, there is provided a broadband radiation source including a photonic integrated circuit as described above.

[0027] According to another aspect of the present disclosure, there is provided a metrology apparatus including a broadband radiation source as described above.

[0028]

[0028] According to another aspect of the present disclosure, there is provided an inspection apparatus including a broadband radiation source as described above.

[0029] According to another aspect of the present disclosure, there is provided a lithographic apparatus including a broadband radiation source as described above.

[0030] According to another aspect of the present disclosure, there is provided a lithocell including a broadband radiation source, a metrology apparatus, an inspection apparatus, and / or a lithography apparatus as described above.

[0031]

[0031] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: [Brief explanation of the drawings]

[0032] [Figure 1] 1 depicts a schematic overview of a lithographic apparatus; [Figure 2]

[0031] A schematic overview of a lithography cell is shown. [Figure 3]

[0031] A schematic diagram of holistic lithography is shown, illustrating the collaboration between three key technologies for optimizing semiconductor manufacturing. [Figure 4]

[0031] A schematic diagram of a scatterometer metrology tool is shown. [Figure 5]

[0031] A schematic diagram of a level sensor metrology tool is shown. [Figure 6]

[0031] A schematic diagram of an alignment sensor metrology tool is shown. [Figure 7]

[0031] A schematic representation of a photonic integrated circuit with multiple nonlinear elements is shown. [Figure 8] 1 shows a schematic representation of a photonic integrated circuit having multiple nonlinear elements, at least two of which have different dimensions. DETAILED DESCRIPTION OF THE INVENTION

[0033]

[0032] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having wavelengths of 365, 248, 193, 157 or 126 nm) and EUV (e.g., extreme ultraviolet radiation having wavelengths in the range of about 5 to 100 nm).

[0034] <Reticle>

[0033] As used herein, the terms "reticle," "mask," or "patterning device" may be broadly interpreted to refer to a general patterning device that can be used to provide an incident radiation beam with a patterned cross-section that corresponds to the pattern to be created on a target portion of a substrate. The term "light valve" is sometimes also used in this context. In addition to classic masks (transmissive or reflective masks, binary masks, phase-shifting masks, hybrid masks, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0035] 1 schematically depicts a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system IL (also called an illuminator) configured to condition a radiation beam B (e.g. UV radiation, DUV radiation or EUV radiation), a mask support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA in accordance with certain parameters, a substrate support (e.g. a wafer 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 in accordance with certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0036]

[0035] In operation, the illumination system IL receives a radiation beam from a radiation source SO (e.g. via a beam delivery system BD). The illumination system IL may include various types of optical components for directing, shaping and / or controlling the radiation, for example refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components or any combination thereof. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section in the plane of the patterning device MA.

[0037]

[0036] As used herein, the term "projection system" PS should be interpreted broadly to encompass various types of projection systems. Such systems may include refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, as required by the exposure radiation being used and / or other factors (e.g., the use of an immersion liquid or the use of a vacuum). Where the term "projection lens" is used herein, it may all be considered as synonymous with the more general term "projection system" PS.

[0038]

[0037] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g. water) so as to fill a space between the projection system PS and the substrate W, which is also known as immersion lithography. Further details about immersion techniques are given in U.S. Patent No. 6,952,253, which is incorporated herein by reference.

[0039] The lithographic apparatus LA may be of a type having two or more substrate supports WT (also known as "dual stage"). In such a "multiple stage" machine, the substrate supports WT may be used in parallel, and / or a substrate W on one of the substrate supports WT may be used to expose a pattern thereon, while a procedure is being performed on another substrate W on the other substrate support WT in preparation for a subsequent exposure of that other substrate W.

[0040] In addition to the substrate support WT, the lithographic apparatus LA may include a measurement stage. The measurement stage is configured to hold a sensor and / or a cleaning apparatus. The sensor may be configured to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning apparatus may be configured to clean part of the lithographic apparatus, for example part of the projection system PS or part of a system for supplying immersion liquid. The measurement stage may move below the projection system PS when the substrate support WT is spaced apart from the projection system PS.

[0041] In operation, a radiation beam B is incident on a patterning device (e.g. a mask MA held on a mask support MT) and is patterned according to a pattern (design layout) on the patterning device MA. After traversing the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and the position measurement system IF, the substrate support WT can be precisely moved, for example so that different target portions C are positioned at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM, and possibly another position sensor (which is not explicitly shown in Figure 1), may be used to precisely position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although substrate alignment marks P1, P2 occupy dedicated target portions as illustrated, they may be located in spaces between target portions. When located between target portions C, substrate alignment marks P1, P2 are referred to as scribe-lane alignment marks.

[0042] 2, the lithography apparatus LA may be part of a lithography cell LC (sometimes called a litho-cell or (litho)-cluster), which often also includes apparatus for performing pre-exposure and post-exposure processes on the substrate W. Conventionally, such apparatus include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH, and a bake plate BK (which, for example, adjust the temperature of the substrate W, e.g., to adjust the solvent in the resist layer). A substrate handler (i.e., robot) RO picks up substrates W from input / output ports I / O1, I / O2, moves them between various process tools, and delivers them to a loading bay LB of the lithography apparatus LA. The devices within a lithocell are often collectively referred to as a track and are typically under the control of a track control unit TCU, which itself may be controlled by a supervisory control system SCS, which may also control the lithographic apparatus LA (e.g., via a lithography control unit LACU).

[0043] To ensure that a substrate W to be exposed by lithographic apparatus LA is exposed accurately, it is desirable to inspect the substrate to measure properties of the patterned structures, such as overlay error between successive layers, line thickness, critical dimension (CD), etc. To that end, an inspection tool (not shown) may be included in lithocell LC. If an error is detected, adjustments may be made, for example, to the exposure of subsequent substrates or other process steps to be performed on substrate W, particularly if inspection is carried out before other substrates W of the same batch or lot are subsequently exposed or processed.

[0044] Inspection apparatus, sometimes called metrology apparatus, are used to measure the properties of substrates W, and in particular to measure how the properties of different substrates W vary, or how properties associated with different layers of the same substrate W vary from layer to layer. The inspection apparatus may alternatively be constructed to identify defects on substrates W and may, for example, be part of a lithocell LC, or integrated into a lithography apparatus LA, or may be a stand-alone apparatus. The inspection apparatus may measure properties related to a latent image (an image in a resist layer after exposure), or a semi-latent image (an image in a resist layer after a post-exposure bake step PEB), or a developed resist image (from which exposed or unexposed parts of the resist have been removed), or even a property related to an etched image (after a pattern transfer step such as etching).

[0045] Typically, the patterning process in a lithography apparatus LA is one of the most critical steps in processing, requiring high accuracy in the dimensioning and placement of structures on a substrate W. To ensure this high accuracy, three systems can be combined in a so-called "holistic" control environment, as shown schematically in FIG. 3 . One of these systems is a lithography apparatus LA, which is (virtually) connected to a metrology tool MT (a second system) and a computer system CL (a third system). The key to such a "holistic" environment is optimizing the coordination between these three systems to enforce the overall process window and achieve a tight control loop so that the patterning performed by the lithography apparatus LA stays within the process window. The process window defines the range of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process will produce a specified result (e.g., a functioning semiconductor device), and typically within which the process parameters of a lithography process or patterning process can vary.

[0046]

[0045] The computer system CL is capable of predicting which resolution enhancement techniques should be used by using (parts of) the design layout to be patterned, and is capable of performing computational lithography simulations and calculations to determine mask layouts and lithography apparatus settings that maximize the overall process window of the patterning process (shown in FIG. 3 by the double-headed arrow at the first scale SC1). Typically, resolution enhancement techniques are tailored to the patterning capabilities of the lithography apparatus LA. The computer system CL is further capable of predicting whether defects are likely to exist (e.g., due to suboptimal processing) by detecting where in the process window the lithography apparatus LA is currently operating (e.g., using input from the metrology tool MT) (shown in FIG. 3 by the arrow pointing to "0" at the second scale SC2).

[0047] The metrology tool MT is capable of providing input to the computer system CL that enables accurate simulations and predictions, and is capable of providing feedback to the lithographic apparatus LA that identifies possible drifts (e.g. in the calibration status of the lithographic apparatus LA) (as indicated by the arrows at a third scale SC3 in Figure 3). Different types of metrology tools MT are described herein for measuring one or more properties related to the lithographic apparatus and / or the substrate to be patterned.

[0048]

[0047] In lithographic processes, it is desirable to frequently measure the structures produced (e.g., for process control and verification). Tools that perform such measurements are commonly called metrology tools MT. Various types of metrology tools MT that perform such measurements are known, such as scanning electron microscopes or various forms of scatterometer metrology tools MT. A scatterometer is a multipurpose instrument that allows measurements of parameters of the lithographic process to be made by having a sensor in the pupil or a conjugate plane to the pupil of the scatterometer objective (usually referred to as pupil-based measurements), or by having a sensor in the image plane or a conjugate plane to the image plane (in which case measurements are usually referred to as image-based or field-based measurements). Such scatterometers and associated measurement techniques are described in detail in U.S. Patent Application Publication Nos. 20100328655, 2011102753A1, 20120044470A, 20110249244, 20110026032, or EP 1,628,164A, which are incorporated by reference in their entireties. The scatterometers described above are capable of measuring gratings using soft x-rays and light in the visible to near-infrared wavelength range.

[0049] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, a reconstruction method may be applied to the measurement signal to reconstruct or calculate the properties of the grating. Such a reconstruction may, for example, be the result of simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulation results with the measurement results. Parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from the real target.

[0050]

[0049] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectroscopic scatterometer MT, radiation emitted by a radiation source is directed towards a target, and radiation reflected or scattered from the target is directed towards a spectrometer detector, which measures the spectrum of the specularly reflected radiation (i.e., measures the intensity as a function of wavelength). From this data, it is possible to reconstruct the structure or profile of the target giving rise to the detected spectrum, for example by means of rigorous coupled wave theory and nonlinear regression, or by comparison with a library of simulated spectra.

[0051] In a third embodiment, the scatterometer MT is an ellipsometric scatterometer. An ellipsometric scatterometer makes it possible to determine parameters of a lithographic process by measuring the scattered radiation for each polarization state. Such a metrology apparatus emits polarized light (e.g., linearly, circularly or elliptically polarized light), for example using appropriate polarizing filters in the illumination section of the metrology apparatus. A source suitable for the metrology apparatus can provide polarized radiation as well. Various embodiments of existing ellipsometric scatterometers are described in U.S. Patent Application Publication Nos. 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, which are incorporated by reference herein in their entireties.

[0052] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlay of two misaligned grating or periodic structures by measuring the asymmetry of the reflectance spectra and / or the detection configuration, where the asymmetry is related to the degree of overlay. The two (typically overlapping) grating structures can be applied in two different (not necessarily consecutive) layers and formed at substantially the same location on the wafer. The scatterometer can have a symmetric detection configuration, for example, as described in co-owned European Patent Application Publication No. 1628164A, so that any asymmetry can be clearly distinguished. This provides a straightforward method for measuring grating misalignment. Further examples for measuring the overlay error between two layers containing periodic structures when the target is measured through the asymmetry of the periodic structures can be obtained from PCT Patent Application Publication No. WO 2011 / 012624 or U.S. Patent Application No. 20160161863, which are incorporated herein by reference in their entirety.

[0053]

[0052] Other parameters of interest can be focus and dose. Focus and dose can be determined simultaneously by scatterometry (or alternatively by scanning electron microscopy), as described in U.S. Patent Application No. 2011-0249244, which is incorporated herein by reference in its entirety. A single structure can be used that has a unique combination of critical dimension and sidewall angle measurements for each point of the focus-energy matrix (FEM, also called focus-exposure matrix). If these unique combinations of critical dimension and sidewall angle are available, focus and dose values ​​can be uniquely determined from these measurements.

[0054]

[0053] A metrology target can be a collection of composite gratings, mostly formed by a lithography process in resist, but also formed after, for example, an etching process. Typically, the pitch and linewidth of the grating structures strongly depend on the measurement optics (specifically, the NA of the optics) so that the diffraction orders obtained from the metrology target can be captured. As previously shown, the diffraction signal can be used to determine the shift between two layers (also called "overlay") or to reconstruct at least a portion of the original grating as produced by the lithography process. This reconstruction can be used to provide guidance on the quality of the lithography process and can be used to control at least a portion of the lithography process. The target can have smaller subsegments configured to mimic the dimensions of the features of the design layout in the target. This subsegmentation causes the target to behave more similarly to the features of the design layout, so that all process parameter measurements closely resemble the features of the design layout. The target can be measured in underfill mode or overfill mode. In underfill mode, the measurement beam generates a spot that is smaller than the entire target. In overfill mode, the measurement beam generates a spot that is larger than the entire target. In such an overfill mode, it may be possible to simultaneously measure different targets, and therefore determine different process parameters therefrom.

[0055] The overall measurement quality of a lithography parameter using a particular target depends, at least in part, on the measurement recipe used to measure that lithography parameter. The term “substrate measurement recipe” can include one or more parameters of the measurement itself, one or more parameters of the measured pattern(s), or both. For example, if the measurement used in the substrate measurement recipe is a diffraction-based optical measurement, one or more of the parameters of the measurement can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. One of the criteria for selecting a measurement recipe can be, for example, the sensitivity of one of the measurement parameters to process variations. Further examples are described in U.S. Patent Application No. 2016-0161863 and published U.S. Patent Application No. 2016 / 0370717A1, which are incorporated herein by reference in their entireties.

[0056] A metrology apparatus such as a scatterometer SM1 is shown in FIG. 4. It includes a broadband (white light) radiation projector 2 that projects radiation onto a substrate 6. Reflected or scattered radiation is sent to a spectrometer detector 4, which measures the spectrum 10 of the specularly reflected radiation (i.e., a measurement of the intensity In1 as a function of wavelength λ). From this data, the structure or profile giving rise to the detected spectrum can be reconstructed by a processing unit (PU), for example by rigorous coupled-wave analysis and nonlinear regression, or by comparison with a library of simulated spectra as shown at the bottom of FIG. 4. Typically, for reconstruction, the general form of the structure is known and some parameters are assumed from knowledge of the process by which the structure was created, thereby leaving only a few parameters of the structure to be determined from the scatterometry data. Such a scatterometer may be configured as a normal-incidence scatterometer or an oblique-incidence scatterometer.

[0057] In lithography processes, it is desirable to frequently measure the structures created (e.g., for process control and verification). Various tools for performing such measurements are known, including scanning electron microscopes or various forms of metrology devices (such as scatterometers). Examples of known scatterometers often rely on the provision of dedicated metrology targets, such as underfilled targets (targets in the form of simple gratings or overlapping gratings of different layers, large enough that the measurement beam can generate a spot smaller than the grating) or overfilled targets (where the illumination spot partially or completely covers the target). Furthermore, the use of metrology tools (e.g., angle-resolved scatterometers illuminating underfilled targets (such as gratings)) allows the use of so-called reconstruction methods, in which the properties of the grating can be calculated by simulating the interaction of scattered radiation with a mathematical model of the target structure and comparing the simulation results with measurements. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from the actual target.

[0058]

[0057] A scatterometer is a multipurpose instrument that allows measurements of parameters of a lithographic process to be made by having a sensor at the pupil or a conjugate plane to the pupil of the scatterometer objective (commonly referred to as pupil-based measurements) or at the image plane or a conjugate plane to the image plane (commonly referred to as image-based or field-based measurements). Such scatterometers and associated measurement techniques are further described in U.S. Patent Application Publication No. 20100328655, U.S. Patent Application Publication No. 2011102753A1, U.S. Patent Application Publication No. 20120044470A, U.S. Patent Application Publication No. 20110249244, U.S. Patent Application Publication No. 20110026032 or European Patent Application Publication No. 1628164A, which are incorporated herein by reference in their entireties. The scatterometer described above can measure multiple targets from multiple gratings in one image using soft x-rays and light in the visible to near infrared wavelength range.

[0059]

[0058] A topography measurement system, a level sensor, or height sensor, and which may be incorporated into a lithographic apparatus, is arranged to measure the topography of the upper surface of a substrate (or wafer). A map of the topography of the substrate (also called a height map) may be generated from these measurements, showing the height of the substrate as a function of position on the substrate. This height map may later be used to correct the position of the substrate during transfer of a pattern onto the substrate, in order to provide an aerial image of the patterning device at the correct focus position on the substrate. It will be understood that "height" in this context refers broadly to the out-of-plane dimension relative to the substrate (also called the Z-axis). Typically, a level or height sensor makes measurements at a fixed position (relative to its own optics), and relative movement of the substrate and the optics of the level or height sensor results in height measurements at locations across the substrate.

[0060]

[0059] An example of a level or height sensor LS known in the art is shown schematically in Figure 5, which shows only the operating principle. In this example, the level sensor includes an optical system, which includes a projection unit LSP and a detection unit LSD. The projection unit LSP includes a radiation source LSO that provides a radiation beam LSB, which is provided by a projection grating PGR of the projection unit LSP. The radiation source LSO may be, for example, a narrowband or broadband radiation source, such as a polarized or unpolarized, pulsed or continuous (such as a polarized or unpolarized laser beam) supercontinuum light source. The radiation source LSO may include multiple radiation sources (such as multiple LEDs) with different colors or wavelength ranges. The radiation source LSO of the level sensor LS is not limited to visible radiation but may additionally or alternatively include UV and / or IR radiation, as well as any wavelength range suitable for reflection from the surface of the substrate.

[0061]

[0060] The projection grating PGR is a periodic grating comprising a periodic structure which results in a radiation beam BE1 with a periodically varying intensity. The radiation beam BE1 with a periodically varying intensity is directed towards a measurement location MLO on the substrate W with an angle of incidence ANG relative to an axis normal to the substrate surface of incidence (Z-axis) of between 0 and 90 degrees, typically between 70 and 80 degrees. At the measurement location MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and directed towards a detection unit LSD.

[0062]

[0061] To determine the height level at the measurement location MLO, the level sensor further comprises a detection system including a detection grid DGR, a detector DET, and a processing unit (not shown) for processing an output signal of the detector DET. The detection grid DGR may be the same as the projection grid PGR. The detector DET generates a detector output signal indicative of the received light, for example indicative of the intensity of the received light (e.g., a photodetector) or representing the spatial distribution of the received intensity (e.g., a camera). The detector DET may comprise any combination of one or more types of detector.

[0063]

[0062] Triangulation techniques allow the height level at the measurement location MLO to be determined. The detected height level is generally related to the signal intensity as measured by the detector DET, which has a periodicity that depends, among other things, on the design of the projection grating PGR and the (oblique) angle of incidence ANG.

[0064]

[0063] The projection unit LSP and / or detection unit LSD may include further optical elements, such as lenses and / or mirrors, along the path of the patterned radiation beam between the projection grating PGR and the detection grating DGR (not shown).

[0065] In an embodiment, the detection grating DGR may be omitted and the detector DET may be placed at the position where the detection grating DGR is located. Such a configuration provides a more direct detection of the image of the projection grating PGR.

[0066]

[0065] In order to effectively cover the surface of the substrate W, the level sensor LS may be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating an array of measurement areas MLO or spots that cover a larger measurement range.

[0067] Various height sensors of the general type are disclosed, for example, in U.S. Patent Nos. 7,265,364 and 7,646,471, both of which are incorporated by reference. A height sensor that uses UV radiation instead of visible or infrared radiation is disclosed in incorporated U.S. Patent Application Publication No. 2010233600A1. In incorporated WO 2016102127A1, a miniature height sensor is described that uses a multi-element detector to detect and recognize the position of a grating image without the need for a detection grating.

[0068] The position measurement system PMS may include any type of sensor suitable for determining the position of the substrate support WT. The position measurement system PMS may include any type of sensor suitable for determining the position of the mask support MT. The sensor may be an optical sensor, such as an interferometer or an encoder. The position measurement system PMS may include a combined interferometer and encoder system. The sensor may be another type of sensor, such as a magnetic sensor, a capacitive sensor or an inductive sensor. The position measurement system PMS may determine the position relative to a reference (e.g., the metrology frame MF or the projection system PS). The position measurement system PMS may determine the position of the substrate table WT and / or the mask support MT by measuring the position or by measuring a time derivative of the position (e.g., the velocity or the acceleration).

[0069] The position measurement system PMS may include an encoder system. Encoder systems are known, for example, from U.S. Patent Application Publication No. 2007 / 0058173 A1, filed September 7, 2006, which is incorporated herein by reference. The encoder system includes an encoder head, a grating, and a sensor. The encoder system may receive a primary radiation beam and a secondary radiation beam. Both the primary radiation beam and the secondary radiation beam originate from the same radiation beam (i.e., the original radiation beam). At least one of the primary radiation beam and the secondary radiation beam is generated by diffracting the original radiation beam with a grating. If both the primary radiation beam and the secondary radiation beam are generated by diffracting the original radiation beam with a grating, the primary radiation beam must have a different diffraction order from the secondary radiation beams. The different diffraction orders may be, for example, +1, −1, +2, and −2 orders. The encoder system optically combines the primary radiation beam and the secondary radiation beam into a combined radiation beam. A sensor in the encoder head determines the phase or phase difference of the combined radiation beam. The sensors generate signals based on the phase or phase difference. The signals represent the position of the encoder heads relative to the gratings. One of the encoder heads or the gratings may be disposed on the substrate structure WT. The other of the encoder heads or the gratings may be disposed on the metrology frame MF or the base frame BF. For example, multiple encoder heads may be disposed on the metrology frame MF, and the gratings may be disposed on the upper surface of the substrate support WT. In another example, the gratings may be disposed on the lower surface of the substrate support WT, and the encoder heads may be disposed below the substrate support WT.

[0070] The position measurement system PMS may include an interferometer system. Interferometer systems are known, for example, from U.S. Pat. No. 6,020,964, filed July 13, 1998, which is incorporated herein by reference. The interferometer system may include a beam splitter, a mirror, a reference mirror, and a sensor. A beam of radiation is split into a reference beam and a measurement beam by the beam splitter. The measurement beam propagates to the mirror, reflects off the mirror, and returns to the beam splitter. The reference beam propagates to the reference mirror, reflects off the reference mirror, and returns to the beam splitter. At the beam splitter, the measurement beam and the reference beam combine into a combined radiation beam. The combined radiation beam is incident on a sensor. The sensor determines the phase or frequency of the combined radiation beam. The sensor generates a signal based on the phase or frequency. The signal represents the displacement of the mirror. In an embodiment, the mirror is connected to the substrate support WT. The reference mirror may be connected to the metrology frame MF. In an embodiment, the measurement beam and the reference beam are combined into a combined radiation beam by an additional optical component instead of a beam splitter.

[0071] In the manufacture of complex devices, typically many lithographic patterning steps are performed, whereby functional features are formed in successive layers on a substrate. Therefore, an important aspect of the performance of a lithographic apparatus is the ability to correctly and accurately position an applied pattern in relation to features built up in previous layers (by the same apparatus or a different lithographic apparatus). For this purpose, one or more sets of marks are provided on the substrate. Each mark is a structure whose position can subsequently be measured using a position sensor (typically an optical position sensor). The position sensor is sometimes called an "alignment sensor" and the marks are sometimes called "alignment marks". The marks are sometimes called metrology targets.

[0072] A lithographic apparatus may include one or more (e.g., multiple) alignment sensors that can accurately measure the position of alignment marks provided on a substrate. Alignment (or position) sensors may use optical phenomena such as diffraction and interference to obtain position information from alignment marks formed on the substrate. One example of an alignment sensor used in current lithographic apparatuses is based on a self-referencing interferometer, such as that described in U.S. Pat. No. 6,961,116. Various improvements and modifications to position sensors have been developed, as disclosed, for example, in U.S. Patent Application Publication No. 2015261097A1. The entire contents of these publications are incorporated herein by reference.

[0073]

[0072] The mark or alignment mark may comprise a series of bars formed on or in a layer provided on the substrate, or formed (directly) in the substrate. The bars are regularly spaced apart to act as grating lines, so that the mark can be considered a diffraction grating with a known spatial period (pitch). Depending on the orientation of these grating lines, the mark may be designed to measure position along the X-axis or along the Y-axis (oriented substantially perpendicular to the X-axis). A mark including bars positioned at +45 degrees and / or -45 degrees relative to both the X-axis and the Y-axis allows combined X and Y measurements using techniques such as those described in U.S. Patent Application Publication No. 2009 / 195768A, which is incorporated by reference.

[0074]

[0073] The alignment sensor optically scans each mark with a radiation spot and obtains a periodically varying signal, such as a sine wave. The phase of this signal is analyzed to determine the position of the mark and thus the substrate relative to the alignment sensor, which is fixed relative to the reference frame of the lithographic apparatus. So-called coarse and fine marks are provided in association with different (coarse and fine) mark dimensions, so that the alignment sensor can distinguish between different cycles of the periodic signal and the exact position (phase) within the cycle. For this purpose, marks of different pitches can also be used.

[0075]

[0074] Measuring the position of the marks may also provide information about deformations of the substrate on which the marks are provided (e.g. the morphology of the wafer grid), which may be caused by, for example, electrostatic clamping of the substrate to the substrate table and / or heating of the substrate when exposed to radiation.

[0076] 6 is a schematic block diagram of an embodiment of a known alignment sensor AS, for example as described in the incorporated US Pat. No. 6,961,116. A radiation source RSO provides a radiation beam RB of one or more wavelengths, which is redirected by redirecting optics as an illumination spot SP onto a mark (such as a mark AM located on a substrate W). In this example, the redirecting optics include a spot mirror SM and an objective lens OL. The illumination spot SP (by which the mark AM is illuminated) may be slightly smaller in diameter than the width of the mark itself.

[0077]

[0076] Radiation diffracted by the mark AM is collimated (in this example by an objective lens OL) into an information-bearing beam IB. The term "diffracted" is intended to include zeroth order diffraction from the mark (which is sometimes called reflection). A self-referencing interferometer SRI, for example of the type disclosed in the above-mentioned U.S. Patent No. 6,961,116, causes the beam IB to interfere with itself, after which the beam is received by a photodetector PD. Further optical components (not shown) may be included to provide separate beams if more than one wavelength is produced by the radiation source RSO. The photodetector may be a single element, or it may include several pixels if required. The photodetector may include a sensor array.

[0078]

[0077] The redirecting optical element (in this example, the redirecting optical element includes a spot mirror SM) can also function to block zero-order radiation reflected from the mark AM so that the information-carrying beam IB contains only higher-order diffracted radiation from the mark AM (this is not essential for the measurement, but improves the signal-to-noise ratio).

[0079]

[0078] The intensity signal SI is fed to a processing unit PU. The combination of optical processing in block SRI and computational processing in unit PU outputs values ​​of the X and Y position on the substrate relative to a reference frame.

[0080] A single measurement of the type shown will only fix the position of the mark within a certain range corresponding to one pitch of the mark. In conjunction with this, coarser measurement techniques are used to identify which period of the sine wave contains the mark position. For improved accuracy and / or for robust detection of marks regardless of the material from which they are made and the material on which they are placed and / or below, the same process can be repeated at coarser and / or finer levels with different wavelengths. Wavelengths may be optically multiplexed and demultiplexed to be processed simultaneously, and / or wavelengths may be multiplexed by time division or frequency division.

[0081] In this example, the alignment sensor and spot SP remain stationary, and it is the substrate W that moves. The alignment sensor can therefore be rigidly and accurately mounted to a reference frame, effectively scanning the mark AM in a direction opposite to the direction of movement of the substrate W. The substrate W is controlled in this movement by a substrate positioning system that controls its mounting on the substrate support and the movement of the substrate support. A substrate support position sensor (e.g., an interferometer) measures the position of the substrate support (not shown). In an embodiment, one or more (alignment) marks are provided on the substrate support. Measuring the position of the marks provided on the substrate support allows the position of the substrate support, as determined by the position sensor, to be calibrated (e.g., relative to a frame to which the alignment system is connected). Measuring the position of the alignment marks provided on the substrate allows the position of the substrate relative to the substrate support to be determined.

[0082]

[0081] Metrology and / or inspection tools (also called metrology tools) such as those described above often use radiation to obtain measurement data. Different types of radiation can be used depending on the measurement target and the properties to be measured. One of the different properties of radiation is the wavelength used to obtain the measurements, since different wavelengths can provide different information about the measurement target. Some measurement tools may measure using broadband radiation or may use broadband radiation such as supercontinuum radiation so that the measurement wavelength used can be adjusted and selected. Depending on the range of output wavelengths and the properties of the broadband radiation source, different methods can be used to obtain broadband radiation. To generate broadband radiation, nonlinear effects can be used to broaden input radiation (also called pump radiation) over a narrow wavelength range. Different known setups and methods exist to achieve nonlinear broadening. Often, these methods rely on confinement of the pump radiation to achieve the high intensities required to produce significant nonlinear effects.

[0083]

[0082] A known method for confining radiation for the purpose of nonlinear broadening involves confining laser pump radiation in an optical fiber to generate supercontinuum radiation. The laser can be an ultrashort pulse laser (e.g., picosecond to femtosecond pulses). The nonlinear propagation dynamics of this radiation in the fiber can result in broadband radiation generation as a result of soliton self-compression and / or modulation instability. This can be used, for example, to generate supercontinuum radiation spanning a wavelength range from IR to UV.

[0084] Soliton dynamics can also be realized in integrated optical elements such as integrated waveguides. Integrated optical elements, also called photonic integrated circuits, in this context can refer to planar optical structures integrated (e.g., patterned) on a substrate such as a semiconductor wafer. They are also sometimes referred to as on-chip optical elements. Many semiconductor lithography methods and techniques known from integrated electronics can be used, although certain optical considerations, such as the transparency of materials to the radiation wavelengths of interest, may need to be taken into account. Integrated optical elements can have dimensions as small as micrometers or submicrometers (e.g., cross-section). By carefully tailoring the dimensions of the integrated optical elements (possible using advanced semiconductor electronics fabrication techniques), the propagation dynamics of radiation within the integrated waveguide can be precisely controlled. Under controlled conditions, strong confinement can be achieved when ultrashort laser pulses propagate through integrated optical waveguides. This can lead to the generation of broadband (e.g., supercontinuum) radiation within the integrated waveguide.

[0085] To control broadband radiation generation, the chromatic dispersion profile in the interaction region between the pump radiation and the nonlinear medium is controlled. In a setup using broadband generation in a hollow-core fiber, this control can be achieved by fine-tuning the dimensions, pressure (e.g., the pressure of the nonlinear gas in the fiber), and cross-sectional shape within the fiber. In a solid-core fiber, fine-tuning the core diameter and the geometry of the microstructured cladding surrounding the core can be used. In both cases, this control relies on fine-tuning the fiber fabrication process, which often relies heavily on human intervention and may not be available with a high degree of automation. For example, the assembly of fiber preforms may be performed manually by experts / craftsmen. In the case of photonic crystal fibers, precisely tuning the optical properties may require small-scale (e.g., nm-scale) control of the cladding geometry. As a result, the accuracy and repeatability of the manual fine-tuning may not be guaranteed in a controllable industrial process, which may reduce fiber yields. Since soliton propagation and the resulting supercontinuum generation depend heavily on the dispersion properties of the fiber, the detailed geometry of the structure plays an important role.

[0086]

[0085] While fiber manufacturing processes can rely on artisanal skill, integrated photonics offers a way to enable highly fine-tuned control of optical elements by utilizing advanced precision semiconductor fabrication techniques, which can provide the high levels of accuracy and repeatability desired in nonlinear propagation media for broadband generation.

[0087] The field of integrated optics has made progress in recent years by using advanced semiconductor (CMOS) fabrication processes to facilitate integrated optics fabrication. Material platforms such as Si3N4 have been advanced to reduce propagation losses. Propagation losses of 3 dB / m can now be achieved in Si3N4. This has enabled the efficient use of optical elements such as integrated optical frequency combs. One of the fundamental building blocks of photonic integrated circuits is the waveguide. Waveguides can confine and guide radiation, for example, among other integrated optical elements. Waveguides can be fabricated using standard lithographic patterning techniques. In photonic integrated waveguides, radiation is confined to a small cross-sectional area. This can be attributed to the high index contrast between the waveguide material and the cladding. Strong confinement enhances the interaction of radiation with the waveguide material, facilitating improved nonlinear processing. As a result, waveguides made from materials with high nonlinear interaction properties can be used to achieve integrated nonlinear interaction of radiation on-chip. This can include, for example, broadband radiation generation.

[0088]

[0087] Although there have been advances in integrated waveguide fabrication methods, their implementation in broadband radiation generation presents challenges. The first challenge is power scalability. The second challenge is the selection of materials that have a large transparency window covering the entire broadband range and are suitable for use with semiconductor fabrication techniques. This specification describes methods for overcoming at least some of these challenges in order to provide improved integrated optical structures for broadband radiation generation.

[0089] 7 shows a schematic representation of a photonic integrated circuit (PIC) 100. The photonic integrated circuit includes an optical input 104 configured to receive pump (input) radiation 106. The photonic integrated circuit further includes multiple nonlinear elements 102 connected to the optical input 104. The nonlinear elements 102 may be photonic integrated waveguides. The multiple nonlinear elements 102 are configured to generate broadband radiation 110 upon receiving the pump radiation 106. At least two of the nonlinear elements 102 differ in at least material and / or dimensions. The broadband radiation 110 may include supercontinuum radiation.

[0090] The broadband radiation 110 can be collected by the merging element 108 and provided as an output from the photonic integrated circuit 100. The merging element 108 can receive the broadband radiation 110 from the multiple nonlinear elements 102 and merge it into a single radiation beam. The multiple nonlinear elements 102 can provide multiple radiation beams. At least two of the multiple radiation beams can have different power density spectra. At least two of the multiple radiation beams can span different wavelength ranges and / or have different beam cross-sectional shapes when they reach the merging element.

[0091]

[0090] The photonic integrated circuits described herein aim to solve some of the problems currently faced by photonic integrated circuits by providing multiple nonlinear elements with different characteristics. An advantage of a photonic integrated circuit such as that shown in FIG. 7 may be that providing multiple parallel nonlinear elements, each receiving input radiation and generating output broadband radiation, allows for improved power scalability of photonic integrated setups with multiple nonlinear elements. Another advantage of a PIC as described herein may be bandwidth scalability, in that different characteristics of at least two nonlinear elements allow the two nonlinear elements to have different dispersion characteristics and, as a result, generate broadband radiation in different ranges. Thus, the resulting broadband radiation generated by the entire photonic integrated circuit may have a wider wavelength range and / or power density spectrum than can be achieved with a single waveguide. Further advantages of providing photonic integrated circuits over, for example, optical fibers may include, as discussed above, smaller structures and more precise control over the structure's geometry. As an illustrative example, a photonic integrated circuit (PIC) has dimensions on the order of about 1 cm by about 1 cm, whereas an optical fiber can be tens of centimeters or even meters long, thus allowing for orders of magnitude of miniaturization.

[0092] To qualify as a material for constructing a portion of a photonic integrated circuit, the material must be suitable for use in integrated fabrication methods, such as semiconductor lithography fabrication methods. Furthermore, the material must also have suitable optical transparency for the desired wavelengths. Many existing known materials (e.g., silicon-on-insulator (SOI), indium phosphide on silicon (IMOS)) used in lithography (e.g., for electronics fabrication) are not transparent to UV and / or visible radiation, including the radiation wavelengths of interest for the applications described herein. Therefore, these known materials may not be suitable for the photonic integrated circuits described herein. Materials with transparency windows in the UV and / or visible wavelength ranges that are compatible with semiconductor lithography fabrication techniques include diamond, silicon nitride, aluminum nitride, lithium niobate, and gallium arsenide. One or more of the numerous nonlinear elements can be made of these materials. In some implementations, all of the nonlinear elements are made from one or more of the same materials. In other implementations, at least two of the nonlinear elements can have different compositions of one or more different materials. Some or all of these materials may be made from the materials mentioned above.

[0093]

[0092] The nonlinear elements may include a stack arrangement made up of layers of material. At least two of the multiple nonlinear elements may have different stack compositions. The stack composition, particularly the difference between the stack compositions of different nonlinear elements, may allow for the design of nonlinear elements with different dispersion characteristics. This may allow for tuning / optimization of broadband generation for different wavelength ranges across the nonlinear elements. An example of a stack composition is "High-efficiency wideband SiN x This is described in "SiN -on-SOI grating coupler with low fabrication complexity" (Pengfei Xu et al., Optics Letters, 42, 17, 2017). xThe -on-SOI example is referenced for illustrative purposes only and is not intended to limit the range of possible compositions of the nonlinear elements described herein. Further examples of materials that may be used in the stack composition or individual compositions are provided in the following paragraphs.

[0094] One or more of the nonlinear elements may comprise aluminum nitride AlN. AlN may be a particularly targeted material for use as a nonlinear element, such as a waveguide, due to its wide transparency window, which covers portions of the UV, visible, and near-infrared radiation. Another reason to consider AlN is that it has a high nonlinear refractive index (n2=2.3×10 -15 cm 2 Because the crystal structure of AlN is non-centrosymmetric, this material has a second-order optical nonlinearity (χ (2) = 4.7 pm / V). Such second-order optical nonlinearities may be essentially absent in other platforms, such as SOI (silicon on insulator) or silicon nitride (SiN). This nonlinear index may be relatively high compared to other nonlinear media. For example, the nonlinear refractive index of argon and helium is 10.9 × 10 at 800 nm and 10.9 × 10 at 800 nm, respectively. -20 cm 2 / W and 0.94×10 -20 cm 2 / W.

[0095] Third-order nonlinear effects such as soliton propagation χ (3) In addition, AlN has the potential to provide a wide range of χ generation technologies, such as second harmonic generation (SHG), sum frequency generation (SFG), and difference frequency generation (DFG). (2) It also supports frequency mixing through soliton-induced supercontinuum generation effects. Furthermore, in addition to soliton-induced supercontinuum generation, SHG can be utilized to broaden the spectral width towards the visible range, for example when using 1030 nm pump radiation. Performing both second-order and third-order optical nonlinear processes on the same platform can have the advantage of enabling cascaded nonlinear effects, further increasing the bandwidth of supercontinuum generation.

[0096] To exploit different linear and nonlinear properties on a single chip, different materials such as silicon nitride, diamond, aluminum nitride and aluminum oxide, or any other suitable material may be grown on the same substrate. Different materials may be grown side-by-side and / or on top of each other. For isolation, cladding materials transparent in the relevant broadband emission range of interest may be grown between layers. An exemplary cladding material may be SiO2. Materials optimized for operation in a particular wavelength range can be used to broaden the spectrum of that wavelength range. All spectra generated in the different waveguides can be combined to obtain a broadband spectrum. Materials such as lithium niobate and gallium arsenide also have established protocols for second harmonic generation on lithographic substrates. χ (2) Broadband quasi-phase matching of the process can be achieved by periodically poling the material, which can be used to further extend the spectral reach of supercontinuum generation in integrated photonic circuits.

[0097]

[0096] In addition to or as an alternative to using different materials (or combinations of materials), as described above, two or more nonlinear elements may have different dimensions. Fabricating waveguides with different dimensions on the same PIC can enhance supercontinuum generation by optimizing broadband generation performance over different wavelength ranges for different waveguides. The dimensions may include the cross section of the waveguide in a plane perpendicular to the propagation direction of radiation in the waveguide. Additionally or alternatively, the lengths of two or more nonlinear elements may be different, and the lengths may be along the propagation direction of the waveguide.

[0098] 8 shows a schematic representation of a photonic integrated circuit (PIC) 200. The photonic integrated circuit includes an optical input 204 configured to receive pump (input) radiation 206. The photonic integrated circuit further includes multiple nonlinear elements 202 connected to the optical input 204. The nonlinear elements 202 may be photonic integrated waveguides. The multiple nonlinear elements 202 are configured to generate broadband radiation 210 (e.g., supercontinuum radiation) upon receiving the pump radiation 206. At least two of the nonlinear elements 202 differ in at least one dimension. The broadband radiation 210 can be collected by a merge element 208 and provided as an output from the photonic integrated circuit 200. Phase matching for dispersive-wave generation at different wavelengths can be designed across the different nonlinear elements to generate radiation over a wide range at sufficient power levels.

[0099] As shown in FIG. 8, the waveguides 202 may have different widths at their cross-sections and in the plane of the photonic integrated circuit 200. Different cross-sectional widths can support different broadband radiation generation ranges. In some implementations, in setups using different dimensions, the material composition of each of the waveguides may be the same. In other implementations, both the material composition and the dimensions may be different. Each of the multiple nonlinear elements may be located in the same plane of the PIC, which may be the plane of the substrate.

[0100]

[0099] The photonic integrated circuits described herein may include in the range of 3 to 50 nonlinear elements, or 15 to 50 nonlinear elements, which may be, for example, a PIC with 3 to 50 waveguides arranged side by side.

[0101] [000100] The optical input may be a single optical input connected to each of multiple nonlinear elements. The optical output may be a single optical output connected to each of multiple nonlinear elements. The input module and / or output module may include a star coupler. Additional elements may be provided in the input module and / or output module to achieve wavelength filtering, source routing, coherence scrambling, etc. In a setup using fiber (e.g., photonic crystal fiber), coupling may be difficult due to different mode sizes. In integrated optics, established packaging techniques at foundries may be used for chip-to-fiber coupling. This may simplify the coupling / connection process for broadband radiation. It may also make the radiation source more robust against power fluctuations associated with coupling. Exploiting packaging possibilities may also reduce maintenance costs, for example, by enabling a quick-change configuration in which PICs can be relatively easily replaced.

[0102] [000101] Some of the waveguides in a PIC may have the same dimensions and material composition. For example, a PIC may be provided with one waveguide of a first thickness, two waveguides of a second thickness, one waveguide of a third thickness, three waveguides of a fourth thickness, etc. The number of waveguides with the same dimensions / composition may be selected to obtain, for example, a chosen / preferred power distribution across a broadband spectrum.

[0103] [000102] Broadband radiation may include supercontinuum radiation. Supercontinuum radiation may include radiation ranging from ultraviolet (UV) radiation to infrared (IR) radiation. This may be in the range of, for example, 100 nm to 2000 nm, 200 nm to 2000 nm, or 200 nm to 1600 nm.

[0104] [000103] The pump radiation may be pulsed pump radiation. The pump radiation may be a single (pulsed) radiation beam provided to the optical input of the PIC. The radiation may be in the range of 400 nm to 2000 nm, or in the range of 800 nm to 1600 nm. The pulsed radiation may include radiation at one or more specific wavelengths, for example, 400 nm, 515 nm, 800 nm, 1030 nm, 1550 nm, and / or 2000 nm.

[0105] [000104] Further embodiments of the present invention are disclosed in the following numbered clause list: 1. an optical input configured to receive pump radiation; a number of nonlinear elements coupled to an optical input and configured to generate broadband radiation upon receiving pump radiation, at least two of the number of nonlinear elements differing in at least material and / or dimension; Photonic integrated circuits comprising: 2. The photonic integrated circuit of clause 1, wherein the nonlinear element is a waveguide. 3. A photonic integrated circuit according to any one of the preceding clauses, wherein at least one nonlinear element comprises aluminum nitride. 4. A photonic integrated circuit according to any one of the preceding clauses, wherein the material of the multiple nonlinear elements comprises one or more of diamond, silicon nitride, aluminum nitride, lithium niobate, and gallium arsenide. 5. A photonic integrated circuit according to any one of the preceding clauses, wherein at least two dimensions of the multiple nonlinear elements are different, the dimensions including cross-sectional thickness in a plane perpendicular to the direction of propagation of radiation in the nonlinear elements. 6. The photonic integrated circuit of clause 5, wherein the thickness varies along a portion of the length of the nonlinear element, the portion being less than the entire length of the waveguide. 7. A photonic integrated circuit according to any one of the preceding clauses, wherein at least two dimensions of the multiple nonlinear elements are different, the dimensions including lengths along the direction of propagation of the nonlinear elements. 8. A photonic integrated circuit according to any one of the preceding clauses, wherein multiple nonlinear elements are located in the same plane of a substrate of the photonic integrated circuit. 9. A photonic integrated circuit as described in any one of the preceding clauses, wherein one or more of the multiple nonlinear elements includes a stacked arrangement made up of layers of material, and at least two of the multiple nonlinear elements have layers of material of different compositions. 10. A photonic integrated circuit according to any one of the preceding clauses, further comprising a merging element configured to receive the broadband radiation generated in each of the multiple nonlinear elements and merge it into a single broadband radiation beam. 11. A photonic integrated circuit according to any one of the preceding clauses, wherein the number of nonlinear elements comprises 3 to 50 nonlinear elements, or 15 to 50 nonlinear elements. 12. A photonic integrated circuit according to any one of the preceding clauses, wherein the broadband radiation comprises supercontinuum radiation. 13. The photonic integrated circuit of clause 12, wherein the supercontinuum radiation comprises radiation having a wavelength in the range of 200 nm to 2000 nm, or in the range of 200 nm to 1600 nm. 14. A photonic integrated circuit according to any one of the preceding clauses, wherein the pump radiation comprises a pulsed pump radiation beam. 15. The photonic integrated circuit of clause 14, wherein the pump radiation comprises one or more wavelengths in the range of 400 nm to 2000 nm, or 1000 to 1500 nm. 16. A photonic integrated circuit according to any one of the preceding clauses, wherein the pump radiation comprises a single beam of pump radiation. 17. A photonic integrated circuit according to any one of the preceding clauses, wherein the optical input comprises a single optical input connected to all of the multiple nonlinear elements. 18. The photonic integrated circuit of clause 17, wherein the single optical input is a star coupler. 19. A broadband radiation source comprising a photonic integrated circuit according to any one of clauses 1 to 18. 20. Metrology apparatus including a broadband radiation source according to clause 19. 21. An inspection device including a broadband radiation source as described in clause 19. 22. A lithographic apparatus comprising a broadband radiation source according to clause 19. 23. A lithocell comprising a device according to any one of clauses 20 to 22.

[0106] [000105] Although specific reference is made in this specification to uses of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optics, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0107] [000106] Although embodiments of the invention may be specifically referenced herein in connection with lithography apparatus, they may be used in other apparatus. They may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses may collectively be referred to as lithography tools. Such lithography tools may use vacuum or ambient (non-vacuum) conditions.

[0108] [000107] Although specific reference has been made above to the use of embodiments of the invention in connection with optical lithography, it will be understood that the invention is not limited to optical lithography and may be used in other applications, for example in imprint lithography, where the context allows.

[0109] [000108] Although specific reference is made to a "metrology apparatus / tool / system" or an "inspection apparatus / tool / system," these terms may refer to the same or similar types of tools, apparatus, or systems. For example, an inspection or metrology apparatus incorporating embodiments of the present invention may be used to determine characteristics of structures on a substrate or wafer. For example, an inspection or metrology apparatus incorporating embodiments of the present invention may be used to detect defects in the substrate or in structures on the substrate or wafer. In such embodiments, the feature of interest in the structure on the substrate may relate to a defect in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate or wafer.

[0110] [000109] While specific embodiments of the present invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The foregoing description is intended to be illustrative and not limiting. Accordingly, it will be apparent to those skilled in the art that modifications can be made to the invention as described without departing from the scope of the claims set forth below.

Claims

1. an optical input configured to receive pump radiation; a number of nonlinear elements coupled to the optical input and configured to generate broadband radiation upon receiving the pump radiation, at least two of the number of nonlinear elements differing in at least material and / or dimension; Photonic integrated circuits comprising:

2. The photonic integrated circuit of claim 1 , wherein the nonlinear element is a waveguide.

3. The photonic integrated circuit of claim 1 , wherein at least one nonlinear element comprises aluminum nitride.

4. The photonic integrated circuit of claim 1 , wherein the material of the multiple nonlinear elements comprises one or more of diamond, silicon nitride, aluminum nitride, lithium niobate, and gallium arsenide.

5. The photonic integrated circuit of claim 1 , wherein the at least two dimensions of the multiple nonlinear elements are different, the dimensions comprising cross-sectional thicknesses in a plane perpendicular to a direction of propagation of radiation in the nonlinear elements.

6. The photonic integrated circuit of claim 5 , wherein the thickness varies along a portion of the length of the nonlinear element, the portion being less than the entire length of the waveguide.

7. The photonic integrated circuit of claim 1 , wherein the at least two dimensions of the multiple nonlinear elements are different, the dimensions comprising lengths along a direction of propagation of the nonlinear elements.

8. The photonic integrated circuit of claim 1 , wherein the multiple nonlinear elements are located in the same plane of a substrate of the photonic integrated circuit.

9. 10. The photonic integrated circuit of claim 1, wherein one or more of the multiple nonlinear elements comprises a stacked arrangement made up of layers of material, and wherein the at least two of the multiple nonlinear elements have layers of material of different compositions.

10. The photonic integrated circuit of claim 1 , further comprising a merging element configured to receive the broadband radiation generated in each of the multiple nonlinear elements and merge them into a single broadband radiation beam.

11. The photonic integrated circuit of claim 1 , wherein the multiple nonlinear elements comprises between 3 and 50 nonlinear elements, or between 15 and 50 nonlinear elements.

12. The photonic integrated circuit of claim 1 , wherein the broadband radiation comprises supercontinuum radiation, including radiation having wavelengths in the range of 200 nm to 2000 nm, or in the range of 200 nm to 1600 nm.

13. The photonic integrated circuit of claim 1 , wherein said optical input comprises a single optical input connected to all of said multiple nonlinear elements.

14. A broadband radiation source comprising a photonic integrated circuit according to any one of claims 1 to 13.

15. 15. A metrology or inspection apparatus comprising a broadband radiation source according to claim 14.

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