Method for determining size parameters of microstructure optical fiber

Abstract

A method of determining a dimensional parameter of a microstructured optical fiber (MOF), the method comprising: directing radiation toward the MOF; obtaining one or more signals associated with interference of radiation between structural elements of the MOF; determining a distance between structural elements of the MOF based on the one or more signals associated with interference of radiation between the structural elements; and determining the dimensional parameter based on the determined distance. A method for obtaining the MOF is also described.

Description

Cross-references to related applications

[0001] This application claims priority to EP application 23197095.5, filed on September 13, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to determining dimensional parameters, such as core diameter, of microstructured optical fibers (MOFs). Specifically, this invention relates to determining dimensional parameters based on one or more signals associated with interference (e.g., Fabry-Perot interference) radiated between structural elements of the MOF. Background Technology

[0003] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. Lithography apparatus can be used, for example, to manufacture integrated circuits (ICs). For instance, a lithography apparatus can project a pattern (often referred to as a “design layout” or “design”) onto a radiation-sensitive material (resist) layer disposed on a substrate (e.g., a wafer) at a patterning device (e.g., a mask).

[0004] To project patterns onto a substrate, photolithography equipment can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the feature that can be formed on the substrate. Typical wavelengths currently used are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Compared to photolithography equipment using radiation with a wavelength of, for example, 193 nm, photolithography equipment using extreme ultraviolet (EUV) radiation in the 4-20 nm range (e.g., 6.7 nm or 13.5 nm) can be used to form even smaller features on the substrate.

[0005] Low-k1 lithography can be used to process features smaller than the traditional resolution limits of lithography equipment. In this process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the radiation wavelength used, NA is the numerical aperture of the projection optics in the lithography equipment, CD is the "critical size" (typically the smallest feature size to be printed, but in this case, half-pitch), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it is to reproduce patterns on the substrate that resemble the shape and size designed by the circuit designer in order to achieve specific electrical functions and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection equipment and / or design layout. These steps include, for example, but not limited to, optimization of NA, customized illumination schemes, the use of phase-shifting 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 generally defined as "resolution enhancement techniques" (RET). Alternatively, tight control loops used to control the stability of the lithography equipment can be used to improve pattern reproduction at low k1.

[0006] In the field of photolithography, numerous measurement systems can be used both inside and outside the photolithography apparatus. Typically, such measurement systems use a radiation source to irradiate a target and a detection system to measure at least one characteristic of a portion of the incident radiation scattered from the target. Examples of measurement systems outside the photolithography apparatus are inspection or measurement devices used to determine the characteristics of a pattern pre-projected onto a substrate by the photolithography apparatus. Such external inspection devices may include, for example, a scatterometer. Examples of measurement systems that can be provided within the photolithography apparatus include: topography measurement systems (also known as level sensors); position measurement systems (e.g., interferometric devices) for determining the position of a mask or wafer stage; and positioning sensors for determining the position of positioning marks. These measurement devices can use electromagnetic radiation to perform the measurements.

[0007] Different types of radiation can be used to inquire about different types of characteristics of a pattern. Some measurement systems can employ broadband radiation sources. Such broadband radiation sources can be supercontinuum sources and can include optical fibers with nonlinear media, such as microstructured fibers (MOFs), through which pulsed pump radiation beams propagate to broaden the radiation spectrum.

[0008] In some examples, the performance of a broadband radiation source can be highly sensitive to the size of the optical fiber. Therefore, it is important to be able to reliably and accurately measure the fiber dimensions. Currently, these critical dimensions are typically measured using microscopes, such as optical microscopes or scanning electron microscopes. This can be done during the fiber manufacturing process (which may be called the drawing process) by sampling a piece of fiber removed from the manufacturing (drawing) process, or after the manufacturing (drawing) process has been completed for a given fiber, by analyzing the end face of the manufactured fiber. Summary of the Invention

[0009] This disclosure provides a method for determining one or more dimensions (or “size parameters”) of a microstructured optical fiber (MOF) or a preform configured to be drawn into the MOF, by obtaining one or more signals associated with interference radiating between structural elements of the MOF or the preform configured to be drawn into the MOF. The method described herein is advantageously applicable during the fiber manufacturing (drawing) process (i.e., “online”), meaning that in some examples, real-time information about the critical dimensions of the fiber can be obtained during manufacturing.

[0010] MOFs can include photonic crystal fibers (PCFs) and / or hollow-core photonic crystal fibers (HCPCFs). An MOF can include a core region (e.g., a hollow core) and multiple anti-resonant elements (AREs) surrounding the core region. In some examples, AREs may be referred to as “capillaries.” Each ARE may be defined by a wall having a wall thickness.

[0011] Existing techniques for determining the dimensional parameters of MOFs typically require interrupting and / or ending the MOF manufacturing process before one or more relevant measurements can be performed. For example, the MOF manufacturing process may include feeding a preform (e.g., a glass preform) into a furnace to heat the preform and drawing the heated preform into fibers by pulling it at one or both ends.

[0012] For example, during the drawing process, fiber fragments can be sampled (i.e., removed from the drawing process) and analyzed under a microscope (e.g., an optical microscope or a scanning electron microscope). If the fiber fragment has one or more dimensional parameters that are outside a specific tolerance range, the parameters of the drawing process can be adjusted. This process can be completed until all dimensional parameters are within their respective tolerance ranges. This approach can have several drawbacks. For example, fiber preforms can be continuously fed into the furnace before and during sampling and characterization, leading to material waste and reduced yield. Furthermore, no direct information is obtained about the subsequently formed fibers (dimensional parameters are inferred only from the sample).

[0013] In another example, once the fiber has been drawn to the desired length, it can be cut at one or both ends, and the dimensional parameters at one or more end faces can be characterized using a microscope (e.g., an optical microscope or a scanning electron microscope). However, this technique does not provide information about the dimensional parameters along the length of the fiber.

[0014] Although X-ray tomography has been used to provide non-invasive measurements of fiber structure along fiber length, the technique is very slow; for example, measuring a short (~cm) fiber may take several hours.

[0015] Dimensional parameters may include the diameter of the core region, the diameter of one or more AREs, the wall thickness of one or more AREs, and / or the distance between AREs.

[0016] It has been proposed (e.g., in MH Frosz et al., Opt. Express 27 (21) pp. 30842-30851 (2019), the contents of which are incorporated herein by reference) to measure the diameter of the ARE (capillary) “online” (i.e., during the fiber manufacturing process) using Whispering Corridor Mode (WGM) spectroscopy. In WGM spectroscopy, a broadband light is irradiated from the side of the optical fiber, thereby exciting light that propagates around the capillary. The light is coupled out of the fiber, and by collecting and analyzing the spectrum of the light that leaves the fiber at an angle equal to the angular spacing of the capillary, the optical path length of the light traveling around the capillary can be determined. The physical path length can be calculated from the optical path length by a priori calculation of the effective index of the WGM mode assuming the capillary wall thickness. The diameter of the capillary can then be deduced.

[0017] However, one drawback of WGM spectroscopy is that it cannot directly measure one of the most critical dimensional parameters (i.e., core diameter) (because the technique relies on light interacting only with the capillary). Furthermore, WGM spectroscopy requires determining the group refractive index of light within the capillary (ARE) wall, which necessitates knowledge of the expected capillary (ARE) wall thickness.

[0018] Therefore, an improved method is needed to determine the dimensional parameters of fibers (e.g., MOFs).

[0019] This article describes a method for determining the dimensional parameters of MOFs.

[0020] This method may include guiding radiation toward the MOF.

[0021] The method may include obtaining one or more signals associated with the interference of radiation between structural elements of the MOF.

[0022] The method may include determining the distance between structural elements based on one or more signals associated with interference of radiation between structural elements of the MOF.

[0023] This method may include determining size parameters based on the determined distance.

[0024] Alternatively or additionally, the method may include obtaining one or more signals associated with interference of radiation within structural elements of the MOF, and the method may include determining the diameter of the structural element based on one or more signals associated with interference of radiation within structural elements of the MOF.

[0025] In one example, a method may include detecting a signal associated with a Fabry-Perot interferometer of radiation within an optical cavity formed by one or more structural elements of an MOF. The method may include determining the width of the optical cavity based on the detected signal. The method may also include determining dimensional parameters based on the determined width of the optical cavity.

[0026] Advantageously, the methods described herein enable online determination of fiber dimensional parameters. In other words, these methods can be performed during the manufacturing (drawing) process without interrupting it. Therefore, if the determined structural parameters are outside the fiber specifications (e.g., outside the tolerance range), process parameters of the manufacturing process can be adjusted in real time (e.g., real-time adjustment of the pressure controlling the diameter of the ARE in the capillary). However, it should be understood that the methods described herein can be used alternatively or additionally to determine fiber dimensional parameters after the drawing process.

[0027] Furthermore, the method described herein allows for the determination of one or more dimensional parameters along the entire length of the manufactured fiber, rather than just at the fiber end face(s). The method also enables non-invasive studies of the entire fiber length more quickly than other techniques, such as X-ray tomography.

[0028] Although it has been demonstrated, for example, in X. Xu et al., Opt. Lett. 43 (13) pp. 3045-3048 (2018) (the contents of which are incorporated herein by reference), that the core diameter of “photonic bandgap” type fibers (i.e., without AREs) can be directly determined using Fabry-Perot interferometry, the authors of that study filled the entire structure with a refractive index-matching liquid to achieve this result. This method is clearly not suitable for in-line measurements of MOFs, which are achieved through the method described in this paper. Furthermore, while not wishing to be bound by theory, the unstable resonators of the core geometry formed by the negative curvature of AREs in MOFs mean that directly measuring the core diameter using Fabry-Perot interferometry is very difficult, or perhaps impossible.

[0029] Furthermore, the method described in this paper does not require prior knowledge of the ARE wall thickness; it only requires knowing that the ARE wall thickness is much smaller than the ARE diameter, which is true for practically relevant situations. However, in some examples, t can be determined by using sufficiently wide radiation, and / or by other methods combined with the method described in this paper, thereby determining one or more dimensional parameters with even greater precision.

[0030] Unlike WGM spectroscopy, the method described in this paper for determining size parameters is also advantageously unaffected by the polarization of the radiation used.

[0031] Furthermore, in the case of WGM spectroscopy, the measurement error of the ARE diameter is affected by the relative rotation between the optical fiber and the measuring device; the greater the deviation of the measurement angle from the optimal value, the greater the measurement error. In contrast, the determination of dimensional parameters according to the method described herein is advantageously unaffected by fiber rotation, which may occur, for example, during the manufacturing process.

[0032] Compared to WGM spectroscopy, the method described herein is also advantageously applicable to fibers with non-circular (e.g., polygonal, such as hexagonal) cross-sections, where light-to-capillary (ARE) coupling is less efficient in the case of non-circular cross-sections than in the case of circular cross-sections. The fiber cross-section can be defined by the fiber's cladding (e.g., inner cladding).

[0033] In some examples, the determined dimensional parameters may correspond substantially directly to the distances between the determined structural elements, the diameters of the determined structural elements, and / or the width of the determined optical cavity.

[0034] For example, structural elements of a MOF may include anti-resonant elements (AREs) or capillaries. The determined dimensional parameters may include the distance or spacing between AREs (i.e., between adjacent AREs), and / or the diameter of the AREs. It should be understood that the distance between AREs is the minimum spacing between adjacent AREs.

[0035] In some examples, determining dimensional parameters based on determined distances may include performing additional calculations or operations based on one or more determined distances, diameters, and / or optical cavity widths determined by the methods described herein.

[0036] In some examples, the method may include determining dimensional parameters based on the determined distances and the geometry of the MOF. For example, the geometry of the MOF may include the arrangement of structural elements, such as the distribution of AREs around the core region.

[0037] MOFs may include a core region, and structural elements may be AREs surrounding the core region. Dimensional parameters may include the core diameter, which is the diameter of the core region.

[0038] In some examples, the method includes: obtaining one or more signals associated with interference of radiation within one or more anti-resonant elements; determining the anti-resonant element diameter of one or more anti-resonant elements based on the one or more signals associated with interference of radiation within one or more anti-resonant elements; and additionally determining dimensional parameters based on the anti-resonant element diameter. For example, the core diameter may be determined based on a mathematical relationship between the distance between structural elements (e.g., AREs) and the diameter of the structural elements, wherein the distance between structural elements and the diameter of the structural elements may be determined experimentally based on signals associated with interference of radiation.

[0039] In some examples, the dimensional parameter (e.g., core diameter) D can be determined based on the following: in δ Let N be the distance between AREs, where N is the total number of AREs, and where N is the distance between AREs. ,in d It is the diameter of ARE, and among which t This refers to the wall thickness of the ARE. In some examples, As described herein, the method currently described advantageously does not require t Any prior knowledge (e.g., where) Preferably, It should be understood that d out It is the outer diameter of ARE, and d It is the inner diameter of ARE.

[0040] In some examples, the dimensional parameters include the wall thickness of the ARE. It should be understood that the wall thickness of the ARE (e.g., t The distance between AREs and the diameter of the AREs can be determined based on measurements, and / or the wall thickness of the AREs can be determined directly from the interference signal. In some examples, d out It can be done t The determination can be made more precisely, either based on the interference signal or by some other technique, such as that described in Y. Xiong et al., Opt. Express 30 (26) pp. 48061-48074 (2022), the contents of which are incorporated herein by reference.

[0041] In some examples, the size parameter includes the distance between AREs (e.g. δ ).

[0042] In some examples, the size parameter includes the ARE diameter (e.g., d ).

[0043] In some examples, the method includes using a first radiation source and a second radiation source to radially direct radiation toward the longitudinal axis of the MOF, the first and second radiation sources being angled around the longitudinal axis. Angular separation, where ,in θ It is the angular spacing between anti-resonant elements, where 0.25 ≤ β ≤0.75, and where n It is a positive integer. For example, the first radiation source and the second radiation source can be angularly separated around the longitudinal axis by an odd multiple of approximately half the angular spacing between the anti-resonant elements.

[0044] Advantageously, if the optical fiber is rotated during the measurement, then a method is used... Performing two measurements simultaneously using angularly spaced first and second radiation sources can prevent measurement signal loss. Measurement signal loss may be due to "dead zones" formed when radiation incident on the optical fiber passes between AREs.

[0045] In contrast, in some examples, a single radiation source can be used to guide radiation toward the MOF. Advantageously, using a single radiation source provides a simple setup for determining the size parameters.

[0046] In some examples, the MOF includes polygonal inner sections. For example, hexagonal or octagonal inner sections. The inner sections may be defined by the cladding described herein.

[0047] In some examples, the ARE can be evenly distributed around the core region. For example, in the case of a polygonal inner section, the ARE can be located at the vertices of the inner section.

[0048] The interference described in this article can include the Fabry-Perot interference.

[0049] The radiation described herein can originate from one or more radiation sources described herein, preferably broadband radiation. For example, broadband radiation can include a range of radiation wavelengths from ultraviolet (UV) to infrared (IR) or near-infrared (NIR) radiation, such as 200–1200 nm. In another example, the radiation described herein can be narrowband radiation from a source with configurable wavelengths, such as a tunable laser. Instead of relying on the use of broadband radiation, measurements can then be performed at multiple (discrete) wavelengths.

[0050] One or more methods described in this article can be implemented using a computer.

[0051] This document also describes a method for obtaining MOFs, comprising: monitoring dimensional parameters during the MOF manufacturing process by determining the dimensional parameters of the MOF manufactured by the MOF manufacturing process; and adjusting the parameters of the MOF manufacturing process if the determined dimensional parameters are outside tolerance ranges. The dimensional parameters can be determined by any of the methods described herein for determining dimensional parameters.

[0052] Examples of parameters in the MOF manufacturing process can include the pressure or ARE in the fiber capillaries during the drawing process. For example, increasing the pressure in the ARE increases the ARE diameter. d And thus reduce the core diameter D .

[0053] Advantageously, by using the dimensional parameter determination method described herein to monitor dimensional parameters, one or more manufacturing process parameters of MOF can be adjusted in real time, reducing material waste and increasing manufacturing yield.

[0054] During or after manufacturing, the same method described in this document for measuring the dimensional parameters of the MOF can be used to measure the dimensions of the preform drawn into the MOF. In this case, the radiation used can preferably come from a tunable narrowband radiation source, such as a tunable laser, because the preform (sometimes called a "preform") is typically about 20 times larger than the MOF, requiring higher spectral resolution. The latter involves measuring a longer resonator length, thus imposing a finer resolution on the measured spectrum (this is an inherent characteristic of Fourier transform-based techniques, where small spectral intervals are transformed into large resonator distances). Conversely, this is why a wide spectrum is needed to measure very small resonator distances (e.g., fiber wall thickness), and then the spectral resolution is less important than the width of the measured spectrum.

[0055] For some applications, the ARE of the MOF includes additional antiresonant elements, typically additional capillaries nested within capillaries surrounding the core region of the MOF. Whispering gallery mode (WGM) techniques have been proposed for deriving the geometry of such nested capillaries, for example in "Non-destructive characterization of nested and double nested antiresonant nodeless fiber microstructure geometry": Optics Express Volume 31, Issue 22, pp 36928-36939. However, the method of the present invention presented in that document (which does not rely on the WGM principle) can also be used to determine the dimensional parameters of the additional ARE / capillary nested within the ARE, such as its diameter(s), wall thickness, and / or distance to the wall of its corresponding capillary.

[0056] This document also describes a non-transitory computer-readable medium including instructions that, when executed by a processor of a computing device, cause the computing device to perform any of the methods described herein. Attached Figure Description

[0057] Embodiments of the invention will now be described by way of example only, with reference to the accompanying schematic overview diagrams, wherein: - Figure 1 A schematic overview diagram of the photolithography equipment is shown; - Figure 2 A schematic overview of the photolithography unit is shown; - Figure 3 A schematic representation of overall photolithography is depicted, illustrating the collaboration between three key technologies for optimizing semiconductor manufacturing; - Figure 4 A schematic overview of the scattering measurement instrument is depicted; - Figure 5 A schematic overview diagram of a horizontal sensor measurement tool is shown; - Figure 6 A schematic overview of the alignment sensor measurement tool is shown; - Figure 7 This is a schematic cross-sectional view of a microstructured optical fiber (MOF) in a transverse plane (i.e., the axis perpendicular to the MOF); - Figure 8 yes Figure 7 A schematic cross-sectional view of the MOF in the plane containing the axis of the MOF; - Figure 9The simulation results of the reflectance spectrum obtained from the simulated MOF are shown, where the Fourier transform has been applied to the data so that various structural parameters can be resolved. - Figure 10 An example of a hexagonal MOF comprising six anti-resonant elements (AREs) is schematically shown; - Figure 11 The simulation results for another MOF are shown; - Figure 12 Measurements of the MOF performed using radiation with different polarizations are shown. - Figure 13 The measurement of the reflectance spectrum resolved by the rotation angle of the MOF is shown; - Figure 14 An example of a measurement setup including a first radiation source and a second radiation source is shown schematically; - Figure 15 An example of a method for determining the dimensional parameters of a MOF according to this disclosure is illustrated schematically; - Figure 16 An example of a method for obtaining MOF according to this disclosure is illustrated schematically; - Figure 17 An example computer system that can implement embodiments of the present disclosure is illustrated schematically; - Figure 18 This is a schematic cross-sectional view of a microstructured optical fiber (MOF) with a nested capillary structure in the transverse plane (i.e., the axis perpendicular to the MOF); and - Figure 19a and Figure 19b The simulation results for the reflectance spectrum obtained from the simulated MOF are shown, similar to... Figure 9 As shown, but now used to characterize the structural parameters of MOFs with nested capillary configurations. Detailed Implementation

[0058] In this document, the terms “radiation” and “beam” are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., wavelengths of 365, 248, 193, 157, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., wavelengths ranging from approximately 5 to 100 nm).

[0059] As used herein, the terms “mask,” “mask,” or “patterning device” can be broadly interpreted to refer to a general patterning device used to impart a patterned cross-section to an incident radiation beam corresponding to a pattern to be produced in a target portion of a substrate. The term “optical valve” may also be used in this context. Examples of other such patterning devices, besides classic masks (transmission or reflection, binary, phase-shifting, hybrid, etc.), include programmable mirror arrays and programmable LCD arrays.

[0060] Figure 1 A lithography apparatus LA is schematically illustrated. The lithography apparatus LA includes: an irradiation system (also called an irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM, the first positioner PM being configured to precisely position the patterning device MA according to certain parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW, the second positioner PW being configured to precisely position the substrate support according to certain parameters; and a projection system (e.g., a lithography system). A refractive projection lens system PS is configured to project a pattern imparted by 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.

[0061] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example, via a beam delivery system BD. The irradiation system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical elements or any combination thereof, which are used for directing, shaping, and / or controlling the radiation. The irradiator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0062] As used herein, the term "projection system" PS should be interpreted broadly to include all types of projection systems, including refractive, reflective, catadioptric, distorting, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, depending on the exposure radiation and / or other factors used, such as the use of immersion liquids or vacuum. Any use of the term "projection lens" herein can be considered synonymous with the more general term "projection system" PS.

[0063] A lithography apparatus LA can be of the type in which at least a portion of the substrate can be covered by a liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system PS and the substrate W; this is also known as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0064] The lithography equipment LA can also be of the type with two or more substrate supports WT (also known as "dual stage"). In such a "multi-stage" machine, the substrate supports WT can be used in parallel, and / or subsequent exposure steps for preparing the substrate W can be performed on the 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 another substrate W.

[0065] Attached to the substrate support WT, the lithography apparatus LA may also include a measurement stage. The measurement stage is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure characteristics of the projection system PS or the radiation beam B. The measurement stage may accommodate multiple sensors. The cleaning devices may be arranged as part of the cleaning lithography apparatus, such as part of the projection system PS or part of a system providing immersion liquid. The measurement stage can move below the projection system PS when the substrate support WT leaves the projection system PS.

[0066] In operation, the radiation beam B is incident on a patterning device (e.g., mask MA) held on a mask support MT and patterned by a pattern (design layout) on the patterning device MA. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be precisely 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 ( Figure 1 (Not explicitly shown) can be used to precisely position the patterning device MA relative to the path of the radiation beam B. The patterning device MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2, as shown, occupy dedicated target portions, they can be located in the space between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are called scribe-lane alignment marks.

[0067] like Figure 2As shown, a lithography apparatus LA can form part of a lithography unit LC, sometimes also called a lithocell or (lithography) cluster. The lithography unit LC typically also includes equipment for performing pre-exposure and post-exposure processes on a substrate W. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH, and a baking plate BK, which are used, for example, to regulate the temperature of the substrate W, and for regulating the solvent in the resist layer. A substrate processor or robot RO picks up the substrate W from input / output ports I / O1, I / O2, moves the substrate W between different processing devices, and delivers the substrate W to the loading chamber LB of the lithography apparatus LA. The devices in the lithography unit, often collectively referred to as a track, are typically under the control of a track control unit TCU, which itself can be controlled by a monitoring system SCS, which can also control the lithography apparatus LA, for example, via a lithography control unit LACU.

[0068] To ensure that the substrate W exposed by the lithography equipment LA is correctly and consistently exposed, it is desirable to inspect the substrate to measure characteristics of the patterned structure, such as overlay error between subsequent layers, line thickness, critical dimension (CD), etc. For this purpose, an inspection tool (not shown) may be included in the lithography unit LC. If an error is detected, adjustments can be made, for example, to the exposure of subsequent substrates or to other processing steps to be performed on the substrate W, especially if the inspection is performed before other substrates W in the same batch or batch are still to be exposed or processed.

[0069] An inspection device, also known as a measurement device, is used to determine the characteristics of a substrate W, particularly how the characteristics of different substrates W vary or how the characteristics associated with different layers of the same substrate W vary layer by layer. Alternatively, the inspection device can be configured to identify defects on the substrate W and can be, for example, part of a photolithography unit LC, or integrated into a photolithography apparatus LA, or even a stand-alone device. The inspection device can measure characteristics on latent images (images in the resist layer after exposure), or semi-latent images (images in the resist layer after the post-exposure baking (PEB) step), or developed resist images (where exposed or unexposed portions of the resist have been removed), or even etched images (after pattern transfer steps such as etching).

[0070] Typically, patterning in photolithography (LA) is one of the most critical steps in the process, requiring high-precision determination of the dimensions and placement of structures on the substrate (W). To ensure this high precision, techniques such as... Figure 3The so-called “holistic” control environment shown combines three systems. One of these systems is the lithography equipment LA, which is (virtually) connected to the metrology tool MT (the second system) and connected to the computer system CL (the third system). The key to this “holistic” environment is optimizing the collaboration 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 equipment LA remains within the process window. The process window defines a set of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device), typically allowing process parameters in the lithography or patterning process to vary within these parameter ranges.

[0071] The computer system CL can use a portion of the design layout to be patterned to predict which resolution enhancement technique to use, and perform computational lithography simulations and calculations to determine which mask layout and lithography equipment setup achieves the maximum overall process window for the patterning process (e.g., ...). Figure 3 (As indicated by the double arrows in the first scale SC1). Typically, resolution enhancement techniques are arranged to match the patterning possibilities of the lithography equipment LA. The computer system CL can also be used to detect the current operating position of the lithography equipment LA within the process window (e.g., using input from the metrology tool MT) to predict whether defects (such as those resulting from suboptimal processing) may occur. Figure 3 (As shown by the arrow pointing to "0" in the second scale SC2).

[0072] The measurement tool (MT) can provide input to the computer system (CL) for accurate simulation and prediction, and can also provide feedback to the lithography equipment (LA) to identify possible drift, for example, in the calibrated state of the lithography equipment (LA). Figure 3 The arrows in the third scale SC3 are shown.

[0073] During photolithography, the resulting structure needs to be frequently measured, for example, for process control and verification. The tools used to perform such measurements are generally called metrology tools (MTs). Different types of metrology tools (MTs) for such measurements are known, including scanning electron microscopes or various forms of scattering metrology tools (MTs). A scatterometer is a versatile instrument that can measure parameters of the photolithography process by mounting a sensor in the pupil of the scatterometer objective or in a plane conjugate to the pupil (often referred to as pupil-based measurement) or by mounting a sensor in the image plane or a plane conjugate to the image plane (in which case the measurement is often referred to as image- or field-based measurement). Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, the entire contents of which are incorporated herein by reference. The aforementioned scatterometer can use light from soft X-rays and the visible to near-infrared wavelength range to measure the grating.

[0074] In the first embodiment, the scatterometer MT is an angle-resolved scatterometer. In this scatterometer, reconstruction methods can be applied to the measurement signal to reconstruct or calculate the characteristics of the grating. For example, this reconstruction can be achieved by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0075] In the second embodiment, the scatterometer MT is a spectroradiometer MT. In this spectroradiometer MT, radiation emitted by a radiation source is directed onto a target, and reflected or scattered radiation from the target is directed to a spectroradiometer detector, which measures the spectrum of the specular reflected radiation (i.e., the intensity as a function of wavelength). Based on this data, the structure or profile of the target that produces the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression, or by comparison with a simulated spectral library.

[0076] In the third embodiment, the scatterometer MT is an elliptic scatterometer. An elliptic scatterometer allows the determination of parameters of the photolithography process by measuring the scattered radiation in each polarization state. This metrology device emits polarized light (such as linear, circular, or elliptical) by using a suitable polarizing filter in the illumination section of the metrology device. The source suitable for the metrology device can also provide polarized radiation. Various embodiments of existing elliptic scatterometers are described in U.S. Patent Applications 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, the entire contents of which are incorporated herein by reference.

[0077] In one embodiment of a scatterometer MT, the scatterometer MT is adapted to measure the overlay error between two misaligned gratings or periodic structures by measuring the reflectance spectrum and / or detecting asymmetry in the configuration, the asymmetry being related to the degree of overlay. These two (typically overlapping) grating structures can be applied to two different layers (not necessarily consecutive layers) and can be formed substantially at the same location on the wafer. The scatterometer can have a symmetrical detection configuration, such as described in the co-owned patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a method for directly measuring grating misalignment. Other examples of measuring overlay error between two layers targeting a periodic structure by means of asymmetry can be found in PCT patent application publication WO 2011 / 012624 or U.S. patent application US 20160161863 (the entire contents of which are incorporated herein by reference).

[0078] Other parameters of interest may be focus and dose. Focus and dose can be determined simultaneously by scattering measurements (or scanning electron microscopy), as described in U.S. Patent Application US2011-0249244, the entire contents of which are incorporated herein by reference. A single structure can be used, having a unique combination of critical size and sidewall angle measurements at each point in the focusing energy matrix (FEM, also known as the focusing exposure matrix). If these unique combinations of critical size and sidewall angles are available, the focus and dose values ​​can be uniquely determined from these measurements.

[0079] The measurement target can be an assembly of composite gratings formed through a photolithography process, primarily in a resist, but also after an etching process. Typically, the spacing and linewidth of the structures within the grating are strongly dependent on the measurement optics (particularly the NA of the optics) to capture the diffraction order from the measurement target. As previously mentioned, the diffraction signal can be used to determine the offset between two layers (also known as "overlap"), and also to reconstruct at least a portion of the original grating produced by the photolithography process. This reconstruction can provide guidance on the quality of the photolithography process and can be used to control at least a portion of the process. The target can have smaller substructures configured to mimic the dimensions of functional portions of the design layout within the target. Due to this subdivision, the target's behavior will more closely resemble the functional portions of the design layout, thus allowing for better measurement of overall process parameters that closely resemble the functional portions of the design layout. The target can be measured in either an unfilled or overfilled mode. In the unfilled mode, the spot generated by the measurement beam is smaller than the overall target. In the overfilled mode, the spot generated by the measurement beam is larger than the entire target. In this overfilled mode, different targets can also be measured simultaneously, allowing for the simultaneous determination of different processing parameters.

[0080] The overall measurement quality of lithography parameters for a specific target is determined at least in part by the measurement formulation used to measure those lithography parameters. The term "substrate measurement formulation" can include one or more parameters of the measurement itself, one or more parameters of one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement formulation is a diffraction-based optical measurement, the one or more parameters being measured can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. For example, one of the criteria used to select the measurement formulation could be the sensitivity of one of the measurement parameters to processing variations. Further examples are described in U.S. Patent Application US2016-0161863 and U.S. Patent Application 15 / 181,126 (not yet published), the entire contents of which are incorporated herein by reference.

[0081] Figure 4 A measurement device such as a scatterometer SM1 is shown. It 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 (i.e., the intensity In1 as a function of wavelength λ). Based on this data, it can be processed by a processing unit PU, for example by rigorous coupled-wave analysis and nonlinear regression, or by... Figure 4The simulated spectral library shown at the bottom is compared to reconstruct the structure or profile that produced the detected spectrum. Typically, for reconstruction, the general form of the structure is known, and some parameters are assumed based on knowledge of the process of manufacturing the structure, leaving only a few parameters of the structure to be determined from the scattering measurement data. This scatterometer can be configured as a vertically incident scatterometer or an obliquely incident scatterometer.

[0082] In photolithography, it is desirable to frequently measure the resulting structure, for example, for process control and verification. Various tools are known for performing such measurements, including scanning electron microscopes or various forms of metrology devices such as scatterometers. Examples of known scatterometers typically rely on providing a dedicated measurement target, such as an underfilled target (in the form of a simple grating or overlapping gratings in different layers, large enough to generate a spot smaller than the grating) or an overfilled target (thereby illuminating a spot that partially or completely contains the target). Furthermore, the use of metrology tools, such as angle-resolved scatterometers illuminating underfilled targets like gratings, allows for the use of so-called reconstruction methods, where the characteristics of the grating can be calculated by simulating the interaction of scattered radiation using a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0083] A scatterometer is a general-purpose instrument that allows for the measurement of parameters of a photolithography process by means of a sensor located in or in a plane conjugate to the pupil of the scatterometer's objective lens; such measurements are typically referred to as pupil-based measurements. Alternatively, parameters of the photolithography process can be measured by means of a sensor located in or in a plane conjugate to the image plane; in this case, the measurements are typically referred to as image- or field-based measurements. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, the entire contents of which are incorporated herein by reference. The aforementioned scatterometers can measure gratings using light from soft X-rays and the visible to near-IR wavelength range.

[0084] A topography measurement system, a level sensor, or a height sensor, which can be integrated into a photolithography apparatus, is arranged to measure the topography of the top surface of a substrate (or wafer). A topography map of the substrate (also called a height map) can be generated from these measurements to indicate the height of the substrate according to its position on the substrate. This height map can then be used to correct the position of the substrate during pattern transfer on the substrate to provide a spatial image of the patterning apparatus at the appropriate focal position on the substrate. It is understood that, in this context, "height" refers to a dimension approximately extending beyond the plane of the substrate (also called the Z-axis). Typically, the level or height sensor measures at a fixed position (relative to its own optical system), and the relative movement between the substrate and the optical system of the level or height sensor yields height measurements at different positions across the substrate.

[0085] Examples of level or height sensors LS known in the art are in Figure 5 The diagram illustrates that, Figure 5 The operating principle is illustrated only. In this example, the horizontal sensor includes an optical system comprising a projection unit LSP and a detection unit LSD. The projection unit LSP includes a radiation source LSO that provides a radiation beam LSB applied by a projection grating PGR of the projection unit LSP. The radiation source LSO can be, for example, a narrowband or broadband light source, such as a supercontinuum light source, polarized or unpolarized, pulsed or continuous, such as a polarized or unpolarized laser beam. The radiation source LSO can include multiple radiation sources with different colors or wavelength ranges, such as multiple LEDs. The radiation source LSO of the horizontal sensor LS is not limited to visible radiation, but may additionally or alternatively include UV and / or IR radiation and any wavelength range suitable for reflection from the substrate surface.

[0086] The projection grating (PGR) is a periodic grating comprising a periodic structure that generates a radiation beam BE1 with periodically varying intensity. The radiation beam BE1 with periodically varying intensity is guided to a measurement position MLO on the substrate W, the measurement position MLO having an incident angle ANG between 0 and 90 degrees relative to an axis perpendicular to the incident substrate surface (Z-axis), typically between 70 and 80 degrees. At the measurement position MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and directed towards the detection unit LSD.

[0087] To determine the height level at the measurement location MLO, the level sensor also includes a detection system comprising a detection grating DGR, a detector DET, and a processing unit (not shown) for processing the output signal of the detector DET. The detection grating DGR can be the same as a projection grating PGR. The detector DET generates a detector output signal indicating the received light, such as an indication of the intensity of the received light, as in a photodetector, or a representation of the spatial distribution of the received intensity, as in a camera. The detector DET can include any combination of one or more detector types.

[0088] The height level at the measurement location MLO can be determined using triangulation techniques. The detected height level is typically related to the signal strength measured by the detector DET, which exhibits periodicity. This periodicity depends on the design of the projection grating PGR, the (tilted) incident angle ANG, and other factors.

[0089] The projection unit LSP and / or the detection unit LSD may include other optical elements, such as lenses and / or mirrors (not shown), along the path of the patterned radiation beam between the projection grating PGR and the detection grating DGR.

[0090] In one embodiment, the detection grating DGR can be omitted, and the detector DET can be placed where the detection grating DGR is located. This configuration provides more direct detection of the image of the projection grating PGR.

[0091] In order to effectively cover the surface of the substrate W, the horizontal sensor LS can be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating an array of spots or measurement regions MLO that cover a larger measurement range.

[0092] Various general types of height sensors are disclosed, for example, in US7265364 and US7646471, both of which are incorporated herein by reference. A height sensor using UV radiation instead of visible or infrared radiation is disclosed in US2010233600A1, which is also incorporated herein by reference. In WO2016102127A1, which is incorporated by reference, a compact height sensor is described that uses a multi-element detector to detect and identify the position of a grating image without requiring the detection of the grating itself.

[0093] A position measurement system (PMS) can include any type of sensor suitable for determining the position of a substrate stage WT. A position measurement system (PMS) can include any type of sensor suitable for determining the position of a mask support MT. The sensor can be an optical sensor, such as an interferometer or encoder. A position measurement system (PMS) can include a combined system of interferometers and encoders. The sensor can be another type of sensor, such as a magnetic sensor, a capacitive sensor, or an inductive sensor. The position measurement system (PMS) can determine the position relative to a reference (e.g., a measurement frame (MF) or a projection system (PS)). The position measurement system (PMS) can determine the position of the substrate stage WT and / or the mask support MT by measuring the position or by measuring the time derivative of the position (e.g., velocity or acceleration).

[0094] A position measurement system (PMS) may include an encoder system. For example, an encoder system is known from U.S. Patent Application US2007 / 0058173A1, 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 can receive a primary radiation beam and a secondary radiation beam. The primary and secondary radiation beams originate from the same radiation beam, i.e., the original radiation beam. At least one of the primary and secondary radiation beams is created by diffracting the original radiation beam using a grating. If the primary and secondary radiation beams are created by diffracting the original radiation beam using a grating, the primary radiation beam needs to have a different diffraction order than the secondary radiation beam. Different diffraction orders are, for example, +1, -1, +2, and -2. The encoder system optically combines the primary and secondary radiation beams into a combined radiation beam. A sensor in the encoder head determines the phase or phase difference of the combined radiation beam. The sensor generates a signal based on the phase or phase difference. This signal indicates the position of the encoder head relative to the grating. One of the encoder head and the grating can be disposed on the substrate structure WT. The other of the encoder head and the grating can be disposed on the measurement frame MF or the base frame BF. For example, multiple encoder heads are disposed on the measurement frame MF, while the grating is disposed on the top surface of the substrate support WT. In another example, the grating is disposed on the bottom surface of the substrate support WT, while the encoder head is disposed below the substrate support WT.

[0095] A position measurement system (PMS) may include an interferometer system. Interferometer systems are known, for example, from U.S. Patent 6,020,964, filed July 13, 1998, which is incorporated herein by reference. An interferometer system may include a beam splitter, a mirror, a reference mirror, and a sensor. A radiation beam is split into a reference beam and a measurement beam by the beam splitter. The measurement beam propagates to the mirror and is reflected back to the beam splitter. The reference beam propagates to the reference mirror and is reflected back to the beam splitter. At the beam splitter, the measurement beam and the reference beam are combined into a combined radiation beam. The combined radiation beam is incident on the sensor. The sensor determines the phase or frequency of the combined radiation beam. The sensor generates a signal based on the phase or frequency. This signal represents the displacement of the mirror. In one embodiment, the mirror is connected to a substrate support WT. The reference mirror may be connected to a measurement frame MF. In one embodiment, the measurement beam and the reference beam are combined into a combined radiation beam by additional optical components instead of a beam splitter.

[0096] In the fabrication of complex devices, numerous photolithographic patterning steps are typically performed to form functional features in successive layers on a substrate. Therefore, a key aspect of the performance of a photolithography apparatus is its ability to correctly and accurately align the applied pattern relative to features arranged in previous layers (using the same or different photolithography equipment). For this purpose, the substrate has one or more sets of markers. Each marker is a structure whose position can be measured at a later time using a position sensor (typically an optical position sensor). The position sensor may be called an "alignment sensor," and the marker may be called an "alignment marker." The marker can also be referred to as a measurement target.

[0097] Photolithography apparatuses may include one or more alignment sensors that can precisely measure the position of alignment marks formed on a substrate. Alignment (or position) sensors can use optical phenomena such as diffraction and interference to obtain position information from alignment marks formed on the substrate. Examples of alignment sensors used in current photolithography apparatuses are based on self-reference interferometers as described in US6961116. Various enhancements and modifications of position sensors have been developed, for example, as disclosed in US2015261097A1. The contents of all these publications are incorporated herein by reference.

[0098] Markings or alignment marks may comprise a series of strips formed on or therein of a layer provided on a substrate, or (directly) in the substrate. These strips may be regularly spaced and used as grating lines, such that the mark can be considered a diffraction grating with a well-known spatial period (pitch). Depending on the orientation of these grating lines, the mark can be designed to allow measurement of position along the X-axis or along the Y-axis (with its orientation substantially perpendicular to the X-axis). Markings comprising strips arranged at +45 degrees and / or -45 degrees relative to the X-axis and Y-axis allow for combined X- and Y-measurements using techniques as described in US2009 / 195768A, which is incorporated herein by reference.

[0099] The alignment sensor uses a radiating point optical scan to obtain a periodically changing signal, such as a sine wave. The phase of this signal is analyzed to determine the position of the mark, and thus the position of the substrate relative to the alignment sensor, which is fixed relative to the reference frame of the lithography apparatus. So-called coarse and fine marks, associated with different (coarse and fine) mark sizes, can be provided, allowing the alignment sensor to distinguish different periods of the periodic signal and the precise position (phase) within each period. Marks with different pitches can also be used for this purpose.

[0100] The location of the measurement marks can also provide information about the deformation of the substrate on which the marks are set, for example, in the form of a wafer grating. The deformation of the substrate can occur, for example, by electrostatically clamping the substrate to a substrate stage and / or by heating the substrate when it is exposed to radiation.

[0101] Figure 6 This is a schematic block diagram of a known embodiment of an alignment sensor AS, such as that described in US6961116, which is incorporated herein by reference. A radiation source RSO provides a radiation beam RB of one or more wavelengths, which is directed by a steering optics onto a mark, such as a mark AM located on a substrate W, as an illumination spot SP. In this example, the steering optics include a spot mirror SM and an objective lens OL. The diameter of the illumination spot SP illuminating the mark AM may be slightly smaller than the width of the mark itself.

[0102] The radiation diffracted by the marker AM is collimated (in this example, by the objective lens OL) into an information-carrying beam IB. The term "diffraction" is intended to include zero-order diffraction from the marker (which may be referred to as reflection). A self-referenced interferometer SRI (such as the type disclosed in US6961116 mentioned above) causes the beam IB to interfere with itself, after which the beam is received by a photodetector PD. Additional optics (not shown) may be included to provide a separated beam if the radiation source RSO generates more than one wavelength. The photodetector may be a single element, or it may comprise multiple pixels, if desired. The photodetector may include a sensor array.

[0103] Steering optics (including the spot mirror SM in this example) can also be used to block the zero-order radiation reflected from the marker, so that the information-carrying bundle IB only includes higher-order diffraction radiation from the marker AM (which is not necessary for measurement but improves the signal-to-noise ratio).

[0104] The intensity signal SI is provided to the processing unit PU. Through optical processing in the combined block SRI and computational processing in the unit PU, the values ​​of the X and Y positions on the substrate relative to the reference frame are output.

[0105] A single measurement of this type fixes the position of the mark within a specific range corresponding to a spacing between the marks. Coarser measurement techniques are used in conjunction with this to identify which period of the sine wave contains the mark's position. The same coarser and / or finer-level process can be repeated at different wavelengths to improve the accuracy and / or robustly detect the marks, regardless of the material on which the marks are made or the material on which they are placed. Wavelengths can be optically multiplexed and demultiplexed for simultaneous processing, and / or they can be multiplexed via time-division or frequency-division multiplexing.

[0106] In this example, the alignment sensor and spot SP remain stationary, while the substrate W moves. Therefore, the alignment sensor can be rigidly and precisely mounted to the reference frame while effectively scanning the mark AM in the direction opposite to the direction of movement of the substrate W. The movement of the substrate W is controlled by mounting the substrate W on a substrate support and a substrate positioning system that controls 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 one embodiment, one or more (alignment) marks are provided on the substrate support. Measuring the position of the marks on the substrate support allows calibration of the substrate support position determined by the position sensor (e.g., relative to the frame to which the alignment system is attached). Measuring the position of the alignment marks on the substrate allows determination of the substrate position relative to the substrate support.

[0107] Measurement tools (MTs) such as scatterometers, topography measurement systems, or position measurement systems described above can perform measurements using radiation derived from a radiation source. The characteristics of the radiation used by the measurement tool can affect the type and quality of the measurements that can be performed. For some applications, it may be advantageous to use multiple radiation frequencies to measure the substrate, for example, broadband radiation. Multiple different frequencies can propagate, illuminate, and scatter away from the measurement target with little or no interference to other frequencies. Therefore, different frequencies can be used, for example, to obtain more measurement data simultaneously. Different radiation frequencies can also interrogate and discover different characteristics of the measurement target. Broadband radiation can be used in measurement systems (MTs) such as level sensors, alignment mark measurement systems, scattering measurement tools, or inspection tools. Broadband radiation sources can be supercontinuum sources.

[0108] Generating high-quality broadband radiation, such as supercontinuum radiation, can be challenging. One approach to generating broadband radiation is, for example, to broaden high-power narrowband or single-frequency input radiation using nonlinear, higher-order effects. The input radiation (which can be generated using a laser) can be referred to as pump radiation. To obtain high-power radiation for the broadening effect, the radiation can be confined to a small region, resulting in strongly localized high-intensity radiation. In these regions, the radiation can interact with the broadening structure and / or material forming the nonlinear medium to generate broadband output radiation. In the high-intensity radiation region, different materials and / or structures can be used to achieve and / or improve radiation broadening by providing a suitable nonlinear medium.

[0109] In some applications, methods and apparatus for broadening input radiation can employ optical fibers used to confine the input radiation. The optical fiber can be a microstructured fiber (MOF), which may include internal structures to achieve efficient guidance and confinement of radiation within the fiber. The MOF can be a photonic crystal fiber (PCF), such as a hollow-core photonic crystal fiber (HCPCF). The hollow core of the fiber may be filled with a gas, which serves as the broadening medium for broadening the input radiation. Such fiber and gas devices can be used to generate supercontinuum radiation sources. The radiation input to the fiber can 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.

[0110] The internal structure of a MOF can be referred to as structural elements, and can specifically include anti-resonant elements (AREs). Such fibers containing AREs are known in the art as anti-resonant fibers, tubular fibers, monocyclic fibers, negative curvature fibers, or anti-coupling fibers. Various designs of such fibers are known in the art.

[0111] It should be understood that ARE is intended to refer to an element arranged to confine radiation primarily within a hollow core via anti-resonance. Specifically, the term "anti-resonant element" is not intended to include elements arranged to confine radiation within a hollow core primarily by creating a photonic bandgap in the cladding portion (e.g., hollow-core photonic bandgap fiber). Pure photonic bandgap fiber provides very low loss over a very limited bandwidth. Fibers using anti-resonant elements to guide radiation can have a wider transmission window (i.e., a larger transmission bandwidth) than photonic bandgap fibers. Advantageously, such fibers are therefore better suited for devices that receive input radiation and broaden the frequency range of the input radiation to provide output radiation (e.g., supercontinuum sources).

[0112] As described herein, MOFs can be incorporated into radiation sources SO, LSO, and RSO, for example, as part of a measurement apparatus for determining parameters of interest for structures on substrates as described herein. The aforementioned measurement apparatus can be incorporated into a measurement device MT. The aforementioned measurement apparatus can be incorporated into an inspection apparatus. The aforementioned measurement apparatus can be included within a photolithography apparatus LA.

[0113] Figure 7 and Figure 8 An example of an MOF (also referred to herein as an optical fiber) 100 according to this disclosure is shown. Figure 7 and Figure 8 This is a schematic cross-sectional view of MOF 100 in two mutually perpendicular planes.

[0114] MOF 100 comprises an elongated body that is longer in one dimension than the other two dimensions of MOF 100. This longer dimension may be referred to as the axial direction and may define the axis 101 of MOF 100. The two other dimensions define a plane that may be referred to as the transverse plane. Figure 7 A cross section of MOF 100 in a transverse plane (i.e., perpendicular to axis 101) is shown, which is labeled as the xy plane. Figure 8 The cross-section of MOF 100 in a plane containing axis 101, specifically the xz plane, is shown. The transverse cross-section of MOF 100 along fiber axis 101 can be substantially constant.

[0115] It should be understood that MOF 100 has a certain degree of flexibility, therefore the direction of the axis 101 is generally not uniform along the length of MOF 100. Terms such as optical axis 101 and transverse section will be understood to refer to local optical axis 101, local transverse section, etc. Furthermore, when the part is described as cylindrical or tubular, these terms will be understood to include the shape that may have deformed as MOF 100 is bent.

[0116] MOF 100 can have any length, and it will be understood that the length of MOF 100 can depend on the application (e.g., the amount of spectral broadening desired in applications within supercontinuum radiation sources). MOF 100 can have a length between 1 cm and 10 m, for example, MOF 100 can have a length between 10 cm and 100 cm.

[0117] MOF 100 includes: a hollow core 102; a plurality of AREs 104 (also called capillaries) surrounding the core region 102 for guiding radiation through the core region 102; and a cladding region 110 surrounding and supporting the AREs 104. Specifically, the plurality of AREs 104 are configured to restrict radiation propagating primarily within the core region 102 through the optical fiber 100 and to guide radiation along the optical fiber 100. The core region 102 of the optical fiber 100 can be substantially disposed in the central region of the optical fiber 100, such that the axis 101 of the optical fiber 100 can also define the axis of the core region 102 of the optical fiber 100.

[0118] The cladding region 110 can be formed of a material comprising glass. That is, the material comprises an amorphous (i.e., non-crystalline) material that exhibits a glass transition when heated to the transition temperature. For example, the material may comprise quartz glass. For example, portions of MOF 100 (e.g., ARE 104 and cladding region 110) may comprise any of the following: high-purity silica (SiO2) (e.g., F300 material sold by Heraeus Holding GmbH, Germany); soft glass, such as lead silicate glass (e.g., SF6 glass sold by Schott AG, Germany); or other specialty glasses, such as chalcogenide glasses or heavy metal fluoride glasses (also known as ZBLAN glasses). Advantageously, the glass material is non-degassed.

[0119] ARE 104 may include tubular capillaries. Each ARE 104 is defined by a generally cylindrical wall 105 that at least partially defines the core region 102 of MOF 100 and separates the core region 102 from the cavity defined by the ARE wall 105. Each portion of the ARE wall 105 facing the core region 102 is used to guide radiation propagating through MOF 100.

[0120] exist Figure 7 and Figure 8 In the example shown, MOF 100 comprises a single ring consisting of six AREs 104, and MOF 100 includes a substantially circular inner cross-section defined by cladding region 110. However, it should be understood that MOF 100 may include any other suitable number of AREs 104, such as five, seven, eight, nine, ten, eleven, twelve, or more AREs 104. Furthermore, as described herein, some examples of MOF 100 may not have a circular inner cross-section. For example, the inner cross-section may be polygonal, such as hexagonal or octagonal.

[0121] Several dimensional parameters of MOF 100 are critical to its performance in generating broadband radiation. These dimensional parameters include: ARE 104 (inner) diameter. d ARE wall thickness 105 t The interval between ARE 104 δ and core diameter D The core diameter is the diameter of core region 102.

[0122] As described herein, it is desirable to be able to determine dimensional parameters along the entire length of MOF 100 and / or during the manufacture of MOF 100 in order to determine whether MOF 100 is within specifications. As described herein, existing methods for determining dimensional parameters, such as Whispering Corridor Mode (WGM) spectroscopy, require ARE wall thickness. t Knowledge.

[0123] According to this disclosure, one or more dimensional parameters of the MOF 100 can be determined by detecting the signal associated with interference (e.g., Fabry-Perot interferometry) of radiation between and / or within the structural elements of the MOF 100. For example, broadband radiation can be directed at the MOF 100, and wavelength-resolved reflectance spectra can be obtained.

[0124] Figure 9 The simulation results of the spectrum obtained by simulating MOF are shown, where Fourier transform has been applied to the data so that the distances between the various surfaces forming the optical cavity to act as a calibrator can be resolved. Figure 9 The results shown correspond to a simulated hexagonal MOF containing six AREs, where D = 35.12μm, d = 17.7μm, and t = 0.15μm. Figure 10 An example of a hexagonal MOF comprising six ARE 104s is illustrated schematically. Figure 10 As shown, the AREs 104 are substantially uniformly distributed around the core region 102, located at the vertices of the hexagonal cross-section defined by the cladding region 110. The AREs have angular spacing. θ In the case of a symmetric hexagonal MOF, such as Figure 10 As shown schematically, θ It is equal to or substantially equal to 60 degrees.

[0125] like Figure 9 As shown, multiple distinct peaks are observed in the transformed spectrum, each corresponding to the interference of radiation within an optical cavity defined by the structural elements of the MOF. For example, this is achieved by two opposing outer ARE surfaces (given...). δ ), two opposing inner ARE surfaces (given) d ) and the inner ARE surface opposite the outer ARE surface (given) δ + dEach of the pair of reflective surfaces formed can be used as an etalon. The distance between each pair of reflective surfaces is determined based on the transmission or reflection of light from each etalon. Figure 9 No corresponding core diameter was observed. D The peak. Not wanting to be bound by theory, lacking a corresponding core diameter... D The observable peaks are likely due to the negative curvature of the outer surface of the ARE wall, forming an unstable resonator. This is useful for detecting the distance between adjacent AREs (given...). δ For this reason, the problem is likely minor because the distance is much smaller than the core diameter. D .

[0126] It should be understood that, although the ARE wall thickness t exist Figure 9 It is indistinguishable in the middle, but can be measured using a sufficiently broad radiation spectrum. t .

[0127] Even the core diameter D If the measurement cannot be directly obtained using this method, it can be calculated using measurable dimensional parameters. D For example, the distance between AREs can be used. δ ARE outer diameter d out and the geometric layout of MOF (i.e., the number of AREs) N For example, knowledge from 6) can be used to calculate the core diameter. D In order to determine using this method D We can assume the ARE wall thickness t Small enough to make (that is, among which) d (It is the inner diameter of ARE). Also assume... Then it can be determined according to the following:

[0128] Figure 11 It shows having D = 31.12μm, d = 19.7μm and t A portion of the transformed simulated spectrum of the MOF at 0.15 μm, where the simulation was repeated several times (“grids” 1 to 4). For example... Figure 11 As shown, when the ARE wall thickness t is included, the agreement with the peak position is extremely high. The peak value and the value excluding... t The deviation of the expected position is less than the measurement resolution (~0.1 μm).

[0129] Figure 12The polarization effects of radiation p-pol (p-polarized) and s-pol (s-polarized) are shown. Measurements are made regarding another MOF. Advantageously, as... Figure 12 As shown, the location of the peak and the ability to detect the peak are not affected by radiation polarization.

[0130] Figure 13 The detected reflections of various peaks associated with the structural elements of a hexagonal MOF, resolved by the rotation angle of the MOF, are shown. Figure 13 As shown, the peak position advantageously does not change with the angle. This contrasts with some other methods used to determine dimensional parameters, such as WGM spectroscopy, in which the measured ARE diameter changes with the rotation angle. Measuring the invariance during MOF rotation can be particularly useful during MOF fabrication, where the MOF may tend to undergo some degree of random rotation.

[0131] Figure 13 The variation of signal strength (peak height shown in grayscale) with rotation angle is also illustrated, including a "dead zone" between approximately 20 and 40 degrees, where the ARE diameter peak decreases to zero. This dead zone can result from the fact that radiation from the radiation source passes between adjacent AREs when the MOF is oriented corresponding to this angular range. To prevent signal loss at these rotation angles, two or more radiation sources are preferably used in the method described herein. For example, Figure 14 The measurement setup is shown, wherein the radiation used for measurement is provided by a first radiation source 1402A and a second radiation source 1402B. The first radiation source 1402A and the second radiation source 1402B are arranged to guide radiation radially toward the longitudinal axis of the MOF (i.e., at the center of the core region 102) and at an angle... Angular separation. To ensure that at least one of the first radiation source 1402A and the second radiation source 1402B is always incident on at least one ARE 104, Angular spacing between ARE 104 θ Related to, for , where 0.25≤ β ≤0.75, and where n is a positive integer (i.e., n = 1, 2, 3, ...). For example, the first radiation source 1402A and the second radiation source 1402B can be angularly separated by approximately half the angular interval between ARE 104 (e.g., in the case of a hexagonal cross-section MOF with six AREs, the first radiation source 1402A and the second radiation source 1402B can be angularly separated by approximately 30 degrees, or by odd multiples of approximately 30 degrees). Although for simplicity, Figure 14Only one radiation line emitted from each of the first radiation source 1402A and the second radiation source 1402B is shown; however, it should be understood that the first radiation source 1402A and the second radiation source 1402B preferably each emit radiation over a wide angular range to ensure that reflections can be detected from optical cavities formed between and within adjacent ARE 104. The reflected radiation can be detected by a suitable detector (not shown).

[0132] In embodiments of the invention, the rotation angle can be varied to selectively measure the dimensional parameters of one or more capillaries, rather than simultaneously measuring the dimensional parameters of all capillaries within the MOF. For example, at a selected angle 'θ', the radiation source can excite only the resonant modes of the top and bottom capillaries in a hexagonally arranged group of capillaries within the MOF. At different rotation angles 'θ + 60 degrees', the dimensional parameters of adjacent pairs of opposite capillaries can be measured.

[0133] In one embodiment of the invention, measurements can be performed on a MOF (e.g., a MOF with a circular cladding) having a circular arrangement of capillaries.

[0134] In embodiments of the invention, the Fabry-Perot based technique is used to individually measure the diameter and wall thickness of each capillary in the MOF by observing the measurement signal at an increased distance while rotating the MOF in a controlled manner. In simulation data, signal pairs have been observed at distances in the range of ≈ 55-61 μm for MOFs with circular cladding. These signal pairs exhibit a parabolic shape during rotation, similar to that when using WGM techniques, but originating from the path of light through the cladding and entering only the capillary closest to the irradiation beam. For example, it has been observed that for an MOF with six capillaries surrounding 'θ'=0, the signal, as a function of the rotation angle 'θ' and the measurement distance, selectively samples capillary 4. This signal at distance... nT (Clad layer thickness = 41.1 mm) + d 4 (diameter of capillary tube 4) + nT 4 (optical thickness of capillary 4) and nT + d 4 + 2 nT There are peaks at 4 locations. For approximately 60 degrees θ, the signal received from capillary 3 is [value missing], and [value missing] nT + d 3 + nT 3 and nT + d 3 + 2 nT There are 3 peaks, etc. Since the difference between two peaks is always due to... nti This allows for the individual detection of each individual capillary. iThe diameter of the fiber is measured, and the thickness of the fiber can be easily detected by rotating the fiber in a controlled manner (or setting it around the fiber).

[0135] In some examples, only one radiation source may be used. In other examples, more than two radiation sources may be used. The radiation source described herein can be a broadband radiation source capable of emitting wavelengths ranging from ultraviolet (UV) to infrared (IR) or near-infrared (NIR), such as radiation in the 200–1200 nm range. Examples of suitable broadband radiation sources include arc lamps, tungsten halogen lamps, xenon lamps, or any other suitable radiation source, including those based on light-emitting diodes (LEDs). In another example, the radiation described herein can be narrowband radiation from a source with configurable wavelengths, such as a tunable laser. Instead of using broadband radiation for measurements, measurements can then be taken at multiple (discrete) wavelengths, each selected by tuning the wavelength of the narrowband radiation source.

[0136] Figure 15 An example of a method 1500 for determining the dimensional parameters of a MOF according to this disclosure is shown.

[0137] In step S1502, method 1500 includes guiding radiation toward the MOF. As described herein, the radiation may be provided by one or more broadband radiation sources, or by selecting multiple wavelengths from tunable narrowband sources.

[0138] In step S1504, method 1500 includes obtaining one or more signals associated with interference of radiation between structural elements of the MOF. As described herein, the interference may be a Fabry-Perot interference. The signals may correspond to the reflection and / or transmission of radiation from an optical cavity defined by the structural elements of the MOF, resolved by the radiation wavelength to give the width of the optical cavity.

[0139] In step S1506, method 1500 includes determining the distance between structural elements based on one or more signals associated with interference of radiation between structural elements of the MOF.

[0140] In step S1508, method 1500 includes determining dimensional parameters based on the determined distances. For example, the dimensional parameters may directly correspond to the determined distances (e.g., the distance between AREs). In some examples, the dimensional parameters may be determined based on additional determined distances and / or knowledge of the geometry of the MOF. For example, the core diameter may be determined based on the distance between AREs, the diameter of the AREs, and the number of AREs (e.g., symmetrically arranged around the core region).

[0141] For some applications, the ARE of the MOF needs to include additional anti-resonant elements, typically additional capillaries nested within capillaries surrounding the core region of the MOF. Figure 18 An example of such a nested MOF 1800 layout is shown in the document. In this example, each of the six additional capillaries 1820 is nested within a corresponding capillary 1810 surrounding the core region 1830 (with a diameter 'Dc') of the fiber 1800. The method disclosed in this document can also be used to determine the dimensional parameters of the additional ARE / capillary 1820 nested within the ARE, such as its diameter 'd', wall thickness 't', and / or distance to the wall of its corresponding capillary 1810. Similarly, the method of the present invention can also be used to obtain the geometry of double-nested or general N-nested structures.

[0142] Figure 19a Depicting MOF (also as Figure 9 A portion of the transformed simulated spectrum (shown) of the MOF, which includes an inner nested capillary with an inner diameter 'd' of 7.9 μm, while an outer capillary has an inner diameter of 32.5 μm. Figure 19b Simulated spectra depicting the transformations were generated when the diameter 'd' of the internally nested capillaries was 16.3 μm. From... Figure 19a and Figure 19b It can be seen that the diameter 'd' of the inner nested capillary shows good agreement with the positions of the peaks at 8 and 16 μm, respectively. Therefore, it can be concluded that the proposed Fabry-Perot-based measurement method can also be used to determine the structural parameters associated with nested capillary tubes with very high precision.

[0143] An example of an MOF manufacturing process according to this disclosure will now be briefly described. It should be understood that other manufacturing processes may be applied alternatively or in combination with the methods described herein. Detailed examples of MOF manufacturing processes are known in the art, such as those described in EP3136143 A1, the contents of which are incorporated herein by reference. It should be understood that the MOF manufacturing process briefly described herein may include additional steps omitted for clarity.

[0144] In the first manufacturing step, glass preforms are typically made by attaching a thin-walled glass tube (a few millimeters in outer diameter) to a hollow cladding (a few centimeters in diameter). The thin-walled glass tube is mechanically fixed to the cladding.

[0145] In the second manufacturing step, the glass preform is then sent to a heating furnace where heat is applied to make the glass viscous (approximately 1900-2000°C).

[0146] In the third manufacturing step, the preform is drawn into fibers at the fiber ends faster than when it is fed into the heating furnace. The internal hollow structure can be modified by applying overpressure / underpressure relative to the environment. Each hollow region (e.g., capillary or ARE 104 and core region 102) can experience different overpressure / underpressure.

[0147] In the fourth manufacturing step, the fibers are then collected on the spool.

[0148] According to this disclosure, an MOF can be obtained by determining one or more dimensional parameters of the MOF "online" during its manufacturing process, so that if the MOF is outside the required specifications, real-time feedback can be used to adjust the manufacturing process parameters.

[0149] Figure 16 An example of a method 1600 for obtaining MOF according to this disclosure is shown.

[0150] In step S1602, method 1600 includes monitoring dimensional parameters during the MOF manufacturing process by determining the dimensional parameters of the MOF manufactured by the MOF manufacturing process. The MOF manufacturing process can be any suitable process as described herein. The dimensional parameters can be determined by any suitable method, such as any method described herein for determining the dimensional parameters of the MOF, for example... Figure 15 Method 1500 is shown. In some examples, dimensional parameters can be monitored continuously, for example, by using continuous output measurements of dimensional parameters. In some examples, dimensional parameters can be determined at regular intervals.

[0151] In step S1604, method 1600 includes adjusting parameters of the MOF manufacturing process if the determined dimensional parameter is outside the tolerance range. For example, if the determined dimensional parameter is any one of the ARE diameter, the spacing between AREs, and / or the core diameter, and one or more dimensional parameters are outside the tolerance range, adjusting the parameters of the MOF manufacturing process may include adjusting the pressure in the capillary to adjust the diameter of the ARE, which will also change the ARE spacing and core diameter of the MOF until (one or more) dimensional parameters are within the desired tolerance range.

[0152] Although the methods described so far involve measuring the dimensional parameters of the MOF during or after manufacturing, these methods can also be used to measure the dimensions of the preform. It may be advantageous to verify the dimensions of the preform before actually drawing fibers from it; it is possible that the preform may not meet dimensional specifications and therefore may not be usable for drawing MOFs that meet applicable specifications. Based on measurements of the preform (preform blank), the decision can be made regarding the initial drawing process, reprocessing the preform, or selecting an alternative preform for MOF manufacturing. In the case of measuring the preform, the radiation used can preferably be from a tunable narrowband radiation source (e.g., a tunable laser) because the preform (sometimes called a "preform blank") is typically ~20 times larger, requiring higher spectral resolution. The latter involves measuring a longer resonator length, thereby imposing finer resolution on the measured spectrum (an inherent characteristic of Fourier transform-based techniques, where small spectral intervals are transformed into large resonator distances).

[0153] The method discussed for measuring the properties of MOFs using Fabry-Perot-based measurements can also be applied to post-manufacturing steps performed on finished MOF products. In one example, a post-manufacturing step could be winding the MOF onto a spool, as described in U.S. Patent Application US2024 / 0280776A1. As described in that patent application, it is important to ensure that the microstructures do not twist along the length of the optical fiber (MOF) when wound onto the spool. To achieve this, the azimuth orientation of the microstructures within the MOF needs to be identified, and then a rotation control system is used to rotate the fiber as it is rewound to ensure that the microstructures do not twist along the length of the fiber when wound onto the spool. This document proposes measuring the properties of the MOF using the method described therein (Fabry-Perot-based) when the MOF is wound onto the spool. This property could include the azimuth orientation of the microstructures (capillaries) relative to the optical axis of the MOF when it is wound onto the spool.

[0154] In one embodiment, a method for determining the orientation of a microstructured optical fiber (MOF) relative to the optical axis of the MOF is disclosed, the method comprising: guiding radiation toward the MOF; obtaining one or more signals associated with interference of the radiation between structural elements of the MOF; determining the orientation of the structural elements based on the one or more signals associated with the interference of the radiation between the structural elements; and determining the orientation based on the determined distance.

[0155] In one embodiment, the method for determining the orientation is performed while the MOF is wound onto a spool. In one embodiment, the determined orientation of the MOF can be used to control the rotation of the MOF during winding to prevent the MOF from twisting on the spool.

[0156] In some examples, one or more methods described herein (including) Figure 15 and 16 The methods illustrated can be implemented by a computer. For example, a non-transitory computer-readable medium (e.g., EEPROM (e.g., flash memory), a disk, a CD-ROM or DVD-ROM, a programmable memory such as read-only memory (e.g., for firmware)) may include instructions that, when executed by a processor of a computing device, cause the computing device to perform one or more methods described herein. The instructions may be provided on one or more carriers. For example, there may be one or more non-transitory memories, such as EEPROM (e.g., flash memory), a disk, a CD-ROM or DVD-ROM, a programmable memory such as read-only memory (e.g., for firmware), one or more transient memories (e.g., RAM), and / or one or more data carriers such as optical or electrical signal carriers. The memory may be integrated into and / or separate from the corresponding processing chip. The code (and / or data) implementing embodiments of this disclosure may include source, object, or executable code or assembly code in a conventional programming language (interpreted or compiled) such as C, code for setting up or controlling an ASIC (Application-Specific Integrated Circuit) or FPGA (Field-Programmable Gate Array), or code in a hardware description language. For example, the instructions may include instructions for controlling one or more radiation sources and / or one or more detectors, as described herein via a suitable hardware interface system. The instructions may also include instructions for analyzing signals detected by the detector(s) to determine the distance(s) between structural elements(s) as described herein.

[0157] Figure 17A detailed view of an example computer system (also known as a user terminal) 1702 is shown, through which instructions corresponding to the methods described herein can be executed. The computer system 1702 includes a central processing unit (“CPU”) 1703, a display 1704 such as a screen or touchscreen, and a user input device such as a keypad 1706 that can be connected to the CPU 1703. The computer system 1702 includes inputs 1712 and outputs 1710. Input 1712 enables a connection between the CPU 1702 and one or more means (e.g., one or more detectors) that can be used to perform the methods described herein. This connection can be wired and / or wireless. The output enables a connection between the CPU 1702 and one or more means (e.g., one or more radiation sources) that can be used to perform the methods described herein. This connection can be wired and / or wireless. An example of such an interface is a USB interface. The CPU 1702 can be connected to a network interface 1724, such as a modem for communicating with a network. The user terminal 1702 also includes a memory 1726 for storing data known in the art. Memory 1726 can be permanent memory, such as ROM. Alternatively, memory 1726 can be temporary memory, such as RAM.

[0158] While this article provides specific references to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein can have other applications. Possible other applications include the fabrication of integrated optical systems, the guiding and detection of patterns in magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0159] Although embodiments of the invention may be specifically referred to herein in the context of lithography equipment, these embodiments can be used in other equipment. Embodiments of the invention can form part of mask inspection equipment, metrology equipment, or any equipment that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These devices are commonly referred to as lithography tools. Such lithography tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0160] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it should be understood that, where the context permits, the invention is not limited to optical lithography and can be used in other applications, such as imprint lithography.

[0161] While specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in ways other than those described. The above description is intended to illustrate and not limit. Therefore, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the following claims.

Claims

1. A method for determining dimensional parameters of a microstructured optical fiber (MOF) or a preform configured to be drawn into the MOF, the method comprising: Radiation is guided toward the MOF or preform; Obtain one or more signals associated with the interference of the radiation between the structural elements of the MOF or preform; The distance between the structural elements is determined based on one or more signals associated with the interference of the radiation between the structural elements; as well as The size parameters are determined based on the determined distance.

2. The method of claim 1, further comprising determining the dimensional parameters based on the determined distance and the geometry of the MOF or preform.

3. The method according to claim 1 or 2, wherein the MOF or preform includes a core region, and wherein the structural element is an anti-resonant element surrounding the core region and / or an additional anti-resonant element nested within the anti-resonant element.

4. The method of claim 3, wherein the dimensional parameter includes the core diameter, the core diameter being the diameter of the core region.

5. The method according to claim 4, further comprising: Obtain one or more signals associated with the interference of the radiation within one or more anti-resonant elements; The diameter of the anti-resonant element in the one or more anti-resonant elements is determined based on the one or more signals associated with the interference of the radiation within the one or more anti-resonant elements. as well as The size parameters are further determined based on the diameter of the anti-resonant element.

6. The method of claim 4 or 5, further comprising determining the dimensional parameter D based on: in δ It is the distance between the anti-resonant elements, where N It is the total number of anti-resonant elements, and among them ,,in d It is the diameter of the anti-resonant element, and among which... t It is the wall thickness of the anti-resonant element.

7. The method of claim 6, wherein .

8. The method of claim 3, wherein the dimensional parameter includes the wall thickness of the anti-resonant element.

9. The method of claim 3, wherein the dimensional parameter includes the distance between the anti-resonant elements or the distance between an anti-resonant element and another anti-resonant element nested within an anti-resonant element.

10. The method of claim 3, wherein the dimensional parameter includes the diameter of the anti-resonant element.

11. The method according to any one of claims 3 to 9, further comprising using a first radiation source and a second radiation source to radially direct the radiation toward the longitudinal axis of the MOF, the first radiation source and the second radiation source being angled around the longitudinal axis. Angular separation, where ,in θ It is the angular spacing between the anti-resonant elements, where 0.25 ≤ β ≤0.75, and where n is a positive integer.

12. The method according to any one of the preceding claims, wherein the MOF comprises a polygonal inner section.

13. The method according to any one of the preceding claims, wherein the interference comprises Fabry-Perot interference.

14. A method for obtaining MOF, comprising: The dimensional parameters are monitored during the MOF manufacturing process by determining the dimensional parameters of the MOF manufactured by the MOF manufacturing process according to any one of the preceding claims; and If the determined dimensional parameters are outside the tolerance range, the parameters of the MOF manufacturing process are adjusted.

15. A non-transitory computer-readable medium comprising instructions that, when executed by a processor of a computing device, cause the computing device to perform the method according to any one of claims 1 to 13.

Images