Method and device for metering

Abstract

A method and apparatus for directing a radiation beam emitted as a result of high harmonic generation (HHG) onto a substrate. A drive radiation source provides drive radiation to an interaction region containing a medium for HHG generation. The radiation generated by the HHG may include multiple soft X-ray (SXR) wavelengths. Different HHG generated wavelengths have different divergence angles. The apparatus also includes an optical system that focuses different HHG wavelengths to different focal planes due to the different divergence angles. The apparatus also includes a substrate support for holding the substrate. One or more of the drive radiation source, the interaction region, the optical system, and the substrate support can control the position of the substrate relative to the multiple focal planes of the HHG radiation.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 18215345.2 filed on December 21, 2018 and EP application 19158015.8 filed on February 19, 2019, and the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to methods and apparatus for use in metrology, in particular in metrology of lithographic patterning processes. In a specific arrangement, the present invention relates to methods and apparatus for use in metrology using soft X-ray (SXR) or extreme ultraviolet (EUV) radiation as defined herein. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits. A lithographic apparatus can, for example, project a pattern (also commonly referred to as a "design layout" or "design") at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

[0005] To project a pattern on a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on a substrate. Typical wavelengths currently used are 365 nanometers (i-line), 248 nanometers, 193 nanometers, and 13.5 nanometers. A lithographic apparatus using extreme ultraviolet (EUV) radiation with a wavelength in the range of 4-20 nanometers (e.g., 6.7 nanometers or 13.5 nanometers) can be used to form smaller features on a substrate than a lithographic apparatus using radiation with a wavelength of 193 nanometers.

[0006] Low k1 lithography can be used to process features with dimensions smaller than the classical resolution limit of the lithographic apparatus. In this process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is the "critical dimension" (usually the smallest feature size printed, but in this case it is half the pitch), and k1 is an empirical resolution factor. In general, the smaller the k1, the more difficult it is to reproduce a pattern on the substrate that is similar in shape and size to that planned by the circuit designer to achieve specific electrical functions and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithographic projection apparatus and / or the design layout. These include, for example, but not limited to, optimization of NA, customized illumination schemes, use of phase-shifted patterning equipment, 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 technology" (RET). Optionally, a tight control loop for controlling the stability of the lithographic apparatus can be used to improve the reproduction of patterns at low k1.

[0007] As an alternative to optical metrology methods, the use of soft X-rays (SXR) or EUV radiation, for example, radiation in a wavelength range between 0.1 nm and 100 nm, or optionally between 1 nm and 50 nm, or optionally between 10 nm and 20 nm, is also contemplated. Applications of SXR include, but are not limited to, current or recent measurement tools in the semiconductor industry. An example of a metrology tool that works in one of the above wavelength ranges is transmission small angle X-ray scattering (such as T-SAXS in US 2007224518A, the entire contents of which are incorporated herein by reference). Lemaillet et al. discussed profile (CD) measurements using T-SAX in Proc. of SPIE, 2013, 8681, “Intercomparison between optical and X-ray scatterometry measurements of FinFET structures”. Reflection techniques using X-rays (GI-XRS) and extreme ultraviolet (EUV) radiation at grazing incidence are known for measuring the properties of films and stacked layers on substrates. Within the general field of reflectometers, angle measurement and / or spectroscopic techniques can be applied. In goniometry, the variation of the reflected light beam at different angles of incidence is measured. Spectral reflectometry, on the other hand, measures the spectrum of wavelengths reflected at a given angle (using broadband radiation). For example, EUV reflectometers are already used for inspection of mask blanks before manufacturing the reticles (patterning equipment) used in EUV lithography.

[0008] The range of applications may make the use of wavelengths in the soft X-ray or EUV domain insufficient. Therefore, published patent applications US20130304424A1 and US2014019097A1 (Bakeman et al. / KLA) describe hybrid metrology techniques in which measurements made with X-rays and optical measurements at wavelengths in the range of 120 nm and 2000 nm are combined to obtain measurements of parameters such as CD. CD measurements are obtained by coupling an X-ray mathematical model and an optical mathematical model through one or more common points. The contents of the cited US patent applications are incorporated herein by reference in their entirety.

[0009] As mentioned above, current optical metrology tools for wafer inspection use light in the visible range. The wavelengths of the visible range are typically much larger than the pitch values ​​that appear on the device. Therefore, metrology solutions either have dedicated targets with large pitches to generate diffraction orders, or measure at resolution but rely on 0th order information provided by the evanescent wave.

[0010] Measurements of targets with large pitches are not necessarily representative of the pitches within the device, and the evanescent wave does not penetrate deeply into the stack of layers that form features on the substrate, limiting the application space. In contrast, SXR potentially provides both sufficient spatial resolution to resolve the small pitches of semiconductor devices and deeper penetration into the stack.

[0011] SXR beams can be generated using high harmonic generation (HHG), where an intense laser pulse of visible light or infrared (IR) radiation (driving radiation) is injected into a gaseous medium, causing the gas atoms to emit SXR (emitted radiation) due to their interaction with the laser. The SXR radiation generated by HHG can then be focused onto a target on a substrate with the aid of an optical system that transfers the radiation from the medium to the target. The radiation can then be reflected and / or diffracted from the target, and detected and processed to infer the properties of the target. Examples of these parameters relevant to semiconductor manufacturing are critical dimension (CD), overlay, material refractive index, etc.

[0012] Typically, optical metrology tools used in the semiconductor industry rely heavily on comparing measurements of light diffracted by features (e.g., targets) on a substrate with predicted diffraction patterns generated by computational models. Parameters of the feature or target, such as feature size, are inferred by identifying which values ​​of the parameters produce the best match between the measured diffraction pattern and the predicted diffraction pattern.

[0013] Using SXR and EUV radiation in metrology poses several challenges. Summary of the invention

[0014] The inventors have recognized that using SXR radiation generated by HHG results in different wavelengths of SXR radiation being focused at different axial positions or focal planes after propagating through an optical system.Exemplary methods and apparatus disclosed herein relate to using these focal planes in metrology of lithographic processes.

[0015] According to one aspect of the invention, there is provided an apparatus for directing a radiation beam emitted as a result of high harmonic generation (HHG) onto a substrate, the apparatus comprising: a drive radiation source; an interaction region configured to receive a medium and positioned such that a drive radiation beam from the drive radiation source interacts with the medium during use to generate an emitted radiation beam by HHG, wherein the emitted radiation beam comprises a plurality of wavelengths and wherein an emission divergence angle of the emitted radiation depends on the wavelength; an optical system located downstream of the interaction region and configured to focus the emitted radiation beam, wherein the plurality of wavelengths of the emitted radiation beam are focused at a plurality of focal planes according to associated emission divergence angles; and a substrate support for holding the substrate at one of a plurality of axial positions relative to the plurality of focal planes, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control a relative position of at least one of the focal planes relative to the substrate.

[0016] Configuring the medium, which may be a gaseous medium, and / or the driving radiation source may affect the emission divergence angle of one or more wavelengths of the emitted radiation, which in turn may affect the axial position of the focal planes for those wavelengths. Configuring the optical system and / or the substrate support, which may be a wafer stage, may affect the axial position of all focal planes. As used herein, the term "axial position" includes position along the optical axis of the device, although changes in axial position may be seen parallel to the optical axis and does not necessarily mean that a feature is on the optical axis.

[0017] Optionally, the interaction region comprises a nozzle for directing the medium to the interaction region or a gas chamber for retaining the medium, and wherein the nozzle or the gas chamber is configured for controlling the axial position of the medium.

[0018] Optionally, the drive radiation source is configured to control the axial position of a focus of the drive radiation beam.

[0019] Optionally, the optical system is configured to control the axial position of one or more focal planes.

[0020] Optionally, the substrate support is configured to control the axial position of a substrate held thereon.

[0021] Optionally, when the emitted radiation beam is diffracted and / or reflected from a feature on the substrate, the intensity of the diffracted and / or reflected radiation depends on the wavelength of the emitted radiation beam, and one or more of the driven radiation source, the interaction region, the optical system and the substrate support can be configured to control the relative position of at least one of the focal planes with respect to the substrate based on the intensity of the diffracted and / or reflected radiation. The intensity of the diffracted and / or reflected radiation can be estimated and / or measured.

[0022] Optionally, the diffracted and / or reflected radiation comprises positive and negative orders, and the intensity difference between the positive and negative orders depends on the wavelength of the emitted radiation beam, and one or more of the driven radiation source, the interaction region, the optical system and the substrate support can be configured to control the relative position of at least one of the focal planes with respect to the substrate based on the intensity difference between the positive and negative orders. The intensity difference of the diffracted and / or reflected radiation can be estimated and / or measured.

[0023] Optionally, the first intensity difference is based on a feature without errors in one or more parameters, and wherein the second intensity difference is based on a feature with specific errors in one or more parameters, and one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control the relative position of at least one of the focal planes with respect to the substrate based on a difference between the first intensity difference and the second intensity difference. The intensity difference of the diffracted and / or reflected radiation can be estimated and / or measured.

[0024] Optionally, one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to position a selected focal plane to substantially coincide with the plane of the substrate, wherein the selected focal plane is determined based on the intensity of the diffracted and / or reflected radiation.

[0025] Optionally, one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to position a plurality of selected focal planes substantially coincident with the substrate.

[0026] Optionally, the apparatus further comprises a first radiation detector configured to detect positive orders of diffracted and / or reflected radiation and a second radiation detector configured to detect negative orders of diffracted and / or reflected radiation.

[0027] Optionally, one or more of the driving radiation source, the interaction region, the optical system and the substrate support are configured so that a first wavelength of the emitted radiation beam forms a first spot size at the substrate and a second wavelength of the emitted radiation beam forms a second spot size at the substrate that is larger than the first spot size, and the device includes at least one radiation detector, the at least one radiation detector being configured to receive first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the first wavelength and second diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the second wavelength; and a processor being configured to execute computer program code to perform the following method: comparing the intensity of the first diffracted and / or reflected radiation with the intensity of the second diffracted and / or reflected radiation; and determining a model of the intensity of the diffracted and / or reflected radiation as a function of the spot size.

[0028] Optionally, the features of the substrate include a plurality of lines fabricated on the substrate, and wherein the model indicates the effect of the lines on the diffracted and / or reflected radiation. For example, a finite number of lines on the target may affect the intensity of the diffracted and / or reflected radiation, and the model may be used to mitigate or eliminate this "finite line effect".

[0029] Optionally, the processor is also configured to: predict the intensity of one or more pixels of the image of radiation diffracted and / or reflected from the feature based on the determined model; compare the predicted intensity with the measured intensity of one or more corresponding pixels of the image of radiation diffracted and / or reflected from the feature; and determine one or more parameters of the patterning process based on the comparison.

[0030] Optionally, one or more of the driving radiation source, the interaction region, the optical system and the substrate support are configured so that at least one wavelength of the emitted radiation beam forms a first spot size at the substrate and subsequently forms a second spot size at the substrate that is different from the first spot size, and the device includes at least one radiation detector, the at least one radiation detector being configured to receive first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at at least one wavelength having the first spot size and second diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at at least one wavelength having the second spot size; and a processor being configured to execute computer program code to perform the following method: determining an intensity of the emitted radiation at the first spot size and an intensity of the emitted radiation at the second spot size; determining an intensity of the first diffracted and / or reflected radiation and an intensity of the second diffracted and / or reflected radiation; and determining a model of the intensity of the diffracted and / or reflected radiation as a function of the spot size based on the determined intensities.

[0031] Optionally, the determined model indicates a non-linear effect of the intensity of the diffracted and / or reflected radiation with the spot size. The non-linear effect may be caused by a high intensity of the emitted radiation beam (e.g., an SXR beam). For example, the emitted radiation beam may affect a sensitive resist on top of a substrate feature, which may cause a change in the intensity of the diffracted and / or reflected radiation. The intensity of the emitted radiation beam incident on the feature is a function of the spot size.

[0032] Optionally, one or more of the driven radiation source, the interaction region, the optical system, and the substrate support are configured such that at least one wavelength of the emitted radiation beam is focused on the substrate to form a spot size having a diameter greater than a threshold value. Maintaining the spot size above the threshold value may maintain an intensity of the emitted radiation beam incident on a substrate feature below a corresponding threshold value.

[0033] Optionally, one or more of the driven radiation source, the interaction region, the optical system and the substrate support are configured such that a first wavelength of the emitted radiation beam forms a first spot size at a first depth of the substrate and a second wavelength of the emitted radiation forms a second spot size at a second depth of the substrate.

[0034] Optionally, the first wavelength is selected based on a sensitivity of the first wavelength to an aspect of a feature of the substrate at a first depth and / or the second wavelength is selected based on a sensitivity of the second wavelength to an aspect of a feature of the substrate at a second depth.

[0035] Optionally, the feature of the substrate includes a target, and wherein one or more of the drive radiation source, the interaction region, the optical system, and the substrate support are configured such that a first wavelength of the emitted radiation forms a spot size that underfills the target and a second wavelength of the emitted radiation forms a spot size that overfills the target.

[0036] Optionally, the first wavelength and / or the second wavelength are selected based on their sensitivity to aspects of the target and / or aspects of other features of the substrate outside the region of the target.

[0037] Optionally, the emitted radiation has a wavelength in the range from 0.1 nanometers to 100 nanometers.

[0038] According to the present invention, in one aspect, there is provided a metering device comprising a device as described herein, in particular as described above.

[0039] According to one aspect of the invention, there is provided a method for directing radiation toward a feature of a substrate, the method comprising: directing a drive radiation beam from a drive radiation source toward an interaction region, the interaction region comprising a medium configured to interact with the drive radiation to produce emitted radiation by HHG, wherein the emitted radiation beam comprises a plurality of wavelengths, and wherein an emission divergence angle of the emitted radiation depends on the wavelength; causing the emitted radiation to propagate through an optical system downstream of the interaction region; focusing the emitted radiation beam onto a substrate held by a substrate support, wherein the plurality of wavelengths of the emitted radiation beam are focused at a plurality of focal planes according to associated emission divergence angles; and controlling one or more of the drive radiation source, the interaction region, the optical system, and the substrate support to be configurable to control a relative position of at least one of the focal planes relative to the substrate.

[0040] Optionally, the method also includes: configuring one or more of the driving radiation source, the interaction region, the optical system and the substrate support so that the first wavelength of the emitted radiation beam forms a first spot size at the substrate, and the second wavelength of the emitted radiation beam forms a second spot size larger than the first spot size at the substrate; receiving, by at least one radiation detector, first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the first wavelength and second diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the second wavelength; comparing the intensity of the first diffracted and / or reflected radiation with the intensity of the second diffracted and / or reflected radiation; and determining a model of the intensity of the diffracted and / or reflected radiation as a function of the spot size.

[0041] Optionally, the method also includes: configuring one or more of the driving radiation source, the interaction region, the optical system and the substrate support so that at least one wavelength of the emitted radiation beam forms a first spot size at the substrate and subsequently forms a second spot size at the substrate that is different from the first spot size, receiving, by at least one radiation detector, first diffracted and / or reflected radiation diffracted and / or reflected from a characteristic of the substrate at the first wavelength and second diffracted and / or reflected radiation diffracted and / or reflected from a characteristic of the substrate at the second wavelength; determining an intensity of the emitted radiation at the first spot size and an intensity of the emitted radiation at the second spot size; determining the intensity of the first diffracted and / or reflected radiation and the intensity of the second diffracted and / or reflected radiation; and based on the determined intensities, determining a model of the intensity of the diffracted and / or reflected radiation as a function of the spot size.

[0042] Optionally, the method further comprises configuring one or more of a driven radiation source, an interaction region, an optical system and a substrate support, wherein the driven radiation source, the interaction region, the optical system and the substrate support are configured such that at least one wavelength of the emitted radiation beam is focused at the substrate to form a spot size having a diameter greater than a threshold.

[0043] Optionally, the method further comprises configuring one or more of the driven radiation source, the interaction region, the optical system and the substrate support so that a first wavelength of the emitted radiation beam forms a first spot size at a first depth of the substrate and a second wavelength of the emitted radiation forms a second spot size at a second depth of the substrate.

[0044] According to one aspect of the invention, there is provided a computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to control an apparatus to perform a specific method according to any method described herein and as defined above.

[0045] According to one aspect of the present invention, there is provided a carrier comprising a computer as mentioned above and elsewhere herein, wherein the carrier is one of an electronic signal, an optical signal, a radio signal and a non-transitory computer-readable storage medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0047] Figure 1 A schematic overview of a lithography apparatus is depicted;

[0048] Figure 2 A schematic overview of a lithography cell is depicted;

[0049] Figure 3 A schematic diagram depicting overall lithography represents the collaboration between three key technologies to optimize semiconductor manufacturing;

[0050] Figure 4 shows a schematic diagram of the SXR metering device;

[0051] Figure 5 A simplified schematic diagram of the SXR metering device is shown;

[0052] Figure 6 a schematic diagram showing radiation emitted by a HHG, diffracted from features of a substrate and received by a radiation detector; and

[0053] Figure 7 An exemplary swing curve is shown. DETAILED DESCRIPTION

[0054] In this document, the terms "radiation" and "beam" are used to include all types of electromagnetic radiation, including UV radiation (e.g., having a wavelength of 365, 248, 193, 157 or 126 nanometers), EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5-100 nanometers), and SXR radiation having a wavelength in the range of 0.1-100 nanometers.

[0055] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam, corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective, binary, phase-shift, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0056] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., a mask stage) MS configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to precisely position the patterning device MA according to specific 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 to precisely position the substrate support according to specific parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0057] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0058] The term "projection system" PS as used herein should be broadly interpreted as including various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation used and / or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered a synonym for the more general term "projection system" PS. A projection system may also be referred to as an optical system.

[0059] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system PS and the substrate W, which is also known as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0060] The lithographic apparatus LA may also be of a type having two or more substrate supports (or substrate tables) WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps to prepare a substrate W for subsequent exposure may be performed on a substrate W located on one of the substrate supports WT while another substrate W on another substrate support WT is being used to expose a pattern on another substrate W.

[0061] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measuring table. The measuring table is arranged to hold sensors (or optical / radiation detectors) and / or cleaning equipment. The sensors may be arranged to measure characteristics of the projection system PS or characteristics of the radiation beam B. The measuring table may hold a plurality of sensors. The cleaning equipment may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of the system for providing immersion liquid. The measuring table may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0062] In operation, a radiation beam B is incident on a patterning device, such as a mask MA, held on a mask support MS, and is patterned by a pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the radiation 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, in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, a first positioner PM and possibly a further position sensor (which is located in the substrate support WT) are provided. Figure 1The patterning device MA can be accurately positioned relative to the path of the radiation beam B using the mask alignment marks M1, M2 and the 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 referred to as scribe-lane alignment marks.

[0063] like Figure 2 As shown, the lithography apparatus LA may form part of a lithography cell LC, sometimes also referred to as a lithography cell or (lithography) cluster, which typically also includes apparatus for performing pre-exposure and post-exposure processes on a substrate W. Typically, these apparatus 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, for example for regulating the temperature of the substrate W, for example for regulating a solvent in the resist layer. A substrate handler or robot RO picks up substrates W from input / output ports I / O1, I / O2, moves substrates W between different processing apparatuses, and transfers substrates W to a loading bay LB of the lithography apparatus LA. The equipment in the lithography cell is also typically collectively referred to as a track, which is under the control of a track control unit TCU, which itself may be controlled by a supervisory control system SCS, which may also control the lithography apparatus LA, for example via a lithography control unit LACU.

[0064] In order for substrates W exposed by the lithography apparatus LA to be correctly and consistently exposed, it is desirable to inspect the substrates to measure properties of the patterned structures, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), etc. To this end, inspection tools (not shown) may be included in the lithography cell LC. If errors are detected, for example, adjustments may be made to the exposure of subsequent substrates or other processing steps to be performed on the substrate W, particularly if the inspection is performed before other substrates W of the same batch or lot that are still to be exposed or processed.

[0065] An inspection apparatus, which may also be referred to as a metrology apparatus, is used to determine properties of a substrate W, in particular how properties vary from one substrate to another W, or how properties associated with different layers of the same substrate W vary from layer to layer. Optionally, the inspection apparatus may be configured to identify defects on the substrate W, and may for example be part of the lithography apparatus LC, or may be integrated into the lithography apparatus LA, or may even be a stand-alone device. The inspection apparatus may measure properties on a latent image (the image in the resist layer after exposure), or a semi-latent image (the image in the resist layer after a post-exposure bake step PEB), or a developed resist image (where exposed or unexposed parts of the resist have been removed), or even an etched image (after a pattern transfer step such as etching).

[0066] Typically, the patterning process in the lithography apparatus LA is one of the most critical steps in the process requiring high precision in dimensioning and placement of structures on the substrate W. To ensure this high precision, the three systems can be combined in a so-called "holistic" control environment, such as Figure 3 Schematically depicted. One of these systems is a lithography apparatus LA, which is (in practice) connected to a metrology tool MT (a second system) and a computer system CL (a third system). The key to this "holistic" environment is to optimize the cooperation between these three systems to enhance the overall process window and provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA stays within the process window. The process window defines the range of process parameters (e.g. dose, focus, overlay) within which a particular manufacturing process produces a defined result (e.g. a functional semiconductor device) - within which process parameters in a lithography process or patterning process may be allowed to vary.

[0067] The computer system CL can use (part of) the design layout to be patterned to predict which resolution enhancement techniques to use and perform computational lithography simulations and calculations to determine which mask layout and lithography apparatus settings achieve the maximum overall process window (in Figure 3 Optionally, the resolution enhancement technique is arranged to match the patterning possibilities of the lithographic apparatus LA. The computer system CL may also be used to detect where within the process window the lithographic apparatus LA is currently operating (e.g. using input from the metrology tool MT) to predict where the lithographic apparatus LA may be due to, for example, suboptimal processing (e.g., Figure 3 whether there may be a defect (depicted by an arrow pointing to "0" in the second scale SC2).

[0068] The metrology tool MT may provide input to the computer system CL to enable accurate simulations and predictions, and may provide feedback to the lithographic apparatus LA to identify possible drifts, e.g. in the calibration state of the lithographic apparatus LA (in Figure 3 SC3 is depicted by multiple arrows in the third scale SC3).

[0069] Figure 4 A schematic representation of a metrology apparatus 302 is depicted in which parameters of structures on a substrate may be measured using radiation in the wavelength range of 0.1 nanometers to 100 nanometers. Figure 4 The metrology device 302 shown in FIG. 3 is suitable for use in the soft X-ray or EUV domain.

[0070] Figure 4A schematic physical arrangement of a metrology device 302 including a spectroscopic scatterometer using EUV and / or SXR radiation at grazing incidence is illustrated by way of example only. Another form of inspection device may be provided in the form of an angle resolved scatterometer using radiation at normal or near normal incidence similar to conventional scatterometers operating at longer wavelengths.

[0071] The inspection apparatus 302 includes a radiation source 310 , an illumination system (or optical system) 312 , a substrate support 316 , a detection system (which may include radiation detectors 318 , 398 , and a metrology processing unit (MPU) 320 ).

[0072] In this example, source 310 comprises a generator of EUV or soft X-ray radiation based on high harmonic generation (HHG) technology. Such sources are available, for example, from KMLabs (http: / / www.KMLabs.com / ) in Boulder, Colorado, USA. The main components of the radiation source are a driving radiation source, such as a laser 330, and an interaction region comprising a medium, in this case in the form of an HHG gas chamber 332. A gas supply 334 supplies a suitable gas to the gas chamber, where the gas is optionally ionized by a power supply 336. The driving laser 300 may be, for example, a fiber-based laser with an optical amplifier, which generates infrared radiation pulses, which may have a duration of, for example, less than 1 ns (1 nanosecond) per pulse, with a pulse repetition rate of up to several megahertz as required. The wavelength of the infrared radiation may, for example, be in the region of 1 micrometer (1 micron). The laser pulses are transmitted as a first radiation beam 340 to the HHG gas cell 332, where a portion of the radiation is converted in the gas to a higher frequency than the first radiation as an emitted radiation beam 342 comprising coherent second radiation of the desired wavelength.

[0073] The second radiation may contain multiple wavelengths. If the radiation is monochromatic, then the measurement calculations (e.g., reconstruction) can be simplified, but it is easier to generate radiation of several wavelengths with HHG. In addition, irradiating the substrate with a wide range of radiation wavelengths allows a greater amount of information to be obtained from the reflected / diffracted radiation. The volume of gas in the gas chamber 332 defines the HHG space, although the space does not need to be completely closed and a gas flow can be used instead of a static volume. The gas can be, for example, an inert gas such as neon (Ne) or argon (Ar). N2, O2, He, Ar, Kr, and Xe gases can all be considered. These are all issues of design choice and may even be optional options within the same device. For example, when imaging structures of different materials, different wavelengths will provide different levels of contrast. For example, for the inspection of metal structures or silicon structures, different wavelengths for imaging features of (carbon-based) resists or for detecting contamination of these different materials can be selected. One or more filtering devices 344 can be provided. For example, filters such as thin films of aluminum (Al) or zirconium can be used to cut off fundamental IR radiation so that it no longer passes further into the inspection device. A grating (not shown) may be provided to select one or more specific harmonic wavelengths from those generated in the gas chamber. Given that SXR radiation is absorbed when propagating in air, part or all of the beam path may be contained within a vacuum environment. Various components of the radiation source 310 and illumination optics 312 may be adjusted to achieve different dosing "recipes" within the same device. For example, different wavelengths and / or polarizations may be selectable.

[0074] Depending on the material of the structure being inspected, different wavelengths may provide the desired level of penetration into the underlying layers. In order to address the smallest device features and defects in the smallest device features, short wavelengths are likely to be preferred. For example, one or more wavelengths in the range of 1-20 nanometers, or optionally in the range of 1-10 nanometers, or optionally in the range of 10-20 nanometers may be selected. Wavelengths less than 5 nanometers suffer from very low critical angles when reflecting off materials of typical interest in semiconductor manufacturing. Therefore, selecting wavelengths greater than 5 nanometers will provide stronger signals at higher angles of incidence. On the other hand, if the inspection task is to detect the presence of a certain material, such as detecting contamination, then wavelengths up to 50 nanometers may be useful.

[0075] The filtered beam 342 enters the inspection chamber 350 from the radiation source 310, in which the substrate W including the structure of interest (or the feature of the substrate) is held in the measurement position for inspection by the substrate support 316. The features of the substrate are marked as T and may include target and / or device or product structures. The atmosphere within the inspection chamber 350 is maintained in a near vacuum state by the vacuum pump 352 so that EUV radiation can pass through the atmosphere without excessive attenuation. The illumination system 312 has the function of focusing the radiation into a focused beam 356, and may include, for example, a two-dimensional curved mirror or a series of one-dimensional curved mirrors, as described in the above-mentioned US patent application US2017 / 0184981A1 (the contents of which are incorporated herein by reference in their entirety). Focusing is performed to obtain a circular or elliptical spot S, which, in some exemplary arrangements, may have a diameter of less than 10 microns when projected onto the features of the substrate. The substrate support 316 includes, for example, an XY translation stage and a rotation stage, by which any part of the substrate W can be brought to the focus of the beam in a desired orientation. Thus, a radiation spot S is formed on the feature of the substrate. Alternatively or additionally, the substrate support 316 includes, for example, a tilting stage, which can tilt the substrate W at a certain angle to control the incident angle of the focused beam on the feature of the substrate T.

[0076] Optionally, the illumination system 312 provides a reference beam of radiation to a reference detector 314, which can be configured to measure the spectrum and / or intensity of different wavelengths in the filtered light beam 342. The reference detector 314 can be configured to generate a signal 315, which is provided to the processor 310, and the filter can include information about the spectrum of the filtered light beam 342 and / or the intensity of different wavelengths in the filtered light beam.

[0077] The reflected and / or diffracted radiation 360 is captured by the radiation detector 318 and the spectrum is provided to the processor 320 for calculating the properties of the features of the substrate T. The illumination system 312 and the detection system 318 thus form an inspection device. The inspection device may include a soft X-ray and / or EUV spectroreflectometer of the type described in US2016282282A1, the contents of which are incorporated herein by reference in their entirety.

[0078] If the features of the substrate T have a certain periodicity, the radiation of the focused beam 356 may also be partially diffracted. The diffracted radiation 397 follows another path at a well-defined angle relative to the angle of incidence of the reflected radiation 360. Figure 4 In FIG. 3 , the plotted diffracted radiation 397 is plotted in a schematic manner, and the diffracted radiation 397 may follow many other paths than the plotted path. The inspection device 302 may also include a further detection system 398 that detects and / or images at least a portion of the diffracted radiation 397. Figure 4 In the embodiment of the inspection apparatus 302, a single further detection system 398 is shown, but embodiments of the inspection apparatus 302 may also include more than one further detection system 398 arranged at different positions to detect and / or image the diffracted radiation 397 in multiple diffraction directions. In other words, the (higher) diffraction orders of the focused radiation beam incident on the feature of the substrate T are detected and / or imaged by one or more further detection systems 398. The one or more detection systems 398 generate a signal 399 that is provided to the metrology processor 320. The signal 399 may include information of the diffracted light 397 and / or may include an image obtained from the diffracted light 397.

[0079] To assist in the alignment and focusing of the spot S with the desired product structure, the inspection device 302 may also provide auxiliary optics using auxiliary radiation under the control of the metrology processor 320. The metrology processor 320 may also communicate with a position controller 372 that operates a translation stage, a rotation stage, and / or a tilt stage. The processor 320 receives highly accurate feedback about the position and orientation of the substrate via sensors. The sensor 374 may include an interferometer, for example, which may give an accuracy in the picometer region. In operation of the inspection device 302, the spectral data 382 captured by the detection system 318 is transmitted to the metrology processing unit 320.

[0080] As described above, another form of inspection device uses soft X-rays and / or EUV radiation at normal incidence or near normal incidence, for example to perform diffraction-based asymmetry measurements. These two types of detection devices can be provided in a hybrid metrology system. The performance parameters to be measured can include overlay (OVL), critical dimension (CD), coherent diffraction imaging (CDI), and high resolution overlay (ARO) metrology. Soft X-rays and / or EUV radiation can, for example, have a wavelength of less than 100 nanometers, for example using radiation in the range of 5-30 nanometers, optionally in the range of 10-20 nanometers. The radiation can be narrowband or broadband. The radiation can have discrete peaks in a particular wavelength band, or can have a more continuous characteristic.

[0081] Similar to optical scatterometers used in today's production facilities, inspection device 302 can be used to measure structures in resist materials processed in a lithography cell (after development inspection or ADI), and / or to measure structures after they have been formed in harder materials (after etching inspection or AEI). For example, inspection device 302 can be used to inspect a substrate after it has been processed by a development device, an etching device, an annealing device, and / or other devices.

[0082] Figure 4The apparatus shown in 310 includes a driving radiation source 330, an interaction region at a HHG gas chamber 332, an optical system 312, and a substrate support 316. The interaction region receives a medium (e.g., a gas) and is positioned so that a driving radiation beam 340 emitted from the driving radiation source 330 interacts with the medium to produce emitted radiation 342 by HHG. The emitted radiation 342 includes radiation of multiple wavelengths, which may be in the SXR range. Each of the multiple wavelengths is emitted from the medium at an emission divergence angle that depends on the wavelength. As used herein, the term emission divergence angle includes the divergence angle of the emitted radiation. The emission divergence angle may be due to the curvature of the wavefront of the radiation emitted at the downstream end of the medium (e.g., a gas medium).

[0083] Figure 5 Shows Figure 4 3. As shown, the driving radiation source 330 emits a driving radiation beam 340. The driving radiation beam 340 interacts with a medium 333, which may be located at a HHG unit 332. The resulting emitted radiation beam 342 includes a plurality of wavelengths, each wavelength being Figure 5 The radiation of multiple wavelengths in the emitted radiation beam 342 has an emission divergence angle that depends on the wavelength, as shown in FIG. Figure 5 The emitted radiation beam 342 propagates through the optical system 312, which is configured to direct the emitted radiation beam toward the substrate W ( Figure 5 The optical system 312 may include multiple optical elements, such as lenses and mirrors, but for simplicity, Figure 5 Due to the different emission divergence angles, the optical system 312 focuses the emitted radiation beam 342 at multiple focal planes 500. This Figure 5 500, which shows the intensity versus wavelength at each focal plane 1-4. As can be seen, the arrangement of the features T of the substrate W relative to the focal plane 500 controls the intensity of each wavelength of light incident on the features T. In addition, the arrangement of the features T of the substrate W relative to the focal plane 500 controls the diameter (or other cross-sectional dimension) of the radiation beam 342 emitted at the substrate W. When the emitted radiation beam 342 has a small diameter, its intensity on the optical axis is high, while when the diameter is large, its axial intensity is low.

[0084] The driving radiation source 330 may be configured to control the emission divergence angle of the emitted radiation beam 342. For example, in some arrangements, the driving radiation source 330 is configured to control the focal point of the driving radiation beam 340 relative to the position of the medium 333. This in turn controls the emission divergence angle of one or more wavelengths of the emitted radiation beam 342. In certain cases, controlling the focal point of the driving radiation beam 340 may change the relative emission divergence angle between the wavelengths of the emitted radiation beam 342, which in turn may control the relative axial position of the focal plane 500. In other arrangements, the driving radiation source 330 may be configured to control one or more of the intensity of the driving radiation beam 340; the waist size of the driving radiation beam 340; and the wavefront or lateral intensity distribution of the driving radiation beam 340, for example, by means of a spatial light modulator (SLM) or other customized optical element. Any of these parameters may change the emission divergence angle of the emitted radiation beam 342, and thus change the relative position of the focus of the emitted radiation beam 342. In other arrangements, the type and composition of the medium may be controlled to control the emission divergence angle. For example, for gas media, the gas type and gas pressure can be controlled.

[0085] The position of the medium 333 relative to the focus of the drive radiation beam 340 also controls the emission divergence angle of one or more wavelengths of the emitted radiation beam 342. In certain cases, controlling the position of the medium relative to the focus of the drive radiation beam 340 controls the relative emission divergence angle between the wavelengths of the emitted radiation beam 342, which in turn can control the relative axial position of the focal plane 500. Thus, in some arrangements, the interaction region can include one or more nozzles configured to direct the medium to a particular axial position. In other arrangements, the axial position of the gas chamber 332 can be controlled.

[0086] In some arrangements, the optical system 312 may be configured to control the focusing of the wavelength of the emitted radiation beam 342. In certain cases, the optical system 312 may control the axial position of the focal plane 500 while keeping their relative positions substantially the same.

[0087] In some arrangements, the substrate support 316 is configured to control the axial position of the substrate W, and thereby the axial position relative to each focal plane 500 .

[0088] In view of the above, one or more of the drive radiation source 330, the medium 333 at the interaction region, the optical system 312, and the substrate support 316 may be configured to control the relative position of at least one of the focal planes with respect to the substrate.

[0089] The above system can be used in a variety of ways to estimate parameters of a feature T, which in turn can be used to estimate parameters of a lithography process. Some exemplary uses are described below, although other uses will be apparent to those skilled in the art.

[0090] Optical metrology, including SXR metrology, provides fast, non-destructive measurements at the expense of a limited amount of measured information. Depending on the application, the measurements may not provide sufficient parameter sensitivity, leading to a problem known as correlation. To clarify what this means, consider, for example, a first semiconductor target with two parameters (e.g., line width L1 and layer thickness T1) that happens to result in almost the same pattern in the diffracted radiation as a second target with line width L2 and layer thickness T2. In this case, one cannot easily distinguish the first and second targets from the measured diffraction patterns. In this case, the line width and layer thickness are considered to be highly correlated, and the parameter sensitivity of the measurement is poor. To alleviate this problem and elicit more information, increasing the diversity of the measurements is a common strategy. Diversity refers to different measurement modes that can provide complementary information about the target, such as measurements with different illumination angles or wavelengths. The methods and devices disclosed herein provide additional measurement modes to increase the sensitivity of the measurements.

[0091] As described above, in an optical metrology tool, when a target or other feature on a substrate (e.g., comprising a grating) is illuminated by a radiation beam, light will be diffracted and / or reflected off the target. When two gratings separated by a stack of other layers have an offset from each other, a difference may occur between the +1st and -1st order diffracted light. This difference can be measured (and calibrated) to determine the overlay error δ between the two gratings. Figure 6 This is described in a simplified way in Figure 6 An emitted radiation beam 342 is shown, which may include radiation of multiple wavelengths within the SXR range and may be emitted by a HHG, incident on a feature T of a substrate W. One or more radiation detectors are configured to receive radiation diffracted and / or reflected from the feature T. Figure 6 In the exemplary arrangement shown, the first radiation detector 318a and the second radiation detector 318b are configured to receive +1 order diffracted radiation 600a and -1 order diffracted radiation 600b, although higher orders may also be used. The +1 and -1 order diffracted radiation 600a, 600b include multiple wavelengths, which are shown by separate arrows and diffract at different angles based on wavelength.

[0092] Thus, the difference in the diffracted radiation 600a, 600b received by the radiation detectors 318a, 318b depends on the wavelength of the emitted radiation incident on the feature T due to the interference of the light in the stack between the gratings of the feature T. This dependence can be plotted in a so-called rocking curve, which is plotted at Figure 7The overlay error is zero (solid line) and the overlay error is 1 a.u. (dashed line) are shown in FIG. 1 . The swing curve also depends on the composition of the intermediate layers in the stack. It is desirable to measure a parameter (e.g., coverage) of characteristic T at the wavelength and / or intensity of the emitted radiation (the radiation has a high sensitivity to errors in this parameter). Figure 7 In the example of overlay, this sensitivity is shown at the wavelength with the largest difference between the solid and dashed lines of the rocking curve.Alternatively, to increase the sensitivity, the emitted radiation may be used to measure across the wavelength spectrum.

[0093] An important condition is that the different wavelengths can be resolved sufficiently to resolve the oscillations in the rocking curve. When the emitted radiation beam 342 is diffracted from the feature T, each wavelength that is diffracted will have an emission divergence angle that is related to the numerical aperture of the emitted radiation beam 342. This emission divergence angle may result in Figure 6 , and a particular pixel of the radiation detector 342 may receive diffracted radiation of multiple wavelengths. This can make solving the rocking curve more difficult. In an exemplary arrangement, one or more of the drive radiation source 330, the medium 333 at the interaction region, the optical system 312, and the substrate support 316 can be configured to control the axial position of the substrate relative to the focal plane 500 to select each of the multiple wavelengths of the emitted radiation beam 342 to be focused on the feature T in turn so that the diffracted radiation 600a, 600b at these wavelengths can be resolved. This can be used to determine the rocking curve.

[0094] In an exemplary arrangement, one or more of the drive radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured to control the axial position of the substrate relative to the focal plane 500 based on the intensity of the diffracted radiation 600a, 600b. The intensity of the diffracted radiation may be predicted based on models and / or measurements made using different substrates.

[0095] In one exemplary arrangement, the radiation detectors 318a, 318b receive +1 and -1 order diffracted radiation 600a, 600b. The difference between the +1 and -1 order diffracted radiation 600a, 600b is wavelength dependent, e.g. Figure 7 One or more of the drive radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured to focus one or more wavelengths at the substrate W based on the difference in the intensity of the +1 and -1 order diffracted radiation. That is, a wavelength having a desired sensitivity to the parameter to be measured may be selected by the axial positioning of the substrate support 316 relative to the focal plane. The wavelength may be selected based on a predicted wavelength from, for example, a previously generated rocking curve.

[0096] In other arrangements, a first rocking curve may be plotted based on a first difference between the +1st and -1st order intensities of diffracted radiation for a feature T with no error in a given parameter. For a feature with a known error in a given parameter, a further rocking curve may be plotted based on a second difference between the +1st and -1st order diffracted radiation intensities. One or more of the drive radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured to focus one or more wavelengths at the substrate W based on a difference between the first intensity difference and the second intensity difference. This may be visualized as a difference between the first and second rocking curves (e.g. Figure 7 If the difference between the first intensity difference and the second intensity difference is greater than a threshold, this may indicate a sensitivity to errors in the parameter / . The axial position of the substrate W relative to the focal plane 500 may be selected based on this sensitivity.

[0097] Optionally, the feature T that may be a metrology target includes some periodic structures (hereinafter referred to as "lines"). Since there are typically a very large number of lines per target, some computational models can simplify the calculations by assuming an infinite number of lines without introducing significant errors. However, since the targets envisioned for SXR metrology are significantly smaller, they may include a smaller number of lines, and a relatively small number of lines may have an effect on the measured diffracted radiation. This effect may be referred to as the "finite line effect" and may be determined by changing the spot size of the radiation 342 emitted at the substrate W, thereby changing the number of illuminated lines in a controlled and wavelength-dependent manner.

[0098] Thus, one or more of the driving radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured to focus a first wavelength of emitted radiation 342 to a first spot size at a feature T of the substrate W. As a result of the first wavelength of emitted radiation 342 being incident on the feature T, the radiation detectors 318a, 318b receive diffracted radiation 600a, 600b. One or more of the driving radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured to focus a second wavelength of emitted radiation 342 to a second spot size at the substrate. As a result of the second wavelength of emitted radiation 342 being incident on the feature T, the radiation detectors 318a, 318b receive diffracted radiation 600a, 600b.

[0099] In addition, the apparatus described herein may include a processor configured to compare the intensity of diffracted radiation caused by diffraction of a first wavelength with the intensity of diffracted radiation caused by diffraction of a second wavelength. The processor may then determine a model of the intensity of the diffracted radiation, the intensity of the diffracted radiation being a function of the spot size and / or wavelength. The model may indicate a finite line effect.

[0100] In other arrangements, one or more of the drive radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured to focus the wavelength of the emitted radiation 342 to a first spot size at a feature T of the substrate W. The radiation detectors 318a, 318b receive diffracted radiation 600a, 600b as a result of the wavelength of the emitted radiation 342 being incident on the feature T at the first spot size. One or more of the drive radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured to focus the same wavelength of the emitted radiation 342 to a second spot size at the substrate. The radiation detectors 318a, 318b receive diffracted radiation 600a, 600b as a result of the wavelength of the emitted radiation 342 being incident on the feature T at the second spot size.

[0101] In addition, the apparatus described herein may include a processor configured to compare the intensity of the diffracted radiation caused by the wavelength of the first spot size with the intensity of the diffracted radiation caused by the wavelength of the second spot size. The processor may then determine a model of the intensity of the diffracted radiation as a function of the spot size and / or wavelength.

[0102] By changing the spot size of a certain wavelength, the intensity of that wavelength will also change (as described above). This enables the determination of non-linear effects in the intensity of diffracted radiation at specific wavelengths, which are suspected to be caused by high SXR intensity. In other arrangements, one or more of the drive radiation source 330, the interaction region 333, the optical system 312 and the substrate support 316 can be configured to maintain the spot size of a specific wavelength greater than a threshold to prevent the intensity of the emitted radiation beam 342 from becoming high enough to cause non-linear and / or destructive effects, such as in the case of sensitive resist on top of a feature. Thus, the determined model can indicate non-linear effects on the intensity of diffracted and / or reflected radiation with a spot size.

[0103] In some arrangements, the determined (one or more) models may be used to determine parameters of the lithography patterning process in a manner that will be understood by those skilled in the art. Specifically, the processor may be configured to predict the intensity of one or more pixels of an image of radiation diffracted from feature T based on the determined model. The emitted radiation beam 342 may then be controlled to be incident on feature T, and the radiation detectors 318a, 318b may then receive the diffracted radiation 600a, 600b to determine a measured diffraction image. The processor may then compare the predicted intensity with the measured intensity of one or more corresponding pixels of the diffraction image of the radiation diffracted from the feature. The processor may then determine one or more parameters of the lithography patterning process based on the comparison.

[0104] Any (expected or unexpected) local variations, i.e. variations within the feature T, can be determined by applying a range of different spot sizes to the target. For example, corner effects are illuminated by a relatively large spot but not by a relatively small spot. For color focusing (using multiple focal planes 500), this can be determined in a wavelength-dependent manner.

[0105] In certain arrangements, one or more of the driving radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured such that a first wavelength of the emitted radiation beam 342 forms a spot size at a first depth of the substrate W and another wavelength forms another spot size at a second depth of the substrate W. The first depth may be the surface of the substrate W. The other wavelength may be selected based on its sensitivity to various aspects of the feature at the second depth. Specifically, the first wavelength may be selected to have a sensitivity to the aspect at the first depth that is above a threshold, and the other wavelength may be selected to have a sensitivity to the aspect at the second depth that is above another threshold.

[0106] In some arrangements, the feature T may be a metrology target. One or more of the drive radiation source 330, the interaction region 333, the optical system 312, and the substrate support 316 may be configured to control the axial position of the substrate W relative to the plurality of focal planes 500 so that a first wavelength of the emitted radiation beam 342 forms a spot size at the substrate that underfills the target, and a second wavelength of the emitted radiation beam 342 forms a spot size that overfills the target. The first wavelength may be selected because it has a sensitivity above a threshold to the target feature. The second wavelength may be selected because it has a sensitivity below a threshold to a feature of the substrate W outside the target region.

[0107] The computer program may be configured to provide any part of the above method. The computer program may be provided on a computer readable medium. The computer program may be a computer program product. The product may include a non-transitory computer usable storage medium. The computer program product may have a computer readable program code contained in a medium configured to perform the method. The computer program product may be configured to cause at least one processor to perform some or all of the method.

[0108] Various methods and apparatus are described herein with reference to apparatus (systems and / or devices) and / or computer program products. Computer program instructions may be provided to a processor circuit of a general-purpose computer circuit, a special-purpose computer circuit, and / or other programmable data processing circuit to produce a machine, such that the instructions executed via the processor of the computer and / or other programmable data processing device transform and control transistors, values ​​stored in memory locations, and other hardware components within such circuits to implement the functions / actions specified herein, and thereby create an apparatus (function) and / or structure for implementing the specified functions / actions.

[0109] Computer program instructions may also be stored in a computer-readable medium, which may direct a computer or other programmable data processing device to operate in a specific manner so that the instructions stored in the computer-readable medium produce an article of manufacture including instructions for implementing the specified functions / actions.

[0110] Tangible, non-transitory computer-readable media may include electronic, magnetic, optical, electromagnetic or semiconductor data storage systems, apparatuses or devices. More specific examples of computer-readable media include the following: portable computer diskettes, random access memory (RAM) circuits, read-only memory (ROM) circuits, erasable programmable read-only memory (EPROM or flash memory) circuits, portable compact disk read-only memory (CD-ROM) and portable digital video disk read-only memory (DVD / Blu-ray).

[0111] Computer program instructions may also be loaded onto a computer and / or other programmable data processing device to cause a series of operational steps to be performed on the computer and / or other programmable device, thereby producing a computer-implemented process, such that the instructions executed on the computer or other programmable device provide steps for implementing specified functions / actions.

[0112] Therefore, the present invention may be implemented in hardware and / or software (including firmware, resident software, microcode, etc.) running on a processor, which may be collectively referred to as a "circuit device," "module" or variations thereof.

[0113] Further embodiments are disclosed in the subsequently numbered items:

[0114] 1. An apparatus for directing a radiation beam emitted as a result of high harmonic generation (HHG) onto a substrate, the apparatus comprising:

[0115] driving the radiation source;

[0116] an interaction region configured to receive a medium and positioned such that a drive radiation beam from the drive radiation source interacts with the medium during use to produce an emitted radiation beam by HHG, wherein the emitted radiation beam comprises a plurality of wavelengths, and wherein an emission divergence angle of the emitted radiation is wavelength dependent;

[0117] an optical system located downstream of the interaction region and configured to focus the emitted radiation beam, wherein the plurality of wavelengths of the emitted radiation beam are focused at a plurality of focal planes according to associated emission divergence angles; and

[0118] a substrate support for holding the substrate at one of a plurality of axial positions relative to the plurality of focal planes,

[0119] Therein, one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control a relative position of at least one of the focal planes with respect to the substrate.

[0120] 2. The device according to claim 1, wherein the interaction area includes a nozzle for directing the medium to the interaction area or a gas chamber for retaining the medium, and wherein the nozzle or the gas chamber is configured to control the axial position of the medium.

[0121] 3. An apparatus according to claim 1 or 2, wherein the drive radiation source is configured to control the axial position of the focus of the drive radiation beam.

[0122] 4. An apparatus according to any preceding claim, wherein the optical system is configured to control the axial position of one or more of the focal planes.

[0123] 5. Apparatus according to any preceding claim, wherein the substrate support is configured to control the axial position of the substrate held thereon.

[0124] 6. An apparatus according to any preceding claim, wherein when the emitted radiation beam is diffracted and / or reflected from a feature on the substrate, the intensity of the diffracted and / or reflected radiation depends on the wavelength of the emitted radiation beam,

[0125] And wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control the relative position of at least one of the focal planes relative to the substrate based on the intensity of the diffracted and / or reflected radiation.

[0126] 7. The device according to claim 6, wherein the diffracted and / or reflected radiation comprises positive and negative orders, and the intensity difference between the positive and negative orders depends on the wavelength of the emitted radiation beam,

[0127] And wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control the relative position of at least one of the focal planes relative to the substrate based on the intensity difference between positive and negative orders.

[0128] 8. The apparatus of claim 7, wherein a first intensity difference is based on the feature having no errors in one or more parameters, and wherein a second intensity difference is based on the feature having a specific error in the one or more parameters,

[0129] And wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control the relative position of at least one of the focal planes relative to the substrate based on the difference between the first intensity difference and the second intensity difference.

[0130] 9. An apparatus according to any one of claims 6 to 8, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to position a selected focal plane to substantially coincide with the plane of the substrate, wherein the selected focal plane is determined based on the intensity of the diffracted and / or reflected radiation.

[0131] 10. The apparatus of claim 9, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configurable to position a plurality of selected focal planes substantially coincident with the substrate.

[0132] 11. The apparatus according to any one of claims 6 to 10, further comprising a first radiation detector configured to detect the positive orders of diffracted and / or reflected radiation and a second radiation detector configured to detect the negative orders of diffracted and / or reflected radiation.

[0133] 12. The apparatus of any preceding claim, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that a first wavelength of the emitted radiation beam forms a first spot size at the substrate and a second wavelength of the emitted radiation beam forms a second spot size at the substrate that is larger than the first spot size,

[0134] The apparatus comprises at least one radiation detector configured to receive first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the first wavelength and second diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the second wavelength; and

[0135] A processor configured to execute computer program code to perform the following method:

[0136] comparing the intensity of the first diffracted and / or reflected radiation to the intensity of the second diffracted and / or reflected radiation; and

[0137] A model that determines the intensity of diffracted and / or reflected radiation as a function of spot size.

[0138] 13. The apparatus of claim 12, wherein the features of the substrate comprise a plurality of lines fabricated on the substrate, and wherein the model is indicative of the effect of the lines on the diffracted and / or reflected radiation.

[0139] 14. An apparatus according to any preceding claim, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that at least one wavelength of the emitted radiation beam forms a first spot size at the substrate and subsequently forms a second spot size at the substrate that is different from the first spot size,

[0140] The apparatus comprises at least one radiation detector configured to receive first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at at least one wavelength having the first spot size and second diffracted and / or reflected radiation diffracted and / or reflected from the feature of the substrate at the at least one wavelength having the second spot size; and

[0141] A processor configured to execute computer program code to perform the following method:

[0142] determining an intensity of radiation emitted at the first spot size and an intensity of radiation emitted at the second spot size;

[0143] determining an intensity of said first diffracted and / or reflected radiation and an intensity of said second diffracted and / or reflected radiation; and

[0144] Based on the determined intensity, a model of the intensity of the diffracted and / or reflected radiation as a function of the spot size is determined.

[0145] 15. The apparatus of claim 15, wherein the determined model is indicative of a non-linear effect on the intensity of diffracted and / or reflected radiation having a spot size.

[0146] 16. The apparatus according to any one of claims 12 to 14, wherein the processor is further configured to:

[0147] predicting, based on the determined model, an intensity of one or more pixels of an image of radiation diffracted and / or reflected from the feature;

[0148] comparing the predicted intensity to a measured intensity of one or more corresponding pixels of an image of radiation diffracted and / or reflected from the feature; and

[0149] One or more parameters of a lithography patterning process are determined based on the comparison.

[0150] 17. An apparatus according to any preceding claim, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured so that at least one wavelength of the emitted radiation beam is focused on the substrate to form a spot size with a diameter greater than a threshold.

[0151] 18. An apparatus according to any preceding claim, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that a first wavelength of the emitted radiation beam forms a first spot size at a first depth of the substrate and a second wavelength of the emitted radiation forms a second spot size at a second depth of the substrate.

[0152] 19. The apparatus of claim 18, wherein the first wavelength is selected based on a sensitivity of the first wavelength to an aspect of a feature of the substrate at the first depth and / or the second wavelength is selected based on a sensitivity of the second wavelength to an aspect of a feature of the substrate at the second depth.

[0153] 20. An apparatus as claimed in any preceding claim, wherein the feature of the substrate comprises a target, and wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that a first wavelength of the emitted radiation forms a spot size that underfills the target and a second wavelength of the emitted radiation forms a spot size that overfills the target.

[0154] 21. An apparatus according to claim 20, wherein the first wavelength and / or the second wavelength are selected based on their sensitivity to aspects of the target and / or aspects of further features of the substrate outside the region of the target.

[0155] 22. An apparatus as claimed in any preceding claim, wherein the emitted radiation has a wavelength in the range 0.1 nanometres to 100 nanometres.

[0156] 23. A metering device comprising a device according to any preceding claim.

[0157] 24. A method of directing radiation toward a feature of a substrate, the method comprising:

[0158] directing a drive radiation beam from a drive radiation source to an interaction region, the interaction region comprising a medium configured to interact with the drive radiation to produce emitted radiation by HHG, wherein the emitted radiation beam comprises a plurality of wavelengths, and wherein an emission divergence angle of the emitted radiation is wavelength dependent;

[0159] causing the emitted radiation to propagate through an optical system downstream of the interaction region;

[0160] focusing the emitted radiation beam onto a substrate held by a substrate support, wherein the plurality of wavelengths of the emitted radiation beam are focused at a plurality of focal planes according to associated emission divergence angles; and

[0161] Controlling one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control a relative position of at least one of the focal planes with respect to the substrate.

[0162] 25. The method according to claim 24, further comprising:

[0163] configuring one or more of the drive radiation source, the interaction region, the optical system, and the substrate support such that a first wavelength of the emitted radiation beam forms a first spot size at the substrate and a second wavelength of the emitted radiation beam forms a second spot size at the substrate that is larger than the first spot size;

[0164] receiving, by at least one radiation detector, first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the first wavelength and second diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the second wavelength;

[0165] comparing the intensity of the first diffracted and / or reflected radiation to the intensity of the second diffracted and / or reflected radiation; and

[0166] A model that determines the intensity of diffracted and / or reflected radiation as a function of spot size.

[0167] 26. The method according to claim 24 or 25, further comprising:

[0168] configuring one or more of the drive radiation source, the interaction region, the optical system, and the substrate support such that at least one wavelength of the emitted radiation beam forms a first spot size at the substrate and subsequently forms a second spot size at the substrate that is different from the first spot size,

[0169] receiving, by at least one radiation detector, first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the at least one wavelength having the first spot size and second diffracted and / or reflected radiation diffracted and / or reflected from the feature of the substrate at the at least one wavelength having the second spot size;

[0170] determining an intensity of radiation emitted at the first spot size and an intensity of radiation emitted at the second spot size;

[0171] determining an intensity of said first diffracted and / or reflected radiation and an intensity of said second diffracted and / or reflected radiation; and

[0172] Based on the determined intensity, a model of the intensity of the diffracted and / or reflected radiation as a function of the spot size is determined.

[0173] 27. The method according to any one of claims 24 to 26 further comprises configuring one or more of the drive radiation source, the interaction region, the optical system and the substrate support so that at least one wavelength of the emitted radiation beam is focused at the substrate to form a spot size having a diameter greater than a threshold value.

[0174] 28. The method of any one of claims 24 to 27, further comprising configuring one or more of the drive radiation source, the interaction region, the optical system, and the substrate support so that a first wavelength of the emitted radiation beam forms a first spot size at a first depth of the substrate, and a second wavelength of the emitted radiation forms a second spot size at a second depth of the substrate.

[0175] 29. A computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to control an apparatus to perform a method according to any one of claims 24 to 28.

[0176] 30. A carrier embodying the computer program according to claim 29, wherein the carrier is one of an electronic signal, an optical signal, a radio signal and a non-transitory computer-readable storage medium.

[0177] It should also be noted that in some alternative implementations, the functions / actions indicated may occur in a non-indicated order. In addition, the functionality of a step may be separated into multiple steps and / or the functionality of two or more steps may be at least partially integrated. Finally, other steps may be added / inserted between the blocks shown.

[0178] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0179] Although embodiments of the invention may be specifically referenced herein in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatuses. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other patterning device). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0180] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0181] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in a manner other than as described. The above description is intended to be illustrative, not restrictive. Therefore, it will be apparent to those skilled in the art that the present invention may be modified as described without departing from the scope of the appended claims.

Claims

1. An apparatus for directing a radiation beam emitted as a result of high harmonic generation (HHG) onto a substrate, the apparatus comprising: driving the radiation source; an interaction region configured to receive a medium and positioned such that a drive radiation beam from the drive radiation source interacts with the medium during use to produce an emitted radiation beam by HHG, wherein the emitted radiation beam comprises a plurality of wavelengths, and wherein an emission divergence angle of the emitted radiation is wavelength dependent; an optical system located downstream of the interaction region and configured to focus the emitted radiation beam, wherein the plurality of wavelengths of the emitted radiation beam are focused at a plurality of focal planes according to associated emission divergence angles; and a substrate support for holding the substrate at one of a plurality of axial positions relative to the plurality of focal planes, One or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control the relative positions of the multiple focal planes with respect to the substrate so that the emitted radiation beam illuminates the substrate at the multiple focal planes.

2. The device according to claim 1, wherein at least one of the following: - The interaction area comprises: a nozzle for directing the medium to the interaction region; or an air chamber for holding the medium, and wherein the nozzle or the air chamber is configured to control the axial position of the medium, - the driving radiation source is configured for controlling the axial position of the focus of the driving radiation beam, - the optical system is configured to control the axial position of one or more of the focal planes, and - the substrate support is configured to control an axial position of the substrate held on the substrate support.

3. The apparatus of claim 1 , wherein when the emitted radiation beam is diffracted and / or reflected from a feature on the substrate, the intensity of the diffracted and / or reflected radiation depends on the wavelength of the emitted radiation beam, And wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to: control the relative position of at least one of the focal planes with respect to the substrate based on the intensity of the diffracted and / or reflected radiation.

4. The device according to claim 3, wherein the diffracted and / or reflected radiation comprises positive and negative orders, and the intensity difference between the positive and negative orders depends on the wavelength of the emitted radiation beam, And wherein said one or more of said drive radiation source, said interaction region, said optical system and said substrate support can be configured to control said relative position of at least one of said focal planes with respect to said substrate based on said intensity difference between positive and negative orders.

5. The apparatus of claim 4, wherein a first intensity difference is based on the feature having no errors in one or more parameters, and wherein a second intensity difference is based on the feature having a specific error in the one or more parameters, And wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to: control the relative position of at least one of the focal planes relative to the substrate based on the difference between the first intensity difference and the second intensity difference.

6. An apparatus according to any one of claims 3 to 5, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to: position a selected focal plane to substantially coincide with the plane of the substrate, wherein the selected focal plane is determined based on the intensity of the diffracted and / or reflected radiation, or in, The one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to position a plurality of selected focal planes substantially coincident with the substrate.

7. The apparatus according to claim 4, further comprising: a first radiation detector configured to detect said positive orders of diffracted and / or reflected radiation; and a second radiation detector configured to detect said negative orders of diffracted and / or reflected radiation.

8. The apparatus of any one of claims 1 to 5, wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that: a first wavelength of the emitted radiation beam forms a first spot size at the substrate, and a second wavelength of the emitted radiation beam forms a second spot size at the substrate that is larger than the first spot size, The apparatus comprises at least one radiation detector configured to receive: first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the first wavelength, and second diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the second wavelength; as well as A processor configured to execute computer program code to perform the following method: comparing the intensity of the first diffracted and / or reflected radiation with the intensity of the second diffracted and / or reflected radiation; as well as A model that determines the intensity of diffracted and / or reflected radiation as a function of spot size.

9. The apparatus of any one of claims 1 to 5, wherein the one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that: at least one wavelength of the emitted radiation beam forms a first spot size at the substrate and subsequently forms a second spot size at the substrate that is different from the first spot size, The apparatus comprises at least one radiation detector configured to receive: first diffracted and / or reflected radiation diffracted and / or reflected from a feature of the substrate at the at least one wavelength having the first spot size, and second diffracted and / or reflected radiation diffracted and / or reflected from the feature of the substrate at the at least one wavelength having the second spot size; as well as A processor configured to execute computer program code to perform the following method: determining an intensity of the emitted radiation of the first spot size and an intensity of the emitted radiation of the second spot size; determining an intensity of said first diffracted and / or reflected radiation and an intensity of said second diffracted and / or reflected radiation; as well as Based on the determined intensity, a model of the intensity of the diffracted and / or reflected radiation as a function of the spot size is determined.

10. The apparatus of claim 8, wherein the processor is further configured to: predicting, based on the determined model, an intensity of one or more pixels of an image of radiation diffracted and / or reflected from the feature; comparing the predicted intensity to a measured intensity of one or more corresponding pixels of an image of radiation diffracted and / or reflected from the feature; as well as One or more parameters of a lithography patterning process are determined based on the comparison.

11. The device according to any one of claims 1 to 5, wherein at least one of the following: - one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that: at least one wavelength of the emitted radiation beam is focused on the substrate to form a spot size having a diameter greater than a threshold value, - one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that: a first wavelength of the emitted radiation beam forms a first spot size at a first depth of the substrate, and a second wavelength of the emitted radiation forms a second spot size at a second depth of the substrate, and wherein, -The feature of the substrate includes a target, and wherein one or more of the drive radiation source, the interaction region, the optical system and the substrate support are configured such that: a first wavelength of the emitted radiation forms a spot size that does not fill the target, and a second wavelength of the emitted radiation forms a spot size that overfills the target.

12. The device according to any one of claims 1 to 5, wherein the emitted radiation has a wavelength in the range of 0.1 nanometers to 100 nanometers.

13. A metering device comprising a device according to any preceding claim.

14. A method of directing radiation toward a feature of a substrate, the method comprising: directing a drive radiation beam from a drive radiation source to an interaction region, the interaction region comprising a medium configured to interact with the drive radiation to produce emitted radiation by HHG, wherein the emitted radiation beam comprises a plurality of wavelengths, and wherein an emission divergence angle of the emitted radiation is wavelength dependent; causing the emitted radiation to propagate through an optical system downstream of the interaction region; focusing the emitted radiation beam onto a substrate held by a substrate support, wherein the plurality of wavelengths of the emitted radiation beam are focused at a plurality of focal planes according to associated emission divergence angles; as well as Controlling one or more of the drive radiation source, the interaction region, the optical system and the substrate support can be configured to control the relative positions of the multiple focal planes with respect to the substrate so that the emitted radiation beam illuminates the substrate at the multiple focal planes.

15. A computer program product comprising instructions which, when executed on at least one processor, cause the at least one processor to control an apparatus to perform the method according to claim 14.

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