Method for spectral configuration of a measurement radiation of a measurement tool and

Abstract

There is disclosed a method of spectrally configuring a measurement illumination of a metrology tool, the method comprising: projecting a measurement radiation using the projection optical system to obtain a projected measurement radiation; measuring, at a detector, a signal amplitude metric of the projected measurement radiation; determining a spectral shape of the projected measurement radiation from the signal amplitude metric; and spectrally configuring the measurement illumination prior to projecting the optical system to adjust the spectral shape to match the desired spectral shape.

Description

Method and associated apparatus for spectral configuration of measurement illumination for measuring instruments Cross-references to related applications

[0001] This application claims priority to EP application 23199669.5, filed on September 26, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to a method for manufacturing equipment using photolithography. Background Technology

[0003] A photolithography apparatus is a machine that applies a desired pattern onto a substrate (typically onto a target portion of the substrate). Photolithography apparatuses can be used, for example, in the fabrication of integrated circuits (ICs). In this case, a patterning apparatus, alternatively referred to as a mask or photomask, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred to a target portion (e.g., a portion comprising one or more dies) on a substrate (e.g., a silicon wafer). Pattern transfer is typically achieved via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions patterned sequentially. During the photolithography process, it is often desirable to measure the created structure, for example, for process control and verification. Various tools are known for performing such measurements, including scanning electron microscopes commonly used to measure critical dimensions (CDs), and specialized tools for measuring overlay, a measure of the alignment accuracy of two layers in the apparatus. Overlay can be described according to the degree of misalignment between two layers; for example, a reference to a measured 1 nm overlay can describe a misalignment of 1 nm between two layers.

[0004] Recently, various types of scatterers have been developed for use in photolithography. These devices guide a radiation beam onto a target and measure one or more characteristics of the scattered radiation, such as intensity at a single reflection angle based on the wavelength; intensity at one or more wavelengths based on the reflection angle; or polarization based on the reflection angle, to obtain a "spectrum" from which the target's characteristics of interest can be determined. The determination of the characteristics of interest can be performed using various techniques: for example, reconstructing the target using iterative methods such as rigorous coupled-wave analysis or the finite element method; library searching; and principal component analysis.

[0005] Conventional scattering instruments use relatively large (e.g., 40 μm by 40 μm) gratings, and the measurement beam generates a spot smaller than the grating (i.e., the grating is underfilled). This simplifies the mathematical reconstruction of the target, as it can be considered infinite. However, to reduce the size of the target, for example, to 10 μm by 10 μm or smaller, so that they can be positioned between product features rather than in scribe lines, measurements have been proposed in which the grating is made smaller than the measurement spot (i.e., the grating is overfilled). Typically, such targets are measured using dark-field scattering measurements, in which zero-order diffraction (corresponding to specular reflection) is blocked, and only higher orders are processed. Examples of dark-field measurements can be found in international patent applications WO2009 / 078708 and WO 2009 / 106279, which are incorporated herein by reference in their entirety. Further developments in the technology have been described in patent publications US20110027704A, US20110043791A, and US20120242940A. The contents of all these applications are also incorporated herein by reference. Diffraction-based overlay using dark-field detection with diffraction order enables overlay measurements on smaller targets. These targets can be smaller than the illumination spot and can be surrounded by the product structure on the wafer. The target can include multiple gratings, which can be measured in a single image.

[0006] Different measurement tools typically employ projection optics systems with varying spectral transmission characteristics, resulting in different spectra at the wafer level for the same illumination settings. Illumination settings can be configured, for example, using a color selection module or an illumination configuration module, to spectrally configure the broadband source illumination for the measurement tool.

[0007] Due to defects in the structure being measured (e.g., the target, alignment mark, or product structure), wavelength-dependent variations may exist in the measurement signal from the target. To address this issue, each structure can be measured (e.g., once or multiple times) with spectrally configured radiation. However, any unknown inter-tool spectral differences in the measurement irradiation will lead to unknown inter-tool measurement discrepancies.

[0008] The aim is to mitigate the impact of the different spectral transmission characteristics of various measurement tools on the measurements performed using those tools. Summary of the Invention

[0009] In a first aspect of the invention, a method for spectrally configuring a measurement illumination of a measurement tool is provided, the method comprising: projecting measurement radiation using the projection optics system to obtain projected measurement radiation; measuring a signal amplitude metric of the projected measurement radiation at a detector; determining a spectral shape of the projected measurement radiation based on the signal amplitude metric; and spectrally configuring the measurement illumination prior to the projection optics system to adjust the spectral shape to match a desired spectral shape.

[0010] Another aspect of the invention includes at least one measuring device operable to perform the method according to the first aspect.

[0011] Other features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. Note that the invention is not limited to the specific embodiments described herein. Such embodiments are presented for illustrative purposes only. Other embodiments will be apparent to those skilled in the art based on the teachings contained herein. Attached Figure Description

[0012] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: FIG1 depicts a lithography apparatus according to an embodiment of the invention; FIG2 depicts a lithography unit or cluster according to an embodiment of the invention; FIG3(a) includes a schematic diagram of a dark-field scattering instrument used when measuring a target using a first illumination aperture pair according to an embodiment of the invention; FIG3(b) illustrates details of the diffraction spectrum of the target grating for a given illumination direction; FIG3(c) illustrates a second illumination aperture pair that provides an additional illumination mode when performing diffraction-based overlay measurements using the scattering instrument; and FIG3(d) illustrates a third illumination aperture pair combining the first aperture pair and the second aperture pair; FIG4(a), FIG4(b) and FIG4(c) schematically depict a grating light valve (GLV), illustrating the basic operation of the grating light valve in (a) top view, (b) end view in a first configuration and (c) end view in a second configuration; Figures 5(a) and 5(b) schematically depict a top view and a side view of the GLV-based illumination configuration module, respectively; Figure 6 is a high-level block diagram of the measurement tool; Figures 7(a) through 7(c) illustrate the problems arising from the different spectral transmission characteristics of different illumination tools: Figure 7(a) includes a graph showing the intensity as a function of wavelength set by the illumination configuration module for each of the two measurement tools; Figure 7(b) includes a graph showing the intensity as a function of wavelength of the spectral transmission characteristics of each of the two illumination tools; and Figure 7(c) includes a graph showing the intensity as a function of wavelength of the spectral characteristics obtained from the measurement illumination at the wafer level for each of the two measurement tools; and Figures 8(a), 8(b), and 8(c) are equivalent graphs to those of Figures 7(a), 7(b), and 7(c), but in which the method according to the embodiment has been employed, for example, using the illumination configuration module. Detailed Implementation

[0013] Before describing the embodiments of the invention in detail, it is beneficial to present an example environment in which the embodiments of the invention can be implemented.

[0014] Figure 1 schematically depicts a photolithography apparatus LA. The apparatus includes: an illumination optics system (illuminator) IL configured to modulate a radiation beam B (e.g., UV radiation or DUV radiation); a patterning apparatus support or support structure (e.g., mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning apparatus according to certain parameters; a substrate stage (e.g., wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate according to certain parameters; and a projection optics system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the radiation beam B onto a target portion C (e.g., including one or more dies) of the substrate W via the patterning apparatus MA.

[0015] Irradiation optical systems may include various types of optical components for guiding, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

[0016] Patterning apparatus supports hold the patterning apparatus in a manner dependent on the orientation of the patterning apparatus, the design of the lithography apparatus, and other conditions, such as whether the patterning apparatus is held in a vacuum environment. The patterning apparatus support can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning apparatus. The patterning apparatus support can be, for example, a frame or stage that can be fixed or moved as needed. The patterning apparatus support ensures that the patterning apparatus is, for example, in the desired position relative to the projection system. Any use of the terms "mask" or "mask" herein may be considered synonymous with the more general term "patterning apparatus".

[0017] As used herein, the term "patterning apparatus" should be interpreted broadly to refer to any apparatus that can be used to impart a pattern to a radiation beam in a cross-section, such as to create a pattern in a target portion of a substrate. It should be noted that, for example, if the pattern includes phase-shifting features or so-called auxiliary features, the pattern imparted to the radiation beam may not perfectly correspond to the desired pattern in the target portion of the substrate. Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in the device being created in the target portion, such as an integrated circuit.

[0018] Patterning apparatus can be transmissive or reflective. Examples of patterning apparatus include masks, programmable mirror arrays, and programmable LCD panels. Masks are well-known in photolithography and include mask types such as binary, alternating phase-shift, and attenuation phase-shift masks, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect incoming radiation beams in different directions. The tilted mirrors impart a pattern to the radiation beams reflected by the mirror matrix.

[0019] As described herein, the device is transmissive (e.g., using a transmissive mask). Alternatively, the device may be reflective (e.g., using a programmable mirror array of the type described above, or using a reflective mask).

[0020] Photolithography apparatuses can also be of this type, in which at least a portion of the substrate can be covered by a liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquids can also be applied to other spaces within the photolithography apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system. The term "immersion" as used herein does not imply that a structure such as the substrate must be submerged in a liquid, but only that the liquid is located between the projection system and the substrate during exposure.

[0021] Referring to Figure 1, the irradiator IL receives a radiation beam from the radiation source SO. For example, when the source is an excimer laser, the source and the lithography apparatus can be separate entities. In such a case, the source is not considered part of the lithography apparatus, and the radiation beam is transmitted from the source SO to the irradiator IL via a beam delivery system BD, which includes, for example, suitable guide mirrors and / or beam expanders. In other cases, such as when the source is a mercury lamp, the source can be an integral part of the lithography apparatus. The source SO and the irradiator IL, together with the beam delivery system BD, can be referred to as the radiation system, depending on the requirements.

[0022] The irradiator IL may include an adjuster AD, which is used to adjust the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial ranges of the intensity distribution in the pupil plane of the irradiator (often referred to as σ-outer and σ-inner, respectively) can be adjusted. Furthermore, the irradiator IL may include various other components, such as an integrator IN and a beam concentrater CO. The irradiator can be used to adjust the radiation beam to achieve a desired uniformity and intensity distribution in its cross-section.

[0023] A radiation beam B is incident on a patterning apparatus (e.g., a mask) MA held on a patterning apparatus support (e.g., a mask stage) MT and patterned by the patterning apparatus. After passing through the patterning apparatus (e.g., the mask) MA, the radiation beam B is passed through a projection optics system PS, which focuses the beam onto a target portion C of a substrate W, thereby projecting an image of the pattern onto the target portion C. The substrate stage WT can be precisely moved, for example, to position different target portions C within the path of the radiation beam B, using a second positioner PW and a position sensor IF (e.g., an interferometer, a linear encoder, a two-dimensional encoder, or a capacitive sensor). Similarly, for example, after mechanical retrieval from a mask library or during scanning, a first positioner PM and another position sensor (not explicitly depicted in Figure 1) can be used to accurately position the patterning apparatus (e.g., the mask) MA relative to the path of the radiation beam B.

[0024] Patterning apparatus (e.g., mask) MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks, as shown, occupy dedicated target portions, they can be positioned in the space between the target portions (these are referred to as scribe alignment marks). Similarly, when more than one die is provided on the patterning apparatus (e.g., mask) MA, mask alignment marks can be positioned between the dies. Small alignment marks can also be included within the die, within the apparatus features, in which case it is desirable that the marks be as small as possible and do not require any imaging or processing conditions different from adjacent features. The alignment system for detecting alignment marks will be described further below.

[0025] The lithography apparatus LA in this example is a so-called dual-platform type, featuring two substrate stages WTa and WTb and two stations (exposure station and measurement station). The two substrate stages can be interchanged between the two stations. While one substrate on one stage is being exposed at the exposure station, another substrate can be loaded onto the other substrate stage at the measurement station, and various preparation steps are performed. Preparation steps may include using a level sensor LS to map the surface control of the substrate, and using an alignment sensor AS to measure the position of alignment marks on the substrate. This enables a significant increase in apparatus throughput.

[0026] The depicted apparatus can be used in various modes, including, for example, stepping mode or scanning mode. The construction and operation of photolithography apparatus are well known to those skilled in the art and do not need to be further described for the purpose of understanding the present invention.

[0027] As shown in Figure 2, the lithography apparatus LA forms part of the lithography system known as the lithography unit LC, lithography pool, or cluster. The lithography unit LC may also include devices for performing pre-exposure and post-exposure processing on the substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chiller CH, and a baking plate BK. A substrate processor or robot RO picks up the substrate from the input / output ports I / O1 and I / O2, moves the substrate between different processing devices, and then transfers the substrate to the feed stage LB of the lithography apparatus. These devices, generally referred to collectively as tracks, are under the control of the track control unit TCU, which is itself controlled by the supervisory control system SCS, which in turn controls the lithography apparatus via the lithography control unit LACU. Therefore, different devices can be operated to maximize throughput and processing efficiency.

[0028] A suitable measurement apparatus for use in embodiments of the invention is shown in Figure 3(a). The target T and the diffracted rays of the measurement radiation used to illuminate the target are illustrated in more detail in Figure 3(b). The illustrated measurement apparatus is of the type referred to as a dark-field measurement apparatus. The measurement apparatus can be a stand-alone device or can be incorporated into a lithography apparatus LA (e.g., at a measurement station) or a lithography unit LC. The optical axis having several branches through the apparatus is indicated by the dashed line O. In this apparatus, light emitted by source 11 (e.g., a xenon lamp) is guided onto the substrate W via a beam splitter 15 through an optical system including lenses 12, 14 and objective lens 16. These lenses are arranged in a double sequence of 4F arrangement. Different lens arrangements can be used as long as it still provides an image of the substrate to the detector and simultaneously allows access to the intermediate pupil plane for spatial frequency filtering. Thus, the angular range of radiation incident on the substrate can be selected by defining the spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane (here referred to as the (conjugate) pupil plane). Specifically, this can be achieved by inserting a suitably shaped aperture plate 13 between lenses 12 and 14 in the plane of the rear-projected image, which serves as the objective lens pupil plane. In the illustrated example, the aperture plate 13 has different forms, labeled 13N and 13S, allowing for the selection of different illumination modes. The illumination system in this example forms an off-axis illumination mode. In the first illumination mode, aperture plate 13N provides off-axis illumination relative to a direction designated "north" for descriptive purposes only. In the second illumination mode, aperture plate 13S is used to provide similar illumination, but relative to the opposite direction, labeled "south." By using different apertures, other illumination modes are possible, such as modes that allow simultaneous illumination and detection from two opposite directions in combination with an optical wedge to separate the resulting image. The remainder of the pupil plane is expected to be dark, as any unwanted light outside the desired illumination mode will interfere with the desired measurement signal.

[0029] As shown in Figure 3(b), the target T is positioned with the substrate W perpendicular to the optical axis O of the objective lens 16. The substrate W may be supported by a support (not shown). The measuring radiation ray I striking the target T at an angle off-axis O produces a zero-order ray (solid line 0) and two first-order rays (dotted line +1 and double-dotted line -1). It should be remembered that for an overfilled small target, these rays are just one of many parallel rays covering the area of ​​the substrate that includes the measuring target T and other features. Due to the limited width of the aperture in plate 13 (necessary to receive a useful amount of light), the incident ray I will actually occupy an angular range, and the diffracted rays 0 and +1 / -1 will be diffused. Depending on the point diffusion function of the small target, each order +1 and -1 will be further diffused within the angular range, rather than a single ideal ray as shown in the figure. Note that the grating pitch and illumination angle of the target can be designed or adjusted so that the first-order rays entering the objective lens are closely aligned with the central optical axis. The rays illustrated in Figures 3(a) and 3(b) are slightly off-axis only to make them easier to distinguish in the figure.

[0030] At least the 0th and +1st diffracted rays from the target T on the substrate W are collected by objective lens 16 and guided back through beam splitter 15. Returning to Figure 3(a), both the first and second illumination modes are illustrated by specifying the diameter-opposite apertures marked North (N) and South (S). When the incident ray I of the measured radiation comes from the north side of the optical axis, i.e., when the first illumination mode is applied using aperture plate 13N, the +1 diffracted ray marked +1 (N) enters objective lens 16. In contrast, when the second illumination mode is applied using aperture plate 13S, the -1 diffracted ray (marked -1 (S)) is the ray entering lens 16.

[0031] The second beam splitter 17 divides the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 uses the zeroth-order and first-order diffracted beams to form the diffraction spectrum (pupil plane image) of the target on the first sensor 19 (e.g., a CCD or CMOS sensor). Each diffraction order hits a different point on the sensor, allowing image processing to compare and contrast the orders. The pupil plane image captured by the sensor 19 can be used to focus the measurement device and / or normalize the intensity measurement of the first-order beam. The pupil plane image can also be used for many measurement purposes, such as reconstruction.

[0032] In the second measurement branch, optical systems 20 and 22 form an image of the target T on sensor 23 (e.g., a CCD or CMOS sensor). In this second measurement branch, an aperture stop 21 is provided in a plane conjugate to the pupil plane. Aperture stop 21 blocks the zero-order diffracted beam, ensuring that the image of the target formed on sensor 23 is formed only by either a -1 or +1 order beam. The image captured by sensors 19 and 23 is output to a processor PU, which processes the image; the functionality of the processor PU will depend on the specific type of measurement performed. Note that the term "image" is used in a broad sense herein. If only one of the -1 or +1 orders is present, the image of the grating lines themselves will not be formed.

[0033] The specific forms of the aperture plate 13 and field stop 21 shown in Figure 3 are merely examples. In another embodiment of the invention, on-axis illumination of the target is used, and an aperture stop with an off-axis aperture is used to transmit essentially only first-order diffracted light to the sensor. In other embodiments, second-, third-, and higher-order beams (not shown in Figure 3) may be used in the measurement instead of a first-order beam or in addition to a first-order beam.

[0034] To adapt the measured radiation to these different types of measurements, the aperture plate 13 may include several aperture patterns formed around a disc-shaped element, which is rotated to position the desired pattern. Note that the aperture plate 13N or 13S can only be used to measure gratings oriented in one direction (X or Y, depending on the setup). To measure orthogonal gratings, the target can be achieved by rotations of 90° and 270°. Different aperture plates are shown in Figures 3(c) and 3(d). The use of these aperture plates, as well as many other variations and applications of the apparatus, are described in the previously disclosed applications mentioned above.

[0035] Overlay measurements are known to be performed using apparatus such as that shown in Figure 3(a). To achieve this, overlay targets can be printed in two layers on a wafer. One overlay measurement method (sometimes called micro-diffraction overlay (μDBO)) infers the overlay based on the asymmetric imbalance of complementary diffraction orders from targets comprising corresponding gratings in each layer. Typically, in μDBO, the gratings in each layer have the same single pitch, but an applied bias can exist between the two targets.

[0036] Measurement tools (MTs), such as scatterometers, topography measurement systems, or the aforementioned position measurement systems, can perform measurements using radiation originating from a radiation source. The characteristics of the radiation used by the measurement tool can affect the type and quality of measurements that can be performed. For some applications, it may be advantageous to use multiple radiation frequencies and / or polarization states to measure the substrate; for example, broadband radiation can be used. Multiple different frequencies can propagate, irradiate, and scatter the measurement target without interference or with minimal interference. Therefore, different frequencies can be used, for example, to obtain more measurement data simultaneously. Different radiation frequencies can also be used to query and discover different characteristics of the measurement target. Broadband radiation can be useful in measurement systems (MTs) such as, for example, level sensors, alignment mark measurement systems, scattering measurement tools, or inspection tools. The broadband radiation source can be a supercontinuum source.

[0037] In many measurement applications, such as those based on scattering or interferometry, for example, to perform pre-exposure measurements (e.g., alignment) or post-exposure measurements (e.g., overlay, CD, focus, or other parameter of interest measurements), different information can be obtained from measurements of the same structure depending on the wavelength and polarization state of the measurement illumination used. For example, some current measurement systems offer configurable measurement illumination over multiple colors and three polarization settings (horizontal, vertical, and both). However, the illumination configuration modules (color switching modules) currently used in such systems tend to be based on slow, bulky mechanical modules. Furthermore, such modules only offer three options when selecting the polarization of the incident beam: all wavelengths under a first polarization state (e.g., horizontal H), all wavelengths under a second polarization state (e.g., vertical V), or all wavelengths under both polarizations. It is highly likely that at some wavelengths, either polarization selection is suboptimal. To measure each wavelength under optimal polarization for each wavelength, twice the measurement would be required for a single polarization measurement, with a slow polarization switch midway. Moreover, it is currently impossible to have arbitrary combinations of different polarization states.

[0038] Rapid illumination configuration modules or color switching modules have been described based on the concept of grating light valves (GLVs). GLV modules disperse light (light has been dispersed onto the GLV), allowing the module to selectively remove or modulate one or more specific wavelengths of light. The resulting spectrum can be configured to include any desired shape and can vary at very high frequencies, potentially up to the MHz range. Such engineered spectra represent a rapid (microsecond-level switchable) way to extract vast amounts of information from a target. However, known literature related to GLV-based illumination configurations only describes color selection, without any polarization selection functionality. Wavelength is only one degree of freedom. Measuring the polarization of the illumination is another useful degree of freedom that can be utilized in measurements.

[0039] By way of example, and with reference to Figures 4 and 5, a GLV-based illumination configuration module will now be described, which is configured to selectively transmit or block (diffract or reflect) at least a portion of incident broadband illumination. A GLV is an electrically programmable diffraction grating based on microelectromechanical systems (MEMS) technology. A GLV device may include configurable diffraction structures for selectively reflecting or diffracting the incident broadband illumination into an output radiation beam. Therefore, the output radiation illumination from such a module may include a spectrally configured beam modulated by the GLV device. The GLV devices used in the embodiments disclosed herein may be GLV devices sold by Silicon Light Machines (SLM) and / or based on the GLV concept described in US6947613B, which is incorporated herein by reference.

[0040] Figures 4(a) through 4(c) illustrate the working principle behind GLV. Figures 4(a) through 4(c) are schematic diagrams of the GLV pixel or component 500 as seen from above and from the end, respectively. Note that the GLV components shown in Figures 4(a) through 4(c) are merely example designs, and other different GLV designs (e.g., the “true GLV” design used in the G1088 and G8192 modules sold by SLM) can also be used in any of the illumination configuration modules disclosed herein.

[0041] GLV components include two alternating types of GLV reflective strips: a static or bias strip 510, which is typically grounded along with a common electrode; and a driven or active strip 520, which is driven by an electronic driver channel. GLV devices can include any number of these GLV components 500 arranged in an array (e.g., a 1D or 2D array). The active and bias strips can be substantially the same except for how they are driven. In one embodiment, as shown in FIG4(b), when no voltage is applied to the active strip 520, they are coplanar with the bias strip. In this configuration, the GLV essentially acts as a mirror, where incident light is specularly reflected (i.e., forming specularly reflected radiation or zero-order diffracted radiation). When a voltage is applied to the active strip 520, as shown in FIG4(c), they are deflected relative to the bias strip 510, thereby establishing a square-well diffraction grating. In this state, the incident light is diffracted to a fixed diffraction angle. The ratio of reflected light to diffracted light can be continuously changed by controlling the voltage on the active band 520 (which controls the amplitude of the deflection of the active band 520). Therefore, the amount of light diffracted by the GLV can be controlled analogously from zero (total specular reflection) to all incident light (zero specular reflection). In the context of this disclosure, such control over the amount of reflected radiation relative to the amount of radiation diffracted into a non-zero diffraction order can be referred to as modulation of the illumination.

[0042] GLV devices can be used in zero-order mode, where diffracted radiation is blocked / discarded, and specularly reflected (zero diffraction order) radiation is selected (e.g., transmitted into the output illumination beam). This has the advantage of maintaining light collection efficiency. Therefore, an aperture stop can be provided in the pupil plane with the aim of maximizing zero-order transmission and maximizing (minimizing transmission) blocking of first-order (and other diffraction orders). However, it is understood that this can be reversed (i.e., operated in first-order mode), where specular radiation is discarded and diffracted radiation is transmitted to the output. This arrangement can have other advantages, such as improved out-of-band suppression.

[0043] Figures 5(a) and 5(b) schematically illustrate a known illumination configuration module from two different perspectives. A broadband beam emitted by a broadband light source LS is dispersed in the X direction by a beam-dispersing element DE (which may include, for example, a prism or a grating). The dispersion of the broadband beam is achieved based on the principle that the direction of light emitted from the beam-dispersing element DE depends on the wavelength. The broadband beam can optionally be collimated by a first optical lens L1 before being dispersed by the beam-dispersing element DE. The dispersed broadband beam can then be focused (e.g., through a second optical lens L2) onto the band of a GLV device, which is substantially located at the focal plane of the second lens L2. Different shading indicates different wavelengths of the dispersed radiation.

[0044] GLV devices can be configured in zero-order mode and operated to apply a certain spatial modulation to a focused broadband beam, selectively reflecting desired wavelengths and diffracting unwanted wavelengths. In some embodiments, the GLV device can operate in wavelength-selective mode to completely select one or more selected wavelengths (e.g., without significant attenuation) and completely block unselected wavelengths. That is, the bands of the GLV device corresponding to the selected wavelengths can be set to equal heights, such that they act as standard mirrors for the selected wavelengths, and other bands are actuated in such a way that they form gratings to diffract unwanted wavelengths to higher diffraction orders, such as -1 and +1 diffraction orders. These higher diffraction orders are then blocked or discarded by beam-blocking elements BL1, BL2, respectively. The GLV device can also operate in intermediate or spectral-shaping modes, for example, to form gratings that partially reflect and partially diffract incident radiation for one or more wavelengths, attenuating but not completely blocking these one or more wavelengths. The degree of attenuation can be controlled via band configuration (offset of the active bands relative to the static bands). In this way, the spectral shape / composition of the output radiation can be dynamically controlled.

[0045] The spatially modulated (zero-order) radiation from the GLV device can be captured by a second optical lens L2. The spatially modulated beam is then recombined on the return path, for example, using the same dispersive element DE used to disperse the beam on the outgoing path (alternatively, separate dispersive elements can be used for both dispersion and combination). The return path within the dispersive element DE can be substantially parallel to the outgoing path and shifted in the Y direction. The recombined output beam can then be guided by a steering mirror SM toward, for example, a third optical lens L3. This third optical lens L3 can act as an output lens to focus the beam into the measurement device, for example, via a suitable optical fiber such as a single-mode photonic crystal fiber.

[0046] The concepts disclosed herein can relate to any measurement device, such as the scatterer illustrated in Figure 3, or other measurement devices described with respect to Figure 1, such as alignment sensors or level sensors. Such devices may include a color selection module or an illumination configuration module that enables the configuration of the illumination spectrum (e.g., selection of one or more colors and / or their respective relative intensities) based on a broadband illumination source. The GLV device illustrated in Figure 5 (or a similar device configured in the first-order mode implementation) can be used as the illumination configuration module of the embodiments disclosed herein. However, it is understood that this is merely exemplary, and any suitable device for spectral configuration / color selection capable of relatively attenuating different wavelengths can be used. Other devices (e.g., non-GLV-based devices) can use other modulation devices (e.g., spatial light modulators, acousto-optic modulators (AOMs), electro-optic modulators (EOMs), or similar devices) instead of GLVs to modulate the dispersed beam. In other embodiments, the irradiation configuration module may include a plurality of spectral filters (or one or more continuously variable spectral filters), which may be switched (individually and / or in different combinations) into the beam path (or selected portions of which may be switched into the beam path) to spectrally configure the irradiation.

[0047] Figure 6 is a block diagram depicting the main modules of the measurement apparatus at a high level. Source 600 generates a broadband illumination beam. Illumination configuration module 610 configures the spectrum of the illumination beam to obtain spectrally configured measurement illumination. To monitor and control illumination configuration module 610, it may include a spectrometer 620 (or the spectrometer may be located between illumination configuration module 610 and projection optics system 630). The spectrometer may measure at least a portion of the spectrum of the spectrally configured measurement illumination before it is projected by projection optics system 630. Projection optics system 630 may be used to illuminate a portion of a wafer (e.g., including structures or targets) with spectrally configured measurement illumination. Illumination scattered, reflected, and / or diffracted from the wafer is then detected on detector 640 (e.g., a camera). In many measurement tools, such as those described in Figure 3, detector 640 is only capable of detecting signal amplitude measurements, such as the intensity of scattered radiation, and does not have functionality for measuring its spectral characteristics.

[0048] For example, due to chromatic aberration and / or other effects, the projection optics of a measurement tool will typically have non-uniform spectral transmission characteristics. Therefore, the spectrum received by the detector is not necessarily the same as the spectrum set by the illumination configuration module. Furthermore, the corresponding projection optics of different measurement tools will typically have different spectral transmission characteristics. Therefore, for the same illumination settings at the illumination configuration module, the measurement illumination at the wafer level (i.e., for the actual measurement) may have significant inter-tool spectral differences.

[0049] In systems where the spectrum can be specified entirely based on the center wavelength and associated bandwidth, such inter-tool spectral differences will manifest as dose differences, resulting in differences in integration time and / or signal levels across different tools.

[0050] In a system where the full spectrum is set, differences in spectral transmission will manifest themselves as poor inter-tool matching. Figure 7 illustrates this in a simple two-color λ1, λ2 example. Figure 7(a) shows a spectral graph (intensity I as a function of wavelength λ) of the spectrally configured measurement illumination immediately following the illumination configuration module (i.e., before the projection optics) for each of the two different measurement tools MET1, MET2. Two color bands λ1, λ2 of equal intensity have been selected by each illumination configuration module of the two measurement tools MET1, MET2, where the same spectrum is selected for each tool.

[0051] Figure 7(b) is a spectral graph illustrating the effect of the corresponding spectral transmission characteristics of the two measurement tools, MET1 and MET2, on the spectrum set in Figure 7(a). In this simplified example, each color λ1 and λ2 of the first measurement tool MET1 is attenuated by a small amount of equal value, while there is a larger difference in the attenuation of the two colors λ1 and λ2 for the second measurement tool MET2, where color λ1 is attenuated more than color λ2. For illustration purposes, the difference in spectral transmission has been exaggerated.

[0052] Figure 7(c) is a spectral graph of the measured illumination at the corresponding configuration at the wafer level. Naturally, these are the same as the graph in Figure 7(b). Again, it should be understood that this spectral information is typically not available at the detector, which will only measure the individual intensities for the entire combination of colors.

[0053] To address this problem, a method is proposed for spectrally configuring the measurement illumination of a measurement tool prior to its projection optics, for example using an illumination configuration module of the measurement tool, to obtain a desired spectral shape (e.g., per wavelength) for the measurement tool. Such a method may include: a) projecting measurement radiation using the projection optics to obtain projected measurement radiation; b) measuring a signal amplitude metric (e.g., any metric related to signal amplitude, such as signal amplitude, intensity, or power) of the projected measurement radiation at a detector; c) determining the spectral shape of the projected measurement radiation based on the signal amplitude metric; and d) spectrally configuring the measurement illumination prior to the projection optics to adjust the spectral shape to match the desired spectral shape.

[0054] Spectral configuration of the measurement illumination can compensate for the spectral transmission characteristics of the projection optics system. The method can be performed on at least a first and a second measuring tool, such that a first spectral shape of the measurement illumination from the first measuring tool and a second spectral shape of the measurement illumination from the second measuring tool are matched for a commonly desired measurement illumination setting using both the first and second measuring tools. The desired illumination setting can be defined, for example, by a measurement formula for a specific measurement.

[0055] The method may include determining the spectral transmission characteristics of the projection optics of a first measuring tool (e.g., a reference measuring device); and determining the desired spectral shape for a second measuring tool (and other measuring tools) based on the determined spectral transmission characteristics of the projection optics of the first measuring tool. For example, the method may include: performing steps a) to c) for the first measuring tool to determine a spectral shape imposed by the spectral transmission characteristics of the projection optics of the first measuring tool; and performing steps a) to d) for the second measuring tool, wherein the desired spectral shape is the determined spectral shape imposed by the first measuring tool.

[0056] The spectral shape can be determined using any device downstream of the projection optics system that does not include spectral measurement capabilities / functions.

[0057] In the context of this paper, a matched spectral shape can be obtained when the corresponding spectral shapes of the projected measured radiation are matched. This may be the case when the relative intensity difference per wavelength within each spectrum matches the relative intensity difference of the desired spectrum, such that there may only be a difference in global intensity or signal amplitude between the spectra. Of course, a spectral match can be considered a match if the spectral shapes are sufficiently similar (e.g., substantially similar) rather than exactly identical, for example, according to a matching threshold.

[0058] Figure 8 illustrates the proposed method according to an embodiment. In this example, the two measurement tools MET1 and MET2 are identical to those in Figure 7, having the same spectral transmission characteristics (i.e., Figure 8(b) is the same as Figure 7(b)). The desired spectral shape in this example is flat across two selected bands (i.e., colors λ1 and λ2 have equal relative intensities). This desired shape may be defined by the spectral response of a reference measurement tool (e.g., in this example, measurement tool MET2 may be matched with reference measurement tool MET1), and / or may be the desired spectral shape to which one or more tools are being matched (e.g., the spectral shapes of both measurement tools MET1 and MET2 are matched to have the desired spectral shape).

[0059] In any case, as described in Figure 8(c), the desired spectral shape can be obtained by altering / adjusting the spectrally configured measurement illumination via the illumination configuration module for the second measurement device to compensate for the relative attenuation difference experienced through the two wavelengths. Of course, it is not possible to increase the intensity of color λ1 (or any color) using the illumination configuration module; therefore, instead, in the measurement tool MET2, the relative intensity of color λ2 can be attenuated relative to the intensity of color λ1.

[0060] In this way, the spectral content under color selection is adjusted to reflect the spectral transmittance of the measuring tool.

[0061] To measure the spectral shape of a measurement illumination at the wafer level, a method is proposed that defines a spectral line (e.g., a narrow bandwidth range) and uses an illumination configuration module to change its color (e.g., sweeping within the wavelength range of interest), while simultaneously measuring a signal amplitude metric at the detector and a corresponding spectrometer signal (e.g., based on the center wavelength and bandwidth) from a spectrometer (e.g., included in the illumination configuration module). The measured spectral shape can be determined by combining the shape of the signal amplitude metric at the detector over time with spectral information from the spectrometer signal, such that the temporal information can be replaced by the temporally corresponding spectral information. This can be done for all measurement instruments to be matched. During sweeping, the line intensity can be kept constant, thereby ensuring that any intensity differences at the detector depend essentially only on the spectral characteristics of the projection optics. However, this is not necessary, and the intensity can change during sweeping (e.g., the detector reading can be related to a known intensity difference in the line).

[0062] It is understood that the measurement of signal amplitude at the detector can be performed on a wafer or other object on the substrate support of the measurement tool, such that the wafer scatters (e.g., reflects and / or diffracts) the measurement illumination onto the detector.

[0063] Although the simplified example described in Figure 8 involves only two wavelengths, the concepts described can certainly be applied to any spectrum, including continuous spectra or multiple discrete bands.

[0064] As can be seen, although the spectral shape can be matched, the overall intensity of the measured irradiation may differ between the matched tools. This can be addressed, for example, by varying the measurement time of each tool to match the effective intensity on the detector (i.e., using a longer measurement time for tools measuring lower irradiation intensities). Alternatively or additionally, the measured irradiation intensity can be altered or increased such that the intensity is optimized (e.g., maximized) for at least one wavelength.

[0065] While the foregoing may have specifically referred to embodiments of the invention in the context of optical lithography, it should be understood that the invention can be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the morphology in a patterning apparatus defines a pattern created on a substrate. The morphology of the patterning apparatus can be pressed into a resist layer supplied to the substrate, wherein the resist is then cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has cured, the patterning apparatus is removed from the resist, leaving a pattern therein.

[0066] As used herein, the terms “radiation” and “beam” encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., with wavelengths of about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., with wavelengths in the range of 5 nm to 20 nm), as well as particle beams, such as ion beams or electron beams.

[0067] The term "lens" can refer to any optical component or combination thereof of various types, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components, as the context allows.

[0068] The foregoing description of specific embodiments so fully reveals the general nature of the invention that others, by applying the knowledge of those skilled in the art, can readily modify and / or alter these specific embodiments for various applications without departing from the overall conception of the invention and without excessive experimentation. Therefore, based on the teachings and guidance presented herein, such changes and modifications are intended to be within the meaning and scope of equivalents of the disclosed embodiments. It should be understood that the terms or terminology used herein are for the purpose of description by way of example and not for limitation, and that the terminology or terminology of this specification should be interpreted by those skilled in the art based on the teachings and guidance.

[0069] The breadth and scope of this invention are not limited to any of the embodiments described above, but should be defined only by the appended claims and their equivalents.

Claims

1. A method for spectral configuration of measurement illumination for a measuring instrument, the method comprising: a) Use a projection optics system to project the measurement radiation to obtain the projected measurement radiation; b) Measure the signal amplitude of the projected measured radiation at the detector; c) Determine the spectral shape of the projected measurement radiation based on the signal amplitude metric; and d) Perform spectral configuration on the measurement illumination prior to the projection optics system to adjust the spectral shape to match the desired spectral shape.

2. The method of claim 1, wherein the spectral transmission characteristics of the projection optical system are compensated by spectral configuration of the measurement illumination.

3. The method according to claim 1 or 2, comprising: For each of at least a first measuring tool and a second measuring tool, the method or at least a subset of the steps of the method is performed such that a first spectral shape of the measurement illumination of the first measuring tool is matched with a second spectral shape of the measurement illumination of the second measuring tool to obtain a commonly desired measurement illumination setting using the first measuring tool and the second measuring tool.

4. The method according to claim 3, comprising: Determine the spectral transmission characteristics of the projection optics system of the first measuring tool; and determine the desired spectral shape for the second measuring tool based on the determined spectral transmission characteristics of the projection optics system of the first measuring tool.

5. The method according to claim 3 or 4, wherein the method comprises: For the first measuring tool, steps a) to c) are performed to determine the spectral shape imposed by the spectral transmission characteristics of the projection optics system of the first measuring tool; and for the second measuring tool, steps a) to d) are performed, wherein the desired spectral shape is the spectral shape determined by the first measuring tool.

6. The method according to any one of claims 3 to 5, comprising: Determine the measurement time difference between the measurement time using the first measurement tool and the measurement time using the second measurement tool, the measurement time difference compensating for the intensity difference between the measurement irradiation or spectrally configured measurement irradiation for the first measurement tool and the spectrally configured measurement irradiation for the second measurement tool in step d).

7. The method according to any one of the preceding claims, comprising: The intensity of the measured irradiation is changed such that the intensity of the spectrally configured measured irradiation in step d) is optimized and / or maximized for at least one wavelength.

8. The method according to any one of the preceding claims, wherein the signal amplitude measurement is measured using a detector that does not have spectral measurement capabilities.

9. The method according to any one of the preceding claims, wherein step c) comprises: The measurement irradiation is spectrally configured to define spectral lines; Change the wavelength of the spectral line within the wavelength range of interest; The signal amplitude metric is measured at the detector, and the corresponding spectrometer signal related to the spectrum of the spectral line is measured at a position before the projection optical system; And determine the spectral shape based on the signal amplitude measurement and the spectrometer signal.

10. The method according to any one of the preceding claims, comprising: The measurement is performed by the spectrally configured measurement irradiation of step d).

11. The method according to any one of the preceding claims, wherein the signal amplitude measurement includes one or more of the following: signal amplitude, signal strength, or signal power.

12. At least one measuring device capable of operating to perform the method according to any one of claims 1 to 11.

13. The at least one measuring device according to claim 12, wherein each of the at least one measuring device comprises: An illumination configuration module is used to perform spectral configuration on the measured radiation to obtain spectrally configured measured radiation. A projection optical system for projecting the spectrally configured measurement radiation onto a substrate; and a substrate support member for supporting the substrate.

14. The at least one measuring device according to claim 13, wherein the illumination configuration module includes a grating light valve device.

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