Metering method related to overlay

Abstract

A metrology method includes obtaining a first absolute position metric of a first structure in a first layer on a substrate and a second absolute position metric of a second structure in a second layer of the substrate; and determining one or more of the following from the first absolute position metric and the second absolute position metric: exposure-induced first layer pattern displacement describing a displacement error of the first structure resulting from exposure of the structure; exposure-induced second layer pattern displacement describing a displacement error of the second structure resulting from exposure of the structure; a process-induced first layer pattern displacement describing a displacement error of the first structure resulting from the processing of the structure; and / or an alignment error describing an error of alignment data used to align the second layer with the first layer.

Description

Cross-references to related applications

[0001] This application claims preference to EP application 23182989.6, filed on July 3, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to control devices and control methods, for example, that can be used to maintain performance during the fabrication of devices through patterning processes such as photolithography. The invention also relates to methods for fabricating devices using photolithography. Furthermore, the invention relates to computer program products for implementing such methods. Background Technology

[0003] Photolithography is a process in which a photolithography apparatus applies a desired pattern onto a substrate, typically onto a target portion of the substrate, and then creates functional features for complex products through various chemical and / or physical processing steps. Accurately placing the pattern on the substrate is a major challenge for reducing the size of circuit components and other products that can be produced by photolithography. Specifically, accurately measuring the features already laid on the substrate is a critical step in ensuring that features in subsequent layers are precisely overlaid, thereby producing functional devices with high yield. Generally, in today's submicron semiconductor devices, so-called overlay should be achieved within tens of nanometers, and down to a few nanometers in the most critical layers.

[0004] Therefore, modern lithography apparatuses involve a large number of measurement or 'mapping' operations before the substrate is actually exposed or patterned at the target location. So-called advanced alignment models have been developed and continue to be developed to more accurately model and correct the nonlinear distortion of the wafer 'mesh' caused by processing steps and / or the lithography apparatus itself.

[0005] Alignment is typically measured using alignment sensors in a lithography apparatus. Alignment sensors measure the positional information (alignment data) of periodic structures or alignment marks so that an alignment model can be fitted to that data. Alignment measurement can be applied sequentially with exposure (e.g., where the lithography apparatus has only a single stage for measurement and a single stage for exposure), or at least partially simultaneously (e.g., where the lithography apparatus has separate measurement and exposure stages).

[0006] It is also known that independent alignment stations are used to perform alignment metrology. Such independent alignment metrology can be performed online (e.g., before each wafer exposure) and / or offline (e.g., on a subset of the exposed wafers).

[0007] In photolithography and other manufacturing processes, it is often necessary to measure the created structures, for example, for process control and verification. Various tools are known for performing these measurements, including scanning electron microscopes, frequently used to measure critical dimensions (CD); and specialized tools for measuring overlay, i.e., the alignment accuracy of two layers in a device. Recently, various forms of scatterometers have been developed for use in photolithography.

[0008] The manufacturing process can be, for example, photolithography, etching, deposition, chemical mechanical planarization, oxidation, ion implantation, diffusion, or a combination of two or more of these.

[0009] Examples of known scatterometers often rely on the availability of a dedicated metrological target. For instance, a method might require a target in the form of a simple grating, large enough that the measurement beam produces a spot smaller than the grating (i.e., grating incomplete). In so-called reconstruction methods, the properties of the grating can be calculated by simulating the interaction between scattered radiation and a mathematical model of the target structure. The parameters of the model are tuned until the simulated interaction produces a diffraction pattern that resembles the diffraction pattern observed from a real target.

[0010] Besides measuring feature shapes through reconstruction, diffraction-based overlay can also be performed using devices such as those described in published patent application US2006066855A1. Scattering-based overlay metrology (using diffraction-order dark-field imaging) enables overlay measurements of smaller targets. These targets can be smaller than the illumination spot and can be surrounded by the product structure on the wafer. Examples of dark-field imaging metrology can be found in numerous published patent applications, such as US2011102753A1 and US20120044470A. Multiple gratings can be measured in a single image using composite grating targets. Known scatterometers often use light in the visible or near-infrared (IR) bands, which requires the grating pitch to be much coarser than the actual product structure whose properties are of interest. Such product features can be defined using extremely short wavelengths of deep ultraviolet (DUV), extreme ultraviolet (EUV), or X-ray radiation. Unfortunately, such wavelengths are often unavailable or unusable for metrology.

[0011] Conventional overlay metrology measures the relative offset between structures (e.g., overlay substructures that typically form overlay structures or overlay targets). This relative measurement does not allow for the separation and individual quantification of individual contributions to overlay (e.g., due to alignment errors, exposure errors, and / or processing errors). This leads to suboptimal correction and / or control strategies.

[0012] The aim is to improve this type of overlay measurement method. Summary of the Invention

[0013] According to a first aspect of the present invention, a metrology method is provided, comprising: obtaining a first absolute position measurement of a first structure in a first layer on a substrate and a second absolute position measurement of a second structure in a second layer of the substrate, the first layer being below the second layer; obtaining first layer shape data describing the shape of the first layer; and determining one or more of the following from the first layer shape data, the first absolute position measurement, and the second absolute position measurement: a first layer pattern displacement caused by exposure, describing a displacement error of the first structure caused by exposure of the structure; a second layer pattern displacement caused by exposure, describing a displacement error of the second structure caused by exposure of the structure; a first layer pattern displacement caused by process, describing a displacement error of the first structure caused by processing of the structure; and / or an alignment error, describing an error in alignment data used to align the second layer with the first layer.

[0014] According to a second aspect of the present invention, a computer program product is provided, comprising one or more machine-readable instruction sequences for implementing computational steps in the method according to the first aspect of the present invention described above.

[0015] The present invention also provides a processing arrangement and photolithography apparatus, including a computer program for the second aspect.

[0016] These and other aspects and advantages of the apparatus and methods disclosed herein will become apparent from the following description and accompanying drawings of exemplary embodiments. Attached Figure Description

[0017] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which corresponding reference numerals denote corresponding parts, and in the drawings: Figure 1 A photolithography apparatus suitable for use in embodiments of the present invention is described; Figure 2 The lithography unit or cluster is depicted, in which the inspection device according to the invention can be used; Figure 3 The schematic diagram illustrates the situation based on known practices. Figure 1 The measurement and exposure process in the device; Figure 4 This is a diagram of a two-layer structure, illustrating the various effects that direct alignment in the example facilitates overlay. Figure 5 This is a diagram of a two-layer structure, illustrating various effects that facilitate overlay in an indirect alignment example; and Figure 6 This is a flowchart, according to an embodiment, for determining whether a variant described by base layer measurement data is correctable. Detailed Implementation

[0018] Before describing the embodiments of the present invention in detail, it is illustrative to present example environments in which the embodiments of the present invention may be implemented.

[0019] Figure 1 A lithography apparatus LA is schematically depicted. The apparatus includes: an illumination system (illuminator) IL configured to modulate a radiation beam B (e.g., UV or DUV radiation); a patterning device support or support structure (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask) MA and connected to a first locator PM configured to accurately position the patterning device according to certain parameters; two substrate stages WTa and WTb (e.g., substrate supports or substrate / wafer stages), each substrate stage including protrusions on its support surface and each substrate stage configured to hold a substrate (e.g., a resist-coated wafer) W; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. Each substrate stage can be connected to a second locator PW configured to accurately position the substrate according to certain parameters. A reference frame RF connects the various components and acts as a reference for setting and measuring the positions of the patterning device and the substrate, and features thereon.

[0020] Lighting systems can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for guiding, shaping, or controlling radiation. For example, reflective optical components are typically used in devices that use extreme ultraviolet (EUV) radiation.

[0021] A patterning apparatus support holds the patterning apparatus in a manner dependent on the orientation of the patterning apparatus, the design of the lithography device, and other conditions, such as whether the patterning apparatus is kept in a vacuum environment. The patterning apparatus support can use mechanical, vacuum, static, or other clamping techniques to hold the patterning apparatus. The patterning apparatus support MT can be a frame or a stage, which can be fixed or movable, for example, as needed. The patterning apparatus support ensures that the patterning apparatus is positioned as required, such as relative to a projection system.

[0022] The term "patterning device" as used herein should be interpreted broadly to refer to any device that can be used to apply a pattern of radiation beams across its cross-section to create a pattern in a target portion of a substrate. It should be noted that the pattern applied to the radiation beams may not precisely correspond to the desired pattern in the target portion of the substrate, for example, if the pattern includes phase-shifting features or so-called auxiliary features. Generally, the pattern applied to the radiation beams will correspond to a specific functional layer in a device (such as an integrated circuit) created in the target portion.

[0023] As described herein, the device is of the transmissive type (e.g., employing a transmissive patterning apparatus). Alternatively, the device may be of the reflective type (e.g., employing a programmable mirror array of the type mentioned above, or a reflective mask). Examples of patterning apparatus include masks, programmable mirror arrays, and programmable LCD panels. Any use of the terms "photomask" or "mask" herein may be considered synonymous with the more general term "patterning apparatus." The term "patterning apparatus" may also be interpreted as a device that digitally stores pattern information used to control such programmable patterning apparatus.

[0024] The term “projection system” as used herein should be interpreted broadly to encompass any type of projection system, including refractive, reflective, reflective-refractive, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, suitable for the exposure radiation used, or suitable for other factors such as the use of immersion or the use of a vacuum. Any use of the term “projection lens” herein may be considered synonymous with the more general term “projection system.”

[0025] Photolithography apparatuses can also fall into this category, where at least a portion of the substrate can be covered with a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system and the substrate. The immersion liquid can also be applied to other spaces within the photolithography apparatus, such as between the mask and the projection system. Immersion techniques are well-known in the art for increasing the numerical aperture of projection systems.

[0026] In operation, the illuminator IL receives a radiation beam from the radiation source SO. The radiation source and the lithography apparatus can be separate entities, such as when the radiation source is an excimer laser. In such cases, the radiation source is not considered part of the lithography apparatus, and the radiation beam is transmitted from the radiation source SO to the illuminator IL by means of a beam delivery system BD (including, for example, suitable directional mirrors and / or beam expanders). In other cases, the radiation source can be an integral part of the lithography apparatus, such as when the radiation source is a mercury lamp. If desired, the radiation source SO, the illuminator IL, and the beam delivery system BD can be referred to as the radiation system.

[0027] The illuminator IL may, for example, include an adjuster AD, an integrator IN, and a concentrator CO for adjusting the angular intensity distribution of the radiation beam. The illuminator can be used to adjust the radiation beam to have the desired uniformity and intensity distribution in its cross-section.

[0028] Radiation beam B is incident on a patterning device MA (which is held on a patterning device support MT) and patterned by the patterning device. After passing through the patterning device (e.g., a mask) MA, radiation beam B passes through a projection system PS, which focuses the radiation beam onto the target portion C of the substrate W. The substrate stage WTa or WTb can be accurately moved, for example, to position different target portions C within the path of radiation beam B, by means of a second positioner PW and a position sensor IF (e.g., an interferometric device, a linear encoder, a 2-D encoder, or a capacitive sensor). Similarly, the first positioner PM and another position sensor (… Figure 1 (Not explicitly shown) can be used to accurately position a patterning device (e.g., a mask) MA relative to the path of the radiation beam B, for example, after mechanical retrieval from a mask library or during scanning.

[0029] Patterning devices (e.g., masks) MA and substrates W can be aligned using mask alignment structures or alignment marks M1, M2 and substrate alignment structures or alignment marks P1, P2. Although the substrate alignment structures shown occupy dedicated target portions, they can be located in the space between target portions (these are referred to as scribing alignment structures). Similarly, when more than one die is disposed on the patterning device (e.g., mask) MA, mask alignment structures can be located between the dies. Small alignment structures can also be included within the die, within device features, in which case it is desirable that the marks be as small as possible and do not require any different imaging or processing conditions different from adjacent features. Alignment systems for detecting alignment structures are also described below.

[0030] The described apparatus can be used in various modes. In scanning mode, the patterning apparatus support (e.g., mask stage) MT and substrate stage WT are scanned synchronously, while the pattern imparting the radiation beam is projected onto the target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate stage WT relative to the patterning apparatus support (e.g., mask stage) MT can be determined by the magnification (reduction) and image inversion characteristics of the projection system PS. In scanning mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), while the length of the scanning motion determines the height of the target portion (in the scanning direction). Other types of lithography apparatuses and operating modes are also possible, as is well known in the art. For example, stepping mode is known. In so-called “maskless” lithography, the programmable patterning apparatus remains stationary but has a changing pattern, and the substrate stage WT is moved or scanned.

[0031] Alternatively, the usage patterns described above or combinations and / or variations of completely different usage patterns can be adopted.

[0032] The lithography apparatus LA is a so-called dual-stage type, featuring two substrate stages WTa and WTb and two stages—an exposure station EXP and a measurement station MEA—between which the substrate stages can be exchanged. 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 can be performed. This significantly increases the throughput of the apparatus. In a single-stage apparatus, for each substrate, the preparation and exposure steps need to be performed sequentially on a single stage. The preparation steps may include mapping the surface height profile of the substrate using a level sensor LS and measuring the position of alignment structures on the substrate using an alignment sensor AS. If the position sensor IF cannot measure the position of the substrate stage when it is at the measurement station and at the exposure station, a second position sensor can be provided to enable tracking of the substrate stage position relative to the reference frame RF at both stages. Other arrangements are known and can be used instead of the dual-stage arrangement shown. For example, other lithography apparatuses are known to have substrate stages and measurement stations. These are docked together during preparation measurements and then disconnected when the substrate stage undergoes exposure.

[0033] like Figure 2 As shown, the lithography apparatus LA forms part of a lithography unit LC (sometimes also referred to as a lithocell or cluster), which also includes devices for pre-exposure and post-exposure processes on the substrate. Typically, these include a spin coater SC for depositing a resist layer, a developer DE for developing the resist, a cooling plate CH, and a baking plate BK. A substrate processor or robot RO picks up substrates from input / output ports I / O1, I / O2, moves them between different processing devices, and then transfers them to the loading chamber LB of the lithography apparatus. These devices (often collectively referred to as tracks) are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which in turn controls the lithography apparatus via the lithography control unit LACU. Therefore, the different devices can be operated to maximize yield and processing efficiency.

[0034] To ensure correct and consistent exposure of the substrate by the lithography unit, it is desirable to inspect the exposed substrate to measure properties such as overlay between subsequent layers, line thickness, and critical dimension (CD). Therefore, the manufacturing facility housing the lithography unit (LC) also includes a metrology system (MET), which receives some or all of the substrate (W) that has already been processed in the lithography unit. The metrology results are provided directly or indirectly to the supervisory control system (SCS). If errors are detected, adjustments can be made to the exposure of subsequent substrates.

[0035] Within a metrology system (MET), inspection devices are used to determine the properties of a substrate, particularly how the properties of different substrates or different layers of the same substrate vary with each layer. Inspection devices can be integrated into a lithography apparatus (LA) or a lithography unit (LC), or they can be standalone devices. For the fastest possible measurements, it may be necessary to measure the properties in the exposed resist layer immediately after exposure. However, not all inspection devices have sufficient sensitivity to perform useful measurements of latent images. Therefore, measurements can be performed after a post-exposure baking (PEB) step, which is typically the first step performed on the exposed substrate and increases the contrast between the exposed and unexposed portions of the resist. At this stage, the image in the resist can be referred to as a semi-latent image. Measurements can also be performed on the developed resist image—at which point either the exposed or unexposed portion of the resist has been removed. Furthermore, exposed substrates can be stripped and reprocessed to improve yield, or discarded, thus avoiding further processing of substrates known to be defective. In cases where only some target portions of the substrate are defective, further exposure can be performed only on those good target portions.

[0036] The metrology step using the MET metrology system can also be performed after the resist pattern has been etched into the product layer. This latter possibility limits the possibility of reprocessing defective substrates, but it can provide additional information about the performance of the overall manufacturing process.

[0037] Figure 3 The illustration shows that in Figure 1 The procedure for exposing a target portion (e.g., a die) on a substrate W in a dual-stage lithography apparatus is described first. The process, according to conventional practice, will be described. This disclosure is not limited to dual-stage apparatuses of the type shown. Those skilled in the art will recognize that similar operations are performed in other types of lithography apparatuses, such as those with a single substrate stage and a mating metrology stage.

[0038] The left-hand side within the dashed box shows the steps performed at the measurement station MEA, while the right-hand side shows the steps performed at the exposure station EXP. Occasionally, one of the substrate stages WTa and WTb will be at the exposure station, while the other is at the measurement station, as described above. For the purposes of this description, it is assumed that substrate W has already been loaded into the exposure station. In step 200, a new substrate W' is loaded into the apparatus via a mechanism not shown. The two substrates are processed in parallel to increase the yield of the lithography apparatus.

[0039] First, referencing a newly loaded substrate W', which may be a previously untreated substrate, is first exposed in the apparatus using a new photoresist to prepare the substrate. However, generally, the described photolithography process will only be one step in a series of exposure and processing steps, such that the substrate W' has been passed through this apparatus and / or other photolithography apparatuses several times, and may also undergo subsequent processes. Particularly for improving overlay performance, the task is to ensure that the new pattern is precisely applied to the correct position on the substrate that has already undergone one or more patterning or processing cycles. Each patterning step can introduce positional deviations in the applied pattern, and subsequent processing steps gradually introduce distortions in the substrate and / or the pattern applied to it, which must be measured and corrected to achieve satisfactory overlay performance.

[0040] Previous and / or subsequent patterning steps can be performed in other lithography apparatuses, as previously described, and even in different types of lithography apparatuses. For example, some layers in device fabrication processes that have high requirements for parameters such as resolution and overlay can be performed in more advanced lithography tools than other layers with lower requirements. Thus, some layers can be exposed in immersion lithography tools, while others are exposed in 'dry' tools. Some layers can be exposed in tools operating at DUV wavelengths, while others are exposed using EUV wavelength radiation. Some layers can be patterned as an alternative to or complement to exposure in the lithography apparatus shown. Such alternative and complementary techniques include, for example, imprint lithography, self-aligned multiple patterning, and oriented self-assembly. Similarly, other processing steps performed on each layer (e.g., CMP and etching) can be performed on different apparatuses for each layer.

[0041] In step 202, alignment measurements using substrate marker P1 and an image sensor (not shown) are used to measure and record the alignment of the substrate relative to the substrate stage WTa / WTb. Additionally, several alignment structures on the substrate W' will be measured using an alignment sensor AS. In one embodiment, these measurements are used to establish a substrate model (sometimes referred to as a "wafer grid") that accurately maps the distribution of markers across the substrate, including any distortions relative to the nominal rectangular grid.

[0042] In step 204, a horizontal sensor LS is also used to measure a map of the substrate height (Z) relative to the XY position. Primarily, the height map is used only to achieve accurate focusing of the exposure pattern. However, it can be used for other purposes.

[0043] When substrate W' is loaded, recipe data 206 is received, which defines the exposure to be performed and also defines the properties of the substrate and the patterns previously fabricated and to be fabricated on it. If there are alignment structures available on the substrate, and if there are alignment sensor settings available, these choices are defined in the alignment recipe in recipe data 206. Therefore, the alignment recipe defines how to measure the position of the alignment structures and which markings are used.

[0044] In step 210, substrates W' and W are swapped so that the substrate W' being measured becomes the substrate W entering the exposure station EXP. Figure 1 In the example apparatus, this exchange is performed by swapping supports WTa and WTb within the apparatus to keep substrates W and W' accurately clamped and positioned on these supports, thereby maintaining relative alignment between the substrate stage and the substrate itself. Therefore, once the stages are swapped, determining the relative position between the projection system PS and the substrate stage WTb (formerly WTa) is necessary in controlling the exposure steps using measurement information 202, 204 of substrate W (formerly W'). In step 212, photomask alignment is performed using mask alignment structures M1, M2. In steps 214, 216, 218, scanning motion and radiation pulses are applied at successive target locations across substrate W to complete the exposure of multiple patterns.

[0045] By using alignment data and height maps obtained at the measurement station during the exposure step, these patterns are accurately aligned relative to the desired location, particularly relative to features previously laid on the same substrate (i.e., to ensure good overlay performance). In step 220, the exposed substrate (now labeled W'') is unloaded from the apparatus for etching or other processing according to the exposed pattern.

[0046] To monitor overlay accuracy and provide process control corrections, overlay metrology can be performed on exposed structures (e.g., on proxy structures such as overlay structures (overlay targets), although overlay metrology can be performed directly on the functional product structure). Typically, overlay is measured as the relative displacement between structures in different layers, rather than measuring the absolute positions of these structures. This is generally simpler and / or faster. For example, diffraction-based overlay (DBO) techniques can use targets comprising periodic structures or gratings in the individual layers that diffract the incident measurement radiation.

[0047] In the absence of overlay errors (and assuming a perfect target), the DBO target will be symmetrical, and the incident measurement radiation will be diffracted equally into each of a pair of complementary diffraction orders so that they each have the same intensity (or other suitable measurement parameter) when measured. Any overlay will result in an imbalance of diffraction orders. Therefore, overlay can be determined by identifying this imbalance (e.g., based on the intensity difference between the +1 and -1 diffraction orders). In practical implementations, a number of pairs of biased DBO targets can be used, for example, to help distinguish overlay in the target from other asymmetries.

[0048] Alternative or complementary overlay metrology methods include image-based overlay (IBO). This method typically uses imaging techniques to measure the relative positions of structures in different layers. IBO targets can include, for example, box-in-box structures, gratings (spatially separated in the substrate plane), or any other suitable structure. It is understood that because IBO targets do not depend on diffraction, grating / periodic structures are not required.

[0049] As is well known, alignment training is performed based on this overlay metrology (including relative overlay measurements). This alignment training optimizes the alignment model to minimize the correlation between alignment data and overlay (after alignment). For example, this minimizes the effect of deformation of alignment structures (alignment marks). An example of this approach is sometimes referred to as WAMM (Wafer Alignment Model Mapping), which is described in more detail in PCT publications WO 2019001871 and WO 2017060054, each of which is incorporated herein by reference. In this alignment training, the use of relative overlay includes inaccuracies caused by alignment errors and / or underlying exposure and processing errors.

[0050] Because overlay measurements are relative, it is impossible to distinguish between different overlay contributing factors, such as contributions due to alignment errors and contributions due to processing (e.g., one or more processing steps typically performed after exposure, such as etching, polishing, etc.). However, for more optimized process control / correction, it would be advantageous to quantify the individual overlay contributing factors, for example, so that process corrections can be implemented at the appropriate time and / or in the appropriate apparatus. For instance, alignment errors are more appropriately addressed during alignment metrology and / or modeling (before exposure), while processing-induced errors can be better addressed, where possible, by controlling the processing apparatus (e.g., the etcher) or by controlling exposure in a manner more optimized for minimizing processing effects.

[0051] Furthermore, training a photonic model based on relative overlay metrology does not allow for the differentiation of non-orthogonal effects between two layers, leading to less accurate models. For example, in the case of substrate / wafer heating, eliminating heating effects during exposure of individual layers is impossible or difficult, especially when the exposure paths are the same.

[0052] It is impossible to use machine drift control based on the overlay on the product because machine drift exists in the two layers of the relative overlay measurement, but originates from different time periods (depending on the processing delay between layers).

[0053] Methods for measuring overlay marks in absolute terms have been described, such as by measuring the absolute position of structures in individual layers (e.g., overlay substructures that together form an overlay structure or an overlay target). For example, in paper 12496-81 presented by Lee et al. at the SPIE Advanced Lithography Conference 2023 (incorporated hereby by reference), “Absolute alignment measurement of underlayer and overlayer of diffraction-based overlay mark by image-based alignment metrology system,” an absolute overlay metrology method using independent alignment stations (e.g., image-based alignment stations) is described.

[0054] Lee et al. described using an image-based independent alignment station to measure IBO overlay structures in two overlay layers by masking the first and second layers separately at the time of positioning (during the image processing step, rather than physically). That is, the absolute position of the top structure can be determined using the masked bottom structure via image processing, and vice versa. If the target is a DBO overlay structure (i.e., where the structure is overlaid in the z-direction perpendicular to the substrate plane), a stacked marker measurement function can be used to distribute the overlay error of each layer to each grid error based on snapshots acquired by the independent alignment station and / or scanning electron microscope / electron beam tool.

[0055] The concepts presented herein can be applied using the same or similar methods and independent alignment stations as those disclosed by Lee et al. in their paper. However, it is understood that this is not necessary, and any method and / or tool suitable for measuring the absolute position of structures in different layers can be used, including, for example, scanning electron microscopy / electron beam tools or transmission electron microscopy.

[0056] In a first embodiment, it is proposed to construct the possibility of measuring the absolute position and thus the absolute shape of each layer by performing processing steps on the absolute position data of each layer to individually determine one or both of the alignment error contribution of the overlay error and the processing contribution of the alignment error. Therefore, the method may include measuring a first absolute position metric of a first structure in a first layer on a substrate and a second absolute position metric of a second structure in a second layer of the substrate, the first layer being below the second layer. The method also includes determining one or more of the following based on the first and second absolute position metrics (e.g., appended to overlay): exposure-induced first layer pattern displacement, describing the displacement error of the first structure caused by exposure of the structure; exposure-induced second layer pattern displacement, describing the displacement error of the second structure caused by exposure of the structure; process-induced first layer pattern displacement, describing the displacement error of the first structure caused by processing of the structure; and / or alignment error, describing the error in alignment data used to align the second layer with the first layer.

[0057] In the context of this disclosure, relative overlay is the positional difference between a first structure and a second structure (or more generally, between two structures in different layers). Absolute position can be defined as the position of a structure relative to a desired position defined by the wafer grid (e.g., calibrated by wafer alignment).

[0058] Two different variations of this first embodiment will be described. The first variation is in the context of direct alignment. This describes a situation where the second layer is directly aligned with the first layer when determining the overlay between the first and second layers (where the second layer (e.g., the top layer) is exposed after the first layer). In other words, the alignment structure in the first layer is measured and used to position the second layer. The second variation is in the case of indirect alignment, where the first and second layers are each aligned with a common, different underlying layer.

[0059] Figure 4 The concept of direct alignment is illustrated, where a first layer structure 400 is formed in a first layer L1, and a second layer structure 410 is formed in a second layer L2. For example, the second and first layer structures may together include an overlay structure. The first layer L1 also includes an alignment structure 420, which is formed (and used) to align the exposure of the second layer L2 with the first layer L1; for example, thereby minimizing overlay errors (maximizing overlay) or other positional parameters of interest, such as edge placement errors. It is understood that although an intermediate layer is not shown between the first and second layers, this is optionally possible within the scope of this disclosure.

[0060] The figure also illustrates various contributions to the (local) overlay OV. These contributions include the first layer pattern displacement PD1, which describes the absolute positional error of the first layer structure 400 caused by exposure and process errors. Therefore, the first layer pattern displacement PD1 includes the first layer pattern displacement PD caused by exposure. E1 The first layer pattern displacement PD caused by the process P1 The combination or sum of the first layer overlay factors. Other contributing factors to the first layer overlay include the first layer shape data AL determined based on the alignment data. S1 For example, the first layer shape data AL S1 The second layer exposure can be prepared by model fitting based on the second layer measurement alignment data MA2 (which is measured from the alignment structure 420 in the first layer) to align the second layer with the first layer.

[0061] Therefore, the first layer shape data may include a fitted alignment model, which has been fitted to the first / lower layer with markers to align the second / upper layer with the first layer, such that the first layer shape data describes the shape of the first layer.

[0062] First layer alignment error AL e1 (Describing the alignment error between the second and first layers (e.g., especially due to alignment structure deformation or modeling errors)) may include the first layer shape data AL. S1 The difference between the first layer pattern displacement PD1 and the second layer pattern displacement PD1 caused by exposure is also shown. E2 In this example, it is assumed that the second layer structure 400 has not yet been processed and therefore has not yet undergone second layer pattern displacement caused by the process (second layer metering after processing / etching is also possible). Furthermore, the shape Ali2 caused by second layer alignment can be caused in particular by alignment structure deformation or modeling errors of the alignment structure 420 and / or its measurement.

[0063] Overlay OV (e.g., determined via post-development inspection of ADI measured before processing steps (such as etching) of the second / last exposed layer) includes the difference between a second absolute position metric associated with a second structure in the second layer and a first absolute position metric associated with a first structure in the first layer. The first absolute position metric includes a first layer pattern displacement PD1, and the second absolute position metric includes a second layer pattern displacement PD caused by exposure. E2 The combination or sum of the shape ALi2 caused by alignment with the second layer. Therefore, direct alignment is obtained by conventional relative overlay measurements: OV = (ALi2 + PD) E2 Equation 1 - PD1 Note that if the metrology is performed after etching (e.g., post-etch inspection of AEI), the second absolute position measurement will include the second layer pattern displacement PD2 (i.e., having both exposure-induced and process-induced components). It is also understood that AEI metrology can be performed in addition to ADI metrology. If this is the case, both ADI and AEI metrology data are available, and therefore the difference in these data can be used to determine the process-induced second layer pattern displacement PD2. P2 ).

[0064] Furthermore, (e.g., conventional) alignment metering is still performed before the second layer exposure, which yields the first layer shape data ALs1. The first layer shape data ALs1 can cause and is therefore equal to the shape ALi2 caused by the second layer alignment.

[0065] Therefore, this conventional metrology does not allow for the separate determination of the first layer alignment error ALe1 and the second layer (exposure-induced) pattern displacement PD. E2 Furthermore, it is not permissible to determine the first-layer pattern displacement PD1 (and its individual exposure and processing contributions) separately. Therefore, it is recommended to perform absolute position metrology to determine the pattern displacement of the first and second layer structures separately. Based on this, one or more of these parameters can be quantized individually.

[0066] According to an embodiment, the first layer metering will generate a first layer pattern displacement PD1 (first absolute position measurement), and the second layer metering will generate a second layer pattern displacement PD caused by exposure. E2 The sum of shapes ALi2 caused by alignment with the second layer ALi2+PD E2 (Second absolute position measurement). The first and second layer measurements can be performed together, for example, using the method described in the paper published by Lee et al. described above. As previously mentioned, the (online) alignment measurement will also be performed on the alignment structure to produce the first layer shape data ALs1.

[0067] Based on the above, overlay can be defined as the difference between the second layer measurement and the first layer measurement (e.g., according to Equation 1 for the overlay OV described above). However, the following can now also be determined separately:

[0068] The alignment error (more specifically, the first-layer alignment error) can be determined as the difference between the first-layer shape data ALs1 and the first-layer pattern displacement PD1: Equation 2: ALe1 = ALs1 - PD1

[0069] Second layer pattern displacement caused by exposure (PD) E2 This can be identified as the difference between the second absolute position metric and the first layer shape data ALs1: PDE2 = (ALi2+ PD E2 Equation 3 - ALs1

[0070] First layer pattern displacement PD caused by process P1 It can be determined as the first absolute position measure or the first layer pattern displacement PD1 and the first layer pattern displacement PD caused by exposure. E1 Differences between them: PD P1 = PD1 - PD E1 Equation 4 This assumes that the exposure-induced pattern displacement (PD) of the first layer has been determined when the first layer is measured relative to the layers preceding it (e.g., ADI, i.e., preprocessing / etching). E1 In this regard, it is understood that the terms "first layer" and "second layer" are used to describe the relative relationship between the two layers, and there may be one or more layers preceding the "first layer" (or between the first and second layers). Therefore, the method described relative to the second layer and Equation 3 may have been used relative to the first layer to determine the first layer pattern displacement PD. E1 For example, according to: PD E1 = (ALi1+ PD E1 Equation 5 – ALs0 Among them (ALi1+ PD E1 ALs0 is the absolute positional measurement of the first layer before the exposure of the second layer (and before processing the first layer), and ALs0 is the measured shape (zero layer shape data) of the layer aligned with the first layer. Again, "zero layer" is used only as a relative term to "first layer," meaning the layer exposed before the first layer. The term should not be interpreted as referring to any absolute position in the stack; any number of layers may exist below and / or between the zero layer and the first layer.

[0071] Figure 5 The diagram illustrates an indirect alignment scenario, in which the first layer L1 (having a first layer structure 500) and the second layer L2 (having a second layer structure 510) are each aligned with an earlier layer L0 or the zero layer (including alignment structure 520).

[0072] Additional parameters described (overlay OV, exposure-induced second layer pattern displacement PD) E2 The shape ALi2 caused by the alignment of the second layer, and the pattern displacement PD1 of the first layer (including the contribution PD caused by exposure). E1 and the contribution of processing to PD P1The second layer measurement alignment data MA2 and the first layer shape data ALs1 are shown, along with the following parameters: the first layer measurement alignment data MA1, the shape ALi1 caused by the first layer alignment, and the second layer shape data ALs2.

[0073] In conventional indirect alignment, relative overlay will produce a second absolute position metric (ALi2+ PD). E2 The difference between (ALi1 + PD1) and the first absolute position metric (ALi1 + PD1): OV = (ALi2 + PD) E2 Equation 6: - (ALi1 + PD1)

[0074] Conventional indirect alignment measurement will also produce first layer shape data ALs1 (as measured from mark 520 in layer 0 for layer 1) and second layer shape data ALs2 (as measured from mark 520 in layer 0 for layer 2) (which are equal to the shape ALi1 caused by the first layer alignment and the shape ALi2 caused by the second layer alignment, respectively).

[0075] Using relative overlay metrology, it is impossible to determine the first layer pattern displacement PD1 and the second layer pattern displacement PD caused by exposure. E2 Or any (relative in this case) alignment error.

[0076] According to the embodiment, absolute position measurement is used for each structure in the first layer structure 500 and the second layer structure 510. The first layer measurement will produce a first absolute position measurement ALi1 + PD1, and the second layer measurement will produce a second absolute position measurement ALi2 + PD. E2 Typically, an (online) alignment measurement will also be performed on the alignment structure to generate first-layer shape data ALs1 and second-layer shape data ALs2.

[0077] Based on the above, overprinting can be defined as the difference between the second layer measurement and the first layer measurement (e.g., according to Equation 6 for the overprinting OV described above). However, the following items can now also be determined separately.

[0078] The first layer pattern displacement PD1 can be determined as the difference between (measured) the first absolute position metric and the first layer shape data ALs1: PD1 = (ALi1 + PD1) – ALs1 Equation 7

[0079] Second layer pattern displacement caused by exposure (PD) E2 This can be determined as the difference between the second absolute position metric and the second layer shape data ALs2: PD E2 = (ALi2+ PD E2Equation 8 – ALs2

[0080] In addition, assuming PD E1 Since this is known from the measurement of the first layer of an earlier layer (as already described), the process contribution of the first layer can be divided into the exposure-induced contribution and the process-induced contribution using Equation 4 in the same manner as in the direct alignment example (that is, the process-induced pattern displacement PD of the first layer can be determined). P1 ).

[0081] Furthermore, alignment error, or more specifically, relative alignment error ALe 2-1 (In this indirect alignment example, any repeated alignment errors between the first and second layers will not be included in the overlay contribution) can be identified as the difference between the second layer shape data ALs2 and the first absolute position metric ALi1+PD1: ALe 2-1 = ALi2- (ALi1+ PD P1 Equation 9 Note that ALi2 and ALi1 are derived from equations 7 and 8.

[0082] Absolute measurements are combinations of different effects (alignment, processing, and exposure). Separating these effects in the manner described allows for better use of the acquired measurements. For example, direct use of ALe1 or ALe can be performed. 2-1 Alignment formulation optimization. For example, alignment errors can be directly minimized in alignment model mapping (WAMM) or optical color weighting (OCW) methods. OCW, and related OCIW (optimized color and intensity weighting), have been put into use or proposed for correcting mark positions for process variations, such as mark asymmetry. These concepts are described in more detail in publications US2019 / 0094721, WO2017032534A2, US2020 / 0272061A1, and US2020 / 0081356A1, all of which are incorporated herein by reference. Another concept that can be directly used for alignment errors includes MCLR (Multicolor Minimum Residual), which is described in more detail in PCT publication WO2022184405A1, which is incorporated herein by reference.

[0083] Similarly, the lithography apparatus (scanner) control can directly utilize the exposure-induced error (PD). E1 PD E2 ......PD ExFor example, it can be used for exposure correction and / or calibration, such as: exposure correction (stage positioning and / or lens control and / or dose control correction), (modular) drift control, photonic model calibration and / or layer-specific wafer-in-progress (WIP) calibration.

[0084] For example, in relative overlay measurements, slow drift hardware degradation is invisible because it is applied equally to the bottom and top layers and cancels out (assuming insufficient exposure time between layers). However, when hardware components (e.g.) change between different layers, overlay penalty (WIP effect) occurs. By being able to determine the displacement caused by the absolute exposure in each layer, no longer any canceling effect appears. This information can be used to track hardware degradation. Furthermore, absolute fingerprints across different layers can be monitored to further identify scanner drift contributions.

[0085] Process control (such as etching machines or other processing equipment) can directly utilize process-guided error parameters (PDs). D1 PD D2 ......PD Dx Based on separately determined exposure process-guided errors and process-guided errors, co-optimization of lithography apparatus and processing tools is now also possible.

[0086] The above embodiments are merely examples, and other variations are possible. While the structure being measured to obtain absolute position data can be a separate substructure of one or more overlay structures, other structures including product structures may also be employed. Although top-layer metrology is not described as ADI metrology, post-processing or post-etching inspection (AEI) (e.g., attached to ADI metrology) may be used to account for effects caused by processing in the top layer.

[0087] Alignment measurement can be performed using a separate alignment station, either as an adjunct to or as an alternative to standard in-line alignment measurement using alignment sensors, such as those employed in a photolithography apparatus. In this case, alignment measurement can also be performed using other structures, such as overlay structures, bottom structures, and / or functional product structures, in addition to (or as an alternative to) the alignment structure.

[0088] It is understood that overlay measurements can be performed in two directions (often referred to as X and Y) of the substrate plane, and these two directions do not necessarily have the same layer stack. Therefore, for measurements of the same structure and / or the same layers in different directions, different alignment strategies (e.g., direct alignment vs. indirect alignment) can be applied, or the same variation can be used in each of the two directions, but aligned with different previous layers during the alignment or overlay process.

[0089] A second relevant embodiment will now be described, relating to the first layer to be exposed on the substrate, referred to herein as the “base layer”, to distinguish it from the term “first layer” used more generally in the above description.

[0090] When this base layer is exposed, the alignment structures have not yet formed because they are part of the exposed image. Therefore, any thermal deformation and / or distortion of the substrate that occurs before and / or during the exposure of this base layer cannot be detected (and corrected) by conventional substrate alignment. Moreover, because this base layer is the first layer to be exposed, it is impossible to perform overlay measurements immediately after the exposure of this layer, as overlay metrology requires the structure of two layers for quantization.

[0091] One approach to addressing one or both of these issues could use algorithms (e.g., machine learning) to detect any potential thermal problems within the lithography apparatus (e.g., a scanner) before and / or during exposure. For example, such an algorithm could consider whether thermal conditions are within specifications or indicate a potentially significant impact on substrate shape. For instance, such an algorithm could use thermal trace signals from a temperature sensor at the wafer stage core. However, there is always a trade-off between false positives and false negatives, meaning that substrates with potential thermal problems may be overlooked or substrates without problems may be incorrectly detected. Furthermore, such detection may only address certain specific underlying causes and may not reveal other causes.

[0092] Therefore, it is proposed to perform base layer metrology on the base layer structure within the base layer (e.g., using the independently described alignment station), and to use this base layer metrology to determine whether any measured deformation is correctable. The base layer structure may include, for example, an alignment structure (alignment structure) and / or an overlay structure (the bottom structure of the overlay mark). The base layer structure may additionally or alternatively include functional product structures. Correctable deformation can be a deformation for which complementary corrections can be performed during exposure of one or more subsequent layers for parameters of interest, such as ensuring overlay is within specifications (e.g., indicating the specifications of a functional device).

[0093] Basic layer metrology can be performed offline, and therefore can include high-resolution or intensive metrology to capture high-resolution feature maps (the spatial distribution of distortions on the substrate).

[0094] Based on this determination, it can be determined whether the substrate should be reprocessed, for example, when its deformation is determined to be uncorrectable, or whether it can be transferred for the next layer exposure. In the latter case, the feedforward correction for that next layer exposure can be determined by base layer metrology.

[0095] The decision to perform base layer metrology on one or more substrates can be determined using an internal detection mechanism of the lithography apparatus that measures lithography apparatus state data before / during base layer exposure. This state data may describe the thermal state of the lithography apparatus and / or the substrate exposed therein, and may also include, for example, thermal trace signals. In this embodiment, only substrates that do not exceed a certain "thermal" (or other lithography apparatus signal) detection threshold may be forwarded for base layer metrology. This can improve efficiency and reduce the cost of implementing this embodiment.

[0096] Figure 6 This is a flowchart illustrating this method. The bare substrate W has not yet undergone any exposure. B EXP exposed F (For example, within a photolithography apparatus), thus exposing the base layer thereon. The resulting substrate W, consisting only of the base layer, F One or more substrates can be selected for (e.g., offline) base layer metrology MET. OFF Optionally, the transfer substrate W can be determined based on the trigger TG generated by the signal-based detection module SBD. F To determine the implementation of basic tier metering MET OFF The SBD detection module monitors specific signals from the lithography apparatus that can indicate potential problems (e.g., thermal issues) that could cause substrate distortion. Based on the base layer metrology, it determines whether the measured feature map is a correctable FP COR (e.g., corrected by actuation of the lithography apparatus in the next / subsequent layer). If it is not determined to be correctable, the substrate can be reprocessed (RW). If the feature map is correctable, the substrate can be transferred for the next (and all subsequent) layer exposure (EXP). F+1 And, for example, conventional online overlay MET. IN And / or the overlay measurement disclosed in the first main embodiment disclosed herein (e.g., in conjunction with...) Figure 4 and Figure 5 Furthermore, (e.g., single-layer) corrected SLC can be fed forward to correct the exposure of the next layer based on the measured feature maps.

[0097] The following clauses describe aspects of the first embodiment: 1. A measurement method, comprising: Obtain a first absolute position measurement of a first structure in a first layer on a substrate and a second absolute position measurement of a second structure in a second layer on the substrate, wherein the first layer is below the second layer; Obtain first layer shape data describing the shape of the first layer; and Based on the first layer shape data, the first absolute position metric, and the second absolute position metric, one or more of the following are determined: first layer pattern displacement caused by exposure, describing the displacement error of the first structure caused by exposure of the structure; second layer pattern displacement caused by exposure, describing the displacement error of the second structure caused by exposure of the structure; first layer pattern displacement caused by process, describing the displacement error of the first structure caused by processing of the structure; and / or alignment error, describing the error in the alignment data used to align the second layer with the first layer. 2. The method according to Clause 1, comprising: determining overlay based on the difference between the first absolute position measure and the second absolute position measure. 3. The method according to Clause 1 or 2, wherein the second layer is aligned with the first layer before the second layer is exposed. 4. The method according to Clause 3, comprising: determining the second layer pattern displacement caused by the exposure based on the difference between the second absolute position metric and the first layer shape data. 5. The method according to Clause 3 or 4, comprising: determining the alignment error as the difference between the first layer shape data and the first absolute position metric. 6. The method according to any one of clauses 3 to 5, comprising: The pattern displacement of the first layer caused by exposure is determined based on the difference between another absolute position measurement of the first structure in the first layer, measured before the exposure of the second layer, and zero-layer shape data related to the layer aligned with the first layer; and The first layer pattern displacement caused by the process is determined as the difference between the first absolute position metric and the first layer pattern displacement caused by the exposure. 7. The method according to clause 1 or 2, wherein the second layer and the first layer are each aligned with a common zero layer exposed prior to the second layer and the first layer; and the method further comprises: Obtain the shape data of the second layer that describes the shape of the second layer. 8. The method according to Clause 7, comprising: describing the displacement error of the first layer pattern as a difference between the first absolute position metric and the first layer shape data. 9. The method described in Clause 8, comprising: The pattern displacement of the first layer caused by exposure is determined based on the difference between another absolute position measurement of the first structure in the first layer, measured before the exposure of the second layer, and zero-layer shape data related to the layer aligned with the first layer; and The first layer pattern displacement caused by the process is defined as the difference between the first layer pattern displacement and the first layer pattern displacement caused by the exposure. 10. The method according to any one of clauses 7 to 9, comprising: determining the second layer pattern displacement caused by the exposure as the difference between the second absolute position metric and the second layer shape data. 11. The method according to any one of clauses 7 to 10, comprising: determining the alignment error as the difference between the second layer shape data and the first absolute position metric. 12. The method according to any one of Clauses 7 to 11, comprising: determining the second layer shape data based on the second layer alignment data. 13. The method according to any one of the preceding clauses, comprising: determining the shape data of the first layer based on the first layer alignment data. 14. The method according to any one of the preceding clauses, comprising: using the first layer pattern displacement caused by the exposure and / or the second layer pattern displacement caused by the exposure to determine exposure correction, optimization and / or calibration for implementation within a photolithography apparatus. 15. The method according to Clause 14, wherein the exposure correction, optimization and / or calibration includes one or more of the following: stage positioning and / or lens control correction, drift control, photonic model calibration and / or layer-specific on-premises correction. 16. The method according to any one of the preceding clauses, comprising: using the first layer pattern displacement caused by the process to determine processing corrections, optimizations and / or calibrations to be implemented in a processing apparatus. 17. The method according to any one of the foregoing clauses includes using the alignment error to determine alignment correction optimization and / or calibration. 18. The method according to any one of the preceding clauses includes measuring the first absolute position measure and the second absolute position measure. 19. The method according to Clause 18, wherein the first absolute position measurement and the second absolute position measurement are measured using an independent alignment station or a scanning electron microscope. 20. A computer program comprising program instructions that, when executed on a suitable device, are operable to perform the method according to any one of the preceding clauses. 21. A transient computer program carrier, comprising the computer program as described in Clause 20. 22. A processing apparatus, comprising: Computer program carrier, including the computer program as described in Clause 21; and A processor, operable to run the computer program. 23. A metering device comprising the processing arrangement described in Clause 22. 24. The metering device according to Clause 22, comprising: Independent alignment station or electron microscope.

[0098] The following clauses describe aspects of the second embodiment: 1. A measurement method, comprising: Obtain base layer metrology data associated with the substrate, on which only the base layer has been exposed, the base layer comprising the first layer exposed on the substrate; the base layer metrology data describes the deformation of the substrate; and Determine whether the deformation described by the base layer metering data is correctable, so that complementary corrections can be performed on parameters of interest within specifications during exposure of one or more subsequent layers. 2. The method according to Clause 1, comprising: if the distortion is not determined to be correctable, transferring the substrate for reprocessing. 3. The method according to Clause 1 or 2, comprising: determining, based on the base layer metering data, a feedforward correction for exposure of one or more subsequent layers, the feedforward correction correcting for the distortion. 4. The method according to any one of the preceding clauses, wherein the base layer measurement data has been obtained by measuring the structure of the base layer, the structure including one or more of alignment marks, overlay structures and / or functional product structures. 5. The method according to any one of the preceding clauses, wherein the base layer measurement data has been obtained by measuring at least the nested structure. 6. The method according to any one of the preceding clauses, comprising: determining to perform base layer metrology on a particular substrate to obtain base layer metrology data based on lithography apparatus state data, the lithography apparatus state data describing the state of the lithography apparatus and / or the substrate exposed in the lithography apparatus. 7. The method according to Clause 6, wherein the photolithography apparatus state data describes the thermal state of the photolithography apparatus and / or the substrate exposed in the photolithography apparatus. 8. The method according to any one of the preceding clauses includes: performing base layer metering to obtain the base layer metering data. 9. The method according to Clause 8, wherein the base layer metering is performed offline. 10. The method according to Clause 8 or 9, comprising: performing the base layer measurement at an independent alignment station. 11. A computer program comprising program instructions that, when executed on a suitable device, are operable to perform the method according to any one of clauses 1 to 7. 12. A measuring device operable to perform the method according to any one of clauses 8 or 9. 13. The metrology equipment described in Clause 12, including an independent alignment station or an electron microscope.

[0099] Associated with the hardware of the lithography apparatus and lithography unit (LC), embodiments may include a computer program containing one or more machine-readable instruction sequences for causing the processor of the lithography manufacturing system to implement the aforementioned model mapping and control methods. This computer program may, for example, be executed in a separate computer system for image calculation / control processes. Alternatively, the calculation steps may be performed wholly or partially within the processor, metrology tools, and / or... Figure 1 and Figure 2 The program is executed in the LACU (Label Control Unit) and / or SCS (Supervisory Control System). A data storage medium (e.g., semiconductor memory, magnetic disk, or optical disk) may also be provided, in which the computer program is stored transiently.

[0100] Although the use of embodiments of the invention in the context of optical lithography has been specifically mentioned above, it will be understood that the invention can be used in other patterning applications, such as imprint lithography. In imprint lithography, the morphology in the patterning apparatus defines the pattern created on the substrate. The morphology of the patterning apparatus can be pressed into a resist layer supplied to the substrate, and the resist is subsequently cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning apparatus is removed from the resist, leaving a pattern therein after the resist has cured.

[0101] The above description of specific embodiments will fully reveal the general nature of the invention, enabling others to easily modify and / or adapt various applications of such specific embodiments by applying knowledge within the scope of the art without departing from the general concept of the invention, without excessive experimentation. Therefore, based on the teachings and guidance set forth herein, such adaptations and modifications are intended to fall within the meaning and scope of equivalents of the disclosed embodiments. It should be understood that the wording or terminology used herein is for illustrative purposes only and not for limitation, so that the terminology or terminology of this specification will be interpreted by those skilled in the art based on the teachings and guidance.

[0102] The breadth and scope of this invention should not be limited to any of the exemplary embodiments described above, but should be defined only according to the following claims and their equivalents.

Claims

1. A metrology method comprising: obtaining a first absolute position measurement of a first structure in a first layer on a substrate and a second absolute position measurement of a second structure in a second layer of the substrate, the first layer being below the second layer; obtaining first layer shape data describing a shape of the first layer; and determining one or more of: an exposure-induced first layer pattern shift, a displacement error of the first structure resulting from exposure of the structure; an exposure-induced second layer pattern shift, a displacement error of the second structure resulting from exposure of the structure; a process-induced first layer pattern shift, a displacement error of the first structure resulting from processing of the structure; and / or an alignment error, an error in alignment data used to align the second layer to the first layer, from the first layer shape data, first absolute position measurement and second absolute position measurement. determining overlay from a difference between the first absolute position measurement and second absolute position measurement.

2. The method of claim 1, comprising:

3. The method of claim 1 or 2, wherein the second layer is aligned to the first layer prior to exposure of the second layer. determining the exposure-induced second layer pattern shift from a difference between the second absolute position measurement and the first layer shape data.

4. The method of claim 3, comprising: determining the alignment error as a difference between the first layer shape data and the first absolute position measurement.

5. The method of claim 3 or 4, comprising:

6. The method of any one of claims 3 to 5, comprising: determining an exposure-induced first layer pattern shift from a difference between a further absolute position measurement measured prior to exposure of the second layer for the first structure in the first layer and zero layer shape data relating to the layer aligned to the first layer; and determining the process-induced first layer pattern shift as a difference between the first absolute position measurement and the exposure-induced first layer pattern shift.

7. The method of claim 1 or 2, wherein the second layer and the first layer are each aligned to a common zero layer exposed prior to the second layer and the first layer; and the method further comprises: obtaining second layer shape data describing a shape of the second layer. describing the first layer pattern shift describing a displacement error of the first structure as a difference between the first absolute position measurement and the first layer shape data.

9. The method of claim 8, comprising:

8. The method of claim 7, comprising: determining an exposure-induced first layer pattern shift from a difference between a further absolute position measurement measured prior to exposure of the second layer for the first structure in the first layer and zero layer shape data relating to the layer aligned to the first layer; and determining the process-induced first layer pattern shift as a difference between the first layer pattern shift and the exposure-induced first layer pattern shift. determining the exposure-induced second layer pattern shift as a difference between the second absolute position measurement and the second layer shape data. determining the alignment error as a difference between the second layer shape data and the first absolute position measurement. ​ 10. The method of any one of claims 7 to 9, comprising: ​ 11. The method of any one of claims 7 to 10, comprising: ​ 12. A method according to any one of the preceding claims, comprising one or more of: using the exposure-induced first layer pattern displacement and / or the exposure-induced second layer pattern displacement to determine an exposure correction, optimisation and / or calibration for implementation in a lithographic apparatus; using the process-induced first layer pattern displacement to determine a process correction, optimisation and / or calibration for implementation in a processing apparatus; and / or using the alignment error to determine an alignment correction optimisation and / or calibration.

13. A method according to any one of the preceding claims, comprising measuring the first absolute position metric and the second absolute position metric.

14. A computer program comprising program instructions operable to perform the method of any one of the preceding claims when run on a suitable apparatus.

15. A metrology apparatus comprising: a computer program carrier comprising a computer program according to claim 14; and a processor operable to run the computer program. ​

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