Method for determining sampling scheme and related measurement method

Abstract

A method of determining a sampling scheme for measuring at least one substrate or a portion thereof, the substrate undergoing a lithographic process to expose a structure on the substrate using a lithographic apparatus comprising a measurement station for measuring the substrate and an exposure station for exposing the substrate is disclosed. The method includes determining a correlation between a measurement action on the measurement station and an exposed portion of the at least one substrate; determining the expected variability of the parameters of interest related to the photoetching process according to the correlation; and determining a sampling scheme according to the expected variability.

Description

Cross-references to related applications

[0001] This application claims priority to EP application 23203062.7, filed on October 11, 2023, the entire contents of which are incorporated herein by reference. Technical Field

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

[0003] Photolithography is a process in which a photolithography device applies a desired pattern onto a substrate, typically onto a target portion of the substrate, and then various processing chemical and / or physical steps are taken to create functional features of a complex product through the patterning. The precise placement of the pattern on the substrate is a major challenge in reducing the size of circuit components and other products that can be manufactured using photolithography. In particular, the challenge of accurately measuring the features already placed on the substrate is a critical step in enabling the stacking of successive feature layers with sufficient precision to produce functional devices with high yield. Typically, 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 equipment involves a significant number of measurement or “mapping” operations prior to the actual exposure or otherwise patterning of the substrate at target locations. So-called advanced alignment models have been and will continue to be developed to more accurately model and correct the nonlinear distortion of the wafer 'mesh' caused by the processing steps and / or the lithography equipment itself.

[0005] Alignment is typically measured using alignment sensors within a lithography apparatus. Alignment sensors measure the positional information (alignment data) of periodic structures or alignment marks, allowing an alignment model to conform to this data. Alignment measurements can be applied sequentially to exposure (e.g., where the lithography apparatus has only one stage for both measurement and exposure), or at least partially simultaneously to exposure (e.g., where the lithography apparatus has separate measurement and exposure stages).

[0006] Alignment measurements are also known to be performed using a separate alignment station. Such separate alignment measurements 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 such measurements, including scanning electron microscopes, which are commonly used to measure critical dimensions (CD); and specialized tools for measuring overlay, i.e., the accuracy of alignment between 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 typically rely on providing a dedicated measurement target. For instance, one approach might require a target in the form of a simple grating, large enough that the spot produced by the measurement beam is smaller than the grating (i.e., the grating is not fully filled). In so-called reconstruction methods, the properties of the grating can be calculated by simulating the interaction between the scattered radiation and a mathematical model of the target structure. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0010] In addition to reconstructing the shape of the measurement feature, such an apparatus can also be used to measure diffraction-based overlay, as described in published patent application US2006066855A1. Diffraction-based overlay metrology using dark-field imaging at the diffraction level allows overlay measurements to be performed on smaller targets. These targets can be smaller than the illumination point 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. It is known that scatterometers tend to use light in the visible or near-infrared (IR) bands, which requires the grating pitch to be much coarser than the actual product structure, the characteristics of which are of interest. Such product features can be defined using deep ultraviolet (DUV), extreme ultraviolet (EUV), or much shorter wavelength X-ray radiation. Unfortunately, these wavelengths are generally not available for measurement.

[0011] Overlay metrology requires determining which substrates in a batch to measure, and / or the location and number of overlay targets to measure for each substrate. This should be done for each product and layer combination. The sampling scheme aims to measure the overlay in each field with sufficient accuracy so that the overlay model can be accurately matched and represent the overlay fingerprint of the product and layer combination.

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

[0013] According to a first aspect of the invention, a method is provided for determining a sampling scheme for measuring at least one substrate or a portion thereof, the substrate undergoing a photolithography process to expose a structure on the substrate using a photolithography apparatus, the photolithography apparatus including a measurement station for measuring the substrate and an exposure station for exposing the substrate; the method includes determining a correlation between a measurement action at the measurement station and the exposed portion of the at least one substrate; determining an expected variability of a parameter of interest related to the photolithography process based on the correlation; and determining a sampling scheme based on the expected variability.

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

[0015] These and other aspects and advantages of the devices and methods disclosed herein will be understood by taking into consideration the following description and accompanying drawings of exemplary embodiments. Attached Figure Description

[0016] 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 embodiments of the present invention is described; Figure 2 A lithography unit or cluster thereof is depicted in which an inspection device according to the invention can be used; Figure 3 This schematic diagram illustrates the situation based on known practices. Figure 1 The measurement and exposure processes in the equipment; and Figure 4 A method according to an embodiment of the present invention is conceptually illustrated. Detailed Implementation

[0017] Before describing the embodiments of the invention in detail, it is helpful to introduce example environments in which the embodiments of the invention may be implemented.

[0018] Figure 1A lithography apparatus LA is schematically depicted. The apparatus includes: an irradiation system (irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation 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 positioner PM configured to precisely position the patterning device according to certain parameters; two substrate stages WTa and WTb (e.g., substrate supports or substrate / wafer stages), each including multiple protrusions on a support surface and each 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 may be connected to a second positioner PW configured to precisely position the substrate according to certain parameters. A reference frame RF connects the various components and serves as a reference for setting and measuring the positions of the patterning device and the substrate and features thereon.

[0019] Irradiation 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, used to guide, shape, or control radiation. For example, reflective optical components are typically used in devices that use extreme ultraviolet (EUV) radiation.

[0020] The patterning apparatus support holds the patterning apparatus in a manner dependent on the orientation of the patterning apparatus, the design of the photolithography equipment, 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 secure the patterning apparatus. The patterning apparatus support MT can be, for example, a frame or table, which can be fixed or movable as needed. The patterning apparatus support ensures that the patterning apparatus is, for example, in the desired position relative to a projection system.

[0021] The term "patterning apparatus" as used herein should be interpreted broadly as any apparatus that can be used to impart a pattern to a radiation beam in the cross-section of the beam (such as creating 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 applied to the radiation beam may not perfectly correspond to the desired pattern in the target portion of the substrate. Typically, the pattern applied to the radiation beam will correspond to a specific functional layer in a device (such as an integrated circuit) created in the target portion.

[0022] As shown in the figure, the device is transmissive (e.g., employing a transmissive patterning device). Alternatively, the device can be reflective (e.g., employing a programmable mirror array of the type described above, or employing a reflective mask). Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. The term "mask" or "mask" as used herein may be considered synonymous with the more general term "patterning device." The term "patterning device" may also be interpreted as a means of storing pattern information in digital form for controlling such a programmable patterning device.

[0023] The term “projection system” as used herein should be interpreted broadly to include any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, provided that it applies to the exposure radiation used, or to other factors such as the use of immersion liquids or vacuum. Any use of the term “projection lens” herein may be considered synonymous with the more general term “projection system.”

[0024] Photolithography apparatuses can also be of the type in which at least a portion of the substrate can be covered by a liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquids can also be applied to other spaces within the photolithography apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system.

[0025] In operation, the irradiator IL receives a radiation beam from the radiation source SO. The source and the lithography apparatus can be separate entities, for example, when the source is an excimer laser. In this case, the source is not considered part of the lithography apparatus, and the radiation beam is delivered from the source SO to the irradiator IL with the aid of a beam delivery system BD, which includes, for example, suitable guide mirrors and / or beam expanders. In other cases, the source can be a component of the lithography apparatus, for example, when the source is a mercury lamp. The source SO and the irradiator IL, along with the beam delivery system BD (if desired), can be referred to as the radiation system.

[0026] An irradiator IL may include, for example, a modulator AD, an integrator IN, and a concentrator CO for adjusting the angular intensity distribution of the radiation beam. The irradiator can be used to adjust the radiation beam to achieve a desired uniformity and intensity distribution across its cross-section.

[0027] A radiation beam B is incident on a patterning device MA held on a patterning device support MT and patterned by the patterning device. After passing through the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C on a substrate W. With the aid of a second positioner PW and a position sensor IF (e.g., an interferometer, a linear encoder, a 2-D encoder, or a capacitive sensor), the substrate stage WTa or WTb can be moved precisely, for example, to position different target portions C within the path of the radiation beam B. Similarly, the first positioner PM and another position sensor ( Figure 1 (Not explicitly shown) can be used to precisely position the patterning device relative to the path of the radiation beam B, for example, after a mechanical retrieval from a mask library, or during scanning.

[0028] 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. While the illustrated substrate alignment structures occupy dedicated target portions, they can be located in the space between target portions (these are called scribe line alignment structures). Similarly, where more than one die is provided 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 device features within the die, in which case it is desirable that the marks be as small as possible and that different imaging or process conditions than adjacent features are not required. Alignment systems for detecting alignment structures will be described further below.

[0029] The depicted 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 applied to the radiation beam is projected onto the target portion C (i.e., 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 (de)magnification 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 apparatus and operating modes are also possible, as is known in the art. For example, stepping mode is known. In so-called “maskless” lithography, the programmable patterning apparatus remains stationary, but the pattern changes continuously, and the substrate stage WT is moved or scanned.

[0030] Alternatively, combinations and / or variations or completely different usage patterns of the above usage patterns can be adopted.

[0031] The lithography apparatus LA is a so-called dual-stage type, featuring two substrate stages WTa and WTb and two stations—an exposure station EXP on the exposure side and a measurement station MEA on the measurement side—with the substrate stages interchangeable. While one substrate on one stage is 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. This allows for a significant increase in the apparatus's throughput. In a single-stage apparatus, preparation and exposure steps need to be performed sequentially on a single stage for each substrate. Preparation steps may include mapping the surface height profile of the substrate using a leveling 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 at the measurement and exposure stations, a second position sensor can be provided to track the position of the substrate stage relative to the reference frame RF at both stations. Other arrangements are known and available instead of the dual-stage arrangement shown. For example, other lithography apparatuses are known to provide both a substrate stage and a measurement stage. These are mated together during preparation measurements and then unmolded during exposure on the substrate stage.

[0032] like Figure 2 As shown, the lithography equipment LA forms part of the lithography unit LC, sometimes also called a lithography unit or cluster, which also includes equipment for performing pre-exposure and post-exposure processes on the substrate. Traditionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH, and a baking plate BK. A substrate processor or robot RO picks up substrates from the input / output ports I / O1, I / O2, moves them between different processing devices, and then delivers them to the loading area LB of the lithography equipment. These devices (often collectively referred to as tracks) are controlled by a track control unit TCU, which in turn is controlled by a monitoring system SCS, which in turn controls the lithography equipment via the lithography control unit LACU. Therefore, different devices can be operated to maximize throughput and processing efficiency.

[0033] To ensure correct and consistent exposure of the substrate by the photolithography equipment, the exposed substrate needs to be inspected to measure characteristics such as overlay error, line thickness, and critical dimension (CD) between subsequent layers. Therefore, the manufacturing facility housing the photolithography unit (LC) also includes a metrology system (MET), which receives some or all of the substrate (W) processed in the photolithography unit. The measurement results are provided directly or indirectly to the monitoring system (SCS). If an error is detected, the exposure of subsequent substrates can be adjusted.

[0034] In metrology systems (METs), inspection equipment is used to determine the performance of a substrate, particularly how the performance of different substrates or different layers of the same substrate varies layer by layer. Inspection equipment can be integrated into lithography equipment (LA) or lithography units (LC), or it can be a standalone device. For the fastest possible measurement, it may be desirable to measure the performance of the exposed resist layer immediately after exposure. However, not all inspection equipment has sufficient sensitivity to perform useful measurements on latent images. Therefore, measurements can be performed after the post-exposure baking (PEB) step, which is typically the first step on the exposed substrate and increases the contrast between the exposed and unexposed areas 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 the exposed or unexposed areas of the resist have been removed. Furthermore, exposed substrates can be stripped and reworked to improve yield, or discarded, thus avoiding further processing of substrates known to be defective. In cases where only some target areas of the substrate are defective, further exposure should only be performed on those good target areas.

[0035] After the resist pattern is etched into the product layer, a measurement step can also be performed using a metrology system (MET). This latter possibility limits the likelihood of reworking defective substrates but can provide additional information about the performance of the overall manufacturing process.

[0036] Figure 3 The illustration shows that in Figure 1 The steps of exposing a target portion (e.g., a die) on a substrate W in a dual-stage apparatus are described first. The process according to conventional practice will be described. This disclosure is by no means limited to dual-stage apparatus of the type shown. Those skilled in the art will recognize that similar operations are performed in other types of lithography apparatus, such as those with a single substrate stage and a mating measurement stage.

[0037] The left side (measurement side) within the dashed box shows the steps performed at the measurement station MEA, while the right side (exposure side) shows the steps performed at the exposure station EXP. As mentioned above, from time to time, one of the substrate stages WTa and WTb is located at the exposure station, while the other is located at the measurement station. 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 device via a mechanism not shown. These two substrates are processed in parallel to improve the throughput of the lithography device.

[0038] First, referencing a newly loaded substrate W', which may be a previously untreated substrate, prepare it with a new photoresist for its first exposure in the lithography apparatus. However, typically, the described lithography process will only be one step in a series of exposure and processing steps, so the substrate W' has already passed through this apparatus and / or other lithography apparatuses multiple times and may require 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 and processing cycles. Each patterning step introduces positional deviations in the applied pattern, and subsequent processing steps gradually introduce distortions in the substrate and / or the pattern applied thereon. These distortions must be measured and corrected to achieve satisfactory overlay performance.

[0039] As described above, the preceding and / or subsequent patterning steps can be performed in other lithography equipment, and even in different types of lithography equipment. For example, some layers in device fabrication that require high parameters such as resolution and overlay compared to other layers with lower requirements can be performed in more advanced lithography tools. 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 by steps that replace or supplement the exposure in the lithography equipment shown. Such replacement and supplement 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 equipment for each layer.

[0040] At 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, alignment sensors AS are used to measure several alignment structures on the substrate W'. In one embodiment, these measurements are used to establish a substrate model (sometimes referred to as a "wafer grid") that maps the distribution of markers on the substrate very accurately, including any distortion relative to the nominal rectangular grid.

[0041] At step 204, a height map of the substrate height (Z) relative to the XY position is also measured using a leveling sensor LS. Initially, the height map is used solely for achieving precise focusing of the exposure pattern. However, it can also be used for other purposes.

[0042] When substrate W' is loaded, recipe data 206 is received, which defines the exposure to be performed, as well as the properties of the substrate and the patterns previously applied to it and to be applied to it. If an alignment structure on the substrate can be selected, the settings for the alignment sensor can also be selected; these selections are defined in the alignment recipe in recipe data 206. Therefore, the alignment recipe defines how to measure the position of the alignment structure and which markings are used.

[0043] At 210, substrates W' and W are swapped, so that the measured substrate W' becomes the substrate W entering the exposure station EXP. Figure 1 In the example apparatus, this exchange is performed via supports WTa and WTb within the exchange apparatus, ensuring that substrates W and W' are precisely clamped and positioned on these supports to maintain relative alignment between the substrate stage and the substrate itself. Therefore, after the stage is exchanged, determining the relative position between the projection system PS and the substrate stage WTb (formerly WTa) is necessary to utilize measurement information 202, 204 of substrate W (formerly W') during the controlled exposure steps. In step 212, mask alignment is performed using mask alignment structures M1, M2. In steps 214, 216, and 218, scanning motion and radiation pulses are applied at successive target locations on the substrate W to complete the exposure of multiple patterns.

[0044] By using alignment data and height maps acquired at the measurement station during the exposure step, these patterns are precisely aligned relative to the desired location, particularly relative to features previously placed on the same substrate (i.e., to ensure good overlay performance). In step 220, the exposed substrate (now labeled W'') is unloaded from the equipment for etching or other processing according to the exposed pattern.

[0045] To monitor whether overlay is within specifications and to provide process control corrections, overlay measurements can be performed on the exposed structure (e.g., on a proxy structure such as an overlay structure (overlay target)), although overlay measurements can be performed directly on the functional product structure; the methods described herein are applicable to either method. Therefore, in the context of this disclosure, a target can include a proxy structure specifically exposed for the purpose of measuring a parameter of interest (e.g., overlay), or any structure used for measuring a parameter of interest (e.g., overlay).

[0046] In the absence of overlay errors (and assuming perfect targeting), a DBO target will be symmetrical, and the incident measurement radiation will be diffracted evenly into each of a pair of complementary diffraction orders such 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 or the asymmetry of the measurement pupil). In practical implementations, paired biased DBO targets can be used, for example, to help distinguish overlay from other asymmetries in the target.

[0047] An alternative or complementary overlay measurement method includes image-based overlay (IBO). This method typically uses imaging techniques to measure the relative positions of structures in corresponding different layers. For example, IBO targets may include box-in-box structures, gratings (spatially separated in the substrate plane), or any other suitable structure. It is understood that since IBO targets are not diffraction-dependent, grating / periodic structures are not required.

[0048] These are merely examples of overlay measurement techniques, and it is understood that the concepts disclosed herein apply to any overlay measurement technique or any related parameter measurement technique of interest.

[0049] Exposure performed on a photolithography device or scanner (such as...) Figure 1 As shown, it is affected by so-called measurement-to-exposure (M2E) crosstalk. The movement of the chuck on the measurement side (measurement station) generates pressure waves, which affect hardware components such as lenses on the exposure side (exposure station), ultimately affecting overlay. This overlay effect is mainly manifested as an increase in overlay variation, and this effect is particularly pronounced when the measurement-side chuck must frequently accelerate and decelerate (e.g., during fine wafer alignment (FIWA) measurements).

[0050] It is understandable that timing on the measurement side is not static and has some inherent variability. For example, non-default measurements (such as process-dependent gain / offset corrections or global horizontal profile measurements) may be performed unpredictably or irregularly. Individual measurements may fail unpredictably, leading to redo or rollback. The substrate may be delivered to the measurement side with delays, which may result in different start times for the measurement sequence. Machine hardware and / or software may be upgraded or changed, resulting in different measurement sequences or faster stages with different timings.

[0051] Overlay measurements can rely on a suitable sampling scheme to be determined for all products and layer combinations. A sampling scheme can describe the measurement strategy for a specific field and / or substrate (e.g., the density of measurements and / or the location of measurements). A drawback of current sampling scheme setups is that they require costly intensive overlay measurements for each product and layer combination. A mature manufacturing facility can produce hundreds of products, each comprising dozens of layers, over a relatively short period (e.g., a few years). This can result in thousands of products and layer combinations. Depending on the strategy, intensive overlay measurements can be performed at least once or possibly multiple times for each layer (independent of the product), with multiple measurements per product and layer combination. These sampling scheme setups are typically one-off and therefore are not updated when any changes occur in the overlay of each field, such as time variations or machine upgrades mentioned in the previous paragraph.

[0052] Therefore, this paper proposes determining a sampling scheme, for example, for each field on the substrate, based on the measurement actions performed on the measurement side of the lithography apparatus when exposing fields on the exposure side. Each exposure field on the substrate can be associated with or related to a measurement action on the measurement side. The sampling scheme or measurement scheme for each exposure field can then be determined or selected based on the measurement action associated with that field (e.g., the measurement action being performed when that field is exposed). Assuming the substrate is subsequently scheduled for overlay measurements, the measurements can be performed according to the sampling scheme determined for each (or at least some) of its fields.

[0053] The correlation between measurement actions and exposure fields can be performed by comparing or correlating the timing data of the lithography apparatus on each side, for example, data logged in the apparatus log (scanner log data). Therefore, by combining the timing of measurement actions and field exposures, it is easy to determine which fields were exposed during each measurement action.

[0054] Sampling schemes can be selected based on the known or determined impact of each measurement action on overlay variability. For example, measurement actions associated with higher overlay variability can be measured more densely, while those with lower overlay variability can be measured sparsely (if any). This can be evaluated by performing each measurement action during exposure of multiple wafers (e.g., in a one-time calibration phase), measuring each of these wafers, and determining the overlay variability of each measurement action to determine calibration variability data. The overlay variability of each measurement action can also be determined from historical lithography equipment and measurement data (historical variability data). Alternatively or in combination, the overlay variability of each measurement action can be estimated based on, for example, expert knowledge. For example, overlay variability can be estimated based on known (chuck) movements associated with each measurement action, such as the number of accelerations / decelerations and / or the magnitude of accelerations / decelerations.

[0055] In another example, given the desired overlay model, the expected overlay variation for each field, and the budget for the total number of overlay measurements per wafer, the optimal sampling scheme can be determined using existing techniques, such as using uncertainty measures like normalized model uncertainty. Specifically, this approach can include minimizing normalized model uncertainty in the optimization, for example, by minimizing the impact of variations in measurements on changes in model predictions.

[0056] It can monitor any changes in the set of measurement actions and calculate their effects using any of the methods already described.

[0057] A sampling scheme is described that effectively minimizes the impact of M2E on the accuracy of the model suitable for measurement and overlay control. This sampling scheme can be dynamically (e.g., in real time) varied according to any changes in the measurement actions or measurement schedule on the measurement side.

[0058] Using the disclosed concepts, costly, intensive overlay measurements for each product and layer combination are no longer necessary, or can be significantly reduced, as the proposed method eliminates overlay variation sources from the scanner. In rework scenarios, measurement budgets can be targeted to where the benefits are greatest, such as where noise suppression is most critical. Sampling schemes can be generated using actual measurement-side timing so they automatically adapt to any changes in measurement-side timing. Users are free to experiment with alternative measurement-side settings or scanner upgrades without having to reconfigure the sampling scheme.

[0059] Figure 4 The concepts in this paper are schematically illustrated. The figure shows a substrate W comprising multiple fields 400, 410, 420, 430, 440, and 450. Shading indicates what happens on the measurement side when each field is exposed. Next to the substrate are example sampling schemes for each field according to the corresponding measurement actions. For example, the white area 450 is the static area exposed when the measurement chuck is stationary; its corresponding sampling scheme SS is the sparsest among the shown sampling schemes. The shaded field 400, exposed during the FIWA measurement action, is the most densely sampled. The other fields 410, 420, 430, and 440 correspond to other measurement actions that occur during field exposure. These include, for example, leveling 410, coarse wafer alignment (COWA) 420, encoder measurement system inconsistency (EMSI) 430, and stage alignment 440. Exemplary sampling schemes SS proposed for each of these fields are also shown, for example, the estimated impact of these measurement actions on the overlay variability within these fields.

[0060] Another measurement action with M2E effects can include loading a closed wafer on the measurement side, for example, immediately after a batch of final production wafers. This closed wafer can be a dummy wafer that ensures the chuck maintains its load, which is ideal for some lithography equipment (e.g., immersion equipment). This closed wafer can fill gaps in or at the end of a batch / batch of substrates to be exposed by the lithography equipment. However, due to M2E crosstalk, these closed wafers can cause noticeable overlay variations in the exposed wafers. This effect can be significant enough that, in addition to adapting the sampling scheme as described above, other decisions can be made regarding how to use this overlay information.

[0061] For example, if the overlay effect of any measurement action or any other action is large enough, small enough, or generally different from routine measurement actions to be unrepresentative (i.e., an outlier), then it is preferable to exclude such unrepresentative overlay measurements as the basis for feedback control. Therefore, anticipated outlier measurement data can be excluded from the processing control loop (e.g., an Advanced Process Control (APC) loop) so that the APC represents wafer performance in mass production. However, it may be desirable to actually measure these outlier fields, for example, to assess whether rework is required.

[0062] Therefore, adaptive sampling methods can predict whether a particular substrate or a portion thereof (e.g., one or more fields) might be an outlier or unrepresentative, for example, having a particularly high estimated overlay variation. It can then be decided not to simply measure these substrates and / or fields, or to designate them for monitoring only the substrate / field. Monitoring only the substrate / field will ensure that its corresponding overlay data is used solely for monitoring, such as for making rework decisions, and not for any control loop or feedback control.

[0063] Therefore, a method is proposed that transmits all lithography equipment information (i.e., post-exposure measurements, such as overlay measurements) related to the exposure of a substrate or a portion thereof (e.g., one or more fields) from the lithography equipment prior to batch measurements. This information may include details of various underlying causes, such as typical measurement sequences, identified / related measurement sequences (e.g., using the methods described above), and identified or estimated local thermal effects. The method may include estimating whether anomalous fingerprint variations are expected on the substrate and / or any fields thereon. The method may then determine to exclude any measurement data associated with substrates and / or fields expected to have anomalous fingerprint variations for feedback control. As previously described, this may include not measuring such substrates and / or fields, or identifying them for monitoring only.

[0064] In conjunction with the hardware of the lithography equipment and the lithography unit (LC), one embodiment may include a computer program containing one or more machine-readable instruction sequences for instructing a processor of the lithography manufacturing system to implement the model mapping and control methods described above. This computer program may, for example, be executed in a separate computer system for the image calculation / control process. Alternatively, the calculation steps may be performed in a processor, measurement tool, and / or... Figure 1 and Figure 2 The computer program is executed, in whole or in part, within the control unit (LACU) and / or monitoring system (SCS). A data storage medium (e.g., semiconductor memory, magnetic disk, or optical disk) may also be provided, which stores the computer program in a non-transitory form.

[0065] Other embodiments of the present invention are disclosed in the list of numbered clauses mentioned below: 1. A method for determining a sampling scheme for measuring at least one substrate or a portion thereof, the substrate undergoing a photolithography process to expose a structure on the substrate using a photolithography apparatus, the photolithography apparatus including a measurement station for measuring the substrate and an exposure station for exposing the substrate; the method comprising: Determine the correlation between the measurement actions at the measurement station and the exposed portion of the at least one substrate; Based on the correlation, determine the expected variability of the parameters of interest related to the lithography process; and The sampling scheme is determined based on the expected variability. 2. The method according to Clause 1, wherein determining the correlation includes determining which measurement actions the measurement station performs during each exposure portion of the at least one substrate at the exposure station. 3. The method according to Clause 1 or 2, wherein determining the correlation includes comparing timing data from the measurement station and the exposure station of the lithography apparatus. 4. The method according to any one of the foregoing clauses, wherein the sample density of the sampling scheme of the substrate or a portion thereof depends on the expected variability. 5. The method according to any one of the preceding clauses, wherein the sample density of the sampling scheme is increased to increase the expected variability. 6. The method according to any one of the preceding clauses, wherein: the budget for the expected parameter of interest model, the expected parameter of interest variation for each region, and the total number of parameter measurements for each wafer: Determine the uncertainty measure for various sampling schemes, and The sampling scheme is determined to be the one that minimizes the uncertainty metric. 7. The method according to Clause 6, wherein the uncertainty measure is normalized model uncertainty. 8. The method according to any one of the preceding clauses, wherein determining the expected variability includes determining the expected variability by referring to historical variability data and / or calibration variability data related to the lithography process. 9. The method according to any one of the preceding clauses, wherein determining the expected variability comprises determining the expected variability based on known motion associated with each measurement action. 10. The method according to any one of the preceding clauses, wherein the parameter of interest is overlay. 11. The method according to any one of the preceding clauses includes assessing whether the expected variability is representative or an outlier; and excluding any measurement data associated with the substrate and / or a portion thereof that is assessed as an outlier from the feedback control of the lithography process. 12. The method according to Clause 11, wherein the exclusion of measurement data includes not measuring the substrate and / or portions thereof that are evaluated as outliers. 13. The method according to Clause 11, wherein the exclusion of measurement data includes specifying that the substrate and / or a portion thereof evaluated as an outlier is used only for monitoring, such that the substrate or a portion thereof is measured, but the resulting measurement data is not used for the feedback control of the lithography process. 14. The method according to Clause 13, wherein the obtained measurement data is evaluated to determine whether the substrate requires rework. 15. The method according to any one of the preceding clauses, wherein each of the said portions includes an exposure field. 16. The method according to any one of the preceding clauses, wherein the method is performed in real time during the photolithography process, such that the sampling scheme is dynamically determined in response to any unscheduled measurement action or changes in the schedule and / or timing of measurement actions performed on each substrate. 17. The method according to any one of the preceding clauses includes measuring the substrate or a portion thereof according to the sampling scheme. 18. A method for measuring on one or more substrates, each substrate undergoing a photolithography process to expose a structure on the substrate using a photolithography apparatus in the photolithography process; the method comprising: Prior to post-exposure measurements on the substrate, acquire lithography equipment information related to the lithography process and / or lithography equipment; The expected variability of the parameters of interest is determined based on the lithography equipment information; and This includes assessing whether the expected variability is representative or an outlier; and Any measurement data related to the substrate and / or portions thereof that are evaluated as outliers are excluded from the feedback control of the photolithography process. 19. The method according to Clause 18, wherein the exclusion of measurement data includes not measuring the substrate and / or portions thereof that are evaluated as outliers. 20. The method according to Clause 18, wherein the exclusion of measurement data includes specifying that the substrate and / or a portion thereof evaluated as an outlier is used only for monitoring, such that the substrate or a portion thereof is measured, but the resulting measurement data is not used for the feedback control of the lithography process. 21. The method according to any one of Clauses 18 to 20, wherein the obtained measurement data is evaluated to determine whether the substrate requires rework. 22. The method according to any one of clauses 18 to 21, wherein each of the said portions includes an exposure field. 23. The method according to any one of Clauses 18 to 22, wherein the parameter of interest is overlay. 24. A computer program comprising program instructions that, when run on a suitable device, are operable to perform the method according to any one of the preceding clauses. 25. A non-transitory computer program carrier, comprising the computer program described in Clause 24. 26. A processing apparatus, comprising: A computer program carrier including a computer program as described in Clause 25; and A processor, operable to run the computer program. 27. A photolithography apparatus, comprising: A measurement station for measuring the substrate; An exposure station for exposing the substrate; and The processing apparatus is operable to perform the method according to any one of clauses 1 to 16. 28. A photolithography unit, comprising: The lithography equipment as described in Clause 27; and A measuring device operable to perform the measurement as described in Clause 17.

[0066] Although specific reference has been made above to embodiments of the invention in the context of optical lithography, it should 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 a pattern created on a substrate. The morphology of the patterning apparatus can be pressed into a resist layer supplied to the substrate, and then the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has cured, the patterning apparatus is removed from the resist to leave a pattern therein.

[0067] The above description of specific embodiments will fully reveal the general nature of the invention, enabling others to readily modify and / or adapt these specific embodiments for various applications by applying knowledge within the scope of the art, without departing from the overall concept of the invention and without excessive experimentation. Therefore, based on the teachings and guidance set forth herein, such adaptations and modifications are intended to be within the equivalent meaning and scope of the disclosed embodiments. It should be understood that the wording or terminology in this specification is for illustrative purposes only and not for limitation, and that the terminology or terminology of this specification will be interpreted by those skilled in the art based on the teachings and guidance.

[0068] The breadth and scope of this invention should not be limited by any of the exemplary embodiments described above, but should be defined only by the following claims and their equivalents.

Claims

1. A method for determining a sampling scheme for measuring at least one substrate or a portion thereof, the substrate undergoing a photolithography process to expose a structure on the substrate using a photolithography apparatus, the photolithography apparatus including a measurement station for measuring the substrate and an exposure station for exposing the substrate; the method comprising: Determine the correlation between the measurement actions at the measurement station and the exposed portion of the at least one substrate; The expected variability of the parameters of interest related to the lithography process is determined based on the correlation. as well as The sampling scheme is determined based on the expected variability.

2. The method according to claim 1, wherein determining the correlation comprises: During the exposure of each exposure portion of the at least one substrate at the exposure station, it is determined which measurement actions are performed at the measurement station.

3. The method of claim 1, wherein determining the correlation comprises comparing timing data from the measurement station and the exposure station of the lithography apparatus.

4. The method of claim 1, wherein the sample density of the sampling scheme of the substrate or a portion thereof depends on the expected variability.

5. The method of claim 1, wherein the sample density of the sampling scheme is increased to increase the expected variability.

6. The method according to claim 1, further comprising: Budget for the expected parameter model, the expected parameter variation for each region, and the total number of parameter measurements for each wafer: Determine the uncertainty measure for various sampling schemes, and The sampling scheme is determined to be the one that minimizes the uncertainty metric.

7. The method of claim 6, wherein the uncertainty measure is normalized model uncertainty.

8. The method of claim 1, wherein determining the expected variability includes determining the expected variability by referring to historical variability data and / or calibration variability data related to the lithography process.

9. The method of claim 1, wherein determining the expected variability comprises determining the expected variability based on known motions associated with each measurement action.

10. The method of claim 1, wherein the parameter of interest is overlay.

11. The method of claim 1, comprising assessing whether the anticipated variability is representative or an outlier; and excluding any measurement data associated with the substrate and / or a portion thereof that is assessed as an outlier from the feedback control of the lithography process.

12. The method of claim 11, wherein excluding measurement data includes not measuring the substrate and / or portions thereof that are evaluated as outliers.

13. The method of claim 11, wherein excluding measurement data includes specifying that the substrate and / or a portion thereof evaluated as an outlier is used only for monitoring, such that the substrate or a portion thereof is measured, but the resulting measurement data is not used for the feedback control of the photolithography process.

14. The method of claim 13, wherein the obtained measurement data is evaluated to determine whether the substrate requires rework.

15. A computer program comprising program instructions that, when run on a suitable device, are operable to perform the method according to any one of claims 1 to 6.

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