Method of tilt measurement and associated device

Abstract

A metrology method is disclosed, comprising: obtaining metrology data relating to a measurement of at least one target, each of the at least one target comprising a plurality of features; the measurement data describe placement errors of one or more pairs of respective features of the at least one target, each pair of features of the one or more pairs of respective features comprising a plurality of pairs of features substantially equidistant from a reference point on the target in a measurement direction of the target; determining an asymmetric component of the placement error from the measurement data; and determining a tilt parameter from the asymmetric component.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European application 22203387.0 filed on October 24, 2022, and the entire contents of this European application are incorporated herein by reference. Technical Field

[0003] The present invention relates to methods and apparatus for applying patterns to substrates during a lithographic process, and more particularly, inspecting such patterns once applied. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (usually to a target portion of the substrate). A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a pattern forming device (which is alternatively referred to as a mask or reticle) can be used to produce a circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., a portion including a die, a die, or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed via imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will include a network of adjacent target portions that are patterned in succession. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at once; and so-called scanners, in which each target portion is irradiated by scanning the substrate synchronously in a given direction (the "scanning" direction) while scanning the pattern via a radiation beam parallel or antiparallel to such a direction. It is also possible to transfer a pattern from a pattern forming device to a substrate by imprinting the pattern onto the substrate.

[0005] To monitor the lithography process, parameters of the patterned substrate are measured. For example, the parameters may include the overlay error between successive layers formed in or on the patterned substrate, and the critical line width or critical dimension (CD) of the developed photoresist. Such measurements may be performed on production substrates and / or on dedicated measurement targets. Various techniques exist for measuring microstructures formed during the lithography process, including the use of scanning electron microscopes and various specialized tools.

[0006] When performing a lithographic process such as applying a pattern on a substrate or measuring such a pattern, process control methods are used to monitor and control the process. Such process control techniques are often performed to obtain corrections to the control of the lithographic process. It would be desirable to improve such process control methods.

[0007] An important parameter associated with the proper operation of devices (e.g., integrated circuits) formed by such lithographic processes is known as tilt. Tilt refers to the unintended tilt of vertical features (perpendicular to the substrate plane) in the patterned substrate relative to the z-direction (vertical axis). This can be particularly a problem for features that include high aspect ratios, such as (for example) contact holes. Large tilts can cause contact holes of consecutive layers to be improperly aligned, resulting in poor contact or even no contact.

[0008] Such process control methods typically rely on inspection or measurement of the exposed pattern using, for example, a scatterometer or scanning electron microscope. Scatterometer-based tilt metrology requires lengthy and complex training and calibration to obtain the relationship between the measured values ​​and the tilt values. Tilt metrology using a SEM is known; however, such methods require physical tilting of the substrate, which is time consuming and therefore not feasible for monitoring in high volume manufacturing scenarios.

[0009] It would be desirable to improve such tilt measurement methods. Summary of the invention

[0010] In a first aspect of the present invention, a measurement method is provided, comprising: obtaining measurement data related to the measurement of at least one target, each of the at least one target comprising a plurality of features; the measurement data describing placement errors of one or more pairs of corresponding features of the at least one target, each pair of features in one or more pairs of corresponding features comprising a pair of features that are approximately equidistant from a reference point on the target in a measurement direction of the target; determining an asymmetric component of the placement error from the measurement data; and determining a tilt parameter from the asymmetric component.

[0011] In a second aspect of the present invention, there is provided a computing device comprising a processor and configured to execute the method of the first aspect.

[0012] In a third aspect of the invention there is provided an inspection apparatus operable to image a plurality of features on a substrate and comprising the computing apparatus of the second aspect.

[0013] In a fourth aspect of the present invention there is provided a computer program comprising program instructions operable to perform the method of the first aspect when run on a suitable device.

[0014] In a fifth aspect of the present invention, a substrate is provided, comprising a target arrangement, the target arrangement comprising at least one target for measuring a tilt parameter, each of the target comprising a plurality of features; wherein the spacing between the features of the target is larger between at least some of the features farther away from the center of the target than between the features closer to the center of the target.

[0015] The following describes in detail other aspects, features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Based on the teachings included herein, (multiple) relevant art technicians will understand additional embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0017] Figure 1 depicts a lithographic apparatus along with other equipment forming a production facility for semiconductor devices;

[0018] Figure 2 The diagram shows the goals that undergo different processes, illustrating the ideas underlying the proposed approach;

[0019] Figure 3 is a plot of placement error versus target position for a target not subjected to a global tilt component and a target subjected to a global tilt component;

[0020] Figure 4 illustrates a target arrangement according to an embodiment; and

[0021] Figure 5 A pattern for forming a target arrangement according to an embodiment is illustrated. DETAILED DESCRIPTION

[0022] Before describing embodiments of the invention in detail, it is instructive to present an example environment that can be used to implement embodiments of the invention.

[0023] Figure 1 At 200, a lithographic apparatus LA is shown as a component of an industrial production facility that implements a high-volume lithographic manufacturing process. In this example, the manufacturing process is adapted for manufacturing semiconductor products (integrated circuits) on substrates such as semiconductor wafers. It will be appreciated by those skilled in the art that a wide variety of products can be manufactured by processing different types of substrates with variations of this process. The production of semiconductor products is used only as an example that has greater commercial significance today.

[0024] Within a lithographic apparatus (or, in short, a "lithography tool" 200), a measurement station MEA is shown at 202 and an exposure station EXP is shown at 204. A control unit LACU is shown at 206. In this example, each substrate visits a measurement station and an exposure station to have a pattern applied. For example, in an optical lithography apparatus, a projection system is used to transfer a product pattern from a patterning device MA to a substrate using conditioned radiation and a projection system. This transfer is accomplished by forming an image of the pattern in a layer of radiation-sensitive resist material.

[0025] The term "projection system" as used in the present invention should be broadly interpreted to cover any type of projection system suitable for the exposure radiation used or for other factors such as the use of immersion liquid or the use of vacuum, including refractive, reflective, reflective-refractive, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof. The patterned MA device can be a mask or mask that imparts a pattern to a radiation beam transmitted or reflected by the pattern forming device. Well-known operating modes include stepping mode and scanning mode. It is well known that the projection system can cooperate with the support and positioning system for the substrate and the pattern forming device in a variety of ways to apply the desired pattern to many target portions across the substrate. A programmable pattern forming device can be used instead of a mask with a fixed pattern. Radiation (for example) can include electromagnetic radiation in the deep ultraviolet (DUV) or extreme ultraviolet (EUV) band. The present invention is also applicable to other types of lithography processes, such as (for example) imprint lithography and direct write lithography by electron beam.

[0026] The lithographic apparatus control unit LACU controls all movements and measurements of the various actuators and sensors to receive the substrate W and mask MA and perform patterning operations. The LACU also includes signal processing and data processing capabilities for performing desired calculations related to the operation of the apparatus. In practice, the control unit LACU will be implemented as a system of many sub-units, each of which delivers real-time data acquisition, processing and control of a subsystem or element within the apparatus.

[0027] Before the pattern is applied to the substrate at the exposure station EXP, the substrate is processed at the measurement station MEA so that various preparatory steps can be performed. The preparatory steps may include using a level sensor to map the surface height of the substrate, and using an alignment sensor to measure the position of the alignment marks on the substrate. The alignment marks are nominally arranged in a regular grid pattern. However, due to the inaccuracy of the marks produced and also due to the deformation of the substrate that occurs throughout its processing, the marks deviate from the ideal grid. Therefore, in the case where the device should print product features at the correct position with very high accuracy, in addition to measuring the position and orientation of the substrate, the alignment sensor must also measure the positions of many marks across the substrate area in detail in practice. The device may belong to the so-called dual-platform type with two substrate stages, each of which has a positioning system controlled by a control unit LACU. While exposing one substrate on one substrate stage at the exposure station EXP, another substrate can be loaded onto another substrate stage at the measurement station MEA, so that various preparatory steps can be performed. Therefore, the measurement of the alignment marks is very time-consuming, and providing two substrate stages will achieve a considerable increase in the production volume of the device. The lithographic apparatus LA may, for example, be of a so-called dual stage type having two substrate tables and two stations - an exposure station and a measurement station - between which the substrate table is exchangeable.

[0028] Within the production facility, the apparatus 200 forms part of a "lithography cell" or "lithography cluster" which also includes a coating apparatus 208 for applying photoresist and other coatings to a substrate W for patterning by the apparatus 200. At the output side of the apparatus 200, a baking apparatus 210 and a developing apparatus 212 are provided for developing the exposed pattern into a physical resist pattern. Between all these apparatuses, a substrate transport system is responsible for supporting the substrate and transferring the substrate from one apparatus to the next. These apparatuses, which are generally collectively referred to as track or coating and developing systems, are under the control of a track or coating and developing system control unit, which itself is controlled by a management control system SCS, which also controls the lithography apparatus via a lithography apparatus control unit LACU. Thus, different apparatuses can be operated to maximize throughput and process efficiency. The management control system SCS receives recipe information R which provides a very detailed definition of the steps to be performed to produce each patterned substrate.

[0029] Once the pattern has been applied and developed in the lithography unit, the patterned substrate 220 is transferred to other processing equipment (such as illustrated at 222, 224, 226). A wide range of processing steps are implemented by various equipment in a typical manufacturing facility. For example, the equipment 222 in this embodiment is an etching station, and the equipment 224 performs a post-etching annealing step. Additional physical and / or chemical processing steps are applied in additional equipment 226, etc. Many types of operations may be required to manufacture real devices, such as deposition of materials, modification of surface material properties (oxidation, doping, ion implantation, etc.), chemical mechanical polishing (CMP), etc. In practice, the equipment 226 can represent a series of different processing steps performed in one or more equipment. As another example, equipment and processing steps for implementing self-aligned multi-patterning can be provided to produce multiple smaller features based on the precursor pattern laid by the lithography equipment.

[0030] As is well known, the manufacture of semiconductor devices involves many repetitions of such processing to create device structures with appropriate materials and patterns layer by layer on the substrate. Therefore, the substrate 230 arriving at the lithography cluster may be a newly prepared substrate, or the substrate 230 may be a substrate that has been completely processed previously in the cluster or in another device. Similarly, depending on the required processing, the substrate 232 leaving the device 226 may be returned for subsequent patterning operations in the same lithography cluster, the substrate 232 may be designated for patterning operations in a different cluster, or the substrate 232 may be a finished product to be sent for dicing and packaging.

[0031] Each layer of the product structure requires a different set of process steps, and the equipment 226 used at each layer can be completely different in type. In addition, even if the processing steps to be applied by the equipment 226 are nominally the same in a larger facility, there may be several assumed identical machines working in parallel to perform steps 226 on different substrates. Small differences in settings or failures between these machines may mean that these machines affect different substrates in different ways. Even steps that are relatively common to each layer, such as etching (equipment 222), can be implemented by several etching equipment that are nominally the same but work in parallel to maximize production. In addition, in practice, different layers require different etching processes, such as chemical etching, plasma etching, depending on the details of the material to be etched, and require specific requirements, such as (for example) anisotropic etching.

[0032] Previous and / or subsequent processes may be performed in other lithographic equipment as just mentioned, and may even be performed in different types of lithographic equipment. For example, some layers in the device manufacturing process that are very demanding on parameters such as resolution and overlay may be performed in more advanced lithographic tools than other layers that are less demanding. Thus, some layers may be exposed in immersion-type lithographic tools, while other layers are exposed in "dry" tools. Some layers may be exposed in tools operating at DUV wavelengths, while other layers are exposed using EUV wavelength radiation.

[0033] In order to correctly and consistently expose the substrate exposed by the lithography equipment, it is desirable to inspect the exposed substrate to measure properties, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), etc. Therefore, the manufacturing facility in which the lithography unit LC is located also includes a measurement system that receives some or all of the substrates W that have been processed in the lithography unit. The measurement results are provided directly or indirectly to the management control system SCS. If an error is detected, especially when the measurement can be completed quickly and quickly enough so that other substrates of the same batch are still to be exposed, the exposure of subsequent substrates can be adjusted. In addition, the already exposed substrates can be stripped and reworked to improve the yield or discarded, thereby avoiding further processing of substrates that are known to be defective. In the case where only some target portions of the substrate are defective, further exposure can be performed only on those target portions that are good.

[0034] Figure 1 Also shown is a metrology device 240, which is provided for measuring parameters of the product at desired stages in the manufacturing process. A common example of a metrology station in a modern lithography production facility is a scatterometer, such as a dark field scatterometer, an angle resolved scatterometer or a spectral scatterometer, and a scatterometer can be applied to measure the properties of the developed substrate before the substrate is etched in the device 222 at 220. With the use of the metrology device 240, it can be determined that important performance parameters such as overlay or critical dimension (CD) do not meet specified accuracy requirements in the developed resist. Prior to the etching step, there is an opportunity to strip the developed resist and reprocess the substrate 220 via the lithography cluster. By making small adjustments over time by the supervisory control system SCS and / or the control unit LACU 206, the metrology results 242 from the device 240 can be used to maintain accurate execution of patterning operations in the lithography cluster, thereby minimizing the risk of producing defective products and requiring rework.

[0035] Another example of a metrology station is a scanning electron microscope (SEM), otherwise known as an electron beam (e-beam) metrology device, which may be included in addition to or as an alternative to a scatterometer. Thus, the metrology equipment 240 may include an e-beam or SEM metrology device alone or in addition to a scatterometer. SEM metrology devices have the advantage of directly measuring features (i.e., SEM metrology devices directly image the features), rather than indirect measurement techniques used in scatterometry (where parameter values ​​are determined from reconstructions from the structure being measured and / or from asymmetries of diffraction orders of radiation diffracted by the structure being measured). SEM tools scan across a sample area with one or more electron beams to produce an image of the area.

[0036] Additionally, metrology equipment 240 and / or other metrology equipment (not shown) may be applied to measure properties of processed substrates 232, 234 and upcoming substrate 230. Metrology equipment may be used on processed substrates to determine important parameters such as overlay or CD.

[0037] In addition to overlap and CD, at least for some devices, another important parameter to be monitored is a parameter often referred to as tilt or etch tilt, that is, the degree of tilt of features such as high aspect ratio (high) features away from the vertical (z axis, perpendicular to the substrate plane). Such features can be contact holes or any other structures formed via lithography and etching. Such high aspect ratio features can be formed in so-called 3D structures for memory devices (e.g., 3D NAND). Such structures can use high aspect ratio channels or contact holes, which are produced by exposing an initial pattern and etching downward from the exposed pattern (e.g., reactive ion etching). Ideally, etching should be vertical to obtain vertical contact holes. However, for a number of reasons (e.g., due to proximity effects), the etched contact hole channel may deviate from vertical, which means that the etched contact hole is tilted. If the etched contact hole tilts too much, the contact hole may fail to contact the structure (e.g., another contact hole) intended for the contact hole, resulting in the device being unable to work. It should be noted that while this specification will largely describe the disclosed concepts in terms of contact holes or etched vias, the concepts are applicable to any structure formed via a lithographic process (eg, photolithography and etching) and subject to etch tilting.

[0038] There are currently multiple methods for measuring etch tilt. One method uses a scatterometer to image the current structure to obtain a pupil image (angle-resolved image or "pupil"). Calibration or training can be performed as an initial step to learn the mapping of these pupils to tilt values. However, this training is complex and requires a complete experimental analysis design, thereby reducing the availability of the scanner and the overall throughput of the lithography plant. Another method can use a scanning electron microscope (SEM) or similar device (e.g., a transmission electron microscopy device) to directly measure the tilt during the measurement using a tilted beam (relative to the substrate). However, this method is typically time-consuming, which is not feasible for monitoring in high-volume manufacturing scenarios.

[0039] After lithographic exposure, the actual position of the printed feature will be at (or very close to) the designed position of the printed feature. However, after etching and in the absence of a global tilt component due to etching, the placement errors of multiple pairs of features that are equidistant (either side) from the center reference in the direction of interest (e.g., due to proximity effects) will tend to be equal in magnitude but opposite in direction. Thus, the outer columns of features will tend to shift outward or inward (depending on the process) after etching; the effects of this situation tend to be symmetrical. However, the presence of a global tilt component will produce measurable additional placement errors. Especially in the outer rows, the profile of the placement error including this additional component will be asymmetric. It is proposed that the global etching tilt can be quantified by measuring and calculating this asymmetric component in the placement error. By quantifying the tilt, the yield can be predicted, and / or corrections (e.g., scanner and / or etcher corrections) for later wafers / batches can be determined, which reduce the tilt and / or mitigate the tilt (e.g., in the case of taking into account the determined tilt, other position corrections are determined to ensure proper contact in the continuous layer).

[0040] A metrology method is proposed that addresses the shortcomings of prior art methods such as those described. The method may include measuring one or more targets or feature sets (e.g., one or more lines or 1D feature arrays) using a metrology device such as a SEM (or any other metrology device capable of measuring placement errors) to measure the placement errors of one or more pairs of corresponding external features of each feature set. The degree of tilt (tilt parameter value) may then be determined from the difference in placement errors of corresponding features of one or more pairs of corresponding features (e.g., features other than a center feature assuming an odd number of features). A pair of corresponding features may include features that are on either side of a reference point such as the center of the target in the measurement direction of the target and are approximately equidistant from the reference point.

[0041] For example, the difference of the outermost feature pairs can be used (e.g., the difference between the placement errors of the first feature of the row and the last feature of the row). Alternatively, the differences between other pairs of corresponding features can be used (e.g., the pairs including the second feature from either end of the row, the pairs including the third feature from either end of the row, etc.).

[0042] The corresponding differences from more than one pair of corresponding features may be averaged to determine the tilt value, or else the curve asymmetry may be integrated over the differences of all corresponding pairs of features (or a subset thereof) outside the center feature (or reference feature).

[0043] Multiple (eg, similar) feature sets may be provided so that the tilt values ​​may be averaged across the sets to average out the SEM noise.

[0044] The placement error may be related to the placement error after etching and hard mask removal, for example measured using a top-down SEM measurement. This may be referenced to a reference position or expected position (e.g., to a file including GDS (graphic design system) information or other reference).

[0045] The features of each feature set may be evenly spaced. Alternatively, the spacing between at least some of the outer features may be larger relative to the inner features. For example, the spacing between the features may increase from the center outward. In this way, asymmetry may be increased and thus detection sensitivity may be amplified.

[0046] If height or thickness data is provided (e.g. using trigonometric functions), the relative tilt value determined from the difference can be converted into an absolute tilt value (e.g. in terms of angle). Such height data may include at least the hard mask height (etch depth height), i.e., to determine the hard mask tilt (actual tilt within the hard mask layer). Thus, this metrology method enables the actual tilt angle introduced by the system to be measured, and the scanner / etcher options to be modified accordingly to eliminate / mitigate said feature marking.

[0047] If the hard mask is etched with the same chemistry and etcher as the feature, then the hard mask tilt will be the same as the feature tilt (the tilt of the entire feature under the hard mask), and the feature tilt can therefore be extrapolated accordingly. Figure 2 The illustrated scenario. The hard mask may be etched with a different chemistry than the feature etch but in the same etch chamber. In such a case, the hard mask tilt is still very likely to be the same as the actual tilt of the feature, so that any difference in tilt can be ignored. In the case where the hard mask is etched with a different chemistry than the feature etch and in a different etch chamber, the measured hard mask etch is not truly indicative of the feature etch. However, this is uncommon.

[0048] The proposed feature set (s) may be included on a product mask and thus printed on a production substrate. Based on measurements of a substrate exposed using such a mask, feature identification of the tilt across the substrate may be obtained. In an embodiment, the calculation of the tilt may be normalized so that the average across the substrate is zero. This operation may be performed to remove any offset that is not of interest so as to obtain a tilt signal whose sign is preserved. Alternatively, if the absolute degree or angle of tilt is of interest rather than the direction of the tilt, an absolute value may be used.

[0049] The number of columns of features in the measurement direction can be any number of features, however, an odd number of features (i.e., three or more) is preferred. Where there are an odd number of features, the center feature or reference feature may be similar to the other features, or may be different; for example, the center feature or reference feature is larger to provide a stronger reference. Providing an odd number of rows greater than three enables better characterization of the asymmetry due to tilt, because the relationship between the asymmetry and the distance can be better determined. This can improve the accuracy of the tilt measurement by averaging or integrating a larger number of measurements. The number of rows of features per target may, for example, be five or more, seven or more, nine or more, eleven or more, thirteen or more, fifteen or more, seventeen or more, or nineteen or more.

[0050] The feature set may be oriented in each direction perpendicular to the plane of the substrate (ie, to measure tilt in both the x-direction and the y-direction of the substrate coordinate system).

[0051] Figure 2 The concept underlying the proposed method is illustrated. The top of the figure shows a collection of features printed on a substrate (e.g., after development but before etching), i.e., the collection of features forms a target 280. Each feature 285 is substantially located at its intended location, with the center of each feature 285 represented here by a dashed line. In the specific example shown, each feature 285 will be a contact hole (i.e., each feature 285 is an imaged pattern in the resist for forming a contact hole), and the target 280 includes nine contact holes. However, the features may, for example, include lines of a line-space target or any other array of similar features.

[0052] Below this, a first etched target 290 (e.g., comprising a contact hole in this example) is shown for a situation where there is no global tilt component. The first etched target 290 may be the result of performing an etching step on the target 280. For all features except the center feature, there is a placement error, where the placement error increases outward from the center of the target. While this displacement is shown as being fairly linear in the illustrative example, the effect is generally non-linear, where features near the center generally experience the smallest placement error, and placement errors increase significantly away from the center region. This situation is not particularly evident in FIG. Figure 3 , which is illustrated in a graph 300 showing placement errors PE relative to rows or positions R (within the target) for such a first etched target 290 (i.e., without a global tilt component). It is particularly noteworthy that such shift or displacement errors are roughly symmetrical throughout the target as a whole (with no placement error at the center of the target). Thus, for example, the magnitude of the placement error for each of a plurality of pairs of corresponding features is roughly the same. A pair of corresponding features in such a scenario may include features that are roughly equidistant from the center of the target in the measurement direction or direction of interest. Thus, in the first etched target 290, features in the first row are shifted by the same amount as features in the ninth row, as are features in the second row and the eighth row, and so on. From Figure 3 This symmetry is also apparent from the graph 300 in FIG.

[0053] Figure 2 Also shown is a second etched target 295, which is an example of a target that may be seen when a global tilt component is present. Like the first etched target 290, this second etched target 295 may be the result of an etching step performed on the target 280, with the difference that a global tilt component is now present. This global tilt component may be measured using the proposed method. The overall placement error is given by Figure 3 300 (i.e., associated with the first etched target 290) illustrates a combination of placement errors (symmetrical across the target) and a global tilt component. However, the global tilt component induces an asymmetric shift across the target, such that the placement errors in the first row of features (in this particular example) have a larger magnitude than the placement errors of the features in the ninth row. This global tilt component can be isolated from other effects and is therefore measured by taking the difference in placement errors of features on either side of the center or center feature of the target (in this particular example, the reference feature or feature 5).

[0054] In particular, the difference in placement error between features in one or more pairs of corresponding features may be used. In the simplest embodiment, this may include taking the difference from the outermost features (e.g., the placement error from the features in the first and ninth rows in the particular example) or another pair of corresponding features (the outermost features will show the greatest sensitivity, but any pair of corresponding features may be used. As already described, other methods of determining a global tilt component may be used based on any measurement or determination of asymmetry in the target, including averaging or integrating the asymmetry across multiple pairs of corresponding features. Figure 3 Also shown is a graph 310 of placement error PE versus column R for such a second etched target 295 having a global tilt component. From such a graph, the target asymmetry is clear.

[0055] The target arrangement may comprise a plurality of such targets or feature sets, such that the determined tilt may be averaged across the plurality of targets.The target arrangement may also comprise a target or multiple targets per x and y direction. Figure 4 Such a target arrangement is illustrated, including an x-directed zone 320 and a y-directed zone 330, each zone including one or more blocks 340 of a plurality of columns 350 of contact holes extending in a direction perpendicular to the measurement direction (e.g., again nine contact holes per target or row). In the particular example shown, each zone has a plurality of such blocks.

[0056] The measurement of the target may include measuring the position of each feature (or at least one or more pairs of corresponding features) after etching and hard mask HM removal. This may then be referenced to the corresponding expected position or reference position (e.g., as indicated by the dotted line) to determine the placement error of the feature. Asymmetry across the target may then be determined from these placement errors already described.

[0057] If the height of the hard mask HM (and optionally the height of the material beneath the hard mask until etching stops) is known, the tilt can be expressed as an actual angle (rather than an arbitrary Δ placement error shift). This tilt can be determined across the substrate to determine a tilt feature identity or a tilt map (distribution of tilt across the substrate).

[0058] Figure 5An exemplary target arrangement (single direction) 400 according to an embodiment is illustrated. Such a target arrangement includes (in this particular example) six individual targets 410, each of which includes multiple pitches, such as such that the spacing of outer features is greater than the spacing of inner features. In such a particular example, the pitch between features increases outward from the center of the target. This amplifies the effect of the global tilt component (asymmetric displacement), thus improving the resolution (sensitivity) when measuring tilt, thereby advantageously enabling the same tool to be used to measure smaller displacements.

[0059] The obtained tilt parameter values ​​can be used, for example, in a feedback control loop to determine scanner and / or etcher (and / or other tools used in the manufacturing process) control corrections. The tilt parameter values ​​can also be used to monitor and / or control drift of the process and / or the tools used.

[0060] The method described herein enables automatic calibration, which saves time and increases throughput. No calibration experimental design (scatterometer) or tilt (current SEM methods) is required. The method can be performed in-line on production substrates to determine tilt feature signatures introduced by etcher or other equipment.

[0061] Additional embodiments are disclosed in the subsequent numbered aspect lists:

[0062] 1. A measurement method, comprising:

[0063] obtaining metrology data associated with a measurement of at least one target, each of the at least one target comprising a plurality of features; the metrology data describing placement errors of one or more pairs of corresponding features of the at least one target, each pair of the one or more pairs of corresponding features comprising a pair of features that are substantially equidistant from a reference point on the target in a measurement direction of the target;

[0064] determining an asymmetric component of the placement error from the measurement data; and

[0065] A tilt parameter is determined from the asymmetric component.

[0066] 2. The measurement method according to aspect 1, wherein the tilt parameter comprises a measure of a global tilt component in the measurement data.

[0067] 3. The measurement method according to aspect 1 or 2, wherein determining the asymmetric component comprises:

[0068] A difference value is determined that describes a difference in placement errors of corresponding features in the one or more pairs of corresponding features.

[0069] 4. The metrology method according to aspect 3, comprising: determining said differences in placement errors of a plurality of pairs of corresponding features; and

[0070] The tilt parameter is determined as an average across multiple pairs of corresponding features.

[0071] 5. The measurement method according to aspect 3, wherein determining the asymmetric component comprises: integrating corresponding differences across a plurality of pairs of corresponding features.

[0072] 6. A measurement method according to any preceding aspect, wherein the measurement data relates to a plurality of said targets and the method comprises averaging the tilt parameter as a mean value across said plurality of targets.

[0073] 7. A metrology method according to any preceding aspect, wherein the placement error is related to the placement of each feature relative to a corresponding reference position after etching and hard mask removal.

[0074] 8. The metrology method of clause 7, wherein each corresponding reference position comprises an expected position for the feature.

[0075] 9. The measurement method according to any of the preceding aspects, wherein the measurement data comprises electron microscope data.

[0076] 10. A metrology method according to any preceding aspect, wherein the features of each target are evenly spaced.

[0077] 11. A measurement method according to any one of aspects 1 to 9, wherein the spacing between the features of each target is larger between at least some features farther from the center of the target than between features closer to the center of the target.

[0078] 12. The metrology method of clause 11, wherein the spacing between features increases outward from the center.

[0079] 13. The metrology method according to any preceding aspect, comprising determining an absolute tilt value from the tilt parameter and height data related to the height of the layer stack and / or the hard mask.

[0080] 14. A metrology method according to any preceding aspect, wherein the metrology data relates to a plurality of locations on a substrate, and the method further comprises: determining a distribution of the tilt parameter across the substrate.

[0081] 15. The metrology method according to clause 14, comprising: normalizing the tilt parameter so that the average value across the substrate is zero.

[0082] 16. A metrology method according to any preceding aspect, wherein the metrology data relates to the at least one target formed by a production reticle.

[0083] 17. A metrology method according to any preceding aspect, comprising: using the determined tilt parameter in a feedback control loop to determine a control correction for an integrated circuit manufacturing process.

[0084] 18. A metrology method according to any preceding aspect, wherein each of the at least one target comprises a one-dimensional array of features.

[0085] 19. A measurement method according to any preceding aspect, wherein each of the at least one target comprises an odd number of features.

[0086] 20. The metrology method according to clause 19, wherein a central feature of each of the at least one target is different from other features of each target.

[0087] 21. The measurement method according to any preceding aspect, wherein each of the at least one target comprises five or more features.

[0088] 22. The measurement method according to any preceding aspect, wherein each of the at least one target comprises seven or more features.

[0089] 23. The measurement method according to any preceding aspect, wherein each of the at least one target comprises nine or more features.

[0090] 24. The measurement method according to any preceding aspect, comprising: determining that the tilt parameter is zero in the absence of an asymmetric component of the placement error.

[0091] 25. A metrology method according to any preceding aspect, wherein each of the features or at least each of the features other than a central feature of the at least one target comprises a contact hole.

[0092] 26. A metrology method according to any one of aspects 1 to 24, wherein each of the features or at least each of the features other than a central feature of the at least one target comprises a line feature.

[0093] 27. A metrology method according to any preceding aspect, wherein the metrology data relates to at least one target oriented in a first direction in a substrate plane and at least one target oriented in a second direction in the substrate plane perpendicular to the first direction; and the method comprises:

[0094] The tilt parameters in the first direction and the second direction are determined.

[0095] 28. The measurement method according to any preceding aspect, comprising: measuring the at least one target to obtain the measurement data.

[0096] 29. A metrology method according to clause 28, comprising an initial step of exposing and etching the at least one target on the substrate.

[0097] 30. The measurement method according to any preceding aspect, wherein the reference point comprises a center of the target in a measurement direction of the target.

[0098] 31. A computing device comprising a processor and configured to perform a method according to any preceding aspect.

[0099] 32. An inspection apparatus operable to image one or more features on a substrate and comprising a computing device according to clause 31.

[0100] 33. Inspection apparatus according to aspect 32, comprising electron microscopy inspection apparatus.

[0101] 34. An inspection apparatus according to aspect 32 or 33, comprising a scanning electron microscopy apparatus or a transmission electron microscopy apparatus.

[0102] 35. A computer program comprising program instructions operable to perform the method according to any one of clauses 1 to 29 when run on a suitable device.

[0103] 36. A non-transitory computer program carrier comprising a computer program according to clause 35.

[0104] 37. A substrate comprising a target arrangement, the target arrangement comprising at least one target for measuring a tilt parameter, each of the target comprising a plurality of features; wherein the spacing between at least some of the features of the target that are farther away from the reference point of the target is larger than the spacing between the features of the reference point that are closer to the target.

[0105] 38. The substrate of clause 37, wherein the spacing between features increases outward from the center.

[0106] 39. A substrate according to aspect 37 or 38, wherein each of the at least one target comprises a one-dimensional array of features.

[0107] 40. A substrate according to any one of clauses 37 to 39, wherein each of the at least one target comprises an odd number of features.

[0108] 41. A substrate according to clause 40, wherein a central feature of each of the at least one target is different from other features of each target.

[0109] 42. A substrate according to any one of clauses 37 to 41, wherein each of the at least one target comprises five or more features.

[0110] 43. A substrate according to any one of clauses 37 to 41, wherein each of the at least one target comprises seven or more features.

[0111] 44. A substrate according to any one of clauses 37 to 41, wherein each of the at least one target comprises nine or more features.

[0112] 45. A substrate according to any one of clauses 37 to 44, wherein the target arrangement comprises: at least one target oriented in a first direction in the plane of the substrate, and at least one target oriented in a second direction in the plane of the substrate perpendicular to the first direction.

[0113] 46. ​​A substrate according to any one of clauses 37 to 45, wherein each of the features or at least each of the features other than a central feature of the at least one target comprises a contact hole.

[0114] 47. A substrate according to any one of clauses 37 to 45, wherein each of the features, or at least each of the features other than a central feature of the at least one target, comprises a line feature.

[0115] 48. A substrate according to any one of clauses 37 to 47, wherein the reference point comprises a centre of the target in a measurement direction of the target.

[0116] 49. A reticle comprising a reticle operable to pattern a substrate to obtain a pattern of the substrate according to any one of clauses 37 to 48.

[0117] The terms “radiation” and “beam” as used with respect to a lithographic apparatus encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of at or about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 nm to 20 nm), as well as particle beams such as ion beams or electron beams.

[0118] The term "lens" may refer to any one or combination of various types of optical elements, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical elements, as the context permits.

[0119] The foregoing description of specific embodiments will fully reveal the general nature of the invention, so that others can easily modify and / or adapt these specific embodiments for various applications without undue experimentation by applying knowledge within the skill of the art without departing from the general concept of the invention. Therefore, based on the teachings and guidance presented herein, these adaptations and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments. It should be understood that the wording or terminology herein is for the purpose of (for example) description rather than limitation, so that the terms or wording of this specification will be interpreted by those skilled in the art in accordance with the teachings and guidance.

[0120] Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A measurement method, comprising: obtaining metrology data associated with a measurement of at least one target, each of the at least one target comprising a plurality of features; the metrology data describing placement errors of one or more pairs of corresponding features of the at least one target, each pair of the one or more pairs of corresponding features comprising a pair of features that are substantially equidistant from a reference point on the target in a measurement direction of the target; determining an asymmetric component of the placement error from the measurement data; as well as A tilt parameter is determined from the asymmetric component.

2. The measuring method according to claim 1, wherein: Determining the asymmetric component comprises: A difference value is determined that describes a difference in placement errors of corresponding features in the one or more pairs of corresponding features.

3. The measuring method according to claim 1 or 2, wherein: The measurement data relates to a plurality of the targets, and the method comprises averaging the tilt parameter as a mean value across the plurality of targets.

4. A measurement method according to any preceding claim, wherein: The metrology data includes electron microscope data.

5. A measurement method according to any preceding claim, wherein: Spacing of the features of each target is greater between at least some of the features farther from the center of the target relative to features closer to the center of the target.

6. A measurement method according to any preceding claim, comprising: An absolute tilt value is determined from the tilt parameter and height data related to the height of the layer stack and / or the hard mask.

7. A measurement method according to any preceding claim, wherein: The metrology data relates to a plurality of locations on a substrate, and the method further comprises determining a cross-substrate distribution of the tilt parameter.

8. A measurement method according to any preceding claim, comprising: The determined tilt parameter is used in a feedback control loop to determine a control correction to an integrated circuit manufacturing process.

9. A measurement method according to any preceding claim, wherein: Each of the at least one target includes an odd number of features.

10. A measurement method according to any preceding claim, wherein: Each of the at least one target includes five or more features.

11. A measurement method according to any preceding claim, wherein: Each of the features, or at least each of the features except a central feature of the at least one target, comprises a contact hole.

12. A measurement method according to any preceding claim, wherein: The metrology data is associated with the at least one target formed by a production reticle.

13. An inspection device operable to image one or more features on a substrate and comprising a computing device including a processor, the computing device being configured to perform a method according to any preceding claim.

14. A computer program comprising program instructions operable to perform the method according to any one of claims 1 to 12 when run on a suitable device.

15. A substrate comprising a target arrangement, the target arrangement comprising at least one target for measuring a tilt parameter, each of the targets comprising a plurality of features; wherein Spacing between at least some features of the target that are farther from the reference point of the target is greater relative to features that are closer to the reference point of the target.

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