Method of wafer alignment using resolution metrology on product features

Abstract

To provide a method of determining a position of a product feature on a substrate.SOLUTION: The method includes: obtaining a plurality of position measurements of one or more product features on a substrate, where the measurements are referenced to either a positioning system used in displacing the substrate between measurements or a plane parallel to the surface of the substrate; and determining a distortion component of the substrate based on the position measurements.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to European Patent Application No. 20174607.0, filed May 14, 2020, European Patent Application No. 20208071.9, filed November 17, 2020, and U.S. Patent Application No. 63 / 180,910, filed April 28, 2021, each of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a method for determining corrections to a process, a semiconductor manufacturing process, a lithographic apparatus, a lithographic cell, and related computer program products. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can project, for example, a pattern (often referred to as a "design layout" or "design") from a patterning device (e.g. mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g. wafer).

[0004]

[0004] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm. To form smaller features on a substrate than lithographic apparatus using radiation with a wavelength of, for example, 193 nm, lithographic apparatus using extreme ultraviolet (EUV) radiation with a wavelength in the range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, may be used.

[0005]

[0005] Low-k1 lithography can be used to process features with dimensions smaller than the conventional resolution limit of a lithographic apparatus. In such a process, the resolution equation can be expressed as CD=k1×λNA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics of the lithographic apparatus, CD is the "critical dimension" (typically the smallest feature size to be printed, but in this case the half-pitch), and k1 is an empirical resolution factor. In general, the smaller k1 is, the more difficult it becomes to reproduce a pattern on a substrate that resembles the shape and dimensions planned by the circuit designer to achieve a particular electrical functionality and performance. To overcome these problems, sophisticated fine-tuning steps can be applied to the lithographic projection apparatus and / or the design layout. These include, for example, but are not limited to, optimization of the NA, customized illumination schemes, use of phase-shifting patterning devices, various optimizations of the design layout such as optical proximity correction (OPC, sometimes also referred to as "optical and process correction") in the design layout, or other methods commonly defined as "resolution enhancement techniques" (RET). Alternatively, tight control loops for controlling the stability of the lithographic apparatus can be used to improve pattern reproduction at low k1.

[0006]

[0006] International Patent Application WO2015049087, the entirety of which is incorporated herein by reference, discloses a method for obtaining diagnostic information for an industrial process. Alignment data and other measurements are taken at multiple stages during a lithography process to obtain object data representative of misregistration or other parameters measured at multiple spatially distributed points on each wafer. Overlay and alignment residuals typically indicate a pattern on the wafer known as a fingerprint.

[0007]

[0007] In semiconductor manufacturing, the critical dimension (CD) performance parameter fingerprint can be corrected using a simple control loop. Typically, a feedback mechanism controls the average dose per wafer using a scanner (a type of lithography device) as an actuator. Similarly, for the overlay performance parameter overlay, the fingerprint induced by the processing tool can be corrected by adjusting the scanner actuator.

[0008]

[0008] Sparse ADI (after-develop inspection) measurements are used as input for a global model used to control the scanner (typically on a run-by-run basis). Dense ADI measurements taken at low frequency are used for exposure-by-exposure modeling. Exposure-by-exposure modeling is performed on fields with large residuals by modeling at high spatial density using dense data. Corrections requiring such dense metrology sampling cannot be performed frequently without adversely affecting throughput.

[0009]

[0009] A problem is that model parameters based on sparse ADI data usually do not accurately represent densely measured parameter values. This can occur as a result of crosstalk between model parameters and uncaptured parts of the fingerprint. Furthermore, for such sparse data sets, the model may be over-dimensioned. This creates a problem that fingerprints not captured by run-by-run control are not fully captured by the field-by-field model. Another problem is that in distributed sampling, different wafers (and different lots) have different sampling, so that superimposing multiple wafer layouts produces a substantially dense measurement result, but the sparse-dense behavior is unstable. There is a large residual between the modeled sparse data and the densely measured parameter values. This leads to an insufficient fingerprint description and suboptimal exposure-by-exposure corrections.

[0010]

[0010] Another problem with alignment control is that only a small number of alignment marks (~40) can be measured during exposure without affecting throughput. Higher order alignment control requires a denser alignment layout, which affects throughput. The solution to this problem is to measure denser alignment marks in an offline tool (Takehisa Yahiro et. al., “Feed-forward alignment correction for advanced overlay process control using a standalone alignment station ‘Litho Booster’” Proc. SPIE 10585, Metrology, Inspection and Process Control for Microlithography XXXII, incorporated herein by reference), as shown in FIG. 5, and feed forward this higher order correction during exposure. In this case, lower order corrections are also calculated during exposure.

[0011] For overlay control, in practice, dense overlay measurements (known as high-order parameter updates) can be performed only once every few lots to update the high-order corrections. The high-order parameters used to determine the scanner control recipe do not change between high-order parameter update measurements.

[0012]

[0012] Most modern alignment methods are based on measuring the position of dedicated alignment marks or overlay marks on the substrate relative to a reference of a position measurement system such as an alignment system (either in the lithographic apparatus or in a stand-alone alignment station).

[0013]

[0013] However, since the available space on the product reticle on which the alignment marks and / or overlay marks (metrology marks) are provided is limited, the number of metrology marks is usually limited. Therefore, the accuracy of the (field-by-field) control operation using the position measurement of the metrology marks is limited, for example, when the intra-field behavior of the alignment mark position is dominated by the high-order distortion of the substrate.

[0014]

[0014] Furthermore, the position of the metrology marks may be subject to sources of variation that should not be subject to the field-by-field control actions discussed above. Summary of the Invention

[0015]

[0015] The object of the present invention is to overcome the problems associated with alignment methods according to the state of the art.

[0016]

[0016] In a first aspect of the invention, there is provided a method for determining the position of a product feature on a substrate. The method comprises obtaining a plurality of position measurements of one or more product features on the substrate. The measurements are referenced either to a positioning system used to displace the substrate between measurements, or to a plane parallel to a surface of the substrate. The method further comprises determining a distortion component of the substrate based on the position measurements. [Brief description of the drawings]

[0017]

[0017] An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings.

[0018] [Figure 1] 1 depicts a schematic overview of a lithographic apparatus; [Diagram 2] FIG. 1 is a general schematic diagram of a lithography cell. [Diagram 3] FIG. 1 is a schematic diagram of holistic lithography, showing the collaboration between three key technologies to optimize semiconductor manufacturing. [Figure 4] 1 is a flow chart describing an alignment method according to one embodiment. [Diagram 5] 1 is a flow chart describing a feedforward overlay method according to one embodiment. [Figure 6] 1 is a flow chart describing a feedback overlay method according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019]

[0018] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet (e.g., having wavelengths of 365 nm, 248 nm, 193 nm, 157 nm or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 to 100 nm).

[0020]

[0019] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted to refer to a general purpose patterning device that can be used to impart a patterned cross-section to an incoming radiation beam, corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. Besides the classical mask (transmissive or reflective mask, binary mask, phase-shifting mask, hybrid mask, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0021] 1 illustrates a lithographic apparatus LA, which includes an illumination system (also called illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation or EUV radiation), a mask support (e.g. mask table) MT constructed to support a patterning device (e.g. mask) MA and coupled to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. wafer table) WT configured to hold a substrate (e.g. resist coated wafer) W and coupled to a second positioner PW constructed to accurately position the substrate support according to certain parameters, and a projection system (e.g. refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0022]

[0021] In operation, the illumination system IL receives a radiation beam from the radiation source SO, for example via the beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution across its cross-section in the plane of the patterning device MA.

[0023]

[0022] The term "projection system" PS as used herein should be interpreted broadly to encompass various types of projection systems including refractive optical systems, catadioptric optical systems, anamorphic optical systems, magnetic optical systems, electromagnetic optical systems, and / or electrostatic optical systems, or any combination thereof, as appropriate to the exposure radiation used and / or other factors such as the use of an immersion liquid or the use of a vacuum. When the term "projection lens" is used herein, this can be considered as synonymous with the more general term "projection system" PS.

[0024]

[0023] The lithographic apparatus LA may be of a type in which a portion of the substrate W, typically a rectangular area on the substrate called a "field" or "exposure field", is exposed by the radiation beam B via the projection system PS while the substrate W is moved horizontally relative to the radiation beam B. While the substrate W is being moved and exposed, the patterning device MA is also moved in a direction opposite to the substrate movement direction relative to the illumination light. By scanning the field with the radiation beam B or by moving the substrate W relative to the radiation beam B, the field on the substrate W being exposed is exposed from one side of the field to the other side of the field along the substrate movement direction. By moving the patterning device MA during exposure, the pattern of the patterning device MA is also scanned by the illumination light from one side of the pattern to the other side along the patterning device movement direction. The portion of the pattern imparted to the radiation beam B changes during the scanning of the pattern by the illumination light. The field is exposed from one side of the field to the other while the portion of the pattern imparted to the radiation beam B changes from one side of the pattern to the other side of the pattern. The entire pattern of the patterning device MA is transferred onto the field by scanning the field and the pattern from one side to the other. The radiation beam B that is illuminated onto the field of the substrate W is called the "slit area" or "exposure slit area". Thus, in this type of lithographic apparatus LA, the slit area scans over each field of the substrate W to transfer the pattern.

[0025]

[0024] During the scanning of the field, the substrate W and the patterning device MA are moved by the second positioner PW and the first positioner PM, respectively. The movements of the substrate W and the patterning device MA by these positioners are controlled synchronously, so that when a slit area on the field is at a certain position in the field, a corresponding part of the pattern to be transferred to that position in the field is imparted to the radiation beam B. For example, the pattern of the patterning device MA is the same size as the field of the substrate W, and the patterning device MA and the substrate W are controlled to move in opposite directions with the same speed. If the pattern of the patterning device MA is X times the field size of the substrate W, the movement of the patterning device MA is controlled to be X times as fast as the movement of the substrate W. If the movement control of the substrate W and the patterning device MA is not synchronized, the pattern transferred to the field will be distorted due to deviations from the synchronized movement control. The pattern transferred to the field may also be distorted due to other causes, such as relative rotation between the substrate W and the patterning device MA during the movement. For example, if the patterning device is scanned with an illumination light slightly offset from the scan direction, the part of the pattern imparted to the radiation beam B will rotate. Then, the part of the pattern transferred to the corresponding location in the field will also rotate. The opposite is true if the substrate W is scanned with a radiation beam B slightly offset from the scan direction. Thus, the relative rotation of the patterning device MA and the substrate W during the scanning of the field will also affect the distortion of the pattern transferred to the field. These factors, such as the relative speed between the substrate W and the patterning device MA, and the relative rotation between the substrate W and the patterning device MA during the scan, affect the accuracy of the pattern transfer. These scan factors that affect the pattern transfer accuracy are called the scan profile.

[0026]

[0025] The lithographic apparatus LA may be of a type in which at least a part of the substrate may be covered with a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system PS and the substrate W. This is also called immersion lithography. More information about immersion techniques is given in US Pat. No. 6,952,253, which is incorporated herein by reference.

[0027] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel and / or a substrate W on one substrate support WT may be used for exposing a pattern thereon while a preparatory step for a subsequent exposure of the substrate W is being performed on another substrate support WT.

[0028]

[0027] In addition to the substrate support WT, the lithographic apparatus LA may include a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean a part of the lithographic apparatus, such as for example a part of the projection system PS or a part of the system for providing immersion liquid. When the substrate support WT is remote from the projection system PS, the measurement stage may be moved below the projection system PS.

[0029]

[0028] In operation, the radiation beam B is incident on the patterning device MA, e.g. a mask, which is held on the mask support MT and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. Using the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, e.g. to position the various target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the patterning device MA can be accurately positioned with respect to the path of the radiation beam B using the first positioner PM and possibly further position sensors (not explicitly shown in Fig. 1). The patterning device MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, it is also possible that they may be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-line alignment marks.

[0030]

[0029] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, sometimes called a lithocell or (litho)cluster. The lithographic cell LC may also often include apparatus for performing pre-exposure and post-exposure processes on the substrate W. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, and a chill plate CH and a bake plate BK for adjusting the temperature of the substrate W, for example to adjust the solvent in the resist layer. A substrate handler or robot RO picks up the substrate W from input / output ports I / O1, I / O2, moves it between the various process apparatus, and delivers the substrate W to a loading bay LB of the lithographic apparatus LA. These devices in the lithocell are often collectively referred to as a track, and are under the control of a track control unit TCU. The TCU itself may be controlled by a supervisory control system SCS. The SCS may also control the lithographic apparatus LA, for example via a lithography control unit LACU.

[0031]

[0030] In order to accurately and consistently expose a substrate W to be exposed by the lithographic apparatus LA, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlay error between subsequent layers, line thickness, critical dimension (CD), etc. For this purpose, an inspection tool (not shown) may be included in the lithocell LC. If an error is detected, particularly if the inspection is performed before exposure or processing of other substrates W in the same batch or lot, then for example the exposure of the subsequent substrate or other processing steps subsequently performed on the substrate W may be adjusted.

[0032]

[0031] An inspection apparatus, sometimes also referred to as a metrology apparatus, can be used to determine the characteristics of the substrate W. In particular, it can determine how the characteristics of different substrates W vary, or how the characteristics associated with different layers of the same substrate W vary from layer to layer. Alternatively, the inspection apparatus can be configured to identify defects in the substrate W and can be, for example, part of a lithocell LC, or integrated in a lithography apparatus LA, or a stand-alone device. The inspection apparatus can measure characteristics of a latent image (image in a resist layer after exposure), or a semi-latent image (image in a resist layer after a post-exposure bake step PEB), or a developed resist image (where exposed or unexposed parts of the resist have been removed), or a post-etch image (after a pattern transfer step such as etching).

[0033] Typically, the patterning process in the lithographic apparatus LA is one of the most critical steps in processing, requiring highly accurate dimensioning and positioning of structures on the substrate W. To guarantee this high accuracy, three systems can be combined in a so-called "holistic" control environment, as shown diagrammatically in FIG. 3. One of these systems is the lithographic apparatus LA, which is (virtually) connected to a metrology tool MT (second system) and a computer system CL (third system). The key to such a "holistic" environment is to optimize the interaction between these three systems to improve the overall process window and provide a tight control loop to ensure that the patterning performed by the lithographic apparatus LA falls within the process window. The process window defines the range of process parameters (e.g. dose, focus, overlay) within which a particular manufacturing process produces a defined result (e.g. a functional semiconductor device). Within this range, variations in the process parameters of the lithographic or patterning process are usually allowed.

[0034]

[0033] The computer system CL can use (part of) the design layout to be patterned to predict the resolution enhancement technique to be used and perform computational lithography simulations and calculations to determine which mask layout and lithography settings will achieve the maximum overall process window of the patterning process (shown in FIG. 3 by the double-headed arrow in the first scale SC1). Typically, the resolution enhancement technique is configured to match the patterning capabilities of the lithography apparatus LA. The computer system CL can also be used to detect where the lithography apparatus LA is currently operating in the process window (e.g., using input from the metrology tool MT) to predict whether defects due to, for example, suboptimal processing may exist (shown in FIG. 3 by the arrow pointing to "0" in the second scale SC2).

[0035]

[0034] The metrology tool MT provides input to the computer system CL to enable accurate simulation and prediction, and can also provide feedback to the lithographic apparatus LA to identify possible drift in the calibration status of the lithographic apparatus LA (as shown in Figure 3 by multiple arrows in the third scale SC3).

[0036]

[0035] Methods of substrate alignment are typically performed by measuring dedicated metrology marks on the substrate. These marks contain mark features with μm-sized pitches to be detectable by alignment sensors. The mark features may be further divided so that the marks optically behave similarly to device structures (product features).

[0037]

[0036] However, even segmented marks respond differently to lens aberrations and process artifacts compared to the actual product features, and therefore the measured alignment mark positions do not represent the actual positions of the product features, even though these are critical parameters for process correction of the semiconductor manufacturing process.

[0038]

[0037] In one embodiment, at resolution metrology, for example using a scanning electron microscope (SEM) or electron beam metrology, is used to perform alignment measurements directly on device structures, such as one or more product features. The electron beam metrology tool can capture an image containing the individual product features and determine the individual positions of the product features by machine vision techniques, such as pattern recognition. In another example, the resolution metrology system is based on optical position measurement of the product features by using a high NA detection system and / or a detection system based on illumination of the product features with short wavelengths (XUV, EUV, DUV), or an atomic force microscope (AFM) or a scanning tunneling microscope (STM).

[0039]

[0038] A resolution metrology (alignment) system acquires the positions of the product features relative to a reference point or reference grid on the substrate itself or on the substrate holder (e.g., wafer table WT). Typically, this is achieved by referencing the field-of-view (FOV) of the resolution metrology system to the coordinate system of a substrate positioning system. The substrate positioning system can be operable in a stand-alone alignment system including the resolution metrology system or in a lithography apparatus including the resolution metrology system. By referencing the FOV as described above, the acquired positions of the product features can be used in reconstructing a deformation (distortion) map of the substrate. The determined distortion map can then be used in controlling a processing step, such as a lithography exposure step. Potentially, position measurements can be performed for a large number of product features contained within an (exposure) field or subfield (e.g., die area within a field), so that the distortion map can be determined accurately and at a very small spatial scale. For example, high-order distortion components can be extracted, allowing high-order intra-field or intra-subfield control. Thus, rather than relying on hard post-exposure data such as overlay measured by a scatterometer, the control components (lenses or stage actuators of the lithographic apparatus) can already be configured for high-order control based on data obtained directly during the alignment stage (e.g. data corresponding to the same substrate being controlled).

[0040]

[0039] Up to now, it has been assumed that the FOV of the resolution metrology system is referenced to the substrate positioning system. This is preferred because inspection of product features usually requires that the position of the substrate be brought into the (fixed) FOV of the resolution metrology system according to the desired position of the substrate (including the product features to be inspected). Thus, during a measurement sequence, it may be necessary to perform translational movements of the substrate. This usually requires accurate referencing of the FOV to the coordinate system of the translational (substrate positioning) system.

[0041]

[0040] Alternatively, the FOV of the resolution metrology system is made to coincide with the desired sampling position on the substrate. For example, if the resolution metrology system is e-beam based, the inspection beam can be guided according to the desired sampling position on the wafer. In this case, the (variable) FOV position needs to be referenced to the coordinate system of the substrate (surface).

[0042]

[0041] Furthermore, product feature-based position measurements typically represent true device structure placement (errors) and are therefore more suitable for use in deriving substrate position and / or projection lens corrections configured to at least partially compensate for deviations of measured product feature positions from their nominal values.

[0043]

[0042] In addition to the measurement of the product features with the resolution metrology system, a separate coarse substrate alignment step may be performed using conventional target-like structures, such as target marks, in order to reference the FOV of the metrology alignment system to the substrate positioning system or substrate (surface) coordinate system. The separate coarse substrate alignment step may be based on the measurement of conventional alignment marks.

[0044] In one embodiment, a device may contain multiple different types of overlay-critical product features. Separate alignment measurements may be performed for each feature type. This allows optimization of the overall device performance based on measurements of these product features.

[0045]

[0044] The alignment metrology of the present invention can be performed in-line (e.g. the alignment tool is located in the lithographic apparatus) or offline (e.g. the alignment tool is located outside the lithographic apparatus). The advantage of in-line measurement is that the alignment measurement is performed by clamping to the substrate table of the lithographic apparatus, so the substrate is held by the same substrate holder as is used during the alignment measurement when exposed in the lithographic apparatus. Therefore, the substrate deformation (distortion) measured during in-line alignment metrology is expected to be (almost) identical to the actual deformation of the substrate during lithographic exposure. The disadvantage of in-line resolution alignment is that throughput may be affected and / or resist degradation may occur.

[0046]

[0045] The advantage of offline resolution alignment measurement is that more alignment marks and product feature positions can be measured without reducing the throughput of the lithography exposure process, allowing higher order alignment modeling and correction. Another advantage of offline measurement is that the exposed resist is not degraded. The disadvantage of offline measurement is that offline alignment measurement is performed on a substrate held by a substrate holder different from the substrate table of the lithography apparatus that will later expose the substrate. Therefore, extra care must be taken to correct the effects of substrate deformation due to clamping differences between the lithography apparatus and the alignment metrology tool.

[0047]

[0046] To account for clamp-induced differences in substrate deformation for off-line resolution metrology alignment measurements, anchoring measurements can be performed. Anchoring measurements may include: 1) Sparse offline measurement of product features and / or alignment marks on the substrate using a resolution metrology tool located outside the lithographic apparatus. The sparse offline measurement can also be a subset of the dense offline measurement. 2) Sparse in-line measurements of the same product features and / or alignment marks on the substrate are performed using an alignment system located within the lithographic apparatus.

[0048]

[0047] The clamp fingerprints corresponding to the offline and in-line measurements are compared and used to determine a delta fingerprint that represents the difference in substrate deformation caused by the use of different substrate holders.The delta fingerprint is then used to correct the substrate distortion determined offline, so that the corrected substrate deformation is more representative of the substrate deformation occurring during lithography exposure.Furthermore, a dense offline measurement of the product features is also performed.The dense offline measurement can then be corrected using the sparse offline measurement.

[0049]

[0048] Before the lithography exposure begins, the corrected substrate deformation information and in-line alignment measurements can be used to configure the lithography exposure step so that the substrate positioning system and projection lens of the lithography apparatus optimally compensate for substrate distortion during exposure of the substrate.

[0050]

[0049] The above description relates to using tools such as SEM / e-beam metrology tools to perform alignment metrology (in addition to CD metrology). This can be further extended to other pattern placement metrology such as overlay. Such pattern placement metrology can be measured at the wafer at the sub-nanometer level.

[0051]

[0050] The e-beam tool used may include one or more stages and a stage metrology system operable to determine the position of each stage with an accuracy of much less than 1 nm (e.g., less than 0.5 nm or less than 0.2 nm). The e-beam tool may also have a sufficiently high incident energy to perform measurements through the stack and / or resist. Such incident energy may be greater than 10 kEV or greater than 20 kEV, for example in the range of 10 kEV to 50 kEV.

[0052]

[0051] For alignment, a metrology image (e.g., an electron beam or SEM image) can be aligned to a reticle reference file, i.e., a .gds file, which describes the layout information or expected position of each reticle feature. Depending on the field of view of the metrology tool, it may be possible to align 1000-10000 features to the reticle reference file. This can be expected to give alignment results (repeatability or measurement uncertainty) at a level much smaller than 1 nm (e.g., 0.1 nm).

[0053]

[0052] The position of the metrology image on the wafer can also be measured at the sub-nanometer level. Thus, the stage position can be determined with approximately the same level of accuracy as a scanner stage. For example, a metrology tool can be equipped with an interferometer system for measuring the stage position, providing sufficient repeatability and relative accuracy of the stage position measurement.

[0054]

[0053] If the stage position is known to the sub-nanometer level, then it is possible to measure the position of both the alignment marks and (directly) any device on the wafer. This allows the measurement of the relative position or offset of the device with respect to the alignment marks. With a sufficiently high incident energy, it allows the measurement of both the alignment marks and the bottom grating of the target device.

[0055]

[0054] Such an e-beam metrology tool can be provided as a stand-alone alignment metrology station that measures wafers before exposure. Because e-beam metrology is slower than optical metrology, the scanner still includes an optical alignment tool, and the e-beam tool measures only a subset or a percentage of all wafers that are exposed, while the optical tool can be used to measure all wafers.

[0056] In this way, the aligned positions of actual devices (e.g., within a die) can be measured at a desired density, which allows the distortion between the scribe lines and the die (e.g., local etch effects, topology effects, within-die stresses) to be captured.

[0057]

[0056] An optical scanner alignment sensor can be used to perform a global wafer alignment (e.g., according to a 6 or 10 parameter model, or higher order model), and the results of this scanner alignment data can be compared to a previously measured aligned position of the same mark using an e-beam tool. In this way, differences in the chuck (wafer load grid) between the stand-alone e-beam tool and the scanner can be corrected.

[0058] FIG. 4 is a flow chart describing an alignment metrology method according to one embodiment.

[0059]

[0058] In step 400, a first tool, i.e., an e-beam tool (e.g., a stand-alone e-beam alignment station), may be used to measure first tool target alignment data including the position of an alignment mark on the wafer. Assuming that the e-beam tool has sufficient incident energy, the alignment mark may be a buried alignment mark. For example, the layer to be aligned is measured regardless of its depth in the stack. Additionally, the wafer may be coated with resist.

[0060] In step 410, an electron beam tool may be used to measure first tool device alignment data including positions of device structures in the same layer as the alignment marks measured in step 400. In contrast to optical alignment metrology, device structures do not need to be periodic to be measured by an electron beam tool.

[0061] In step 420, the first tool target alignment data is referenced to a reference grid, and in step 430, the first tool device alignment data is referenced to the reference grid.

[0062] In step 440, the referenced first tool target alignment data and the first tool device alignment data can be used to establish alignment-to-device offsets for some or all of the devices being measured. Such offsets can include differences in the measurement positions for each device in the first tool device alignment data relative to the measurement positions in the first tool target alignment data. The device measurements can be averaged over multiple occurrences of each device per die to average out the actual intra-die distortion.

[0063] In step 450, the offsets determined in step 440 may be combined to generate a dense grid of alignment offsets for each alignment mark, for example, on one or more of a die, a field, and a wafer.

[0064]

[0063] In step 460, a scanner alignment tool, i.e., an optical alignment tool (second metrology tool), can be used to measure the alignment marks on the wafer to obtain second tool target alignment data. The first tool target alignment data and the second tool target alignment data can be compared to determine a difference or delta grid between these two data sets. This delta grid is primarily due to differences caused by a different stage being used for alignment in the stand-alone alignment station than is used for alignment in the scanner (i.e., chuck differences or delta wafer load grid).

[0065] In step 470, a fine alignment correction grid is determined from the fine grid of alignment offsets (eg, by device) obtained in step 450 to correct for the chuck differences determined in step 460.

[0066]

[0065] The dense grid correction can be applied as a feed-forward correction to the scanner (e.g., alignment grid). Thus, by using a dense alignment grid, the alignment can be corrected for all wafers for which alignment data is acquired using only an optical metrology tool (e.g., in the scanner). Since this is the majority of wafers, only a small number may actually be measured using an e-beam metrology tool. The e-beam metrology tool may only be used periodically, e.g., only the first wafer of a lot. In this way, the optical alignment measurement performed by the scanner on the alignment mark can be corrected to (at least close to) the direct measurement by the e-beam tool on a particular feature.

[0067]

[0066] The same basic principles can be applied to the correction of overlay metrology, which has the same problems as alignment metrology. Specifically, the target on which overlay metrology performs measurements must usually be large enough and have a periodic pattern with a large enough pitch to be measured optically. This means that the target does not necessarily represent the device exactly, resulting in what is called metrology-to-device offset (the difference between the overlay measured on the target and the actual overlay of the product structure). Target-based optical overlay metrology can include microdiffraction-based overlay metrology (μDBO). In μDBO, overlay is determined from the intensity difference of corresponding or complementary higher diffraction orders (e.g., +1 and -1 orders). These diffraction orders can be imaged at an image plane (e.g., dark-field images with the zeroth order blocked in front of the image plane) and the intensity averaged in a region of interest (ROI) within each image of the diffraction orders. It is also known to perform optical overlay metrology directly on the product structure or on a target that mimics the product structure. This is often referred to as in-device metrology (IDM). IDM can be based on detection of angle resolved spectra scattered from device structures at the pupil plane. However, not all device structures can be measured in this manner, as IDM requires periodic structures. Another optical overlay metrology technique to which the concepts disclosed herein can be applied is image based overlay (IBO). IBO metrology can include determining the relative offset between two or more layers on a sample based on the relative imaged positions of features of overlay targets in different layers of interest. Such methods can use dedicated targets, such as box-in-box targets, where the overlay is determined from the position of a first box imaged in one layer relative to a second box imaged in another layer, where one box is smaller than and located within the other box.There are other IBO methods and target types to which the concepts herein are equally applicable.

[0068]

[0067] Figure 5 is a flow chart describing a method for performing overlay feed-forward correction according to an embodiment. In step 500, an optical metrology tool (second metrology tool) can be used to measure the overlay fingerprint of a previous layer (e.g., after etch) and measure overlay targets for each wafer. Such measurements can be, for example, IBO, DBO, μDBO, or IDM target-based measurements to obtain second tool target overlay data. This can include high-throughput measurements for every wafer so that wafer-level feed-forward corrections can be determined for the wafer. This step can be performed for each wafer and can therefore include sparse measurements (e.g., one or two targets per field).

[0069] In step 510, an electron beam metrology tool is run on the same overlay target (e.g., an after etch inspection (AEI) target) to obtain first tool target overlay data (essentially the difference in position measurements of each of the overlay target's two constituent gratings or components). This may be performed on a subset of wafers (e.g., one per lot). As with the previous embodiment, the second tool target overlay data and the first tool target overlay data may be compared to determine the difference or delta grid between these two data sets. This delta grid is primarily due to differences between the tools used (i.e., chuck differences).

[0070] In step 520, an e-beam tool may be used to measure the overlay of the device structures (which may be irregular and / or periodic) to obtain first tool device overlay data. Again, this may essentially include position measurements of the device structures relative to a previous layer or structures within a previous layer. This step may be performed on the same wafer subset as step 510.

[0071] In step 530, a dense intra-die overlay grid may be determined from the first tool target overlay data and the first tool device overlay data. This dense intra-die overlay grid may describe intra-die distortion for the overlay target measurements (e.g., a dense grid describing MTD offsets).

[0072]

[0071] In step 540, the second tool target overlay data, the first tool target overlay data, and the first tool device overlay data can be used to determine wafer level feed forward corrections for exposure in the scanner to be performed on each wafer measured to obtain the second tool target overlay data. This can include optimization for edge placement error (EPE) or overlay based on a dense intra-die overlay grid. The correction can be based on a measured offset (MTD offset) of the first tool device overlay data to the second tool target overlay data corrected for chuck differences (e.g., dense intra-die overlay grid). For example, the optimization can be a weighted optimization for multiple MTD offsets determined (e.g., by device type and / or by wafer area) based on the (EPE) criticality (process window) of various devices using the first target metrology data as input. Such multiple feature overlay optimization can be similar to CD die optimization currently used for dose control.

[0073] It will be appreciated that the embodiments of Figures 4 and 5 may be combined to obtain feedforward exposure corrections based on both alignment data according to the embodiment of Figure 4 and overlay data according to the embodiment of Figure 5. For example, both alignment data and overlay data may be used to determine fine control grid corrections for exposure.

[0074] In another embodiment, overlay feedback control assisted by electron beam measurements is also disclosed. Figure 6 is a flow chart describing such an embodiment.

[0075] In step 600, a first overlay fingerprint can be measured after etch using an optical metrology tool to measure overlay targets for each wafer. Such measurements can be, for example, IDM target-based measurements to obtain second tool post-etch overlay data or second tool AEI overlay fingerprints (e.g., IDM overlay fingerprints). This step can be performed for the entire wafer.

[0076] In step 610, the second overlay fingerprint can be measured after development using an optical metrology tool to measure the overlay targets for each wafer. Such measurements can be, for example, IBO, DBO, or μDBO target based measurements to obtain second tool post-develop overlay data or second tool ADI overlay fingerprints (e.g., IBO or DBO overlay fingerprints). This step can be performed for the entire wafer.

[0077] In step 620, ADI e-beam metrology can be performed, for example, on a subset of the wafers measured in step 610 to obtain first tool post-develop overlay data. This first tool ADI overlay data can include metrology data from IBO or DBO target measurement ADI, metrology data from IDM target measurement ADI, and metrology data for device structures ADI (e.g., at least critical devices).

[0078]

[0077] In step 630, AEI e-beam metrology can be performed, for example, on a subset of the wafers measured in step 600 to obtain first tool post-etch overlay data. This first tool AEI overlay data can include metrology data from the IDM target measurement AEI and metrology data for device structures AEI (e.g., at least critical devices). Step 630 can be performed instead of or in addition to step 620.

[0079] In step 640, the first and second tool ADI overlay data and / or the first and second tool AEI overlay data are used to determine (as appropriate): One or more ADI MTD offsets per device (e.g., Device-DBO) by comparing the target measurements and device measurements acquired in step 620 to obtain a DBO measurement grid; One or more AEI MTD offsets per device (e.g., Device-IDM) by comparing the target measurements and device measurements obtained in step 630 to obtain an IDM measurement grid; · Process offset per device (e.g., device measurement difference between ADI performed in step 620 and AEI performed in step 630) to obtain a dense grid per device (and within a die).

[0080] In step 650, the feedback correction can be determined using all the data sets determined in the above embodiment. This can be performed based on a multi-feature overlay optimization similar to the CD die optimization used for dose, and can include weights based on overlay margin / device (EPE criticality). This step can also include using process offsets per device and MTD per device to allow control of the actual on-device overlay. As mentioned above, the second tool overlay data can be used together with one or both of the first tool post-develop overlay data and the first tool post-etch overlay data to determine corrections for stage differences or chuck differences between the tools used.

[0081] It will be appreciated that the embodiment of FIG. 6 may be combined with either or both of the embodiments of FIG. 4 and FIG.

[0082]

[0081] The images captured by the e-beam tool are of course also used for CD / local CDU measurements. This gives CD measurement data describing the on-device CD (e.g. for multiple devices). This data can be used for feedback scanner (dose) correction for exposure of the same layer of a subsequent lot, or can be used in combination with the misregistration data to determine feed-forward corrections for exposure of the next layer of the measured wafer (for dose / overlay).

[0083]

[0082] Finally, an electron beam tool can be used in-line (e.g., instead of or together with an optical alignment sensor such as that shown as AS in FIG. 1) to perform alignment measurements directly on the device structures. In this way, a closer alignment can be performed on any structure without the need to include more (or any) alignment marks. Since alignment measurements are performed directly on the device structures, metrology problems for device offsets (targets behaving differently for device structures) are obviated.

[0084]

[0083] Off-line resolution alignment measurements allow the measurement of many more alignment mark and product feature locations than is feasible with current in-line metrology strategies, creating the possibility of using improved (e.g., higher order) alignment models. Typically, with in-line metrology strategies, there is not enough metrology time available to measure the amount of marks required to implement a more desirable modeling strategy. For example, currently the following alignment granularities are typically used: Between fields: Global wafer placement and deformation. This is currently done using linear models (e.g. 6 parameter models), or "higher order" models (usually up to 5th order). · Intra-field: Align the average field fingerprints. · Zone Alignment: An interpolation / extrapolation method that can be used to capture more local deformations.

[0085]

[0084] A drawback of existing alignment granularities is that they cannot properly compensate for very high order fingerprints, such as those caused by scanner exposure. As a result, these fingerprints need to be corrected by other means, such as overlay control based on feedback control loops. Such feedback control loops are essentially always "catching up" because fingerprints change over time and therefore corrections tend to lag behind. Also, they are prone to wafer-to-wafer variations and lot-to-lot noise.

[0086]

[0085] Thus, the offline measurement embodiments disclosed herein are proposed to measure alignment layouts (which may include product structures and / or dedicated targets) that are significantly denser than those currently used (e.g. for inline alignment metrology), thereby enabling higher order alignment modeling.

[0087]

[0086] Such a proposal may include implementing any of the following granularity and alignment modeling strategies, or a combination thereof (where applicable). · Per-field (exposure) modeling: If there are enough targets in each field, per-field modeling can be performed. All fields can be modeled individually. Alternatively, per-field modeling can be performed only on a subset of fields. For example, a first subset of fields in a first substrate region (e.g., an inner substrate region) can be modeled using a first strategy, such as an average field fingerprint strategy, and a second subset of fields in a second substrate region (e.g., an outer substrate region where greater variation may be expected) can be modeled using a second strategy, such as the per-field modeling strategy described above. Of course, the decision of where and how often to perform per-field modeling can depend on the overlay behavior / requirements. · Average subfield modelling: This can for example be performed if little variation is observed in the subfields. · Subfield-by-subfield modelling, where some or all of the subfields are modelled separately. -This can be very costly in terms of metrology effort, and so may only be performed if there is a large variation in the subfield, and possibly only for a small subset of the fields on the wafer (e.g. the leading edge). · Per die: This is effectively a special case of per subfield, but with a higher granularity than a subfield that contains several dies. Modelling of the distortion fingerprint in the area related to the scanning of the radiation beam B over the substrate (the so-called slit area), e.g. the slit fingerprint. The slit fingerprint is often characterized in large part by the contribution of the projection optics (e.g. lenses) to the distortion fingerprint of the lithographic apparatus. The lens contribution (lens fingerprint) typically contains higher order components and therefore requires dense distortion (alignment) measurements if it needs to be determined. On-product alignment methods such as those described above allow the determination of the slit fingerprint by only exploiting the presence of product features, without the need to provide many alignment marks in a small region on the reticle corresponding to the slit area. The slit fingerprint may also include reticle errors. - The slit fingerprint represents the distortion component of the substrate above the exposure slit area. For example, this distortion is plotted against the non-scanning distance from the center of the exposure slit area. To calculate the distortion against the non-scanning distance from the slit center, measurements of product features at the same non-scanning distance from the slit center can be averaged. Measurements of product features on the substrate can then be used to identify a high order slit fingerprint, which can, for example, identify the lens fingerprint of a lithographic apparatus used to expose a previous layer of the substrate. The identified lens fingerprint can then be used to control the projection lens to compensate for the lens fingerprint of a subsequent layer and / or substrate exposed using the lithographic apparatus. Modeling of distortion fingerprints in the field along the scan direction, e.g. profile fingerprints. - the scan profile fingerprint is the distortion of the transferred pattern in the field along the scan direction due to the scan profile of the lithographic apparatus used for the exposure. The scan profile is often characterized in large part by the contribution of the relative velocity variations between the positioning device of the patterning device and the positioning device of the substrate during the scan. The scan profile fingerprint also contains higher order components and therefore requires dense distortion (alignment) measurements if it needs to be determined. The above-mentioned on-product alignment method allows the determination of the scan profile fingerprint by only exploiting the presence of product features, without the need to provide many alignment marks in the pattern on the reticle. The scan profile fingerprint represents the distortion component of the substrate in the scan direction of the field. For example, this distortion is plotted against the scan direction position in field coordinates. The scan profile distortion can be calculated by averaging measurements for the same field coordinate position in the scan direction. The above-mentioned on-product alignment method is advantageous in determining the scan profile fingerprint because, similar to the slit fingerprint, the dense measurements necessary to determine high order distortions can be performed using product features without introducing a large number of alignment marks. - The scan profile fingerprint can be performed on an average field, such as an average scan-up field or a scan-down field, or the scan profile can be performed on a single field (per exposure field). The measurements of the product features on the substrate can then be used to identify a high order scan profile fingerprint, which can identify distortions of the transferred pattern on the substrate due to scan profiles such as relative velocity and / or relative rotational variations between a positioning device of the substrate stage and a positioning device of the patterning device. The identified scan profile fingerprint can then be used to calibrate and / or control the positioning devices of the substrate and the patterning device to compensate for the scan profile fingerprints of subsequent layers and / or subsequent substrates exposed using the lithographic apparatus.

[0088]

[0087] Also, these strategies and granularity can be combined with existing alignment strategies / granularity if desired (and applicable). In all of the above, the term subfield can refer to any subset of a die, a single die, or a portion of a die, or a subfield can include multiple portions of a die.

[0089]

[0088] In addition to or instead of the above strategies, modeling may be performed on a product feature-by-feature basis. For example, in edge placement optimization (e.g., optimizing individual feature placement), it is important to know the location of various (e.g., critical) product features. Critical features may require special attention in placement (e.g., have narrow process windows). Measuring and modeling on a feature-by-feature basis allows for edge placement optimization. For example, different weights may be used for different features depending on their criticality (e.g., depending on the feature's location in the layout and / or the feature's type).

[0090] Potentially, if the alignment fingerprints per field are stable within a particular group or set (e.g., a lot, a chuck, or another group of wafers), then it is possible to perform a finer grain alignment (e.g., subfield metrology) only on a single wafer (e.g., the first wafer) or other subset per group. The results of this alignment can then be used (at least in part) for the other wafers in the group. Thus, these subsequent wafers only require a coarse measurement, which can then be supplemented by the fine modeling performed on the single wafer. In such an embodiment, in some cases, the finely measured wafers in the group are measured offline, and the remaining coarsely measured wafers are measured inline. The latter wafers can be measured more coarsely than current strategies (or at least current high-order alignment strategies). This can improve the overall throughput.

[0091] Another option is to perform distributed sampling on the wafer when measurements are performed offline. This allows higher-order modeling per lot / per chuck / per group of wafers while performing lower-order modeling per wafer. This is not possible inline, since all measurement data is required before modeling can be performed. Distributed sampling may also (alternatively or additionally) include distribution over a subset of fields in the wafer. For example, per-field modeling can be performed on only a subset of the fields. This latter form of distributed sampling may be performed in conjunction with inline alignment measurements.

[0092]

[0091] On-device offline alignment measurements offer the advantage of scanner availability, but are not a requirement of the present invention. Offline or in-line measurements, on the marks or on the device, are possible.

[0093]

[0092] Further embodiments may be described in the following clauses. 1. A method for determining a distortion component of a substrate, comprising: obtaining a plurality of position measurements of one or more product features on a substrate, the measurements being referenced either to a positioning system used to displace the substrate or to a plane parallel to a surface of the substrate; determining a distortion component of the substrate based on the plurality of position measurements; A method comprising: 2. The method of claim 1, wherein the distortion component is related to an in-plane distortion of the substrate and / or a position of a product feature on the substrate. 3. Obtaining measurements of one or more alignment marks on the substrate; and determining a position of the product feature based on measurements of the product feature and / or the image of the product feature and measurements of the one or more alignment marks; 3. The method of claim 2, further comprising: 4. A method according to any of clauses 1 to 3, wherein at least some of the measurements of the product features and / or images of the product features are performed in-line using an alignment tool located within the lithographic apparatus. 5. A method according to any of clauses 1 to 4, wherein at least some of the measurements of the product features and / or images of the product features are performed offline using an alignment tool located outside the lithographic apparatus or connected to the lithographic apparatus. 6. A method according to any of clauses 3 to 5, wherein at least some of the measurements of the product features and / or images of the product features are performed offline and at least some of the measurements of the one or more alignment marks are performed inline. 7. The method according to clause 6, wherein the offline and in-line measurements are combined by combining deformation grids of the alignment tools used for the offline and in-line measurements. 8. The method of clause 1 or 2, wherein the multiple position measurements include first tool metrology data measured using a first metrology tool, or include first tool metrology data measured using the first metrology tool and second tool metrology data measured using a second metrology tool. 9. The method of clause 8, wherein the first metrology tool is a scanning electron microscope tool and / or the second metrology tool is an optical metrology tool. 10. The method of claim 9, wherein the scanning electron microscope measures at least one of a plurality of position measurements of one or more product features and / or targets on the substrate below an upper layer of the substrate. 11. The method of claim 10, wherein at least one of the multiple position measurements of one or more product features and the target are on the same layer. 12. A method according to any one of clauses 9 to 11, wherein the electron beam of the scanning electron microscope has an incident energy of greater than 10 keV. 13. The method of any of clauses 9 to 12, wherein the electron beam of the scanning electron microscope has an incident energy of less than 50 keV. 14. The method of any of clauses 8 to 13, wherein the first tool metrology data includes first tool target metrology data measured on the target and first tool device metrology data measured on the device structure. 15. The method of clause 14, comprising determining one or more metrology-to-device offsets for one or more device structures associated with the first tool device metrology data from the first tool target metrology data and the first tool device metrology data, wherein the one or more metrology-to-device offsets include a comparison of measurements for each device in the first tool device metrology data to corresponding measurements in the first tool target metrology data. 16. The method of claim 15, comprising combining and aggregating one or more metrology-to-device offsets into a dense grid of metrology offsets for each target. 17. A method according to clause 15 or 16, comprising applying a dense grid of metrology offsets and / or one or more metrology-to-device offsets to a reference grid of the exposure apparatus as feedforward corrections. 18. A method according to clause 15 or 16, comprising applying a dense grid of metrology offsets and / or one or more metrology-to-device offsets to a reference grid of the exposure apparatus as feedback corrections. 19. Determining stage and / or exposure corrections from a comparison of the first tool target metrology data and the second tool target metrology data; applying a stage correction and / or exposure correction to a feedforward correction or a feedback correction; 19. The method according to clause 17 or 18, comprising: 20. A method according to any of clauses 14 to 19, wherein the first tool target metrology data comprises first tool target alignment data measured on an alignment mark and the first tool device metrology data comprises first tool device alignment data measured on a device structure. 21. The method of clause 20, wherein the second tool metrology data includes second tool target data measured on the alignment mark. 22. The method of clause 20 or 21, wherein the second metrology tool includes an optical alignment sensor. 23. The method of any of clauses 14 to 19, wherein the first tool target metrology data includes first tool target overlay data measured on an overlay target and the first tool device metrology data includes first tool device overlay data measured on a device structure. 24. The method of clause 23, wherein the first tool target overlay data includes one or both of first tool post-etch target overlay data acquired after an etch step is performed on the target and first tool post-develop target overlay data acquired before an etch step is performed on the target, and the first tool device metrology data includes one or both of first tool post-etch device overlay data acquired after an etch step is performed on the device structure and first tool post-develop device overlay data acquired before an etch step is performed on the device structure. 25. The method of clause 24, comprising the additional step of determining an offset between the first tool post-etch device overlay data and the first tool post-develop device overlay data. 26. The method of any of clauses 23 to 25, wherein the second tool metrology data includes second tool target data measured on an overlay target. 27. The method of any of clauses 23 to 26, wherein the second metrology tool comprises an optical scatterometer metrology tool. 28. A method according to any preceding clause, further comprising modelling distortion components of the substrate for at least one exposure field or subfield on the substrate according to the first field or subfield model. 29. The method of clause 28, wherein the modelling in accordance with the first field or subfield model is performed on a first average field or subfield of a first subset of fields or subfields on the substrate. 30. The method of clause 29, wherein a first subset of fields or subfields is in a first substrate region of the substrate, and a second field or subfield in a second substrate region of the substrate is modelled according to a second field or subfield model. 31. The method of clause 30, wherein the first region is an inner region of the substrate and the second region is an outer region of the substrate. 32. The method of any of clauses 28 to 31, wherein the first field model or sub-field model comprises a die model or sub-die model that models one or more dies or sub-dies on the substrate. 33. A method according to any of clauses 28 to 32, wherein a first field or subfield modelling is performed on a first subset of the substrate group and results of the first field or subfield modelling are used for a second subset of the substrate group. 34. The method of any of clauses 28 to 33, further comprising modelling a plurality of locations of the one or more locations of different product features. 35. The method of clause 34, wherein the different product features include different types of product features and / or product features located at different positions within a plurality of fields of the substrate. 36. A method according to any of clauses 1 to 35, comprising modelling the distortion components of the substrate for at least one exposure field or sub-field on the substrate and / or modelling the exposure slit of a lithographic apparatus used to manufacture a previous layer of the substrate according to a slit fingerprint model. 37. The method of claim 36, wherein the slit fingerprint model includes a lens fingerprint model. 38. The method of claim 36 or 37, wherein the modelling according to the slit fingerprint model is performed on a second average field of a second subset of the fields or subfields of the substrate. 39. A method according to any preceding clause, further comprising modelling distortion components of the substrate for at least one exposure field or sub-field on the substrate in accordance with the scan profile fingerprint model. 40. The method of claim 39, wherein the modelling in accordance with the scan profile fingerprint model is performed on a third average field of a third subset of the fields or subfields of the substrate. 41. The method of clause 40, wherein the third subset of fields or subfields includes a scan up field or a scan down field. 42. The method according to clause 39, wherein the modelling according to the scan profile fingerprint model is performed for each exposure field. 43. A method according to any of clauses 28 to 42, wherein at least some of the measurements of the product features and / or images of the product features are performed offline using an alignment tool located outside the lithographic apparatus or connected to the lithographic apparatus. 44. The method of any of clauses 1 to 43, wherein at least a portion of the multiple position measurements are distributed across multiple substrates. 45. The method of any of clauses 2 to 44, further comprising determining an edge placement control for the product feature based on a position of the product feature. 46. ​​The method of claim 45, further comprising weighting the product features according to their criticality. 47. A method of exposing a substrate using a lithographic apparatus, comprising: Determining a location of a product feature on a substrate according to any of clauses 2 to 44; exposing the substrate based at least in part on the determined locations of the product features; A method comprising: 48. A method according to any of clauses 2 to 47, wherein the step of obtaining measurements of the product features or images of the product features is carried out using an electron beam device. 49. An exposure apparatus comprising an electron beam device configured to carry out the method according to any one of clauses 1 to 48. 50. An exposure system comprising an exposure apparatus for exposing a substrate and an electron beam apparatus, the exposure beam apparatus being configured to carry out the method according to any of clauses 1 to 48.

[0094]

[0093] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein have other applications, such as in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0095]

[0094] Although particular reference is made herein to embodiments of the invention in connection with an inspection or metrology apparatus, embodiments of the invention may also be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a lithography apparatus, or any apparatus that measures or processes an object, such as a wafer (or other substrate) or a mask (or other patterning device). It should also be noted that the term metrology apparatus or metrology system may encompass or be substituted for the term inspection apparatus or inspection system. The metrology or inspection apparatus disclosed herein may be used to detect defects on or in a substrate and / or defects of a structure on a substrate. In such an embodiment, the characteristics of the structure on the substrate may relate, for example, to a defect in the structure, the absence of a particular part of the structure, or the presence of an undesired structure on the substrate.

[0096]

[0095] Although specific reference is made to a "metrology apparatus / tool / system" or an "inspection apparatus / tool / system," these terms can refer to the same or similar types of tools, apparatus, or systems. For example, an inspection or metrology apparatus including an embodiment of the present invention may be used to determine characteristics of a physical system, such as a structure on a substrate or on a wafer. For example, an inspection or metrology apparatus including an embodiment of the present invention may be used to detect defects in a substrate or a structure on a substrate or wafer. In such embodiments, the characteristics of the physical structure may relate to, for example, a defect in the structure, the absence of a particular portion of the structure, or the presence of an undesirable structure on the substrate or wafer.

[0097]

[0096] Although specific reference has been made above to the use of embodiments of the present invention in connection with optical lithography, it will be understood that the present invention may be used in other applications, such as imprint lithography, and is not limited to optical lithography, where the context permits.

[0098]

[0097] Although the targets or target structures (more generally, structures on a substrate) described above are metrology target structures specifically designed and formed for the purpose of measurement, in other embodiments, the properties of interest can be measured in one or more structures that are functional parts of a device formed on a substrate. Many devices have a regular grid-like structure. As used herein, the terms structure, target grid, and target structure do not require that the structure is specifically provided for the measurement to be performed. For embodiments of multi-sensitivity targets, different product features may include many regions with different sensitivities (such as different pitches). Furthermore, the pitch p of the metrology target is close to the resolution limit of the scatterometer optics, but may be much larger than the dimensions of typical product features created in a lithography process in the target portion C. In fact, the lines and / or spaces of the overlay grid in the target structure may be made to include smaller structures with similar dimensions to the product features.

[0099]

[0098] Although specific embodiments of the present invention have been described above, it will be understood that the present invention can be practiced in other ways than as described. The above description is illustrative and not restrictive. Thus, it will be apparent to one skilled in the art that the present invention as described can be modified without departing from the scope of the claims.

Claims

1. 1. A method for determining a distortion component of a substrate, comprising the steps of: obtaining a plurality of position measurements of one or more product features on a substrate, the measurements being referenced either to a positioning system used to displace the substrate or to a plane parallel to the surface of the substrate; determining a distortion component of the substrate based on the plurality of position measurements; and A method comprising:

2. The method of claim 1 , wherein the distortion components are associated with an in-plane distortion of the substrate and / or a position of a product feature on the substrate.

3. obtaining measurements of one or more alignment marks on the substrate; determining the position of the product feature based on the measurements of the product feature and / or the image of the product feature and the measurements of the one or more alignment marks; The method of claim 2 further comprising:

4. At least a portion of the measurements of the product features and / or the images of the product features are performed offline; The method of claim 3 , wherein at least a portion of the measuring of the one or more alignment marks is performed in-line.

5. The method of claim 4 , wherein the offline and in-line measurements are combined by combining modified grids of alignment tools used for the offline and in-line measurements.

6. The method of claim 1 , wherein the plurality of position measurements includes first tool metrology data measured with a first metrology tool and second tool metrology data measured with a second metrology tool.

7. the first metrology tool is a scanning electron microscope tool; and / or The method of claim 6 , wherein the second metrology tool is an optical metrology tool.

8. The method of claim 7 , wherein the scanning electron microscope measures at least one of the plurality of position measurements of one or more product features and / or targets on the substrate below the top layer of the substrate.

9. The method of claim 6 , wherein the first tool metrology data comprises first tool target metrology data measured on a target and first tool device metrology data measured on a device structure.

10. determining, from the first tool target metrology data and the first tool device metrology data, one or more metrology-to-device offsets for one or more device structures associated with the first tool device metrology data; 10. The method of claim 9, wherein the one or more metrology-to-device offsets include a comparison of the measurements for each device in the first tool device metrology data to the corresponding measurements in the first tool target metrology data.

11. The method of claim 10 , comprising combining and aggregating the one or more metrology-to-device offsets into a dense grid of metrology offsets for each target.

12. 11. The method of claim 10, comprising applying the one or more metrology-to-device offsets as a feedforward or feedback correction to a reference grid of an exposure apparatus.

13. the first tool target metrology data includes first tool target alignment data measured on an alignment mark; The method of claim 9 , wherein the first tool device metrology data comprises first tool device alignment data measured on a device structure.

14. the first tool target metrology data includes first tool target overlay data measured on an overlay target; The method of claim 9 , wherein the first tool device metrology data comprises first tool device overlay data measured on a device structure.

15. - modelling the distortion components of the substrate for at least one exposure field or subfield on the substrate according to a first field or subfield model or a scan profile fingerprint model; and / or Modeling the exposure slit of a lithographic apparatus used to manufacture a previous layer of said substrate according to a slit fingerprint model The method of claim 1 , comprising:

Images