Measurement apparatus and method for determining substrate grid

Abstract

To provide a measurement apparatus (10) and method for determining a substrate grid describing a deformation of a substrate (12) prior to exposure of the substrate (12) in a lithographic apparatus (LA) configured to fabricate one or more features on the substrate (12).SOLUTION: Position data for a plurality of first features and / or a plurality of second features on a substrate (12) is obtained. Asymmetry data for at least a feature of the plurality of first features and / or the plurality of second features is obtained. A substrate grid based on the position data and the asymmetry data is determined. The substrate grid and asymmetry data are passed to the lithographic apparatus LA for controlling at least part of an exposure process to fabricate one or more features on the substrate (12).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 18154053.5, filed January 30, 2018, and U.S. Application No. 62 / 773,576, filed November 30, 2018, which applications are incorporated by reference in their entireties into this specification.

[0002] This description relates to a measurement apparatus and method for determining a substrate grid. [Background technology]

[0003]

[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 devices such as integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern (often called a "design layout" or "design") in a patterning device (e.g., mask) onto a layer of radiation-sensitive material (resist) provided on the substrate (e.g., wafer).

[0004]

[0004] Lithographic apparatus may use electromagnetic radiation to project a pattern onto a substrate. 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. Lithographic apparatus using extreme ultraviolet (EUV) radiation with a wavelength in the range 4-100 nm, e.g. 6.7 nm or 13.5 nm, are able to form smaller features on a substrate than lithographic apparatus using radiation with a wavelength of, for example, 193 nm.

[0005]

[0005] In order to process features having dimensions smaller than the classical resolution limit of lithography equipment, low-k 1 Lithography may be used. In such a process, the equation for resolution is CD=k 1× λ / NA, 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” (generally the smallest feature size to be printed, but in this case the half pitch), and k 1 is an empirical resolution factor. In general, k 1 The smaller the k, the more difficult it becomes to replicate 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 such difficulties, advanced fine-tuning steps may be applied to the lithographic projection apparatus and / or the design layout, such as, but not limited to, optimizing the NA, customizing the illumination scheme, using phase-shifting patterning devices, various optimizations of the design layout, such as, but not limited to, optical proximity correction (OPC) in the design layout, or other methods commonly defined as "resolution enhancement techniques" (RET). Additionally or alternatively, low k 1 In order to improve pattern reproduction at 100 nm, a tight control loop can be used to manage the stability of the lithographic apparatus. Summary of the Invention

[0006]

[0006] Prior to exposure of a substrate in a lithographic apparatus, it is known to measure the positions of a number of substrate alignment marks in order to generate a substrate grid that provides a representation of the deformation of the substrate.

[0007]

[0007] The embodiments described herein may have use in EUV lithography apparatus. The embodiments may have use in deep ultraviolet (DUV) lithography apparatus and / or other type tools.

[0008]

[0008] In an aspect, there is provided a method for determining a substrate grid representing a deformation of a substrate prior to exposure of the substrate in a lithographic apparatus configured to fabricate one or more features on the substrate, the method comprising: acquiring position data for a plurality of first features and / or a plurality of second features on the substrate, acquiring asymmetry data for at least one of the plurality of first features and / or plurality of second features, determining a substrate grid based on the position data, and sending the substrate grid and asymmetry data to the lithographic apparatus for controlling at least a portion of an exposure process to fabricate the one or more features on the substrate.

[0009]

[0009] In an aspect, in a lithographic apparatus configured to fabricate one or more features on a substrate, there is provided a measurement apparatus configured to determine a substrate grid representative of a deformation of the substrate prior to exposure of the substrate, the measurement apparatus including an optical system configured to acquire position data for a plurality of first features and / or a plurality of second features on the substrate, the optical system further configured to acquire asymmetry data for at least one of the plurality of first features and / or plurality of second features, the measurement apparatus configured to determine a substrate grid based on the position data, or both the position data and the asymmetry data, and to send the substrate grid and asymmetry data to the lithographic apparatus for controlling at least a portion of an exposure process to fabricate one or more features on the substrate.

[0010]

[0010] In an aspect, a method is provided for calculating a value for a process parameter measurement error obtained from measurement of a substrate including a target exposed to a manufacturing process and having process distortions, the process parameter measurement error being a result of the process distortions, the method including obtaining alignment asymmetry data indicative of asymmetry in one or more alignment marks used to align the substrate, obtaining a model correlating the alignment asymmetry data to the process parameter measurement error, and using the alignment asymmetry data and the model to obtain a value for the process parameter measurement error.

[0011]

[0011] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: [Brief description of the drawings]

[0012] [Figure 1] 1 depicts a schematic overview of a lithographic apparatus; [Diagram 2]

[0013] 1 shows a schematic overview of a lithography cell. [Diagram 3]

[0014] 1 shows a schematic representation of lithography technology including cooperation between three technologies to optimize semiconductor manufacturing. [Figure 4]

[0015] 1 shows a schematic representation of a measurement apparatus for determining feature position and asymmetry. [Diagram 5]

[0016] 1 shows a schematic representation of an alignment and levelling sensor and an exposure apparatus in a lithographic apparatus. [Figure 6]

[0017] 1 shows a schematic representation of a metrology apparatus for measuring overlay. [Figure 7]

[0018] 1 shows a flow diagram of a method for determining a substrate grid, alignment and overlay measurements in a lithographic apparatus. [Figure 8]

[0019] 4 illustrates a flow diagram of a method for calculating a value for an overlay measurement error in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013]

[0020] As used herein, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet (e.g., having wavelengths of 365, 248, 193, 157, or 126 nm) and EUV (e.g., extreme ultraviolet having wavelengths in the range of about 5 to 100 nm).

[0014]

[0021] The terms "reticle," "mask," or "patterning device" as used herein may be broadly interpreted to refer to any general patterning device that can be used to provide an incident radiation beam with a patterned cross-section that corresponds to the pattern to be created on a target portion of a substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective masks, binary masks, phase-shifting masks, hybrid masks, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0015]

[0022] 1 illustrates diagrammatically a lithographic apparatus LA, comprising: an illumination system IL (also called an illuminator) configured to condition a radiation beam B (e.g. UV, DUV or EUV radiation), a support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g. a 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.

[0016]

[0023] In operation, the illumination system IL receives a radiation beam from a radiation source SO (e.g. via a beam delivery system BD). The illumination system IL may include various types of optical components for directing, shaping and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components or any combination of these. The illuminator IL may be used to condition the radiation beam B such that it has a desired spatial and angular intensity distribution in its cross-section in the plane of the patterning device MA.

[0017]

[0024] The term "projection system" PS as used herein should be broadly interpreted to encompass various types of projection systems. Such systems may include refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems or any combination thereof, as required by the exposure radiation being used and / or other factors (e.g., the use of an immersion liquid or the use of a vacuum). Where the term "projection lens" is used herein, it may all be considered as synonymous with the more general term "projection system" PS.

[0018]

[0025] The lithographic apparatus LA (or scanner) may be of a type in which at least a part of the substrate may be covered in 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, which is also referred to as immersion lithography. Details of immersion techniques are given in U.S. Patent No. 6,952,253, which is incorporated herein by reference in its entirety.

[0019]

[0026] The lithographic apparatus LA may be of a type having two or more substrate supports WT (also referred to as "dual stage"), and in such a "multiple stage" machine, the substrate supports WT may be used in parallel, and / or a substrate W on one of the substrate supports WT may be used to expose a pattern thereon, while a procedure is being performed on another substrate W on the other substrate support WT in preparation for a subsequent exposure of the other substrate W.

[0020]

[0027] In addition to the substrate support WT, the lithographic apparatus LA may include a measurement stage. The measurement stage may be configured to hold a sensor and / or a cleaning apparatus. The sensor may be configured to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold a number of sensors. The cleaning apparatus may be configured to clean part of the lithographic apparatus, for example part of the projection system PS or part of a system for supplying immersion liquid. The measurement stage may move below the projection system PS when the substrate support WT is spaced apart from the projection system PS.

[0021]

[0028] In operation, a radiation beam B is incident on a patterning device (e.g. a mask MA held on a support MT) and is patterned according to a pattern (design layout) on the patterning device MA. After traversing the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and a position measurement system IF (e.g. an LA alignment sensor), the substrate support WT can be precisely moved, e.g. such that the various target portions C are positioned at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM and possibly another position sensor (which is not explicitly shown in FIG. 1 ) may be used to precisely position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Substrate alignment marks P1, P2 occupy dedicated target portions as illustrated, but may be located in spaces between target portions. When substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe-lane alignment marks.

[0022]

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

[0023]

[0030] To ensure that a substrate W to be exposed by the lithographic apparatus LA is exposed accurately, it is desirable to inspect the substrate to measure the value of one or more properties of the patterned structures, such as the overlay error value between successive layers, the line thickness, the critical dimension value (CD), etc. For that purpose, one or more inspection tools (not shown) may be included in the lithocell LC. If an error is detected, adjustments may be made, for example, to the exposure of subsequent substrates or other processing steps to be performed on the substrate W, especially if inspection is performed before other substrates W of the same batch or lot are exposed or processed.

[0024]

[0031] The inspection apparatus, which may also be called metrology apparatus, is used to measure one or more properties of the substrate W, in particular to determine how the values ​​of one or more properties of different substrates W vary, or how the values ​​of one or more properties associated with different layers of the same substrate W vary from layer to layer. The inspection apparatus may instead be constructed to identify defects on the substrate W, and may for example be part of a lithocell LC, or integrated into the lithographic apparatus LA, or even be a stand-alone apparatus. The inspection apparatus may measure one or more properties of a latent image (image in the resist layer after exposure), one or more properties of a semi-latent image (image in the resist layer after a post-exposure bake step PEB), one or more properties of a developed resist image (where exposed or unexposed parts of the resist have been removed), or even one or more properties of an etched image (after a pattern transfer step such as etching).

[0025]

[0032] Typically, the patterning process in the lithography apparatus LA is a critical step in the process and requires high accuracy in the dimensional measurement and placement of structures on the substrate W. To help ensure this high accuracy, three systems may be combined in a controlled environment, as shown diagrammatically in FIG. 3. One of these systems is the lithography apparatus LA, which is (virtually) connected to a metrology tool MET (second system) and a computer system CL (third system). The goal of such a controlled environment is to optimize the coordination between these three systems to enhance the overall process window, and to provide a tight control loop to help ensure that the patterning performed by the lithography apparatus LA stays within the process window. The process window defines the range of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process will yield a defined result (e.g., a functioning semiconductor device), and within which the process parameters of the lithography process or patterning process may typically vary.

[0026]

[0033] The computer system CL can predict which resolution enhancement technique should be used by using (part of) the design layout to be patterned, and can perform computational lithography simulations and calculations to determine the patterning device (e.g., mask) layout and lithography apparatus settings that achieve maximization of the overall process window of the patterning process (indicated by the double-headed arrow at the first scale SC1 in FIG. 3). Typically, the resolution enhancement techniques are arranged to match the patterning capabilities of the lithography apparatus LA. The computer system CL can further predict whether defects are likely to be present (e.g., due to suboptimal processing) by detecting (e.g., using input from the metrology tool MET) where in the process window the lithography apparatus LA is currently operating (indicated by the arrow pointing to "0" at the second scale SC2 in FIG. 3).

[0027]

[0034] The metrology tool MET is capable of providing input to the computer system CL enabling accurate simulation and prediction, and is capable of providing feedback to the lithographic apparatus LA identifying possible drifts (e.g., in the calibration status of the lithographic apparatus LA) (as shown by multiple arrows at the third scale SC3 in Figure 3).

[0028]

[0035] The lithographic apparatus LA is configured to accurately reproduce the pattern on the substrate. The position and dimensions of the applied features should be within a certain tolerance. Position errors can occur due to overlay errors (often referred to as "overlay"). Overlay is the error in placing a first feature during a first exposure relative to a second feature during a second exposure. The lithographic apparatus aims to reduce or minimize the overlay errors by precisely aligning each substrate with a reference prior to patterning. This is done by measuring the position of alignment marks on the substrate with an alignment sensor. More information on alignment procedures can be found in US Patent Application Publication No. 2010-0214550, which is incorporated herein by reference in its entirety. Pattern dimension measurement (CD) errors can occur, for example, when the substrate is not precisely positioned with respect to the focal plane of the lithographic apparatus. Focus position errors may be associated with non-flatness of the substrate surface. Lithographic apparatus use level sensors to reduce or minimize focus position errors by measuring the substrate surface topography prior to patterning. Substrate height corrections are applied during subsequent patterning to help ensure accurate imaging (focusing) of the patterning device pattern onto the substrate. More information regarding level sensor systems can be found in U.S. Patent Application Publication No. 2007-0085991, which is incorporated herein by reference in its entirety.

[0029]

[0036] In addition to the lithography apparatus LA and metrology apparatus MET, one or more other processing apparatus may also be used during device fabrication. An etching station (not shown) processes the substrate after exposure of the pattern onto the resist. The etch station transfers the pattern from the resist to one or more layers below the resist layer. Typically, etching is based on the application of a plasma medium. One or more local etching characteristics may be controlled, for example, using temperature control of the substrate or managing the plasma medium using a voltage control ring. More information regarding etching control can be found in WO 2011 / 081645 and US Patent Application Publication No. 2006-0016561, each of which is incorporated herein by reference in its entirety.

[0030]

[0037] During the manufacture of a device (such as an IC), it is desirable for the process conditions for processing a substrate using one or more processing equipment, such as a lithography equipment or an etching station, to remain stable so that the values ​​of one or more characteristics of the features remain within certain control limits. Process stability is particularly important for device functional features that are product features. To help ensure stable processing, process control capabilities should be in place. Process control involves monitoring of process data and implementation of measures for process correction, such as controlling a processing equipment based on characteristics of the process data. Process control may be based on periodic measurements by a metrology equipment MET, often referred to as "advanced process control (also called APC)". More information on APC can be found in U.S. Patent Application Publication No. 2012-0008127, which is incorporated herein by reference in its entirety. A typical APC implementation involves periodic measurements of metrology features on a substrate to monitor and correct drifts associated with one or more processing equipment. The metrology features reflect the response of the product features to process variations. The sensitivity of metrology features to process variations may be different compared to product features. In that case, a so-called "metrology-to-device" offset (also called MTD) may be calculated. To mimic the behavior of product features, metrology targets may incorporate segmented features to support feature(s) with specific geometries and / or dimensions. A carefully designed metrology target should respond to process variations in a similar manner as product features. More information on metrology target design can be found in WO 2015 / 101458, which is incorporated herein by reference in its entirety.

[0031]

[0038] The distribution of locations across the substrate and / or patterning device where metrology targets reside and / or are measured is often referred to as a "sampling scheme". Typically, the sampling scheme is selected based on the expected fingerprint of the process parameters involved. Areas on the substrate where the process parameters are expected to vary are typically sampled more densely than areas where the process parameters are expected to remain constant. Furthermore, there are limitations on the number of metrology measurements that can be performed based on the acceptable impact of the metrology measurements on the throughput (e.g., number of substrates processed per unit time) of the lithography process. A carefully selected sampling scheme is important to accurately control the lithography process without affecting the throughput and / or allocating too large an area on the reticle or substrate to the metrology features. Techniques related to optimal positioning and / or measurement of metrology targets are often referred to as "scheme optimization". More information on scheme optimization can be found in WO 2015 / 110191 and WO 2018 / 069015, each of which is incorporated herein by reference in its entirety.

[0032]

[0039] In addition to metrology measurement data, contextual data may be used for process control as well. The contextual data may include data related to one or more of the selected processing tool (from a pool of processing equipment), the specific characteristics of the processing equipment, the processing equipment settings, the design of the patterning device pattern, and / or measurement data related to the processing conditions (e.g., substrate geometry). Examples of using contextual data for process control purposes can be found in WO 2017 / 140532 and WO 2017 / 060080, each of which is incorporated herein by reference in its entirety. The contextual data may be used to control or predict processing in a feed-forward manner, where the contextual data relates to a process step that was performed prior to the currently controlled process step. Often the contextual data is statistically correlated to one or more product feature characteristics. This allows for context-driven control of one or more processing equipment with a view to achieving improved or optimal values ​​of one or more product feature characteristics. Contextual data and metrology data may also be combined to enrich scarce metrology data, for example to the extent that more detailed (dense) data becomes available that is more useful for control and / or diagnostic purposes. More information regarding combining contextual data and metrology data can be found in WO 2017 / 144379, which is incorporated herein by reference in its entirety.

[0033]

[0040] Since process monitoring is based on the acquisition of process-related data, the data sampling rate and sampling density (per lot or per substrate) depend on the desired level of accuracy of pattern reproduction. For low k1 lithography processes, even small substrate-to-substrate process variations can be significant. The contextual and / or metrology data should then be sufficient to enable process control on a substrate-by-substrate basis. Additionally, if process variations cause property variations across the substrate, the density of the contextual and / or metrology data should be sufficiently distributed across the substrate. However, the time available for metrology (measurement) is limited given the desired throughput of the process. As a result of this limitation, the metrology tool may only measure selected substrates and / or selected locations across the substrate. Strategies for determining which substrates should be measured are further described in WO 2018 / 072980 and WO 2018 / 072962, each of which is incorporated herein by reference in its entirety.

[0034]

[0041] In practice, it may be necessary to derive a denser map of values ​​from a sparse set of measurements related to the process parameters (across a substrate or substrates). Typically, such a dense map of measurements may be derived from sparse measurement data in conjunction with a model related to the expected fingerprint of the process parameters. More information on modeling of measurement data can be found in WO 2013 / 092106, which application is incorporated herein by reference in its entirety.

[0035]

[0042] In lithographic processes, it is desirable to make frequent measurements of the structures created, e.g. for process control and verification. Tools for making such measurements are typically called metrology tools. Different types of metrology tools are known for making such measurements, including scanning electron microscopes or various forms of scatterometer metrology tools. Scatterometers are versatile tools, they allow the measurement of parameters of the lithographic process by having a sensor at or in a conjugate plane with respect to the pupil of the scatterometer objective lens (the measurement is usually called pupil-based measurement) or by having a sensor at or in a conjugate plane with respect to the image plane (the measurement is usually called image- or field-based measurement). Such scatterometers and associated measurement techniques are further described in U.S. Patent Application Publication Nos. 2010-0328655, 2011-102753, 2012-0044470, 2011-0249244, and 2011-0026032, and European Patent Application Publication No. 1628164. Each of the foregoing patent application publications is incorporated herein by reference in its entirety. The foregoing scatterometers may measure gratings using soft x-ray radiation, extreme ultraviolet radiation, and radiation from the visible to near infrared wavelength range.

[0036]

[0043] In one arrangement, the scatterometer is an angle-resolved scatterometer. In such a scatterometer, a reconstruction method may be applied to the measurement signal to reconstruct or calculate values ​​of one or more properties of the grating. Such a reconstruction may result, for example, from simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulation results with the measurement results. Parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from the real target.

[0037]

[0044] In a further embodiment, the scatterometer is a spectroscopic scatterometer. In such a spectroscopic scatterometer, radiation emitted from a radiation source is directed towards a target and radiation reflected or scattered from the target is directed towards a spectrometer detector which measures the spectrum of the specularly reflected radiation (i.e. the intensity as a function of wavelength). From this data it is possible to reconstruct the structure or profile of the target giving rise to the detected spectrum, for example by rigorous coupled wave theory and nonlinear regression, or by comparison with a library of simulated spectra.

[0038]

[0045] The scatterometer is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring the asymmetry in the reflectance spectrum and / or the detection configuration, the asymmetry being related to the degree of overlay. The two (typically overlapping) grating structures can be applied, for example, in two different layers (not necessarily in consecutive layers) and formed at approximately the same location on the substrate. The scatterometer can have a symmetric detection configuration, for example as described in EP 1 628 164 (incorporated herein by reference in its entirety), so that any asymmetry is clearly identifiable. This provides a direct way to measure the misalignment of the gratings. Further examples for measuring the overlay error between two layers containing periodic structures as targets by measuring through the asymmetry of the periodic structures can be found in WO 2011 / 012624 and US 2016-0161863, each of which is incorporated herein by reference in its entirety.

[0039]

[0046] 4 shows a measurement apparatus, hereafter referred to as a Feed-Forward Metrology Cluster (FFMC) 10, that is arranged to perform measurements of a substrate 12 before the substrate 12 is sent to a lithography apparatus LA for exposure. The FFMC 10 may be arranged after a photoresist deposition tool and before the lithography apparatus LA. The FFMC 10 may be a dual stage system having a first stage 14 and a second stage 16.

[0040]

[0047] The first stage 14 of the FFMC 10 includes an alignment sensor 18. Typically, the first stage 14 may also include a sensor system that provides leveling of the substrate relative to another sensor system (e.g., alignment sensor 18), typically referred to as a level sensor. Any class of level sensor may be utilized, such as a gas (e.g., air) gauge, optical level sensor, stamp-based sensor (based on mechanical interaction with the substrate), etc. Typically, the level sensor does not provide a single distance number between the substrate and the other sensor, but it samples the height of the substrate at multiple locations to determine a height profile of the substrate. The alignment sensor 18 is configured to measure position data of a plurality of first features, which in this exemplary case are alignment marks. The alignment marks may include a diffraction grating having a particular pitch. Typically, the pitch of the alignment marks is substantially larger than the wavelength of the radiation used to measure the position of the alignment marks, and therefore the alignment sensor 18 may have a low numerical aperture (NA), desirably 0.9 or less. Considering the required NA of an alignment sensor for measuring the position of the first features, these first features are referred to herein as "low NA alignment marks."

[0041]

[0048] It can be advantageous for alignment sensor 18 to be a low NA sensor because alignment and leveling are performed on the same substrate and space is needed between the level sensor and substrate 12 to perform the leveling.

[0042]

[0049] To acquire position data for a plurality of low NA alignment marks, alignment sensor 18 is scanned across substrate 12 (eg, by moving substrate 12 relative to alignment sensor 18).

[0043]

[0050] The second stage 16 of the FFMC 10 includes one or more, in this exemplary case three, metrology sensors 20 (i.e., optical systems) configured to measure the positions of the multiple low NA alignment marks. The metrology sensors 20 may also measure asymmetries of features of the multiple low NA alignment marks. In other examples, the second stage 16 may include more or less than three metrology sensors 20.

[0044]

[0051] Metrology sensors 20 may include high numerical aperture (NA) optics, e.g., having an NA greater than 0.9. That is, one or more of metrology sensors 20 are high NA sensors. Thus, as shown in step 102 of FIG. 7, position and asymmetry data for low NA alignment marks may be acquired using high NA optics, e.g., including a sensor with an NA greater than 0.9.

[0045]

[0052] The metrology sensor 20 may be located relatively closer to the substrate 12 when compared to the alignment sensor 18, and therefore may have a relatively large NA.

[0046]

[0053] The metrology sensor 20 may, for example, measure position data of the low NA alignment mark by detecting the low NA alignment mark in the image plane of the metrology sensor 20, and measure asymmetry data by observing the low NA alignment mark in the pupil plane of the metrology sensor 20.

[0047]

[0054] In particular, the analysis is performed on radiation scattered from a low NA alignment mark. Asymmetries in the intensity associated with the diffracted (angular) spectrum of the scattered radiation from the low NA alignment mark allow the asymmetry of the low NA alignment mark to be determined. The metrology sensor 20 may be a high NA sensor in order to be able to detect the diffracted spectrum of the scattered radiation.

[0048]

[0055] The use of multiple (e.g., three) metrology sensors 20 allows an increased number of low NA alignment marks to be measured within a limited time frame. The metrology sensors 20 may be spaced relative to one another such that the substrate 12 is located directly underneath them. Having three sensors 20 allows three measurements from three separate low NA alignment marks to be made simultaneously. This may allow, for example, 200 low NA alignment marks to be measured by the metrology sensor 20 during a scan of the substrate 12 (e.g., by moving the substrate 12 relative to the metrology sensor 20).

[0049]

[0056] In another example, one of the metrology sensors 20 may be an IR (infrared) sensor. An example of such an IR sensor is given in European Patent Application No. 17181375.1, which is incorporated herein by reference in its entirety. The IR sensor may be configured to detect radiation having a wavelength that passes through an opaque layer of the substrate 12. This allows for measurements of features (e.g., alignment marks) that are not possible using the other metrology sensors 20. In another example, one of the metrology sensors may be any suitable sensor that allows measurements to be made from below a top (e.g., opaque) layer of the substrate 12.

[0050]

[0057] 7 illustrates a flow of a method according to an embodiment. First position data for a plurality of (e.g., low NA) alignment marks is acquired (e.g., using a low and / or high NA sensor) (step 100). Next, asymmetric data of the (e.g., low NA) alignment marks is acquired (step 102), for example, using a high NA sensor.

[0051]

[0058] Step 104 includes determining a substrate grid based on the position data and, optionally, the asymmetry data. The substrate 12 may have been deformed from the processes to which it was subjected, and the substrate grid indicates where these deformations are located. However, the low NA alignment marks may also have been deformed from the processes to which the substrate 12 was subjected. That is, the low NA alignment marks may have an asymmetry. This means that the position data from the low NA alignment marks may not be accurate, and thus the substrate grid representing the deformations may not be accurate. The asymmetry data from the low NA alignment marks may be used to correct the asymmetry of the low NA alignment marks, and thus provide an improved substrate grid (asymmetry corrected substrate grid). In other words, the asymmetry data may be used to reduce or minimize the effect of the asymmetry of the low NA alignment marks on the substrate grid. As such, the asymmetry corrected substrate grid may include a more accurate substrate grid representing the deformations of the substrate 12, as determined from the position and asymmetry data.

[0052]

[0059] This asymmetry corrected substrate grid is sent to the lithographic apparatus in step 106. Alternatively (or additionally) in step 106, an uncorrected substrate grid (a substrate grid based only on position measurements) may be determined and sent to the lithographic apparatus together with the asymmetry data.

[0053]

[0060] As such, once the substrate grid has been determined and the asymmetry data measured, the substrate 12, together with the asymmetry-corrected and / or uncorrected substrate grid and the asymmetry data, is sent to the lithography apparatus LA, as indicated by arrow 22 in FIG. 4.

[0054]

[0061] If the substrate grid delivered in step 106 is not asymmetry corrected, then an asymmetry corrected substrate grid may be determined by / within the lithographic apparatus, which should be done before the substrate grid is used to control a subsequent step 108 of exposing a substrate to create one or more features on the substrate.

[0055]

[0062] 5 shows a lithography apparatus with a LA first stage 24 and a LA second stage 26. In the LA first stage 24, a LA alignment sensor 28 (hereafter referred to as LA alignment sensor 28) is provided. The LA alignment sensor 28 may be a low NA sensor. In the LA second stage 26, an exposure apparatus 30 is provided. After exposure of the substrate, the substrate may be transferred to a metrology apparatus (e.g. an overlay measurement apparatus), as indicated by arrow 32.

[0056]

[0063] Together with a position measurement system IF, for example as shown in FIG. 1, the LA alignment sensor 28 is used to align the substrate 12 in the lithographic apparatus LA and further determine the substrate grid as measured in the lithographic apparatus (the "lithographic apparatus substrate grid").

[0057]

[0064] As described, if the substrate grid as determined by FFMC 10 is an asymmetry-corrected substrate grid, this already accurate substrate grid may be mapped to a substrate grid as determined by an alignment process in the lithographic apparatus (e.g. with a lithographic apparatus substrate grid). The substrate grid obtained by mapping the asymmetry-corrected substrate grid to the lithographic apparatus substrate grid may be used to control at least a part of an exposure process to fabricate one or more features on the substrate 12 (step 108 of FIG. 7). This may include aligning the substrate 12 in the lithographic apparatus LA based on the substrate grid and the asymmetry data (step 110 of FIG. 7), e.g. based on the asymmetry-corrected substrate grid.

[0058]

[0065] If the substrate grid as determined by FFMC 10 has not already been corrected for asymmetry, then lithographic apparatus LA may use the substrate grid and asymmetry data to reduce or minimize the effect of the alignment mark asymmetry relative to the lithographic apparatus substrate grid and the substrate grid as measured by FFMC 10. A general method of using asymmetry data to improve the accuracy of the substrate grid based on measurements of marks is disclosed in U.S. Patent No. 9,778,025, which is incorporated herein by reference in its entirety.

[0059]

[0066] Measuring the position and asymmetry data of the low NA alignment marks before the substrate 12 is sent to the lithography apparatus LA allows to measure more alignment marks than can be performed in the lithography apparatus LA, since there are time limitations set for in-process measurements (during exposure), e.g. to allow maximum throughput of the substrate 12 in the lithography apparatus LA. For example, by using the FFMC 10, it is possible to perform e.g. 200-600 measurements of the xy positions of the alignment marks, compared to only about 40 different alignment mark measurements that can be performed in the lithography apparatus LA. The more marks that are measured, the better the accuracy of the determined substrate grid (representing a certain substrate deformation).

[0060]

[0067] In another example, the metrology sensor 20 may measure position data of a second feature, which may include a metrology target in an exemplary case. The metrology target may be a collection of composite gratings formed by a lithography process (e.g., in a resist (more commonly) or after an etching process). Typically, the pitch and line width of the structures in the gratings are selected based on the measurement optics (particularly the NA of the optics) so as to be able to capture the diffraction orders coming from the metrology target.

[0061]

[0068] The diffracted radiation may be used to determine the position shift between the two layers (also called "overlay") or to reconstruct at least a part of the geometry of the grating as produced by the lithography process. This reconstruction may be used to provide guidance on the quality of the lithography process and to control at least a part of the lithography process. The metrology target may be an overlay target. The overlay target may be a diffraction grating with a specific pitch, and the overlay target is usually smaller than the alignment mark. In another example, the metrology sensor 20 may measure the asymmetry data of the second feature. Since the function of the second feature (e.g., the metrology target) is most associated with alignment purposes in this document and the second feature needs to be measured with a high NA sensor (metrology sensor), they are referred to as high NA alignment marks in this document. High NA alignment marks are typically densely distributed across the substrate and are dense enough to allow characterization of substrate deformations on a spatial scale comparable to an individual exposure field. High NA alignment marks are, for example, located in scribe lanes between dies within an exposure field and / or in scribe lanes between exposure fields, in other words, position measurements relative to the high NA alignment marks may enable higher resolution (typically within a field) characterization of the substrate grid.

[0062]

[0069] The high NA alignment mark positions within a field may be used to determine targeted control to optimize or improve exposure of individual fields across the substrate. The metrology data within a field may be associated with the same layer of the substrate 12 for which overlay is measured (the lower grid of overlay marks is distributed across two layers). The data within a field may be sampled at high spatial frequency across the substrate 12. The alignment data (for all fields) may be analyzed for deformations of the substrate 12 and alignment marks (either low NA or high NA alignment marks). The positions of the high NA alignment marks within a field may be further added to the substrate grid (based initially on the low NA alignment mark position measurements).

[0063]

[0070] In effect, the positions of the high NA alignment marks within the field as measured in the FFMC 10 are sent to the exposure tool 30. The additional data improves the accuracy of the characterization of the substrate-to-substrate variations of the substrate grid and the spatial corrections performed during exposure with the lithographic tool. This reduces the substrate-to-substrate variations in e.g. overlay quality as measured after exposure. All existing feedback, feedforward and advanced process control loops can remain in place.

[0064]

[0071] Asymmetry measurements can be made from both low and high NA alignment marks. High NA alignment marks generally have a smaller pitch than low NA alignment marks. The effect of processing (e.g., chemical mechanical planarization (CMP)) on the asymmetry of both mark types is usually not the same. Typically, the asymmetry of smaller pitch marks is not as sensitive to processing as the asymmetry associated with larger pitch marks. Therefore, dedicated asymmetry measurements for both low and high NA alignment marks are typically used. However, in the embodiments described below, this requirement may be relaxed or removed.

[0065]

[0072] When both the low NA alignment mark position data and the high NA alignment mark positions are available, they may be individually corrected using the available asymmetry data and, after correction, merged to define a high resolution substrate grid, which may be mapped to a lithographic apparatus substrate grid and subsequently used to control the lithographic apparatus LA during exposure of a substrate, as previously explained.

[0066]

[0073] Previously, substrate-to-substrate variations existed in the substrate grid because there was insufficient high frequency spatial information (e.g., information with a spatial resolution of 1-10 mm). The concepts described herein provide a high resolution substrate grid, thus significantly alleviating the problem. Furthermore, there was no in-field substrate-to-substrate correction capability. The high resolution substrate grid includes in-field information, thus also significantly reducing this problem. Alignment measurements performed in the lithographic apparatus were limited to position measurements of low NA alignment marks, and therefore did not directly correspond to the positions of metrology targets used for overlay control of the lithographic apparatus. It is proposed to include position measurements of high NA alignment targets, which are typically identical to the targets used for overlay measurement. Thus, embodiments of the present invention provide an efficient method of controlling a lithographic apparatus based on alignment measurements that are expected to show greater effectiveness in reducing substrate-to-substrate variations in the measured overlay.

[0067]

[0074] Typically, a calibration is performed to match the FFMC10 alignment results with those of the lithographic apparatus LA. This calibration mainly covers the sensor-to-sensor and substrate table WT-to-substrate table WT differences between the FFMC10 and the lithographic apparatus LA. The FFMC10 alignment data is mapped to the alignment data of the lithographic apparatus LA. The alignment data may be taken from alignment markers on a reference substrate followed by storage of the calibration parameters, or alternatively the alignment data may be taken from alignment markers for each substrate passing through the FFMC and the lithographic apparatus.

[0068]

[0075] One of the metrology sensors 20 may be calibrated to the LA alignment sensor 28 in order to correlate the position measurements made by the metrology sensor 20 with the position measurements made by the LA alignment sensor 28. The low NA alignment mark positions would then need to be measured by both the FFMC 10 and the lithographic apparatus LA. Alternatively, the metrology sensor 20 may be calibrated to the alignment sensor 18 on the first stage of the FFMC 10. If the alignment sensor 18 is calibrated to the LA alignment sensor 28 in the lithographic apparatus, then the metrology sensor 20 is also calibrated to the alignment sensor 28.

[0069]

[0076] At least one selected one of the position data associated with the plurality of high NA alignment marks may be calibrated against the position data associated with the plurality of low NA alignment marks. At least one selected one of the position data may be calibrated against further position data acquired during alignment of the substrate 12 in the lithographic apparatus LA. In general, it is desirable that the positions associated with a common set of low NA alignment marks are measured by the alignment sensor 18 on the first stage of the FFMC 10, the alignment sensor of the lithographic apparatus LA, and the metrology sensor 20 on the second stage of the FFMC 10. The further position data acquired during alignment of the substrate 12 in the lithographic apparatus LA may be calibrated against at least one selected one of the position data.

[0070]

[0077] 6 shows an overlay measurement apparatus 36 that includes a stage 34. Overlay is a measure of how accurately features on one layer of substrate 12 are fabricated over underlying features in another layer of substrate 12.

[0071]

[0078] Using the asymmetric data of the high NA alignment marks allows for better overlay measurements because the asymmetry of the high NA alignment marks is expected to be the same as the asymmetry of the overlay target. Therefore, the asymmetric data of the high NA alignment marks may be sent to the metrology tool 36 to measure the overlay (step 112 of FIG. 7). In step 114 of FIG. 7, the overlay data can be determined based on the overlay measurement and the asymmetric data from step 112. The use of the asymmetric data of the high NA alignment marks results in improved accuracy of the overlay measurement since the position of the overlay target can be more accurately determined. An example of how asymmetric data can be used to improve overlay measurement accuracy is disclosed in U.S. Pat. No. 9,134,256, which is incorporated herein by reference in its entirety.

[0072]

[0079] The asymmetric data is used to reduce or minimize the effect of the asymmetry of the overlay target on the overlay measurement, as performed in the overlay measurement apparatus 36. The improved overlay measurement provides increased feedback accuracy to the lithographic apparatus LA.

[0073]

[0080] There are two main optical OV (overlay) metrology concepts: Image-Based OV Metrology (IBO) and Diffraction-Based OV Metrology (DBO). In the case of IBO, the OV target is made of X and Y resist gratings that are spatially separated from the X and Y gratings in the product layer. DBO uses gratings in the top and bottom layers, but in contrast to IBO, the gratings are placed on top of each other, not beside each other. When the gratings are perfectly aligned (=zero overlay error), they form a symmetric compound grating with symmetric scattering properties. However, small misalignments (overlay error ≠ 0) produce asymmetric compound gratings that produce an asymmetry in the intensity of the diffracted radiation.

[0074]

[0081] Previously, there was substrate-to-substrate variation in metrology measurements due to variations in bottom grid asymmetry (BGA) per substrate. Now, the BGA can be measured prior to overlay measurement in the FFMC using metrology sensor 20. Now, the determination of overlay data can use asymmetry data related to the bottom grid portion of the overlay target (as provided by metrology sensor 20), leading to smaller measured substrate-to-substrate variation in the overlay data.

[0075]

[0082] Although the above description shows that the FFMC 10 is located outside the lithographic apparatus LA, in other examples, the FFMC 10 may be located in the lithographic apparatus LA or may be part of the lithographic apparatus LA. Alignment in the lithographic apparatus LA may be considered to be similar to pre-exposure metrology. The alignment system in the lithographic apparatus LA may be able to measure both the positions of the low NA alignment marks and the high NA alignment marks as well as the asymmetry of the marks, for example by using a high NA sensor.

[0076]

[0083] A further embodiment will now be described of determining process distortions (e.g. process asymmetries) at a first feature, such as an alignment mark (e.g. a low NA alignment mark), using the process distortions at the first feature to correct a measurement of a process parameter, such as overlay, for process distortions (e.g. process asymmetries) at a second feature (e.g. a metrology target, such as an overlay target used to measure overlay). The process asymmetries are asymmetries caused by processing effects such as floor slope or sidewall angle asymmetries. This should be the only asymmetry in the alignment mark. However, the overlay target will typically include other asymmetries caused by the overlay being measured and any intentional biases (if present). In this embodiment, the asymmetries in the alignment mark may be measured using the FFMC 10. However, in another embodiment, which will be described more fully, the asymmetries in the alignment mark are measured using the lithography apparatus LA (e.g. as part of a standard alignment process using the LA alignment sensor 28 to align the substrate for exposure). As such, this embodiment may or may not include the use of an FFMC 10.

[0077]

[0084] Currently, in lithographic apparatus, there may be no feed-forward of alignment mark asymmetry from alignment mark measurements (e.g. by LA alignment sensor 28) to overlay measurements performed on a metrology device (e.g. a scatterometry device) such as overlay measurement apparatus 36. Since the physics of alignment sensors and metrology sensors are typically similar, i.e. based on interference of + / -1 diffraction orders from a grating, it is reasonable to assume that there will be some correlation in alignment position measurements versus overlay measurements from mark asymmetry in the alignment marks and overlay targets, respectively.

[0078]

[0085] As already mentioned, the effect of asymmetry on alignment measurements is different from the effect of asymmetry on overlay measurements because LA alignment sensor 28 typically measures targets (e.g., low NA alignment marks) that have a different (e.g., larger) pitch than the targets (e.g., high NA overlay targets) measured by overlay measurement device 36. Asymmetry in the alignment marks causes alignment errors, which in turn cause errors in the overlay measurements that are added to any errors in the overlay measurements that result from process (non-overlay / bias) asymmetries in the overlay targets.

[0079]

[0086] The process asymmetry in the alignment marks is typically different from the process asymmetry in the overlay target due to loading effects. Furthermore, one or both of these process asymmetries may be different from the in-product process asymmetry. Sometimes there is no in-product process asymmetry, but there is a process asymmetry in alignment and overlay, and the asymmetry is different for these two. In addition, the alignment error resulting from the alignment mark asymmetry is typically different from the overlay measurement error due to the overlay target process asymmetry, because the overlay measurement and the alignment measurement typically have different sensitivity to the asymmetry in the respective features being measured. As a result, there is a complex combination of overlay measurement errors resulting from the alignment mark asymmetry and resulting from the overlay target process asymmetry. A method for decoupling these effects is described.

[0080]

[0087] Measured Alignment Grid

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[0081]

[0088] Measured Overlay

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[0082]

[0089] The goal of this embodiment is to measure overlay

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[0083]

[0090] The alignment misregistration APD and in particular the color-to-color alignment misregistration (hereafter C2C APD) is an overlay asymmetry component.

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[0084]

[0091] It is therefore proposed that the C2C APD is used to correct the overlay measurement, e.g. as a feed-forward correction from the alignment measurement. Based on the C2C APD data, a correction for the effect of process asymmetry in the overlay target may be fed forward to the overlay measurement device (or a processing device that processes overlay data from the overlay measurement device) to correct the overlay measurement. In this way, it becomes possible to separate the effects of overlay target process asymmetry and alignment mark asymmetry on the overlay measurement.

[0085]

[0092] 8 is a flow chart illustrating a method according to this embodiment.

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[0086]

[0093] Next, true overlay

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[0087]

[0094] A training or modeling phase should be performed to determine the functions h and g. These functions may be determined through machine learning training and / or suitable models. The model may be constructed, for example, by correlating the C2C APD data to the expected deformation characteristics (asymmetry) of the overlay target. Suitable modeling techniques may include a technique known as "design for control", abbreviated as D4C, which is described in U.S. Patent Application Publication No. 2016-0140267, which is incorporated herein by reference in its entirety. In the D4C method, the individual steps of the lithography process are modeled into a single process sequence to simulate physical substrate processing. The process sequence does not "build" the device geometry element by element, but rather performs the generation of the device geometry as a whole. This differs from the conventional approach of using purely graphical volume elements in a 3D schematic editor to build the metrology target. The method allows for the automatic generation of robust metrology targets in a simulation domain that can accommodate a variety of lithography processes and process perturbations.

[0088]

[0095] As such, the calibration stage may include simulating (e.g., using the D4C modeling techniques described above or other suitable methods) various alignment marks and overlay targets (e.g., having various different design parameters, pitches, etc.) exposed to the same (simulated) processing and manufacturing steps on one or more common substrates (e.g., formed by a common simulated deposition, exposure, and / or etching process, etc.). The simulation may vary the effects of the various steps and / or vary different degrees and / or types of asymmetry in the marks and targets. The simulated alignment marks and overlay targets and corresponding simulated measurement data (e.g., data from simulated alignment measurements of simulated alignment marks to obtain simulated C2C APD data, and data from simulated overlay measurements of simulated overlay targets to obtain simulated overlay data) may then be used as training data. Alternatively and / or additionally, the training data may include actual measurements of physical features (i.e., machine learning on actual measured data).

[0089]

[0096] Machine learning techniques can then be used to determine the functions h and g from the simulated (and / or measured) alignment marks and overlay targets and associated parameters of the simulated (and / or measured) measurement data (e.g., from the simulated measurement data from the simulated features and known true values ​​and asymmetries). For example, training data can be used to train a neural or Boolean network to determine the functions g and h from the training data (which may be a particular or another measurement recipe).

[0090]

[0097] Once these functions are determined, they can be used in a manufacturing setting to correct overlay measurements (e.g., single wavelength overlay measurements) for undesired process asymmetries, i.e., asymmetry effects from effects other than overlay (including any intentional bias) based on feedforward corrections determined from the process asymmetries of alignment measurements (e.g., more specifically, C2C APD measurements).

[0091]

[0098] Alternatively, a suitable machine learning network (neural or Boolean network) can be used to measure other measurement data, e.g. C2C APD measurement data.

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[0092]

[0099] It was mentioned above that the measured overlay may include single wavelength overlay data. Currently, overlay may be measured using (at least) a three wavelength method (called HMQ) to remove overlay mark asymmetry from the overlay measurement. Further details of HMQ can be found in WO 2015 / 018625, which is incorporated herein by reference in its entirety. Very briefly, HMQ involves measuring a target including a +d bias sub-target and an ad bias sub-target with multiple wavelengths, and fitting a line through a plot of the asymmetry measurement for the first sub-target against the asymmetry measurement for the second sub-target structure, where the linear regression model is not necessarily fitted through the origin. The offset of this line from the origin (also called the distance to origin DTO) represents the target process asymmetry.

[0093] [000100] However, the MAM (move-acquire-measure) time for overall overlay measurement tends to be directly proportional to the number of wavelengths measured (e.g., MAM for three wavelength measurement is roughly three times that of single wavelength measurement). Due to the long MAM times of current overlay measurements, it is typical to only measure overlay on one substrate per lot. The proposed method can be used to significantly reduce the MAM (move-acquire-measure) time for (HMQ) overlay, since three wavelengths may not be required, thereby increasing the measurement speed and thus the throughput. As such, the measurement may include only the measurement of a single illumination characteristic (e.g., only a single wavelength measurement). Alternatively or additionally, the proposed method can be used to drive improvements in overlay and yield by allowing more overlay targets to be accurately measured.

[0094] [000101] The method of this embodiment can further improve the accuracy of the current HMQ method. Typically, only one substrate per lot is sampled in the overlay measurement without reducing the cluster throughput. The alignment position measurement is measured for each substrate, but can be used in the overlay measurement to determine whether more substrates need to be sampled per lot or different points should be measured per substrate.

[0095] [000102] More specifically, C2C APD is a method for detecting the overlay asymmetric component

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[0096] [000103] As explained in the previous paragraph, alignment or overlay measurements are typically based on detecting diffraction orders scattered by metrology structures. Examples of such metrology structures are alignment marks and overlay marks (including at least a bottom grating). The energy contained in the diffraction orders depends on the diffraction efficiency of the metrology structure. This diffraction efficiency depends in part on the pitch and duty cycle of the metrology structure, and in part on the stack characteristics in which the metrology structure is embedded.

[0097] [000104] The mentioned metrology systems generally derive properties of interest related to metrology structures based on a metric that has as input a measurement of the diffraction order intensity (or energy). For example, it is common practice to base overlay measurements on the calculation of the difference in intensity between the first and minus first diffraction orders scattered by an overlay mark. Thus, in the case of overlay measurements, the metric is the difference between the two diffraction order intensities. Typically, measurements using overlay metrology tools or alignment measurement systems are based on signals provided by a sensor located at or near a pupil plane, e.g., the diffraction orders are spatially separated at the plane where the sensor surface lies.

[0098] [000105] To facilitate accurate measurement of individual diffraction orders, it may be necessary to configure the illumination pupil of the light source used to illuminate the metrology structure. The illumination pupil may be configured such that there is no or very limited overlap, for example, between the first and minus first diffraction orders, and between the first and zeroth diffraction orders.

[0099] [000106] The difference metric scales with the overall diffraction efficiency of the metrology structure, which is determined in large part by the properties of the stack, and in particular by the interaction of the stack and the properties of the light used to illuminate the metrology structure (wavelength, polarization mode). For small diffraction efficiencies, the signal generated by the metrology system is too small to allow accurate measurement of the difference metric.

[0100] [000107] However, a sufficiently large diffraction efficiency may be achieved by selecting an appropriate wavelength and / or polarization mode of light used for illumination of the metrology structure. For example, measurements of the intensity of the first diffraction order may be performed for multiple wavelengths and / or polarization modes. In another example, a sum metric of the intensity of the first and minus first orders may be measured over a range of wavelengths and / or polarization modes, and then the wavelength and / or polarization mode may be selected based on an optimal sum metric related to the intensity contained within the first and minus first orders. The sum metric may be determined based on asymmetry data (as disclosed in any of the previous paragraphs) including the intensity of the diffraction orders as measured at multiple wavelengths and / or polarization modes. The asymmetry data may also include intensity data of the diffraction orders scattered by multiple features, for example, by the alignment marks and the overlay (bottom grating) marks.

[0101] [000108] Once the optimal range of wavelengths and / or polarization modes has been determined based on the sum metric above, a more optimal configuration of both the overlay metrology tool and / or the alignment measurement system may be achieved. For example, the optimal wavelength and polarization mode determined by optimizing the sum metric as measured by the overlay metrology tool may be communicated to a computer system configured to optimize settings of a metrology tool, such as an alignment measurement system or scatterometer (e.g., configured to measure overlay of a semiconductor manufacturing process). The computer system may then provide an optimized alignment measurement recipe that yields a more accurate position measurement of the alignment marks.

[0102] [000109] The functional dependence of the sum metric on the wavelength and / or polarization mode of light may further be used to monitor the evolution of stack properties due to changes in processing steps (e.g., performed by a CMP tool, a deposition tool, or an etching tool). For example, if the CMP tool used drifts in time, the thickness of the layers included in the stack is likely to change. As a result, since there is a strong coupling between the stack properties (e.g., layer thicknesses) and the diffraction efficiency of the metrology structures, the optimal wavelength of light in terms of the maximum sum metric is likely to change as well. Thus, both the value of the sum metric and its associated optimal wavelength and / or polarization mode of light may be used for monitoring the processing steps applied in manufacturing a semiconductor device.

[0103] [000110] In many cases, knowledge of the value of the sum metric and / or the optimal wavelength may be linked to precisely determined values ​​of one or more stack parameters. For example, a modeled relationship between stack thickness and diffraction efficiency of metrology structures may be available. The modeled relationship may be used to translate observed changes in the sum metric into expected changes in stack thickness. The expected changes in stack thickness may be used for process control purposes, for example to apply corrective control actions to deposition tools and / or CMP tools used in applying and polishing the layers included in the stack. Thus, apart from process monitoring, process control may also be based on knowledge of the sum metric and / or the optical properties of the light used in optimizing said sum metric.

[0104] [000111] It is recognized that a sum metric is a preferred metric that enables the above-mentioned configuration of a metrology system, monitoring of a semiconductor process, or control of a semiconductor manufacturing process. However, in general, knowledge of the integrated intensities or energies of at least the Nth and −Nth diffraction orders may be sufficient, and the integrated intensities or energies are typically added to produce the above sum metric, but also weighted sums may be considered in cases where one of the diffraction orders is found to be less relevant than the other diffraction orders.

[0105] [000112] The sum metric may also be used as a process parameter indicative of a performance (or quality) parameter, such as overlay, CD, or focus. In this case, a model may be trained that correlates the sum metric to the measured performance parameter data. The trained model may then be used to predict the performance parameter based on the sum metric, which may further be used in the context of a virtual / hybrid metrology system, where the sum metric is for example used to upsample the performance parameter data (e.g. as obtained by direct measurement of the performance parameter). In an embodiment, a model is trained on the sum metric and the performance parameter data, and the model is subsequently used to provide dense performance parameter data across a substrate based on knowledge of the sum metric associated with the substrate.

[0106] [000113] Further embodiments are disclosed in the following numbered clause listings: 1. A method for determining a substrate grid representative of a deformation of a substrate prior to exposure of the substrate in a lithographic apparatus configured to fabricate one or more features on the substrate, comprising: Obtaining position data for a plurality of first features and / or a plurality of second features on the substrate; acquiring asymmetry data for at least one feature of the plurality of first features and / or the plurality of second features; determining a substrate grid based at least on the position data; providing substrate grid and asymmetry data to a lithographic apparatus for controlling at least a portion of an exposure process to create one or more features on the substrate; A method comprising: 2. The method of claim 1, wherein the determination of the substrate grid is additionally based on the asymmetric data, such that the step of sending the substrate grid and the asymmetric data includes sending a substrate grid corrected for the asymmetry. 3. The method of claim 1, wherein the plurality of first features include alignment marks. 4. The method of claim 3, further comprising acquiring position data for the alignment marks using a low numerical aperture (NA) optical system including a sensor having an NA of 0.9 or less. 5. The method of any one of clauses 1-4, wherein the plurality of second features includes metrology targets and optionally overlay targets. 6. The method of claim 5, wherein the plurality of first features include alignment marks, and further comprising acquiring asymmetric data for the alignment marks and / or metrology targets using a high NA optical system including a sensor having an NA greater than 0.9. 7. The method of claim 6, wherein the high NA optical system includes a plurality of spatially distributed high NA sensors. 8. The method of any one of clauses 1 to 7, further comprising calibrating at least one selected one of the position data associated with the plurality of second features to the position data associated with the plurality of first features. 9. The method of clause 8, further comprising calibrating at least one selected one of the position data against further position data acquired during aligning of the substrate in the lithographic apparatus. 10. The method of claim 8, further comprising calibrating further position data acquired during aligning of the substrate in the lithographic apparatus against at least one selected one of the position data. 11. The method of any one of clauses 1-10, further comprising aligning the substrate in the lithographic apparatus based on the substrate grid and asymmetry data. 12. A method according to any one of clauses 1 to 11, further comprising controlling at least a part of an exposure process in a lithographic apparatus to fabricate one or more further features on the substrate based on the substrate grid and the asymmetry data, wherein the first and / or second features are located in a first layer and the one or more further features are located in a second or higher layer. 13. The method of any one of clauses 1-12, further comprising sending the asymmetric data to a metrology tool for measuring overlay. 14. The method of claim 13, further comprising determining overlay data based on the asymmetry data. 15. In a lithographic apparatus configured to fabricate one or more features on a substrate, a measurement apparatus for determining a substrate grid indicative of a deformation of the substrate prior to exposure of the substrate, comprising: the measurement apparatus includes an optical system configured to acquire position data for a plurality of first features and / or a plurality of second features on the substrate; the optical system is further configured to acquire asymmetric data for at least one feature of the plurality of first features and / or the plurality of second features; The measurement apparatus is configured to determine a substrate grid based on the position data, and to send substrate grid and asymmetry data to a lithographic apparatus for controlling at least a portion of an exposure process to create one or more features on the substrate. 16. The measurement apparatus of claim 15, wherein the plurality of first features include alignment marks. 17. A measurement apparatus as described in clause 16, wherein the optical system includes low numerical aperture (NA) optical systems including a sensor having an NA of 0.9 or less configured to acquire position data for the alignment mark. 18. The measurement apparatus of any one of clauses 15-17, wherein the plurality of second features include a metrology target and optionally an overlay target. 19. The measurement apparatus of clause 18, wherein the plurality of first features include alignment marks, and the optical system includes a high NA optical system including a sensor having a NA greater than 0.9 configured to acquire asymmetric data for the alignment marks and / or metrology targets. 20. The measurement apparatus of claim 19, wherein the high NA optical system includes a plurality of spatially distributed high NA sensors. 21. A measurement apparatus as described in clause 20, wherein the multiple spatially distributed high NA sensors include at least one sensor configured to detect radiation having a wavelength that passes through an opaque layer of the substrate, and optionally at least one sensor is an IR (infrared sensor). 22. A measuring device described in any one of clauses 15 to 21, wherein the measuring device is configured to calibrate at least one selected one of the position data associated with a plurality of second features against the position data associated with a plurality of first features. 23. A lithographic apparatus configured to use the substrate grid and asymmetric data of clause 1, comprising: A lithographic apparatus configured to align a substrate in the lithographic apparatus based on the position data and / or the asymmetry data. 24. A lithographic apparatus according to clause 23, comprising a metrology apparatus configured to determine overlay data based on the asymmetric data. 25. A lithographic apparatus according to clause 23, comprising a measurement apparatus according to clause 15. 26. A method for calculating a value for a process parameter measurement error obtained from measurements of a substrate including a target exposed to a manufacturing process and having process distortions, the process parameter measurement error being a result of the process distortions, the method comprising: obtaining alignment asymmetry data indicative of asymmetry in one or more alignment marks used to align the substrate; Obtaining a model correlating the alignment asymmetry data to process parameter measurement errors; using the alignment asymmetry data and the model to obtain a value of the process parameter measurement error; A method comprising: 27. The method according to clause 26, wherein the process parameter is an overlay. 28. The method of clause 26 or 27, wherein the alignment asymmetry data comprises a difference in a first measured position of one or more alignment marks when measured using radiation having a first characteristic and a second measured position of the one or more alignment marks when measured using radiation having a second characteristic. 29. The method of claim 28, wherein the property that is changed between the first property and the second property is wavelength and / or polarization. 30. A method according to any one of clauses 26 to 29, comprising determining a correction for the measurement of the process parameter from the process parameter measurement error. 31. The method of claim 30, wherein the measurement of the process parameter is based on a measurement of a target performed with a single illumination characteristic measurement. 32. A method according to any one of clauses 26 to 31, comprising performing a calibration stage to calibrate the model. 33. The method of claim 32, wherein the calibration stage is performed using simulated training data including simulated targets and simulated alignment marks, and simulated measurement responses of the simulated targets and simulated alignment marks. 34. The method of claim 33, wherein the calibration stage calibrates the model such that the model is capable of characterizing process parameter measurement errors based on the alignment asymmetry data. 35. The method of any one of clauses 26 to 34, wherein the model comprises a neural network. 36. The method of any one of clauses 26-35, wherein the alignment asymmetry data is further used to determine whether the manufacturing process is within specification. 37. The method of claim 36, including determining modifications to metrology operations for measuring process parameters based on a determination as to whether the manufacturing process is within specification. 38. A method according to any one of clauses 26 to 37, comprising reducing the number of acquisitions of a metrology operation for measuring a process parameter, each acquisition being performed with different illumination characteristics. 39. The method of any one of clauses 26-37, comprising comparing the alignment asymmetry data to an alignment asymmetry threshold, and classifying the substrate based on the comparison. 40. The method of clause 39, wherein classifying the substrate includes determining whether the substrate is within specification or outside specification based on the comparison. 41. A lithocell comprising a lithography apparatus, a metrology apparatus, and at least one processor operable to perform the method according to any one of clauses 26 to 40. 42. The lithographic apparatus is operable to perform alignment measurements to obtain alignment asymmetry data; the metrology device is operable to measure a process parameter; 42. The lithocell of claim 41, wherein the at least one processor is operable to correct the measured process parameter with a value of the process parameter measurement error. 43. A method for configuring a metrology tool for use in a semiconductor manufacturing process, comprising: obtaining integrated intensity or energy contained within Nth and −Nth diffraction orders scattered from a metrology structure applied to a layer on a substrate illuminated with a plurality of wavelengths and / or polarization modes; and configuring a metrology tool based on the dependence of the integrated intensity or integrated energy on wavelength and / or polarization mode; The method, wherein the configuration provides at least one selected one of a wavelength and / or a polarization mode of a radiation source within a metrology tool. 44. A method for monitoring a semiconductor manufacturing process, comprising: obtaining integrated intensity or energy contained within Nth and −Nth diffraction orders scattered from a metrology structure applied to a layer on a substrate illuminated with a plurality of wavelengths and / or polarization modes; monitoring a semiconductor manufacturing process based on a characteristic of the dependence of integrated intensity or integrated energy on wavelength and / or polarization mode; A method comprising: 45. A method for controlling a semiconductor manufacturing process, comprising: obtaining integrated intensity or energy contained within Nth and −Nth diffraction orders scattered from a metrology structure applied to a layer on a substrate illuminated with a plurality of wavelengths and / or polarization modes; Controlling processing equipment used in a semiconductor manufacturing process based on a characteristic of the layer resulting from a dependence of integrated intensity or integrated energy on wavelength and / or polarization mode; A method comprising: 46. ​​A method according to any one of clauses 43 to 45, wherein the obtaining is based on measurement data provided by a measuring device. 47. The method of claim 46, wherein the measurement device includes an alignment system. 48. The method of any one of clauses 43-47, wherein the metrology structures include alignment marks. 49. The method of claim 46, wherein the measurement device comprises a scatterometer. 50. The method of any one of clauses 43-49, wherein the metrology structure includes a bottom grating of the overlay mark. 51. The method according to clause 46, wherein the acquisition is based on measurements in a pupil plane of a measuring device. 52. The method of claim 51, wherein the illumination of the metrology structure uses a light source having an illumination pupil configured to have no or very limited overlap between the diffraction orders and / or between the diffraction orders and the zeroth order. 53. A method according to any one of clauses 43 to 52, wherein the obtaining further comprises summing the integrated intensity and / or the integrated energy contained within the Nth and -Nth diffraction orders. 54. The method of clause 1, wherein the asymmetric data further comprises intensity data or energy data of individual diffraction orders scattered from the first and / or second features illuminated at multiple wavelengths and / or polarization modes. 55. Obtaining integrated intensities or integrated energies contained within the Nth and / or −Nth diffraction orders at multiple wavelengths and / or polarization modes based on the asymmetric data; monitoring a semiconductor manufacturing process based on a characteristic of the dependence of integrated intensity or integrated energy on wavelength and / or polarization mode; 55. The method of claim 54, further comprising: 56. Obtaining integrated intensities or integrated energies contained within the Nth and / or −Nth diffraction orders at multiple wavelengths and / or polarization modes based on the asymmetric data; Controlling processing equipment used in a semiconductor manufacturing process based on a characteristic of the layer resulting from a dependence of integrated intensity or integrated energy on wavelength and / or polarization mode; 55. The method of claim 54, further comprising: 57. Obtaining integrated intensities or integrated energies contained within the Nth and / or −Nth diffraction orders at multiple wavelengths and / or polarization modes based on the asymmetric data; and configuring the metrology tool based on the dependence of the integrated intensity or integrated energy on wavelength and / or polarization mode; 55. The method of claim 54, wherein the configuration provides at least one selected one of a wavelength and / or a polarization mode of a radiation source within a metrology tool.

[0107] [000114] Although specific reference is made in this specification to the use of the lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optics, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0108] [000115] Although embodiments of the invention may be specifically referred to herein in connection with lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a patterning device (e.g. mask) inspection apparatus, a metrology apparatus or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other patterning device). Collectively, these apparatus may be referred to as a lithography tool. Such lithography tools may use vacuum or ambient (non-vacuum) conditions.

[0109] [000116] Although specific reference has been made above to the use of embodiments of the invention in connection with optical lithography, it will be appreciated that the invention, where the context permits, is not limited to optical lithography and may be used in other applications, for example in imprint lithography.

[0110] [000117] To the extent that any U.S. patents, U.S. patent applications, or other materials (e.g., articles) have been incorporated by reference, the text of such U.S. patents, U.S. patent applications, and other materials is only incorporated by reference to the extent that there is no conflict between such materials and the statements and drawings set forth herein. In the event of such a conflict, any such conflicting text in such U.S. patents, U.S. patent applications, and other materials incorporated by reference is not specifically incorporated by reference herein.

[0111] [000118] In the block diagram, the illustrated components are represented as separate functional blocks, but embodiments are not limited to a system in which the functionality described herein is organized as illustrated. The functionality provided by each of the components may be provided by software or hardware modules that are organized differently than as currently depicted, for example, such software or hardware may be mixed, combined, replicated, disaggregated, distributed (e.g., in a data center or geographically), or otherwise organized differently. The functionality described herein may be provided by one or more processors of one or more computers executing code stored on a tangible, non-transitory, machine-readable medium. In some cases, a third-party content distribution network may host some or all of the information communicated through the network, in which case, to the extent information (e.g., content) is provided or otherwise provided, the information may be provided by sending instructions to retrieve the information from the content distribution network.

[0112] [000119] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. 1. A method for calculating a value for a process parameter measurement error obtained from a measurement of a substrate exposed to a manufacturing process and including a target having a process distortion, the process parameter measurement error being a result of the process distortion, the method comprising: obtaining alignment asymmetry data indicative of asymmetry in one or more alignment marks used to align the substrate; obtaining a model correlating alignment asymmetry data to said process parameter measurement errors; using the alignment asymmetry data and the model to obtain a value of the process parameter measurement error; A method comprising:

2. The method of claim 1 , wherein the process parameter is overlay.

3. 2. The method of claim 1 , wherein the alignment asymmetry data comprises a difference in a first measured position of the one or more alignment marks when measured using radiation with a first characteristic and a second measured position of the one or more alignment marks when measured using radiation with a second characteristic.

4. The method of claim 3 , wherein the property that is varied between the first property and the second property is wavelength and / or polarization.

5. The method of claim 1 , comprising determining a correction for the measurement of the process parameter from the process parameter measurement error.

6. The method of claim 5 , wherein the measurement of the process parameter is based on a measurement of the target performed in a single illumination characterization measurement.

7. The method of claim 1 , comprising performing a calibration stage to calibrate the model.

8. 8. The method of claim 7, wherein the calibration stage is performed using simulated training data including simulated targets and simulated alignment marks, and simulated measurement responses of the simulated targets and the simulated alignment marks.

9. The method of claim 8 , wherein the calibration stage calibrates the model such that the model is capable of characterizing the process parameter measurement error based on the alignment asymmetry data.

10. The method of claim 1 , wherein the model comprises a neural network.

11. The method of claim 1 , wherein the alignment asymmetry data is further used to determine whether the manufacturing process is within specifications.

12. The method of claim 11 , comprising determining modifications to metrology operations for measuring the process parameters based on the determination as to whether the manufacturing process is within specification.

13. The method of claim 1 , further comprising reducing a number of acquisitions of a metrology operation for measuring the process parameter, each acquisition being performed with a different illumination characteristic.

14. The method of claim 1 , comprising: comparing the alignment asymmetry data to an alignment asymmetry threshold; and classifying the substrate based on the comparison.

15. The method of claim 14 , wherein the classification of the substrate comprises determining whether the substrate is in or out of specification based on the comparison.

16. 1. A method for determining a substrate grid representative of a deformation of a substrate prior to exposure of the substrate in a lithographic apparatus configured to fabricate one or more features on the substrate, the method comprising: obtaining position data for a plurality of first features and / or a plurality of second features on the substrate; acquiring asymmetric data for at least one feature of the plurality of first features and / or the plurality of second features; determining the substrate grid based at least on the position data; providing the substrate grid and the asymmetry data to the lithographic apparatus for controlling at least a portion of an exposure process to create one or more features on the substrate; A method comprising:

17. 17. The method of claim 16, wherein the determination of the substrate grid is additionally based on the asymmetric data, such that the step of sending the substrate grid and asymmetric data includes sending a substrate grid that is corrected for asymmetry.

18. The method of claim 16 , wherein the plurality of first features comprises alignment marks.

19. 20. The method of claim 18, further comprising acquiring the position data for the alignment marks using a low numerical aperture (NA) optical system including a sensor having an NA of 0.9 or less.

20. The method of claim 16 , wherein the plurality of second features includes a metrology target and optionally an overlay target.

21. 21. The method of claim 20, wherein the plurality of first features include alignment marks, and further comprising acquiring the asymmetry data for the alignment marks and / or the metrology target using a high NA optical system including a sensor with a NA greater than 0.

9.

22. The method of claim 16 , further comprising calibrating at least a selected one of the position data associated with the plurality of second features to the position data associated with the plurality of first features.

23. 23. The method of claim 22, further comprising calibrating at least a selected one of the position data against further position data acquired during the aligning of the substrate in the lithographic apparatus.

24. The method of claim 16 , further comprising sending the asymmetry data to a metrology tool for measuring overlay.

25. The method of claim 16 , wherein the asymmetry data further comprises intensity or energy data of diffraction orders scattered from the first and / or second features in multiple wavelengths and / or polarization modes.

26. obtaining an integrated intensity or energy contained within an Nth and / or −Nth diffraction order at the plurality of wavelengths and / or polarization modes based on the asymmetry data; configuring a metrology tool based on the characteristic of the dependence of the integrated intensity or integrated energy on the wavelength and / or polarization mode, the configuration providing at least selected ones of the wavelengths and / or polarization modes of a radiation source within the metrology tool; 26. The method of claim 25, further comprising:

27. 1. A measurement apparatus for determining a substrate grid indicative of a deformation of a substrate prior to exposure of the substrate in a lithographic apparatus configured to create one or more features on the substrate, the measurement apparatus comprising: the measurement device includes an optical system configured to acquire position data for a plurality of first features and / or a plurality of second features on the substrate; the optical system is further configured to acquire asymmetric data for at least one feature of the plurality of first features and / or the plurality of second features; The measurement apparatus is configured to determine the substrate grid based on the position data, and to send the substrate grid and asymmetry data to the lithographic apparatus for controlling at least a portion of an exposure process to create one or more features on the substrate.

28. 28. The measurement apparatus of claim 27, wherein the optical system comprises low numerical aperture (NA) optics including a sensor having an NA of 0.9 or less configured to acquire the position data for the alignment mark.

29. 30. The measurement apparatus of claim 28, further comprising a plurality of spatially distributed high NA sensors.

30. 17. A lithographic apparatus configured to use the substrate grid and asymmetric data of claim 16, comprising: A lithographic apparatus configured to align the substrate in the lithographic apparatus based on the position data and / or the asymmetry data.

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