Method and apparatus for patterning process performance determination

Abstract

A method for determining performance of a patterning process, the method comprising: receiving an image of a portion of a substrate, the portion of the substrate comprising a first region and at least a second region, the first region comprising a first feature associated with a first patterning process and the second region comprising a second feature associated with a second patterning process, the first feature and the second feature form a Moire pattern when irradiated by radiation, and a performance of the patterning process is determined based on a characteristic of the Moire pattern.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 23152757.3 filed on January 20, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to an apparatus and method for determining the performance of a patterning process, such as a photolithography process. In particular, the present invention relates to determining the performance of a patterning process based on characteristics of a boundary between a first region and a second region. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. Lithographic apparatuses are used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can project a pattern (often also referred to as a "design layout" or "design"), for example, at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

[0005] To project patterns onto substrates, lithographic equipment uses electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Compared to lithographic equipment using radiation with a wavelength of, for example, 193 nm, lithographic equipment using extreme ultraviolet (EUV) radiation with a wavelength in the 4 nm to 20 nm range (e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on substrates.

[0006] Low-k1 lithography can be used to process features with dimensions smaller than the classical resolution limit of the lithographic apparatus. In such processes, the resolution equation can be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation employed, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is the "critical dimension" (typically the smallest feature size printed, but in this case, the half-pitch), and k1 is the empirical resolution factor. Generally, the smaller k1, the more difficult it is to replicate a pattern on a substrate with a shape and size similar to that planned by the circuit designer to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithographic projection apparatus and / or design layout. These fine-tuning steps include, for example, but are not limited to, optimization of the NA, customized illumination schemes, the use of phase-shifting patterning devices, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also called "optical process correction") in the design layout), or other methods generally referred to as "resolution enhancement techniques" (RET). Alternatively, rigorous control loops for controlling the stability of the lithographic apparatus can be used to improve pattern reproduction at low k1.

[0007] Patterning a layer on a substrate can involve multiple steps. For example, a patterning device (such as a mask) may not be large enough to pattern the substrate in one location. In some cases, the pattern to be exposed can fit on a single mask. A single mask can then be moved across the entire substrate to expose the same pattern multiple times. In other cases, the pattern to be exposed on the substrate (e.g., the pattern forming a device) may be too large to fit on a single mask. Multiple masks can be moved across the substrate in separate steps, each mask containing a different portion of the pattern to be exposed. Multiple masks can be moved across an area of the substrate to sequentially pattern different portions of the pattern. This separation of the pattern between different regions on the substrate can result in errors in the positioning of the exposed portions of the pattern relative to one another. For example, the exposure pattern may include alignment and / or magnification errors. Due to the small size of the patterned features, a high degree of precision and accuracy is required when positioning the different patterned regions relative to one another. This relative position error is referred to as stitching error. Stitching error can affect the quality of the exposed pattern on the substrate and the yield of the resulting patterning process. Therefore, it is desirable to provide methods and apparatus for reducing stitching errors and their negative impact on the lithographic patterning process. Stitching errors can be measured in a variety of ways known in the art. Stitching errors can be measured using overlapping targets, wherein the overlapping error is an indication of stitching errors. Stitching errors can be measured using SEM imaging tools, wherein the positioning of the imaging features is an indication of stitching errors. However, with the reduction in resist required for high precision nodes in the lithographic process, existing methods suffer from insufficient signal due to thin layers of resist less than 40 nm not providing sufficient diffraction efficiency nor sufficient reflectivity. In the case of SEM-based methods for determining stitching errors, such thin resists can be easily damaged, thereby reducing the imaging process. Therefore, it is desirable to provide methods for measuring stitching errors of structures including thin layers of resist having a thickness of less than 40 nm in the example. Summary of the Invention

[0008] According to a first aspect of the present disclosure, there is provided a method for determining the performance of a patterning process, the method comprising: receiving an image of a portion of a substrate, the portion of the substrate comprising a first area and at least a second area, the first area comprising a first feature associated with a first patterning process, the second area comprising a second feature associated with a second patterning process, wherein the first feature and the second feature form the image comprising a moiré pattern when illuminated by radiation, and determining the performance of the patterning process based on characteristics of the moiré pattern.

[0009] According to a second aspect of the present disclosure, there is provided an apparatus for determining the performance of a lithography process, the apparatus comprising one or more processors, the one or more processors being configured to: receive an image of a portion of a substrate, the portion of the substrate comprising a first region and at least a second region, the first region comprising a first feature associated with a first patterning process, the second region comprising a second feature associated with a second patterning process, wherein the first feature and the second feature form the image comprising a moiré pattern when irradiated with radiation; and determine the performance of the patterning process based on characteristics of the moiré pattern. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0011] Figure 1 depicts a schematic overview of a lithographic apparatus;

[0012] Figure 2 depicts a schematic overview of a lithography unit;

[0013] Figure 3 depicts a schematic representation of overall lithography showing the collaboration between three key technologies for optimizing semiconductor manufacturing;

[0014] Figure 4 Depicts Figure 4 (a) and Figure 4 (b) The exposure field, according to Figure 4 (c) Target arrangement of multiple exposure fields, Figure 4 (d) Figure 4 (e) and Figure 4 (f) The pattern to be exposed, and Figure 4 (g) When irradiated with radiation Figure 4 (c) The image formed when the target is

[0015] Figure 5 Another embodiment of the present invention is described, wherein Figure 5 The exposure field in (a) is at the same level and also depicts Figure 5 (b) and Figure 5 (c) The pattern to be exposed. DETAILED DESCRIPTION

[0016] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 nm to 100 nm).

[0017] As used herein, the terms "reticle," "mask," or "patterning device" should be broadly interpreted to refer to a general patterning device that can be used to impart an incident radiation beam with a patterned cross-section corresponding to the pattern to be produced in a target portion of the substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective, binary, phase-shift, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0018] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also called illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., mask table) T configured to support a patterning device (e.g., mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to specific parameters, a substrate support (e.g., wafer stage) WT configured 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 specific 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.

[0019] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example, 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 thereof. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0020] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic types, or any combination thereof, which projection system is appropriate for the exposure radiation used and / or other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0021] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be overlapped by a liquid having a relatively high refractive index (e.g. water) to fill the space between the projection system PS and the substrate W - this is also known as immersion lithography. More information on immersion technology is given in US6952253, which is incorporated herein by reference.

[0022] The lithographic apparatus LA may also be of a type having two (also referred to as "dual stage") or more substrate supports WT. In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps preparing for subsequent exposure of the substrate W may be performed on a substrate W on one of the substrate supports WT while another substrate W on another substrate support WT is being used to expose a pattern on another substrate W.

[0023] In addition to the substrate support WT, the lithographic apparatus LA can include a measurement stage. The measurement stage is arranged to hold sensors and / or cleaning equipment. The sensors can be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measurement stage can hold multiple sensors. The cleaning equipment can be arranged to clean part of the lithographic apparatus, such as part of the projection system PS or part of the system for providing immersion liquid. The measurement stage can be moved beneath the projection system PS when the substrate support WT is away from the projection system PS.

[0024] In operation, a radiation beam B is incident on a patterning device MA (e.g. a mask) held on a mask support T and is patterned by a pattern (design layout) present on the patterning device MA. After having passed the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of a substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, e.g. in order to position different target portions C in the path of the radiation beam B at focused and aligned positions. Similarly, a first positioner PM and possibly a further position sensor (the further position sensor not being in position) are provided. Figure 1 The patterning device MA (shown explicitly in FIG) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The mask alignment marks M1, M2 and the substrate alignment marks P1, P2 can be used to align the patterning device MA and the substrate W. Although the substrate alignment marks P1, P2 are shown occupying dedicated target portions, the substrate alignment marks P1, P2 shown can be located in spaces between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe lane alignment marks.

[0025] like Figure 2As shown, the lithography apparatus LA may form part of a lithocell LC, sometimes also referred to as a litho cell or (lithography) cluster. The lithocell LC typically also includes equipment for performing pre-exposure and post-exposure processes on a substrate W. Typically, this equipment includes a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH for adjusting the temperature of the substrate W, for example, for adjusting the solvent in the resist layer, and a bake plate BK. A substrate handling device (or robot) RO picks up substrates W from input / output ports I / O1 and I / O2, moves the substrates W between various processing equipment, and delivers them to a loading station LB of the lithography apparatus LA. The equipment in the lithocell, often collectively referred to as a track or coating and developing system, is typically controlled by a track or coating and developing system control unit TCU, which itself may be controlled by a supervisory control system SCS, which in turn controls the lithography apparatus LA, for example, via a litho control unit LACU.

[0026] In order to correctly and consistently expose substrates W exposed by lithographic apparatus LA, it is desirable to inspect the substrates to measure properties of the patterned structures, such as overlay errors between subsequent layers, line thickness, critical dimensions (CDs), etc. To this end, an inspection tool (not shown) may be included in lithography cell LC. If an error is detected, particularly if the inspection is performed before exposing or processing other substrates W from the same batch or lot, adjustments may be made to the exposure of subsequent substrates and / or other processing steps to be performed on substrates W, for example.

[0027] Inspection equipment, which may also be referred to as metrology equipment, is used to determine properties of a substrate W, and in particular, to determine how properties vary between different substrates W, or how properties associated with different layers of the same substrate W vary from layer to layer. Alternatively, the inspection equipment may be configured to identify defects on the substrate W and may, for example, be part of a lithography cell LC, or may be integrated into the lithography apparatus LA, or may even be a standalone device. The inspection equipment may measure properties on a latent image (the image in the resist layer after exposure), a semi-latent image (the image in the resist layer after a post-exposure bake step (PEB), a developed resist image (in which either exposed or unexposed portions of the resist have been removed), or even an etched image (after a pattern transfer step such as etching).

[0028] Typically, the patterning process in the lithographic apparatus LA is one of the most critical steps in the process requiring high-precision sizing and placement of structures on the substrate W. To ensure this high precision, the three systems can be combined into a so-called "holistic" control environment, such as Figure 3Schematically shown. One of these systems is a lithography apparatus LA connected to a metrology tool MT (second system) and a computer system CL (third system). Key to this "holistic" environment is optimizing the collaboration between these three systems to enhance the overall process window and providing a tight control loop to ensure that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines the range of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process produces a defined outcome (e.g., a functional semiconductor device). Typically, process parameters in the lithography or patterning process are allowed to vary within this range.

[0029] The computer system CL can use (a portion of) the design layout to be patterned to predict which resolution enhancement technology to use and perform computational lithography simulations and calculations to determine which mask layouts and lithographic equipment settings achieve the largest overall process window for the patterning process (in Figure 3 Typically, the resolution enhancement technique is arranged to match the patterning possibilities of the lithographic apparatus LA. The computer system CL may also be used (e.g. by using input from a metrology tool MT) to detect where within the process window the lithographic apparatus LA is currently operating, to predict whether defects may be present (e.g. due to suboptimal processing). Figure 3 , which is represented by an arrow pointing to “0” in the second scale SC2).

[0030] The metrology tool MT may provide input to the computer system CL to enable accurate simulations and predictions, and may provide feedback to the lithographic apparatus LA to identify possible drift in, for example, the calibration state of the lithographic apparatus LA (e.g., Figure 3 represented by multiple arrows in the third scale SC3).

[0031] During photolithography, it is often desirable to measure the resulting structures, for example, for process control and verification. The tool that performs such measurements is often referred to as a metrology tool MT. Different types of metrology tools MT are known for performing such measurements, including scanning electron microscopes or various forms of scatterometer metrology tools MT. Scatterometers are versatile instruments that allow parameters of the photolithography process to be measured by placing a sensor in the pupil of the scatterometer's objective, or in a plane conjugate to the pupil, in which case the measurement is often referred to as pupil-based measurement, or by placing a sensor in the image plane, or in a plane conjugate to the image plane, in which case the measurement is often referred to as image-based or field-based measurement. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP1,628,164A, the entire contents of which are incorporated herein by reference. Such scatterometers can measure gratings using light from soft X-rays and visible to near IR wavelength ranges.

[0032] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, reconstruction methods can be applied to the measured signals to reconstruct or calculate the properties of the grating. For example, such a reconstruction can be obtained by simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulation results with the measured results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to the diffraction pattern observed from a real target.

[0033] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectroscopic scatterometer MT, radiation emitted by a radiation source is directed toward a target, and radiation reflected or scattered from the target is directed toward a spectroscopic detector, which measures the spectrum of the specularly reflected radiation (i.e., a measurement of intensity as a function of wavelength). From this data, the structure or profile of the target that produced the detected spectrum can be reconstructed, for example, by rigorous coupled wave analysis and nonlinear regression, or by comparison with a library of simulated spectra.

[0034] In a third embodiment, the scatterometer MT is an ellipsometry scatterometer. An ellipsometry scatterometer allows parameters of a lithography process to be determined by measuring scattered radiation for each polarization state. Such a metrology device emits polarized light (e.g., linearly, circularly, or elliptically) by, for example, using a suitable polarization filter in the illumination portion of the metrology device. A source suitable for the metrology device can also provide polarized radiation. Various embodiments of existing ellipsometry scatterometers are described in U.S. patent applications Ser. Nos. 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, the entire contents of which are incorporated herein by reference.

[0035] Examples of known scatterometers typically rely on providing a dedicated metrology target, such as an underfilled target (a target in the form of a simple grating or overlapping gratings in different layers, which is large enough that the measurement beam produces a spot smaller than the grating) or an overfilled target (where the illumination spot partially or completely encompasses the target). Furthermore, the use of metrology tools (e.g., angle-resolved scatterometers that illuminate an underfilled target such as a grating) allows the use of so-called reconstruction methods, in which the properties of the grating can be calculated by simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to the diffraction pattern observed from a real target.

[0036] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring the reflection spectrum and / or an asymmetry in the detection configuration, the asymmetry being related to the degree of overlap. The two (typically overlapping) grating structures can be applied in two different layers (not necessarily consecutive layers) and may be formed at substantially the same location on the wafer. The scatterometer can have a symmetry detection configuration as described in patent application EP1,628,164A, so that any asymmetry is clearly distinguishable. This provides a straightforward method for measuring misalignment in gratings. Further examples for measuring overlay error between two layers comprising a periodic structure when the target is measured by the asymmetry of the periodic structure can be found in PCT patent application publication No. WO 2011 / 01624 or U.S. patent application US20160161863, which are incorporated herein by reference in their entirety.

[0037] Other parameters of interest may be focus and dose. Focus and dose can be determined simultaneously by scatterometry (or alternatively, by scanning electron microscopy) as described in U.S. Patent Application No. US2011-0249244, which is incorporated herein by reference in its entirety. A single structure can be used that has a unique combination of critical dimension and sidewall angle measurements for each point in the focus energy matrix (FEM, also called the focus exposure matrix). If these unique combinations of critical dimension and sidewall angle are available, focus and dose values can be uniquely determined based on these measurements.

[0038] A metrology target can be a collection of composite gratings, typically formed in resist by a photolithography process (but also after, for example, an etching process). The pitch and linewidth of the structures in the grating are typically largely determined by the measurement optics (particularly the optical density) needed to capture the diffraction orders from the metrology target. As previously mentioned, the diffraction signal can be used to determine the shift between two layers (also known as "overlay") or to reconstruct at least a portion of the original grating produced by the photolithography process. This reconstruction can be used to provide guidance on the quality of the photolithography process and to control at least a portion of the photolithography process. The target can have smaller subsegments configured to mimic the dimensions of functional portions of the design layout in the target. Due to this subsegmentation, the target's behavior more closely resembles that of the functional portions of the design layout, resulting in overall process parameter measurements that better resemble those of the functional portions of the design layout. The target can be measured in either underfill mode or overfill mode. In underfill mode, the measurement beam produces a spot that is smaller than the entire target. In overfill mode, the measurement beam produces a spot that is larger than the entire target. In this overfill mode, different targets can also be measured simultaneously, allowing for the simultaneous determination of different process parameters.

[0039] The overall measurement quality of a particular target for a lithography parameter is determined at least in part by the measurement profile used to measure the lithography parameter. The term "substrate measurement profile" may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement profile is an optical measurement based on diffraction, the one or more parameters measured may include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, and the like. For example, one of the criteria for selecting a measurement profile may be the sensitivity of one of the measurement parameters to process variations. Further examples are described in U.S. patent application US2016-0161863 and published U.S. patent application US 2016 / 0370717A1, which are incorporated herein by reference.

[0040] Different areas on the substrate can be exposed in sequence. For example, the reticle or mask can include a pattern to be exposed multiple times on the substrate. When exposing a layer on the substrate, the reticle can be moved relative to the substrate so as to expose different areas on the substrate in sequence. As described above, the reticle can be associated with a first positioner PM for accurately positioning the reticle within the lithographic apparatus LA. The substrate W can be associated with a second positioner PW for accurately positioning the substrate W within the lithographic apparatus LA. The positioners PM and PW can be used to accurately position the substrate W and the reticle relative to each other to set the position of the exposure pattern on the substrate. Other settings and factors that may affect the position of the pattern on the substrate may include, for example, the projection system PS used to project the pattern of the reticle onto the substrate W, the properties of the substrate (such as the topography), the wafer stage, the WT, and the properties of the radiation used to expose the pattern.

[0041] In an exemplary embodiment, the entire device to be photolithographically exposed may be too large to fit on a single reticle. Therefore, the entire device may be divided into two or more separate regions. These regions can, for example, be exposed sequentially, separately from one another. For the entire device to function properly, the individually exposed regions need to be accurately and precisely connected at or near the boundaries between the regions.

[0042] In order to accurately position multiple sequentially patterned areas relative to each other, precise parameter control may be required. The settings of the different elements of the lithographic apparatus LA can be optimized to obtain accurate positioning of the exposure areas on the substrate. Measurement data of the exposed substrate can be obtained to determine the positioning of the multiple areas. The measurement data can be used to check whether the exposed substrate has acceptable positioning of the exposure areas, for example, for quality control. The measurements can also be used to determine how to improve the settings for future exposures performed by the lithographic apparatus LA. For example, the positioning errors of multiple areas can be determined. The determined positioning errors can indicate that there is an error in the x-direction alignment of two adjacent areas. The error can be analyzed to determine one or more causes of the error. One or more equipment or option settings can be updated to address the error to avoid errors in future exposures.

[0043] The positioning of sequentially exposed areas relative to each other can be discussed in terms of stitching errors. The performance of a photolithography patterning process can include one or more stitching errors. A stitching error can be an error in the desired position of an exposure area. Stitching can refer to the connection or relative placement of two areas. These areas can be adjacent areas. These areas can include features that are related to each other. For example, these areas may belong to the same device being exposed on substrate W. Photolithography exposure can expose a pattern on a two-dimensional area. The area can be rectangular. For example, the area can be square. However, the area can have any two-dimensional shape in the plane of the substrate. Along the boundaries of the area, there can be boundaries with adjacent areas. In the case of a rectangular area, the directions along which the boundaries of the area are located can be referred to as the x-direction and the y-direction. The directions of the boundaries can also be referred to as the horizontal direction and the vertical direction.

[0044] As described above, measurement data can be used to control the in-plane placement of exposure regions on the substrate. For example, the measurement data can be used to determine and / or analyze stitching errors between regions on substrate W. The measurement data can be obtained based on metrology targets. For example, the metrology targets can be overlay metrology targets. One or more metrology targets can be positioned on the substrate as part of a pattern design exposed on the substrate. The metrology targets can be exposed as part of a photolithographic exposure. Structures included in the targets (e.g., diffraction gratings) can be analyzed to determine properties of the exposure pattern. Analysis of the metrology target(s) can include measurements to determine the position of one or more metrology targets relative to one or more other metrology targets on the substrate. For example, the measurements can include overlay and / or alignment measurements. The metrology target(s) and the other metrology target(s) can be located in different regions on the substrate. Including metrology targets can increase costs due to the space occupied on substrate W, as this reduces the space available for exposing product features. On the other hand, including fewer metrology targets on the substrate can result in sparse available metrology data. This, in turn, can reduce the quality of analysis and / or control of the exposure pattern. Another potential drawback of using metrology targets to determine in-plane placement of regions is that the measurement data may not represent the actual stitching error of the exposed features. For example, the metrology targets being measured may be designed and / or patterned differently, meaning they behave differently. For example, the patterns may respond differently to aberrations and / or process effects of the exposure process. The limited availability of metrology data and the potential discrepancy between stitching error data and actual stitching error can create drawbacks for using metrology targets for in-plane positioning control.

[0045] Metrology targets are formed within the layers representing each exposure or patterning step. These metrology targets are used to determine information needed to quantify the patterning process, particularly the stitching error between different exposure fields. In one example, the patterning process is a photolithography process. The photolithography process patterns a resist layer, as is known in the art. Reducing the pattern feature size that can be used in EUV lithography processes can result in a reduction in resist layer thickness. However, in this case, the resist layer thickness does not possess sufficient optical properties for metrology purposes. Specifically, the diffraction efficiency of a resist layer of 40 nm or less (particularly a layer of 10 nm) is so low that such metrology targets cannot provide a measurable signal when illuminated with light. Furthermore, when imaging metrology targets used to determine stitching error between exposure fields using an SEM (scanning electron microscope) tool, resist layers of 40 nm or less in thickness can be damaged, resulting in insufficient image quality of the measured target. This article describes methods for overcoming at least some of these challenges.

[0046] Therefore, a method for determining the performance of a patterning process is proposed, the method comprising: receiving an image of a portion of a substrate, the portion of the substrate comprising a first area and at least a second area, the first area comprising a first feature associated with a first patterning process, the second area comprising a second feature associated with a second patterning process, wherein the first feature and the second feature form an image comprising a Moire pattern when illuminated by radiation; and determining the performance of the patterning process based on characteristics of the Moire pattern.

[0047] Figure 4 (a) shows an element 405 which may be a pattern on a reticle that may be exposed by a lithographic apparatus in an exposure field 401. 410a shows the exposure of this exposure field 401 in layer N of the semiconductor device stack without losing a substantial portion. Figure 4 (b) shows exposure fields 402 and 403 in the next layer N+1 of the semiconductor device stack. Exposure field 402 prints pattern 406 on the reticle as a target for measuring stitching errors. Exposure field 403 prints pattern 407 on the reticle as a target for measuring stitching errors. Patterns 406 and 407 are adjacent. When printed, patterns 406 and 407 on the reticle produce a pattern on the substrate having a thickness according to the thickness of the substrate. Figure 4 (e) and Figure 4 (f) The area of the features, i.e., the area of the grating, where each grating has features of this pitch. The resulting pattern on the substrate is as follows Figure 4(c) is shown. 410c indicates that the pattern area 400x on the substrate is formed by the overlap of the pattern 405 in layer N and the patterns 406 and 407 in layer N+1. Therefore, the area on the substrate 400x includes the grating generated by the upper half of the pattern 405 and the grating generated by the pattern 406. This area is formed by Figure 4 (c) The area above the dotted line 400y. The area on the substrate 400x also includes the area formed by the grating generated by the lower half of the pattern 405 and the grating generated by the pattern 407 when the substrate is exposed. Figure 4 The area below the dashed line 400y in (c).

[0048] In an embodiment, the pitch of the gratings in regions 406 and 407 is p2. In an embodiment, p2 is 600 nm. In an embodiment, p2 is between 400 nm and 900 nm. In an embodiment, the pitch of the gratings in region 405 is p1. In an embodiment, p1 is 500 nm. In an embodiment, the pitch p1 is between 400 nm and 900 nm. Figure 4 (c) Region 400x thus includes two targets: in the upper half of region 400x above dashed line 400y, there is a target having overlapping gratings with a bottom grating having a pitch of p1 in layer N and a top grating having a pitch of p2 in layer N+1, and in the lower half of region 400x below dashed line 400y, there is a target having overlapping gratings with a bottom grating having a pitch of p1 in layer N and a top grating having a pitch of p2 in layer N+1. The target formed in region 400x above dashed line 400y includes patterning information formed during exposure with exposure field 402. The target formed in region 400x below dashed line 400y includes patterning information formed during exposure with exposure field 403. The patterning information generated by exposure field 401 is the same in the two regions below and above dashed line 400y.

[0049] Figure 4 (g) shows the image formed when the area 400x is irradiated with radiation. The targets above the dashed line 400y are targets with different pitches (i.e., p1 in layer N and p2 in layer N+1). The targets below the dashed line 400y are also targets with different pitches (i.e., p1 in layer N and p2 in layer N+1). When irradiated with radiation, the two targets will produce an image on the detection camera, as shown in FIG. Figure 4As shown in (g), image 406i is formed by the target in area 400x located above dashed line 400y, and image 407i is formed by the target in area 400x located below dashed line 400y. Images 406i and 407i include moiré fringes with a period of 400 pm, clearly visible on the detection camera. Although the resist forming layer N+1 is very thin, the signal from layer N is relatively strong because the signal from layer N is formed by the grating in layer N, which has good optical properties (such as diffraction efficiency and reflectivity). Although the radiation scattered from layer N+1 is weak, it modulates the signal, and the resulting measurable moiré fringes (as imaged by 406i and 407i) are detectable. If there were no stitching errors between exposure fields 402 and 403 (the exposure error due to exposure in field 401 is the same for both targets), the moiré fringes would be similarly positioned on the measured image. However, if there is a stitching error in exposure fields 402 and 403, the moiré fringes of image 406i and image 407i are offset relative to each other. By measuring the offset or phase between the moiré fringes (in Figure 4 (g) shows 400 ) to determine the performance of exposure fields 402 and 403 .

[0050] Reference below Figure 5 Another embodiment is shown. Figure 5 (a) shows exposure field 502 that will pattern pattern 506 on the substrate and exposure field 503 that will pattern pattern 507 on the substrate. The two exposures transfer patterns 506 and 507 from the reticle to areas on the substrate in the same layer of the semiconductor device stack. Exposure fields 502 and 503 overlap in the areas depicted by 506 and 507. Figure 5 (b) shows the pattern exposed during exposure field 506. The pattern includes a top region with pitch p2 located above line 500y and a bottom region with pitch p1 located below line 500y. Figure 5 (c) shows the pattern exposed during exposure field 507. The pattern includes a top region with a pitch of p1 located above line 500y and a bottom region with a pitch of p2 located below line 500y. After exposure with exposure fields 506 and 507, the pattern generated in the region above line 500y forms an image with moiré fringes when irradiated with radiation (the generated fringes are not shown). After exposure with exposure fields 506 and 507, the pattern generated in the region below line 500y forms an image with moiré fringes when irradiated with radiation (the generated fringes are not shown). The stitching error between exposure field 506 and exposure field 507 can be found in the region located at ( Figure 5 The characteristics of the moiré fringe of the image above line 500y are similar to those of the image above line 500y. Figure 5This is visible in the change in a characteristic of the moiré fringes of the image below line 500y. This characteristic may be the phase of each moiré fringe.

[0051] Determining the performance of the patterning process may include determining the quality of the patterning process. The quality may relate to how different regions that were exposed separately from each other are positioned relative to each other. Determining the performance may include determining a stitching error between a first exposure field (such as 406 or 506) and a second exposure field (407 or 507). Determining the performance may include determining one or more properties of the exposure pattern, which may be referred to as process characteristics. Determining the performance may include determining one or more corrections to the patterning process. The corrections may be based on the determined process characteristics and / or the performance of the lithographic patterning process. The determined corrections may be used to update the lithographic patterning process for future iterations. Determining the performance of the lithographic patterning process may also include validating the patterning process.

[0052] An image used to determine the performance of the patterning process can be obtained by illuminating a measurement target with optical radiation. The image used to determine the performance of the patterning process can be a scanning electron microscope image (SEM). The image can be a voltage contrast image. The voltage contrast image can provide a measure of the electrical contact of features with underlying layers. The image can be obtained after the exposed substrate has been processed, for example, after performing one or more post-exposure development steps on the patterned substrate. The measurement of the contact with the underlying layer can provide an indication of the degree to which features of the exposed layer match features of the underlying layer. This, in turn, can be used to determine whether stitching errors exist. The image can be obtained while the substrate is in the lithography cell LC. The image can be of a patterned photoresist layer on the substrate. The image can be of a layer of material that has been patterned by an etching process.

[0053] The same photolithography patterning exposure can be performed on multiple substrates over a period of time. The number and location of images analyzed to determine the performance of the patterning process may vary over time. When starting a new exposure pattern, more intensive performance maps can be prepared, as the new process may initially require more calibration. Once the process settings have been calibrated one or more times, performance may improve and / or stabilize. In response, the number of images analyzed to determine process performance can be reduced. The method can also be flexible in terms of the intensity of performance analysis across the substrate. The method can identify one or more regions of interest for performance analysis. For example, when performing the same exposure on another substrate, regions identified as exhibiting poor performance can be analyzed in greater detail. As another example, a substrate may include critical areas where product features may have more stringent manufacturing requirements (i.e., lower tolerances for deviations from design standards). These critical areas can receive more intensive performance monitoring. This can improve the performance of the patterning process in these critical areas.

[0054] The model may be used in whole or in part to determine a method for determining the performance of a lithographic patterning process. The model may include vision techniques, such as machine vision techniques. The model may be a machine learning model. The model may be used to determine one or more process characteristics. In an exemplary embodiment, the model may receive one or more feature characteristics as input. In another exemplary embodiment, the model may receive one or more received images of the first region and the second region and their boundaries as input, such as Figure 4 406i and 407i in (g). The method may use multiple models. For example, the method may use two separate models. The first model may be a vision technology model. The vision technology model may be used to interpret one or more images provided as input to the model. The model that receives the one or more images as input may be a convolutional neural network. The first model may provide one or more process characteristics as output. The second model may receive one or more process characteristics determined by the first model. The second model may receive process characteristics of multiple regions on the substrate. The second model may interpret the received process characteristics to convert them into patterning corrections. The second model may provide correction data as output for adjusting the photolithography patterning process (e.g., to correct for stitching errors). For example, the correction data may include one or more updated values for photolithography patterning process settings. The model may include a classification model. For example, the classification model may be used to verify the patterning process. For example, the model may classify an image as having a region stitching property that falls within (passes) or outside (fails) one or more set exposure tolerances.

[0055] Methods described herein can use one or more images to determine characteristic features of patterns depicted in those images. Characteristic features (e.g., overlap, alignment, or other properties indicative of stitching quality) can be determined directly from analysis of the images. In order to detect subtle changes or variations in characteristic features, it may be advantageous to improve the quality of the image(s) before analyzing the image(s) to determine the characteristic features. Enhancing the images can, for example, include removing noise, filtering out unwanted signals, and / or extracting relevant features for analysis. Advantages of extracting relevant features can include reducing the dimensionality of the analysis. As described herein, determining one or more characteristic features from an image can include some or all of the steps of pre-processing the image, extracting features from the pre-processed image, and / or determining a measure of stitching quality based on the pre-processed image.

[0056] Characteristic features may include overlap. It may be desirable to separate the analysis of overlap into separate dimensions on the substrate, such as two dimensions in the plane of the patterned substrate. These dimensions may be perpendicular to each other and may be referred to as the x- and y-directions, or the horizontal and vertical directions. These dimensions may be parallel and / or perpendicular to the direction of the boundary to be analyzed.

[0057] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0058] Although specific reference may be made herein to embodiments of the present invention in the context of lithographic equipment, embodiments of the present invention may be used in other equipment. Embodiments of the present invention may form part of mask inspection equipment, metrology equipment, or any equipment that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These equipment may generally be referred to as lithographic tools. Such lithographic tools may utilize vacuum conditions or ambient (non-vacuum) conditions.

[0059] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications such as imprint lithography where the context permits.

[0060] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be practiced in other ways than those described. The above description is intended to be illustrative rather than restrictive. Therefore, it will be clear to those skilled in the art that modifications may be made to the described invention without departing from the scope of the claims set forth below.

[0061] Although specific reference is made to a "metrology device / tool / system" or an "inspection device / tool / system," these terms may refer to the same or similar types of tools, devices, or systems. For example, an inspection or metrology device including embodiments of the present invention may be used to determine characteristics of structures on a substrate or wafer. For example, an inspection or metrology device including embodiments of the present invention may be used to detect defects in a substrate or defects in a structure on a substrate or wafer. In such embodiments, the characteristic of interest in a structure on a substrate may be related to a defect in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate or wafer.

Claims

1. A method for determining the performance of a patterning process, the method comprising: receiving an image of a portion of a substrate, the portion of the substrate comprising a first area including first features associated with a first patterning process and at least a second area including second features associated with a second patterning process, wherein the first features and the second features form the image comprising a moiré pattern when illuminated by radiation; and The performance of the patterning process is determined based on characteristics of the moiré pattern.

2. The method according to claim 1, wherein The first region is a first field exposed on the substrate, the second region is a second field exposed on the substrate, and determining the performance of the patterning process includes determining a stitching error between the first field and the second field exposed on the substrate.

3. The method according to claim 1 or claim 2, wherein: The characteristic of the moiré pattern is the phase of the moiré pattern formed on the imaging sensor.

4. The method according to claims 1 to 3, wherein: The performance of the patterning process is obtained from the phase of the moiré pattern.

5. The method according to claims 1 to 4, wherein: The first patterning process and the second patterning process are performed on a same layer of a stack of semiconductor devices.

6. The method according to any one of the preceding claims, wherein Determining the performance of the patterning process includes determining a stitching error between exposures in the first patterning process and exposures in the second patterning process.

7. The method according to any one of the preceding claims, wherein Determining the performance of the patterning process includes determining one or more corrections to the patterning process.

8. A method according to any one of the preceding claims, wherein Receiving the image includes receiving an image formed when the measurement target is irradiated with optical radiation, or receiving an image from a scanning electron microscope (SEM), or receiving a voltage contrast image.

9. The method according to any one of the preceding claims, wherein Determining the performance of the patterning process includes a model, wherein the model includes a machine learning model or a neural network model or a vision technology model.

10. The method according to any one of the preceding claims, wherein Determining the performance of the patterning process includes analyzing an image to determine one or more feature characteristics of the first feature and / or second feature associated with a boundary between the first region and the second region.

11. A computer program product comprising computer readable instructions for performing the method according to claims 1 to 10 when executed on a suitable device.

12. An apparatus for determining performance of a lithographic process, the apparatus comprising one or more processors, the one or more processors being configured to: receiving an image of a portion of a substrate, the portion of the substrate comprising a first region comprising a first feature associated with a first patterning process and at least a second region comprising a second feature associated with a second patterning process, wherein the first features and the second features, when illuminated by radiation, form the image comprising a moiré pattern; and The performance of the patterning process is determined based on characteristics of the moiré pattern.

13. The apparatus according to claim 12, wherein The apparatus is configured to determine a stitching error between the first patterning process and the second patterning process using a phase of the moiré pattern.

14. The apparatus according to any one of claims 12 or 13, wherein The one or more processors are further configured to determine one or more corrections to the patterning process based on the performance of the patterning process.

15. The apparatus according to any one of claims 12 to 14, wherein The device is a metrology device or an inspection device or a scanning electron microscope or a device suitable for voltage contrast imaging.

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