Method and apparatus for measuring a target field design

Abstract

A method and apparatus for providing accurate and robust measurement of lithographic features or metrology parameters is described. The method includes providing a range of values ​​or multiple values ​​for each of a plurality of metrology parameters of a metrology target, providing constraints for each of the plurality of metrology parameters, and calculating by a processor to optimize / modify the parameters within the range of values ​​or multiple values, thereby resulting in a plurality of metrology target designs having metrology parameters that satisfy the constraints.

Description

[0001] This application is a divisional application of the international application PCT / EP2017 / 066297, which entered the Chinese national phase on January 15, 2019 and has application number 201780043927.5.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Application No. 62 / 362,812 filed on July 15, 2016 and U.S. Application No. 62 / 385,615 filed on September 9, 2016, the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present description relates to methods and apparatus for determining one or more structural parameters of a metrology target that may be used, for example, in manufacturing a device by photolithography, and to manufacturing methods using photolithography. Background Art

[0005] A lithographic apparatus is a machine that applies a desired pattern to a substrate, usually on a target portion of the substrate. For example, a lithographic apparatus may be used in the manufacture of integrated circuits (ICs). In this case, a pattern forming device, which may alternatively be referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on a single layer of the IC. The pattern may be transferred to a target portion (e.g., including a portion of a die, one or more dies) on a substrate (e.g., a silicon wafer). Typically, the transfer of the pattern is performed by imaging the pattern onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned in succession. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern along a given direction (the "scanning" direction) by a radiation beam, while simultaneously scanning the substrate in a direction parallel or antiparallel to that direction. It is also possible to transfer a pattern from a pattern forming device to a substrate by imprinting the pattern onto the substrate.

[0006] During the lithography process, it is often desirable to measure the generated structure, for example for process control and verification. Typically, one or more parameters of the structure are measured or determined, for example, the overlay error between successive layers formed in or on a substrate. There are various techniques for measuring the microstructures formed during the lithography process. Various tools are known for making such measurements, including scanning electron microscopes, which are commonly used to measure critical dimensions (CDs), and specialized tools for measuring overlay, which is the accuracy of the alignment of two layers in a device. An example of such a tool is a scatterometer developed for use in the field of lithography. Such a device directs a radiation beam onto a target on the surface of a substrate and measures one or more properties of the redirected radiation - such as the intensity as a function of wavelength at a single reflection angle; the intensity as a function of reflection angle at one or more wavelengths; or the polarization as a function of reflection angle - to obtain a "spectrum", from which the properties of interest of the target can be determined. Determining the properties of interest can be performed by various techniques: for example, reconstruction of the target structure by iterative methods such as rigorous coupled wave analysis or finite element methods, library searching, and principal component analysis. Summary of the invention

[0007] The present invention relates to a method for designing a measurement target and a method for measuring photolithography characteristics using the measurement target and a measurement device.

[0008] Optical metrology uses light scattered from a target to provide information about the lithographic process. The measurements are performed in an optical instrument such as a scatterometer. The information that a scatterometer is suitable for measuring is the overlay, which is the relative distance between two overlapping gratings in a plane parallel to them.

[0009] In diffraction-based overlay measurements, the overlay is extracted from the intensity difference of the positive and negative first diffraction orders. The overlay sensitivity is defined as the ratio of the overlay sensitivity K, which is a scaling factor linking the measured intensity and the overlay OV, to the averaged intensity Im (ratio times 20 nm).

[0010] Examples of known scatterometers include those described in US2006033921A1, US2010201963A1, US2006066855A1, US2014192338, US2011069292A1, US20110027704A, US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A, and WO2016083076A1. The contents of all of these applications are specifically and entirely incorporated herein by reference.

[0011] Furthermore, it is desirable to be able to use a metrology target that has been selected so that when the metrology target is used in a metrology measurement, it provides optimal and robust results, which in turn leads to accurate overlay measurements.More information on target design is in the Appendix, which is specifically and entirely incorporated herein by reference.

[0012] One of the problems faced by diffraction-based overlay metrology applications is that the overlay sensitivity (one of the parameters of the metrology measurement process, ie, the metrology parameter) is proportional to the wavelength of the light used to illuminate the target.

[0013] The described scaling of stack sensitivity to wavelength also exhibits a decreasing periodicity as a function of wavelength as the vertical or perpendicular distance (thickness) between the gratings used to form the target becomes larger.

[0014] Furthermore, the process of selecting and / or adjusting the light used in the metrology process is difficult as it limits the type of light source that provides the light that illuminates the target and it also limits the wavelength selection devices that can be used in such metrology equipment.

[0015] For example, it would be desirable to provide methods and apparatus for designing metrology targets.Also, although not limited thereto, it would be advantageous if the methods and apparatus could be applied to accurately measure and minimize overlay errors in a lithography process.

[0016] An object of the present invention is to provide an accurate and robust method for measuring lithographic characteristics.

[0017] According to the present invention, a method for measuring a target design is provided, the method comprising: receiving illumination parameters for measuring a target, and selecting and / or adjusting measurement parameters associated with the target design to improve the accuracy and / or robustness of measuring the target design using the illumination parameters.

[0018] Furthermore, according to the present invention, a method for determining parameters of a lithography process is provided, comprising: receiving light scattered from an area comprising at least two metrology targets, wherein the at least two metrology targets are optimized to provide robust and optimal metrology measurements; and determining the parameters of the lithography process based on a weighted contribution of each individual metrology target.

[0019] The illumination parameter is, for example, the wavelength or the polarization of the illumination beam of the measurement device.

[0020] The measurement parameter is, for example, the pitch of the grating used to form the measurement target. Further measurement parameters are the CD, the angle of the lines constituting the grating, the duty cycle of the lines and spaces constituting the beam.

[0021] In one embodiment of the invention, the pitch of the targets is selected and / or adjusted in a metrology simulation package, such as for a control package design, to have a larger K value for overlap sensitivity when the targets are illuminated with radiation received from a user or selected in the metrology target design.

[0022] In another embodiment of the present invention, a cluster of N targets is designed by selecting and / or adjusting the pitch, CD, angle of the grating forming the lines, duty cycle of the lines and spaces.

[0023] When illuminated with illumination radiation having a wavelength received and used in the design of the metrology target and / or used as a constraint in the design phase, the cluster of targets will provide at least N overlapping sensitivity values ​​K i .

[0024] Simulate the package selection and / or adjust the measurement parameters so that K i The weighted sum of is the largest.

[0025] Each K i The weight of i The other design condition is α i = the sum of 1 and -1<αi<1.

[0026] Parameters of the lithography process, such as overlay, are determined, for example, as a weighted sum of the overlay values ​​measured from each target, where the weight is the coefficient α i .

[0027] In another embodiment of the present invention, a cluster of N targets is designed by selecting and / or adjusting the pitch, CD, angle of the grating forming the lines, duty cycle of the lines and spaces.

[0028] The cluster of targets will provide at least N overlap numbers OV when illuminated with illumination radiation having a wavelength received and used in the design of the metrology targets. i .

[0029] Simulate package selection and / or adjust measurement parameters to make OV i The weighted sum of is the largest.

[0030] Each K i The weight is the parameter

[0031] The final overlap number is then a combination, such as a linear combination, of the individual overlap numbers of the different targets.

[0032] The reference overlap number is the target to be approached and is provided by self-referencing metrology methods, or by CD-SEM measurements.

[0033] Weight The value is not limited to the interval [-1,1].

[0034] parameter For example, it is determined based on correlation analysis. One example of correlation analysis is PCA (Principal Component Analysis).

[0035] Parameters of the lithography process, such as overlay, are determined, for example, as a weighted sum of the overlay values ​​measured from each target, where the weights are coefficients

[0036] In one aspect of the present disclosure, a range or multiple values ​​is provided for each of a plurality of measurement parameters of a measurement target, constraints are provided for each of the plurality of measurement parameters, and calculations are performed by a processor to optimize the parameters within the range of the plurality of values, resulting in a plurality of measurement target designs having measurement parameters that satisfy the constraints.

[0037] In one aspect of the present disclosure, a method is provided, comprising measuring a modification value and a lithography process parameter of each of a plurality of metrology targets, the plurality of metrology targets having been produced by the metrology parameters and the manufacturing process. The method further comprises determining a multiplication factor for each metrology target based on the corresponding modification value of each metrology target, and determining an overall lithography process parameter of the plurality of metrology targets using the modification value and the determined multiplication factor.

[0038] In one aspect of the present disclosure, a method is provided, comprising measuring a modification value and a lithography process parameter of each of a plurality of metrology targets, the plurality of metrology targets having been produced by the metrology parameters and the manufacturing process. The method further comprises determining a multiplication factor for each metrology target based on the corresponding modification value of each metrology target and the reference lithography process parameter, and determining an overall lithography process parameter of the plurality of metrology targets using the determined multiplication factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0040] Figure 1 An embodiment of a lithographic apparatus is schematically depicted;

[0041] Figure 2 An embodiment of a lithographic cell or cluster is schematically depicted;

[0042] Figure 3 An embodiment of a scatterometer is schematically depicted;

[0043] Figure 4 Another embodiment of a scatterometer is schematically depicted;

[0044] Figure 5 schematically depicting the form of multiple grating targets and the contours of the measurement spots on the substrate;

[0045] Fig. 6A and 6B The model structure of one cycle of the overlapping target is schematically depicted, which shows an example of the asymmetry change caused by the target and the ideal (for example) two types of processes;

[0046] Fig. 7A , Figure 7B and Figure 7C Schematic cross sections of overlapping periodic structures with different overlap values ​​in the zero region are shown respectively;

[0047] Fig.7D is a schematic cross section of an overlapping periodic structure having structural asymmetry in the bottom periodic structure due to processing effects;

[0048] Figure 8 The principle of overlapping measurements in an ideal target that does not suffer from structural asymmetry is shown;

[0049] Fig. 9 The principle of overlay measurement in non-ideal targets with correction for structural asymmetry as disclosed in the embodiments herein is shown;

[0050] Fig.10 shows example graphs of stack sensitivity as a function of incident radiation wavelength for different incident illumination polarizations;

[0051] Fig.11 schematically shows a case where there is no stacking difference between a first target periodic structure having an offset of +d and a second target periodic structure having an offset of -d, and shows diffraction signals after diffraction by the first target periodic structure and the second target periodic structure;

[0052] Fig.12 schematically shows intensity changes of a combined +1 diffraction order signal and a combined -1 diffraction order signal diffracted by a first target periodic structure;

[0053] Fig.13 schematically shows intensity changes of a combined +1 diffraction order signal and a combined -1 diffraction order signal diffracted by a second target periodic structure;

[0054] Fig.14 Schematically shows a case where there is a stacking difference between a first target periodic structure having an offset of +d and a second target periodic structure having an offset of -d, and shows diffraction signals after diffraction by the first target periodic structure and the second target periodic structure;

[0055] Fig.15shows an example graph of stack sensitivity as a function of incident radiation wavelength for different metrology target designs according to one embodiment;

[0056] Fig.16 is a flow chart of steps of a method for improving robustness and measurability of measuring a target stack according to one embodiment;

[0057] Fig.17A is a flow chart of steps of a method for improving robustness and measurability of measuring a target stack according to another embodiment;

[0058] Fig. 17B is an example graph of K values ​​for different measurement target designs as a function of measurement target location according to one embodiment;

[0059] Fig.18A is a flow chart of steps of a method for improving robustness and measurability of measuring a target stack according to another embodiment;

[0060] Fig.18B is an example graph of overlap values ​​as a function of measurement target location for different measurement target designs according to one embodiment;

[0061] Fig.19 is a flow chart of steps of a method for measuring photolithography process parameters using a metrology target according to one embodiment;

[0062] Fig. 20 is a flow chart of steps of a method for calibrating a measurement system using a measurement target according to one embodiment;

[0063] Fig.21 is a flow chart of steps of a method for designing a metrology target according to one embodiment.

[0064] Fig. 22 is a schematic diagram of a form of a multi-grating metrology target according to one embodiment. DETAILED DESCRIPTION

[0065] Before describing the embodiments in detail, it is instructive to provide an exemplary environment in which the embodiments may be implemented.

[0066] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus comprises:

[0067] - an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. DUV radiation or EUV radiation);

[0068] a support structure (e.g. mask table) MT configured to support a patterning device (e.g. mask) MA and connected to a first positioning device PM configured to accurately position the patterning device according to certain parameters;

[0069] a substrate table (e.g., wafer stage) WTa configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate according to certain parameters; and

[0070] - a projection system (eg a refractive projection lens system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg comprising one or more dies).

[0071] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape, or control the radiation.

[0072] The support structure of the patterning device holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions such as, for example, whether the patterning device is held in a vacuum environment. The support structure of the patterning device can hold the patterning device using mechanical, vacuum, electrostatic or other clamping techniques. The support structure of the patterning device can be a frame or a stage, for example, which can be fixed or movable as required. The support structure of the patterning device can ensure that the patterning device is located in a desired position (for example relative to a projection system). Any term "reticle" or "mask" used herein may be considered synonymous with the more general term "patterning device".

[0073] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to form a pattern in a target portion of a substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so-called assist features. Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in a device (e.g. an integrated circuit) to be created in the target portion.

[0074] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable liquid crystal display (LCD) panels. Masks are well known in photolithography and include mask types such as binary mask types, alternating phase-shift mask types, attenuated phase-shift mask types, and various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be independently tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.

[0075] The term "projection system" as used herein should be broadly interpreted to include any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems or any combination thereof, for example as appropriate for the exposure radiation used or for other factors such as the use of 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".

[0076] As shown here, the device is of the transmissive type (eg, employing a transmissive mask). Alternatively, the device may be of the reflective type (eg, employing a programmable mirror array of the type mentioned above, or employing a reflective mask).

[0077] The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g. two or more substrate tables, two or more patterning device supports, or a substrate table and a metrology table). In such a "multi-stage" machine, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

[0078] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. It is well known in the art that immersion techniques are used to increase the numerical aperture of the projection system. The term "immersion" as used herein does not mean that structures such as the substrate must be immersed in the liquid; rather, "immersion" only means that the liquid is located between the projection system and the substrate during exposure.

[0079] Reference Figure 1, the illuminator IL receives a radiation beam from a radiation source SO. For example, when the source is an excimer laser, the source and the lithographic apparatus may be separate entities. In this case, the source is not considered to form part of the lithographic apparatus, and the radiation beam is transferred from the source SO to the illuminator IL by means of a beam delivery system BD comprising, for example, suitable directional mirrors and / or a beam expander. In other cases, for example, when the source is a mercury lamp, the source may be an integral part of the lithographic apparatus. The source SO and the illuminator IL, together with the beam delivery system BD provided if necessary, may be referred to as a radiation system.

[0080] The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer radial extent and / or the inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. Furthermore, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0081] The radiation beam B is incident on the patterning device (e.g. mask) MA held on a support structure for the patterning device (e.g. mask table MT) and is patterned by the patterning device. Having traversed the patterning device (e.g. mask) MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioning device PW and a position sensor IF (e.g. an interferometer device, a linear encoder, a two-dimensional encoder or a capacitive sensor), the substrate table WTa can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B. Similarly, the first positioning device PM and a further position sensor ( Figure 1 The first positioning device PM comprises a first positioning device (not explicitly shown) for accurately positioning the pattern forming device (e.g. mask) MA relative to the path of the radiation beam B. Typically, movement of the support structure of the pattern forming device (e.g. mask table) MT may be achieved with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) forming part of the first positioning device PM. Similarly, movement of the substrate table WTa may be achieved using a long-stroke module and a short-stroke module forming part of the second positioning device PW. In the case of a stepper (as opposed to a scanner), the support of the pattern forming device (e.g. mask table) MT may be connected to the short-stroke actuator only, or may be fixed.

[0082] The pattern forming device (e.g., mask) MA and substrate W can be aligned by using mask alignment marks M1, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks shown occupy dedicated target portions, they can be located in spaces between multiple target portions (these are known as scribe alignment marks). Similarly, in the case where more than one die is set on the pattern forming device (e.g., mask) MA, the mask alignment marks can be located between the dies. In the case where it is desired that the mark is as small as possible and does not require any imaging or process conditions that are different from adjacent features, small alignment marks can also be included in the die among the device features. The alignment system for detecting the alignment marks is further described below.

[0083] The device shown can be used in at least one of the following modes:

[0084] 1. In step mode, the entire pattern imparted to the radiation beam is projected once onto a target portion C (i.e. a single static exposure) while the patterning device support (e.g. mask table) MT and substrate table WTa are held substantially stationary. The substrate table WTa is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C that is imaged in a single static exposure.

[0085] 2. In scan mode, the patterning device support (e.g. mask table) MT and substrate table WTa are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The speed and direction of the substrate table WTa relative to the patterning device support (e.g. mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), while the length of the scanning motion determines the height of the target portion (in the scanning direction).

[0086] 3. In another mode, a patterning device support (e.g. mask table) MT holding a programmable patterning device is held substantially stationary and the substrate table WTa is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, a pulsed radiation source is typically employed and the programmable patterning device is updated as required after each movement of the substrate table WTa, or between successive radiation pulses during a scan. This mode of operation may be readily applicable to maskless lithography using a programmable patterning device such as a programmable mirror array of the type mentioned above.

[0087] Combinations and / or variations on the above described modes of use, or entirely different modes of use, may also be employed.

[0088] The lithographic apparatus LA is of a so-called dual-platform type having two tables WTa, WTb (e.g., two substrate tables) and two stations—an exposure station and a measurement station—between which the table can be exchanged. For example, while a substrate on one table is being exposed at the exposure station, another substrate can be loaded onto another substrate table at the measurement station and various preparatory steps performed. The preparatory steps may include using a level sensor LS to map the surface control of the substrate and using an alignment sensor AS to measure the position of alignment marks on the substrate, both sensors being supported by a reference frame RF. If the position sensor IF cannot measure the position of the table when the table is at the measurement station and at the exposure station, a second position sensor may be provided to enable the position of the table to be tracked at both stations. As another example, while a substrate on one table is being exposed at the exposure station, another table without a substrate is waiting at the measurement station (where measurement activities may optionally occur). The other table has one or more measuring devices and may optionally have other tools (e.g., cleaning equipment). When the substrate has finished exposure, the stage without the substrate moves to the exposure station to perform, for example, measurement, and the stage with the substrate moves to a position (for example, a measurement station) where the substrate is unloaded and another substrate is loaded. These multi-stage arrangements can greatly increase the throughput of the apparatus.

[0089] like Figure 2 As shown, the lithography equipment LA forms part of the lithography unit LC, and is sometimes referred to as a lithography cell or a lithography cluster, and the lithography unit also includes equipment for performing one or more pre-exposure and post-exposure processes on the substrate. Conventionally, these equipment 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 chilling plates CH and one or more baking plates BK. The substrate handler or robot RO picks up the substrate from the input / output ports I / O1, I / O2, moves the substrate between different processing devices, and then transfers it to the loading station LB of the lithography equipment. These devices are generally collectively referred to as tracks and are controlled by a track control unit TCU, which itself is controlled by a management control system SCS, which also controls the lithography equipment via the lithography control unit LACU. Therefore, different equipment can be operated to maximize production volume and processing efficiency.

[0090] Figure 3An embodiment of a scatterometer SM1 is depicted. It comprises a broadband (white light) radiation projector 2 which projects radiation onto a substrate 6. The reflected radiation is passed to a spectrometer detector 4 which measures the spectrum 10 of the specularly reflected radiation (i.e. a measure of the intensity as a function of wavelength). From this data, the structure or profile causing the detected spectrum can be reconstructed by a processing unit PU, for example by rigorous coupled wave analysis and nonlinear regression, or with Figure 3 The reconstruction is performed by comparison with a library of simulated spectra at the bottom. In general, for the reconstruction, the general form of the structure is known and some parameters are assumed based on knowledge of the process by which the structure was made, leaving only a few parameters of the structure to be determined from the scatterometry data. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0091] Figure 4 Another embodiment of a scatterometer SM2 is shown. In this device, radiation emitted by a radiation source 2 is focused using a lens system 12, passes through an interference filter 13 and a polarizer 17, is reflected by a partially reflective surface 16, and is focused onto a substrate W via a microscope objective 15, which has a high numerical aperture (NA), desirably at least 0.9 or at least 0.95. An immersion scatterometer may even have a lens with a numerical aperture greater than 1. The reflected radiation is then transmitted through the partially reflective surface 16 to a detector 18 in order to detect the scatter spectrum. The detector may be located in a back-projected pupil plane 11, which is located at the focal length of the lens 15, however, the pupil plane may alternatively be re-imaged onto the detector 18 using auxiliary optics (not shown). The pupil plane is the plane in which the radial position of the radiation defines the angle of incidence, and the angular position defines the azimuth angle of the radiation. The detector is desirably a two-dimensional detector so that a two-dimensional angular scatter spectrum (i.e., a measurement of the intensity as a function of the scatter angle) of a substrate target can be measured. The detector 18 may be, for example, an array of CCD or CMOS sensors, and may have an integration time of, for example, 40 milliseconds per frame.

[0092] For example, a reference beam is often used to measure the intensity of the incident radiation. To this end, when the radiation beam is incident on the partially reflecting surface 16, a portion of it is transmitted through the surface as a reference beam towards the reference mirror 14. The reference beam is then projected onto a different portion of the same detector 18.

[0093] One or more interference filters 13 may be used to select wavelengths of interest in the range of, for example, 405-790 nm or even lower (e.g., 200-300 nm). The interference filter may be tunable, rather than comprising a bank of different filters. A grating may be used instead of one or more interference filters, or may be used in addition to one or more interference filters.

[0094] The detector 18 can measure the intensity of the scattered radiation at a single wavelength (or a narrow wavelength range), the intensity at multiple wavelengths, or the intensity integrated over the wavelength range. In addition, the detector can measure the intensity of transverse magnetic (TM) polarization and transverse electric (Te) polarization radiation and / or the phase difference between transverse magnetic polarization and transverse electric polarization radiation.

[0095] It is feasible to use a broadband radiation source 2 (i.e., a radiation source with a wide range of radiation frequencies or wavelengths and therefore with multiple colors), which provides a large light collection rate, thereby allowing multiple wavelengths to be mixed. It is expected that the multiple wavelengths in the broadband each have a bandwidth of δλ and a spacing of at least 2 bandwidths (i.e., twice the wavelength bandwidth). Several "sources" of radiation can be different parts of an extended radiation source, which have been separated using, for example, a fiber bundle. In this way, angle-resolved scattering spectra can be measured in parallel at multiple wavelengths. A 3-dimensional spectrum (wavelength and two different angles) can be measured, which contains more information than a 2-dimensional spectrum. This allows more information to be measured, which increases the robustness of the measurement process. This is described in more detail in U.S. Patent Application Publication No. US 2006-0066855, which is incorporated herein by reference in its entirety.

[0096] By comparing one or more properties of the beam before and after being redirected by the target, one or more properties of the substrate can be determined. For example, this can be done by comparing the redirected beam with a theoretical redirected beam calculated using a model of the substrate and searching for a model that gives the best fit between the measured redirected beam and the calculated redirected beam. Typically, a parameterized general model is used, and the parameters of the model, such as the width, height, and sidewall angle of the pattern, are varied until the best match is obtained.

[0097] There are two main types of scatterometers used. Spectral scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function of wavelength) of the radiation scattered into a specific narrow angular range. Angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity (or intensity ratio and phase difference in the case of an elliptical configuration) of the scattered radiation as a function of angle. Alternatively, the measurement signals of different wavelengths can be measured separately and combined at the analysis stage. Polarized radiation can be used to generate more than one spectrum from the same substrate.

[0098] In order to determine one or more parameters of the substrate, the best match is usually found between a theoretical spectrum generated from a model of the substrate and a measured spectrum generated by a beam that changes direction as a function of wavelength (spectral scatterometer) or angle (angle-resolved scatterometer). There are various methods for finding the best match, which can be combined. For example, a first method is an iterative search method, in which a first set of model parameters is used to calculate a first spectrum and compare it to the measured spectrum. Then, a second set of model parameters is selected, a second spectrum is calculated, and the second spectrum is compared to the measured spectrum. These steps are repeated with the aim of finding a set of parameters that gives the best matching spectrum. Typically, information from the comparison is used to guide the selection of subsequent parameter sets. This process is called an iterative search technique. The model with the set of parameters that gives the best match is considered to be the best description of the measured substrate.

[0099] The second approach is to make a library of spectra, each corresponding to a specific set of model parameters. Typically, the set of model parameters is selected to cover all or nearly all possible variations in substrate properties. The measured spectrum is compared to the spectra in the library. Similar to the iterative search method, the model with a set of parameters corresponding to the spectrum that gives the best match is considered to be the best description of the measured substrate. Interpolation techniques can be used to more accurately determine the optimal set of parameters in this library search technique.

[0100] In any method, sufficient data points (wavelength and / or angle) in the calculated spectrum should be used to enable accurate matching, usually between 80 to 800 data points or more for each spectrum. Using an iterative approach, each iteration for each parameter value will involve the calculation performed at 80 or more data points. This is multiplied by the required number of iterations to obtain the correct profile parameters. Thus, many calculations may be required. In practice, this results in a compromise between accuracy and processing speed. In the library method, there is a similar compromise between accuracy and the time required to set up the library.

[0101] In any of the scatterometers discussed above, the target on the substrate W may be a grating which is printed such that after development, the bars consist of solid resist lines. The bars may alternatively be etched into the substrate. The target pattern is selected to be sensitive to parameters of interest such as focus, dose, overlap, chromatic aberration, etc. in the lithographic projection apparatus, such that changes in the relevant parameters will manifest as changes in the printed target. For example, the target pattern may be sensitive to chromatic aberration in the lithographic projection apparatus (particularly the projection system PL) and illumination symmetry, and the presence of such aberrations will manifest themselves as changes in the printed target pattern. Accordingly, the scatterometry data of the printed target pattern are used to reconstruct the target pattern. The parameters of the target pattern (such as line width and line shape) may be input into a reconstruction process, which is performed by the processing unit PU based on knowledge of the printing steps and / or other scatterometry processes.

[0102] Although various embodiments of scatterometers have been described herein, other types of metrology equipment may be used in one embodiment. For example, dark field metrology equipment such as described in U.S. Patent Application Publication No. 2013-0308142, which is incorporated herein by reference in its entirety, may be used. Furthermore, those other types of metrology equipment may use techniques that are completely different from scatterometry.

[0103] Figure 5An exemplary composite metrology target formed on a substrate according to known practice is shown. The composite target comprises four gratings 32, 33, 34, 35 positioned closely together so that they will all be within the measurement spot 31 formed by the illumination beam of the metrology device. Thus, all four targets are illuminated simultaneously and imaged simultaneously on the sensors 4, 18. In an example dedicated to overlay measurement, the gratings 32, 33, 34, 35 are themselves composite gratings formed by overlapping gratings, which are patterned in different layers of a semiconductor device formed on a substrate W. There are multiple composite targets placed at different locations on the substrate W so that information and measurements about the entire substrate W can be obtained. The gratings 32, 33, 34, 35 can have overlap offsets that are biased differently to facilitate overlap measurements between layers where different parts of the composite grating are formed. The gratings 32, 33, 34, 35 can also be different in their directions, as shown in the figure, so as to diffract the incident radiation in the X direction and the Y direction. In one example, gratings 32 and 34 are X-direction gratings with +d, -d offsets, respectively. This means that grating 32 has its overlapping components arranged so that if they are both printed exactly at their nominal locations, one of the overlapping components will be offset by a distance d relative to the other overlapping component. Grating 34 has its components arranged so that if it is printed perfectly, it will be an offset of d, but in the opposite direction of the first grating, and so on. Gratings 33 and 35 can be Y-direction gratings with offsets of +d and -d, respectively. Although four gratings are shown, another embodiment may include a larger matrix to obtain the desired accuracy. For example, a 3×3 array of 9 composite gratings can have offsets of -4d, -3d, -2d, -d, 0, +d, +2d, +3d, +4d. Independent images of these gratings can be identified in the images captured by sensors 4, 18.

[0104] The metrology targets described herein may be, for example, overlay targets designed for use with metrology tools such as the Yieldstar stand-alone or integrated metrology tools, and / or alignment targets such as those commonly used in TwinScan lithography systems, both of which are commercially available from ASML.

[0105] In general, metrology targets used with these systems should be printed on a substrate with dimensions that conform to the design specifications of the specific microelectronic device to be imaged on that substrate. As processes continue to approach the limits of lithographic equipment imaging resolution in advanced process nodes, design rules and process compatibility requirements put pressure on the selection of appropriate targets. As the targets themselves become more advanced, resolution enhancement techniques such as phase-shift patterning devices and optical proximity correction are often required, and the printability of the target within the process design rules becomes more uncertain. As a result, the proposed metrology target design may be subjected to testing and / or simulation to confirm its suitability and feasibility from both a printability and detectability perspective. In a commercial environment, good overlay mark detectability can be viewed as a combination of lower overall measurement uncertainty and shorter "move-acquire-move" time, since slow acquisition is detrimental to the overall throughput of the production line. Modern microdiffraction-based overlay targets (μDBO) can be on the order of 10 μm on a side, which is comparable to 40×160 μm. 2 Provides an inherently lower detection signal than targets such as those used in the context of monitoring substrates.

[0106] In addition, once a metrology target has been selected that meets the above criteria, there is a possibility that detectability will change with respect to process variations, such as film thickness variations, various etch biases, and geometric asymmetries induced by the etching and / or polishing processes. Therefore, it may be useful to select a target with low detectability variations and low overlay / alignment variations for various process variations. Likewise, typically, the fingerprint (printing characteristics, including, for example, lens aberrations) of the specific machine used to produce the microelectronic device to be imaged will affect the imaging and production of the metrology target. Therefore, it may be useful to ensure that the metrology target is resistant to the effects of fingerprints, since some patterns will be more or less affected by a particular lithographic fingerprint.

[0107] Fig. 6A and 6B The model structure of one cycle of an overlapping target is schematically shown, which shows an example of the variation of the target from the ideal, an example of the variation of the asymmetry caused by (for example) two types of processes. Fig. 6A, a substrate W is patterned with a bottom grating 500, which is etched into the substrate layer. The etching process for the bottom grating causes the bottom plate 502 of the etched groove to be tilted. The bottom plate tilt (FT) can be expressed as a structural parameter, for example as a measure of the height difference across the bottom plate 502, in nm. A BARC (bottom anti-reflective coating) layer 504 supports the patterned resist features of the top grating 506. In this example, the alignment overlay error between the top grating and the bottom grating is zero because the centers of the top grating features and the bottom grating features are at the same lateral position. However, the asymmetry caused by the underlying process, i.e. the bottom plate tilt, causes errors in the measured overlay offset, giving a non-zero overlay offset in this case. Figure 6B Another type of underlying process-induced asymmetry is shown that can lead to errors in the measured overlay offset. This is the sidewall angle (SWA) imbalance, SWAun. Fig. 6A Features of the same are labeled identically. Here, one sidewall 508 of the bottom grating has a different slope than the other sidewall 510. The imbalance can be expressed as a structural parameter, such as the ratio of the two sidewall angles relative to the substrate plane. Both asymmetric parameters of the substrate tilt and the SWA imbalance will produce an "apparent" overlay error between the top and bottom gratings. This apparent overlay error appears on the "real" overlay error to be measured between the top and bottom gratings.

[0108] Therefore, in one embodiment, it is desirable to simulate various metrology target designs in order to confirm the suitability and / or feasibility of one or more proposed target designs.

[0109] In the above patent application disclosure, various techniques are disclosed for improving the quality of overlay measurement using the above basic method. These techniques are not explained in detail here. They can be used in combination with the newly disclosed techniques in this application.

[0110] Figures 7A-7D A schematic cross section of a target periodic structure (overlapping periodic structure) with different bias offsets is shown. These can be used as a target T on a substrate W. For exemplary purposes only, a periodic structure with periodicity in the X direction is shown. Different combinations of these periodic structures with different biases and different directions can be provided separately or as part of a target. Further details of the design of these periodic target structures are described in U.S. Patent Publication US 20150186582, the entire contents of which are incorporated herein by reference.

[0111] from Fig. 7AInitially, a target 600 is shown formed in at least two layers labeled L1 and L2. In the lower or bottom layer L1, a first periodic structure (lower or bottom periodic structure), such as a grating, is formed of features 602 and spaces 604 on a substrate 606. In layer L2, a second periodic structure, such as a grating, is formed of features 608 and spaces 610. (The cross section is drawn so that the features 602, 608 (e.g., lines) extend into the page.) The periodic structure pattern repeats in both layers at a pitch P. Features 602 and 608 can take the form of lines, dots, blocks, and vias. In Fig. 7A In the case shown, there is no overlay contribution due to misalignment (eg, no overlay error and no applied bias), such that each feature 608 of the second structure is located exactly over a feature 602 in the first structure.

[0112] exist Figure 7B In FIG. 5 , the same target is shown with a first known applied bias of +d, so that the feature 608 of the first structure is shifted to the right relative to the feature of the second structure by a distance d. The bias distance d may in practice be a few nanometers, for example 10nm-20nm, while the pitch P is, for example, in the range of 300-1000nm, such as 500nm or 600nm. Figure 7C , another feature with a second known applied bias -d is depicted, causing feature 608 to be shifted to the left. The value of d does not have to be the same for each structure. Figures 7A to 7C A periodic structure of this type of bias is shown.

[0113] Fig.7D The phenomenon of structural asymmetry is schematically illustrated, in this case the structural asymmetry in the first structure (bottom structural asymmetry). Figures 7A to 7C The features in the periodic structure in are shown as being perfectly square, when the real features have some slope and some roughness on the sides. However, they are intended to be at least symmetrical in profile. Fig.7D The features 602 and / or spaces 604 in the target no longer have a symmetrical form at all, but have become distorted by one or more processing steps. Thus, for example, the bottom surface of each space has been tilted (bottom wall tilted). For example, the side wall angles of the features and spaces have become asymmetric. Thus, the overall target asymmetry of the target will include an overlay contribution that is independent of the structural asymmetry (i.e., an overlay contribution due to misalignment of the first structure and the second structure; which itself includes overlay error and any known applied bias) as well as a structural contribution due to such structural asymmetry in the target.

[0114] When overlay is measured by the method of FIG6 using only two biased periodic structures, process-induced structural asymmetry cannot be distinguished from overlay contributions due to misalignment, and the overlay measurement (especially measuring undesired overlay errors) results become unreliable. Structural asymmetry in the first structure of the target (the bottom periodic structure) is a common form of structural asymmetry. For example, it can originate from substrate processing steps performed after the first structure is initially formed, such as chemical mechanical polishing (CMP).

[0115] In PCT Patent Application Publication No. WO2013-143814, it is suggested to use three or more component periodic structures to measure overlay by a modified version of the method of FIG. 6 . Figures 7A to 7C Three or more periodic structures of the type shown in are used to obtain overlay measurements that are corrected to some extent for structural asymmetries in the target periodic structure, such as those caused by asymmetries in the underlying structure during the actual patterning process. However, this method requires new target designs (e.g., Figure 4 ) and thus a new patterning device or patterning device pattern will be required. Furthermore, the target area is larger and thus consumes more substrate area. Additionally, the phase element of the overlapping contribution due to structural asymmetry is ignored in this and other prior art methods, which means that the correction is not as accurate as would be achievable if the phase element were also corrected.

[0116] exist Figure 8 , curve 702 shows the relationship between the overlap OV and the intensity asymmetry A of an "ideal" target with zero bias and no structural asymmetry within the individual periodic structures forming the target (particularly within a single periodic structure of the first structure). Thus, the target asymmetry of the ideal target includes only the overlap contribution due to the misalignment of the first and second structures caused by the known applied bias and overlay error OV. The graph and Fig. 9 The graphs of only illustrate the principles upon which the present disclosure is based, and in each graph, the units of intensity asymmetry A and overlap OV are arbitrary. Examples of actual dimensions are given further below.

[0117] exist Figure 8 In the "ideal" case of , curve 702 indicates that the intensity asymmetry A has a nonlinear periodic relationship (e.g., a sinusoidal relationship) with an overlap. The period P of the sinusoidal variation corresponds to the period or pitch P of the periodic structure, which is of course converted to the appropriate ratio. The sinusoidal form is pure in this example, but in real cases harmonics may be included.

[0118] As described above, a biased periodic structure (with a known applied overlay bias) can be used to measure overlay, rather than relying on a single measurement. The bias has a known value defined in the patterning device (e.g., reticle) from which it is made, which serves as an on-substrate calibration of the overlay corresponding to the measured intensity asymmetry. In the Figures, the calculation is graphically illustrated. In steps S1-S5, intensity asymmetry measurements A are obtained for periodic structures with applied biases of +d and -d, respectively. +d and A -d (For example, Figure 7B and Figure 7C As shown). Fitting these measurements to a sine curve gives points 704 and 706, as shown. Knowing the offset, the true overlay error OV can be calculated. The pitch P of the sine curve is known from the design of the target. The vertical scale or amplitude of curve 702 is not known at the beginning, but is an unknown factor that can be called the K value. The K value is a measure of the sensitivity of the intensity asymmetry measurement to the stacking of the target. If the determined K value is inaccurate, the determined overlap will also be inaccurate. In addition, the K value can be target specific, and the K value varies across the substrate due to process variations across the substrate. For example, the K value between each target may vary due to chemical mechanical polishing or stack thickness.

[0119] In the terms of the equation, the relationship between the overlay error OV, the K value and the intensity asymmetry A is assumed to be:

[0120] A±d=K sin(OV±d) (1)

[0121] where the overlay error OV is expressed in a scale such that the target pitch P corresponds to an angle of 2π radians. In the case of two measurements using gratings with different known offsets (e.g. +d and -d), the overlay error OV is calculated using the following equation:

[0122]

[0123] Fig.10 An example graph of stack sensitivity as a function of incident radiation wavelength is depicted. Stack sensitivity can be understood as a measure of how the sensitivity of the intensity asymmetry measurement changes when the incident radiation wavelength changes. Stack sensitivity or K-values ​​vary between different target stacks and are also highly dependent on the wavelength of the incident radiation. Measurements made at higher K-values ​​are more reliable, and thus the stack sensitivity or K-value is an indication of target measurability. Fig.10In the example shown, a metrology target in the form of a composite grating having, for example, a pitch of 625 nm is illuminated with incident radiation comprising a spectrum of wavelengths and orthogonal polarizations, and the value of the stack sensitivity forms a swing curve that oscillates, for example, between 0 and ±0.3 (in arbitrary units) as the wavelength changes. Curves 1010 and 1012 are plots of the average stack sensitivity versus the wavelength of the incident radiation, for example for orthogonal polarizations of 0 and 90 degrees, respectively. It should be noted that the stack sensitivity or K values ​​presented here are for exemplary purposes only and may vary under different radiation conditions or for different targets.

[0124] like Fig.10 As shown, it is desirable to select a specific wavelength at which the stacking sensitivity reaches a maximum value in order to achieve a more robust and reliable measurement. However, in order to meet this condition, the wavelength selection may have to be accurate, and any process variation or change in the incident radiation may result in a shift in the swing curve, and under the previously selected radiation conditions, the stacking sensitivity may no longer be at its maximum value. For example, changes in the stacking properties of a thick stack device may result in a shift in the swing curve. When the vertical distance between the gratings used to form the target becomes larger, the ratio of the stacking sensitivity to the wavelength shows a reduced periodicity as a function of wavelength. This is obvious for modern high-density circuits such as 3D NAND devices, because there may actually be considerable height steps. Stacking differences between adjacent periodic structures of the target or between adjacent targets may be a factor that adversely affects measurement accuracy, especially overlapping measurements. Further details on stacking differences and measurement accuracy can be found in European patent application EP16166614.4, the entire contents of which are incorporated herein by reference.

[0125] Stack differences may be understood as undesigned differences in the physical configuration between adjacent periodic structures or targets. Stack differences result in differences in the optical properties (e.g., intensity, polarization, etc.) of the measurement radiation between adjacent periodic structures or targets due to factors other than overlay errors, other than intentional biases, and other than structural asymmetries common to adjacent periodic structures or targets. Stack differences include, but are not limited to, thickness differences between adjacent periodic structures or adjacent targets (e.g., differences in thickness of one or more layers such that one periodic structure or target is higher or lower than another periodic structure or target designed to be at substantially the same level), refractive index differences between adjacent periodic structures or targets (e.g., differences in the refractive index of one or more layers such that the combined refractive index of one or more layers of one periodic structure or target is different from the combined refractive index of one or more layers of another periodic structure or target designed to have a substantially equal combined refractive index), material differences between adjacent periodic structures or targets (e.g., differences in material type, material homogeneity, etc. in one or more layers such that the material of one periodic structure or target is different from that of the one being measured). difference in the grating period of the structure of adjacent periodic structures or targets (e.g., a difference in the grating period of one periodic structure or target from another periodic structure or target designed to have substantially the same grating period), a difference in the depth of the structure of adjacent periodic structures or targets (e.g., a difference caused by etching in the depth of the structure of one periodic structure or target from etching in the depth of the structure of another periodic structure or target designed to have substantially the same depth), a difference in the width (CD) of features of adjacent periodic structures or targets (e.g., a difference in the width of a feature of one periodic structure or target from another periodic structure or target designed to have substantially the same width), etc. In some examples, stackup differences are introduced by processing steps (e.g., CMP, layer deposition, etching, etc.) during patterning.

[0126] As described above, stack differences result in variations in the optical properties of the measured radiation between adjacent periodic structures or targets, and thus stack sensitivity measurements can be tuned by varying target design parameters such as grating pitch, CD, or target profile, as further described below. Fig.11 Explanatory.

[0127] Fig.11A first periodic structure 1101 of a target in the form of a composite grating having an offset of +d and an adjacent second periodic structure 1106 of a target in the form of a composite grating having an offset of -d are shown. A first incident measuring radiation beam 1110 impinges on a first structure 1105 and a second structure 1103 of the first periodic structure 1101, wherein an offset of +d exists between the first structure 1105 and the second structure 1103. As a result, -1 diffraction order signals 1130 and 1120 are diffracted by the first structure 1105 and the second structure 1103, respectively. The -1 diffraction order signal diffracted by the first periodic structure 1101, i.e. 1101, It can be understood as the combination of -1 diffraction order signals 1130 and 1120. In addition, +1 diffraction order signals 1150 and 1140 are diffracted by the first structure 1105 and the second structure 1103, respectively. The +1 diffraction order signal diffracted by the first periodic structure 1101, i.e., 1101, can be understood as a combination of the +1 diffraction order signals 1150 and 1140. Therefore, the -1 diffraction order signal 1101 diffracted by the first periodic structure 1101 is and the +1 diffraction order signal diffracted by the first periodic structure 1101, 1101, can be expressed by the following equation:

[0128]

[0129] where C represents the contrast of the signal (which is a function of the periodic structure design, measurement wavelength, etc.), T is the thickness of the first periodic structure, λ is the wavelength of the measured radiation, and the phase term OV is the actual overlap (due to any unintentional misalignment of the layers), and P is the pitch of the first structure 1105 and the second structure 1103 of the first periodic structure 1101. Fig.12 , the intensity profile of the -1 diffraction order signal diffracted by the first periodic structure 1101, and the +1 diffraction order signal diffracted by the first periodic structure 1101 These are depicted in traces 1160 and 1170, respectively, according to equation (3).

[0130] Similarly, the second incident measurement radiation beam 1115 impinges on the first structure 1109 and the second structure 1107 of the second periodic structure 1106, wherein there is an offset -d between the first structure 1109 and the second structure 1106. As a result, -1 diffraction order signals 1135 and 1125 are diffracted by the first structure 1109 and the second structure 1107 of the second periodic structure 1106, respectively. The -1 diffraction order signal diffracted by the second periodic structure 1106, i.e. It can be understood as the combination of -1 diffraction order signals 1135 and 1125. In addition, +1 diffraction order signals 1155 and 1145 are diffracted by the first structure 1109 and the second structure 1107, respectively. The +1 diffraction order signal diffracted by the second periodic structure 1106, i.e. can be understood as a combination of the +1 diffraction order signals 1155 and 1145. Therefore, the -1 diffraction order signal diffracted by the second periodic structure 1106 is and the +1 diffraction order signal diffracted by the second periodic structure 1106, can be expressed by the following equation:

[0131]

[0132] Where C represents the contrast of each signal, T is the thickness of the second periodic structure, λ is the measured radiation wavelength, and the phase term OV is the actual overlap (due to any unintentional misalignment of the layers), and P is the pitch of the first structure 1109 and the second structure 1107 of the second periodic structure 1106. Fig.13 , the intensity profile of the -1 diffraction order signal diffracted by the second periodic structure 1106, and the intensity profile of the +1 diffraction order signal diffracted by the second periodic structure 1106, These are depicted in traces 1180 and 1190, respectively, according to equation (4).

[0133] Now, Fig.14 The case where there is a stacking difference between a first periodic structure 1201 with a bias of +d and an adjacent second periodic structure 1206 with a bias of -d is shown. In this case, the stacking difference is as follows Fig.14 The thickness shown is different and is described below. Fig.13 , the first incident measurement radiation beam 1210 is irradiated on the first structure 1205 of the first periodic structure 1201 and the second structure 1203 of the first periodic structure 1201 respectively. As a result, the -1 diffraction order signals 1230 and 1220 are diffracted by the first structure 1205 and the second structure 1203 respectively. Therefore, the -1 diffraction order signal diffracted by the first periodic structure 1201 is It can be understood as a combination of -1 diffraction order signals 1230 and 1220. In addition, +1 diffraction order signals 1250 and 1240 are diffracted by the first structure 1205 and the second structure 1203, respectively. Therefore, the +1 diffraction order signal diffracted by the first periodic structure 1201 is It can be understood as a combination of the +1 diffraction order signals 1250 and 1240.

[0134] Similarly, the second incident measurement radiation beam 1215 impinges on the first structure 1209 and the second structure 1207 of the second periodic structure 1206, respectively. As a result, the -1 diffraction order signals 1235 and 1225 are diffracted by the first structure 1209 and the second structure 1207, respectively. Therefore, the -1 diffraction order signal diffracted by the second periodic structure 1206 is can be understood as a combination of -1 diffraction order signals 1225 and 1235. In addition, +1 diffraction order signals 1255 and 1245 are diffracted by the first structure 1209 and the second structure 1207, respectively. Therefore, the +1 diffraction order signal diffracted by the second periodic structure 1206 is It can be understood as a combination of the +1 diffraction order signals 1255 and 1245.

[0135] As an example of stacking difference, the first periodic structure 1201 and the second periodic structure 1206 may have a thickness difference, such as Fig.14 As shown. However, in another example, the stacking difference can be caused by one or more other factors, which allow additional or alternative differences in the undesigned physical configuration between the first periodic structure 1201 and the second periodic structure 1206. For example, a stacking difference can be generated when the first periodic structure 1201 is more opaque to the first measurement radiation beam 1210 than the second periodic structure 1206. For example, there can be a difference in material between the first periodic structure 1201 and the second periodic structure 1206 (e.g., the same type of material with different refractive indices, different types of materials, etc.). As another example, there can be a difference in the pitch of the first periodic structure 1201 relative to the second periodic structure 1206, even if they are designed to have substantially the same pitch. These examples of stacking differences are not the only ways in which stacking differences can exist and therefore should not be considered limiting.

[0136] Referring back to equations (3) and (4), stackup differences can introduce three additional terms in each of equations (3) and (4). The first term ΔI N The second term ΔC represents the actual change in the intensity of the corresponding signal. N represents the actual change in contrast of the corresponding signal. The third term Δβ represents the actual change in phase of the corresponding signal. These three terms depend on the wavelength and / or polarization of the measurement radiation beams 1210 and 1215. Therefore, in the presence of stacking differences, the -1 diffraction order signal diffracted by the first periodic structure 1201 is and the +1 diffraction order signal diffracted by the first periodic structure 1201 can be collectively expressed by the following equation:

[0137]

[0138] As described above, an example of stacking difference or target design is pitch difference, i.e., the pitch difference between the first periodic structure 1201 and the second periodic structure 1206. According to equations (1) to (5), the swing curve of stacking sensitivity is a function of the target design. Appropriate adjustments can be made for different target design parameters, such as pitch, CD, sidewall angle, target profile, etc., and multiple design parameters can be adjusted simultaneously.

[0139] Fig.15 Various swing curves with respect to modified target pitches are shown according to one embodiment, while other target design parameters remain unchanged for simplicity in this example. Figure 4 , 13 14, target clusters have been manufactured with target pitches varying between 600nm and 740nm. Curves 1501, 1503, and 1505 are selected to be shown in multiple graphs herein, wherein each curve plots stacking sensitivity relative to incident radiation wavelength for target pitches of 600nm, 620nm, and 640nm, respectively. It should be noted that these pitches, wavelengths, and resulting swing curves are selected only as examples and should not be considered restrictive. As the target pitch changes, the amplitude of the swing curve changes and the peak value (maximum stacking sensitivity) also shifts horizontally along the x-axis (incident radiation wavelength). As a result, for a specific incident radiation wavelength, there may be a desired target design with maximum stacking sensitivity. Alternatively, the desired incident radiation wavelength may be determined for each target design for which the stacking sensitivity reaches a maximum value. Similarly, for a specific incident radiation polarization, there may be a desired target design with maximum stacking sensitivity. Alternatively, the desired incident radiation polarization may be determined for each target design for which the stacking sensitivity reaches a maximum value.

[0140] The above-mentioned metrology targets are also designed for one or more specific layers associated with a specific process stack (i.e., the process stack is the processes and materials used to construct a specific device or part thereof of the layer, for example, one or more material layers involved (e.g., their thickness and / or material type), lithography exposure process, resist development process, baking process, etching process, etc.), with the flexibility that the metrology target will provide measurement robustness against nominal variations in the process stack. That is, the knowledge of the process layers (e.g., their materials, thickness, etc.), process variations or processing steps applied to the layers, etc. are used to design the metrology target to arrive at a metrology target that will give the best measurement results for the measured lithography process parameters.

[0141] As described above, metrology target measurements are most robust and reliable when the absolute value of the stack sensitivity or K value is greatest for a particular incident radiation wavelength, polarization, or process stack.

[0142] Fig.16 1 is a flow chart of an exemplary method 1600 for improving robustness and measurability of a metrology target stack according to an embodiment of the present disclosure. Other method steps may be performed between various steps of method 1600, and other method steps are omitted only for clarity. Not all steps of method 1600 described below are required, and in some cases, the steps may not be performed in the order shown.

[0143] Method 1600 begins at step 1602, where a number N of multi-layer targets are fabricated on a wafer for use in any suitable lithography / metrology equipment. Figure 3 7A-7B describe examples of target design and construction. The number of multi-layer targets N is not limited to Figure 3 Four are shown and can be selected based on measurement needs. Multi-layer targets can be clustered at one location on the wafer, or can be placed at different locations to study target properties across a larger area on the wafer. The design of the multi-layer target can be varied between each target by modifying one or more geometric or manufacturing parameters (including but not limited to pitch, CD, sub-segmentation, sidewall angle, duty cycle of lines and spaces, height, width, material, etc.).

[0144] The method 1600 continues to step 1604, where the multi-layer target is illuminated with incident illumination radiation. The incident illumination radiation may include variations in wavelength, polarization, or beam profile, etc. The illumination profile may be determined based on the measurement target design. An overlay measurement value for each measurement target is extracted from the difference in the intensity of the positive first diffraction order and the negative first diffraction order reflected by the measurement target.

[0145] Method 1600 continues to step 1606 where at least N number of clusters from the multi-layer target are determined based on the overlap measurements. i , where i∈[1,N]. Stack sensitivity value K i The determination of can be performed by a computer processor using a computer-implemented method. As described above, due to process disturbances, the stack sensitivity or K value may vary across the wafer and may be different between each multilayer target. Therefore, each multilayer target T i With K i K value, where i∈[1,N].

[0146] Method 1600 continues to step 1608, where the measurement parameters of the multilayer target are selected or adjusted to achieve a large K value. The determination of the measurement parameters can be performed by a computer processor using a computer-implemented method. The measurement parameters may include, but are not limited to, geometric or manufacturing parameters, such as pitch, CD, sub-segmentation, sidewall angle, duty cycle of lines and intervals, height, width, refractive index, etc. The simulation package can be used to select or adjust the measurement parameters of the multilayer target design so that the maximum K value is achieved to provide the most robust and reliable measurement. An example of a simulation package may include the most important method known as "Design for Control" (abbreviated as D4C). Further details of D4C can be found in U.S. Patent Publication US20160140267, which is incorporated herein by reference in its entirety.

[0147] The processing parameters of the metrology system may also be calibrated to achieve the most robust and reliable measurements based on the determination process described above with reference to method 1600. For example, processing parameters such as the wavelength of radiation used in the metrology system for the target, the polarization of radiation used in the metrology system, and the numerical aperture of the metrology system may be adjusted.

[0148] Fig.17A 1 is a flow chart of an exemplary method 1700 for improving robustness and measurability of a metrology target stack according to another embodiment of the present disclosure. Other method steps may be performed between the various steps of method 1700, and other method steps are omitted only for clarity. Not all steps of method 1700 described below are required, and in some cases, the steps may be performed in a different order.

[0149] Fig. 17B is an example graph of K values ​​as a function of measurement target location for different measurement target designs according to one embodiment.

[0150] Method 1700 begins at step 1702, where a number N of multilayer targets are fabricated on a wafer by any suitable lithography / metrology equipment. Similar to the metrology target design described above in step 1602, the metrology parameters of the multilayer targets may include, but are not limited to, geometric or manufacturing parameters, such as pitch, CD, sub-segmentation, sidewall angle, duty cycle of lines and spaces, height, width, refractive index, etc. Clusters of multilayer targets may be formed on different regions across the wafer, and each region may include multiple targets with different designs. Thus, targets of similar design may be placed across the wafer surface simultaneously, while targets of different designs may be placed in close proximity at specific regions on the wafer.

[0151] Method 1700 continues to step 1704, where the multi-layer target is illuminated with incident illumination radiation. The incident illumination radiation may include variations in wavelength, polarization, or beam profile, and the illumination profile may be determined based on the measurement target design. Overlay measurements for each measurement target are extracted from the difference in the intensity of the positive first diffraction order and the negative first diffraction order reflected by the measurement target.

[0152] Method 1700 continues to step 1706, where at least N number of clusters from the multi-layer target are determined based on the overlap measurements. i , where i∈[1,N]. Stack sensitivity value K i The determination of can be performed by a computer processor using a computer-implemented method. As described above, due to process disturbances, the stack sensitivity or K value may vary across the wafer and may be different between each multilayer target. Therefore, each multilayer target T i With K i The K value is given a multiplication factor α i , where i∈[1,N]. It should be noted that the sensitivity values ​​are presented here as exemplary modification (or optimization) parameters, and any suitable modification parameters with any reference values ​​may be used, such as but not limited to target coefficients or overlap errors. Multiplication factor α i are coefficients that can be modified based on processing conditions and can be the result of any correlation analysis, such as principal component analysis (PCA). Different correlation analysis methods can be used, and PCA analysis is only referred to as an example here. PCA is a mathematical procedure well known in the art and does not need to be discussed in detail here.

[0153] Method 1700 continues to step 1708, where the weighted sum of Ki is adjusted to achieve a maximum value. The determination and optimization of the stack sensitivity value Ki may be performed by a computer processor using a computer-implemented method. According to an embodiment of the present disclosure, when At the maximum value, the measurement target is the most robust and reliable, and and α i ∈[-1,1]. For example, a larger multiplication factor (such as α i = 1) are assigned to target measurements with higher sensitivity values ​​so that they are given more weight in the calculated sum, while i A lower multiplication factor of = -1 may be assigned to target measurements with lower sensitivity values ​​so that they are given less weight in the calculated sum. Fig. 17BAs an example, K values ​​are measured for various target designs at various locations across the wafer. At a particular location, K values ​​1711, 1713, 1715, and 1717 are determined for metrology targets 1711', 1713', 1715', and 1717' (not shown), respectively. It should be understood that the K values ​​or metrology targets herein are for purposes of description by example and not for purposes of limitation, and that multiple metrology targets with different designs may be formed on the wafer. Large multiplication factor α i = 1 is assigned to the K value 1711 because it has a high sensitivity value. Similarly, a low multiplication factor α i = -1 is assigned to the K value 1717 because it has a low sensitivity value. The determination of the multiplication factor may also rely on the correlation between the optimization factor and any target attribute, such as location, stack indicator, pitch, CD, sub-segment, sidewall angle, duty cycle of lines and spaces, height, width, material, etc. As described above, different correlation analysis methods may be used.

[0154] The method 1700 continues to step 1710, where the measurement parameters of the multi-layer targets are calculated. The final measurement parameter value of the cluster of N multi-layer targets is the measurement parameter P measured for each multi-layer target. i The linear combination of is shown in the following equation:

[0155]

[0156] where i∈[1,N]. Therefore, it is possible to calculate the individual measurement parameters P from each multi-layer target. i and the multiplication factor α i The linear combination of is used to modify (or optimize) the final measurement parameter P.

[0157] Based on the determination process described above with reference to method 1700, the metrology target design, such as the grating design, can be further modified to adapt to various lithography processes and process perturbations and achieve maximum robustness and measurability. For example, methods and systems for automatically generating robust metrology targets include D4C.

[0158] Based on the determination process described above with reference to method 1700, processing parameters of the lithography system may be calibrated to achieve the most robust and reliable measurements. For example, processing parameters such as the wavelength of radiation used in the metrology system of the target, the polarization of radiation used in the metrology system, the numerical aperture of the metrology system, may be adjusted based on overlay sensitivity measurements from the metrology target.

[0159] Fig.18A1 is a flow chart of an exemplary method 1800 for improving robustness and measurability of overlay in a metrology target stack according to another embodiment of the present disclosure. Other method steps may be performed between the various steps of method 1800, and other method steps are omitted only for clarity. Not all steps of method 1800 described below are required, and in some cases, the steps may be performed in a different order.

[0160] Fig.18B is an example graph of overlap values ​​as a function of measurement target location for different measurement target designs according to one embodiment.

[0161] Method 1800 begins at step 1802, wherein Figure 3 A number N of multilayer targets are fabricated on a wafer used in the overlay measurement method using an inspection device or any suitable lithography / metrology device. Similar to the metrology target design described above in step 1602, the design may be varied between each multilayer target by modifying one or more geometric or manufacturing parameters (including but not limited to pitch, CD, sub-segmentation, sidewall angle, duty cycle of lines and spaces, height, width, refractive index, etc.). As noted above, clusters of multilayer targets may be formed on different regions across the wafer, and each region may include multiple targets having different designs.

[0162] The method 1800 continues to step 1804, where the multi-layer target is illuminated with incident illumination radiation. The incident illumination radiation may include variations in wavelength, polarization, or beam profile, etc. The illumination profile may be determined based on the measurement target design. An overlap measurement value for each measurement target is extracted from the intensity difference of the positive first diffraction order and the negative first diffraction order of scattered light from the measurement target.

[0163] Method 1800 continues to step 1806 where at least N number of clusters from the multi-layer target are determined based on the overlap measurements. i , where i∈[1,N]. Stack sensitivity value K i The determination of can be performed by a computer processor using a computer-implemented method. As described above, due to process disturbances, the stack sensitivity or K value may vary across the wafer and may be different between each multilayer target. Therefore, each multilayer target T i With K i As noted above, the stack sensitivity values ​​are thus presented as exemplary modified values, and any suitable modified values ​​with any reference value may be used.

[0164] Method 1800 continues to step 1808, where by using equation (2) from above and To calculate each multi-layer target T iThe overlap value OV i Each sensitivity value K i Given a multiplication factor where i∈[1,N]. Multiplication factor is a coefficient that can be modified based on processing conditions and external reference overlap values, and can also be the result of any correlation analysis, such as principal component analysis (PCA). As mentioned above, different correlation analysis methods can be used, and PCA analysis is only mentioned here as an example.

[0165] Method 1800 continues to step 1810, where the weighted sum of stack sensitivity values ​​is adjusted. The determination and optimization of stack sensitivity values ​​may be performed by a computer processor using a computer-implemented method. At the maximum value, the metrology target measurement is the most robust and reliable.

[0166] Multiplication Factor can be further adjusted based on an external reference overlap value to provide a more accurate measure of the final overlap value. Fig.18B An exemplary method for optimizing (or modifying) a final overlay value OV using an external reference overlay value is described. It should be understood that the overlay values ​​or metrology targets herein are for purposes of description by way of example and not limitation, and that multiple metrology targets of different designs may be formed on a wafer. Overlay values ​​are measured for various target designs at various locations across the wafer. At a particular location, overlay values ​​1811, 1813, 1815, and 1817 are determined for metrology targets 1811', 1813', 1815', and 1817' (not shown), respectively. For example, if multiple multilayer targets T i If the overlap values ​​are systematically deviated from the external reference overlap value 1819, each individual multiplication factor may also be adjusted based on the difference between the corresponding overlap value and the external reference overlap value. As a result, a multilayer target having an overlap value closer to the external reference overlap value 1819 may have a relatively high multiplication factor so that they are given more weight in the calculated sum, while multilayer targets with overlap values ​​that deviate from the external reference overlap value can have a relatively low multiplication factor So that they are given less weight in the calculated sum. For example, a low multiplication factor will be assigned to the overlap value 1811 because it has a relatively large difference between the external reference sensitivity values ​​1819. Similarly, a high multiplication factor will be assigned to overlap value 1815 because it has a relatively small difference between the external reference sensitivity values ​​1819. Therefore, the final overlap value OV can be further optimized (or modified) based on a linear combination of the individual overlap value calculations from each multi-layer target, thereby providing a more robust measurement than using a single target.

[0167] The method 1800 continues to step 1812, where the final overlap value OV for the cluster of N multi-layer objects is calculated by calculating each overlap value OV via the following equation: i The linear combination of is calculated as:

[0168]

[0169] where i∈[1,N]. Therefore, the final overlap value OV can be optimized (or modified) based on a linear combination of the individual overlap value calculations from each multi-layer target.

[0170] Similarly, the final overlap value OV can also be based on the multiplication factor α i and an external reference overlap value obtained from an external source, such as a CD-SEM measurement or a holistic metrology evaluation (HMQ) estimate. Further details of HMQ can be found in PCT application WO2015 / 018625A1, which is incorporated herein by reference in its entirety.

[0171] Based on the determination process of the final overlay value OV described above, an appropriate metrology target design can be selected or further modified to adapt to various lithography processes and process perturbations and achieve maximum robustness and measurability. For example, a method and system for automatically generating a robust metrology target includes D4C.

[0172] Based on the determination process described above with reference to method 1800, the processing parameters of the lithography system can be calibrated to achieve the most robust and reliable measurements. For example, processing parameters such as the wavelength of radiation used in the metrology system for the target, the polarization of radiation used in the metrology system, and the numerical aperture of the metrology system can be adjusted.

[0173] Fig.19 1 is a flow chart of an exemplary method 1900 for measuring lithography process parameters using a metrology target according to an embodiment of the present disclosure. Other method steps may be performed between various steps of method 1900, and other method steps are omitted only for clarity. Not all steps of method 1900 described below are required, and in some cases, the steps may not be performed in the order shown.

[0174] Method 1900 begins at step 1902, where light scattered by a plurality of metrology targets is measured. The plurality of metrology targets may be illuminated with incident radiation having an illumination profile such as wavelength or polarization. The measurement of the scattered light is performed in an optical instrument such as a scatterometer or other metrology tool. The plurality of metrology targets are designed using metrology parameters and produced by a manufacturing process. Examples of metrology parameters include, but are not limited to, the pitch of a grating used to form the metrology target, the CD, the angle of the lines forming the grating, the duty cycle of the lines and spaces forming the grating. An example of a manufacturing process is, but is not limited to, a photolithography manufacturing process using a lithography projection apparatus. A pattern (e.g., in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, the substrate may undergo various steps such as primer coating, resist coating, and soft baking. After exposure, the substrate may undergo other steps such as post-exposure baking (PEB), development, hard baking, and measurement / inspection of imaged features. The array of this step is used as the basis for patterning a single layer of a device (e.g., a metrology target or IC). Such a patterned layer can then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, chemical mechanical polishing, etc., all of which are aimed at completing a single layer.

[0175] The method 1900 continues at step 1904 where lithography process parameters for the plurality of metrology targets are determined using weighted contributions from each metrology target.

[0176] A weighted contribution from each metrology target may be determined using a method similar to method 1700, wherein a modification value is determined for each metrology target based on their respective scattered light measurements, and a multiplication value is determined for each modification value. The multiplication factors are determined by calculating and maximizing the sum of the multiplication factors multiplied by their corresponding modification values. For example, larger multiplication factors may be assigned to target measurements with higher modification values ​​so that they are given more weight in the calculated sum, while lower multiplication factors may be assigned to target measurements with lower modification values ​​so that they are given less weight in the calculated sum. Individual lithography process parameters are also determined for each metrology target, and these individual lithography process parameters are used to determine the lithography process parameters for multiple metrology targets by calculating the sum of the determined multiplication factors multiplied by their corresponding individual lithography process parameters.

[0177] Alternatively, a weighted contribution from each metrology target may be determined using a method similar to method 1800, wherein the multiplication value is further determined using a reference lithography process parameter. First, a modified value for each of the plurality of metrology targets is determined based on the scattered light measurement values ​​of the plurality of metrology targets, and the multiplication value for each modified value is determined by maximizing the sum of the multiplication factor multiplied by its corresponding modified value. The multiplication factor is then further adjusted by determining individual lithography process parameters for each metrology target and adjusting the multiplication factor based on the difference between the reference lithography process parameter and its corresponding respective lithography process parameter. The lithography process parameter is then determined by determining the sum of the multiplication factor multiplied by its corresponding respective lithography process parameter.

[0178] Fig. 20 2 is a flow chart of an exemplary method 2000 for using a measurement target for measurement system calibration according to an embodiment of the present disclosure. Other method steps may be performed between various steps of the method 2000, and other method steps are omitted only for clarity. Not all steps of the method 2000 described below are required, and in some cases, the steps may not be performed in the order shown.

[0179] Method 2000 begins at step 2002, where light scattered by a plurality of measurement targets is measured. Similar to method 1900, the plurality of measurement targets may be illuminated with incident radiation having an illumination profile such as wavelength or polarization. The measurement of the scattered light is performed in an optical instrument such as a scatterometer or other measurement tool. The plurality of measurement targets are designed using measurement parameters and produced by a manufacturing process.

[0180] Method 2000 continues to step 2004, where a modification value is determined for each measurement target using the scattered light measurement value of each measurement target. Thus, each multi-layer target has a determined modification value and multiplication factor. Examples of modification values ​​include, but are not limited to, stack sensitivity, target coefficient, or overlay error.

[0181] Method 2000 continues to step 2006, where multiplication factors are determined by calculating and maximizing the sum of the multiplication factors multiplied by their corresponding modification values. Similar to method 1700, multiplication factors are determined by calculating and maximizing the sum of the multiplication factors multiplied by their corresponding modification values. For example, larger multiplication factors can be assigned to target measurement values ​​with higher modification values ​​so that they are given more weight in the calculated sum, while lower multiplication factors can be assigned to target measurement values ​​with lower modification values ​​so that they are assigned less weight in the calculated sum. The measurement process can be calibrated by using the determined multiplication factors and their corresponding measurement targets.

[0182] Using a metrology target that provides a higher modification value, the processing parameters of the metrology system can also be calibrated to achieve the most robust and reliable measurement. For example, the processing parameters based on which the metrology target with a high modification value is designed to provide the most robust measurement can be selected for subsequent measurements. The processing parameters include, but are not limited to, the wavelength or polarization of the incident radiation used in the metrology system for the metrology target measurement, the process stack configuration, or the numerical aperture of the metrology system.

[0183] Fig.21 21 is a flow chart of an exemplary method 2100 for measuring target design according to an embodiment of the present disclosure. Other method steps may be performed between the various steps of method 2100, and other method steps are omitted only for clarity. Not all steps of method 2100 described below are required, and in some cases, the steps may not be performed in the order shown.

[0184] The method 2100 begins at step 2102, where a plurality of metrology parameters are provided to a computer device for generating a plurality of metrology target designs corresponding to a plurality of metrology targets. Similar to the metrology targets described in the method 1700, the metrology parameters are geometric or manufacturing parameters for the metrology targets, and examples include but are not limited to pitch, CD, sub-segment, sidewall angle, duty cycle of lines and spaces, height, width, refractive index, etc. Each metrology target is designed to be disposed at a different location on the substrate. As described above with reference to Figure 5 As described, multiple composite targets are placed at different locations on the substrate W so that measurements and information can be obtained about desired areas on the substrate W. Thus, clusters of multi-layer targets can be formed at different areas across the wafer, and each area can include multiple sub-targets with different designs. Targets of similar design can be placed across the wafer surface while also placing targets of different designs in close proximity at specific areas on the wafer.

[0185] The method 2100 continues to step 2104, where illumination parameters for incident radiation used to measure a plurality of metrology targets are received in a computer device. The illumination parameters may include changes in wavelength, polarization, or beam profile, among others.

[0186] Method 2100 continues to step 2106, where the computer device uses the process stack information or the illumination parameters of the substrate to determine the measurement parameters of each measurement target. The measurement parameters are determined so that selecting different measurement targets will provide different measurement results under the incident radiation or process stack configuration. Fig.15As described above, there may be a desired target design that provides maximum stack sensitivity for a particular illumination parameter or process stack. For example, a target design may be determined such that the stack sensitivity for a measurement using a desired incident radiation wavelength or polarization is maximized. Similarly, a target design may be determined such that the stack sensitivity for a desired incident process stack is maximized.

[0187] Fig. 22 Schematically depicts the form of a multi-grating metrology target disposed on a substrate through a manufacturing process according to an embodiment of the present disclosure. Figure 5 The composite target described, the multi-grating measurement target 2202 includes at least two sub-targets positioned closely together so that they will both be located within the measurement spot formed by the illumination beam of the measurement device. The two sub-targets have different geometric or manufacturing parameters, such as pitch, CD, sub-segmentation, sidewall angle, duty cycle of lines and spaces, height, width, refractive index, etc. This can be achieved by adjusting the measurement parameters used to design the measurement target. The design of the sub-target is determined so that the stacking sensitivity of the sub-target reaches a maximum value for the expected incident radiation wavelength or polarization. Similarly, the sub-target design can be determined so that the stacking sensitivity reaches a maximum value for the expected incident process stack. Therefore, the measurement target provides different measurement sensitivities under various incident radiation or process stack configurations.

[0188] Multiple multi-grating metrology targets 2202 are placed at different locations on the substrate W. Location selection is determined based on measurement requirements, such as, but not limited to, whether measurement information is needed for that location of the substrate W, or whether to eliminate process variation effects on the metrology measurement, such as stack depth variation effects. Thus, similarly designed metrology targets, each with multiple sub-targets, can be placed across the wafer surface simultaneously, while also placing targets of different designs in close proximity at specific areas on the wafer.

[0189] Although the target structures described herein are metrology targets specifically designed and formed for measurement purposes, in other embodiments, properties may be measured on a target that is a functional part of a device formed on a substrate. Many devices have regular grating-like structures. The terms "target," "target grating," and "target structure" as used herein do not require that the structure has been specifically configured for the measurement being made.

[0190] Although overlay targets in the form of rasters have been described, in embodiments, other target types may be used such as overlay targets based on box-in-box images.

[0191] Although metrology targets have been primarily described for determining overlap, alternatively or additionally, the metrology targets may be used to determine one of more other characteristics such as focus, dose, etc.

[0192] The measurement target according to the embodiment can be defined using a data structure such as a pixel-based data structure or a polygon-based data structure. For example, a polygon-based data structure can be described using a GDSII data format, which is quite common in the chip manufacturing industry. However, any suitable data structure or data format can be used without departing from the scope of the embodiment. The measurement target can be stored in a database, from which a user can select a desired measurement target for a specific semiconductor processing step. Such a database can include multiple measurement targets or a single measurement target selected or identified according to an embodiment. The database can also include multiple measurement targets, wherein the database includes additional information for each measurement target in the multiple measurement targets. The additional information may include, for example, information related to the suitability and / or quality of the measurement target for a specific lithography process step, and may even include the suitability and / or quality of a single measurement target for different lithography process steps. The suitability and / or quality of the measurement target can be represented by a suitability value and / or a quality value, respectively, or any other value that can be used in the selection process of selecting a measurement target from a database for a specific lithography process step.

[0193] In one embodiment, the computer-readable medium may include instructions for activating at least some method steps using a connection from a remote computer or remote system to the computer-readable medium. For example, such a connection may be generated through a secure network or via a (secure) connection on the World Wide Web (Internet). In this embodiment, a user may log in, for example, from a remote location to use a computer-readable medium to determine the suitability and / or quality of a measurement target design. The proposed measurement target design may be provided by a remote computer (or provided by an operator who uses a remote computer to provide the measurement target design to the system to determine the suitability of the measurement target design). Therefore, the proposed measurement target design simulated using the model may be owned by a different entity or company than the model used in the simulation process. Subsequently, the determined suitability obtained for evaluating the quality of the measurement target may be provided back to the remote computer, for example, without leaving any residual details more than the proposed measurement target design or the simulation parameters used. In such an embodiment, a customer may be provided with the option of running an evaluation of a separately proposed measurement target design without having the software or a copy of the software at its remote location. Such an option may be obtained, for example, through a user agreement. The benefit of such a user agreement can be that the model used in the simulation may always be the most up to date and / or the most detailed model available, without the need to update any software locally. Furthermore, by separating the model simulation and the proposed metrology target proposal, the details of the design identification or different layers for processing do not need to be shared by two companies.

[0194] In association with the physical grating structure of a target implemented on a substrate and a pattern forming device, an embodiment may include a computer program comprising one or more sequences of machine-readable instructions describing a target, a method of producing a target on a substrate, measuring a target on a substrate, and / or analyzing the measurements to obtain information about a lithography process. The computer program may be, for example, Figure 3 and Figure 4 Unit PU and / or Figure 2 A data storage medium (e.g. a semiconductor memory, a magnetic disk or an optical disk) in which such a computer program is stored may also be provided. Figure 1-4 In the event that a computer program product of the type shown in is already in production and / or in use, the embodiments may be implemented by providing an updated computer program product to cause the processor of the device to execute the method as described herein.

[0195] Embodiments of the present invention may take the form of a computer program comprising one or more sequences of machine-readable instructions for describing the methods disclosed herein or a data storage medium (e.g., a semiconductor memory, a magnetic disk, or an optical disk) in which the computer program is stored. Furthermore, the machine-readable instructions may be embodied in two or more computer programs. The two or more computer programs may be stored on one or more different memories or data storage media.

[0196] Any controller described herein may be operable individually or in combination when one or more computer processors within at least one component of the lithographic apparatus read one or more computer programs. The controllers may each or in combination have any suitable configuration for receiving, processing, and sending signals. One or more processors are configured to communicate with at least one controller. For example, each controller may include one or more processors for executing a computer program including machine-readable instructions for the above-described method. The controller may include a data storage medium for storing such a computer program, and / or hardware for accommodating such a medium. Therefore, the controller may operate according to the machine-readable instructions of one or more computer programs.

[0197] The present disclosure may also be described using the following aspects:

[0198] I. A method for measuring target design, the method comprising:

[0199] receiving illumination parameters for measuring a metrology target, and

[0200] Metrology parameters associated with a metrology target design are selected and / or adjusted to improve accuracy and / or robustness of measurements of the metrology target design using the illumination parameters.

[0201] II. A method for determining parameters of a lithography process, comprising:

[0202] receiving light scattered from a region including at least two metrology targets optimized to provide robust and optimal metrology measurements, and

[0203] Parameters of the lithography process are determined based on the weighted contribution of each individual metrology target.

[0204] Other embodiments according to the invention are further described in the following numbered aspects:

[0205] 1. A method comprising:

[0206] measuring light scattered by a plurality of metrology targets that have been designed using the metrology parameters and produced by a manufacturing process; and

[0207] Lithography process parameters are determined for the plurality of metrology targets using weighted contributions from each metrology target.

[0208] 2. The method according to aspect 1, wherein the weighted contribution is calculated by determining a modification value and a multiplication factor for each measurement target.

[0209] 3. The method of aspect 2, wherein determining the multiplication factor further comprises determining a sum of the multiplication factors multiplied by their respective modification values.

[0210] 4. The method of clause 3, wherein determining the lithography process parameter comprises adjusting the multiplication factor such that the sum is maximized.

[0211] 5. The method of clause 4, wherein determining the lithography process parameters further comprises determining individual lithography process parameters for each metrology target, and determining a sum of the multiplication factors multiplied by their respective individual lithography process parameters.

[0212] 6. The method according to aspect 1, wherein the modification value is a target coefficient or an overlay error of the plurality of measurement targets.

[0213] 7. The method according to clause 1, wherein the modification value is an overlay sensitivity value of the plurality of measurement targets.

[0214] 8. The method of clause 1, wherein the lithography process parameter is an overlay value.

[0215] 9. The method of clause 1, wherein the metrology parameter comprises material selection, critical dimension, sub-segmentation, or sidewall angle.

[0216] 10. The method of clause 1, wherein the plurality of metrology targets comprises a multi-layer periodic structure.

[0217] 11. The method of clause 10, wherein the metrology parameters of the multi-layer periodic structure include pitch, duty cycle of lines and spaces, height or width.

[0218] 12. The method of clause 1, wherein the plurality of metrology targets are designed for incident radiation or process stacks of different wavelengths or polarizations.

[0219] 13. The method of clause 1, wherein determining the lithography process parameters further comprises using reference lithography process parameters.

[0220] 14. A method according to clause 13, wherein the weighted contribution is calculated by determining a modification value and a multiplication factor for each metrology target.

[0221] 15. A method according to aspect 14, wherein the multiplication factor is determined using the sum of the multiplication factors multiplied by their respective modification values.

[0222] 16. The method of clause 15, wherein the multiplication factor is further determined by determining individual lithography process parameters for each metrology target and adjusting the multiplication factor based on a difference between the reference lithography process parameters and their respective individual lithography process parameters.

[0223] 17. The method of clause 16, wherein determining the lithography process parameters further comprises determining a sum of the multiplication factors multiplied by their respective lithography process parameters.

[0224] 18. A method comprising:

[0225] measuring light scattered by a plurality of metrology targets that have been designed using the metrology parameters and produced by a manufacturing process;

[0226] Determine the modified value for each measurement target; and

[0227] A multiplication factor for each measurement target is determined based on the corresponding modification value for each measurement target.

[0228] 19. The method of clause 18, wherein determining the multiplication factors comprises determining a sum of the multiplication factors multiplied by their respective modification values.

[0229] 20. The method of clause 19, wherein determining the multiplication factor further comprises adjusting the multiplication factor such that the sum is maximized.

[0230] 21. The method of clause 18, wherein the modification value is a target coefficient or an overlay error of the plurality of measurement targets.

[0231] 22. The method of clause 18, wherein the modification value is an overlay sensitivity value of the plurality of metrology targets.

[0232] 23. The method of clause 18, wherein the lithography process parameter is an overlay value.

[0233] 24. The method of clause 18, wherein the metrology parameter comprises material selection, critical dimension, sub-segmentation, or sidewall angle.

[0234] 25. The method of clause 18, wherein the plurality of metrology targets comprises a multi-layer periodic structure.

[0235] 26. The method of clause 25, wherein the metrology parameters of the multi-layer periodic structure include pitch, duty cycle of lines and spaces, height or width.

[0236] 27. The method of clause 18, wherein the plurality of metrology targets are designed for incident radiation or process stacks of different wavelengths or polarizations.

[0237] 28. A method for measuring a target design, the method comprising:

[0238] Providing a plurality of measurement parameters for generating a plurality of measurement target designs corresponding to a plurality of measurement targets, wherein each measurement target is designed to be disposed at a different location on the substrate;

[0239] receiving illumination parameters for measuring the plurality of metrology targets; and

[0240] A plurality of metrology parameters for each metrology target is determined by a computer device using process stack information or illumination parameters of the substrate.

[0241] 29. A method according to clause 28, wherein the illumination parameter comprises a wavelength value or polarization of incident radiation.

[0242] 30. The method of clause 28, wherein at least one metrology target is designed for different illumination parameters.

[0243] 31. The method of clause 28, wherein at least one metrology target is designed for a different process stack.

[0244] 32. The method of clause 28, wherein at least one metrology target is designed for incident radiation of different wavelength or polarization.

[0245] 33. A measurement target, comprising:

[0246] A plurality of metrology targets are disposed at different locations on a substrate through a manufacturing process, wherein each metrology target includes at least a first metrology sub-target and a second metrology sub-target that are different in design.

[0247] 34. The metrology target of clause 33, wherein the first metrology sub-target and the second metrology sub-target are designed for different process stacks.

[0248] 35. The metrology target of clause 33, wherein the first metrology sub-target and the second metrology sub-target are designed for different illumination parameters.

[0249] 36. The metrology target of clause 35, wherein the illumination parameter comprises a wavelength value or polarization of incident radiation.

[0250] Although specific reference has been made above to the use of embodiments in the context of optical lithography, it will be appreciated that embodiments of the invention may be used in other applications, such as imprint lithography, and are not limited to lithography where the context permits. In imprint lithography, the topography in the patterning device defines the pattern produced on the substrate. The topography of the patterning device may be pressed into a layer of resist provided to the substrate, whereupon the resist is cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist after the resist has been cured, leaving a pattern therein.

[0251] Moreover, although specific reference may be made herein to the use of lithographic apparatus for the manufacture of integrated circuits, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. It will be understood by those skilled in the art that in the context of such alternative applications, any term "wafer" or "die" used herein may be considered synonymous with the more general term "substrate" or "target portion", respectively. The substrate referred to herein may be processed before or after exposure, such as in a track (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, the substrate may be processed more than once, such as to produce a multi-layer IC, so that the term "substrate" used herein may also refer to a substrate that already contains multiple processed layers.

[0252] The terms "radiation" and "beam" as used herein include all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 nm to 20 nm), as well as particle beams such as ion beams or electron beams.

[0253] The term "lens," where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components.

[0254] The above description is intended to be exemplary rather than restrictive. Therefore, it will be appreciated by those skilled in the art that the invention described may be modified without departing from the scope of the claims set forth below. For example, one or more aspects of one or more embodiments may be combined with or replaced by one or more aspects of one or more other embodiments as appropriate. Therefore, based on the teachings and guidance provided herein, these adaptations and modifications are intended to fall within the meaning and scope of the equivalents of the disclosed embodiments. It should be understood that the wording or terminology here is for the purpose of description by example and not for restrictive purposes, so that the terms or wording of this specification will be interpreted by the technician according to teaching and guidance. The breadth and scope of the present invention should not be limited by any of the above-mentioned exemplary embodiments, but should only be limited by the following claims and their equivalents.

Claims

1. A measurement target, comprising: a plurality of measurement targets, the plurality of measurement targets being arranged at different positions on the substrate during the manufacturing process, Each measurement target includes at least a first measurement sub-target and a second measurement sub-target, and the first measurement sub-target and the second measurement sub-target are different in design; and The first measurement sub-target and the second measurement sub-target are designed so that, for a selected incident radiation or a selected process stack configuration, the stack sensitivity of each measurement sub-target reaches a maximum value.

2. The metrology target of claim 1, wherein the first metrology sub-target and the second metrology sub-target are designed using process stack information of the substrate, or are designed for different process stacks.

3. The measurement target of claim 1 or 2, wherein the first measurement sub-target and the second measurement sub-target are designed for different illumination parameters.

4. The measurement target of claim 3, wherein the illumination parameter comprises a wavelength value or polarization of the incident radiation.

5. A measurement target design method, the method comprising: Providing a plurality of measurement parameters to generate a plurality of measurement target designs corresponding to a plurality of measurement targets, wherein each measurement target is designed to be disposed at a different position on the substrate; receiving illumination parameters for measuring illumination of the plurality of metrology targets; and determining, by a computer device, one or more values ​​of the plurality of metrology parameters for each metrology target using the illumination parameters or process stack information of the substrate, wherein the one or more values ​​of the plurality of metrology parameters are determined such that a maximum overlay sensitivity is achieved for measurement using a selected incident radiation or a selected process stack configuration; as well as Based on the determination of one or more values ​​of the plurality of metrology parameters designed for the metrology target, the plurality of metrology targets are generated.

6. The method of claim 5, wherein: The illumination parameters include the wavelength value or polarization of the incident radiation.

7. The method of claim 5 or 6, wherein at least one measurement target is designed for different illumination parameters.

8. The method of claim 5 or 6, wherein at least one metrology target is designed using process stack information of the substrate, or is designed for a different process stack.

9. The method of claim 5 or 6, wherein at least one measurement target is designed for different wavelengths or polarizations of incident radiation.

10. The method according to claim 5 or 6, wherein: Each measurement target includes at least a first measurement sub-target and a second measurement sub-target, wherein the first measurement sub-target and the second measurement sub-target are designed so that for the illumination, the stacking sensitivity of each measurement sub-target reaches a maximum value.

11. A measurement target design method, the method comprising: Providing a plurality of measurement parameters to generate a plurality of measurement target designs corresponding to a plurality of measurement targets, wherein each measurement target is designed to be disposed at a different position on the substrate; receiving illumination parameters for measuring illumination of the plurality of metrology targets; determining, by a computer device, one or more values ​​of the plurality of metrology parameters for each metrology target using the illumination parameters or the process stack information of the substrate, wherein the one or more values ​​of the plurality of metrology parameters are determined such that a maximum stack sensitivity is achieved for the measurement using a selected incident radiation or a selected process stack configuration; and For each measurement target of the measurement target design, the plurality of measurement targets are generated based on determining the one or more values ​​of a plurality of measurement parameters.

12. A measurement target, comprising: a plurality of measurement targets, the plurality of measurement targets being arranged at different positions on the substrate during the manufacturing process, Each measurement target includes at least a first measurement sub-target and a second measurement sub-target, wherein the first measurement sub-target and the second measurement sub-target are different in design, and The first measurement sub-target and the second measurement sub-target are designed so that for a selected incident radiation or a selected process stack configuration, the stack sensitivity of each measurement sub-target reaches a maximum value.

13. The metrology target of claim 12, wherein the first metrology sub-target and the second metrology sub-target are designed for different process stacks.

14. The measurement target according to claim 12, wherein: The first measurement sub-target and the second measurement sub-target are designed for different illumination parameters.

15. The metrology target of claim 14, wherein the illumination parameter comprises a wavelength value or polarization of incident radiation.

16. A non-transitory computer program product stored in a medium and comprising machine-readable instructions therein, the instructions being configured to cause a computer system to at least cause the computer system to perform the method of any one of claims 5-11 when executed by the computer system.

Images