Method and apparatus for inspection of structures and associated equipment

Abstract

A method for determining an overlay metric from a target structure is disclosed, comprising obtaining angle-resolved distributed spectral data associated with a measurement of the target structure, the angle-resolved distributed spectral data comprising a symmetric component. An overlay-related profile of a feature of the target structure is determined based on the angle-resolved distributed spectral data, wherein the overlay metric is determined based on the profile. The method comprises: exposing an exposed feature onto a shielding layer, the shielding layer comprising a mask defining shielded areas and unshielded areas of the layer, such that a first portion of the exposed feature is exposed on the shielded areas of the layer and a second portion of the exposed feature is exposed on the unshielded areas of the layer, the size of the first portion relative to the second portion being overlay-related; and performing an etching step to define an etched feature, the etched feature corresponding to the second portion of the exposed feature.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of European application No. 18201147.8 filed on October 18, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to metrology of microstructures, for example to assess the overlay performance of a lithographic apparatus. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (usually to a target portion of the substrate). A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a pattern forming device (which may alternatively be referred to as a mask or reticle) can be used to produce a circuit pattern to be formed on a single layer of an IC. This pattern can be transferred to a target portion (e.g., a portion including a die, a die, or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed via imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will 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 substrate synchronously in a given direction (the "scanning" direction) while scanning the pattern through a radiation beam, parallel to or anti-parallel to such a scanning direction. It is also possible to transfer the pattern from the patterning device to a substrate by imprinting the pattern onto the substrate.

[0005] In order to monitor the lithographic process, it is necessary to measure the parameters of the patterned substrate. For example, the overlay error between successive layers formed in or on the substrate. There are various techniques for measuring the microstructures formed during the lithographic process, including the use of scanning electron microscopes and various special tools. One form of a special inspection tool is a scatterometer, in which a radiation beam is directed to a target on the surface of the substrate and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before it is reflected or scattered by the substrate with the properties after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. For example, this determination can be made by comparing the reflected beam with data stored in a library of known measurement results associated with known substrate properties. Two main types of scatterometers are known. 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. Angular resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0006] Due to the size of the structures measured, these scatterometers cannot directly measure the dimensions of the structures (e.g., overlap, critical dimension (CD), or edge placement error (EPE)). In practice, these dimensional or size measurements are usually made using reconstruction techniques. These reconstruction techniques belong to the group of problems known in general as inverse scattering, in which the observed data are matched to possible physical scenarios. The goal is to find the physical scenario that causes the observed data as closely as possible. In the case of scatterometry, electromagnetic theory (Maxwell's equations) allows to predict which data will be the measured (scattered) data for a given physical scenario. This is called the forward scattering problem. The inverse scattering problem is now to find the appropriate physical scenario that corresponds to the actual measured data, which is usually a highly nonlinear problem. To solve this inverse scattering problem, a nonlinear solver is used, which uses many solutions to the forward scattering problem. In the known methods for reconstruction, nonlinear problems with three components are found:

[0007] Minimization of the difference between the measured data and the data calculated from the estimated scattering settings, for example by the Gauss-Newton method or similar numerical algorithms;

[0008] Parameterized shapes in the scattering setup, e.g., radius and height of contact holes;

[0009] • Sufficiently high accuracy of the solution to the forward problem (eg, calculated reflection coefficients) each time the parameters are updated. Summary of the invention

[0010] According to a first aspect of the present invention, there is provided a method for determining an overlap metric from a target structure, the method comprising: obtaining angularly resolved distributed spectral data associated with a measurement of the target structure, the angularly resolved distributed spectral data comprising a symmetric component; determining an overlap-related profile of a feature of the target structure based on the angularly resolved distributed spectral data; and determining the overlap metric based on the profile.

[0011] According to a second aspect of the present invention, a method for forming a target structure on a substrate is provided, the method comprising: exposing an exposed feature onto a shielding layer, the shielding layer comprising a mask that defines a shielded area and an unshielded area of ​​the layer, so that a first portion of the exposed feature is exposed on the shielded area of ​​the layer and a second portion of the exposed feature is exposed on the unshielded area of ​​the layer, and the size of the first portion relative to the second portion is overlapping; and performing an etching step to define an etched feature, the etched feature corresponding to the second portion of the exposed feature.

[0012] According to a third aspect of the invention, there is provided an inspection device, comprising: a projection optical device for projecting measurement radiation onto a structure on a substrate; a detection arrangement, the detection arrangement being operable to obtain a measured response resulting from scattering of the measurement radiation by the structure; and a processor; wherein the inspection device is operable to perform the method according to the first aspect.

[0013] According to a fourth aspect of the present invention, there is provided a manufacturing device, comprising: a photolithography exposure device, the photolithography exposure device comprising: an illumination source for providing exposure illumination; a mask platform for holding a pattern forming device for patterning the exposure illumination; and a substrate platform for holding the substrate; the photolithography exposure device is operable to perform the exposure step according to the second aspect.

[0014] According to a fifth aspect of the present invention, there is provided a computer program product comprising one or more sequences of machine-readable instructions, the instructions being adapted to cause one or more processors to perform the method according to the first aspect.

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

[0016] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and enable one skilled in the relevant art to make and use the invention.

[0017] Figure 1 Describe the lithography equipment.

[0018] Figure 2 Delineate lithographic cells or clusters.

[0019] Figure 3 Depict the first scatterometer.

[0020] Figure 4 Depicts the second scatterometer.

[0021] Figure 5 A first example process using an embodiment of the present invention for reconstructing a structure from scatterometry measurements is described.

[0022] Figure 6A second example process using an embodiment of the present invention for reconstructing a structure from scatterometry measurements is depicted.

[0023] Figure 7 Schematically depicted are (a) a first step of a self-aligned BEOL process to expose a via and (b) a second step of a self-aligned BEOL process to etch the via.

[0024] Figure 8 schematically depicting (a) a first step of a self-aligned BEOL process to expose vias to form a target according to a first embodiment of the present invention and (b) a second step of a self-aligned BEOL process to etch vias to form a target according to a first embodiment of the present invention;

[0025] Fig. 9 (a) to (c) each schematically depict the three different overlap values. Figure 8 The details of the goal formed by the steps depicted.

[0026] Fig.10 Schematically depicting (a) a first step of a self-aligned BEOL process to expose vias to form a target according to a second embodiment of the present invention and (b) a second step of a self-aligned BEOL process to etch vias to form a target according to a second embodiment of the present invention.

[0027] Features and advantages of the present invention will be apparent from the above detailed description set forth in conjunction with the accompanying drawings, in which like reference numerals identify corresponding elements throughout. In the accompanying drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit in the corresponding reference numeral. DETAILED DESCRIPTION

[0028] This specification discloses one or more embodiments that incorporate features of the present invention. The disclosed embodiments merely illustrate the present invention. The scope of the present invention is not limited to the disclosed embodiments. The present invention is defined by the claims appended to this specification.

[0029] The described embodiments and references in this specification to "one embodiment," "an embodiment," "an example embodiment," etc. indicate that the described embodiments may include certain features, structures, or characteristics, but each embodiment may not necessarily include the certain features, structures, or characteristics. Furthermore, these phrases do not necessarily refer to the same embodiment. In addition, when a certain feature, structure, or characteristic is described in conjunction with an embodiment, it should be understood that it is within the purview of those skilled in the art to implement such feature, structure, or characteristic in conjunction with other embodiments, whether or not explicitly described.

[0030] Embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, a machine-readable medium may include a read-only memory (ROM); a random access memory (RAM); a disk storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and such actions are actually caused by a computing device, processor, controller, or other device that executes firmware, software, routines, instructions, etc.

[0031] However, before describing such embodiments in further detail, it is instructive to provide an example environment in which embodiments of the invention may be implemented.

[0032] Figure 1 A lithographic apparatus is schematically depicted. The lithographic apparatus comprises an illumination system (illuminator) configured to condition a radiation beam B (e.g. UV radiation or DUV radiation), 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, a substrate table (e.g. wafer stage) WT configured to hold a substrate (e.g. resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate according to certain parameters, and a projection system (e.g. refractive projection lens system) PL configured to project a pattern imparted to the radiation beam B via the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0033] 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, for directing, shaping or controlling the radiation.

[0034] The support structure supports the pattern forming device, i.e. bears the weight of the pattern forming device. The way in which it holds the pattern forming device depends on the orientation of the pattern forming device, the design of the lithographic apparatus, and other conditions, such as, for example, whether the pattern forming device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the pattern forming device. The support structure can be, for example, a frame or a table that can be fixed or moved as required. The support structure can ensure that the pattern forming device is in a desired position, for example relative to the projection system PS. Any use of the term "reticle" or "mask" herein may be considered synonymous with the more general term "pattern forming device".

[0035] 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, for example to create 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 (such as an integrated circuit) created in the target portion.

[0036] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary masks, alternating phase shift masks, and attenuated phase shift masks, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam reflected by the matrix of mirrors.

[0037] The term "projection system" as used herein should be broadly interpreted to include any type of projection system, including refractive, reflective, refractive-reflective, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate, appropriate to the exposure radiation being used or other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system".

[0038] As depicted here, the device is transmissive (eg, using a transmissive mask). Alternatively, the device may be reflective (eg, using a programmable mirror array of the type described above, or using a reflective mask).

[0039] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such a "multi-stage" machine, the extra tables may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other tables are being used for exposure.

[0040] 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, for example, 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, but only means that the liquid is located between the projection system and the substrate during exposure.

[0041] Reference Figure 1 , the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In this case, the source is not regarded as forming part of the lithographic apparatus, and the radiation beam is delivered 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, the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD where necessary, may be referred to as a radiation system.

[0042] The illuminator IL may include 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 include various other components, such as an integrator In and a condenser CO. The illuminator IL may be used to condition the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0043] The radiation beam B is incident on a patterning device (e.g. a mask MA) held on a support structure (e.g. a mask table MT) and is patterned by the patterning device. After having passed through the mask MA, the radiation beam B passes through a projection system PL which focuses the beam B 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 interferometric device, a linear encoder, a two-dimensional encoder or a capacitive sensor), the substrate table WT can be precisely moved, for example, in order to position a different target portion C in the path of the radiation beam B. Similarly, the first positioning device PM and a further position sensor (not shown) are provided. Figure 1The first positioning device PM (as explicitly depicted in the figure) can be used to accurately position the mask MA relative to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during scanning. In general, movement of the mask table MT can be achieved with the help 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 WT can 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 mask table MT may be connected to the short-stroke actuator only, or may be fixed. The mask MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as shown occupy dedicated target portions, they can be located in the space between target portions (these are called scribe alignment marks). Similarly, where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0044] The depicted device LA can be used in at least one of the following modes:

[0045] 1. In step mode, the mask table MT and substrate table WT are held substantially stationary while an entire pattern imparted to the radiation beam is projected at once onto a target portion C (i.e. a single static exposure). The substrate table WT 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 imaged in a single static exposure.

[0046] 2. In scan mode, the mask table MT and substrate table WT 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 WT relative to the mask table MT may be determined by the (or less) magnification and image reversal characteristics of the projection system PL. In scan mode, the maximum size of the exposure field limits the width of the target portion C in a single dynamic exposure (in the non-scanning direction), while the length of the scanning movement determines the height of the target portion (in the scanning direction).

[0047] 3. In another mode, the mask table MT is held substantially stationary, the programmable patterning device is held, and the substrate table WT 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 used and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography utilising a programmable patterning device, such as a programmable mirror array of the type described above.

[0048] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0049] like Figure 2 As shown in the figure, the lithography equipment LA forms part of a lithography cell LC (sometimes also called a lithocell or cluster), which also includes equipment for performing pre-exposure and post-exposure processes on the substrate. Conventionally, these equipment include: a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH and a baking plate BK. A substrate transport device or robot RO picks up substrates from input / output ports I / O1, I / O2, moves these substrates between different process equipment, and then transfers them to the loading station LB of the lithography equipment. These devices are generally collectively referred to as coating and developing systems or tracks, and are controlled by a coating and developing system control unit or track control unit TCU, which is itself controlled by a management control system SCS, which also controls the lithography equipment via the lithography control unit LACU. Thus, different equipment can be operated to maximize throughput and processing efficiency.

[0050] In order to correctly and consistently expose substrates exposed by a lithographic apparatus, it is desirable to inspect the exposed substrates to measure properties such as overlay errors between subsequent layers, line thickness or thickness of lines, critical dimensions (CD), etc. If errors are detected, the exposure of subsequent substrates can be adjusted, especially if the inspection can be performed quickly and quickly enough so that other substrates of the same batch are still to be exposed. In addition, already exposed substrates can be stripped and reworked (to improve yield) or discarded, thereby avoiding exposure of substrates that are known to be defective. In the case where only some target portions of the substrate are defective, further exposure can be performed only on those target portions that are good.

[0051] Inspection equipment is used to determine the properties of substrates, and in particular to determine how the properties of different substrates or different layers of the same substrate vary between different layers. Inspection equipment can be integrated into the lithographic equipment LA or the lithographic cell LC, or can be an independent device. In order to achieve the fastest measurement, it is necessary to make the inspection equipment measure the properties in the exposed resist layer immediately after exposure. However, the latent image in the resist has a very low contrast (there is only a very small refractive index difference between the part of the resist that has been exposed to radiation and the part of the resist that has not been exposed to radiation) and not all inspection equipment has enough sensitivity to carry out useful measurement of the latent image. Therefore, it can be measured after the post-exposure baking step (PEB), which is usually the first step performed on the exposed substrate and increases the contrast between the exposed and unexposed parts of the resist. At this stage, the image in the resist can be called a semi-latent image. Measurements can also be made on the image of the developed resist (at which point the exposed or unexposed parts of the resist have been removed), or after a pattern transfer step such as etching. The latter possibility limits the possibilities for reworking defective substrates, but can still provide useful information.

[0052] Figure 3 A scatterometer which can be used in an embodiment of the present invention is depicted. It comprises a broadband (white light) radiation projector 2 which projects radiation onto a substrate W. The reflected radiation is passed to a spectrometer detector 4 which measures a spectrum 10 (intensity as a function of wavelength) of the specularly reflected radiation. From this data, the structure or profile causing the detected spectrum can be reconstructed by a processing unit PU, for example conventionally by rigorous coupled wave analysis (RCWA) and nonlinear regression, or by comparison with a library of simulated spectra, such as Figure 3 Typically, 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 some parameters of the structure to be determined from the scatterometry data. Such a scatterometer can be configured as a vertical incidence scatterometer, i.e. a normal incidence scatterometer, or an oblique incidence scatterometer.

[0053] exist Figure 4Another scatterometer that can be used in embodiments of the present invention is shown in FIG. In this device, the radiation emitted by the radiation source 2 is focused using a lens system 12 and is passed through an interference filter 13 and a polarizer 17, reflected by a partially reflective surface 16, and focused onto a substrate W via a microscope objective 15, which has a high numerical aperture (NA), preferably at least 0.9 and more preferably at least 0.95. An immersion scatterometer can even have a lens with a numerical aperture greater than 1. The reflected radiation is then transmitted through the partially reflective surface 16 into a detector 18 so that the scattered spectrum can be detected. The detector can be located in a back-projected pupil plane 11, which is located at the focal length of the lens system 15, however, the pupil plane can instead be re-imaged onto the detector using auxiliary optics (not shown in the figure). The pupil plane is a 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 a two-dimensional detector, so that a two-dimensional angular scatter spectrum can be measured of the substrate target 30. The detector 18 can be, for example, an array of CCD or CMOS sensors, and can use an integration time of, for example, 40 milliseconds per frame.

[0054] For example, a reference beam is often used to measure the intensity of the incident radiation. To make this measurement, when the radiation beam is incident on the beam splitter 16, a portion of the radiation beam is transmitted through the beam splitter as a reference beam towards the reference mirror 14. The reference beam is then projected onto a different portion of the same detector 18.

[0055] A set of interference filters 13 may be used to select wavelengths of interest in the range of, for example, 405 nm to 790 nm, or even lower, such as 200 nm to 300 nm. The interference filters may be tunable, rather than comprising a set of different filters. Instead of interference filters, gratings may be used, for example.

[0056] The detector 18 can measure the intensity of scattered light at a single wavelength (or a narrow wavelength range), the intensity of scattered light at multiple wavelengths, or the intensity of scattered light integrated over the entire wavelength range. In addition, the detector can separately measure the intensity of transverse magnetic polarized light and transverse electric polarized light, and / or the phase difference between transverse magnetic polarized light and transverse electric polarized light.

[0057] It is possible to use a broadband light source for the radiation source 2 (i.e., a broadband light source with a wide range of optical frequencies or wavelengths - and therefore a wide range of colors), which gives a large etendue, thereby allowing multiple wavelengths to be mixed. The multiple wavelengths in the broadband preferably each have a bandwidth of Δλ and a spacing of at least 2Δλ (i.e., twice the bandwidth). Several radiation "sources" can be different parts of an extended radiation source that has been split using an optical fiber bundle. In this way, angle-resolved scattering spectra can be measured in parallel at multiple wavelengths. 3-D spectra (wavelength and two different angles) can be measured, and the 3-D spectrum contains more information than the 2-D spectrum. This allows more information to be measured, thereby increasing the stability of the measurement process, i.e., robustness. This is described in more detail in EP 1,628,164 A2.

[0058] The target 30 on the substrate W may be a grating which is printed so that after development the bars are formed by solid resist lines. The bars may alternatively be etched into the substrate. Such a pattern is sensitive to chromatic aberrations in the lithographic projection apparatus (particularly the projection system PL) and to illumination symmetry, and the presence of such aberrations will manifest itself as variations in the printed grating. Therefore, the scatterometry data of the printed grating is used to reconstruct the grating. The parameters of the grating (such as line width and shape) may be input to a reconstruction process performed by the processing unit PU based on knowledge of the printing step and / or other scatterometry processes.

[0059] Modeling

[0060] The purpose of rigorous optical diffraction theory in measurement is actually the calculation of the diffraction spectrum reflected from the target. The target can be any target that is intentionally provided for measurement (such as a grating) or an actual device structure that needs to be measured. Target shape information is obtained for CD (critical dimension) uniformity and overlay measurement. Overlay measurement is a measurement system that measures the overlap of two targets in order to determine whether two layers on a substrate are aligned. CD uniformity is simply a measurement result of the spectral uniformity of the grating, which is used to determine how the exposure system of the lithography equipment operates. Specifically, CD (or critical dimension) is the width of the object "written" on the substrate, and is the limit of the lithography equipment that can physically write on the substrate. Another metric, edge placement error (EPE) is essentially a combination of overlap and CD.

[0061] When using one of the scatterometers described above in conjunction with modeling a target structure such as target 30 and its diffraction properties, the measurement of the shape and other parameters of the structure may be performed in a number of ways. Figure 5In the first type of process represented, a diffraction pattern based on a first estimate of the target shape (a first candidate structure) is calculated and compared to the observed diffraction pattern. The parameters of the model are then systematically varied and the diffraction recalculated in a series of iterations to generate new candidate structures and thus reach the best fit. Figure 6 In the process of the second type represented, diffraction spectra for many different candidate structures are pre-calculated to create a "library" of diffraction spectra. Next, the diffraction pattern observed from the measurement target is compared to the library of calculated spectra to find the best fit. The two methods can be used together: a rough fit can be obtained from the library, followed by an iterative process to find the best fit.

[0062] For more details, refer to Figure 5 , the manner in which measurements of the shape and / or material properties of an object are performed will be generally described. For this description, the object will be assumed to be a one-dimensional (1-D) structure. In practice, the object may be two-dimensional or three-dimensional, and the processing will be adapted accordingly.

[0063] In step 502, a scatterometer (such as those described above) is used to measure the response of the actual target on the substrate, and more specifically the diffraction pattern. This measured diffraction pattern is forwarded to a computing system such as a computer. The computing system may be the processing unit PU mentioned above, or it may be a different device.

[0064] In step 503, a "model matching scheme" is established, wherein the model matching scheme is based on a certain number of parameters p i (p1, p2, p3, etc.) are used to define a parameterized model of the target structure. In a 1D periodic structure, these parameters can represent, for example, the angle of the sidewalls, the height or depth of the features, the width of the features. The properties of the target material and the underlying layers are also represented by parameters such as the refractive index (at the specific wavelength present in the scattered measurement radiation beam). Specific examples are given below. Importantly, while the target structure can be defined by many parameters that describe its shape and material properties, for the purposes of the following process steps, the model selection scheme will define many of these parameters as having fixed values, while others will be variable or "floating" parameters. For the purpose of describing Figure 5 For the purpose of i .

[0065] In step 504: by setting the initial value p for the floating parameter i (0) (i.e., p1 (0) 、p2 (0) 、p3 (0)Each floating parameter will be generated within certain predetermined ranges, as defined in the matching scheme.

[0066] The parameters representing the estimated shape, together with the optical properties of the different components of the model, are used to calculate the scattering properties, for example using a rigorous optical diffraction method such as RCWA or any other solver of Maxwell's equations, in step 506. This gives an estimated diffraction pattern or a model diffraction pattern for the estimated target shape.

[0067] In steps 508 and 510, the measured diffraction pattern is then compared to the model diffraction pattern, and a "merit function" for the model target shape is calculated using the similarities and differences between the measured diffraction pattern and the model diffraction pattern.

[0068] In step 512, new parameters p1 are estimated, assuming that the merit function indicates that the model needs to be improved before it can accurately represent the actual object shape. (1) 、p2 (1) 、p3 (1) And so on and the new revised parameter value is iteratively fed back to step 506. Steps 506 to 512 are repeated.

[0069] To assist in the search, the calculation in step 506 may also generate partial derivatives of the evaluation function in such a specific region in the parameter space, the partial derivatives indicating the sensitivity to which increasing or decreasing a parameter will increase or decrease the evaluation function. The calculation of the evaluation function and the use of derivatives are generally well known in the art and will not be described in detail here.

[0070] In step 514, when the merit function indicates that the iterative process has converged to a solution with a desired accuracy, the currently estimated parameters are reported as the measurement results of the actual target structure.

[0071] The computation time of this iterative process is largely determined by the forward or forward diffraction model used, i.e., the estimated model diffraction pattern is calculated based on the estimated target structure using rigorous optical diffraction theory. If more parameters are needed, there are more degrees of freedom. (It should be noted that the context of "parameters" (degrees of freedom) is internal to the Maxwell solution process and is different from and usually more than the model parameters described in the above steps). The computation time in principle increases with the power of the number of degrees of freedom.

[0072] The estimated diffraction pattern or model diffraction pattern (or more generally, response) calculated at 506 can be expressed in a variety of forms. If the calculated pattern is expressed in the same form as the measured pattern produced in step 510, comparison is simplified. For example, the modeled spectrum can be easily compared to the measured spectrum obtained by Figure 3 The modeled pupil pattern can be easily compared with the spectrum measured by the device; Figure 4 The pupil pattern is measured by the device.

[0073] Throughout this specification, from Figure 5 To begin, assume that Figure 4 In the case of a scatterometer of type 1, the term "diffraction pattern" will be used. A person skilled in the art will be able to readily adapt the teachings to different types of scatterometers, or even to other types of measurement instruments.

[0074] Figure 6 An alternative example process is illustrated in which multiple model diffraction patterns for different estimated target shapes (candidate structures) are pre-computed and stored in a library for comparison with real measurements. Figure 5 The underlying principles and terminology of the process are the same. Figure 6 The steps of the process are as follows:

[0075] In step 602, a process of generating the library is performed. A separate library may be generated for each type of target structure. The library may be generated as required by the user of the measurement device, or may be pre-generated by the supplier of the device.

[0076] In step 603, a "model matching scheme" is established, wherein the model matching scheme is based on a certain number of parameters p i (p1, p2, p3, etc.) to define the parameterized model of the target structure. The considerations are similar to those in step 503 of the iterative process.

[0077] In step 604, the parameter p1 is generated, for example, by generating random values ​​for all parameters. (0) ,p2 (0) ,p3 (0) etc., each parameter is within its expected range of values.

[0078] In step 606, an estimated diffraction pattern or model diffraction pattern is calculated and stored in a library, the diffraction pattern representing the diffraction pattern expected based on the target shape represented by the parameters.

[0079] In step 608, the parameter p1 is generated (1) ,p2 (1) ,p3 (1)The new set of etc. is repeated dozens, hundreds or even thousands of times until the library including all stored modeled diffraction patterns is judged to be sufficiently complete. Each stored pattern represents a sample point in the multidimensional parameter space. The samples in the library should be filled into the sample space with sufficient density so that any real diffraction pattern will be represented closely enough.

[0080] In step 610, after the library is generated (but may be before the library is generated), a real target 30 is placed in the scatterometer and the diffraction pattern of the real target is measured.

[0081] The measured pattern is compared to the modeled patterns stored in the library to find the best matching pattern in step 612. The comparison may be performed with every sample in the library, or a more systematic search strategy may be used to reduce the computational burden.

[0082] In step 614, if a match is found, the estimated target shape used to generate the matching library pattern can be determined as the approximate object structure. The shape parameters corresponding to the matching sample are output as the measured shape parameters. The matching process can be performed directly on the model diffraction signal, or it can be performed on a surrogate model that is optimized for rapid evaluation.

[0083] In step 616, the closest matching sample is optionally used as a starting point and a refinement process is used to obtain the final parameters for reporting. For example, such a refinement process may include Figure 5 The iterative process shown is very similar to the iterative process.

[0084] A method for measuring an overlay metric will now be described. In such a context, the overlay metric may include the overlay itself (the result of the relative position error measurement between the layers) and / or a related / derivative metric such as an edge placement error (EPE). The EPE provides a change in the location of the edge of the structure produced by the patterning process. In an embodiment, the EPE is derived from the overlay value. In an embodiment, the EPE is derived from a combination of the overlay value and the CD value. In an embodiment, edge placement is derived from a combination of the overlay value, the CD value, and a value corresponding to a local variation (e.g., edge roughness, shape asymmetry, etc. of each individual structure). In an embodiment, the EPE includes an extreme value (e.g., 3 times the standard deviation, i.e., 3σ) of the combined CD error and overlay error. In a specific embodiment, in a multi-patterning process involving forming a structure and involving "cutting" a structure by removing a portion of the structure by etching the pattern provided by the patterning process with respect to the structure, the EPE may have the following form (or include one or more of the following items):

[0085]

[0086] where σ is the standard deviation, σ overlay corresponds to the standard deviation of the overlap; corresponds to the standard deviation of the critical dimension uniformity (CDU) of the structures produced during the patterning process; corresponds to the standard deviation of the critical dimension uniformity (CDU) of the cuts (if any) produced during the patterning process; σ OPE,PBA corresponds to the standard deviation of the optical proximity effect (OPE) and / or the proximity bias average (PBA), which is the difference between the CD at the spacing and the reference CD; and σ LER,LPE corresponds to the standard deviation of the line edge roughness (LER) and / or the local placement error (LPE). Although the above formula refers to the standard deviation, it can be formulated in a different comparable statistical way, such as variance.

[0087] At present, overlap measurements for determining overlap metrics or derived overlap metrics such as EPE are usually performed based on measuring asymmetries in structures and inferring overlaps from the measured asymmetries. As discussed above, a fast and non-invasive form of a dedicated measurement tool is a measurement tool in which a radiation beam is directed to a target on the surface of the substrate and the properties of the scattered beam (diffraction beam / reflection beam) are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. This can be referred to as diffraction-based measurement. One such application of such diffraction-based measurement is in the measurement of characteristic asymmetries within a target. For example, asymmetry can be measured by comparing relative portions of the diffraction spectrum (e.g., comparing -1 order with +1 order in the diffraction spectrum of a periodic grating). This measurement can be accomplished in the manner described above, and as described in U.S. Patent Application Publication US2006-066855, which is incorporated herein by reference in its entirety, for example. Other methods include measuring the intensity of the dark field image, for example, by comparing the intensity of the -1 order and the +1 order in these images. Another overlay measurement technique is based on the measurement of the structural asymmetry of the product resolution structure (rather than the grating pair), hereinafter referred to as ARO measurement (overlay measurement at resolution). ARO measurement is described in PCT patent application publication WO2017 / 149009, which is incorporated herein by reference. ARO measurement is a reconstruction-based overlay measurement that does not require a biased target. The method described in this document is based on the measurement of an "asymmetric pupil" or an asymmetric spectrum / intensity distribution. An asymmetric pupil is a pupil (the measured intensity distribution of the pupil or Fourier plane) in which the symmetric intensity distribution component has been removed; that is, a particular pupil image pixel can remove the symmetric intensity distribution component by subtracting the intensity of the symmetrically positioned pupil image pixel from the intensity at the particular pupil image pixel, and vice versa.

[0088] Currently, while these techniques are effective, it is desirable to provide new measurement techniques, and in particular techniques that can derive overlay metrics from changes in symmetric structures, e.g., techniques that are not based on measuring changes in structural asymmetry. In embodiments, such methods may include using the entire or full pupil without removing the symmetric component of the pupil. By not discarding the symmetric component, a much stronger overlay metric signal is obtained.

[0089] In one embodiment, where it is known that the measured structure should be symmetric, the residual asymmetric pupil (asymmetric pupil component) can be used to model the (unknown) source for the asymmetry of the signal. This new model can be used to extrapolate across the wafer / target to find possible non-yielding targets (i.e., targets that indicate non-yielding or bad dies). In an alternative embodiment, only the symmetric component of the pupil may be used, thereby removing the unwanted asymmetry (e.g., by removing the derived asymmetric component as described above, or by an equivalent method). This should produce a more easily converged model with lower residuals.

[0090] Such a method may include: measuring the pupil (angular resolved intensity and / or phase distribution) in the pupil (Fourier) plane resulting from radiation reflected and / or diffracted from the target structure (e.g., including zero-order and / or higher-order diffraction); and using reconstruction techniques (such as those described above) to perform a reconstruction of the geometry of the target structure (e.g., as used in CD metrology). In an embodiment, such a method will provide a combined determination of CD and overlay (and, therefore, a result of the measurement of EPE). This will increase measurement speed and throughput compared to current methods, in which overlay and CD are typically measured separately using different techniques.

[0091] To facilitate this approach, a target structure with an overlay-related profile should be formed on the substrate from which the overlay metric can be inferred. The overlay-related profile need not rely on any asymmetry and can therefore be symmetric about the direction of the overlay being measured.

[0092] A specific method for defining the profile associated with the overlap will now be described. This method is based on "self-aligned" lithography techniques. These self-aligned techniques are typically used in back-end-of-line (BEOL) processing, but are not limited thereto, and can be applied in front-end-of-line (FEOL) and / or middle-end-of-line (MOL) processing, such as to form gate contacts in transistor or other integrated circuit manufacturing processes.

[0093] In a self-aligned process flow, etch selectivity is used to help align the positioning of target structures or features, for example by defining feature profiles so that relatively small deviations of exposed features (before etching) do not result in significant changes in the position of the resulting etched features. In this way, the etching step causes the features to be self-aligned relative to other features in the hard mask or layer (such as the resulting metal features).

[0094] Figure 7A specific example of two steps of a BEOL self-alignment process is illustrated schematically. The figure shows (a) a hard mask line 700 and a hard mask block 710 for forming a metal layer on a dielectric layer 730, where a via 720 has been exposed on the dielectric layer 730; and (b) the same arrangement after an etching step to etch a via 720' into the dielectric 730. In general, overlap and CD are involved in forming the final via shape, which is important for interconnect resistance and final device yield. The etching step etches the exposed via 720 only into the dielectric 730 and not the hard masks 700, 710 to obtain an etched via 720'. To take advantage of this situation, the exposed vias 720 are overexposed; that is, larger than required with respect to the width of the dielectric 730 into which they are etched. It will be appreciated that because of this, there is some tolerance or range for variations in the position (i.e., overlap) of the exposed via 720 in the Y direction relative to the hard mask line 700, as well as variations in the shape / profile or CD of the exposed via, without significantly affecting the shape and functionality of the etched via 720'. As such, the EPE of the etched via 720' is largely resilient to variations in the CD or overlap in the exposed via 720.

[0095] Figure 8 and Fig. 9 A novel target concept based on the self-alignment technique described above is illustrated, which provides an overlay target at a resolution that can be measured and the overlay extracted using the symmetric components of the pupil. Figure 8 The layout and Figure 7 The arrangement of is largely synonymous with and shows (a) a hard mask line 800 and a block 810 on a dielectric 830 where a via 820 is exposed on the dielectric 830; and (b) the same arrangement after an etching step to etch the exposed via 820 into the dielectric 830 to obtain an etched via 820'. This target arrangement is similar to Figure 7 The difference between the product layouts of FIG. 8 and FIG. 1 is that for the target layout, there is an intentional overlap offset in the Y direction between the location of the exposed via 820 and the hard mask line 800, so that the etched via 820′ has the same Figure 8The offset may be such that (assuming the overlay error is zero) the exposed via 820 only contacts one hard mask line 800, and thus each etched via 820' comprises a semi-circular shape (of course, this would be highly undesirable for an actual product structure, and thus the offset should only be implemented in dedicated target areas for metrology purposes). Thus, the offset may be such that (without overlap) the etching step removes approximately half (e.g., more than 40%, more than 45%) of the exposed via. However, this is merely an example, and other feature shapes and position offsets are possible.

[0096] Such a target may be exposed in one or more target areas (e.g., in a region such as Figure 7 ), and each target area may include only one or more than one etched through-hole 820'. Where the target includes more than one etched through-hole 820', the measured overlap metric may include an average (or other combination) of the values ​​corresponding to each etched through-hole 820'. It will be appreciated that the target 820' will have the same or similar feature size and the same spacing as the product structure 720' it will be used to measure. Due to such small feature sizes, current scatterometers may not be able to measure isolated single features (etched through-holes) (but future scatterometers or scanning electron microscope (SEM) devices may be able to do so). Where single feature measurements are not possible, the measurement may include reconstructing multiple etched through-holes 820'. In this case, an average or other representative value may be used to determine one or more of overlap, CD, or EPE. Outliers may optionally be removed prior to averaging.

[0097] Fig. 9 An exposed via 820 and a corresponding etched via 820' are shown for (a) a first Y-direction overlap value, (b) a second Y-direction overlap value, and (c) a third Y-direction overlap value. In each case, the relative position in the Y direction between the exposed via 820 and the metal layer, and therefore the hard mask line 800, is expected to be the same (i.e., the vias are exposed with the same intentional offset), so that Fig. 9 The differences between the arrangements depicted in (a) to (c) of FIG. 1 only result in the formation of overlay errors and / or overlay metric variations (e.g., variations in the EPE). In each case, it can be seen that the etched through-hole 820' has a significantly different profile. It can also be seen that for this embodiment, the profile is substantially symmetrical about the Y axis, so that Fig. 9 The differences in the profiles in (a), (b) and (c) do not result in a significant change in the asymmetry.

[0098] The scattering measurement will be sensitive to such changes in the profile. Specifically, the (angularly resolved) intensity and / or phase distribution spectrum (pupil) measured by the angular resolution (pupil plane) (which includes (or only includes) its symmetric components) will be sensitive to such changes. This is because changes in overlap result in actual changes in the profile and / or CD of the measured feature (through hole 820'), rather than simply causing a shift in the feature. Therefore, it is proposed to reconstruct the profile from the distribution spectrum and to derive the overlap metric from the reconstructed profile. In an embodiment, the reconstruction will (for example, simultaneously) reconstruct both the CD and the profile to derive the overlap and CD. In an embodiment, this derived overlap and CD are used to derive the EPE (or the EPE is derived directly from the reconstructed profile). The reconstruction of the profile can be performed using the above reference. Figure 5 and Figure 6 Any of the methods described. It is also possible to use the method described in the above-mentioned WO2017148982 to infer overlap from the distribution spectrum, but without the step of removing the symmetric component from the distribution spectrum. This method determines weights and assigns weights to each pixel in the measured distribution, which depends on the sensitivity of the pixel to overlap, where the pixels are summed according to the weighting to determine the overlap.

[0099] Fig.10 A second BEOL embodiment is shown that is capable of measuring overlay in the X direction in addition to (or instead of) overlay in the Y direction. As previously described, such an embodiment also enables simultaneous measurement of CD, and therefore EPE. Fig.10 The layout and Figure 8 The arrangement of is largely synonymous with and shows (a) a hard mask line 1000 and a hard mask block 1010 on a dielectric 1030 where a via 1020 is exposed on the dielectric; and (b) the same arrangement after an etching step for etching the exposed via 1020 into the dielectric 1030 to obtain an etched via 1020'. This target arrangement is similar to Figure 8 The difference between the product arrangement of 1020 and 1021 is that, for the metal layer, the vias 1020 are each exposed adjacent to and partially overlapping the hard mask block 1010. It will be appreciated that the result is that the etched vias 1020' will have a profile that depends on the overlap in X (and Y). However, the target formed according to this embodiment may have a different pitch than the product structure (compared to Figure 8 embodiment, will have the same spacing as the product structure).

[0100] In yet another embodiment, instead of measuring a dedicated target, the measurement may be performed on an actual product structure, for example, the target structure may include a Figure 7. In such an embodiment, it may not be possible to measure small overlap / CD variations. However, if the vias are formed with overlap / CD deviations that are large enough to produce a non-functional device, the self-alignment process will likely result in a measurable change in profile using the methods described herein.

[0101] In the specific context of via formation in a BEOL process, an advantage of the method described above is that it provides a serial metric or index for measuring vias. Currently, electrical techniques are used to measure the resistance of the interconnect (formed in the via) after a metallization step including forming an additional metal layer. Since the via is one of the more important parameters for determining the resistance of the interconnect, the ability to monitor the via using a serial scattering measurement method before metallization will be very beneficial. In addition, these methods provide non-destructive post-etch measurements of the via shape. Such measurements can be used to simultaneously infer or reconstruct the CD and overlap (and therefore EPE) of the via. Such information can be used to determine the correction of the overlap and / or CD contribution obtained from the scanner and / or etcher, which can be fed back to the appropriate device.

[0102] The embodiments of the present invention can be described by referring to Figure 3 and Figure 4 The described processing unit PU implements the methods described herein to provide an inspection apparatus for reconstructing an approximate structure of an object. Furthermore, although metrology is described using a scatterometer, the disclosed target structures may be measured using any other type of suitable metrology device (eg, SEM).

[0103] refer to Figure 3 or Figure 4 The described processors may operate under the control of a computer program comprising one or more sequences of machine-readable instructions for calculating electromagnetic scattering properties of a structure, the instructions being adapted to cause the one or more processors to perform the methods described herein.

[0104] Although specific reference may be made herein to the use of inspection equipment in IC manufacturing, it should be understood that the inspection equipment described herein may have other applications, such as manufacturing integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. It should be understood by those skilled in the art that in the context of these alternative applications, any use of the term "wafer" or "die" in the present disclosure may be considered synonymous with the more general term "substrate" or "target portion", respectively. The substrates referred to herein may be processed in, for example, a coating and developing system or track (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a measurement tool, and / or an inspection tool before or after exposure. Where applicable, the disclosure herein may be applied to such substrate processing tools and other substrate processing tools. In addition, the substrate may be processed more than once, for example 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.

[0105] The method according to the embodiments of the present invention described above may be incorporated into a forward or diffraction model for reconstructing the approximate structure of an object (not limited to 1D periodic objects) based on detected electromagnetic scattering properties (such as diffraction patterns caused by irradiating the object with radiation), as described above with reference to Figure 5 and Figure 6 Described above. Figure 3 and Figure 4 The described processing unit PU may be configured to reconstruct an approximate structure of an object using this method.

[0106] Further embodiments according to the invention are depicted in the following numbered aspects:

[0107] 1. A method for determining an overlap metric from a target structure, the method comprising:

[0108] Obtaining angle-resolved distribution spectrum data related to measurement of the target structure, wherein the angle-resolved distribution spectrum data includes a symmetric component;

[0109] Determining an overlap-related profile of a feature of the target structure from the angle-resolved distributed spectral data; and

[0110] The overlap metric is determined based on the contour.

[0111] 2. The method according to aspect 1, wherein the step of determining an overlap-related profile of a feature of the target structure from the angle-resolved distributed spectral data comprises determining the profile from the angle-resolved distributed spectral data without first removing the symmetric component.

[0112] 3. A method according to aspect 2, wherein the step of determining the overlap-related contour comprises: performing a reconstruction of the target structure using a parameterized geometric model of the target structure.

[0113] 4. The method according to any preceding aspect, further comprising: simultaneously with determining the overlay metric, determining a critical dimension of the feature from the contour.

[0114] 5. A method according to any preceding aspect, wherein the overlay metric comprises an overlay or edge placement error.

[0115] 6. A method according to any preceding clause, wherein the angle resolved distributed spectral data relates to measurements of the target structure performed after an etching step.

[0116] 7. The method of clause 6, wherein the features comprise features formed by a self-aligned process such that etch selectivity during the etching step defines the overlay-related profile.

[0117] 8. The method of clause 6 or 7, wherein the feature is an etched via that has been exposed with an intentional offset relative to the masking layer.

[0118] 9. The method of clause 8, wherein the intentional offset is such that approximately half of the exposed vias are removed during the etching step without overlap, the actual amount removed depending on the overlap.

[0119] 10. The method according to any preceding aspect, comprising: performing a scatterometry measurement step to obtain the angle-resolved distributed spectral data.

[0120] 11. A method according to any preceding aspect, wherein the target structure comprises a plurality of said features, and the overlap metric is an average of a plurality of individual values ​​of the overlap metric determined for each of a plurality of individual features.

[0121] 12. A method according to any preceding aspect, comprising removing an asymmetric component from the angle resolved distributed spectral data, thereby determining the overlap related profile based solely on the symmetric component.

[0122] 13. A method according to any one of aspects 1 to 11, comprising: determining the cause of an asymmetric component in the angle-resolved distributed spectral data.

[0123] 14. The method according to aspect 13, comprising: performing yield prediction based on the determined cause of the asymmetric component.

[0124] 15. A method according to any preceding clause, comprising performing exposure and etching steps to form the target structure.

[0125] 16. A method for forming a target structure on a substrate, the method comprising:

[0126] exposing the exposed features onto a masking layer, the masking layer comprising a mask defining masked areas and unmasked areas of the layer, such that a first portion of the exposed features is exposed on the masked areas of the layer and a second portion of the exposed features is exposed on the unmasked areas of the layer, the first portion being overlaid relative to the size of the second portion; and

[0127] An etching step is performed to define etched features corresponding to the second portions of the exposed features.

[0128] 17. The method of clause 16, wherein the features are formed by a self-aligned process such that etch selectivity defines an overlay-dependent profile of the etched features during the etching step.

[0129] 18. The method of clause 17, wherein the masked and unmasked regions are such as to divide the first portion from the second portion in a single direction, such that the profile of the etched feature is dependent on overlap in only the first direction.

[0130] 19. The method of clause 18, wherein the feature is substantially symmetric about an axis in the first direction.

[0131] 20. The method of clause 19, wherein the etched features have a substantially semicircular shape.

[0132] 21. A method according to aspects 18, 19 or 20, wherein the target structure comprises a plurality of the features having the same spacing as the surrounding product structure.

[0133] 22. The method of clause 17, wherein the masked and unmasked areas are such as to divide the first portion from the second portion in two directions, such that a profile of the etched feature depends on the overlap in the two directions.

[0134] 23. The method of clause 22, wherein the etched feature has a substantially quarter-annular shape.

[0135] 24. The method of any of clauses 16 to 23, wherein the exposed features correspond to exposed features used to form vias, but are exposed with an intentional offset relative to the masking layer.

[0136] 25. A substrate comprising a target structure formed by the method according to any one of clauses 16 to 24.

[0137] 26. A reticle set comprising complementary patterns for exposing a target structure according to a method according to any one of clauses 16 to 24.

[0138] 27. An inspection device, comprising:

[0139] projection optics for projecting the measurement radiation onto the structure on the substrate;

[0140] a detection arrangement operable to obtain a measured response resulting from scattering of said measurement radiation by said structure; and

[0141] processor; wherein

[0142] The inspection apparatus is operable to perform a method according to any one of aspects 1 to 14.

[0143] 28. A manufacturing device, comprising:

[0144] A photolithography exposure device, comprising:

[0145] an illumination source, the illumination source being used to provide exposure illumination;

[0146] a reticle stage for holding a patterning device for patterning the exposure radiation; and

[0147] A substrate platform, the substrate platform is used to hold the substrate;

[0148] The lithographic exposure apparatus is operable to perform an exposure step according to any one of clauses 16 to 24.

[0149] 29. The manufacturing apparatus according to aspect 28, comprising an etching apparatus for performing the etching step according to any one of aspects 16 to 24.

[0150] 30. A lithography cell comprising a manufacturing apparatus according to clause 28 or 29 and an inspection apparatus according to clause 27, the lithography cell being further operable to:

[0151] using the overlay metric to determine a correction to a manufacturing process performed by the manufacturing equipment; and

[0152] The correction is used in a subsequent execution of the manufacturing process.

[0153] 31. A lithocell according to clause 30, wherein the inspection apparatus is operable to determine the overlay metric prior to performing a metallisation step in the manufacturing process.

[0154] 32. A computer program product comprising one or more sequences of machine-readable instructions adapted to cause one or more processors to perform the method of any of aspects 1 to 14.

[0155] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it should be understood that the invention may be used in other applications, such as imprint lithography, and is not limited to optical 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 imprinted into a layer of resist provided to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist, leaving the pattern behind after the resist is cured.

[0156] As used herein, the terms "radiation" and "beam" include all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365, 355, 248, 193, 157, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 to 20 nm), as well as particle beams, such as ion beams or electron beams.

[0157] The term "lens," where the context permits, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components.

[0158] The term "electromagnetic" encompasses both electrical and magnetic.

[0159] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be practiced in ways other than those described. For example, the present invention may be in the form of a computer program comprising one or more machine-readable instruction sequences describing the methods disclosed above, or a data storage medium (e.g., a semiconductor memory, a magnetic disk, or an optical disk) having a computer program stored therein.

[0160] It should be understood that it is the "Detailed Description" section, rather than the "Summary" and "Abstract" sections, that is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present disclosure contemplated by the inventors, and therefore, the Summary and Abstract sections are not intended to limit the present invention and the appended claims in any way.

[0161] The present invention has been described above by means of functional building blocks that illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined here. As long as the specified functions and their relationships are properly performed, other boundaries can be defined.

[0162] The foregoing description of the specific embodiments will fully reveal the general nature of the invention, and by applying knowledge within the technical scope of the art, others can easily modify and / or adapt such specific embodiments for various applications without excessive experimentation, without departing from the general concept of the invention. Therefore, based on the teachings and guidance given herein, these changes 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 describing by example rather than limiting, so that the terms or wording of this specification will be interpreted by the technician according to the teachings and guidance.

[0163] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A method for determining an overlap metric from a target structure, the method comprising: Obtaining angle-resolved distribution spectrum data related to measurement of the target structure, wherein the angle-resolved distribution spectrum data includes a symmetric component; determining an overlap-related profile of a feature of the target structure based on the angle-resolved distributed spectral data; as well as The overlap metric is determined based on the contour.

2. The method according to claim 1, wherein the step of determining the overlap-related profile of the features of the target structure from the angle-resolved distributed spectral data comprises: The profile is determined from the angle resolved distributed spectral data without first removing the symmetric component.

3. The method of claim 2, wherein the step of determining a contour associated with an overlap comprises: Reconstruction of the target structure is performed using a parameterized geometric model of the target structure.

4. The method according to any preceding claim, further comprising: Simultaneously with determining the overlay metric, a critical dimension of the feature is determined from the profile.

5. A method according to any preceding claim, wherein the overlay metric comprises an overlay or edge placement error.

6. A method according to any preceding claim, wherein the angle resolved distributed spectral data relates to measurements of the target structure performed after an etching step.

7. The method of claim 6, wherein the features comprise features formed by a self-aligned process such that etch selectivity during the etching step defines the overlay-related profile.

8. A method according to claim 6 or 7, wherein the features are exposed vias which have been exposed with an intentional offset relative to a masking layer and subsequently etched.

9. The method of claim 8, wherein the intentional offset is such that approximately half of the exposed vias are removed during the etching step without overlap, and the actual amount of approximately half of the exposed vias removed is dependent upon the overlap.

10. A method according to any preceding claim, comprising: A scatterometry measurement step is performed to obtain the angle-resolved distribution spectrum data.

11. A method according to any preceding claim, wherein the target structure comprises a plurality of said features and the overlap measure is an average of a plurality of individual values ​​of the overlap measure determined for each of a plurality of individual features.

12. A method according to any preceding claim, comprising: Asymmetric components are removed from the angle-resolved distributed spectral data, whereby the overlap-related profile is determined solely from the symmetric components.

13. The method according to any one of claims 1 to 11, comprising: The cause of the asymmetric component in the angle-resolved distribution spectral data is determined.

14. An inspection device, comprising: projection optics for projecting the measurement radiation onto the structure on the substrate; detection means operable to obtain a measured response resulting from scattering of said measurement radiation by said structure; as well as processor; in The inspection apparatus is operable to perform a method according to any one of claims 1 to 13.

15. A machine-readable medium having recorded thereon one or more sequences of machine-readable instructions, the instructions being adapted to cause one or more processors to perform the method according to any one of claims 1 to 13.

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