Method and measuring device for measuring parameters of device manufacturing process

Abstract

A method for measuring a parameter of a device manufacturing process is disclosed. The method comprises measuring a target on a substrate by illuminating the target with measurement radiation and using an optical device to detect the measurement radiation scattered by the target. The target comprises a target structure having a first periodic component and a second periodic component. The optical device receives radiation produced by diffraction of the measurement radiation from the target structure. The received radiation comprises at least one diffraction order that would not be received from diffraction of the measurement radiation from the first periodic component alone and would not be received from diffraction of the measurement radiation from the second periodic component alone.

Description

[0001] This application is a divisional application of the international application PCT / EP2017 / 077914, which entered the Chinese national phase on May 10, 2019 and has application number 201780069940.8.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of European Application No. 16198272.3 filed on November 10, 2016, the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present invention relates to a method for measuring parameters of a device manufacturing process, a measuring device, a substrate, a target, a device manufacturing system and a device manufacturing method. Background Art

[0005] A lithographic apparatus is a machine that applies a desired pattern to a substrate, typically to a target portion of the substrate. A lithographic apparatus can be used, for example, in a device manufacturing process, such as in the manufacture of integrated circuits (ICs). In this case, a pattern forming device, optionally referred to as a mask or reticle, can be used to generate a circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., including a portion of a die, one or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed by imaging the pattern onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will include a network of adjacent target portions that are patterned continuously. Conventional lithographic apparatus includes a so-called stepper in which each target portion is irradiated by exposing the entire pattern to the target portion at one time; and a so-called scanner in which each target portion is irradiated by scanning the pattern along a given direction (the "scanning" direction) with a radiation beam while simultaneously scanning the substrate in a direction parallel or antiparallel to the direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0006] In order to monitor a device manufacturing process such as a lithography process, parameters of a patterned substrate (and therefore parameters of any aspect of a device manufacturing process that affects a patterned substrate) are measured. For example, the parameters may include overlay errors between successive layers formed in or on the patterned substrate, and critical dimensions (typically line widths) of developed photoresist and / or etched product features. The parameters may include feature heights and / or feature spacings. These measurements may be performed on a product substrate and / or on a dedicated metrology target. There are various techniques for measuring microstructures formed in a lithography process, including the use of scanning electron microscopes and various dedicated tools. A rapid and non-invasive form of dedicated inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the surface of a substrate and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and 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 measurements associated with known substrate properties, or data calculated in real time from a model of the scattering structure. Two main types of scatterometers are known. Spectral scatterometers direct a broadband radiation beam onto a 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.

[0007] Multiple patterning is a class of techniques used to increase feature density. For example, in double patterning, the lithography process is enhanced to halve the minimum spacing between individual features. In quadruple patterning, the lithography process is enhanced to reduce the minimum spacing to one-quarter.

[0008] Spacer patterning, which may also be referred to as spacer process technology (SPT), is a multiple patterning technique in which multiple layers are formed on the sidewalls of pre-patterned features. The pre-patterned features are subsequently removed to leave two residual sidewall features for each pre-patterned feature. In the case where the width of the pre-patterned features is exactly equal to the separation between the pre-patterned features, the features formed using the residual sidewall features will be spaced apart from each other by a single common separation distance. However, errors in the spacer patterning process may cause the separation between adjacent features to change. In the case of double patterning, the changes may include alternating separation distances. Alternating separation distances may be referred to as pitch walking. For example, when errors in the lithography process cause the width of the pre-patterned features to be different from the separation between the pre-patterned features, pitch walking may occur. Pitch walking may also occur in other forms of multiple patterning, such as in non-spacer techniques such as lithography-etch-lithography-etch (LELE).

[0009] Accurate measurement of properties of device fabrication processes, including measurement of spacing variations resulting from multiple patterning processes, can be difficult, time consuming, or both. Summary of the invention

[0010] It would be desirable to provide improved methods and apparatus for measuring parameters of a device fabrication process and for performing the device fabrication process.

[0011] According to one aspect of the present invention, a method for measuring parameters of a device manufacturing process is provided, the method comprising: measuring the target by illuminating a target on a substrate with measuring radiation and using an optical device to detect the measuring radiation scattered by the target, wherein: the target comprises a target structure having a first periodic component and a second periodic component; and the optical device receives radiation generated by diffraction of the measuring radiation from the target structure, the received radiation comprising at least one diffraction order that will not be received from diffraction of the measuring radiation from the first periodic component alone and will also not be received from diffraction of the measuring radiation from the second periodic component alone.

[0012] According to another aspect of the present invention, there is provided a substrate comprising a target for measuring parameters of a device manufacturing process, the measurement being performed by irradiating the target with measuring radiation and detecting the measuring radiation scattered by the target, wherein: the target comprises a target structure having a first periodic component and a second periodic component; the first periodic component is arranged in a first layer and the second periodic component is arranged in a second layer, the second layer being above or below the first layer; and the second periodic component is configured so that a spacing of a combination of the first periodic component and the second periodic component is longer than a spacing of the first periodic component alone and longer than a spacing of the second periodic component alone.

[0013] According to another aspect of the present invention, there is provided a target for use in device manufacturing in a measurement process, wherein: the target comprises a target structure having a first periodic component and a second periodic component; the first periodic component is arranged in a first layer and the second periodic component is arranged in a second layer, the second layer being above or below the first layer; and the second periodic component is configured so that a spacing of a combination of the first periodic component and the second periodic component is longer than a spacing of the first periodic component alone and longer than a spacing of the second periodic component alone.

[0014] According to another aspect of the present invention, a measurement device for measuring parameters of a device manufacturing process is provided, the measurement device comprising: a substrate including a target; and an optical device for measuring the target by illuminating the target with measurement radiation and detecting the measurement radiation scattered by the target, wherein: the target comprises a target structure having a first periodic component and a second periodic component; and the optical device is configured to receive radiation generated by diffraction of the measurement radiation from the target structure, the received radiation comprising at least one diffraction order that will not be received from diffraction of the measurement radiation from the first periodic component alone and will not be received from diffraction of the measurement radiation from the second periodic component alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Embodiments of the present disclosure will now be described by way of example only with reference to the accompanying schematic drawings, in which corresponding reference characters indicate corresponding parts, and in which:

[0016] Figure 1 Describe the lithographic equipment;

[0017] Figure 2 delineating lithographic cells or clusters;

[0018] Figure 3 Describe the scatterometer used in the measurement;

[0019] Figures 4 to 9 depicts stages in an example double patterning process using spacer patterning;

[0020] Fig.10 A periodic target structure formed by double patterning with zero pitch variation is depicted in schematic side cross-section;

[0021] Fig.11 depicts in schematic side cross-section a periodic target structure formed by double patterning having a non-zero pitch variation;

[0022] Fig.12 An example target is depicted in schematic side cross-section, the example target comprising a target structure having a first periodic component in a first layer and a second periodic component in a second layer, wherein the first periodic component comprises a zero pitch variation;

[0023] Fig.13 Depicting the case where the first periodic component includes non-zero pitch variations Fig.12 Targets;

[0024] Fig.14 (a) is a schematic top view of a target structure with zero pitch variation;

[0025] Fig.14(b) Describe the Fig.14 (a) The first diffraction order of the target structure falling outside the input to the optical device;

[0026] Fig.15 (a) is the case where the spacing variation is non-zero Fig.14 (a) Schematic top view of the target structure;

[0027] Fig.15 (b) Describe the Fig.15 (a) The first diffraction order of the target structure still falls outside the input to the optical device;

[0028] Fig.16 (a) is a schematic top view of a target structure having a first periodic component and a second periodic component, wherein the first periodic component comprises a grating having zero pitch variation and the second periodic component comprises a periodic region where a portion of the grating is removed;

[0029] Fig.16 (b) Describe the Fig.16 (a) The first diffraction order of the target structure still falls outside the input to the optical device;

[0030] Fig.17 (a) is a schematic top view of a target structure having a first periodic component and a second periodic component, wherein the first periodic component comprises a grating having a non-zero pitch variation and the second periodic component comprises a periodic region with a portion of the grating removed;

[0031] Fig.17 (b) Describe the Fig.17 (a) The first diffraction order of the target structure falling within the input to the optical device;

[0032] Fig.18 (a) is a schematic top view of a first periodic feature in a first layer of a target;

[0033] Fig.18 (b) Describe the Fig.18 (a) a first order diffraction of the first periodic component falling outside the input to the optical device;

[0034] Fig.19 (a) includes Fig.18 (a) is a schematic top view of a target of a first periodic component and a second periodic component formed in a second layer above or below the first layer, the spatial period of the second periodic component being twice the spatial period of the first periodic component;

[0035] Fig.19 (b) Describe the Fig.19(a) The first order diffraction of the target falling outside the input to the optical device;

[0036] Fig. 20 (a) Yes Fig.19 Schematic top view of the target of (a), except that the spatial period of the second periodic component is three times the spatial period of the first periodic component and there is an overlay error between the first periodic component and the second periodic component resulting in asymmetric diffraction;

[0037] Fig. 20 (b) Describe the Fig. 20 (a) Asymmetric first-order diffraction of the target falling within the input to the optical device;

[0038] Fig.21 (a) Yes Fig. 20 (a) is a schematic top view of the target, except that there is a different overlay error between the first periodic component and the second periodic component;

[0039] Fig.21 (b) Describe the Fig.21 (a) Asymmetric first-order diffraction of the target, the asymmetry being different from Fig. 20 (b) Asymmetry in the first-order diffraction;

[0040] Fig. 22 is a graph depicting the variation of the first order signal (FOS) according to the separation deviation S1-S2 and the value for three different targets;

[0041] Fig.23 is a graph depicting the variation of the first order signal (FOS) according to the overlap offset (OV) and the separation deviation S1-S2;

[0042] Fig.24 and Fig.25 The derivative of the first-order signal (DFOS) (proportional to the sensitivity) and the first-order signal (FOS) are shown respectively according to the separation deviation S1-S2;

[0043] Fig.26 is a graph depicting the variation of the first order signal (RDS) as a function of the separation deviation S1-S2 and the value for two relatively offset target structures;

[0044] Fig. 27 is a graph depicting changes in the second order difference signal (SODS) according to the overlap offset (OV) and the separation deviation S1-S2. DETAILED DESCRIPTION

[0045] This specification discloses one or more embodiments incorporating features of the present invention. The disclosed embodiments are merely illustrative of the present invention. The scope of the present invention is not limited to the disclosed embodiments. The present invention is defined by the appended claims.

[0046] The described embodiments and references to "one embodiment", "an embodiment", "an example embodiment", etc. in this specification indicate that the described embodiments may include specific features, structures, or characteristics, but each embodiment may not necessarily include the specific features, structures, or characteristics. In addition, these phrases do not necessarily refer to the same embodiment. In addition, when specific features, structures, or characteristics are described in conjunction with an embodiment, it should be understood that, whether or not explicitly described, it is within the knowledge of a person of ordinary skill in the art to implement these features, structures, or characteristics in conjunction with other embodiments.

[0047] However, before describing these embodiments in more detail, it is instructive to present an exemplary environment in which embodiments of the invention may be implemented.

[0048] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus comprises an illumination system (illuminator) IL 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 pattern forming device (e.g. mask) MA and connected to a first positioning device PM configured to accurately position the pattern forming device according to certain parameters, a substrate table (e.g. wafer stage) WT configured to hold a substrate (e.g. a wafer coated with resist) 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) PS configured to project a pattern imparted to the radiation beam B by the pattern forming device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0049] 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.

[0050] The support structure supports the pattern forming device, i.e., carries the weight of the pattern forming device. The support structure holds the pattern forming device in a manner that depends on the orientation of the pattern forming device, the design of the lithographic equipment, and other conditions such as whether the pattern forming device is maintained 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 a frame or a table, for example, which can be fixed or movable as required. The support structure can ensure that the pattern forming device is located in a desired position (for example relative to a projection system). Any term "reticle" or "mask" used in the present invention can be considered to be synonymous with the more general term "pattern forming device".

[0051] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a pattern to a radiation beam in its cross-section so as to produce a pattern in a target portion of the 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 produced in the target portion, such as an integrated circuit.

[0052] 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.

[0053] 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, 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."

[0054] In this embodiment, for example, 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).

[0055] The lithographic apparatus may be of a type having two ("dual stage") or more substrate tables and, for example, two or more mask tables. In these "multi-stage" machines, the extra 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.

[0056] 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. Immersion techniques are known in the art for increasing the numerical aperture of the projection system. The term "immersion" as used herein does not mean that structures such as the substrate are necessarily immersed in the liquid, but only means that the liquid is located between the projection system and the substrate during exposure.

[0057] refer to 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 a part of the lithographic apparatus, and the radiation beam is transferred from the source SO to the illuminator IL with the help 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 and, if necessary, the beam delivery system BD may be referred to as a radiation system.

[0058] The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent (which are generally referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, 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.

[0059] The radiation beam B is incident on a patterning device (e.g. a mask MA) held on the support structure (e.g. a mask table MT) and is patterned by the patterning device. After traversing the 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 interferometry device, a linear encoder, a 2D encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example, 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 (which is not in the Figure 1The first positioning device PM (shown explicitly 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 acquisition of the mask library or during scanning). In general, movement of the mask table MT can be realized 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 realized 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 a short-stroke actuator only, or may be fixed. The mask MA and the 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 the spaces between multiple target portions (these are commonly known as scribe alignment marks). Similarly, in the case where more than one tube core is arranged on the mask MA, the mask alignment marks may be located between the tube cores.

[0060] The depicted device can be used in at least one of the following modes:

[0061] 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 to enable exposure of a different target portion C. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

[0062] 2. In step mode, the mask table MT and the 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 (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 movement determines the height of the target portion (in the scanning direction).

[0063] 3. In another mode, the mask table MT holding the programmable patterning device is held substantially stationary, 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 employed, 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 using a programmable patterning device, such as a programmable mirror array of the type mentioned above.

[0064] Combinations and / or variations on the above-described modes of use, or entirely different modes of use, may also be employed.

[0065] 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 may also include 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. The substrate handler or robot RO picks up the substrate from the input / output ports I / O1, I / O2, moves the substrate between different process equipment, 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 is itself controlled by a management control system SCS, which also controls the lithography equipment through the lithography control unit LACU. Therefore, different equipment can be operated to maximize production volume and processing efficiency.

[0066] In order for substrates exposed by the lithographic apparatus to be correctly and consistently exposed, it is necessary to inspect the exposed substrates in order to measure properties such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), etc. If errors are detected, then, for example, 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 remain to be exposed. Also, already exposed substrates can be stripped and reworked to improve yield or possibly discarded, thereby avoiding exposure of substrates 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 considered to be non-defective.

[0067] Inspection equipment (which may also be referred to as metrology equipment) is used to determine the properties of the substrate, and in particular to determine how the properties of different substrates or different layers of the same substrate vary from layer to layer. The inspection equipment may be integrated into the lithography equipment LA or the lithography unit LC, or may be a stand-alone device. In order to achieve the fastest measurement, it is necessary to measure the properties in the exposed resist layer immediately after the exposure. However, the latent image in the resist has a very low contrast, because there is only a very small refractive index difference between the part of the resist that has been exposed to the radiation and the part of the resist that has not been exposed to the radiation - and not all inspection equipment has sufficient sensitivity to perform useful measurements of the latent image. Therefore, the measurement can be performed 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 referred to as a semi-latent image. It is also possible to measure the developed resist image at the moment when the exposed or unexposed parts of the resist have been removed, or to measure the developed resist image after a pattern transfer step such as etching. The latter possibility limits the possibility of reworking defective substrates, but can still provide useful information.

[0068] Figure 3 is a schematic diagram of an optical device in the form of a scatterometer suitable for use with Figure 2The lithography element combination shown performs measurement. The device can be used to measure the critical dimensions of features formed by lithography, measure the overlap between layers, etc. Product features or special measurement targets are formed on substrate W. The device can be a stand-alone device, or incorporated into a lithography device LA at, for example, a measurement station, or incorporated into a lithography unit LC. The optical axis with several branches running through the device is represented by a dotted line O. In this device, the light emitted by the source 11 is directed to the substrate W via a beam splitter 15 by an optical system including lenses 12, 14 and an objective lens 16. These lenses are arranged in a double sequence of 4F arrangements. Different lens arrangements can be used, assuming that it still provides an image of the source on the substrate and at the same time allows access to the intermediate pupil plane for spatial frequency filtering. Therefore, by limiting the spatial intensity distribution in the plane that presents the spatial spectrum of the substrate plane (here referred to as the (conjugate) pupil plane), the angle range of the radiation incident on the substrate can be selected. In particular, this selection can be made by inserting an aperture plate 13 of suitable form between lenses 12 and 14 in the plane of the back-projected image of the objective lens pupil plane. For example, as shown, the aperture plate 13 can take different forms, two of which are marked as 13N and 13S, thereby allowing different illumination modes to be selected. The illumination system in the illustrated example forms an off-axis illumination mode. In a first illumination mode, the aperture plate 13N provides off-axis from a direction designated as "north" for the sake of description only. In a second illumination mode, the aperture plate 13S is used to provide similar illumination, but this similar illumination comes from the opposite direction marked as "south". Other illumination modes are possible by using different apertures. The remaining pupil planes are ideally dark, because any unnecessary light outside the desired illumination mode will interfere with the desired measurement signal.

[0069] At least the 0th order and one of the -1st and +1st orders of the target diffraction on the substrate W are collected by the objective lens 16 and directed back through the beam splitter 15. The second beam splitter 17 divides the diffraction beam into two measurement branches. In the first measurement branch, the optical system 18 forms a diffraction spectrum (pupil plane image) of the target on a first sensor 19 (e.g., a CCD or CMOS sensor) using the zeroth order diffraction beam and the first order diffraction beam. Each diffraction order hits a different point on the sensor, so that image processing can compare and distinguish several orders. The pupil plane image collected by the sensor 19 can be used to focus the measurement device and / or normalize the intensity measurement of the first order beam. The pupil plane image can be used for many measurement purposes such as reconstruction.

[0070] In the second measurement branch, the optical system 20, 22 forms an image of the target on the substrate W on a sensor 23 (e.g., a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is arranged in a plane conjugate to the pupil plane. The aperture stop 21 serves to block the zero-order diffraction beam so that the image of the target formed on the sensor 23 is formed only from the -1 or +1-order beam. The image detected by the sensor 23 is therefore called a "dark field" image. It should be noted that the term "image" is used here in a broad sense. Thus, if only one of the -1 order and the +1 order is present, no image of the grating lines will be formed.

[0071] The images acquired by the sensors 19 and 23 are output to an image processor and controller PU, the functionality of which will depend on the particular type of measurement being performed.

[0072] Examples of scatterometers and techniques can be found in patent applications US2006 / 066855A1, WO2009 / 078708, WO2009 / 106279, and US2011 / 0027704A, all of which are incorporated herein by reference in their entirety.

[0073] In the following, a method for measuring parameters of a device manufacturing process (particularly a lithography process) according to an embodiment is described. The method is particularly suitable for measuring parameters of a lithography process including multiple patterning (e.g., double patterning or quadruple patterning). Figures 4 to 9 An example of a double patterning process using spaced patterning is described. Embodiments of the invention are also applicable where other forms of multiple patterning (spaced or non-spaced) are used, and even in processes that do not involve multiple patterning.

[0074] Figure 4 A substrate 34 is depicted. A base layer 32 is formed on the substrate 34. A patterned layer is formed on the base layer 32 including a plurality of pre-patterned features 30 (eg, lines) forming a first pattern.

[0075] In subsequent steps, such as Figure 5 As depicted in , a membrane layer 35 is deposited onto the patterned layer.

[0076] In subsequent steps, such as Figure 6 , an etch is performed on the horizontal surfaces to remove material from the membrane layer 36. This leaves behind a layer 36 formed on the sidewalls of the pre-patterned features 30. The layer 36 may be referred to as a spacer.

[0077] In subsequent steps, such as Figure 7As depicted in , the pre-patterned features 30 are removed, leaving behind the layer (spacers) 36, which forms a pattern with a density twice that of the original pattern of the pre-patterned features 30 (this is because each of the pre-patterned features 30 has two sidewalls and each sidewall produces one of the layers (spacers) 36).

[0078] In subsequent steps, such as Figure 8 As depicted in , the layer (spacer) 36 is used as a mask to define the selective etching of the base layer.

[0079] In subsequent steps, such as Fig. 9 As depicted in FIG. 1 , the layer (spacer) 36 is removed, leaving a second pattern of features 38 formed by the remaining material of the base layer. The second pattern ( Fig. 9 ) includes up to a first pattern ( Figure 4 The features are twice as many as those shown in .

[0080] References Figures 4 to 9 The process described is sometimes referred to as self-aligned double patterning (SADP). The process can be repeated based on features of the second pattern instead of the features of the first pattern, thereby doubling the feature density again. This type of process is sometimes referred to as self-aligned quadruple patterning (SAQP). In principle, the process can be further repeated to produce a further increase in feature density.

[0081] See also Fig. 9 , the separation distance S1 is determined by the width of the pre-patterned features 30. The separation distance S2 is determined by the separation distance between adjacent pairs of pre-patterned features 30. The difference between S1 and S2 will cause an effective overlay error between odd features and even features. For non-zero S1-S2, the separation distance between adjacent features will therefore alternate. The alternating separation distance can be referred to as spacing variation. Fig.10 A portion of a structure with zero spacing variation (S1 = S2) is depicted. Fig.11 Depicted is a portion of a structure with non-zero spacing variation (S1#S2). Any difference between S1 and S2 needs to be monitored and controlled (eg, to ensure that the difference does not exceed a predetermined threshold).

[0082] Prior art techniques for measuring S1-S2 have various disadvantages.

[0083] Scanning electron microscopy (CD-SEM) has been used to measure S1-S2. However, scanning electron microscopy is relatively slow (typically requiring several seconds to make a measurement). CD-SEM makes measurements with high localization on the device, meaning that a large number of inspection points are required to check the overall target performance. In addition, it is difficult to distinguish S1 from S2.

[0084] Scatterometry techniques increase speed but can suffer from low sensitivity, especially for small S1-S2 values.

[0085] See below Figures 12 to 21 A method for measuring parameters of a device manufacturing process (eg, a photolithography process) according to an embodiment is described. Fig.12 , Fig.13 , Fig.16 , Fig.17 , Fig. 20 and Fig.21 An example target for use in the method is shown. The term "target" as used in the present invention should be broadly interpreted as referring to any structure that is used or can be used in a measurement process. The target may include a dedicated measurement target, or the target may form part of a structure that is provided partially or completely for other purposes. The target may, for example, be formed by a product feature. The method includes measuring the target 40 by illuminating a target 40 on a substrate W with measurement radiation and detecting the measurement radiation scattered by the target 40. Any of the disclosed methods may be implemented using appropriately configured measurement equipment. The measurement equipment may include a device as described above with reference to Figure 3 The optical device discussed. A device manufacturing system including a device manufacturing device and the measurement device may be provided. The device manufacturing system may include a lithography system, the lithography system including a lithography device and the measurement device. The device manufacturing device (e.g., a lithography device) performs a device manufacturing process (e.g., a lithography process) on a substrate. The measurement device measures parameters of the device manufacturing process (e.g., a lithography process). The device manufacturing device uses the parameters measured by the measurement device in a subsequent device manufacturing process (e.g., a lithography process). In the case where the parameters represent an error in the device manufacturing process (e.g., a lithography process), the device manufacturing device (e.g., a lithography device) may use the parameters to reduce the magnitude of the error.

[0086] The target 40 includes a target structure having a first periodic component 42 and a second periodic component 44. In various embodiments, the first periodic component and the second periodic component are formed at different times, formed using different photolithography processes, or formed at different times using different photolithography processes. In various embodiments, the first periodic component 42 is disposed in a first layer and the second periodic component 44 is disposed in a second layer, the second layer being above or below the first layer. Fig.12 , Fig.13 , Fig. 20 and Fig.21In such an embodiment as shown in the example, the structure provided with the first periodic component 42 may be referred to as a first layer target substructure. The structure provided with the second periodic component 44 may be referred to as a second layer target substructure. In other embodiments, the first periodic component 42 and the second periodic component 44 are provided in the same layer, or in multiple layers, and the first periodic component 42 and the second periodic component 44 overlap each other in a direction perpendicular to the plane of each layer in the multiple layers. Fig.16 and Fig.17 Examples of such objectives 40 are discussed.

[0087] Fig.12 and Fig.13 An embodiment is depicted, wherein the first periodic component 42 and the second periodic component 44 are arranged in different layers. In this embodiment, the second periodic component 44 is arranged on the upper side of the first periodic component 42. The upper side is defined as the side facing the incident measurement radiation. In other embodiments, the second periodic component 44 is arranged below the first periodic component 42, but is arranged in a manner such that the measurement radiation still interacts with both the first periodic component 42 and the second periodic component 44. The second periodic component 44 may be specifically arranged to assist in monitoring a device manufacturing (e.g., lithography) process. Alternatively, the second periodic component 44 may be arranged for other reasons, such as a layer forming part of a process chain in product manufacturing. In the latter case, the method according to the embodiment utilizes the presence of the second periodic component 44 arranged for other reasons to improve the measurement of the lithography process performed on the first periodic component 42 that is distinguished from the second periodic component 44.

[0088] In embodiments where the first periodic component 42 and the second periodic component are disposed in different layers relative to each other, the second periodic component 44 may be directly adjacent to the first periodic component 42, overlap with the first periodic component 42 (in a direction perpendicular to the plane of the second periodic component), or be separated from the first periodic component 42 by one or more intervening layers.

[0089] In one embodiment, the first periodic component 42 is formed by a device manufacturing (e.g., lithography) process to be monitored. The method measures parameters of such a process by measuring one or more properties of the first periodic component 42. The second periodic component 44 modifies the measurement radiation scattered from the combination of the first periodic component 42 and the second periodic component 44, so that information about the first periodic component 42 can be extracted more easily or with improved accuracy relative to the situation where the second periodic component 44 is not set and the measurement radiation is scattered only from the first periodic component. In one embodiment, this is achieved by arranging the second periodic component 44 so that the received radiation originating from the diffraction of the measurement radiation from the target structure includes at least one diffraction order that will not be received by the diffraction of the measurement radiation from the first periodic component 42 alone, and preferably will not be received by the diffraction of the measurement radiation from the second periodic component 44 alone. In a number of embodiments, this is achieved by arranging the spacing of the combination of the first periodic component 42 and the second periodic component 44 so that it is longer than the spacing of the first periodic component 42 alone, and preferably also longer than the spacing of the second periodic component 44 alone. Each spacing may represent a two-dimensional periodicity or a three-dimensional periodicity. Providing a spacing of the combination that is longer than the spacing of the first periodic component 42 alone (and / or the second periodic component 44 alone) means that the diffraction pattern from the target will be less scattered relative to the case where the second periodic component 44 is not provided. Providing a diffraction pattern that is less scattered makes it possible to more easily detect the high-order components of the diffraction pattern. It is easier to extract information about the one or more parameters of interest from the high-order components of the diffraction pattern than from the low-order components of the diffraction pattern, for example because there is a smaller influence from noise or unconcerned geometric factors. In one embodiment, the high-order components include first-order diffraction components. Advantageously, the first order diffraction component is invariant to geometric changes such as the spatial offset between the second periodic component 44 and the first periodic component 42, or line width changes in the pattern of the second periodic component 44. The zero order diffraction component will be more affected by these factors, thereby reducing the signal to noise ratio. Compared to the higher order diffraction components, the zero order diffraction component can also be less sensitive to the parameters of interest.

[0090] The invariance of the first-order diffraction component to the overlap offset (OV) (i.e., the offset between the second periodic component 44 and the first periodic component 42) is Fig.23 The graph shows that a relatively large change in the overlay offset (OV) has a negligible effect on how the first order diffraction component (first order signal FOS) varies according to S1-S2.

[0091] Figures 14 to 17 The figure shows the application of the method in the case of measuring pitch variations using a target having the first periodic components 42 and the second periodic components 44 located in the same layer. Figures 18 to 21 The figure shows the application of the method in the case of measuring the overlay error using a target having the first periodic components 42 and the second periodic components 44 located in different layers.

[0092] exist Fig.14 In the arrangement of (a), a target 40 is provided which comprises a grating having a pitch p. The pitch p is relatively small. The small pitch P means that the first-order diffracted beam generated by the incident measurement radiation is therefore relatively spread out, e.g. Fig.14 The first order diffracted beam is diffracted at too large an angle to enter the input of the optical device used to measure the scattered radiation (eg objective lens 16) and is therefore effectively lost.

[0093] like Fig.15 (a) and Fig.15 As shown in (b), the spacing variation is introduced into Fig.14 (a) will cause the grating pitch to increase to 2p. The increased pitch causes the first-order diffraction to spread less, but the angle with respect to the first-order radiation is still too large to enter the objective lens 16 (e.g. Fig.15 (as shown in (b)).

[0094] Fig.16 (a) depicts a target 40 having a first periodic component 42 and a second periodic component 44. The first periodic component and Fig.14 The grating of the target 40 of (a) is the same. The pitch of the first periodic component is therefore p. The second periodic component 44 comprises a periodic region in which a portion of the grating is removed. The periodic region is composed of Fig.16 The dashed box in (a) depicts the pitch of the second periodic component 44 (defined by the separation of the periodic regions) is 3p. The pitch 46 of the combination of the first periodic component 42 and the second periodic component 44 is also equal to 3p. Fig.14 and Fig.15 The increased spacing of the arrangement causes the first-order diffraction to spread out even less, but the angle with respect to the first-order radiation is still too large to enter the objective lens 16 (e.g. Fig.16 (as shown in (b)).

[0095] Fig.17 (a) illustrates a case where there is a pitch variation in the grating forming the first periodic component 42. Fig.16(a) The pitch variation increases the pitch of the first periodic component 42 to 2p (with Fig.15 ). The pitch variation also causes the pitch 46 of the combination of the first periodic component 42 and the second periodic component 44 to increase (from 3p to 6p). Thus, this embodiment is an example of a class of embodiments in which the pitch of the combination of the first periodic component and the second periodic component is increased in the presence of a pitch variation (which can be indicated by a deviation in the separation distance between features that are nominally spaced apart from each other by a common separation distance, as described above with reference to Figures 10 to 13 The first order diffraction beam is longer when there is no pitch variation (i.e., deviation in separation distance) when the first order diffraction beam is discussed. The longer pitch eventually causes the diffraction angle of the first diffraction beam to be a sufficiently low value so that the first diffraction beam enters the objective lens 16. The target 40 is modified to incorporate the second periodic component 44, thereby making it possible to collect the first order diffraction beam and make the first order diffraction beam useful for measuring parameters of the device manufacturing process (e.g., the size of the pitch variation).

[0096] exist Fig.18 In the arrangement of (a), a target 40 is provided which comprises a grating having a pitch p. The grating provides a first periodic component 42. Fig.14 (a), the pitch p is relatively small and the first-order diffraction beam from the first periodic component 42 does not enter the objective lens 16 ( Fig.18 (b)).

[0097] Fig.19 (b) and Fig.19 (b) shows Fig.18 The target 40 is a target 40 in which a second periodic component 44 is added. The second periodic component 44 is provided by a grating having a period of 2p. The first periodic component 42 and the second periodic component 44 are arranged in different layers relative to each other. The pitch of the combination of the first periodic component 42 and the second periodic component 44 is also equal to 2p. Fig.18 The increased spacing of the arrangement causes the first-order diffraction to spread out less, but the angle with respect to the first-order radiation is still too large to enter the objective lens 16 (e.g. Fig.19 (as shown in (b)).

[0098] Fig. 20 (a) depicting a target 40, wherein the first periodic component 42 has a Fig.19 The first periodic component 42 has the same pitch p as the first periodic component 42, but the second periodic component 44 has a pitch p greater than Fig.19 The combined pitch 46 (equal to 6p) is large enough to cause the first order diffraction to enter the objective lens 16 (such as Fig. 20(b) depicted). It is therefore possible to collect the first order diffraction, and use the first order diffraction to facilitate the measurement of parameters (such as overlay error) of the device manufacturing process. In the example shown, the first order diffraction is used to measure a parameter representing the degree of asymmetry in the target structure. In this example, the asymmetry is due to the overlay error between the first periodic component 42 in one layer and the second periodic component 44 in a different layer. The asymmetry results in a difference between opposite or different diffraction orders. In this example, the difference is between the -1 diffraction order and the +1 diffraction order.

[0099] Fig.21 (a) Description Fig. 20 The objective 40 is the same as that of the embodiment of the present invention, except that there are different overlay errors between the first periodic component 42 and the second periodic component 44. Different overlay errors result in different asymmetries between opposite or different diffraction orders (as can be seen by comparing Fig. 20 (b) with Fig.21 (b) able to see).

[0100] In one embodiment, the first periodic component 42 is formed by multiple or multiple patterning. In one embodiment, the first periodic component 42 is formed by using an interval patterning process (such as the above reference Figures 4 to 9 In this embodiment, the first periodic feature 42 is formed by one or more iterations of forming a layer 36 on the sidewalls of each feature 30 in a first pattern of a plurality of features, and in a subsequent step, removing each feature 30 of the first pattern of the plurality of features to form a second pattern having twice as many features 38 as the features in the first pattern. In other embodiments, the first periodic feature 42 is formed using a non-spaced multiple patterning process such as LELE.

[0101] In one embodiment, the first periodic component 42 is formed by a photolithography process that is configured to form three or more features that are nominally spaced apart from each other by a common separation distance (S1=S2). Thus, in the absence of any errors in the photolithography process, the separation between each pair of adjacent features will be the same. In practice, one or more errors in the photolithography process will cause a deviation in the separation distance (making S1#S2). The method includes measuring the target 40 to measure the deviation in the separation distance caused by one or more errors in the photolithography process (including, for example, errors in the etching process).

[0102] In one embodiment, the deviation of the separation distance includes a repeating sequence of different separation distances. For example, a spacer patterning process will produce this type of deviation of the separation distance. In the case of double patterning, the repeating sequence of different separation distances includes an alternating sequence of a first separation distance S1 and a second separation distance S2. This is called walking. Fig.12 A target 40 comprising a first periodic feature 42 having zero pitch variation (S1 = S2) formed by double patterning is depicted. Fig.13 A target 40 is depicted that includes first periodic features 42 having non-zero pitch variations (S1#S2) formed by double patterning. Each separation distance S1 may be referred to as a first separation distance S1. Each separation distance S2 may be referred to as a second separation distance.

[0103] In one embodiment, the second periodic component 44 comprises a periodic structure having a pitch p, the pitch p being selected such that the pitch of the combination of the first periodic component 42 and the second periodic component 44 is longer when there is a deviation in the separation distance than when there is no deviation in the separation distance. The change in the pitch caused by the deviation allows the deviation to be detected with high sensitivity. For example, the change in the pitch can be used to detect new higher-order diffraction components (i.e., higher-order diffraction components that were too scattered to be detected by the optical system before the change in the pitch) when a change in the pitch occurs. Fig.12 , Fig.13 , Fig.16 and Fig.17 Describe an embodiment of this type. Fig.12 (zero pitch variation), the combined pitch 46 is equal to twice the pitch p of the second periodic component 44. Fig.13 (non-zero pitch variation), the combined pitch 46 is doubled to four times the pitch p of the second periodic component 44. Fig.16 (zero pitch variation), the combined pitch 46 is equal to the pitch of the second periodic component 44. Fig.17 In the embodiment, the combined pitch 46 is equal to twice the pitch of the second periodic components 44 .

[0104] Fig.12 and Fig.13 The second periodic component 44 of is an example of a class of second periodic components 44, in which a periodic structure having a pitch p is provided, the pitch p being given by the following expression: p = (n + l / 2) d, where d = (S1 + S2) / 2, and n is a positive integer. Arranging the pitch p to satisfy the above expression ensures that the pitch 46 of the combination of the first periodic component 42 and the second periodic component 44 is longer when there is a deviation in the separation distance than when there is no deviation in the separation distance. Fig.12 and Fig.13In the specific example of , n=2.

[0105] Fig. 22 , which is a measurement of the first order diffraction component scattered from the target 40. Point 50 corresponds to a target 40 including a first periodic component 42 with zero spacing variation (see inset). Point 51 corresponds to a target 40 including a first periodic component 42 with intermediate or medium non-zero spacing variation (see inset). Point 52 corresponds to a target 40 including a first periodic component 42 with relatively high non-zero spacing variation (see inset).

[0106] Fig. 22 It is shown that relatively high sensitivity is achieved for larger values ​​of S1-S2 (indicated by the relatively high steepness in the curve). However, for smaller values ​​of S1-S2, the curve becomes flat, indicating lower sensitivity. In one embodiment, sensitivity is improved by using two relatively biased target structures to produce a differential signal. The bias is selected so that the average sensitivity for small differences in S1-S2 caused by errors in the lithography process is higher for the two target structures than for a single target structure without bias. In one embodiment, a method is provided, the method comprising two steps.

[0107] The first step comprises measuring a first target structure comprising a first periodic feature 42 formed by a process configured to form three or more features nominally spaced apart from each other by a common separation distance. The process is biased in a first orientation so as to nominally form an alternating sequence of a first separation distance S1 and a second separation distance S2, wherein S1-S2=Δd. Thus, the lithographic process, when perfectly performed, will form a pattern having a pitch variation that is exactly equal to the positive bias Δd. Deviations in the lithographic process will cause the pitch variation to be equal to the bias plus an error associated with the pitch variation introduced by the lithographic process.

[0108] The second step comprises measuring a second target structure comprising a first periodic feature 42 formed by the same process as that used to form the first periodic feature 42 of the first target structure, except that the process is biased in a second orientation opposite to the first orientation. The process is thus configured to nominally form an alternating sequence of a first separation distance S1 and a second separation distance S2, wherein S1-S2=-Δd. Thus, the lithography process, when perfectly performed, will form a pattern with a pitch variation that is exactly equal to the negative bias Δd. Deviations in the lithography process will cause the pitch variation to be equal to the negative bias plus an error associated with the pitch variation introduced by the lithography process.

[0109] The derivative of the first order signal (DFOS) that varies according to S1-S2 with respect to the change in S1-S2 (which is proportional to the sensitivity) is Fig.24 The first order signal (FOS) varies with S1-S2. Fig.25 The graph shows that for a bias Δd in the first period 54, the sensitivity will increase for small values ​​of pitch variation caused by errors in the lithography process (ie, S1-S2 before biasing).

[0110] Forming a differential signal from the outputs of the first and second steps cancels out the deliberately applied offsets +Δd and -Δd and allows the errors associated with pitch variations introduced by the lithographic process to be obtained with high sensitivity. In a typical embodiment, the difference between the signals from each of the two relatively offset targets will be a linear function of the average of S1-S2 (before offsetting), but it is also possible to arrange for the variation to be non-linear. Fig.26 Depicts example points for measurements performed on two relatively offset target structures with small pitch variation errors using a lithography process. The two signals are located on relatively steep portions of the FOS versus S1-S2 curve, and are therefore relatively sensitive to any changes in S1-S2 caused by one or more errors in the lithography process. The difference 56 between the two signals is proportional to S1-S2 caused by the lithography process (in the absence of bias).

[0111] In an embodiment, the method is adapted to allow simultaneous measurement of 1) an overlap offset between the second periodic component 44 and the first periodic component 42, and 2) a deviation in separation distances between nominally equally spaced features in the target structure (e.g., S1-S2). In an embodiment, the method comprises illuminating the target 40 with measurement radiation in a first frequency band centered at a first wavelength and illuminating the target with measurement radiation in a second frequency band centered at a second wavelength. The illuminating with measurement radiation in the first frequency band and the second frequency band may be performed simultaneously or at different times. In an embodiment, the first wavelength is in the range of 650 nanometers to 750 nanometers, optionally about 700 nanometers, and the second wavelength is in the range of 400 nanometers to 450 nanometers, optionally about 425 nanometers. In this method, the detected measurement radiation of the second frequency band generated by diffraction from the target structure is on average from higher orders of diffraction than the detected measurement radiation of the first frequency band generated by diffraction from the target structure.

[0112] In an embodiment, the detected measurement radiation of a first frequency band resulting from diffraction from the target structure above the zeroth order is mainly from the first order diffraction. The detected measurement radiation of a second frequency band resulting from diffraction from the target structure above the zeroth order includes radiation from the second order diffraction.

[0113] The inventors have discovered that the first order diffracted radiation is sensitive to deviations in separation distance (e.g., S1-S2) between nominally equally spaced features (e.g., pitch variations) and is substantially independent of changes in the overlay offset (OV) between the second periodic feature 44 and the first periodic feature 42. Example behavior of this type is shown in Fig.23 It has been further discovered that the second order diffracted radiation is sensitive to both deviations in separation distances (e.g., S1-S2) between nominally equally spaced features (e.g., pitch variations) and changes in the overlap offset (OV) between the second periodic component 44 and the first periodic component 42. Fig. 27 An example behavior of this type is depicted in FIG. 1 . The signal (vertical axis) does not vary substantially with the overlap offset (OV) for any fixed value of S1-S2. Fig.23 In contrast, Fig. 27 It is shown that for most fixed values ​​of S1-S2, the second order difference signal (SODS) (which corresponds to a differential measurement using second order diffracted radiation scattered from a relatively offset target structure) does vary substantially with the overlap offset (OV). For most fixed values ​​of the overlap offset (OV), the second order signal (SODS) also varies significantly with S1-S2.

[0114] According to the above, in an embodiment where the first periodic component 42 is formed by a process configured to form three or more features nominally spaced apart from each other by a common separation distance, the detected measurement radiation of the first frequency band is used to measure the deviation of the separation distance (e.g., S1-S2) caused by one or more errors in the process. The detected measurement radiation of the second frequency band is used to measure a combination of the following items: 1) the deviation of the separation distance (e.g., S1-S2) caused by one or more errors in the process; and 2) the overlap offset between the first periodic component 42 and the second periodic component 44 caused by one or more errors in the process. The detected measurement radiation of the second frequency band can then be used to obtain the overlap offset (OV) between the first periodic component 42 and the second periodic component 44, and the detected measurement radiation of the first frequency band is used to measure the deviation of the separation distance (e.g., S1-S2). The method thus allows both the deviation of the separation distance (e.g., S1-S2) and the overlap offset (OV) to be independently obtained from the same target 40 (or a group of targets, such as a pair of targets 40) in an accurate and efficient manner. As discussed above, one or more pairs of relatively offset target structures can be used to improve sensitivity.

[0115] In one embodiment, the method comprises measuring a first target structure comprising a first periodic component formed by a process configured to form three or more features nominally spaced apart from each other by a common separation distance. The process is biased in a first orientation so as to nominally form an alternating sequence of a first separation distance S1 and a second separation distance S2, wherein S1-S2=Δd. Δd is selected so that the sensitivity of a measurement of an overlay error between the first periodic component 42 and the second periodic component 44 using the detected measurement radiation of the second frequency band is greater than when S1-S2=0.

[0116] In one embodiment, the method further comprises measuring a second target structure comprising a first periodic component 42 formed by the same process as the process used to form the first periodic component 42 of the first target structure, except that the process is biased in a second orientation opposite to the first orientation so as to nominally form an alternating sequence of a first separation distance S1 and a second separation distance S2, wherein S1-S2=-Δd. In this way, a differential signal can be obtained in which the bias Δd is canceled. Fig. 27 The variation of this signal (SODS) with respect to the overlap offset and S1-S2 is depicted in FIG.

[0117] Fig. 27Depicts how the sensitivity of the overlay offset varies as a function of S1-S2 (as indicated by the change in the steepness of the curve in a direction parallel to the overlay offset (OV) axis). By selecting a bias Δd corresponding to the steep portion of the curve in a direction parallel to the overlay offset (OV) axis, it is possible to achieve high sensitivity in the measurement of the overlay offset (OV).

[0118] In an embodiment, the method comprises measuring or estimating a measured sensitivity of an overlay error between the first periodic component 42 and the second periodic component 44 for a plurality of different values ​​of Δd. In a subsequent step, the overlay error is measured using a target structure having a value of Δd selected based on the measured or estimated sensitivity (e.g., in order to achieve a relatively high sensitivity).

[0119] In one embodiment, the method includes: for a plurality of different values ​​of Δd: 1) measuring or estimating the sensitivity of a measurement of an overlay error between the first periodic component 42 and the second periodic component 44; and 2) measuring or estimating the sensitivity of a measurement of a deviation (e.g., S1-S2) of the separation distance. The method of this embodiment also includes measuring the overlay offset and the deviation of the separation distance using a target structure having a value of Δd selected based on the measured or estimated sensitivities in steps (1) and (2) (e.g., to achieve a desired balance of sensitivity for both the measurement of the overlay offset and the measurement of the deviation of the separation distance).

[0120] The following items may be used to further describe the embodiments:

[0121] 1. A method for measuring parameters of a device manufacturing process, the method comprising:

[0122] The target is measured by illuminating the target on the substrate with measurement radiation and using an optical device to detect the measurement radiation scattered by the target, wherein:

[0123] The target comprises a target structure having a first periodic component and a second periodic component; and

[0124] The optical device receives radiation resulting from diffraction of the measurement radiation from the target structure, the received radiation comprising at least one diffraction order which would not be received from diffraction of the measurement radiation from the first periodic component alone and would not be received from diffraction of the measurement radiation from the second periodic component alone.

[0125] 2. The method according to item 1, wherein a pitch of a combination of the first periodic component and the second periodic component is longer than a pitch of the first periodic component alone, and longer than a pitch of the second periodic component alone.

[0126] 3. The method according to item 1 or 2, wherein the first periodic component and the second periodic component are arranged in the same layer, or are arranged in multiple layers, and the first periodic component and the second periodic component overlap each other in a direction perpendicular to the plane of each layer in the multiple layers.

[0127] 4. The method according to item 3, wherein the first periodic component comprises a grating and the second periodic component comprises a periodic region in which a portion of the grating is removed.

[0128] 5. The method according to item 1 or 2, wherein the first periodic component is arranged in a first layer and the second periodic component is arranged in a second layer, the second layer being above or below the first layer.

[0129] 6. The method according to any preceding item, wherein the first periodic feature and the second periodic feature are formed at different times, formed using different photolithography processes, or formed at different times using different photolithography processes.

[0130] 7. A method according to any preceding item, wherein the radiation received by the optical device is used to measure a parameter representing the degree of asymmetry in the target structure, the asymmetry causing differences between opposite or different diffraction orders in the measurement radiation diffracted from the target structure.

[0131] 8. A method according to any preceding item, wherein:

[0132] The first periodic component is formed by a process configured to form three or more features that are nominally spaced apart from each other by a common separation distance; and

[0133] The method includes measuring the target structure to obtain a deviation in the separation distance caused by one or more errors in the process.

[0134] 9. The method according to item 8, wherein the spacing of the combination of the first periodic component and the second periodic component is longer when there is a deviation in the separation distance than when there is no deviation in the separation distance.

[0135] 10. A method as described in item 9, wherein the measurement of the target causes predetermined higher-order diffraction components to be detected when the spacing of the combination is longer due to the presence of a deviation in the separation distance, compared to when the spacing of the combination is not longer due to the absence of the deviation in the separation distance.

[0136] 11. A method according to item 10, wherein the deviation of the separation distance comprises a repeated sequence of different separation distances.

[0137] 12. The method according to item 11, wherein the repeating sequence of different separation distances comprises an alternating sequence of a first separation distance S1 and a second separation distance S2.

[0138] 13. A method according to item 12, wherein the second periodic component has a pitch p, which is given by the following expression: p = (n + l / 2)d, where d = (S1 + S2) / 2, and n is an integer.

[0139] 14. A method according to any preceding clause, wherein:

[0140] The target includes a first target structure in the target structure and a second target structure in the target structure;

[0141] The first of the target structures comprises a first periodic component formed by a process configured to form three or more features nominally spaced apart from each other by a common separation distance, wherein the process is biased in a first orientation to nominally form an alternating sequence of a first separation distance S1 and a second separation distance S2, wherein S1-S2=Δd; and

[0142] The second one of the target structures comprises a first periodic component formed by the same process as the process used to form the first periodic component of the first one of the target structures, except that the process is biased in a second orientation opposite to the first orientation so as to nominally form an alternating sequence of a first separation distance S1 and a second separation distance S2, where S1-S2=-Δd.

[0143] 15. The method according to any preceding item, wherein the first periodic feature is formed by multiple patterning.

[0144] 16. A method according to any preceding clause, wherein:

[0145] illuminating the target with measurement radiation comprises illuminating the target with measurement radiation in a first frequency band centered at a first wavelength and illuminating the target with measurement radiation in a second frequency band centered at a second wavelength; and

[0146] The detected measurement radiation of the second frequency band resulting from diffraction from the target structure comes on average from higher orders of diffraction than the detected measurement radiation of the first frequency band resulting from diffraction from the target structure.

[0147] 17. The method according to item 16, wherein:

[0148] the detected measurement radiation of the first frequency band resulting from diffraction above the zeroth order from the target structure is mainly from the first order diffraction; and

[0149] The detected measurement radiation of the second frequency band resulting from diffraction above the zeroth order from the target structure comprises radiation from second order diffraction.

[0150] 18. The method according to item 16 or 17, wherein

[0151] The first periodic component is formed by a process configured to form three or more features that are nominally spaced apart from each other by a common separation distance;

[0152] The detected measurement radiation of the first frequency band is used to measure a deviation of the separation distance caused by one or more errors in the process; and

[0153] The detected measurement radiation of the second frequency band is used to measure a combination of: 1) the deviation in the separation distance caused by one or more errors in the process; and 2) the overlap offset between the first periodic component and the second periodic component caused by one or more errors in the process.

[0154] 19. The method according to item 18, comprising using the detected measurement radiation of the second frequency band to obtain the overlap offset between the first periodic component and the second periodic component, and using the detected measurement radiation of the first frequency band to measure the deviation of the separation distance.

[0155] 20. The method according to item 18 or 19, wherein the method comprises:

[0156] measuring a first one of the target structures comprising a first periodic component formed by a process configured to form three or more features nominally spaced apart from each other by a common separation distance, wherein the process is biased in a first orientation to nominally form an alternating sequence of a first separation distance S1 and a second separation distance S2, wherein S1-S2=Δd; and

[0157] Δd is selected such that the sensitivity of the measurement of the overlay error between the first periodic component and the second periodic component using the detected measuring radiation of the second frequency band is greater when S1 - S2 =0.

[0158] 21. The method according to item 20, further comprising:

[0159] A second target structure in the target structure is measured, wherein the first periodic component is formed by a process identical to the process used to form the first periodic component of the first target structure in the target structure, except that the process is biased in a second orientation opposite to the first orientation so as to nominally form an alternating sequence of first separation distances S1 and second separation distances S2, wherein S1-S2=-Δd.

[0160] 22. The method according to item 20 or 21, comprising:

[0161] measuring or estimating the sensitivity of the measurement of the overlay error between the first periodic structure and the second periodic structure for a plurality of different values ​​of Ad; and

[0162] The overlay error is measured using a target structure having a value of Δd selected based on measured or estimated sensitivity.

[0163] 23. The method according to item 20 or 21, comprising:

[0164] for a plurality of different values ​​of Δd: 1) the sensitivity of the measurement to measure or estimate the overlay error between the first periodic component and the second periodic component; and 2) the sensitivity of the measurement to measure or estimate the deviation of the separation distance; and

[0165] The overlay offset and the deviation in the separation distance are measured using a target structure having a value of Ad selected based on the sensitivities measured or estimated in steps (1) and (2).

[0166] 24. A measurement device configured to perform a method according to any preceding item.

[0167] 25. A substrate comprising a target for use in measuring a parameter of a device manufacturing process, the measurement being performed by illuminating the target with measurement radiation and detecting measurement radiation scattered by the target, wherein:

[0168] The target includes a target structure having a first periodic component and a second periodic component;

[0169] The first periodic component is disposed in a first layer and the second periodic component is disposed in a second layer, the second layer being above or below the first layer; and

[0170] The second periodic component is configured such that a pitch of a combination of the first periodic component and the second periodic component is longer than a pitch of the first periodic component alone and longer than a pitch of the second periodic component alone.

[0171] 26. A target for use in measuring device manufacturing in a process, wherein:

[0172] The target includes a target structure having a first periodic component and a second periodic component;

[0173] The first periodic component is disposed in a first layer and the second periodic component is disposed in a second layer, the second layer being above or below the first layer; and

[0174] The second periodic component is configured such that a pitch of a combination of the first periodic component and the second periodic component is longer than a pitch of the first periodic component alone and longer than a pitch of the second periodic component alone.

[0175] 27. A measurement device for measuring parameters of a device manufacturing process, the measurement device comprising:

[0176] a substrate, including a target; and

[0177] Optical device for measuring a target by illuminating the target with measuring radiation and detecting the measuring radiation scattered by the target, wherein:

[0178] The target comprises a target structure having a first periodic component and a second periodic component; and

[0179] The optical device is configured to receive radiation generated by diffraction of the measurement radiation from the target structure, the received radiation including at least one diffraction order that would not be received from diffraction of the measurement radiation from the first periodic component alone and would not be received from diffraction of the measurement radiation from the second periodic component alone.

[0180] 28. A device manufacturing system, comprising:

[0181] a device manufacturing apparatus configured to perform a device manufacturing process on a substrate; and

[0182] The metrology apparatus according to item 27, configured to measure parameters of the device manufacturing process, wherein:

[0183] The device manufacturing equipment is configured to use the parameters measured by the metrology equipment in a subsequent device manufacturing process.

[0184] 29. A device manufacturing method comprising:

[0185] performing a device manufacturing process on the substrate;

[0186] Using the method according to any one of items 1 to 23 to measure a parameter of the device manufacturing process; and

[0187] The measured parameters are used to modify the execution of subsequent device fabrication processes.

[0188] Although specific reference may be made herein to the use of lithographic apparatus in the manufacture of integrated circuits (ICs), it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guide and inspection 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.

[0189] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated 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 topology in a patterning device defines the pattern produced on a substrate. The topology of the patterning device may be imprinted into a layer of resist provided to the substrate, the resist being cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist, leaving the pattern behind after the resist has cured.

[0190] The terms "radiation" and "beam" as used herein include all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength equal to or approximately 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), soft X-rays, and particle beams such as ion beams or electron beams.

[0191] 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.

[0192] 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 overall 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 herein is for illustrative purposes rather than restrictive purposes, so that the terms or wording of this specification will be interpreted by those skilled in the art based on teaching and guidance.

[0193] 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 measuring parameters of a device manufacturing process, comprising: obtaining a measurement of a target on a substrate, the measurement being derived by illuminating the target with measurement radiation and using an optical device to detect the measurement radiation scattered by the target, wherein the target comprises a target structure having a first periodic component and a second periodic component, and the optical device is configured to receive radiation resulting from diffraction of the measurement radiation from the target structure, the received radiation comprising at least one diffraction order that would not be received from diffraction of the measurement radiation from the first periodic component alone and would not be received from diffraction of the measurement radiation from the second periodic component alone; as well as Parameters of a device fabrication process for processing the substrate are determined based on the measurement results. 2 . The method of claim 1 , wherein a pitch of a combination of the first periodic component and the second periodic component is longer than a pitch of the first periodic component alone and longer than a pitch of the second periodic component alone.

3. A method according to claim 1, wherein the parameter is indicative of a degree of asymmetry in the target structure, the asymmetry causing a difference between opposite or different diffraction orders in the measurement radiation diffracted from the target structure.

4. The method of claim 1 , wherein the first periodic component is formed by a process configured to form three or more features that are nominally spaced apart from each other by a common separation distance; and the determining comprises determining a deviation in one or more of the separation distances caused by one or more errors in the process. 5 . The method according to claim 1 , wherein the first periodic component and the second periodic component are disposed in the same layer or in a plurality of layers which overlap each other in a direction perpendicular to a plane of each of the plurality of layers.

6. A measurement device for measuring parameters of a device manufacturing process, the measurement device comprising: Optical device for measuring a target by illuminating the target with measuring radiation and detecting the measuring radiation scattered by the target, wherein: The target comprises a target structure having a first periodic component and a second periodic component; and The optical device is configured to receive radiation generated by diffraction of the measurement radiation from the target structure, the received radiation including at least one diffraction order that would not be received from diffraction of the measurement radiation from the first periodic component alone and would not be received from diffraction of the measurement radiation from the second periodic component alone.

7. A measuring device, configured to at least: obtaining a measurement of a target on a substrate, the measurement being derived by illuminating the target with measurement radiation and using an optical device to detect the measurement radiation scattered by the target, wherein the target comprises a target structure having a first periodic component and a second periodic component, and the optical device is configured to receive radiation resulting from diffraction of the measurement radiation from the target structure, the received radiation comprising at least one diffraction order that would not be received from diffraction of the measurement radiation from the first periodic component alone and would not be received from diffraction of the measurement radiation from the second periodic component alone; and Parameters of a device fabrication process for processing the substrate are determined based on the measurement results. 8 . The metrology apparatus according to claim 7 , wherein a pitch of a combination of the first periodic component and the second periodic component is longer than a pitch of the first periodic component alone and longer than a pitch of the second periodic component alone.

9. The metrology apparatus of claim 7, wherein the parameter is indicative of a degree of asymmetry in the target structure, the asymmetry causing differences between opposite or different diffraction orders in the measurement radiation diffracted from the target structure.

10. The metrology apparatus of claim 7, wherein the first periodic component is formed by a process configured to form three or more features nominally spaced apart from each other by a common separation distance; and the determining comprises determining a deviation in one or more of the separation distances caused by one or more errors in the process. 11 . The measurement apparatus according to claim 7 , wherein the first periodic component and the second periodic component are disposed in the same layer or in a plurality of layers that overlap each other in a direction perpendicular to a plane of each of the plurality of layers.

12. A method for measuring parameters of a device manufacturing process, the method comprising: The target is measured by illuminating the target on the substrate with measurement radiation and using an optical device to detect the measurement radiation scattered by the target, wherein: The target comprises a target structure having a first periodic component and a second periodic component; and the optical device receiving radiation resulting from diffraction of the measurement radiation from the target structure, the received radiation comprising at least one diffraction order which would not be received from diffraction of the measurement radiation from the first periodic component alone and would not be received from diffraction of the measurement radiation from the second periodic component alone; illuminating the target with measurement radiation comprises illuminating the target with measurement radiation in a first frequency band centered at a first wavelength and illuminating the target with measurement radiation in a second frequency band centered at a second wavelength; and The detected measurement radiation of the second frequency band resulting from diffraction from the target structure comes on average from higher orders of diffraction than the detected measurement radiation of the first frequency band resulting from diffraction from the target structure.

13. The method according to claim 12, wherein the detected measurement radiation of the first frequency band resulting from diffraction above the zeroth order from the target structure is mainly from the first order diffraction; and The detected measurement radiation of the second frequency band resulting from diffraction above the zeroth order from the target structure comprises radiation from second order diffraction.

14. The method according to claim 12 or 13, wherein The first periodic component is formed by a process configured to form three or more features that are nominally spaced apart from each other by a common separation distance; The detected measurement radiation of the first frequency band is used to measure a deviation of the separation distance caused by one or more errors in the process; and The detected measurement radiation of the second frequency band is used to measure a combination of: 1) the deviation in the separation distance caused by one or more errors in the process; and 2) the overlap offset between the first periodic component and the second periodic component caused by one or more errors in the process.

15. The method of claim 14, comprising using the detected measurement radiation of the second frequency band to obtain the overlap offset between the first periodic component and the second periodic component, and using the detected measurement radiation of the first frequency band to measure the deviation of the separation distance.

16. The method according to claim 14 or 15, wherein the method comprises: measuring a first one of the target structures comprising a first periodic component formed by a process configured to form three or more features nominally spaced apart from each other by a common separation distance, wherein the process is biased in a first orientation to nominally form an alternating sequence of a first separation distance S1 and a second separation distance S2, wherein S1-S2=Δd; and Δd is selected such that the sensitivity of the measurement of the overlay error between the first periodic component and the second periodic component using the detected measuring radiation of the second frequency band is greater when S1 - S2 =0.

17. The method according to claim 16, further comprising: A second target structure in the target structure is measured, wherein the first periodic component is formed by a process identical to the process used to form the first periodic component of the first target structure in the target structure, except that the process is biased in a second orientation opposite to the first orientation so as to nominally form an alternating sequence of first separation distances S1 and second separation distances S2, wherein S1-S2=-Δd.

18. The method according to claim 16 or 17, comprising: measuring or estimating the sensitivity of the measurement of the overlay error between the first periodic structure and the second periodic structure for a plurality of different values ​​of Δd; and The overlay error is measured using a target structure having a value of Δd selected based on measured or estimated sensitivity.

19. The method according to claim 16 or 17, comprising: For a plurality of different values ​​of Δd: 1) measuring or estimating the sensitivity of the measurement of the overlay error between the first periodic component and the second periodic component; and 2) the sensitivity of the measurement for measuring or estimating the deviation of said separation distance; and The overlay offset and the deviation in the separation distance are measured using a target structure having a value of Ad selected based on the sensitivities measured or estimated in steps (1) and (2).

Images