JP7000454B2 - Metrology parameter determination and metrology recipe selection - Google Patents

Description

Cross-reference of related applications
[0001] This application claims the priority of US Patent Application No. 62 / 501,047 filed May 3, 2017 and European Patent Application No. 18152479.4 filed January 19, 2018. , All of these patent documents are incorporated herein by reference.

[0002] The present disclosure relates to, for example, methods and devices for inspection (eg, metrology) that can be used to manufacture devices by lithographic techniques, and methods of manufacturing devices using lithographic techniques.

[0003] A lithographic device is a machine that adds a desired pattern to a substrate, usually to a target portion of the substrate. Lithographic devices can be used, for example, in the manufacture of integrated circuits (ICs). In doing so, a patterning device, also referred to as a mask or reticle, can be used as an alternative to generate circuit patterns formed in the individual layers of the IC. This pattern can be transferred to a target portion (eg, including a portion of one or more dies) of a substrate (eg, a silicon wafer). The transfer of the pattern is usually by imaging on a radiation sensitive material (resist) layer provided on the substrate. Generally, a single substrate contains a network of continuously patterned, adjacent target portions.

[0004] The process of creating a device or other structure, including patterning (ie, patterning (such as lithography exposure or imprinting)), usually comprising one or more related processing steps such as developing or etching a resist. An important aspect to enable) is to develop the process itself, set it up for monitoring and control, and then actually monitor and control the process itself. Be done. Patterning Device Assuming the principle configuration of the patterning process such as pattern, resist type, post-lithographic process steps (eg development and etching), one or more devices are set up in the patterning process for transferring the pattern onto the substrate. It is desirable to develop a metrology target to monitor the process, set up the metrology process to measure the metrology target, and then carry out the process of monitoring and / or controlling the process based on the measured amount.

[0005] Therefore, in the patterning process, the critical dimensions of the structure (CD), overlay errors between continuous layers formed in or on the substrate (ie, undesired and unintended continuous layer misalignment), etc. It is desirable to determine the parameters of one or more objects (eg, to measure or to simulate using one or more models that model one or more aspects of the patterning process).

[0006] For the structure created by the patterning process, the parameters of one or more such objects are determined and for the design, control and / or monitoring of the patterning process, eg, process design, control, etc. And / or it is desirable to use this parameter for verification. The parameters of one or more determined objects of the patterned structure shall be used for designing, correcting and / or verifying, defect detection or classification, yield estimation, and / or process control of the patterning process. Can be done.

[0007] Therefore, in the pattern formation process, it is often preferable to measure the formed structure, for example, for process control and verification. Various tools for making the above measurements include a scanning electron microscope often used to measure critical dimensions (CDs) and a dedicated tool for measuring overlays, which is a measure of the alignment accuracy of the two layers of the device. It is known. The overlay can be represented by the degree of misalignment between the two layers, for example, the expression measured 1 nm overlay can represent a state in which the two layers are offset by 1 nm.

[0008] Various forms of inspection equipment (eg, metrology equipment) have been developed for use in the lithographic field. These devices direct a radiating beam to the target and one or more characteristics of the re-guided (scattered) radiation, in order to obtain a "spectrum" that allows the target characteristics to be determined. For example, the intensity illuminance according to the wavelength at a single reflection angle, the intensity illuminance according to the reflection angle at one or a plurality of wavelengths, or the polarization according to the reflection angle is measured. The properties of interest can be determined by a variety of techniques, such as target reproduction, library search, and principal component analysis by iterative techniques such as tightly coupled wave analysis or the finite element method.

[0009] A further technique involves blocking 0th order diffraction (corresponding to specular reflection) and only higher order diffraction is processed. Examples of such metrology can be found in WO 2009/07878 and WO 2009/106279, which are incorporated herein by reference in their entirety. Further developments of this technique are described in U.S. Patent Application Publication No. 2011/0027704, U.S. Patent Application Publication No. 2011/0043791, and U.S. Patent Application Publication No. 2012/02424940, and each of these patent applications as a whole. Is incorporated herein by reference. Usually such diffraction-based techniques are used to measure overlays. The target for the technique may be smaller than the illumination spot and may be surrounded by the product structure on the substrate. The target can have multiple periodic structures, which can be measured in one image. In certain embodiments of such metrology techniques, overlay measurement results are targeted to separately obtain the intensity of the normal diffractive order (eg +1 order) and the complementary diffractive order (eg -1st order). It is obtained by measuring the target twice under certain conditions while rotating or changing the illumination mode or imaging mode. Intensity asymmetry with respect to a given target, comparison of these diffraction order intensities, provides a measurement of target asymmetry, i.e., asymmetry at the target. This asymmetry at the target can be used as an indicator of overlay error.

[0010] In the overlay measurement example, the above technique relies on the assumption that overlay (ie, overlay error and intentional bias) is the sole cause of target asymmetry in the target. Any other asymmetry in the target or measurement, such as the structural asymmetry of features in the periodic structure in the upper and / or lower layers, or the asymmetry in measurements using sensors, is a primary (or higher) order. It also causes measurement intensity asymmetry. This intensity asymmetry, independent of overlays (including intentional bias), which may result from such other asymmetries in the target and / or measurement, disturbs the overlay measurement and gives an inaccurate overlay measurement. ..

[0011] In one embodiment, a method of determining patterning process parameters from a metrology target, obtaining multiple values of diffracted radiation from the metrology target, where each value of the plurality of values is relative to the target. A method is provided that accommodates different illumination conditions among multiple illumination conditions of illumination radiation and uses a combination of values to determine the same value of the patterning process parameter for the target.

[0012] In one embodiment, the first patterning process parameter determination technique is used to determine the first value of the patterning process parameter from the metrology target illuminated by the measured radiation, and for the metrology target. By using a second patterning process parameter determination technique that is different from the first patterning process parameter determination technique so that a plurality of second values of the patterning process parameter are reached, each of the second values is Determining for different lighting conditions of the measured radiation and identifying the lighting conditions of the measured radiation for the metrology recipe for the measurement of the metrology target based on the first and second values. Methods to include are provided.

[0013] In one embodiment, a measurement method comprising measuring a metrology target on a substrate according to the metrology recipe described herein is provided.

[0014] In one embodiment, a metrology device for measuring parameters of a lithography process is provided that is operable to implement the methods described herein.

[0015] In one embodiment, a non-temporary computer program product is provided that includes machine-readable instructions for causing a processor to perform the methods described herein.

[0016] An inspection apparatus configured to provide a radiation beam to two adjacent periodic structures or measurement targets on a substrate and to detect radiation diffracted by said target to determine parameters for a patterning process and the present specification. A system is provided with the non-temporary computer program described in the book. In one embodiment, the system has a support structure configured to hold a patterning device to modulate the radiated beam and projection optics arranged to project the modulated radiated beam onto a radiation sensitive substrate. Further equipped with a system and a lithography apparatus including.

[0017] Further features and advantages, as well as the structure and operation of the various embodiments, are described in detail below with reference to the accompanying drawings. The present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for purposes of illustration only. Further embodiments will be apparent to those of skill in the art from the teachings described herein.

[0018] Embodiments are described below, by way of example only, with reference to the accompanying drawings.

[0019] It is a figure which shows one Embodiment of a lithography apparatus. [0020] It is a figure which shows one Embodiment of a lithography cell or a cluster. [0021] It is a diagram schematically showing an exemplary inspection device and metrology technique. [0022] FIG. 6 is a diagram schematically showing an exemplary inspection device. [0023] It is a figure which shows the relationship between the illumination spot of an inspection apparatus, and a metrology target. [0024] It is a figure which shows the process which derives the variable of a plurality of objects based on the measurement data. [0025] Schematic representation of an inspection device (eg, a darkfield scatometer in this case) configured to measure a target using a first pair of illumination apertures. [0026] The figure schematically shows the details of the diffraction spectrum of the target periodic structure with respect to a given illumination direction. [0027] FIG. 2 schematically illustrates a second pair of illumination apertures that provide additional illumination modes when using the inspection device of FIG. 7A for diffraction-based overlay measurements. [0028] FIG. 6 is a diagram schematically showing a third pair of illumination apertures in which a first pair of apertures are combined. [0029] It is a figure which shows the form of the multi-period structure target, and the outline of the measurement spot on a substrate. [0030] It is a figure which shows the image of the target of FIG. 8 obtained by the inspection apparatus of FIG. 7A. [0031] It is a flow chart which shows the step of the overlay measurement method using the inspection apparatus of FIG. [0032] FIG. 3 is a schematic cross-sectional view of an overlay period structure having different overlay values within a region of zero. [0032] FIG. 3 is a schematic cross-sectional view of an overlay period structure having different overlay values within a region of zero. [0032] FIG. 3 is a schematic cross-sectional view of an overlay period structure having different overlay values within a region of zero. [0033] FIG. 3 is a schematic cross-sectional view of an overlay periodic structure having structural asymmetry in the bottom periodic structure due to the effect of processing. [0034] FIG. 3 is a schematic top view of an overlay target having a periodic structure with an intentional bias. [0035] It is a figure which shows the example of the detected diffraction signal of the radiation of a specific order from the target, such as the one shown in FIG. 11E. [0036] FIG. 6 is a diagram illustrating an example of a detected diffracted signal of another particular order of radiation from a target, such as that shown in FIG. 11E. [0037] A schematic depiction of a simple model for explaining the diffraction of radiation from a target having a two-layer periodic structure. [0038] It is a figure which shows the principle of overlay measurement with an ideal target which is not subjected to structural asymmetry. [0039] It is a diagram showing the principle of overlay measurement in a non-ideal target using the correction of structural asymmetry as disclosed in the embodiments herein. [0040] It is a flow chart of one Embodiment of the method. [0041] It is a flow chart of one Embodiment of the method. [0042] A flow chart illustrating a process in which a metrology target is used to monitor performance and as a basis for controlling a metrology, design and / or manufacturing process. [0043] A graph of overlay sensitivity for a target in measurements at various wavelengths for a single polarization (in this case, linear X polarization). [0044] A graph of overlay sensitivity for a target in measurements at various wavelengths for a single polarization (in this case, linear Y polarization). [0045] A ₊ vs. A _- plot for an overlay grid with no feature asymmetry.

[0046] Before elaborating on an embodiment, it is useful to show an exemplary environment in which the embodiment can be implemented.

[0047] FIG. 1 schematically shows a lithography apparatus LA. The device is configured to support an illumination optical system (illuminator) IL configured to adjust the radiation beam B (eg UV radiation or DUV radiation) and a patterning device (eg mask) MA and is specific. Holds a patterning device support or support structure (eg, mask table) MT connected to a first positioning device PM configured to accurately position the patterning device according to parameters, and a substrate (eg, resist coated wafer) W. A substrate table (eg, a wafer table) WT connected to a second positioning device PW configured to accurately position the substrate according to specific parameters, and a target portion C (eg, one) of the substrate W. Also included is a projection optical system (eg, a refraction projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning the device MA on it (including a plurality of dies).

Illumination optics are of various types, such as refraction, reflection, magnetism, electromagnetics, static electricity, or other types of optical components, or any combination thereof, for inducing, shaping, or controlling radiation. May include optical components of.

The patterning device support holds the patterning device in a manner depending on the orientation of the patterning device, the design of the lithography device, and other conditions such as whether the patterning device is held in a vacuum environment. The patterning device support can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The patterning device support may be a frame or table, for example fixed or movable as required. The patterning device support can ensure that the patterning device is in the desired position, eg, with respect to the projection system. The use of the term "reticle" or "mask" herein can be considered synonymous with the more general term "patterning device".

[0050] As used herein, the term "patterning device" refers to any device that can be used to pattern a cross section of a beam, such as creating a pattern on a target portion of a substrate. It should be broadly interpreted as a thing. Note that, for example, if the pattern contains phase shift features or so-called assist features, the pattern applied to the emitted beam may not exactly correspond to the desired pattern at the target portion of the substrate. In general, the pattern imparted to the radiated beam corresponds to a particular functional layer in a device created in a target portion such as an integrated circuit.

[0051] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each mirror can be individually tilted to reflect an incident radiating beam in different directions. The tilted mirror imparts a pattern to the radiated beam, which is reflected by the mirror matrix.

[0052] As shown herein, the device may be transmissive (eg, adopting a transmissive mask). Alternatively, the device may be reflective (eg, adopting a programmable mirror array of the type mentioned above, or adopting a reflective mask).

The lithography apparatus may be of a type in which at least a part of the substrate can be covered with a liquid having a relatively high refractive index, for example, water so as to fill the space between the projection system and the substrate. Immersion may be applied to other spaces within the lithography equipment, such as between the mask and the projection system. Immersion techniques for increasing the numerical aperture of projection systems are well known in the art. As used herein, the term "immersion" does not mean that a structure such as a substrate must be immersed in a liquid, but that there is liquid between the projection system and the substrate during exposure. It just means.

[0054] Referring to FIG. 1, the illuminator IL receives a radiated beam from the source SO. For example, when the radiation source is an excimer laser, the radiation source and the lithography device may be separate. In such cases, the source is not considered to form part of the lithography appliance and the emitted beam is sent from the source SO to the illuminator IL by a beam delivery system BD containing, for example, a suitable induction mirror and / or beam expander. Sent. In other cases, for example when the source is a mercury lamp, the source may be part of a lithography appliance. The radiation source SO and the illuminator IL can be referred to as a radiation system, if necessary, together with the beam delivery system BD.

[0055] The illuminator IL can include a regulator AD for adjusting the angular intensity distribution of the radiated beam. In general, it is possible to adjust at least the outer and / or inner radial range (usually referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the pupil plane of the illuminator. In addition, the illuminator IL can include various other components such as an integrator IN and a capacitor CO. An illuminator can be used to adjust the radiated beam to have the desired uniformity and intensity distribution in its cross section.

[0056] The radiated beam B is incident on the patterning device (for example, mask) MA held in the patterning device support (for example, mask table) MT, and is patterned by the patterning device. Upon passing through the patterning device (eg, mask) MA, the radiating beam B passes through the projection optical system PS, which focuses the beam on the target portion C of the substrate W, thereby targeting the image of the pattern. Project to C. A second positioning device PW and a position sensor IF (eg, an interferometer device, linear encoder, 2-D encoder, or capacitive sensor) are used to position, for example, a different target portion C in the path of the radiation beam B. The board table WT can be moved accurately as described above. Similarly, using the first positioning device PM and another position sensor (not specified in FIG. 1), for example, after mechanical removal from the mask library or during scanning, the path of the radiated beam B. The patterning device (eg, mask) MA can be accurately positioned with respect to the patterning device (eg, mask) MA.

[0057] The patterning device (eg, mask) MA and the substrate W can be aligned using the patterning device alignment marks M ₁ and M ₂ and the substrate alignment marks P ₁ and P ₂ . The illustrated substrate alignment marks occupy a dedicated target portion, but may be located in the space between the target portions (these are known as scribe lane alignment marks). Similarly, in situations where the patterning device (eg, mask) MA is provided with multiple dies, the patterning device alignment mark can be located between the dies. Small alignment markers may be contained within the die between device features, in which case it is desirable that the markers be as small as possible and do not require different imaging or process conditions than adjacent features. The alignment system for detecting the alignment marker will be further described below.

[0058] The lithography apparatus LA in this example is of a so-called dual stage type, has two substrate tables WTa and WTb, and two stations (exposure station and measurement station), and is between the stations. You can replace the board table with. While one substrate on one substrate table is exposed at the exposure station, another substrate can be loaded into the other substrate table at the measurement station and various preliminary steps can be performed. Preliminary steps may include mapping the surface control of the substrate using the level sensor LS and measuring the position of the alignment marker on the substrate using the alignment sensor AS. This can significantly increase the throughput of the device.

[0059] The illustrated device can be used in various modes including, for example, step mode or scan mode. The configuration and operation of the lithography apparatus are well known to those skilled in the art and do not need to be further described in order to understand the embodiments of the present invention.

[0060] As shown in FIG. 2, the lithography apparatus LA forms part of a lithography system called a lithography cell LC or a lithocell or cluster. The lithography cell LC can also include an apparatus for performing pre-exposure and post-exposure processes on the substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developing device DE for developing an exposed resist, a cooling plate CH, and a bake plate BK. The board handler or robot RO takes the boards from the I / O ports I / O1 and I / O2, moves them between different process devices, and then delivers them to the loading bay LB of the lithography device. These devices, often collectively referred to as tracks, are under the control of the track control unit TCU, which is itself controlled by the monitoring control system SCS, which is also a lithography control. The lithography equipment is controlled via the unit LACU. Therefore, different devices can be operated to maximize throughput and processing efficiency.

[0061] A patterned substrate can be inspected and patterned to design, monitor, control, etc. a patterning process (eg, a device manufacturing process) that includes at least one patterning step (eg, an optical lithography step). One or more parameters of the board are measured. One or more parameters may be, for example, an overlay between continuous layers formed in or on a patterned substrate, eg, a critical dimension (CD) of features formed in or on a patterned substrate (CD). Limit line width), focal or focal error of the optical lithography step, dose amount or dose error of the optical lithography step, optical aberration of the optical lithography step, and the like may be included. This measurement can be performed on the target of the product substrate itself and / or on a dedicated metrology target provided on the substrate. There are various techniques for measuring the structures formed in the patterning process, including the use of scanning electron microscopes, image-based measurement or inspection tools, and / or various specialized tools. A relatively fast, non-invasive form of specialty metrology and / or inspection tool is one in which the radiated beam is directed at a target on the surface of the substrate and the characteristics of the scattered (diffraction / reflection) beam are measured. By comparing the characteristics of one or more of the beams before and after being scattered by the substrate, the characteristics of one or more of the substrates can be determined. This is sometimes referred to as diffraction-based metrology or inspection.

[0062] FIG. 3 shows an exemplary inspection device (eg, a scatometer). This inspection device includes a wideband (white light) radiation projection device 2 that projects radiation onto the substrate W. The reguided radiation is sent to the spectroscope detector 4, which measures, for example, the spectrum 10 (intensity as a function of wavelength) of specularly reflected radiation as shown in the lower left graph. From this data, the structures or profiles that give rise to the detected spectra can be combined with a library of simulated spectra as shown in the lower right of FIG. 3 by the processor PU, for example by tightly coupled wave analysis and non-linear regression. Can be reconstructed by comparison of. In general, for reconstruction, the general form of the structure is known, some variables are assumed from the knowledge of the process in which the structure was made, and only a few variables of the structure are determined from the measured data. Is. Such an inspection device can be configured as a vertical incident inspection device or an oblique incident inspection device.

[0063] Another inspection device that can be used is shown in FIG. In this device, the radiation emitted by the radiation source 2 is collimated using the lens system 120, transmitted through the interference filter 130 and the polarizing element 170, reflected by the partially reflecting surface 160, and passed through the objective lens 150 to the substrate. Focused on the spot S on W. The objective lens 150 has a high numerical aperture (NA), preferably at least 0.9 or at least 0.95. Immersion inspection equipment (using a fluid with a relatively high index of refraction such as water) can even have a numerical aperture greater than one.

[0064] Similar to the lithography apparatus LA, one or more substrate tables can be provided to hold the substrate W during the measurement operation. The substrate table may have the same or the same shape as the substrate table WT of FIG. In the example where the inspection equipment is integrated with the lithography equipment, they may be the same board table. A coarse movement positioning device and a fine movement positioning device can be provided in the second positioning device PW configured to accurately position the substrate with respect to the measurement optical system. For example, various sensors and actuators are provided to acquire the position of the target of interest and place the target below the objective lens 150. Usually, many measurements are made on the target at various positions across the substrate W. The substrate support can be moved in the X and Y directions to obtain different targets and moved in the Z direction to obtain the desired position of the target with respect to the focal point of the optical system. For example, in practice the optics can remain substantially stationary (typically in the X and Y directions, but perhaps even in the Z direction), and when only the substrate moves, the objectives vary with respect to the substrate. It is convenient to consider and describe the operation as if it were guided to a certain position. Assuming that the relative positions of the substrate and the optics are correct, in principle, which of them is moving in the real world, or both are moving, or part of the optics is moving (eg Z and). / Or in the tilt direction), the rest of the optical system is stationary, and the substrate is moving (eg, in the X and Y directions, but also optionally in the Z and / or tilt direction). It doesn't matter.

[0065] The radiation reguided by the substrate W then passes through the partially reflective surface 160 and enters the detector 180, where the spectrum is detected. The detector 180 may be located on the back projection focal length 110 (ie, the focal length of the lens system 150), or the surface 110 is reimaged onto the detector 180 using an auxiliary optical system (not shown). You may. The detector may be a two-dimensional detector so that the two-dimensional angular scattering spectrum of the substrate target 30 can be measured. The detector 180 may be, for example, an array of CCD or CMOS sensors, and may use, for example, an integration time of 40 ms per frame.

[0066] For example, a reference beam can be used to measure the intensity of an incident ray. To do this, when the radiating beam is incident on the partially reflecting surface 160, a portion of the radiating beam is transmitted through the partially reflecting surface 160 as a reference beam and directed towards the reference mirror 140. The reference beam is then projected onto different parts of the same detector 180 or to different detectors (not shown).

[0067] One or more interference filters 130 may be used to select a wavelength of interest, eg, in the range of 405 to 790 nm, and even lower, eg, 200 to 300 nm. Interference filters may be tuned rather than having a set of various filters. A grid can also be used instead of the interference filter. Aperture diaphragms or spatial light modulators (not shown) can be provided in the illumination path to control the range of angles of incidence of radiation on the target.

[0068] The detector 180 can measure the intensity of reinduced radiation at a single wavelength (or a narrow wavelength range) and measures the intensity individually at multiple wavelengths or integrated over a wavelength range. You can also do it. In addition, the detector can individually measure the intensity of the lateral magnetically polarized radiation and the laterally polarized radiation and / or the phase difference between the laterally polarized radiation and the laterally electrically polarized radiation. ..

[0069] The target 30 on the substrate W may be a 1-D grid printed so that bars are formed from the solid resist lines after development. The target 30 may be a 2-D grid and is printed so that a grid is formed from the solid resist pillars or vias in the resist after development. Bars, pillars, or vias can be etched into or on the substrate (eg, in one or more layers on the substrate). Patterns (eg, bars, pillars, or vias) are sensitive to processing changes in the patterning process (eg, photoaberration, focus changes, dose changes, etc. in lithography projection equipment (especially projection system PS)). , Appears as variations in the printed grid. Therefore, the grid is reconstructed using the measured data of the printed grid. One or more parameters of the 1-D grid such as line width and / or shape, or one or more parameters of the 2-D grid such as width or length or shape of pillars or vias, printing steps and / or others. From the knowledge of the inspection process of, it is possible to input to the reconstruction process carried out by the processor PU.

[0070] In addition to measuring parameters by reconstruction, diffraction-based metrology or inspection can be used to measure feature asymmetry in products and / or resist patterns. Certain uses of asymmetry measurement are, for example, related to overlay measurements, but other uses are also known. In this case, the target 30 typically comprises a set of periodic features superimposed on each other. For example, asymmetry can be measured by comparing opposite parts of the diffraction spectrum from the target 30 (eg, comparing -1st and +1st order in the diffraction spectrum of a periodic lattice). The concept of asymmetry measurement using the instrument of FIG. 3 or 4 is described, for example, in US Patent Application Publication No. 2006066855, which is incorporated herein by reference in its entirety. Briefly, the position of the diffraction order in the diffraction spectrum of the target is determined only by the periodicity of the target, but the asymmetry in the diffraction spectrum indicates the asymmetry of the individual features that make up the target. In the device of FIG. 4, where the detector 180 may be an image sensor, such diffraction order asymmetry manifests directly as the asymmetry of the pupil image recorded by the detector 180. This asymmetry can be measured by digital image processing on a PU-by-PU basis and calibrated to known values for overlays.

[0071] FIG. 5 shows a plan view of the spread of a typical target 30 and illumination spot S in the apparatus of FIG. In order to obtain a diffraction spectrum without interference from the surrounding structure, in one embodiment, the target 30 is a periodic structure (eg, a grid) that is larger than the width (eg, diameter) of the illumination spot S. The width of the spot S may be smaller than the width and length of the target. In other words, the target is "underfilled" by illumination and the diffracted signal essentially does not contain any signal from product features or the like outside the target itself. Illumination configurations 2, 120, 130, 170 can be configured to provide uniform intensity illumination over the posterior focal plane of the objective lens 150. Alternatively, lighting can be restricted to on-axis or off-axis directions, for example by including apertures in the illumination path.

[0072] FIG. 6 schematically illustrates an exemplary process of determining the value of one or more variables of interest in a target pattern 30'based on measurement data obtained using metrology. The radiation detected by the detector 180 provides the measured radiation distribution 108 for the target 30'.

[0073] For a given target 30', the radiation distribution 208 can be calculated / simulated from the parameterized model 206, for example using the numerical Maxwell solver 210. Parameterized model 206 shows exemplary layers of various materials that make up and relate to the target. The parameterized model 206 may include one or more variables relating to the features and layers of the portion of the target under consideration, which variables can be modified and derived. As shown in FIG. 6, one or more variables are the thickness t of one or more layers t, the width w of one or more features (eg CD), the height of one or more features. h and / or may include sidewall angles α of one or more features. Although not shown, one or more variables are, but are not limited to, the index of refraction of one or more layers (eg, real refractive index or complex index of refraction, refractive index tensor, etc.), one or more layers. Absorption index of, absorption of one or more layers, resist loss during development, footing of one or more features, and / or line edge roughness of one or more features can be further included. The initial value of the variable may be what is expected for the target being measured. The measured radiation distribution 108 is then compared at 212 with the calculated radiation distribution 208 to determine the difference between the two radiation distributions. If there is a difference, the value of one or more variables in the parameterized model 206 can be changed until there is a sufficient match between the measured radiation distribution 108 and the calculated radiation distribution 208. The calculated radiation distribution 208 can be calculated and compared with the measured radiation distribution 108. At that point, the values of the variables in the parameterized model 206 provide a good or best match for the geometry of the actual target 30'. In one embodiment, there is a sufficient match when the difference between the measured radiation distribution 108 and the calculated radiation distribution 208 is within the tolerance threshold.

Further inspection devices suitable for use in embodiments are shown in FIG. 7A. For example, there may be such a metrology device, or any other suitable metrology device. The diffracted radiation of the target T and the measured radiation used to illuminate the target is shown in more detail in FIG. 7B. The illustrated inspection device is a type known as a dark field metrology device. The inspection device can be a stand-alone device, or can be incorporated into the lithography device LA, for example, at either a measuring station or a lithography cell LC. The optical axis with some branches throughout the device is shown by the dotted line O. In this device, the radiation emitted by the radiation source 11 (eg, a xenon lamp) is guided to the substrate W via the optical element 15 by an optical system including the lenses 12, 14 and the objective lens 16. These lenses are arranged in a double 4F configuration. Different lens configurations can be used, provided that, for example, a substrate image is formed on the detector and at the same time allows access to the intermediate pupil surface for spatial frequency filtering. Therefore, the angular range in which the radiation is incident on the substrate can be selected by defining the spatial intensity distribution of the plane showing the spatial spectrum of the plane of the substrate, which is referred to here as the (conjugated) pupil plane. In particular, this can be done by inserting an appropriate form of the aperture plate 13 between the lenses 12 and 14 in a plane which is a rear projection image of the pupil surface of the objective lens. In the illustrated example, the aperture plate 13 has various forms labeled 13N and 13S that allow different lighting modes to be selected. The lighting system in this example forms an off-axis lighting mode. In the first illumination mode, the aperture plate 13N provides off-axis radiation from the direction designated "north (N)" for illustration purposes only. In the second irradiation mode, the aperture plate 13S is used to illuminate from the opposite direction, similarly but labeled "south (S)". Other lighting modes are possible by using different apertures. Any unwanted radiation other than the desired illumination mode will interfere with the desired measurement signal, so it is desirable to darken the rest of the pupil surface.

As shown in FIG. 7B, the target T is arranged in a state where the substrate W is perpendicular to the optical axis O of the objective lens 16. The substrate W can be supported by a support (not shown). The measured radiation I that hits the target T from an angle off the axis O produces a zero-order ray (solid line 0) and two primary rays (dashed-dotted line + 1 and alternate-dashed line-1). It should be remembered that if the small target is overfilled, these rays are just one of many parallel rays over the area of the substrate containing the metrology target T and other features. Since the aperture of the plate 13 has a finite width (necessary to receive useful radiation), the incident ray I effectively occupies a predetermined angular range, diffracted ray 0 and diffracted ray + 1 / -1. Spreads somewhat. According to the point spread function of the small target, each order +1, -1 is not a single ideal ray as shown, but further spreads over a predetermined angular range. It should be noted that the periodic structural pitch and illumination angle of the target can be designed and adjusted so that the primary ray incident on the objective lens is closely aligned with the central optical axis. The rays shown in FIGS. 7A and 7B are shown somewhat off-axis simply to allow the rays to be more easily distinguished in the figure.

[0076] At least 0th and +1st order diffracted by the target T on the substrate W are collected by the objective lens 16 and reverted to pass through the optical element 15. Returning to FIG. 7A, both the first and second illumination modes are shown by designating apertures on both sides in the radial direction, labeled as north (N) and south (S). When the incident ray I of the measurement radiation comes from the north side of the optical axis, that is, when the first illumination mode using the aperture plate 13N is applied, the +1 diffracted ray labeled +1 (N) is the objective lens. It is incident on 16. On the other hand, when the second illumination mode using the aperture plate 13S is applied, the -1 diffracted ray (coded with -1 (S)) is incident on the lens 16.

[0077] The beam splitter 17 splits the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 uses zero-order and first-order diffraction beams to form a diffraction spectrum (pupil image) of the target on the first sensor 19 (eg, a CCD or CMOS sensor). Since each diffraction order corresponds to a different part of the sensor, each order can be compared and contrasted by image processing. The pupil image captured by the sensor 19 can be used to focus the inspection device and / or to normalize the intensity and illuminance measurements of the primary beam. The pupillary image can also be used for many measurement purposes such as reproduction.

[0078] In the second measurement branch, the optical systems 20 and 22 form an image of the target T on the sensor 23 (eg, a CCD or CMOS sensor). In the second measurement branch, the aperture stop 21 is provided on a plane conjugate with the pupil surface. Since the aperture stop 21 functions to block the zero-order diffraction beam, the image of the target formed on the sensor 23 is formed only from the -1 or +1 primary beam. The image captured by the sensors 19 and 23 is output to the processor PU, which processes the image, and the function of the processor PU is determined by the specific type of measurement made. Note that the term "image" is used broadly here. No image of periodic structure features is formed when only one of the orders -1 and +1 is present.

[0079] The specific forms of the aperture plate 13 and the field diaphragm 21 shown in FIGS. 7A, 7C and 7D are merely examples. In one embodiment, on-axis illumination of the target is used and an aperture diaphragm with an off-axis aperture is used to deliver substantially only one primary diffracted radiation to the sensor. In yet another embodiment, a secondary, tertiary and even higher order beam (not shown in FIGS. 7A, 7B, 7C or 7D) is used for the measurement instead of or in addition to the primary beam. Can be done.

[0080] To provide measurement radiation adaptable to these various types of measurements, the aperture plate 13 can include a plurality of aperture patterns formed around the disc, which disc is the desired pattern. Rotate to fit in place. It should be noted that the aperture plate 13N or aperture plate 13S can only be used to measure periodic structures oriented in one direction (X or Y depending on the configuration). For measurements of orthogonal periodic structures, the target can be rotated by 90 ° and 270 °. 7C and 7D show different aperture plates. These uses, as well as many other modifications and applications of the device, are described in the patent application publication described above.

[0081] FIG. 8 shows a (composite) target formed on a substrate according to known conventions. The target in this example comprises four periodic structures (eg, grids) 32-35 positioned in close proximity to each other, all of which are within the measurement spot 31 formed by the metrology radiated illumination beam of the inspection device. Therefore, all four periodic structures are illuminated simultaneously and imaged simultaneously on sensors 19 and 23. In an example specialized for overlay measurement, the periodic structures 32-35 themselves are composite periodic structures formed by overlaying themselves, for example, a patterned periodic structure on different layers of a semiconductor device formed on a substrate W. Is. Periodic structures 32-35 may have overlay offsets of different biases to facilitate the measurement of overlays between layers where different parts of the composite periodic structure are formed. The significance of the overlay bias will be described below with reference to FIG. Further, the periodic structures 32 to 35 may have different directions as shown so as to diffract the incident radiation in the X direction and the Y direction. In one example, the periodic structures 32 and 34 are X-direction periodic structures having bias offsets + d and −d, respectively. The periodic structures 33 and 35 are Y-direction periodic structures having bias offsets + d and −d, respectively. Individual images of these periodic structures can be identified within the image captured by the sensor 23. This is just one example of a target. The target may have more than four or less than four periodic structures, or only one periodic structure.

[0082] FIG. 9 is an example of an image that can be formed on the sensor 23 using the aperture plate 13NW or 13SE of FIG. 7D with the target of FIG. 8 in the apparatus of FIG. 7 and can be detected by the sensor 23. show. The pupil surface image sensor 19 cannot resolve different individual periodic structures 32 to 35, but the image sensor 23 can resolve them. The dark rectangle represents a field of images on the sensor, within which the illuminated spot 31 on the substrate is imaged within the corresponding circular area 41. Within the circular area 41, the rectangular areas 42-45 represent images of the small target periodic structures 32-35. If the target is in the product area, product features may also be visible around this image field. The image processing apparatus and control system PU use pattern recognition to process these images to identify separate images 42-45 of periodic structures 32-35. In this way, the image does not need to be very accurately aligned to a particular position within the sensor frame. This greatly improves the throughput of the entire measuring device.

[0083] Once the individual images of the periodic structure have been identified, the intensity of those individual images can be measured, for example, by averaging or summing the selected pixel intensity values within the identified area. The intensity and / or other properties of the image can be compared to each other. These results can be combined to measure various parameters of the patterning process. Overlay performance is an important example of such a parameter.

[0084] FIG. 10 shows two layers comprising component period structures 32-35, for example using the method described in WO 2011/012624, which is hereby incorporated by reference in its entirety. Overlay error (ie, undesired and unintentional overlay misalignment) is measured. This measurement identifies the target asymmetry revealed by comparing the intensities in the image of the normal diffraction order of the target periodic structure with the image of the complementary diffraction order to obtain a measure of intensity asymmetry. It is done by. In one embodiment, the normal diffractive order is +1 radiation and the complementary diffractive order is -1st order radiation. The discussion herein focuses on the normal diffraction order as +1st order radiation and the complementary diffraction order as -1st order radiation, but other corresponding higher orders (eg, +2nd order and-. The strength of the secondary) can be compared.

[0085] In step S1, the substrate, eg, a semiconductor wafer, is processed once or multiple times by a lithography apparatus such as the lithography cell of FIG. 2 to create a target including periodic structures 32 to 35. In step S2, using the inspection device of FIG. 7, images of periodic structures 32 to 35 are taken using only one of the primary diffraction beams (eg, +1 order). In step S3, another primary diffraction beam (-1st order) is used by changing the illumination mode, changing the imaging mode, or rotating the substrate W by 180 ° within the field of view of the inspection device. It is possible to obtain a second image of the periodic structure. As a result, the -1st order diffracted radiation is captured in the second image.

[0086] Note that the "image" here is not a conventional darkfield microscope image, as each image contains only half of the primary diffracted radiation. Individual target features in the target periodic structure are not resolved. Each target periodic structure is simply represented by an area of a particular intensity level. In step S4, a region of interest (ROI) is identified within the image of each component target periodic structure from which the intensity level is measured.

[0087] By identifying the ROI for each individual target periodic structure and measuring its intensity, the asymmetry of the target, and thus the overlay error, can be determined. This will compare the intensity values obtained for normal and complementary diffraction order radiation for each of the target period structures 32 to 35 in step S5 and their intensity asymmetry (eg, their intensity difference). Is identified (eg, by the processor PU). The term "difference" is not intended to refer only to subtraction. The difference may be calculated in the form of a ratio. In step S6, the measured intensity asymmetry of some target periodic structures is used in conjunction with the knowledge of any known imposed overlay bias of those target periodic structures for the patterning process in the vicinity of the target T. Calculate one or more performance parameters.

[0088] FIGS. 11A-11D show schematic cross-sectional views of a target periodic structure (overlay periodic structure) having different bias offsets. As seen in FIGS. 7-9, these can be used as the target T on the substrate W. Just as an example, a periodic structure with periodicity in the X direction is shown. Different combinations of these periodic structures with different biases and different orientations can be provided individually or as part of the target.

Starting with FIG. 11A, the target 600 formed in at least two layers represented by the reference numerals L1 and L2 is shown. In the bottom or bottom layer L1, a first periodic structure (bottom or bottom periodic structure), such as a grid, is formed by the features 602 and space 604 of the substrate 606. In layer L2, a second periodic structure, eg, a grid, is formed by features 608 and space 610 (cross sections are drawn such that features 602, 608 (eg, lines) extend deep into the paper). The periodic structure pattern repeats at pitch P in both layers. Features 602 and 608 may take the form of lines, dots, blocks, and via holes. In the situation shown in FIG. 11A, there is no overlay contribution due to misalignment, such as overlay error and imposed bias, so that each feature 608 of the second structure is located directly above the feature 602 in the first structure. do.

[0090] In FIG. 11B, the same target with the first known imposed bias + d is shown, with the feature 608 of the first structure shifted to the right by a distance d with respect to the feature of the second structure. The bias distance d may actually be several nanometers, such as 10 nm to 20 nm, and the pitch P may be, for example, in the range of 300 to 1000 nm, such as 500 nm or 600 nm. FIG. 11C shows another feature with a second known imposed bias-d, with feature 608 shifted to the left. The value of d does not have to be the same for each structure. This type of bias period structure shown in FIGS. 11A-11C is described in the prior patent application publication described above.

[0091] FIG. 11E schematically shows an exemplary target 600 having subtargets 612, 614, 616, 618 including periodic structures in the upper and lower layers, such as those shown in FIGS. 11A-C. The lower layer is not shown in FIG. 11E. In one embodiment, the sub-targets 612, 614, 616, 618 are designed to measure overlays in two vertical directions (eg, X and Y), with a bias d imposed to facilitate the measurement. (As described above with respect to FIGS. 11B and 11C). The embodiment of FIG. 11E shows four sub-targets, but may be different numbers, all of which are used to measure overlays in one direction or to measure overlays in more than two directions. Can be done.

[0092] In one embodiment, the sub-targets 612 and 614 are both designed to measure overlay in the X direction. In one embodiment, the sub-target 612 has a + d bias and the sub-target 614 has a −d bias. In one embodiment, the sub-targets 616 and 618 are both designed to measure overlay in the Y direction. In one embodiment, the sub-target 616 has a + d bias and the sub-target 618 has a −d bias.

[0093] FIG. 11F shows an example of a detected diffraction signal of normal order (eg, +1 order) radiation from step S2 from target 600, such as that shown in FIG. 11E. FIG. 11G shows an example of a detected diffracted signal of complementary order (eg, -1) order radiation from step S3 from target 600, such as that shown in FIG. 11E. For each periodic structural direction (X and Y), intentional bias in the opposite direction as indicated by "+" (in the case of + d bias) and "-" (in the case of −d bias) in FIGS. 11F and 11G. There are two periodic structures that have. Therefore, X + represents the diffraction signal detected from the sub-target 612, X- represents the diffraction signal detected from the sub-target 614, Y + represents the diffraction signal detected from the sub-target 618, and Y- Represents the diffraction signal detected from the sub-target 616. Therefore, four diffraction intensity signals are detected for each periodic direction of the periodic structure.

[0094] FIG. 11H is a simple model for explaining the diffraction of radiation from a target (such as subtarget 612, 614, 616 or 618) having a two-layer periodic structure (such as those shown in FIGS. 11A-C). It is a schematic description of. The complex amplitudes of the radiation diffracted from the upper and lower layers are shown. Radiation diffracted from the underlying layer contains phase contributions from the overlay.

[0095] In FIG. 12, the curve 702 has no offset and no structural asymmetry within the individual periodic structures forming the target, especially within the individual periodic structures of the first structure. The relationship between the overlay OV and the intensity asymmetry A with respect to the target is shown. As a result, the target asymmetry of this ideal target includes only the overlay contribution due to the misalignment of the first and second structures resulting from the known imposed bias and overlay error _OVE . This graph and the graph of FIG. 13 show only the principles behind the present disclosure, in which the units of intensity asymmetry A and overlay OV are arbitrary. Examples of actual dimensions are further presented below.

[0096] In the "ideal" situation of FIG. 12, curve 702 shows that the intensity asymmetry A has a non-linear periodic relationship (eg, a sine relationship) with the overlay. The period P of the sinusoidal fluctuation corresponds to the period or pitch P of the periodic structure and is, of course, converted to an appropriate scale. In this example, the sine and cosine waveform is pure, but in real life it may contain harmonics.

[0097] As mentioned above, a bias period structure (with known imposed overlay bias) can be used to measure the overlay, rather than relying on a single measure. This bias has a known value as defined by the patterning device from which it was generated (eg, the reticle), which acts as a calibration on the substrate of the overlay corresponding to the measured intensity asymmetry. In the drawing, the calculation result is shown in a graph. In steps S1-5, intensity asymmetry measures A _{+ d} and _Ad are obtained for periodic structures with biases + d and −d, respectively, imposed (eg, as shown in FIGS. 11B and 11C). When these measures are applied to a sinusoidal curve, points 704 and 706 are obtained as shown. Knowing the bias, the true overlay error _OVE can be calculated. The pitch P of the sinusoidal curve is known from the design of the target. The vertical scale of curve 702 is initially unknown and is an unknown coefficient and can be referred to as the first harmonic proportionality constant K. Therefore, the overlay sensitivity K is a measure of the sensitivity of the intensity asymmetry measure to the overlay. In one embodiment, the overlay sensitivity K is the ratio of the measured intensity to the overlay. Therefore, the overlay sensitivity K helps detect the process dependency of the overlay.

[0098] As an equation, the relationship between the overlay error _OVE and the intensity asymmetry A is assumed as follows.
A _{± d} = _Ksin (OVE ± d) (1)
Here, the overlay error _OVE is expressed by adjusting the scale so that the target pitch P corresponds to the angle 2π radians. Overlay error _OVE can be calculated using the following equation using two measures of periodic structure with different known biases (eg + d and −d).

ここで、

は、オーバーレイ及びバイアスによる位相差であり、

は、上層から回析された放射線と下層から回析された放射線との残りの位相差であり、上部周期構造と下部周期構造との間の層の厚さＴに比例し、入射放射線の波長に反比例する。 [0099] Returning to _FIG . 11H, the overlay OV (also referred to as overlay error OVE) can also be evaluated as follows. Specifically, based on the model shown in FIG. 11H, the +1 and -1st order diffracted radiation intensities can be calculated as follows.

here,

Is the phase difference due to overlay and bias.

Is the remaining phase difference between the radiation diffracted from the upper layer and the radiation diffracted from the lower layer, proportional to the layer thickness T between the upper and lower periodic structures, and the wavelength of the incident radiation. Is inversely proportional to.

[00100] For convenience, the four strengths in one periodic structural direction (eg, X) can be specified as follows.
-PBN (+1st order diffraction from positive bias period structure)
-PBC (-1st order diffraction from positive bias period structure)
-NBN (+1st order diffraction from negative bias period structure)
-NBC (-1st order diffraction from negative bias period structure)
Therefore, ΔI _PB can be designated as PBN-PBC, and ΔI _NB can be designated as NBN-NBC. The amplitude and phase of the diffracted waves from the + 1 and -1st order radiation (excluding the overlay phase) are then equal, and the amplitude and phase of the diffracted waves from the positive and negative bias period structures. Assuming that the phases are equal and the optics of the metrology device themselves are symmetric, the difference between the intensity of the +1st order radiation and the intensity of the -1st order radiation is ΔI = K. et al. Derived as sin (Φ _OV ), K is the overlay proportional coefficient and K = 4A. B. Equal to sin (β). Therefore, the overlay can be calculated as follows.

[00101] Here, FIG. 11D schematically shows the phenomenon of structural asymmetry, in this case structural asymmetry (downward or bottom structural asymmetry) in the first structure. The features in the periodic structure in FIGS. 11A-11C are shown as completely quadrangular faces, but the actual features have some slope and some roughness on the faces. Nevertheless, they are intended to have a profile that is at least symmetrical. The features 602 and / or space 604 of the first structure in FIG. 11D are no longer quite symmetrical and are distorted by one or more processing steps. Therefore, for example, the bottom surface of each space is inclined (bottom wall inclination). For example, the side wall angles of features and spaces are asymmetric. As a result, the overall target asymmetry of the target is an overlay contribution independent of structural asymmetry (ie, overlay contribution due to misalignment of the first and second structures; itself, overlay error and any. Consists of known imposed biases) and the structural contribution of this structural asymmetry in the target.

[00102] When overlays are measured by the method of FIG. 10 using only two bias period structures, the structural asymmetry due to the process is indistinguishable from the overlay contribution due to misalignment, resulting in Overlay measurements (especially measurements of unwanted overlay errors) are unreliable. Structural asymmetry in the first structure of the target (bottom periodic structure) is a common form of structural asymmetry. This structural asymmetry can occur, for example, in substrate processing steps such as chemical mechanical polishing (CMP) performed after the first structure is first formed.

[00103] FIG. 13 shows the first effect of introducing structural asymmetry, eg, bottom periodic structural asymmetry as shown in FIG. 11D. The "ideal" sinusoidal curve 702 no longer applies. However, at least in general, bottom periodic structural asymmetry or other structural asymmetry has the effect of adding the intensity shift term K ₀ and the phase shift term φ to the intensity asymmetry A _{± d} . The resulting curve is shown in the graph as reference numeral 712, where label K ₀ indicates the intensity shift term and label φ indicates the phase offset term. The intensity shift term K ₀ and the phase shift term φ depend on the combination of the target and the selected characteristics of the measured radiation, such as the wavelength and / or polarization of the measured radiation, and are sensitive to process variability. As an equation, the relationship used for the calculation in step S6 is as follows.
A _{± d} = K ₀ + _Ksin (OVE ± d + φ) (5)

[00104] In the presence of structural asymmetry, the overlay model described by Eq. (2) provides overlay error values affected by the intensity shift term K ₀ and the phase shift term φ, resulting in inaccuracies. Become. Also, structural asymmetry is due to the fact that the intensity and phase shift depend, for example, on wavelength and / or polarization, so when mapping overlay errors, one or more different measurement parameters (eg, the wavelength of the measurement beam or the measurement beam). It results in measurement differences for the same target using (such as polarization).

[00105] The modified step S6 overlay calculation relies on some assumptions. First, it is assumed that the intensity asymmetry behaves as an overlay sine function and the period P corresponds to the grid pitch. These assumptions are valid for the current overlay range. The small pitch-wavelength ratio allows only a small number of propagation diffraction orders from the grid, so the number of harmonics can be designed to be small. However, in practice, the overlay contribution to intensity asymmetry due to misalignment may not always be a true sinusoidal waveform and may not always be perfectly symmetric with respect to OV = 0.

[00106] Therefore, the effect of structural asymmetry can generally be formulated as follows.
ΔI ₊ = K (OV + d) + ΔI _BG (6)
ΔI ₋ = K (OV−d) + ΔI _BG (7)
Here, ΔI ₋ (also synonymous with A−) and ΔI ₊ (also synonymous with A ₊ ) represent the measured intensity asymmetry, and ΔI _BG is the contribution of the structural asymmetry to the intensity asymmetry. Therefore, the overlay error ΔOV can be regarded as a function of ΔI _BG / K.

[00107] Here, in addition to or instead of structural asymmetry within the target, stack differences between adjacent periodic structures of the target or between adjacent targets adversely affect the accuracy of measurements such as overlay measurements. It is further clear that it can be a factor. Stack differences can be understood as undesigned differences in the physical configuration between adjacent periodic structures or targets. Stack differences are the optical properties of measured radiation between adjacent periodic structures or targets (eg, intensity, polarization, etc.) due to non-intentional bias and non-structural asymmetry, other than overlay errors common in adjacent periodic structures or targets. ) Causes a difference. Stack differences are, but are not limited to, differences in thickness between adjacent periodic structures or targets (eg, another periodic structure or target designed so that one periodic structure or target is at substantially equal levels. Designed to have substantially equal synthetic refraction (eg, differences in the thickness of one or more layers), differences in refractive index between adjacent periodic structures or targets, such as higher or lower. If so, one or more such that the synthetic refractive index for one or more layers with respect to one periodic structure or target is different from the synthetic refractive index for one or more layers with respect to another periodic structure or target. Differences in refractive index between multiple layers), material differences between adjacent periodic structures or targets (eg, one periodic structure or target and another periodic structure or target designed to have substantially the same material) Differences in material type, material uniformity, etc. of one or more layers such that there are material differences with respect to, and lattice periodic differences in adjacent periodic or target structures (eg, substantially the same lattice). Differences in the depth of one periodic structure or target and another periodic structure or target designed to have a period, adjacent periodic structures or target structures (eg, substantially the same) Differences in depth due to etching of one periodic structure or target and another periodic structure or structure designed to have depth), differences in the width (CD) of adjacent periodic structures or features of the target (For example, the difference in the width of a feature from one periodic structure or target to another periodic structure or target designed to have substantially the same width of the feature) and the like. In some examples, stack differences are introduced in the patterning process by processing steps such as CMP, layer deposition, etching. In one embodiment, the periodic structure or target is within 200 μm of each other, within 150 μm of each other, within 100 μm of each other, within 75 μm of each other, within 50 μm of each other, within 40 μm of each other, within 30 μm of each other, within 20 μm of each other, or within 10 μm of each other. Adjacent.

に比例し得る。 [00108] The effect of stack differences (also called lattice imbalances between lattices) can generally be formulated as follows.
ΔI ₊ = (K + ΔK) (OV + d) (8)
ΔI ₋ = (K−ΔK) (OV−d) (9)
Here, ΔK represents the difference in overlay sensitivity due to the stack difference. Therefore, the overlay error ΔOV is

Can be proportional to.

[00109] Therefore, one or more stack difference parameters can be defined to characterize the stack difference. As mentioned above, the stack difference parameter is a measure of the adjacent periodic structure or a different physical configuration outside the design of the target. In one embodiment, the stack difference parameter can be determined by evaluating adjacent periodic structures or cross sections of the target.

[00110] In one embodiment, the stack difference parameter can be determined for the lower adjacent grid of the composite grid by evaluating the lower adjacent grid before the upper grid is applied. In one embodiment, the stack difference parameter can be derived by reconstructing an adjacent periodic structure or target from an optical measure of an adjacent periodic structure or target, or from an adjacent periodic structure or cross-sectional area of the target. .. That is, the physical dimensions, features, material properties, etc. are reconstructed and the difference between adjacent periodic structures or targets is determined to reach the stack difference parameter.

ここで、

は、＋ｄバイアスを有する第１の周期構造によって回折された＋１次回折強度信号

と、＋ｄバイアスを有する第１の周期構造によって回折された－１次回折強度信号

との平均値である。同様に、

は、－ｄバイアスを有する第２の周期構造によって回折された＋１次回折強度信号

と、－ｄバイアスを有する第２の周期構造によって回折された－１次回折強度信号

との平均値である。一実施形態では、周期構造強度不均衡（ＧＩ）は、

などの導出バージョンでよい。 [00111] One embodiment of the stack difference parameter is a periodic structural strength imbalance (GI) that can be defined as follows.

here,

Is a + 1st order diffraction intensity signal diffracted by a first periodic structure with a + d bias.

And the -1st order diffraction intensity signal diffracted by the first periodic structure with + d bias.

Is the average value of. Similarly,

Is a + 1st order diffraction intensity signal diffracted by a second periodic structure with a −d bias.

And the -1st order diffraction intensity signal diffracted by the second periodic structure with -d bias.

Is the average value of. In one embodiment, the periodic structural strength imbalance (GI) is

It may be a derived version such as.

[00112] The problem with the overlay calculation method described above is that it is often not possible to maintain the assumptions made for its derivation. For example, the optical path characteristics and / or the source may not be perfectly symmetric with normal radiation and complementary radiation, which can be confused with the actual diffraction intensity. In addition to or as an alternative, metrology targets are not structurally symmetric. As mentioned above, this usually occurs due to the processing steps of the patterning process. The asymmetric behavior is due, for example, to the structural asymmetry (BGA) of the lower periodic structure of the target and / or due to the stack difference between the positive and negative bias periodic structures (periodic structure). It can occur between normal and complementary intensities (which can be characterized by intensity imbalance (GI)).

[00113] To help eliminate one or more errors resulting from such asymmetry, calibration can be used, for example, to address some degree of asymmetry in optical path characteristics and / or sources. Then, with respect to physical differences in the target (eg, structural asymmetry (BGA) and / or stack difference of the lower periodic structure), one or more measurement criteria (periodic structure strength imbalance (GI in the case of stack difference)). ) Etc.) can be used, for example, to identify wavelengths that are unlikely to be a problem. For example, the "best" wavelength can be selected based on indirect metrics that attempt to predict good regions of the wavelength spectrum. Identifying such "best" wavelengths is a very difficult task, even considering that the measurement criteria sometimes do not match. Moreover, even with the "best" wavelengths selected, one cannot always be confident that the overlay accuracy will be optimal.

[00114] Therefore, it is desirable to be able to address and / or correct for these errors using new overlay determination techniques. Such overlay determination techniques can be used in a variety of applications. The first exemplary use is, for example, to derive overlay values as part of the patterning process execution for use in patterning processes such as control, design, etc., in large quantities or during manufacturing desired overlay values. Is to derive. Another exemplary use is to derive overlay values for use in the design, control, etc. of a metrology process, for example to select conditions for the metrology process, such as the radiation wavelength used for measurement. That is (the metrology process can use different overlay calculation techniques such as those described above for equations (1)-(4)).

[00115] In embodiments of the new overlay determination technique, some asymmetries in radiation, excluding those caused by overlay errors, are considered and designed to measure accurate overlays (eg, target asymmetry and /). Or a mathematical model (which is robust to sensor asymmetry) is used. In one embodiment, the model involves equations based on multiple different wavelengths. In one embodiment, 16 simultaneous equations with four different wavelengths are provided as variables thereof. Therefore, in this embodiment, in order to derive the overlay value, a measure is obtained for four different wavelengths, 16 simultaneous equations are solved, and the equation has, for example, 16 unknowns.

ここで、Ｆ_１…Ｆ_１６は、最適化（例えば、それらの絶対値を最小化する）のための関数であり、ＯＶは、オーバーレイであり、λ_１…λ_４は、測定のためにターゲットを照明するように使用された照明測定放射線の異なる波長であり、Ａは、サブターゲットの上部周期構造から回析された波の振幅であり、Ｂ_１…Ｂ_４は、サブターゲットの下部周期構造から回析された波の振幅であり（この場合、４つの変数Ｂが存在し、各々は、サブターゲットと回折次数の組合せのそれぞれと関連付けられ、以下でさらに説明されるように特定の方法で互いに異なり得る（例えば、無関係であり得る）（例えば、異なる値を有する））、β_１…β_４は、下部周期構造に入射する放射線と上部周期構造に入射する放射線との間で生じる位相差であり（この例では、４つの変数βが存在し、各々は、サブターゲットと回折次数の組合せのそれぞれと関連付けられ、以下でさらに説明されるように特定の方法で互いに異なり得る（例えば、異なる値を有する））、Ｐは、ターゲットのピッチであり、ｄは、ターゲットのバイアスであり、α_１及びα_２は、センサ非対称性誤差を説明する係数であり（この例では、２つの変数αが存在し、各々は、回折次数のそれぞれと関連付けられ、以下でさらに説明されるように特定の方法で互いに異なり得る（例えば、異なる値を有する））、γ_１…γ_４は、異なる波長による測定の間の照明測定放射線強度の変化を説明する係数であり（具体的には、通常は異なる時間に行われるため、強度は、異なる波長で測定すると変化させることができる、及び／又は、強度は、異なる波長を得るために変化させることができ、その数は、波長の数に等しい）、Ｉ_ＰＢＮ、Ｉ_ＰＢＣ、Ｉ_ＮＢＮ及びＩ_ＮＢＣは、それぞれ識別された波長λ_１…λ_４の放射線を使用して測定された抽出平均強度であり、それぞれが、正のバイアス周期構造（例えば、サブターゲット６１２）からの＋１次回折の放射線（ＰＢＮ）、正のバイアス周期構造（例えば、サブターゲット６１２）からの－１次回折（ＰＢＣ）、負のバイアス周期構造（例えば、サブターゲット６１４）からの＋１次回折（ＮＢＮ）、及び、負のバイアス周期構造（例えば、サブターゲット６１４）からの－１次回折（ＮＢＣ）に対応する。 [00116] Below is an example of a set of equations for a target, such as that shown in FIG. 11E, based on four different wavelengths. Specifically, the equation is for a particular overlay direction (eg, X or Y direction) and a subtarget associated with that overlay direction. For example, the equation can be for a combination of sub-targets 612 and 614 for measuring overlays in the X direction, with sub-target 612 having a + d bias and sub-target 614 having a −d bias. Alternatively, the equation can be for a combination of sub-targets 616 and 618 for measuring overlays in the Y direction, with sub-target 616 having a + d bias and sub-target 618 having a −d bias. The simultaneous equations include the following equations.

Where F ₁ ... F ₁₆ is a function for optimization (eg, minimizing their absolute values), OV is an overlay, and λ ₁ ... λ ₄ is a target for measurement. Are the different wavelengths of the illumination measured radiation used to illuminate, where A is the amplitude of the wave diffracted from the upper periodic structure of the subtarget and _B1 ... _B4 are the lower periodic structures of the subtarget. The amplitude of the wave diffracted from (in this case, there are four variables B, each associated with each of the subtarget and diffraction order combinations, in a particular way as described further below. Beta ₁ ... β ₄ that can be different from each other (eg, can be irrelevant) (eg, have different values) are the phase differences that occur between the radiation incident on the lower periodic structure and the radiation incident on the upper periodic structure. (In this example, there are four variables β, each associated with each of the subtarget and diffraction order combinations, which can differ from each other in a particular way as further described below (eg, different). (Having a value)), P is the pitch of the target, d is the bias of the target, and α ₁ and α ₂ are coefficients that explain the sensor asymmetry error (in this example, the two variables α). Are present, each associated with each of the diffraction orders and may differ from each other in a particular way (eg, having different values) as further described below, γ ₁ ... γ ₄ due to different wavelengths. Illumination during measurement A coefficient that describes the change in measured radiation intensity (specifically, because it is usually done at different times, the intensity can be changed when measured at different wavelengths and / or intensity. Can be varied to obtain different wavelengths, the number of which is equal to the number of wavelengths), _IPBN , _IPBC , _INNB and _INBC are the identified wavelengths λ ₁ … λ ₄ respectively. The average intensity of the extractions measured using -1st order diffraction (PBC) from), + 1st order diffraction (NBN) from a negative bias periodic structure (eg, subtarget 614), and -1 from a negative bias periodic structure (eg, subtarget 614). Corresponds to the next diffraction (NBC).

[00117] In this example, four different wavelengths are used, but different numbers of wavelengths can be used. For example, two wavelengths can be used, with various assumptions. As another example, more than four wavelengths can be used. Addition of information from more than 4 (or more than 2) wavelengths can be used to increase the robustness of the model to variation. In addition to or as an alternative, using more than four wavelengths, such as spot non-uniformity (specifically, asymmetry from different sensors between positive and negative bias intensities), etc. Additional unknown parameters can be determined.

[00118] In one embodiment, different sources of error can be considered in the simultaneous equations. For example, in one embodiment, sensor asymmetry between positive-order (eg, +1-order) radiation and negative-order (eg, -1st-order) radiation, structural asymmetry of the target, and / or stack within the target. difference.

[00119] In one embodiment, the sensor asymmetry between positive order (eg, +1 order) radiation and negative order (eg, -1 order) radiation is by having different variables α ₁ and α ₂ . Be explained. In one embodiment, α ₁ corresponds to positive order (eg, +1) radiation and α ₂ corresponds to negative order (eg, -1) radiation. Normally, α ₁ and α ₂ have different values when the equation is evaluated to determine the overlay.

[00120] In one embodiment, the structural asymmetry of the target is described by having certain different amplitude B variables and certain different β variables. Specifically, in one embodiment, the radiation amplitude variable (eg, B ₁ and / or B ₃ ) for a positive value of a particular diffraction order (eg, +1 order) of the measured radiation is the measured radiation. Unlike the radiation amplitude variables for negative values of a particular diffraction order (eg, -1st order) (eg, B ₂ and / or B ₄ for B ₁ and / or B ₃ , respectively), the measured radiation. At least a phase variable of radiation for a positive value of a particular diffraction order of (eg, β ₁ and / or β ₃ ) is a phase variable of radiation for a negative value of a particular diffraction order of measured radiation (eg, β ₁ and / or β 3). / Or β ₃ is different from β ₂ and / or β ₄ ), respectively. In one embodiment, B ₁ , B ₃ , β ₁ and / or β ₃ correspond to +1 primary radiation, and B ₂ , B ₄ , β ₂ and / or β ₄ correspond to -1 primary radiation. B ₁ and B ₂ , B ₃ and B ₄ , β ₁ and β ₂ , and β ₃ and β ₄ are different when the equation is evaluated to determine the overlay, usually because of some target asymmetry. Has a value.

[00121] In one embodiment, stack differences within a target are described by having specific different amplitude B variables and specific different β variables. Specifically, in one embodiment, the radiation amplitude variable (eg, B ₁ and / or B ₂ ) to the sub-target of the target having a positive bias (eg, + d) has a negative bias (eg, −d). ) Of the target with a positive bias (eg, + _d ), unlike the amplitude variables of radiation to the subtarget of the target with) (eg, B3 and / or _B4 with respect to _B1 and / or B2 _, respectively). At least the phase variable of radiation to the subtarget (eg β ₁ and / or β ₂ ) is the phase variable of radiation to the subtarget of the target having a negative bias (eg −d) (eg β ₁ and / or β). ₂ is different from β ₃ and / or β ₄ ), respectively. In one embodiment, B ₁ , B ₂ , β ₁ and / or β ₂ correspond to sub-targets of targets with a positive bias, while B ₃ , B ₄ , β ₃ and / or β ₄ are negative. Corresponds to sub-targets of biased targets. Since there is usually some stack difference, B ₁ and B ₃ , B ₂ and B ₄ , β ₁ and β ₃ , and β ₂ and β ₄ are different values when the equation is evaluated to determine the overlay. Has.

[00122] In a further embodiment, in the simultaneous equations (9) to (24), the variable corresponding to the amplitude (A, B, etc.) is determined by the illumination condition (for example, wavelength), and the correction parameters (α ₁ and α ₂ etc.) are determined. ) Can be formed so that the variable corresponding to) is not always determined by the illumination condition (for example, wavelength). Simultaneous equations (9)-(24) may include additional offset constants to be added to each of the terms on the right side of equations (9)-(24).

[00123] Therefore, in order to evaluate equations (9)-(24), the average intensity of the target is extracted for four different wavelengths as described above for FIG. 10 (eg, by pattern recognition methods). .. Specifically, in one embodiment, _IPBN , _IPBC , _INNB and _INBC are obtained for each of λ ₁ ... λ ₄ and yield 16 intensity values. Further, the pitch P, the bias d and the wavelength values λ ₁ ... λ ₄ are known numbers in the equation. Therefore, 16 unknowns (ie, overlay OV, amplitude A, amplitude B ₁ ... B ₄ , phase difference β ₁ ... β ₄ , sensor asymmetry error coefficients α ₁ and α ₂ , and illumination measurement radiation intensity coefficient γ ₁ ). … Gamma ₄ ) exists. Equations (9)-(24) are then solved using techniques for solving nonlinear equations so that at least the overlay OV value is reached.

[00124] Therefore, in one embodiment, in order to obtain the parameters of the model (and to derive the value of the overlay OV), the optimization problem of the equation is formulated and one or more known nonlinear equation solving methods are used. Can be solved. One or more different algorithms can be used to solve optimization problems such as the interior point method and the trust region method algorithms. Moreover, by providing an analytical calculation of the gradient of the objective function and an optimization algorithm using the calculated gradient, the rate of convergence and the accuracy of the result can be significantly increased.

が定義される。したがって、最適化問題は、以下の目的関数として記載することができる。

条件：ｌｂ≦ｘ≦ｕｂ
ここで、

であり、ｌｂ及びｕｂはそれぞれ、変数の下限及び上限であり、最適化アルゴリズムの検索空間制限を厳しくするために定義される。限度は、変数の物理的解釈（例えば、Ａ、Ｂ_ｉは回析された波の振幅を表し、β_ｉは２層間の回析された波の位相差を表す）に基づいて事前決定される。 [00125] Here we discuss certain non-limiting examples of techniques for solving equations. For a clearer presentation of the final optimization problem, some auxiliary variables, ie

Is defined. Therefore, the optimization problem can be described as the following objective function.

Condition: lb ≤ x ≤ ub
here,

Lb and ub are the lower and upper limits of the variable, respectively, and are defined to tighten the search space limitation of the optimization algorithm. The limits are predetermined based on the physical interpretation of the variable (eg, A, Bi represent the amplitude of the diffracted wave and β _i represents the phase difference of the diffracted wave between the two layers ₎ . ..

に置き換える。したがって、結果として得られる最適化問題（新しい変数

に基づく）は、制約を受けないものである。
３． Ｆ’のヤコビアンを算出する。

４． ｎ＜Ｎの場合、
４．１ Ｕｎｉｆｏｒｍ（０，π）から初期点ｘ’（０）を引き出す。
４．２ ｋ≧０の場合
修正されたレーベンバーグ・マルカート反復アルゴリズムを使用して、ｘ’（ｋ＋１）を算出する。

目的関数の勾配▽Ｊ（ｘ（ｋ＋１））＝２▽Ｆ’（ｘ（ｋ＋１））Ｆ’（ｘ（ｋ＋１））を演算し、ゼロに非常に近い場合は、勾配ベクトルの最大絶対値を停止基準として取り入れる。そうでなければ、ｘの値又は目的関数の相対変化を停止基準として取り入れる。
４．３ ループ反復ｎに対応する局所的最適解ｘ^＊及びＪ^＊を格納する。また、満たされている対応する停止基準を報告する。外ループカウンタ（最適化の多スタートのために使用される）をｎ＋１に増加する。
５． 最適な目的関数の最小値Ｊ^＊を算出する（以前のステップのランダムな初期点に対して得られる）。最小最適値に対し、対応する停止基準が勾配関連のものであった（すなわち、勾配がゼロに非常に近い）かどうかをチェックする。この場合、考えられる大域的解としてこの目的値及び対応する最適点を報告する。 [00126] In order to efficiently solve this nonlinear constraint optimization problem, in one embodiment, the nonlinear optimization algorithm has several to avoid reaching only the local optimal solution and to increase the rate of convergence. Combined with mathematical techniques. The following provides an overview of the algorithm and the steps taken to solve the problem.
1. 1. The limits lb and ub are defined based on the physical knowledge of the parameter values.
2. 2. The objective function x _i

Replace with. Therefore, the resulting optimization problem (new variable)

Based on) is unconstrained.
3. 3. Calculate the Jacobian of F'.

4. When n <N,
4.1 Extract the initial point x'(0) from the Uniform (0, π).
4.2 If k ≧ 0 Use the modified Leebenberg-Marquardt iteration algorithm to calculate x'(k + 1).

Gradient of objective function ▽ J (x (k + 1)) = 2 ▽ F'(x (k + 1)) F'(x (k + 1)) is calculated, and if it is very close to zero, the maximum absolute value of the gradient vector is calculated. Incorporate as a stop criterion. If not, the relative change of the value of x or the objective function is taken as the stop criterion.
4.3 Stores the local optimal solutions x ^* and J ^* corresponding to the loop iteration n. It also reports the corresponding outage criteria that have been met. Increase the outer loop counter (used for multiple start of optimization) to n + 1.
5. Calculate the minimum value J ^* of the optimal objective function (obtained for the random initial points of the previous step). Check if the corresponding stop criteria was gradient related (ie, the gradient is very close to zero) for the minimum optimal value. In this case, this objective value and the corresponding optimum point are reported as a possible global solution.

[00127] The above disclosure obtains simultaneous equations (eg, equations (9)-(24)) by performing multiple measurements of the target at multiple wavelengths (eg, λ ₁ ... λ ₄ of the above equation). Explain that. However, the wavelength is just one example of the illumination conditions and can be modified to obtain simultaneous equations. Therefore, the concepts described herein can more generally be applied to changes in the illumination conditions of illumination radiation. For example, other lighting conditions that can be changed include polarization or angle of incidence.

[00128] The reason why it is useful to combine images of different wavelengths is the fact that many of the model parameters have wavelength dependence (dependencies that are summarized in so-called swing curves, as will be explained in more detail later). Therefore, images of different wavelengths are considered to be independent samplings of the sensors and targets taken together (thus, all error sources and overlays are combined). This independence is important. That is, each image provides unique information and can be combined or separated by a carefully selected model. Also, measurements at different polarizations highlight different interactions of light with the stack and are therefore independent (at least partially). Measurements associated with different angles of incidence may require further consideration, as described below.

[00129] In many metrological devices, such as those shown in FIG. 7A, it is the aperture 13 that determines the illumination profile (and thus at what angle of incidence it penetrates the target). Like the wavelength, the angle of incidence contributes significantly to the swing curve (due to wave interference and stack material properties), so different angles of incidence (ie, different points in the pupil) can provide independent sampling of the system. can. The concept of the swing curve is described in more detail below. Ideally, each wave should be sampled independently (ie, by scanning the laser over different angles). However, a typical metrological lighting source emits a series of waves simultaneously at different angles (because it is a partially coherent light source). Therefore, pupil sampling is currently dependent on the aperture. Many of the available apertures have overlapping lighting profiles with respect to each other and therefore do not provide completely independent samples. This is fundamentally different from images taken at different wavelengths (wavelengths have no or little spectral overlap).

[00130] Therefore, we describe several ways in which changes in lighting conditions extend to the angle of incidence. Such a method can significantly increase the number of independent images that can be supplied to a multi-image overlay extraction algorithm, such as those described by equations (9)-(24). The central idea is that separate acquisitions are performed using the smallest possible unique section of the pupil. This can be done in many ways, some of which are shown.

[00131] The first method, which does not require hardware changes, takes an image using currently available apertures and performs a linear combination of the obtained intensities, thereby providing essentially independent pupil sampling. Including making. This is an effective technique because the image is formed by the incoherent sum of all the waves involved. For example, the image A can be obtained using the first aperture plate that defines the first lighting profile and the image B can be obtained using the second aperture plate that defines the second lighting profile. , The first and second lighting profiles overlap such that the first lighting profile is completely (spatial) contained within the second lighting profile. When the images are correctly aligned, it is possible to determine the difference between the acquired image B and the acquired image A in order to obtain a new derived image C (eg, after careful normalization, eg, by energy sensor reading). can. Therefore, image C contains (mainly) information from waves outside the first aperture profile (but within the second aperture profile). Therefore, the acquired image A and the derived image C should be substantially independent and can be used in the algorithms described by equations (9)-(24), where the term λ _n is used. Then, different images and different incident angles are shown. Therefore, different bases of independent pupil sampling can be constructed from the different aperture plates available. The linear combination example above involves the difference between the two images, but the concept also includes the use of linear combinations of more than two images to obtain different bases that better match the actual swing curve of the target. It may be said that this is the case.

[00132] The advantage of this method is that the aperture plate used for each measurement can be chosen to be larger than the sampling area, which minimizes blurring and edge effects in the image and makes hardware changes. Means you don't need it.

[00133] Alternatively, the aperture profile may be selectable for defining multiple non-overlapping profiles. For example, an aperture profile (or multiple aperture profiles) can be added to the lighting mode selector (IMS), which is continuous across the pupil by rotating the IMS wheel in small steps. Can be moved. In this way, the pupil can be continuously sampled and the optimum sampling can be identified. This provides greater flexibility than the first solution because the area of the sampled aperture profile is not fixed. Also, the image blur due to these small aperture profiles will be the same over sampling. Several such aperture profiles of different lengths can be combined in the same way, as described in the first method, thereby providing an even better foundation. Note that the aperture should not be so small that the darkfield image is severely blurred.

[00134] The above solution requires sequential acquisition, which requires additional time to block the large pupil area in front of the objective lens. However, by using a wedge prism that projects different parts of the pupil onto different regions of the detection camera (eg, four quadrants measured in a single shot), we get parallel acquisition of waves moving at different angles. Can be done. Taking this wedge idea further by projecting a smaller area of the pupil's quadrant onto separate areas of the detection camera, it is synonymous with the parallel wavelengths measured in the "hyperspectral" setup. "Measurement becomes possible. Such a system can be implemented using finely segmented wedges or spatial light modulators (SLMs), where the phase of the light changes from pixel to pixel. SLMs can replace wedges and allow dynamic selection of pupil regions to be sampled at the same time (this is currently used for detection cameras at equal pixel densities to maintain adequate resolution. May require a larger total CCD area than what is being done).

[00135] The behavior of parameter values for different targets on the substrate has been found to be comparable and appear to be stable. Therefore, it is possible to use the results from a small number of targets to limit the extent of the search space for parameter optimization, which can significantly speed up the convergence of the optimization algorithm.

[00136] Therefore, with reference to FIG. 14, embodiments of the methods involved in the multi-wavelength technique described above are schematically shown. At 1400, the simultaneous equations described herein are provided. For example, a system of equations can have 16 or more equations and is a function of overlay and measured radiation wavelength. At 1410, radiation values are obtained for use in solving simultaneous equations. In one embodiment, the radiation value can be measured from a physical target on a physical substrate. In one embodiment, the radiation value can be determined by a simulator that simulates the illumination of the metrology target and the detection of radiation reguided by the metrology target. In 1420, radiation values are used in simultaneous equations to determine the values of one or more parameters of the equations. In one embodiment, the parameter for which the value is obtained is an overlay. In one embodiment, one or more of the optimization techniques described above can be used. At 1430, the application is made up of parameters for finding one or more values. For example, the parameter for which the value is determined can be an overlay determined in large quantities or as part of manufacturing and can be used, for example, to control, design, etc. aspects of the patterning process. As another example, the parameter for obtaining the value is determined for use in the design, control, etc. of the metrology process, for example, to select the conditions of the metrology process, such as the radiation wavelength used for the measurement. It can be an overlay (the metrology process can use different overlay calculation techniques such as those described above for equations (1)-(4)). Examples of the use of overlays determined for use in the design, control, etc. of metrology processes are described below in connection with FIG.

[00137] In short, a new physical model is provided from the diffraction metrology target to determine the exact overlay based on considering some parameters of the radiation scattering problem. This method can provide a more accurate determination of the overlay and / or a robust calculation of the overlay. In one embodiment, this is achieved on the basis of a mathematical description of the scattering problem, a set of nonlinear simultaneous equations for each periodic structure of multiple periodic structures and for the two diffraction orders of wave formation. Parameters are formed and include multiple wavelengths and overlays as at least some of such parameters. With this description, at least two periodic structures (two) at multiple different wavelengths (eg, four different wavelengths) to obtain multiple radiation values (eg, 16 measured or simulated intensity values). It may be sufficient to measure two diffraction orders (the periodic structure has positive and negative biases respectively). By making at least a plurality of radiation values and wavelengths known values, a nonlinear simultaneous equation can be solved, and some parameters (including overlays) of the scattering problem are unknown.

[00138] Moreover, simultaneous equations can specifically take into account the effects of structural asymmetry, stack differences and / or sensor asymmetry when calculating overlays. That is, one or more parameters of the simultaneous equations are configured to incorporate the effects of structural asymmetry, stack differences and / or sensor asymmetry in determining overlay values, as described herein. .. Therefore, this method can provide a more accurate estimate of the overlay. Moreover, in the case of sensor asymmetry, this method is used to eliminate sensor asymmetry when configured with one or more parameters for sensor asymmetry as described herein 180. The need for additional information from the degree of board rotation can be avoided. This is because the overlay determination can directly explain the sensor asymmetry by having one or more parameters for the sensor asymmetry in the simultaneous equations.

[00139] As described above, the techniques described herein can be used as the default overlay calculation method for metrology devices (eg, instead of using equation (2) or equation (4)). From a throughput standpoint, the use of this technique may be possible, for example, if switching between wavelengths is fast enough and / or solving simultaneous equations fast enough. With the development of hardware, it is possible to make actual measurements at multiple wavelengths by using high speed hardware switches to switch between different wavelengths. In addition, the solutions described herein can allow for increased speed, for example, in terms of solving nonlinear simultaneous equations to obtain overlay values. Therefore, this technique is promising as a default overlay calculation method.

[00140] Further, the measurement accuracy and / or sensitivity of the target is one or more attributes of the target itself and / or one or more attributes of the measured radiation provided to the target, such as the wavelength of radiation, the radiation. Can vary with respect to the polarization and / or radiation intensity distribution (ie, angular or spatial intensity distribution). In one embodiment, the wavelength range of radiation is limited to one or more wavelengths selected from a range (eg, from a range of about 400 nm to 900 nm). In addition, different polarization choices of the radiated beam can be provided, eg, different apertures can be used to provide different illumination shapes.

[00141] Therefore, to enable such selection and measurement, a metrology recipe can be used that specifies one or more parameters of the measurement using the measurement system. In one embodiment, the term "metrologic recipe" includes one or more parameters of the measurement itself, one or more parameters of the measured target pattern, or both.

[00142] In this regard, the pattern of the measured target (also referred to as "target" or "target structure") may be an optically measured pattern, eg, a pattern whose diffraction is measured. The target pattern to be measured may be a pattern specifically designed or selected for measurement purposes. Multiple copies of the target may be placed in many places on the board.

[00143] In one embodiment, if the metrology recipe comprises one or more parameters of the measurement itself, the one or more parameters of the measurement itself is the measurement beam and / or measurement used to make the measurement. It may contain one or more parameters for the device. For example, if the measurement used in the metrology recipe is a diffraction-based optical measurement, one or more parameters of the measurement itself are the wavelength of the measured radiation and / or the polarization of the measured radiation and / or the measured radiation intensity. Distribution and / or illumination angle of the measured radiation to the substrate (eg incident angle, azimuth angle, etc.), and / or relative orientation of the diffraction measured radiation to the pattern on the substrate, and / or of the measured point or instance of the target. It may include a number and / or the location of an instance of the target as measured on the substrate. One or more parameters of the measurement itself may include one or more parameters of the metrology device used for the measurement, which may include detector sensitivity, numerical aperture, and the like.

[00144] In one embodiment, if the metrology recipe contains one or more parameters of the measured pattern, the one or more parameters of the measured pattern will be one or more geometric features. (The shape of at least a portion of the pattern and / or the orientation of at least a portion of the pattern, and / or the pitch of at least a portion of the pattern (eg, the pitch of the upper periodic structure in a layer above the layer of the lower periodic structure). And / or the pitch of the periodic structure, including the pitch of the lower periodic structure), and / or including at least a portion of the size of the pattern (eg, CD) (eg, the CD of the features of the upper periodic structure and / or the lower periodic structure). CD of periodic structure features) and / or segmentation of periodic structure features (eg, division of periodic structure features into substructures) and / or periodic or periodic structure feature lengths), and / or It may include at least some material properties of the pattern (eg, refractive index, absorbance coefficient, material type, etc.) and / or identification of the pattern (eg, distinction between one pattern and another).

[00145] The metrology recipe can be expressed in the form of (r ₁ , r ₂ , r ₃ , ..., r _n ; t ₁ , t ₂ , t ₃ , ..., T _m ). Here, r ₁ is one or more parameters of the measurement, and t _j is one or more parameters of the one or more patterns to be measured. As will be understood, n and m may be 1. Moreover, the metrology recipe need not have both one or more parameters of the measurement and one or more parameters of the one or more patterns to be measured. It may have only one or more parameters of the measurement, or it may have only one or more parameters of the one or more patterns to be measured.

[00146] Two metrology recipes A and B can be used to measure a target, wherein the metrology recipes A and B are, for example, at different stages in which the target is measured (eg, A has a latent target). The target is measured when the image structure is provided, and B measures the target when the target does not have the latent image structure), and / or the parameters of those measurements are different. Metrology recipes A and B may at least measure different targets (eg, A measures a first target and B measures a second different target). Metrology recipes A and B may have different measurement and target measurement parameters. Substrate measurement recipes A and B do not have to be based on the same measurement technique. For example, Recipe A may be based on diffraction-based measurements and Recipe B may be based on scanning electron microscopy (SEM) or atomic force microscopy (AFM) measurements.

[00147] Therefore, another possible use of the multi-wavelength technique described herein is, for example, for metrology recipe selection performed in large quantities or prior to production measurements. Therefore, the technique can be used to provide an accurate overlay as a reference to the metrology recipe selection. That is, for example, the desired optimum of a metrology recipe (target measurement parameter combination) to obtain more accurate process parameter measurements and / or to generate measurements of the desired process parameters robust to process variability. It is desirable to reach a good choice.

[00148] Accordingly, in one embodiment, an accurate measure of the desired process parameter (eg, overlay) is generated and / or a measurement of the desired process parameter that is robust to process variability is generated 1. To determine one or more metrology recipes, the results of the multi-wavelength technique described above can be used to identify such one or more accurate and / or robust metrology recipes.

[00149] With reference to FIG. 15, one embodiment of the method of selecting a metrology recipe is schematically presented. In essence, the method is a first patterning process parameter determination technique (multi-wavelength technique described above) to determine a first value of a patterning process parameter (such as an overlay) from a metrology target illuminated by measured radiation. And so on, and a second patterning process parameter determination technique that is different from the first patterning process parameter determination technique so that multiple second values of the patterning process parameters (such as overlays) for the metrology target are reached. By using the techniques described above for equations (1)-(4) or, for example, another technique provided by a metrology device), each of the second values is determined at different wavelengths of the measured radiation. It involves identifying the measured radiation wavelength for the metrology recipe for the measurement of the metrology target based on the first and second values. Here, a more detailed example of this method using the multi-wavelength technique described above as the first patterning process parameter determination technique will be described in relation to FIG.

At [00150] 1450, a preselection is optionally performed to select multiple wavelengths of the measured radiation from a larger wavelength set of the measured radiation. An example of such preselection is described below.

[00151] In 1460, a plurality of wavelengths (eg, 1450) were preselected in combination with the multi-wavelength simultaneous equations described above (eg, the first overlay determination technique) to reach the first value of the overlay. Wavelengths or multiple wavelengths provided by other means) are used. As will be understood, the number of wavelengths should match the number for which the simultaneous equations were set up. If more are present, the best wavelength selection from multiple wavelengths that match the required number in the simultaneous equations can be selected. In one embodiment, the preselection technique provided measurement criteria for each wavelength to allow selection of the best wavelength. Alternatively, various sub-combinations of several wavelengths used in the simultaneous equations can be selected and the first of the overlays to the sub-combinations of those wavelengths to reach multiple first values of the overlay. The values were calculated (then the values can be used separately or statistically combined (eg, arithmetic mean to obtain the arithmetic mean of the first value of the overlay)). The radiation values used in the simultaneous equations can be simulated values or physically measured values.

In 1470, for example, in the situation where the metrology device provides a particular wavelength, equations (1)-(1) to derive a second value of overlay for the metrology target at each of the plurality of wavelengths. With respect to 4), the overlay determination technique described above or another overlay determination technique provided by, for example, a metrology device (eg, a second overlay determination technique) is used. In one embodiment, those wavelengths are all or a subset of the wavelengths provided by the metrology device for which the metrology recipe is selected. In one embodiment, those wavelengths are all or a subset of the wavelengths used in 1460. The radiation value used by the second overlay determination technique can be a simulated value or a physically measured value.

[00153] Then, using the second value, the wavelength at which the second value of the overlay is closest to the first value of the overlay is selected. Therefore, in one embodiment, identifying the measurement recipe wavelength is the overlay determination technique described above with respect to the second overlay determination technique (eg, equations (1)-(4) or another overlay provided by, for example, a metrology device. Which of the second values determined using the determination technique) is closest to the first value determined using the first overlay determination technique (such as the multi-wavelength technique described above). The measured wavelength identified for the metrology recipe, including identifying, is the measured radiation wavelength associated with the closest second value. In one embodiment, multiple wavelengths can be identified.

[00154] In 1480, for example, in situations where the metrology device can flexibly provide wavelengths over a wide range of wavelengths (eg, adjust a particular wavelength from a continuous range of wavelengths), each of the plurality of wavelengths. In order to derive a second value of overlay for a metrology target in, the overlay determination technique described above with respect to equations (1)-(4) or another overlay determination technique provided by, for example, a metrology device (eg, a second). Overlay determination technique) is used. In one embodiment, those wavelengths are wavelength sampling (eg, uniform sampling) over a wide range of wavelengths provided by the metrology device for which the metrology recipe is selected. In one embodiment, those wavelengths are all or a subset of the wavelengths used in 1460. The radiation value used by the second overlay determination technique can be a simulated value or a physically measured value.

[00155] Then, using the second value, the second value is fitted as a function of wavelength. The optimum wavelength is then extrapolated or interpolated from this fit having a second value equal to or closest to the first value of the overlay. Therefore, in one embodiment, identifying the measured recipe wavelength is provided by a second overlay determination technique (eg, the overlay determination technique described above with respect to equations (1)-(4) or, for example, a metrology device. The second value determined using the overlay determination technique) is applied as a function of the measured radiation wavelength, and the first overlay determination technique (such as the multi-wavelength technique described above) is used to determine the first value. Includes extrapolating or interpolating the identified measurement wavelength from the fitting, which has an overlay value that is closest to or equal to the value. In one embodiment, multiple wavelengths can be identified.

[00156] At 1490, one or more metrology recipes are output for use in the metrology process of the metrology target, and each of the one or more metrology recipes is identified from 1460, 1470 or 1480. Has a recipe. In one embodiment, the metrology recipe has a wavelength identified from 1470 or 1480 and the overlay determination technique described above with respect to the second overlay determination technique (eg, equations (1)-(4)). Or for use in a metrology process that determines overlays using, for example, another overlay determination technique provided by a metrology device). In one embodiment, a plurality of metrology recipes are provided, the plurality of metrology recipes having wavelengths identified from 1460, 1470 or 1480, and a first overlay determination technique (eg, the multi-wavelength technique described above). Is intended for use in the metrology process to determine overlays using.

[00157] FIG. 16 shows a flow chart showing a process in which a metrology recipe is used to monitor performance and as a basis for controlling a metrology, design and / or manufacturing process. In step D1, the substrate is processed to generate product features and one or more metrology targets as described herein according to applicable metrology recipes. In step D2, patterning process parameter (eg, overlay) values are measured using one or more measurement parameters of the metrology recipe, if applicable, and calculated using the method of FIG. 6 or 10. Will be done. In optional step D3, the measured patterning process parameters (eg, overlays) are used (eg, along with other information that may be available) to update the metrology recipe (eg, described herein). The wavelength can be changed using the method). The updated metrology recipe is used for remeasurement of patterning process parameters and / or for measurement of patterning process parameters for subsequent processing boards. In this way, the accuracy of the calculated patterning process parameters is improved. The update process can be automated as needed. In step D4, the patterning process parameter values are used to update the recipe that controls the lithography patterning step and / or other process steps in the device manufacturing process for rework and / or further substrate processing. Again, this update can be automated as needed.

[00158] As mentioned above, preselection can be used to reach a particular wavelength. In the following, various steps for such preselection are shown in sequence, but they do not necessarily have to be performed in that order. Moreover, not all steps need to be performed. For example, one or more of the steps may be performed. Therefore, any combination selected from the steps can be implemented.

[00159] Preselection can analyze overlay data of a metrology target for a plurality of different wavelengths. Data can be obtained from experiments or from product measurements using the target. For example, multiple instances of the target under consideration can be printed across the substrate using the patterning process in which the target is used, and then each instance can be configured with multiple different configurations using an applicable metrology device. It can be measured (eg different wavelengths). Further or alternatives, overlay measurements obtained by using metrology recipes to measure targets can be simulated. In the simulation, one or more parameters of the measurement are determined using the parameters r _i and / or t _j of the metrology recipe (eg, provided by or determined from them). For example, the radiation-target interactions corresponding to the metrology recipe can be obtained from those parameters of the metrology recipe, for example by using Maxwell solver and tightly coupled wave analysis (RCWA), or by other mathematical modeling. Can be decided. Therefore, the expected measurements using the target and associated metrology recipes can be determined from the above interactions. Thus, in certain situations, data can be obtained using a simulator of the measurement process, for example to determine a target that produces a strong signal. The simulator uses a metrology device to identify specific features by calculating the intensity measured by a detector, such as the device of FIG. 7, according to the measurement technique of the inspection device (eg, diffraction-based overlay measurement). It is possible to mathematically derive how the target of (eg, the target specified in terms of pitch, feature width, material type, etc.) is measured. To obtain robustness data, the simulator may run within a range (eg, up to 10% change, up to 5% change, up to 2% change, up to 1% change, or up to 0.5% change). Perturbations can be introduced in to mimic process variability (which can be extended across the substrate).

[00160] Thus, an experimental method or simulation can generate values for a particular parameter or index, such as OV or K, using, for example, the equations described above.

[00161] One such indicator is stack sensitivity (SS) (also considered signal contrast). Stack sensitivity can be understood as a measure of how much the signal strength changes as the overlay changes due to diffraction between target (eg, grid) layers. That is, in the context of overlay, stack sensitivity detects the contrast between the upper and lower periodic structures of the overlay target and thus represents the balance of diffraction efficiency between the upper and lower periodic structures. Therefore, stack sensitivity is an exemplary measure of the sensitivity of a measure. In one embodiment, stack sensitivity is the ratio of intensity asymmetry to arithmetic mean intensity. In one embodiment, the stack sensitivity can be formulated as SS = KL / IM, where _L is a user-defined constant (eg, in one embodiment, the value L is 20 nm and / or the value of bias d). ), And _IM is the average intensity of the measured beam diffracted by the target. In one embodiment, the stack sensitivity for metrology recipes should be maximized. However, it has become clear that the use of metrology recipes at maximum stack sensitivity may not be the best. For example, the measured beam wavelength with maximum stack sensitivity may correspond to low overlay sensitivity and low process robustness.

[00162] Examples of metrology recipe data are shown in FIGS. 17 and 18. The data can represent the dependence of the measurement data as a function of one or more metrology recipe parameters, in particular one or more parameters of the measurement itself, such as the wavelength of the measurement beam. In one embodiment, the data can represent the vibration dependence of the measured data as a function of the measured radiation wavelength (eg, the intensity obtained as field data (in the image plane) or pupil data (in the pupil plane)). .. FIG. 17 is an exemplary graph of data for a target in measurements at various wavelengths for a single polarization (in this case, linear X polarization). A curve is fitted to the data, so this representation can be called a swing curve. As you can see, you don't need to generate a graph as you can only process the data. FIG. 18 is a graph of data for a target in measurements at various wavelengths for another single polarization (in this case, linear Y polarization). In both FIGS. 17 and 18, stack sensitivity and overlay sensitivity are graphed for various measured beam wavelengths. Further, the polarization here is linear X and Y polarization, but may be different polarization or additional polarization (such as left elliptically polarized radiation or right elliptically polarized radiation).

[00163] Using this data, one or more specific metrology recipes (eg, wavelengths) are excluded from the study and a set of metrology recipes for further possible study is selected. In this case, the metrology recipes share the same target, but differ in terms of measured radiation wavelength.

[00164] Here, a particular wavelength can be removed because it exceeds the pitch / wavelength limit for that particular target. That is, the pitch of the target feature and the measured radiation wavelength are such that the measurement with this combination becomes ineffective. These one or more metrology recipes are excluded in region 1500.

[00165] A possible embodiment of this option is stack sensitivity that meets or exceeds a threshold (ie, is within a certain range of stack sensitivity values) (eg, average stack sensitivity obtained from multiple instances of the target across the substrate (and then). This can be determined for multiple substrates)) to select one or more metrology recipes. In one embodiment, stack sensitivity should be maximized (but as discussed above, without sacrificing other indicators or parameters; upper bound on stack sensitivity that can affect robustness to process variation. There can be). For example, for further study, one or more metrology recipes with an absolute value of stack sensitivity of 0.05 or greater can be selected. Of course, it is not necessary to use 0.05. In this case, the larger the number, the more measurement recipes are excluded. Therefore, the number of stack sensitivities in this case is relatively low. Therefore, one or more metrology recipes excluded by this aspect of selection are described as region 1510 (this region roughly corresponds to the wavelengths available by the inspection device in this situation. The analysis applied to the curves in FIGS. 17 and 18 is more accurate if a range is available and the inspection device can accurately and stably tune to any wavelength within that range). ..

[00166] A possible embodiment of this option is the consideration of target sigma. Target sigma (TS) can be understood as statistical variation in measured parameters (eg, overlays) for multiple measured pixels across the target. In theory, the detector should measure each pixel to read the same parameter value for a particular target. However, in reality, there may be variations between pixels. In one embodiment, the target sigma is in the form of standard deviation or dispersion. Therefore, a low value of target sigma means the desired small variability of the measured parameters across the target. High values of target sigma (TS) span target printing problems (eg, distorted grid lines), contamination problems (eg, significant particles on the target), measurement beam spot positioning problems, and / or targets. It is possible to notify the problem of measurement beam intensity variation.

[00167] Therefore, a further aspect of this selection is a target sigma that meets or exceeds the threshold (ie, is within a certain range of target sigma values) (eg, an average target sigma obtained from multiple instances of the target across the substrate). This may then be determined for multiple substrates)) by selecting one or more metrology recipes. In one embodiment, the target sigma should be minimized. For example, one or more metrology recipes with a target sigma of 10 nm or less can be selected for further study. Of course, it is not necessary to use 10 nm. In this case, smaller numbers exclude more metrology recipes. Therefore, the number of target sigma in this case is relatively high. Therefore, one or more metrology recipes excluded by this aspect of selection are described as region 1515 (this region roughly corresponds to the wavelengths available by the inspection device in this situation).

[00168] For example, in order to reduce overlay measurement error, a set of measurement conditions (eg, target selection, measurement beam wavelength, measurement beam polarization, etc.) should be selected with a large overlay sensitivity K. A possible aspect of this choice is overlay sensitivity that meets or exceeds the threshold (ie, is within a certain range of overlay sensitivity values) (eg, average overlay sensitivity obtained from multiple instances of the target across the substrate (and thus multiple). It is possible to select one or more metrology recipes having))). In one embodiment, overlay sensitivity should be maximized for metrology recipes. For example, for further study, one or more metrology recipes with an absolute value of overlay sensitivity within the absolute value range of the highest overlay sensitivity can be selected. For example, this range may be within 35%, within 30%, within 25%, within 20%, within 15%, or within 10% of the maximum overlay sensitivity value. For example, one or more metrology recipes within a range from the local minimum or maximum overlay sensitivity can be selected. For example, this range may be within 35%, within 30%, within 25%, within 20%, within 15%, or within 10% of the local minimum or maximum value. Of course, different ranges can be used. The wider the range, the more metrology recipes will be retained. Therefore, one or more metrology recipes excluded by this aspect of selection are described as region 1520 (this region roughly corresponds to the wavelengths available by the inspection device in this situation).

[00169] A possible aspect of this choice is to consider the stack difference parameter with respect to the threshold. In one embodiment, the stack difference parameter comprises lattice imbalance (GI). Thus, for example, a grid imbalance (GI) (eg, obtained from multiple instances of the target across the substrate (which can then be determined for multiple substrates)), an average grid imbalance or a variation in the grid imbalance (eg,). , Variance, standard deviation, etc.)) can be evaluated against a threshold to select one or more subsets of metrology recipes. For example, for further study, one or more metrology recipes with a lattice imbalance of 0.05 or 5% or less can be selected. Of course, it is not necessary to use 0.05 or 5%. In one embodiment, the stack difference parameter is minimized.

[00170] A possible embodiment of this option is to evaluate a self-reference index, which is obtained from multiple instances of the target across the substrate (which can then be determined for multiple substrates) against the threshold. .. In one embodiment, the self-reference index is a self-reference performance parameter obtained using the A ₊ vs. A _- analysis described in WO 2015/018625, which is incorporated herein by reference in its entirety. (Eg overlay), or includes it.

[00171] The A ₊ vs. A _- analysis in this context provides a metrology recipe for multiple instances of a target with a periodic structure with a positive bias (A ₊ ) and a periodic structure with a negative bias (A- ₎ . Means to evaluate. Therefore, for overlays as performance parameters, for each metrology recipe, and for each instance of the target, A ₊ and A _- are determined and the determined A ₊ value is evaluated against the determined A-value. Then, a fitting is generated through such data, and the value associated with that fitting corresponds to the more accurate value of the actual overlay for the target instance. This is repeated for each instance of the target, producing multiple values for the self-referencing performance parameter. In one embodiment, the plurality of values are averaged to produce a more accurate value of the arithmetic mean (eg, average) of the actual overlay across the substrate (where each instance of the target has the same overlay). Suppose).

[00172] FIG. 19 is an exemplary plot of A ₊ vs. A- for overlay grids without feature asymmetry, just as the only asymmetry that exists is bias and overlay asymmetry. show. In this case, the relationship between A ₊ and A- is on a straight line through the origin (because feature asymmetry is not assumed). The corresponding A ₊ vs. A _- data points for all metrology recipes are on this line. The slope of this line (fitting) is related to the more accurate value of the actual overlay. FIG. 19 shows a dotted line representing OV = 0 (a line showing a zero overlay with a slope of -1) and a dotted line representing OV∞ (a line with a slope of +1 and a slope approaching infinity). Line), a solid line represented by OV <0 (a line with a slope less than -1 and showing an overlay less than 0), and a solid line represented by OV> 0 (with a slope greater than -1). , A line indicating an overlay greater than zero). Further, it can be seen that an overlay equal to + d (where d is the grid bias) results in lines plotted along the y-axis, and an overlay equal to -d results in lines plotted along the x-axis. ..

[00173] Therefore, A ₊ vs. A-regression provides a more accurate value of the overlay as if there were no contributions due to feature asymmetry by determining the slope of the fitting line through the dataset. Can be done. This line does not always fit through the origin. Optionally, feature asymmetry can be determined by the offset of the fitting line from the origin (eg, the intercept term).

[00174] Further, the actual measurement of the overlay can be determined for each instance of the target and for each metrology recipe (assuming each instance of the target has the same overlay). These values can be processed statistically to generate the arithmetic mean and statistical variability (eg, standard deviation) of the overlay for a particular metrology recipe.

[00175] The self-reference indicator can then be a comparison of the determined more accurate value of the overlay with the measured value of the overlay for a particular metrology recipe. In one embodiment, the self-reference index is the difference between the more accurate value of the determined arithmetic mean of the actual overlay and the sum of the arithmetic mean measurement of the overlay and three times the standard deviation. Can be evaluated against a threshold (eg, a metrology recipe is selected if the self-reference index in this case is 3 nm or less, although values different from 3 nm can be used). Therefore, this self-reference indicator is practically a residual fingerprint across the substrate. In one embodiment, the self-reference index should be minimized.

[00176] Therefore, in practice, this technique applies process parameters (eg, overlays) to the asymmetry of periodic structures (eg, bias overlay grids) detected using several different metrology recipes across the substrate. ) Accompanied by generating a self-referenced fingerprint with a more accurate value. A more accurate self-referenced process parameter value (eg, overlay) is then compared to the measured value of the process parameter (eg, overlay) of one or more metrology recipes, which one or more metrology recipes. Helps identify whether to produce results close to self-reference fingerprints and use one or more of those metrology recipes to ensure the accuracy of the measurements.

As a result, one or more metrology recipes (eg, measurement wavelengths) should remain after the one or more evaluations described above (of course, if no metrology recipes remain). One or more other metrology recipe parameters (eg, one or more parameters of the target itself) may need to be modified). At this point, one or more selected metrology recipes for preselection can be output and used in step 1460.

[00178] Accordingly, in one embodiment, for example, using the multi-wavelength technique described above, a method for accurately calculating the overlay is provided, and as a result, the metrology is used using the exact overlay. The selection of the optimal metrology recipe is guided so that the overlay measured using the recipe is more accurate or most accurate. Therefore, rather than the recipe selection algorithm reaching the "optimal" metrology recipe for accurate overlays based on approximate or heuristic steps, the methods described herein apply the multi-wavelength technique described above to recipe selection. And therefore, it provides a metrology recipe selection using a more analytically based format.

[00179] As a further note, in most cases, as long as the stack sensitivity is not too low (ie, not too noisy at the input), even if constrained by working with non-optimal wavelengths, it is mentioned above. Multi-wavelength techniques can still determine the exact overlay (for any application, such as for metrology recipe selection or for high volume or manufacturing measurements). Penalties for working with non-optimal wavelengths are situations where the inputs are too noisy (eg, low stack sensitivity) and / or the wavelengths are too far apart from each other and the material of the metrological target is highly wavelength dependent. It can be an inaccurate overlay in. However, in most cases, these situations are unlikely to occur in a well-designed metrology process with a well-designed metrology target.

[00180] In one embodiment, a method of determining patterning process parameters from a metrology target, obtaining multiple values of diffracted radiation from the metrology target, where each value of the plurality of values is relative to the target. Methods are provided that correspond to, obtain, and use a combination of values to determine the same value of the patterning process parameter for the target, corresponding to different wavelengths of the illumination radiation.

[00181] In one embodiment, the value of diffracted radiation is obtained for each of at least four wavelengths of the plurality of wavelengths. In one embodiment, the target comprises at least two sub-targets, each sub-target has a different bias, and each value corresponds to diffracted radiation from a particular sub-target. In one embodiment, the values correspond separately to positive radiation of a particular diffraction order of diffracted radiation and negative radiation of a particular diffraction order of diffracted radiation. In one embodiment, using a combination of values to determine the same value for a patterning process parameter involves using a system of equations containing each of a plurality of wavelengths as a variable in at least one of the system of equations. .. In one embodiment, the simultaneous equations include at least 16 equations. In one embodiment, the simultaneous equations contain up to 16 unknowns. In one embodiment, the target comprises an upper periodic structure and a lower periodic structure, and each equation of the simultaneous equation is a function of a variable representing the amplitude of radiation from the lower periodic structure of the target and a variable representing the phase of radiation from the target. The at least amplitude variable of radiation for a positive value of a particular diffraction order of diffracted radiation is different from the amplitude variable of radiation for a negative value of a particular diffractive order of diffracted radiation. At least the phase variable of radiation for a positive value of a particular diffraction order of is different from the phase variable of radiation for a negative value of a particular diffraction order of diffracted radiation. In one embodiment, the target comprises a subtarget of the target having a positive bias of the periodic structure and a subtarget of the target having a negative bias of the periodic structure, and each equation of the simultaneous equation is of radiation from the target. At least the amplitude variable of radiation for a subtarget with a positive bias contains one or more terms that are a function of the variable representing the amplitude and the variable representing the phase of radiation from the target, with respect to the subtarget with a negative bias. Unlike the amplitude variable of radiation, at least the phase variable of radiation for a subtarget with a positive bias is different from the phase variable of radiation for a subtarget with a negative bias. In one embodiment, each equation of simultaneous equations comprises one or more terms that are a function of variables representing the sensor asymmetry error. In one embodiment, at least the sensor asymmetry error variable of radiation for a positive value of a particular diffraction order of diffracted radiation is different from the sensor asymmetry error variable of radiation for a negative value of a particular diffraction order of diffracted radiation. In one embodiment, using simultaneous equations involves solving a non-linear simultaneous equation to reach the values of the patterning process parameters. In one embodiment, the patterning process parameter is an overlay. In one embodiment, the diffracted radiation value is the diffraction value obtained from the measurement of the metrologi target on the substrate processed using the patterning process. In one embodiment, the diffracted radiation value is a diffracted value obtained from a simulation of the measurement of a metrology target.

[00182] In one embodiment, the first patterning process parameter determination technique is used to determine the first value of the patterning process parameter from the metrology target illuminated by the measured radiation, and to the metrology target. By using a second patterning process parameter determination technique that is different from the first patterning process parameter determination technique so that a plurality of second values of the patterning process parameter are reached, each of the second values is Includes the use, which is determined by different wavelengths of the measured radiation, and the identification of the measured radiation wavelength for the metrology recipe for the measurement of the metrology target based on the first and second values. The method is provided.

[00183] In one embodiment, identifying includes identifying which of the second values is closest to the first value, and the identified measurement wavelength is the closest second value. The measured radiation wavelength associated with. In one embodiment, the identification is a measurement identified from the fitting, which fits the second value as a function of the measured radiation wavelength and has a patterning process parameter value closest to or equal to the first value. Includes extrapolating or interpolating wavelengths. In one embodiment, the first patterning process parameter determination technique is to obtain a plurality of values of diffracted radiation from a metrology target, where each value of the plurality of values is among the plurality of wavelengths of measured radiation relative to the target. Corresponding to different wavelengths of, and using a combination of values to determine the same value of patterning process parameters for the target. In one embodiment, the method further comprises performing preselection of multiple wavelengths from a larger wavelength set based on measurement criteria. In one embodiment, the metric includes stack sensitivity that is below a certain threshold. In one embodiment, the value of diffracted radiation is obtained for each of at least four wavelengths of the plurality of wavelengths. In one embodiment, the target comprises at least two sub-targets, each sub-target has a different bias, and each value corresponds to diffracted radiation from a particular sub-target. In one embodiment, the values correspond separately to positive radiation of a particular diffraction order of diffracted radiation and negative radiation of a particular diffraction order of diffracted radiation. In one embodiment, using a combination of values to determine the same value for a patterning process parameter involves using a system of equations containing each of a plurality of wavelengths as a variable in at least one of the system of equations. .. In one embodiment, the simultaneous equations include at least 16 equations. In one embodiment, the simultaneous equations contain up to 16 unknowns. In one embodiment, using simultaneous equations involves solving a non-linear simultaneous equation to reach the values of the patterning process parameters. In one embodiment, the patterning process parameter is an overlay. In one embodiment, the values are obtained from measurements of metrological targets on the substrate processed using a patterning process. In one embodiment, the values are obtained from a simulation of the measurement of a metrology target.

[00184] The embodiments described above have been described with respect to diffraction-based overlay measurements on the field surface (eg, measurements made using the second measurement branch of the device shown in FIG. 7A), but in principle. The same model can be used for pupil-based overlay measurements (eg, measurements made using the first measurement branch of the device shown in FIG. 7A). Therefore, it should be understood that the concepts described herein are similarly applicable to diffraction-based overlay measurements on field and pupillary surfaces.

[00185] Embodiments of the metrology targets and process parameters described herein have often been described with respect to overlay targets used to measure overlays, but embodiments of the metrology targets described herein are described. It can also be used to measure one or more additional or alternative patterning process parameters. For example, a metrology target can be used to measure exposure fluctuations, exposure focus / defocus, edge-mounted measurement errors, CD measurements, and the like. Further, the description in the present specification can be applied to alignment of a substrate and / or a patterning device in a lithography apparatus using an alignment mark, with appropriate modifications. Similarly, an appropriate recipe for alignment measurements can be determined.

[00186] Therefore, the performance parameter of interest is an overlay, but other parameters of the performance of the patterning process (eg, dose amount, focus, CD, etc.), eg, with appropriate modifications to the multi-wavelength equation, are booked. It can also be determined using the method described herein. Performance parameters (eg, overlay, CD, focus, dose amount, etc.) can be fed back (or feedforward) to improve the patterning process, target, and / or the modeling, measurement described herein. And can be used to improve the calculation process.

[00187] The target structure described above is a metrology target specifically designed and formed for measurement purposes, but in other embodiments it is characterized with respect to the target, which is a functional part of the device formed on the substrate. Can be measured. Many devices have a regular periodic structure that resembles a grid. As used herein, the term "target", "grid", or "periodic structure" of a target does not require that the applicable structure be provided specifically for the measurements performed. .. In addition, the pitch P of the metrology target may be close to the resolution limit of the measurement tool's optical system, but much larger than the dimensions of typical product features formed in the target portion C by the patterning process. In practice, the features and / or spaces of the periodic structure may be formed to include smaller structures similar in size to the product features.

[00188] In connection with the physical structure of the target as realized by the substrate and patterning device, one embodiment comprises a computer program containing one or more sequences of machine-readable instructions and / or functional data. These machine-readable instructions and / or functional data describe the target design, describe how to design the target for the board, describe how to generate the target on the board, and measure the target on the board. Describe the method and / or describe how to analyze the measurements to obtain information about the patterning process. This computer program can be executed, for example, in the unit PU in the apparatus of FIG. 7 and / or in the control unit LACU of FIG. A data storage medium (eg, a semiconductor memory or a magnetic or optical disk) that stores such a computer program can also be provided. For example, if an existing inspection device of the type shown in FIG. 7 is already in production and / or in use, embodiments have been updated to allow the processor to perform one or more of the methods described herein. It can be carried out by providing a computer program product. The program can optionally be configured to control the optical system, substrate support, etc. to implement a method of measuring parameters of the patterning process for a plurality of suitable targets. The program can update the lithography and / or metrology recipes for further substrate measurements. The program can be configured to control the lithography equipment (directly or indirectly) for further substrate patterning and processing.

[00189] Further, in the present specification, an embodiment has been described with respect to a diffraction-based metrology method for measuring the relative position of overlapping periodic structures, for example, from the intensity from the diffraction order. However, embodiments herein can also be applied to image-based metrology, with appropriate modifications if necessary, for example, using a high quality image of the target to target Layer 1. The relative position from 1 to the target 2 of the layer 2 is measured. Usually, these targets are periodic structures or "boxes" (Box-in-Box (BiB)).

[00190] As used herein, the terms "optimize" and "optimize" mean or mean to regulate an apparatus and / or process of a patterning process, which refers to a lithography process or apparatus. It may include adjusting, or adjusting a metrology process or device (eg, target, measuring tool, etc.), whereby the performance index has a more desirable value, such as a measure, pattern formation and /. Or the device manufacturing result and / or the process has one or more desirable features, for example, the projection of the design layout onto the substrate is more accurate and the process window is wider. Therefore, "optimize" and "optimize" are one or more values for one or more design variables that result in an improvement in figure of merit, eg, local optimization, compared to an initial set of values for the design variables. Represents or means the process of identification. "Optimal" and other related terms should be interpreted accordingly. In one embodiment, the optimization steps can be iteratively applied to further improve one or more figure of merit.

[00191] An embodiment of the invention is a computer program comprising one or more sequences of machine-readable instructions describing the methods disclosed herein, or data storage in which such computer programs are stored. It can take the form of a medium (eg, semiconductor memory, magnetic or optical disk). Further, machine-readable instructions can be embodied in two or more computer programs. The two or more computer programs may be stored in one or more different memories and / or data storage media.

[00192] One or more aspects disclosed herein can be implemented within a control system. Any control system described herein, individually or in combination, may operate when one or more computer programs are read by one or more computer processors located within at least one component of the device. Can be. The control system, individually or in combination, can have any suitable configuration for receiving, processing, and transmitting signals. One or more processors are configured to communicate with at least one of the control systems. For example, each control system may include one or more processors for executing computer programs including machine-readable instructions for the methods described above. The control system can include a data storage medium for storing such computer programs and / or hardware for receiving such media. Therefore, the control system can operate according to machine-readable instructions of one or more computer programs.

[00193] Although specific references could be made above to the use of embodiments in the context of optical lithography, of course, embodiments of the present invention are used in other applications such as imprint lithography. It is not limited to optical lithography if it can be used and the situation allows. In imprint lithography, the topography of the patterning device defines the pattern formed on the substrate. The topography of the patterning device can be pressed against the resist layer supplied to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has hardened, the patterning device is pulled away from the resist, leaving a pattern in the resist.

[00194] The terms "radiation" and "beam" as used herein are ultraviolet (UV) (eg, having wavelengths of 365, 355, 248, 193, 157, or 126 nm, or near them). ) Lines and extreme ultraviolet (EUV) rays (eg, having wavelengths in the range of 5-20 nm), as well as all types of electromagnetic radiation including particle beams such as ion beams or electron beams.

[00195] The term "lens" is used, where the situation allows, any one of various types of optical components, including refracting, reflective, magnetic, electromagnetic, and electrostatic optical components, or It can refer to a combination of them.

[00196] The aforementioned description of a particular embodiment reveals the general nature of the embodiments of the present invention, so that others may apply knowledge within the skill of one of ordinary skill in the art to excessive. Such particular embodiments can be easily modified and / or adapted to a variety of applications without experimentation and without departing from the general concepts of the invention. .. Accordingly, such conformances and modifications are intended to be within the spirit and scope of the disclosed embodiments equivalent, based on the teachings and guidance presented herein. As a matter of course, the terminology or terminology herein is for illustration purposes and is not intended to be limiting, and the terminology or terminology herein is in the light of teaching and guidance. Should be interpreted by peers.

[00197] Further embodiments of the present invention are described in the following numbered clauses.
1. 1. A method of determining patterning process parameters from a metrology target,
Obtaining multiple values of diffracted radiation from a metrology target, where each value of the multiple values corresponds to a different illumination condition of the multiple illumination conditions of the illumination radiation to the target.
Using a combination of values to determine the same value for the patterning process parameters for the target,
Including, how.
2. 2. The method of clause 1, wherein the value of diffracted radiation is obtained for each of at least four lighting conditions out of a plurality of lighting conditions.
3. 3. The method of clause 1 or 2, wherein the target comprises at least two sub-targets, each sub-target has a different bias, and each value corresponds to diffracted radiation from a particular sub-target.
4. The method according to any one of Articles 1 to 3, wherein the value separately corresponds to a positive value radiation of a specific diffraction order of diffracted radiation and a negative value radiation of a specific diffraction order of diffracted radiation. ..
5. Using a combination of values to determine the same value for a patterning process parameter comprises using a simultaneous equation containing each of multiple lighting conditions as a variable in at least one of the simultaneous equations, clauses 1-. The method according to any one of 4.
6. The method of clause 5, wherein the system of equations comprises at least 16 equations.
7. The method of clause 5 or 6, wherein the simultaneous equations contain up to 16 unknowns.
8. The target contains an upper periodic structure and a lower periodic structure, and each equation of the simultaneous equations is one that is a function of a variable representing the amplitude of radiation from the lower periodic structure of the target and a variable representing the phase of radiation from the target. The specific diffraction order of the diffracted radiation is different from the amplitude variable of the radiation for the negative value of the specific diffractive order of the diffracted radiation, which contains multiple terms and the at least amplitude variable of the radiation for the positive value of the specific diffractive order of the diffracted radiation. 5. The method of any one of clauses 5-7, wherein at least the phase variable of the radiation with respect to the positive value of is different from the phase variable of the radiation with respect to the negative value of the particular diffraction order of the diffracted radiation.
9. The target includes a sub-target of the target having a positive bias of the periodic structure and a sub-target of the target having a negative bias of the periodic structure, and each of the simultaneous equations is a variable representing the amplitude of radiation from the target. And at least the amplitude variable of radiation to a subtarget with a positive bias, including one or more terms that are functions of variables representing the phase of radiation from the target, the amplitude variable of radiation to a subtarget with a negative bias. The method of any one of clauses 5-8, wherein at least the phase variable of radiation to a subtarget having a positive bias is different from the phase variable of radiation to a subtarget having a negative bias.
10. The method of any one of clauses 5-9, wherein each equation of the system of equations comprises one or more terms that are a function of a variable representing the sensor asymmetry error.
11. The method of clause 10, wherein at least the sensor asymmetry error variable of radiation for a positive value of a particular diffraction order of diffracted radiation is different from the sensor asymmetry error variable of radiation for a negative value of a particular diffraction order of diffracted radiation.
12. The method of any one of clauses 5-11, wherein using the simultaneous equations comprises solving the nonlinear simultaneous equations to reach the values of the patterning process parameters.
13. The method according to any one of clauses 1 to 12, wherein the patterning process parameter is an overlay.
14. The method according to any one of clauses 1 to 13, wherein the value of diffracted radiation is a diffraction value obtained from a measurement of a metrology target on a substrate treated using a patterning process.
15. The method according to any one of Articles 1 to 14, wherein the value of diffracted radiation is a diffraction value obtained from a simulation of measurement of a metrology target.
16. The method according to any one of Articles 1 to 15, wherein the lighting conditions include wavelength and / or polarization.
17. The method according to any one of clauses 1 to 15, wherein the illumination conditions include an angle of incidence with respect to the target.
18. 17. The method of clause 17, wherein the plurality of values of diffracted radiation include values associated with each corresponding image, each of which corresponds to a different non-overlapping illumination profile of the illumination radiation.
19. The image includes a derived image, and each of the derived images has two or more to remove information related to a portion of the acquired lighting profile that overlaps with the acquired lighting profile associated with another of the images. 28. The method of clause 18, wherein the acquired lighting profile, obtained from a linear combination of the acquired images, comprises the actual lighting profile used to acquire the image.
20. Using the first patterning process parameter determination technique to determine the first value of the patterning process parameter from the metrology target illuminated by the measured radiation,
The second value is to use a second patterning process parameter determination technique that is different from the first patterning process parameter determination technique so that the plurality of second values of the patterning process parameter for the metrology target are reached. Each of them is determined by different lighting conditions of the measured radiation,
Identifying the lighting conditions of the measured radiation for the metrology recipe for the measurement of the metrology target based on the first and second values.
Including, how.
21. Identification involves identifying which of the second values is closest to the first value, and the identified measurement lighting conditions are of the measured radiation associated with the closest second value. The method described in Article 20, which is a lighting condition.
22. Identifying the measured illumination conditions identified from the fitting, which fits the second value as a function of the illumination conditions of the measured radiation and has the values of the patterning process parameters closest to or equal to the first value. The method of clause 20, including extrapolation or interpolation.
23. The first patterning process parameter determination technique
Obtaining multiple values of diffracted radiation from a metrology target, where each value of the multiple values corresponds to a different lighting condition among the multiple lighting conditions of the measured radiation for the target.
Using a combination of values to determine the same value for the patterning process parameters for the target,
The method according to any one of Articles 20 to 22, including.
24. 23. The method of clause 23, further comprising performing preselection of multiple lighting conditions from a larger set of lighting conditions based on metric.
25. 24. The method of clause 24, wherein the metric comprises a stack sensitivity that is less than or equal to a particular threshold.
26. The method according to any one of Articles 23 to 25, wherein the value of diffracted radiation is obtained for each of at least four lighting conditions among a plurality of lighting conditions.
27. 13. Method.
28. The method according to any one of Articles 23 to 27, wherein the value separately corresponds to a positive value radiation of a specific diffraction order of diffracted radiation and a negative value radiation of a specific diffraction order of diffracted radiation.
29. Using a combination of values to determine the same value for a patterning process parameter comprises using a system of equations containing each of multiple lighting conditions as a variable in at least one of the system of equations, clause 23-. The method according to any one of 28.
30. 29. The method of clause 29, wherein the system of equations comprises at least 20 equations.
31. The method of clause 29 or 30, wherein the simultaneous equations contain up to 20 unknowns.
32. The method of any one of clauses 29-31, wherein using the simultaneous equations comprises solving a non-linear simultaneous equations such that the values of the patterning process parameters are reached.
33. The method of any one of clauses 20-32, wherein the patterning process parameter is an overlay.
34. The method of any one of clauses 20-33, wherein the values are obtained from measurements of a metrological target on a substrate processed using a patterning process.
35. The method of any one of clauses 20-34, wherein the value is obtained from a simulation of the measurement of a metrology target.
36. The method of any one of clauses 1-35, wherein the illumination conditions include wavelength and / or polarization.
37. The method according to any one of clauses 1 to 35, wherein the illumination condition includes an angle of incidence with respect to the target.
38. A measurement method comprising measuring a metrology target on a substrate according to the metrology recipe according to any one of clauses 20-37.
39. A metrology device for measuring parameters of a lithography process, which is capable of operating to perform the method according to any one of clauses 1-38.
40. A non-temporary computer program product comprising a machine-readable instruction for causing a processor to perform the method according to any one of clauses 1-38.
41. An inspection device configured to provide a radiation beam to the metrology target on the substrate and detect the radiation diffracted by the target.
With the non-temporary computer program products described in Clause 40,
The system.
42. Further lithographic equipment comprising a support structure configured to hold a patterning device to modulate the radiated beam and a projected optical system arranged to project the modulated radiated beam onto a radiation sensitive substrate. The system according to clause 41.
[00198] The breadth and scope of the invention should not be limited by any of the above exemplary embodiments, but should be defined only by the appended claims and their equivalents.

Claims (14)

A method of determining patterning process parameters from a metrology target,
Obtaining a plurality of values of diffracted radiation from the metrology target, wherein each value of the plurality of values corresponds to a different lighting condition among the plurality of lighting conditions of the illumination radiation for the metrology target. ,
Using the combination of the plurality of values corresponding to the different lighting conditions to determine the same value of the patterning process parameter for the metrology target, and
Including
Using the combination of the plurality of values to determine the same value of the patterning process parameter may include the plurality of unknowns for each of the plurality of lighting conditions as variables in at least one of the simultaneous equations. Including the use of equations
The method comprising said that the plurality of unknowns includes an overlay, the amplitude of the diffracted radiation, the phase difference between the illuminated radiation, the sensor asymmetry error coefficient, and the illumination measured radiation intensity coefficient. The method according to claim 1, wherein the value of the diffracted radiation is obtained for each of at least four lighting conditions among the plurality of lighting conditions. The metrology target comprises at least two sub-targets.
Each subtarget has a different overlay bias and
The method of claim 1 or 2, wherein each of the above values corresponds to diffracted radiation from a particular subtarget. Any one of claims 1 to 3, wherein the value separately corresponds to a positive value radiation of a specific diffraction order of the diffracted radiation and a negative value radiation of the specific diffraction order of the diffracted radiation. The method described in the section. The method according to any one of claims 1 to 4, wherein the simultaneous equations include at least 16 equations. The method according to any one of claims 1 to 5, wherein the simultaneous equations include an unknown number corresponding to the number of equations included in the simultaneous equations at a maximum. The metrology target comprises an upper periodic structure and a lower periodic structure.
Each of the simultaneous equations contains a function consisting of one or more terms.
One of the terms constituting the function includes a variable representing the amplitude of radiation from the lower periodic structure of the metrology target and a variable representing the phase of radiation from the metrology target .
The at least amplitude variable of the radiation with respect to the positive value of the particular diffraction order of the diffracted radiation is different from the amplitude variable of the radiation with respect to the negative value of the particular diffraction order of the diffracted radiation.
6. The method described in item 1. The metrology target comprises a subtarget of the metrology target having a positive overlay bias of the periodic structure and a subtarget of the metrology target having a negative overlay bias of the periodic structure.
Each of the simultaneous equations contains a function consisting of one or more terms.
One of the terms constituting the function includes a variable representing the amplitude of radiation from the metrology target and a variable representing the phase of radiation from the metrology target .
The at least amplitude variable of radiation to the sub-target with the positive overlay bias is different from the amplitude variable of radiation to the sub-target with the negative overlay bias.
The invention according to any one of claims 1 to 7, wherein at least the phase variable of the radiation to the sub-target having the positive overlay bias is different from the phase variable of the radiation to the sub-target having the negative overlay bias. Method. Each of the simultaneous equations contains a function consisting of one or more terms.
The method according to any one of claims 1 to 8, wherein any one of the terms constituting the function includes a variable representing a sensor asymmetry error. 9. Claim 9 where at least the sensor asymmetry error variable of the radiation with respect to the positive value of the particular diffraction order of the diffracted radiation is different from the sensor asymmetry error variable of the radiation with respect to the negative value of the particular diffraction order of the diffracted radiation. The method described. The method of any one of claims 1-10, wherein using the simultaneous equations comprises solving the nonlinear simultaneous equations such that the values of the patterning process parameters are reached. A metrology device for measuring the parameters of the lithography process.
A metrology device capable of operating to perform the method according to any one of claims 1-11. A computer program comprising a machine-readable instruction for causing a processor to execute the method according to any one of claims 1 to 11. An inspection device configured to provide a radiation beam to the metrology target on the substrate and detect the radiation diffracted by the metrology target.
The computer program according to claim 13 and
The system.

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