Metrology systems and lithography systems

Abstract

The present invention provides a metrology system comprising a pre-alignment metrology tool capable of operating to measure multiple targets on a substrate in order to acquire measurement data, and a processing unit. [Solution] The processing unit is operable to process measurement data to determine, for each target, at least one position distribution that describes the variation in position values ​​over at least a portion of the target, and to determine a measurement correction from that at least one position distribution to correct for intra-target variation in each of the targets, and the measurement correction for correcting the measurement is performed by an alignment sensor.

Description

[Technical Field]

[0001] Cross-reference of related applications

[0001] This application claims priority to European Application No. 20207987.7, filed on 17 November 2020, which is incorporated herein by reference in its entirety. [Background technology]

[0002]

[0002] The present invention relates to a method and apparatus that can be used, for example, in the manufacture of a device by lithography technology, and to a method for manufacturing a device using lithography technology. More particularly, the present invention relates to a metrologic sensor such as a position sensor.

[0003]

[0003] A lithography apparatus is a machine that applies a desired pattern to a substrate, usually to a target area of ​​the substrate. Lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device, also called a mask or reticle, can be used to generate the circuit pattern to be formed on individual layers of the IC. This pattern can be transferred to a target area on a substrate (e.g., a silicon wafer) (e.g., including a part of a die, one die, or several dies). The transfer of the pattern is usually done by imprinting it onto a layer of radiation-sensitive material (resist) provided on the substrate. Generally, a single substrate contains a network of adjacent target areas to which patterns are sequentially applied. These target areas are generally called "fields".

[0004]

[0004] In the manufacture of complex devices, typically many lithography patterning steps are performed, thereby forming functional features on successive layers on a substrate. Therefore, a crucial aspect of the performance of a lithography apparatus is its ability to accurately and precisely position the applied pattern relative to features defined on previous layers (by the same or different lithography apparatus). For this purpose, one or more sets of alignment marks are provided on the substrate. Each mark is constructed such that its position can be later measured using a position sensor, typically an optical position sensor. A lithography apparatus includes one or more alignment sensors, which can accurately measure the position of the marks on the substrate. Various types of marks and various types of alignment sensors are known from different manufacturers and from different products of the same manufacturer.

[0005]

[0005] In other applications, metrologic sensors are used to measure exposed structures on a substrate (in and / or after etching). A dedicated inspection tool in a fast, non-invasive form is the scatromometer. In a scatromometer, a radiation beam is directed at a target on the surface of the substrate, and the properties of the scattered or reflected beam are measured. Known examples of scatromometers include angle-resolved scatromometers of the type described in U.S. Patent Application Publication 2006033921A1 and U.S. Patent Application Publication 2010201963A1. In addition to measuring feature shapes by reconstruction, diffraction-based overlays can be measured using devices such as those described in U.S. Patent Application Publication 2006066855A1. Diffraction-based overlay metrologic with diffraction-order dark-field imaging enables overlay measurements for smaller targets. Examples of dark-field imaging metrometry can be found in International Patent Publication Nos. 2009 / 078708 and 2009 / 106279. Both documents are incorporated herein by reference in their entirety. Further developments of the technology are described in U.S. Patent Publication Nos. 20110027704A, 20110043791A, 2011102753A1, 20120044470A, 20120123581A, 20130258310A, 20130271740A, and International Publication No. 2013178422A1. These targets can be smaller than the illumination spot and can be surrounded by the product structure on the wafer. Using a composite grid target, multiple grids can be measured within a single image. The contents of all these applications are also incorporated herein by reference.

[0006]

[0006] In some metrologic applications, such as some scatorometers or alignment sensors, it is often desirable to be able to measure increasingly smaller targets while maintaining compatibility with current or larger target sizes.

[0007]

[0007] The metrology targets or marks used for alignment typically include asymmetries due to processing effects and other issues, which can have an undesirable impact on the measurement position, similar to the interaction between non-ideal marks and non-ideal sensors. It is desirable to improve the accuracy of the alignment method for such imperfect targets.

Summary of the Invention

[0008]

[0008] The present invention in a first aspect provides a pre-alignment metrology tool operable to measure a plurality of targets on a substrate to obtain measurement data, and a processing unit operable to process the measurement data to determine, for each target, at least one position distribution that describes the variation of position values over at least a part of that target, and to determine measurement corrections to correct the intra-target variation in each of the targets from the at least one position distribution, wherein the measurement corrections for correcting the measurements are performed by an alignment sensor.

[0009]

[0009] The above and other aspects of the present invention will be understood from the consideration of the examples described hereinafter.

Brief Description of the Drawings

[0010]

[0010] Embodiments of the present invention will be described below by way of example only with reference to the accompanying drawings.

[0011] [Figure 1] A lithographic apparatus is illustrated. [Figure 2] Schematically shows the measurement process and the exposure process in the apparatus of FIG. 1. [Figure 3] Schematic diagram of an example of a metrology device adaptable according to an embodiment of the present invention. [Figure 4]The system includes (a) an pupil image of the input radiation, (b) an pupil image of the off-axis illumination beam illustrating the operating principle of the metronidology device in Figure 3, and (c) an pupil image of the off-axis illumination beam illustrating another operating principle of the metronidology device in Figure 3. [Figure 5] (a) an example of a target usable for alignment, (b) a pupil image of the detection pupil corresponding to single-order detection, (c) a pupil image of the detection pupil corresponding to four diffraction orders, and (d) a schematic example of the interference pattern imaged following the measurement of the target in Figure 4(a). [Figure 6] The interference patterns corresponding to (a) the first substrate position and (b) the second substrate position, which are imaged during alignment measurement, are schematically shown. [Figure 7] This is a flowchart of the method according to one embodiment of the present invention. [Figure 8] (a) A weighting determination of the position distribution according to one embodiment of the present invention, and (b) a weighting determination of the position distribution and non-position parameter distribution according to one embodiment of the present invention are conceptually shown. [Modes for carrying out the invention]

[0012]

[0011] Before detailing embodiments of the present invention, it would be useful to present exemplary environments in which embodiments of the present invention can be carried out.

[0013]

[0012] Figure 1 schematically shows a lithography apparatus LA. The apparatus includes an illumination system (illuminator) IL configured to adjust the radiation beam B (e.g., UV radiation or DUV radiation), a patterning device support or support structure (e.g., mask table) MT connected to a first positioner PM, which is constructed to support a patterning device (e.g., mask) MA and configured to precisely position the patterning device according to specific parameters, two substrate tables (e.g., wafer tables) WTa and WTb, which are configured to hold a substrate (e.g., a resist-coated wafer) W, respectively, and connected to a second positioner PW, which is configured to precisely position the substrate according to specific parameters, and a projection system (e.g., refractive projection lens system) PS configured to project the pattern applied to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (e.g., including one or more dies). A reference frame RF connects the various components and serves as a reference for setting and measuring the positions of the patterning device and the substrate, as well as the positions of features on them.

[0014]

[0013] The lighting system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for inducing, shaping, or controlling radiation.

[0015]

[0014] The patterning device support MT holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithography apparatus, and conditions such as whether the patterning device is held in a vacuum environment. The patterning device support can hold the patterning device using mechanical, vacuum, electrostatic or other clamping techniques. The patterning device support MT may be, for example, a frame or table that can be fixed or movable as needed. The patterning device support may ensure that the patterning device is positioned as desired relative to, for example, the projection system.

[0016]

[0015] The term “patterning device” as used herein should be interpreted broadly to refer to any device that can be used to impart a pattern to a cross-section of a radiation beam in order to generate a pattern on a target portion of a substrate. Note that the pattern imparted to the radiation beam may not precisely correspond to a desired pattern on the target portion of the substrate, for example, if the pattern includes phase-shift features or so-called assist features. Generally, the pattern imparted to the radiation beam corresponds to a specific functional layer of a device to be generated on the target portion, such as an integrated circuit.

[0017]

[0016] As shown herein, the apparatus is of the transmissive type (for example, using a transmissive patterning device). Alternatively, the apparatus may be of the reflective type (for example, using a programmable mirror array of the type mentioned above, or using a reflective mask). Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Where the terms “reticle” or “mask” are used herein, these terms can be considered synonymous with the more general term “patterning device.” The term “patterning device” can also be interpreted as referring to a device that stores pattern information in digital form for use in controlling such a programmable patterning device.

[0018]

[0017] The term “projection system” as used herein should be interpreted broadly to encompass any type of projection system, including, for example, refractive optical systems, reflective optical systems, reflector-refractor optical systems, magneto-optical systems, electromagnetic optical systems, and electrostatic optical systems, or any combination thereof, depending on the exposure radiation used or other factors such as the use of immersion liquid or vacuum. When the term “projection lens” is used herein, it can be considered synonymous with the more general term “projection system.”

[0019]

[0018] The lithography apparatus may be of a type in which at least a portion of the substrate W is covered with a liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system and the substrate. The immersion liquid can also be applied to other spaces in the lithography apparatus, such as between the mask and the projection system. Immersion techniques are well known in the art to increase the numerical aperture of the projection system.

[0020]

[0019] During operation, the illuminator IL receives a radiation beam from the radiation source SO. The radiation source and the lithography apparatus may be separate components, for example, when the radiation source is an excimer laser. In such cases, the radiation source is not considered to form part of the lithography apparatus, and the radiation beam is delivered from the radiation source SO to the illuminator IL with the help of a beam delivery system BD, which includes, for example, a suitable guidance mirror and / or beam expander. In other cases, for example, when the radiation source is a mercury lamp, the radiation source may be an integral part of the lithography apparatus. The radiation source SO and the illuminator IL may, if necessary, be referred to as a radiation system together with the beam delivery system BD.

[0021]

[0020] The illuminator IL may include, for example, an adjuster AD, an integrator IN, and a capacitor CO for adjusting the angular intensity distribution of the radiated beam. The illuminator can be used to adjust the radiated beam to give its cross-section a desired uniformity and intensity distribution.

[0022]

[0021] The radiant beam B is incident on a patterning device MA held on a patterning device support MT and patterned by the patterning device. After crossing the patterning device (e.g., mask) MA, the radiant beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the help of a second positioner PW and a position sensor IF (e.g., an interferometer device, a linear encoder, a 2-D encoder, or a capacitive sensor), the substrate table WTa or WTb can be precisely moved to position, for example, various target portions C in the path of the radiant beam B. Similarly, a first positioner PM and another position sensor (not shown in Figure 1) can be used to precisely position the patterning device (e.g., mask) MA relative to the path of the radiant beam B after mechanical removal from the mask library or during scanning.

[0023]

[0022] The patterning device (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks, as shown in the figure, occupy dedicated target areas, but may also be located in the space between target areas (known as scribe line alignment marks). Similarly, in situations where multiple dies are provided on the patterning device (e.g., mask) MA, mask alignment marks may be placed between the dies. Small alignment marks can also be included within the dies, between device features, in which case it is desirable that the markers be as small as possible and not require different imaging or process conditions from adjacent features. Alignment systems for detecting alignment markers are described further below.

[0024]

[0023] The illustrated apparatus can be used in various modes. In scan mode, the patterning device support (e.g., mask table) MT and the substrate table WT are scanned synchronously while the pattern applied to the radiation beam is projected onto the target area C (i.e., single dynamic exposure). The speed and direction of the substrate table WT relative to the patterning device support (e.g., mask table) MT can be determined by the (reduction) magnification and image inversion characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width of the target area (non-scanning direction) during single dynamic exposure, while the length of the scan operation determines the height of the target area (scanning direction). As is well known in the art, other types of lithography apparatuses and operating modes are conceivable. For example, step mode is known. In so-called "maskless" lithography, the pattern is changed while the programmable patterning device is kept stationary, and the substrate table WT is moved or scanned.

[0025]

[0024] Combinations and / or variations of the above-described modes of use, or entirely different modes of use, can also be used.

[0026]

[0025] The lithography apparatus LA is a so-called dual-stage type, having two substrate tables WTa, WTb and two stations, an exposure station EXP and a measurement station MEA, the substrate tables being interchangeable between stations. While one substrate on one substrate table is being exposed at the exposure station, another substrate can be loaded onto the other substrate table at the measurement station and various preparation steps can be performed. This allows for a substantial increase in the throughput of the apparatus. Preparation steps may include mapping the surface height contour of the substrate using a level sensor LS and measuring the position of alignment markers on the substrate using an alignment sensor AS. If the position sensor IF cannot measure the position of the substrate table when it is at the measurement station and when it is at the exposure station, a second position sensor may be provided to allow tracking of the position of the substrate table at both stations relative to a reference frame RF. Other configurations are known and can be used instead of the illustrated dual-stage configuration. For example, other lithography apparatuses are known that have substrate tables and measurement tables. These components are docked when preliminary measurements are performed, and then undocked while the substrate table is exposed to light.

[0027]

[0026] Figure 2 shows the steps for exposing a target portion (e.g., die) on a substrate W in the dual-stage apparatus of Figure 1. The dotted box on the left shows the steps performed at the measurement station MEA, and the box on the right shows the steps performed at the exposure station EXP. At each stage, as described above, one of the substrate tables WTa and WTb is at the exposure station and the other is at the measurement station. In this explanation, it is assumed that the substrate W is already loaded into the exposure station. In step 200, a new substrate W' is loaded into the apparatus by a mechanism not shown. These two substrates are processed in parallel to increase the throughput of the lithography apparatus.

[0028]

[0027] First, referring to a newly loaded substrate W', this substrate may be an untreated substrate and is equipped with fresh photoresist for the first exposure in the apparatus. However, generally speaking, the lithography process described is only one step in a series of exposure and processing steps, and therefore the substrate W' has already passed through this apparatus and / or other lithography apparatus several times, and there may be subsequent processing. In particular, with regard to the problem of improving overlay accuracy, the challenge is to ensure that a new pattern is applied to the precise location on a substrate that has already undergone one or more patterning and processing cycles. These processing steps gradually introduce distortion to the substrate, and such distortion must then be measured and corrected to achieve satisfactory overlay accuracy.

[0029]

[0028] The preceding and / or subsequent patterning steps may be carried out in other lithography apparatuses, as described above, and may even be carried out in different types of lithography apparatuses. For example, some layers that have very stringent requirements for parameters such as resolution and overlay in the device manufacturing process may be carried out with more advanced lithography tools than other layers that do not have such stringent requirements. Thus, some layers may be exposed with an immersion type lithography tool, while other layers may be exposed with a "dry" tool. Some layers may be exposed with a tool that operates at DUV wavelengths, while other layers may be exposed using EUV wavelength radiation.

[0030]

[0029] In 202, the alignment of the substrate with respect to the substrate table WTa / WTb is measured and recorded using substrate marks P1 and an image sensor (not shown). In addition, several alignment marks across the entire substrate W' are measured using the alignment sensor AS. These measurements are used in one embodiment to establish a "wafer grid," which maps the distribution of marks across the entire substrate with great precision, including distortion relative to a nominal rectangular grid.

[0031]

[0030] In step 204, a map of wafer height (Z) relative to the XY position is also measured using the level sensor LS. Conventionally, the height map is used only to achieve precise focusing of the exposure pattern. The height map may also be used for other purposes.

[0032]

[0031] When the substrate W' is loaded, recipe data 206 is received that defines the exposure to be performed and the characteristics of the wafer and the patterns previously and to be created on it. Measurements of wafer position, wafer grid, and height maps performed in 202, 204 are added to this recipe data so that a complete set of recipe and measurement data 208 can be passed to the exposure station EXP. Alignment data measurements include, for example, the X and Y positions of alignment targets formed in a fixed or nominally fixed relationship with respect to the product pattern, which is the product of the lithography process. These alignment data acquired immediately before exposure are used to generate an alignment model with parameters that fit the model to the data. These parameters and the alignment model will be used during the exposure operation to correct the position of the pattern applied in the current lithography step. The model in use interpolates the positional misalignment between the measurement positions. A conventional alignment model may include four, five, or six parameters that together define the translation, rotation, and scaling of an "ideal" grid of different dimensions. More advanced models that use more parameters are known.

[0033]

[0032] In step 210, wafers W' and W are swapped, and the measured substrate W' becomes the substrate W that enters the exposure station EXP. In the exemplary apparatus of Figure 1, this swapping is performed by exchanging the supports WTa and WTb in the apparatus, so that the substrates W, W' remain precisely pressed and positioned on their supports, maintaining the relative alignment between the substrate table and the substrate itself. Therefore, once the tables are swapped, all that is needed to utilize the measurement information 202,204 of the substrate W (formerly W') that manages the exposure step is to determine the relative position between the projection system PS and the substrate table WTb (formerly WTa). In step 212, reticle alignment is performed using mask alignment marks M1,M2. In steps 214, 216, and 218, scanning and radiation pulses are applied to continuous target positions across the entire substrate W to complete the exposure of multiple patterns.

[0034]

[0033] By using the alignment data and height map acquired at the measurement station during the exposure step, these patterns are precisely aligned to the desired location and, in particular, to features previously defined on the same substrate. The exposed substrate, labeled W″, is unloaded from the apparatus in step 220 and subjected to etching or other processing according to the exposure pattern.

[0035]

[0034] Those skilled in the art will see that the above description is a simplified overview of several very detailed steps relating to an example of a real-world manufacturing situation. For example, rather than measuring alignment in a single pass, there are often separate phases of rough and fine measurements using the same or different marks. The rough alignment measurement step and / or the fine alignment measurement step may be performed before or after the height measurement, or alternately.

[0036]

[0035] Certain types of metrologic sensors for both alignment and product / process monitoring metrologic applications are described in PCT Patent Application International Publication 2020 / 057900A1, incorporated herein by reference. This describes a metrologic device with optimized coherence. More specifically, the metrologic device is configured to generate multiple spatially incoherent beams of measurement illumination, each of which beams (or a measurement pair of which each beam corresponds to a certain measurement direction) has corresponding regions in a cross-section, and the phase relationship between the beams in these regions is known for that cross-section. That is, there is spatial coherence between the corresponding regions.

[0037]

[0036] Such metrologic devices can measure small-pitch targets with acceptable (minimal) interference artifacts (speckles) and may also operate in dark-field mode. Such metrologic devices may be used as position sensors or alignment sensors for measuring substrate position (e.g., measuring the position of periodic structures or alignment marks relative to a fixed reference position). However, metrologic devices can also be used for overlay measurements (e.g., measuring the relative position of periodic structures in different layers or in the same layer in the case of stitching marks). Metrologic devices can also measure the asymmetry of periodic structures and may therefore be used to measure any parameter based on target asymmetry measurements (e.g., overlay using diffraction-based overlay (DBO) techniques or focus using diffraction-based focusing (DBF) techniques).

[0038]

[0037] Figure 3 shows one possible implementation of such a metrology device. This metrology device operates substantially as a standard microscope with a novel illumination mode. The metrology device 300 comprises an optical module 305 which contains the main components of the device. An illumination source 310 (located outside the module 305 and potentially optically connected to the module by a multimode fiber 315) provides the optical module 305 with a spatially incoherent radiant beam 320. An optical component 317 feeds the spatially incoherent radiant beam 320 to a coherent off-axis illumination generator 325. This component is particularly important to the concept described herein and will be described in more detail. The coherent off-axis illumination generator 325 generates several (e.g., four) off-axis beams 330 from the spatially incoherent radiant beam 320. The characteristics of these off-axis beams 330 will be described in detail below. The zero-order illumination of the illumination generator may be shielded by the zero-order illumination shielding element 375. This zero-order illumination exists only for some of the coherent off-axis illumination generator examples described in this document (e.g., phase-grate based illumination generators), and therefore may be omitted when such zero-order illumination is not generated. The off-axis beam 330 is fed to the (e.g., high NA) objective lens 345 via the (optical component 335 and) spot mirror 340. The objective lens focuses the off-axis beam 330 onto a sample located on the substrate 350 (e.g., periodic structure / alignment mark), where the off-axis beam scatters and diffracts. The scattered higher-order diffraction 355+, 355- (e.g., +1 and -1, respectively) propagate back through the spot mirror 340 and are focused onto a sensor or camera 365 by the optical component 360, where they interfere to form an interference pattern. Then, a processor 380 running appropriate software can process one or more images of the interference pattern captured by the camera 365.

[0039]

[0038] The zero-order diffraction (specular reflection) radiation is shielded at a suitable location within the detection branch, for example, by the spot mirror 340 and / or a separate detection zero-order shielding element. There is a zero-order reflection for each off-axis illumination beam. That is, in this embodiment there are a total of four such zero-order reflections. An example of an aperture profile suitable for shielding the four zero-order reflections is shown in Figures 4(b) and 4(c), labeled 422. Thus the metrometry device operated as a “dark-field” metrometry device.

[0040]

[0039] The main concept of the proposed metrology device is to induce spatial coherence in the measurement illumination only when necessary. More specifically, spatial coherence is induced between each corresponding set of pupils of the off-axis beam 330. More specifically, one set of pupils has a corresponding single pupil in each of the off-axis beams, and the pupils of that set are spatially coherent with each other, but each pupil is incoherent with respect to all other pupils of the same beam. By optimizing the coherence of the measurement illumination in this way, it becomes possible to perform dark-field off-axis illumination for small-pitch targets, while speckle artifacts are minimized because each off-axis beam 330 is spatially incoherent.

[0041]

[0040] Figure 4 shows three pupil images to illustrate this concept. Figure 4(a) shows the first pupil image relating to the pupil plane P1 of Figure 2, and Figures 4(b) and 4(c) show the second pupil images relating to the pupil plane P2 of Figure 2, respectively. Figure 4(a) shows a spatially incoherent radiation beam 320 (in cross-sectional view), and Figures 4(b) and 4(c) show the off-axis beam 330 generated by a coherent off-axis illumination generator 325 (in cross-sectional view) in two different embodiments. In all cases, the range of the outer circle 395 corresponds to the maximum detectable NA of the microscope's objective system. This may be 0.95 NA, as a pure example.

[0042]

[0041] Each triangle 400 in the pupil represents a set of pupil points that are spatially coherent with respect to each other. Similarly, the cross marks 405 represent another set of pupil points that are spatially coherent with respect to each other. The triangles are spatially incoherent with respect to the cross marks and all other pupil points corresponding to beam propagation. The general principle (in the example shown in Figure 4(b)) is that each set of pupil points that are spatially coherent with respect to each other (each coherent set of points) has the same spacing within the illumination pupil P2 as all other coherent sets of points. Thus, in this embodiment, each coherent set of points is a translation within the pupil of all other coherent sets of points.

[0043]

[0042] In Figure 4(b), the spacing between each pupil point in the first coherent set of points represented by triangle 400 must be equal to the spacing between each pupil point in the coherent set of points represented by cross marks 405. In this context, "spacing" refers to directionality. That is, the set of cross marks (the second set of points) is inrotational with respect to the set of triangles (the first set of points). Thus, each of the off-axis beams 330 has incoherent radiation, but the off-axis beams 330 as a whole have the same beam with corresponding sets of points having known phase relationships (spatial coherence) within their cross-sections. Note that the points in each set of points do not need to be equally spaced (for example, the spacing between the four triangles 405 in this example does not need to be equal). Thus, the off-axis beams 330 do not need to be symmetrically arranged within the pupil.

[0044]

[0043] Figure 4(c) shows that this basic concept can be extended to provide mutual spatial coherence only between beams corresponding to a single measurement direction, when beam 330X corresponds to a first direction (X direction) and beam 330Y corresponds to a second direction (Y direction). In this example, the square and the plus sign represent sets of pupils that correspond to sets of pupils represented by triangles and crosses, respectively, but are not necessarily spatially coherent. However, the crosses are spatially coherent with each other, as are the plus signs, and the crosses are geometric translations of the pupils of the plus signs. Thus, in Figure 4(c), the off-axis beams are coherent only in pairs.

[0045]

[0044] In this embodiment, the off-axis beams are considered separately for each direction, for example, the X direction 330X and the Y direction 330Y. The pair of beams 330X that generate the captured diffraction order in the X direction only need to be coherent with respect to each other (therefore, the pair of points 400X is coherent with respect to each other, and so is the pair of points 405X). Similarly, the pair of beams 330Y that generate the captured diffraction order in the Y direction only need to be coherent with respect to each other (therefore, the pair of points 400Y is coherent with respect to each other, and so is the pair of points 405Y). However, there is no need for coherence to exist between the pair of points 400X and the pair of points 400Y, or between the pair of points 405X and the pair of points 405Y. Thus, the pair of off-axis beams corresponding to each measurement direction under consideration contains a pair of coherent points. As before, for each pair of beams corresponding to the measurement direction, each pair of coherent points is a geometric translation within the pupil of all other pairs of coherent points.

[0046]

[0045] Figure 5 illustrates the operating principle of a metrologic system, for example, for alignment / position detection. Figure 5(a) illustrates a target 410 that can be used as an alignment mark in some embodiments. The target 410 may be similar to those used in microdiffraction-based overlay techniques (μDBO), but typically consists of only a single layer when forming the alignment mark. Thus, the target 410 comprises four subtargets, including two gratings (periodic structures) 415a in a first direction (X direction) and two gratings 415b in a second perpendicular direction (Y direction). The grating pitch may be, for example, in the same order of magnitude as 100 nm (more specifically, in the range of 300 to 800 nm).

[0047]

[0046] Figure 5(b) shows a pupil representation corresponding to the pupil plane P3 (see Figure 2). This figure shows the radiation resulting from the scattering of only one of the off-axis illumination beams, more specifically the off-axis illumination beam 420 (the leftmost in this representation) (this off-axis illumination beam would not be within this pupil. The location of this off-axis illumination beam on the pupil plane P2 corresponds to its location in the illumination pupil, which is shown here for illustrative purposes only). The shaded region 422 corresponds to the occlusion (i.e., reflection or absorption) region of a particular spot mirror design used in one embodiment (white represents the transmission region). Such a spot mirror design is a pure example of pupil occlusion that ensures unwanted light (e.g., zero-order and zero-order surrounding light) is not detected. Other spot mirror profiles (or zero-order occlusion in general) may be used.

[0048]

[0047] As can be seen, only one of the higher diffraction orders, more specifically the diffraction order 425 in the -1X direction, is captured. The diffraction order 430 in the +1X direction, the diffraction order 435 in the -1Y direction, and the diffraction order 440 in the +1Y direction fall outside the pupil (the detected NA is represented by the range of the spot mirror 422) and are not captured. Any higher order (not shown) also falls outside the detected NA. The zeroth order 445 is shown for illustrative purposes, but in reality it would be shielded by the spot mirror or zeroth order shielding 422.

[0049]

[0048] Figure 5(c) shows the pupil (captured orders only) resulting from all four off-axis beams 420 (also shown purely for illustrative purposes). The captured orders include diffraction order 425 in the -1X direction, diffraction order 430' in the +1X direction, diffraction order 435' in the -1Y direction, and diffraction order 440' in the +1Y direction. These diffraction orders are imaged by the camera and interfere to form a fringe pattern 450 as shown in Figure 5(d). In the illustrated example, the fringe pattern is oblique because the diffraction orders are arranged obliquely in the pupil, but other arrangements are possible, thereby resulting in different fringe pattern orientations.

[0050]

[0049] Similar to other metronome devices that can be used for alignment detection, a shift in the target grid position causes a phase shift between the +1 diffraction order and the -1 diffraction order in each direction. Since the diffraction orders interfere on the camera, the phase shift between diffraction orders results in a corresponding shift in the interference fringes on the camera. Therefore, it is possible to determine the alignment position from the position of the interference fringes on the camera.

[0051]

[0050] Figure 6 illustrates how the alignment position can be determined from the interference fringes. Figure 6(a) shows a set of interference fringes 500 (i.e., corresponding to one quadrant of the fringe pattern 450) when the target is in a first position, and Figure 6(b) shows a set of interference fringes 500' when the target is in a second position. A fixed reference line 510 (i.e., in the same position for both images) is shown to highlight the movement of the fringe pattern between the two positions. Alignment can be determined by known methods by comparing the position determined from the pattern with a position obtained from measurements of a fixed reference (e.g., a transmission image sensor (TIS) fiducial). Alignment can use a single fringe pattern (e.g., from a single grid alignment mark) or a single pattern for each direction (e.g., from two grid alignment marks). Another option for performing two-directional alignment would be to use alignment marks having a single 2D periodic pattern. Non-periodic patterns can also be measured by the metrologic devices described herein. Another option for alignment marks may be a target design with four grids, as illustrated in Figure 5(a), which is similar to those currently commonly used to measure overlays. Thus, such targets are typically already present on the wafer, and similar sampling can be used for alignment and overlay. Such alignment methods are known and will not be further described.

[0052]

[0051] International Publication No. 2020 / 057900 further describes the possibility of measuring multiple wavelengths (and possibly higher diffraction orders) to become more process-robust (facilitating measurement diversity). It has been suggested that this would allow the use of techniques such as optimal chromatic weighting (OCW) to be robust to grating asymmetry. In particular, target asymmetry typically results in different aligned positions for each wavelength. This makes it possible to determine the asymmetry in the target by measuring the difference in aligned positions for various wavelengths. In one embodiment, measurements corresponding to multiple wavelengths may be imaged sequentially with the same camera to obtain a sequence of individual images, each corresponding to a different wavelength. Alternatively, these wavelengths may be imaged in parallel with separate cameras (or separate areas of the same camera), separated using appropriate optical components such as dichroic mirrors. In another embodiment, it is possible to measure multiple wavelengths (and diffraction orders) in a single camera image. When illumination beams corresponding to various wavelengths are at the same location in the pupil, the corresponding fringes on the camera image will have various orientations for the various wavelengths. Most off-axis illumination generator configurations would fall into this category (with the exception of single gratings, where the wavelength dependencies of the illumination grating and target grating tend to cancel each other out). Proper processing of such images allows for the determination of alignment positions at multiple wavelengths (and orders) in a single capture. These multiple positions can then be used as input for algorithms such as OCW.

[0053]

[0052] International Publication No. 2020 / 057900 also describes the possibility of variable region of interest (ROI) selection and variable pixel weighting to improve accuracy / robustness. Instead of determining the alignment position based on the entire target image or a fixed region of interest (such as the entire central region of each quadrant or the entire target, i.e., excluding edge regions), it is possible to optimize the ROI for each target. The optimization can determine one or more ROIs of any shape. It is also possible to determine weight combinations of the optimized ROIs, and the weights are assigned according to one or more quality metrics or key performance indicators (KPIs).

[0054]

[0053] Targets in general, and especially small targets, are typically subject to deformation during their formation (e.g., due to processing and / or exposure conditions). Often, such deformation is not uniform within the target and includes multiple local or in-target effects that lead to local or in-target variations, such as random edge effects, wedge effects on marks, local lattice asymmetry variations, local thickness variations, and / or (local) surface roughness. These deformations may not be repeatable between marks or between wafers and should therefore be measured and corrected before exposure to avoid misprints on the device. Due to these local effects, when performing substrate alignment on deformed marks, simply averaging the entire mark or a fixed region of interest will typically lead to alignment errors.

[0055]

[0054] The tools disclosed in International Publication No. 2020 / 057900 are described (in the context of alignment) as alignment sensors for measuring the alignment / position of a wafer before exposure (for example, to determine the exposure grid based on the measurement of alignment marks). Such tools may be incorporated, for example, into the measurement station of a two-stage lithography exposure device or scanner.

[0056]

[0055] However, replacing currently used alignment sensors (e.g., those based on the self-referencing interferometer (SRI) principle) with optimized coherence metrology tools such as those described in International Publication No. 2020 / 057900 presents commercial and / or practical challenges. In particular, maintaining backward compatibility with current systems is highly desirable, which would be difficult with optimized coherence metrology tools.

[0057]

[0056] Thus, a standalone pre-alignment tool and method is disclosed that can provide in-target correction for another alignment tool to correct alignment mark defects, for example. The pre-alignment tool may be an optimized coherence metrology tool (for example, based on the teachings of International Publication No. 2020 / 057900), or any other tool that can obtain local position measurements (e.g., position distribution or local position map) from the target. The position distribution may describe the variability of aligned positions across the target or at least a portion of the target (or a captured image thereof), e.g., local positions for each pixel or group of pixels (e.g., a group of adjacent pixels).

[0058]

[0057] The position distribution can then be used to determine alignment corrections (e.g., feedforward corrections) for alignment measurements performed using, for example, a more conventional (e.g., SRI-based) alignment sensor. Such alignment sensors may (or may not) be included in a measurement station integrated into the scanner.

[0059]

[0058] In one embodiment, the pre-alignment tool may have a simplified stage configuration and stability compared to an alignment sensor, for example, a stage that does not have the control accuracy and / or stability required for alignment (e.g., an alignment sensor contained within a scanner). Such a tool may have the same stability and stage performance as a (e.g., standalone) metrology station currently used in overlay metrology (e.g., a scantrometer device). Thus, the pre-alignment tool is conceptually different from an external alignment sensor or complementary alignment tool that has sufficient stage performance to measure a wafer coordinate system across multiple targets. In the case of an alignment sensor or complementary alignment tool, determining the actual target position of each measurement is essential to avoid errors in the coordinate system (all targets are basically relative to each other in order to span the entire coordinate system). Known complementary alignment tools of this type can be used in combination with a scanner alignment sensor to measure a coordinate system, for example, by enabling measurements of a large number of targets. This densely measured coordinate system is fed forward to the scanner. This means that fewer targets need to be measured by the scanner itself. In contrast, the pre-alignment tools disclosed herein are not necessarily configured to measure the wafer coordinate system; instead, it is proposed that the tool measure only individual targets and, for each target, consider parameters that are relative only to its corresponding target. These parameters can then be fed forward to the scanner to improve the target-by-target accuracy of the alignment sensor measurements.

[0060]

[0059] Figure 7 is a schematic flowchart of a system and / or method employing a pre-alignment tool PAT according to one embodiment. The pre-alignment tool must be of a type that can provide local in-target positions (e.g., position data as a function of target position). For example, the pre-alignment tool may form an image that directly represents a position pattern or position distribution. Such a tool may be an optimized coherence metrology tool as described in relation to Figures 3-6, or any other suitable tool, e.g., any other suitable optical microscope (dark-field or bright-field) or any suitable scanning probe microscope tool (e.g., atomic force microscope (AFM), near-field microscope (NFM), scanning electron microscope (SEM), acoustic microscope, scanning tunneling microscope (STM), or other similar techniques that can provide position data as a function of target position). Scanning diffraction-based alignment sensors may also be used in the pre-alignment tool PAT. These alignment sensors measure an interferogram based on line tracing on marks, rather than an “image” or “map” from which positions are extracted. This line tracing, which describes intensity as a function of position, produces an interferogram from which the aligned position is determined. In the context of this disclosure, the interferogram may be interpreted as a positional distribution, i.e., a 1D positional map. Many of these devices can also measure the corresponding intensity asymmetry and thus determine non-positional parameter distributions. Another example of a scanning sensor is an atomic force microscope (AFM), where the AFM cantilever performs a raster scan across a surface, yielding a "topographic image".

[0061]

[0060] The pre-alignment tool PAT performs alignment correction Δ based on the measurement of the wafer W (which includes at least alignment marks or targets on it and is exposed, for example, in the previous layer or base layer) AL This can be determined. Below is the alignment correction Δ ALThe method for determining alignment is described below. The same wafer is then supplied to a measurement station MEA equipped with an alignment sensor AS. The measurement station may be located within a scanner SC as shown herein, or it may be located within a separate (standalone) alignment station or a single station scanner. The alignment sensor measures alignment marks on the wafer W to obtain alignment data AL. The alignment data AL may, for example, have a single alignment value for each mark, or (depending on the system) have multiple alignment values, including alignment values ​​for each wavelength (or other measurement setting) for each mark. However, the alignment sensor does not need to have, and does not need to have, the ability to measure within mark position variation. The processing unit PU then processes the alignment data AL and alignment correction Δ AL The control grid CG can be determined from both, for example, by which the alignment data AL and / or (ultimately) the control grid CG is corrected for deformation within the target. This corrected control grid CG is then used in the exposure station EXP of the scanner SC to expose the next layer, thereby exposing the exposed wafer W exp This is generated.

[0062]

[0061] Note that the representation of the processing unit PU as a single processor outside the scanner is purely illustrative. Processing may be performed, for example, by a processor inside the scanner. Processing may be distributed across multiple processors inside and / or outside the scanner or any other tool used. The processing unit receives raw image data from the pre-alignment tool PAT and performs alignment correction Δ AL This can be determined, or this process may be performed within the pre-alignment tool PAT as shown herein. Those skilled in the art will readily understand that other processing configurations and strategies may also be applicable.

[0063]

[0062] The proposed method is alignment correction Δ ALThe following steps may be taken to determine the position. In the first step, a pre-alignment tool is used to measure each mark and obtain in-target metrology data such as one or more position distributions (e.g., position data as a function of target position, such as position data for each pixel or group of pixels). For example, multiple position distributions for each target may be obtained for different measurement settings. Position distributions may be obtained, for example, by measuring the fringe position individually for each pixel or group of adjacent pixels to obtain the position for each pixel / group of pixels (it is not always possible to assign a position from a single pixel). The images may relate to various sensor settings that are sensitive to mark deformation, such as multiple wavelength / polarization states (otherwise separate images may be obtained for different wavelength / polarization states), and a local position map may be determined for each of the wavelength / polarization states.

[0064]

[0063] Other non-positional parameter distribution data can also be optionally measured using the pre-alignment tool and / or another metrology tool, and may also include multiple per-target distributions obtained for different measurement settings. Such non-positional parameter distributions may include pixel-by-pixel intensity asymmetry (e.g., the difference in intensity between complementary diffraction orders (optionally normalized by the sum of these intensities, optionally calibrated to compensate for tool defects, and / or optionally pre-processed to compensate for nominal stack characteristics)). Alternatively, such pixel-by-pixel intensity asymmetry information may be obtained using different instruments or tools, such as scantometry-based metrology tools. Other non-positional parameters that can be measured from the pre-alignment tool or different tools include one or more of the following (per pixel or group of pixels): fringe visibility of the alignment pattern in the image, local intensity, wafer quality, and amplitude of the alignment pattern.

[0065]

[0064] Once the position distribution / other distribution is obtained, two position values ​​are obtained for each mark, namely the first representative correction value X RE and the second corrected position value X COcan be determined. A representative correction value X RE may represent a value that the alignment sensor AS would "see" during alignment (e.g., an estimate of the alignment sensor AS readings for the same target). This may include, for example, an average (e.g., mean) of one or more measured position distributions. A representative correction value X RE does not have correction for within-target variations (however, it may optionally include correction for non-local effects that the alignment sensor can also perform, especially when the pre-alignment tool has higher capabilities than the alignment sensor, e.g., when it can measure in more colors). The corrected position value X CO may include a position value corrected for within-target variations. An exemplary method for doing this is described herein.

[0066]

[0065] Alignment correction Δ AL can be determined as the difference between these two position values or as another comparison (e.g., Δ AL = X RE - X CO ). This alignment correction may include combined data from multiple measurement settings (e.g., the position data X RE - X CO each relates to multiple measurement settings). Thus, the alignment correction Δ AL may include correction values for each target or alignment mark. This correction may essentially include corrections that the alignment sensor can apply when the alignment sensor has within-target measurement capabilities (e.g., can resolve local deformations). In some embodiments, multiple alignment correction Δ AL values can be determined for each target, and each of these is transferred to the processing unit PU. For example, the alignment correction Δ AL values can be determined for all measured colors and polarizations.

[0067]

[0066] The alignment sensor AS can be used to perform alignment and acquire alignment data AL. Within the processing unit PU and / or scanner SC, the Δ corresponding to each target AL The value is applied to each of the measured alignment values ​​of the target, correcting the alignment data AL for local deformation effects.

[0068]

[0067] Position X RE and X CO (Measured by the pre-alignment tool) is the position X measured by the alignment sensor in the scanner. RE Note that it may have any offset relative to . However, alignment correction Δ AL These offsets cancel each other out, so this offset should not have any effect. One possible reason for such an offset could be the relatively low precision of the wafer stage of the pre-alignment tool, which causes the marks to be measured at slightly different positions relative to the sensor.

[0069]

[0068] Alignment Correction Δ AL and / or corrected position X CO To determine this, weighting may be determined using only pre-alignment tool images (i.e., measurements of the target itself), but embodiments using other data from other sources are also disclosed and are within the scope of the present invention.

[0070]

[0069] Alignment Correction Δ AL and / or corrected position X CO This can be determined from local pixel-level information combined from at least one parameter distribution (parameter per-pixel maps), each of which describes the variation in parameter values ​​across at least corresponding portions of one or more captured images (for example, each parameter distribution relates to a common region of interest of the target) and where at least one of the parameter distributions contains a location distribution (or local location map).

[0071]

[0070] In one embodiment, alignment correction Δ AL This can be determined as the difference between two statistical measures with the same positional distribution. For example, representative position X RE This may include the average value of the respective positional distributions (for each target), and the corrected position X CO This may include the median of the same positional distribution. While the median is a useful statistical tool for removing outliers from a distribution, this would be useful because many current alignment sensors cannot determine the median.

[0072]

[0071] Next, corrected position X CO Further methods for determining this will be described in more detail. Such methods involve a combined corrected location distribution or a corrected location distribution map X. COmap The system may also include finding the optimal coefficients C and (optionally) D that minimize the within-target variation in X COmap teeth

[0073]

number

[0074]

number

[0075] is the positional distribution (local position for each pixel / group of pixels), and C is the weighting coefficient for the positional distribution.

[0076]

number

[0077] is a non-positional parameter distribution correlated with target deformation, and D is the weighting coefficient of the non-positional parameter distribution. Thus, the combined corrected position map XCOmap This can be evaluated for all sensor settings (here, various wavelengths λ and polarizations P) applicable to one or more pre-alignment tools used. The weighting coefficients can be determined by minimizing the in-target variation metric across the combined distribution and forming a self-referential method.

[0078]

[0072] Equation 1 is purely the combined corrected position map X COmap This is an example of the formula. In another embodiment, for example, only the location distribution is used, and therefore the second term is unnecessary, and the combined corrected location map X COmap This can be determined from the first term alone (and therefore only the weight C is determined). In another embodiment, only one positional distribution (i.e., relating to a single measurement setting, e.g., illumination setting such as a wavelength / polarization combination) is used together with one or more non-positional parameter distributions (e.g., again relating to a single measurement setting, or the sum of non-positional parameter distributions of two or more measurement settings as described). Additional terms may be added for different non-positional parameters (e.g., distributions of two or more non-positional parameters). The measurement setting can vary more than wavelength / polarization. For example, the measurement setting can vary one or more of the following (any combination): wavelength, polarization, angle distribution of illumination, and spatial and / or temporal coherence characteristics of illumination. For other tools such as scanning probe microscopy, the varying measurement setting can be any suitable for that tool (e.g., electron accelerating voltage in SEM, tip force on sample in atomic force microscopy, or acoustic wavelength in acoustic microscopy).

[0079]

[0073] In order to enable inter-wafer correction of target asymmetry, it may be preferable that the measurement data include only pre-exposure measurement data. Pre-exposure data may include any data performed on the wafer (e.g., per wafer) before exposure of a layer, as opposed to post-exposure measurement data (e.g., overlay metrology) measured on an exposed wafer, such as data measured using an alignment sensor. However, the scope of this disclosure may also include the use of any post-exposure measurement data.

[0080]

[0074] The result is a weighted corrected position map X with minimal variation within the target, or minimal variation relative to the nominal target shape. COmap In the latter case, the nominal target shape can be the average target shape or the design target shape. This minimizes the variation between targets (for nominally similar targets). The weighting coefficient can be determined by the mark measurement itself and does not need to rely on other external data sources such as simulations, measured overlay values, or wafer geometry.

[0081]

[0075] In one preferred embodiment, weighted optimization is constrained ΣC λ,P It can accept =1. This prevents removing the average value from a combined map, which could introduce positional errors. For example, a weighted location map X COmap If it is determined from two identical position maps relating to two wavelengths, then both maps will show the same pattern containing the same variation between n+1nm and n-1nm. It would be straightforward to subtract these measurements, resulting in a combined measurement where the variation is zero but the average value n is removed, where n is presumably a correction value.

[0082]

[0076] Figure 8(a) shows the combined weighted location map X COmapThis conceptually demonstrates the optimization of weight coefficients C1 and C2 based on two positional distributions or local positional maps PM1 and PM2, corresponding to the first wavelength λ1 and the second wavelength λ2, respectively, in order to minimize fluctuations in the region. As already explained, the weight coefficients C1 and C2 can also be functions of (e.g.) pixel indices or mark coordinates. This approach shares some similarities with OCW, but is self-referential and does not depend on external data or training.

[0083]

[0077] Figure 8(b) shows the weighted location map X COmap This conceptually illustrates the optimization of a weighting coefficient D based on a single positional distribution or local positional map PM and a non-positional parameter map IAM (e.g., a local intensity asymmetric map describing the difference between the intensities of corresponding pixels diffracted from the target at +1 and -1 diffraction orders). Since this approach effectively determines the weighting coefficient D, the weighted non-positional parameter map IAM corrects the local positional map PM to obtain a weighted positional map X COmap This can be determined. In one embodiment, a local position map PM and a non-position parameter map IAM, and consequently a corrected weighted position map X COmap This can be obtained from a single measurement. Note that in this example only one location measurement is used, so the weight coefficient C for the location map is not determined here. Due to the preference that the sum of the weight coefficients C for the location map should be 1, the weight of a single location measurement should typically be 1. In general, when there are n location measurements and m other non-location parameter measurements, all weights should be co-optimized to flatten or approach "nominal" one or more images as much as possible. If there are more available measurements (e.g., location maps and / or non-location parameter maps for other measurement settings), this method can co-optimize the weight coefficients C and D for both datasets.

[0084]

[0078] Weighted location map X COmap Once obtained, a single aligned position X CO(i.e., the corrected position used to determine alignment correction) is weighted into position map X COmap Aligned locations can be determined as the mean or other statistical measure. For example, the mean may be the average of locations described in a weighted location map (e.g., within a region of interest). Other means that may be used include, for example, the median, circular mean, or circular median. Outlier removal or other processing techniques may also be employed. Statistical tools such as histograms may be created for each location map from which aligned locations can be determined. For example, a histogram of the number of pixels for aligned location bins can be determined from a weighted location map. This histogram can be used to determine aligned locations via the mean, median, outlier filter, etc.

[0085]

[0079] In one embodiment, the weight values ​​of a typical position are

[0086]

number

[0087] This is then determined to be, for example, a (single-value) alignment correction Δ AL It can be used to calculate the value.

[0088]

[0080] Equation 1 is the alignment correction map or distribution Δ for each target. ALmap The offset may be slightly modified to directly optimize it in order to obtain a single offset value Δ for each target. AL It should be noted that this can be averaged to obtain the formula. Such a modified formula may take the following form (where the second term is, as before, arbitrarily chosen if there are multiple positional distributions for each target):

[0089]

number

[0090] Here, X RE The above is a single representative position value, X COmap This is a corrected position map (for example, for each mark and measurement setting). Therefore, the difference term X RE -X COmap This is itself a positional distribution or map. Alignment correction map Δ ALmap This can be evaluated for all sensor settings applicable to one or more pre-alignment tools used. As before, alignment correction Δ ALmap This is the alignment correction Δ AL To obtain this, it can be converted to a single value for each target by taking the average over the target or its applicable area.

[0091]

[0081] Such embodiments would be particularly useful, for example, when color is measured continuously and / or when significant (e.g., about 1 nm) unknown wafer stage position variations occur between measurements. This is described in Section X REλ,P However, this is because it provides a mechanism to deal with these situations (for example, different representative positions for each wavelength).

[0092]

[0082] In either Equation 1 or Equation 2, the weighting coefficients C and, where applicable, D, can be determined by minimizing the variation metric in the resulting combined location map for the weighted location map. More specifically, this can be done in many ways, for example, according to various norms.

[0093]

[0083] One such method is to minimize a variability metric such as variance, for example

[0094]

number

[0095] This may include minimizing the following:

[0096]

number

[0097] This is a weighted position map of pixel coordinates (i,j),

[0098]

number

[0099] is the average value across the weighted position map (i.e., the average value across all pixels). However, other norms may be used in other embodiments (e.g.,

[0100]

number

[0101] Minimize the following: where k can be a different number, e.g., 1 / 2, 1 (L1 norm, more tolerant of outliers), 3, 4, or infinity (less tolerant of outliers). To further improve robustness to outliers, parts of a mark for which it is not possible to find weights that improve the variation metric to better match the rest of the mark or the nominal mark (or parts whose weights would be very different from the other weights of that mark) may be completely discarded.

[0102]

[0084] In a further embodiment,

[0103]

number

[0104] This can be replaced by another statistical measure, such as the median of a location map. Another example might involve minimizing variability (rather than variance). This can be done by many methods, including manual, visual judgment.

[0105]

[0085] The advantage of an image-based measurement device like the one shown in Figure 3 is that all parameter distributions can be obtained from the same image. Such a device can provide two or more images (separately or in combination), each corresponding to a specific measurement setting (e.g., wavelength / polarization combination), from which a corresponding local location map can be determined, as well as a weighting coefficient C that minimizes variation / variance. λ,P This can be calculated (for example, based on the first term of Equation 1 or 2). Also, as explained, the same image may be used to obtain a non-positional parameter distribution / map, and therefore weighted optimization can be performed for a more robust alignment measurement by applying weighting coefficients C based on both terms of Equation 1 or 2. λ,P ,D λ,P This can be optimized.

[0106]

[0086] In one embodiment, the weighting coefficient may be determined for each target or mark. However, such an approach may be affected by, for example, sensor noise and uncorrected mark process noise. Therefore, it would be more robust to use an average weighting coefficient over a portion of a wafer, the entire wafer, or multiple wafers (e.g., one lot). The average may be the mean, median, or any other statistical measure. Such a method may involve determining the weighting coefficient for the corresponding image of each mark collectively in order to minimize variance / variation in a combined position map corresponding to multiple marks.

[0107]

[0087] The more measurement settings or wavelengths used, or the more other different types of data used, the better the estimated aligned position may be. Depending on the stack geometry and type of deformation, minimizing variation may result in an overall offset from the ideal position of the marks, for example, caused by insufficient different wavelengths for a particular stack. This can be partially corrected by using other sources such as wafer or lot statistics, overlay feedback loops, or by measuring at more wavelengths.

[0108]

[0088] For example, key performance indicators (KPIs) can be extracted from the location map to check the quality of marks for process monitoring and control. Such KPIs can be determined, for example, from a histogram of the number of pixels for the aforementioned aligned location bins. In this context, the determined coefficients C and / or D can also be used as KPIs for process monitoring.

[0109]

[0089] Equation 1 is the observed quantity

[0110]

number

[0111] and / or

[0112]

number

[0113] It is described as a linear superposition of . Similarly, Equation 2 is given by the observable (X RE -X COmap ) and / or

[0114]

number

[0115] It is described as a linear superposition of . However, in either case, for example, quadratic or cubic terms and / or higher-order nonlinear terms may also be included in the optimization.

[0116]

[0090] It would be desirable that the weighting coefficients C and / or D depend on the location of the target (selecting a smaller ROI in the location / non-location parameter map for which the weighting coefficients C and / or D are optimized). For example, the weighting coefficients C and / or D may vary within the target (or as a function of the pixel index), and for example, a target in the edge region of the target may be assigned a different weight compared to a region in the center of the target. Thus, although the above embodiments mainly focus on determining the weight for each camera pixel (or group of pixels), it is also possible and within the scope of this disclosure to determine the weight for each location within the target (for example, as a function of the distance from the edge of the target). Theoretically, these may differ when the target is measured at slightly different locations relative to the camera, but in practice, this difference is typically small.

[0117]

[0091] The above description may describe a proposed concept relating to determining alignment correction for alignment measurement, but this concept may also be applied to the correction of one or more other parameters of interest that can be measured, for example, using an alignment sensor. For example, a pre-alignment metrology tool (or more generally, a pre-measurement metrology tool) can be used as a correction station for an overlay technique that compares the difference in positions of two or more grids. For example, if each grid is in a different layer, it is possible to determine the overlay by comparing the positions of two (e.g., larger) grids relative to each other. Concepts disclosed herein may provide improved values ​​for the established positions of each grid and therefore a better determined overlay.

[0118]

[0092] Although specific embodiments of the present invention have been described above, it should be understood that the present invention can also be put into practice in ways other than those described.

[0119]

[0093] While we have made particular reference to the use of embodiments of the present invention in the field of optical lithography, it should be understood that the present invention can be used in other fields, such as imprint lithography, depending on the context, and is not limited to optical lithography. In imprint lithography, a topography in a patterning device defines the pattern to be created on a substrate. The topography of the patterning device is imprinted into a resist layer supplied to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist, and once the resist has cured, the pattern remains inside.

[0120]

[0094] As used herein, the terms “radiation” and “beam” encompass all types of electromagnetic radiation, including not only particle beams such as ion beams or electron beams, but also ultraviolet (UV) radiation (e.g., having wavelengths of 365, 355, 248, 193, 157 nm or 126 nm, or around these wavelengths) and extreme ultraviolet (EUV) radiation (e.g., having wavelengths in the range of 1 to 100 nm).

[0121]

[0095] The term “lens” can refer to any one or a combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic-optical components, where circumstances permit. Reflective components are likely to be used in devices operating in the UV and / or EUV region.

[0122]

[0096] The scope and width of the present invention are not limited by any of the exemplary embodiments described above, but are defined solely by the claims and their equivalents.

[0123]

[0097] Embodiments can also be described using the following clauses. 1. A pre-alignment metrology tool that can operate to measure multiple targets on a substrate in order to acquire measurement data, A processing unit, To process the measurement data and determine, for each target, at least one positional distribution that describes the variation in positional values ​​over at least a portion of that target, and A processing unit is capable of determining a measurement correction to compensate for intra-target variation in each target from at least one positional distribution, and the measurement correction for correcting the measurement is performed by an alignment sensor. A metrologic system equipped with [the following features]. 2. The measurement correction is provided by the metrology system of Clause 1, which includes at least one independent measurement correction for each target. 3. A metrology system according to Clause 1 or 2, comprising multiple independent measurement corrections for each target or subset thereof. 4. The metrology system of Clause 3, each of which has multiple independent measurement corrections for each target, each corresponding to its respective measurement setting. 5. A metrology system according to any of clauses 1 to 4, wherein the processing unit is operable to determine the measurement correction as, for each target, the difference or comparison between at least a representative position value that is not corrected for intra-target variation and a corrected position value that is corrected for intra-target variation. 6. The metrology system of Clause 5, wherein the processing unit is operable to determine a representative position value for each target as the average position of at least one position distribution for each target. 7. The metrologic system of Clause 5 or 6, wherein each difference or comparison comprises, for each target, the difference between a first statistical measure of the location distribution and a second statistical measure of the same location distribution. 8. The metrology system of Clause 7, wherein the processing unit is further operable to determine the corrected position value as the median position value of at least one position distribution of each of its targets, and the representative position value as the average position of at least one position distribution of each of its targets. 9. A metrology system according to any of clauses 1 to 6, wherein the processing unit is operable to process measurement data and determine at least two parameter distributions, including at least one positional distribution. 10. A metrologic system according to Clause 9, wherein the processing unit is operable to determine, for each target, at least one weighting coefficient for at least one of at least two parameter distributions, and to obtain a corresponding corrected position distribution having a combination of at least two parameter distributions to which the at least one weighting coefficient applies, the at least one weighting coefficient minimizing the variation metric in the corrected position distribution. 11. The metrology system of Clause 10, wherein the processing unit is capable of determining the corrected position value for each target from each corrected position distribution for each target. 12. The metrology system of Clause 11, wherein the processing unit is capable of determining the corrected position value for each target as the average of each corrected position distribution for each target. 13. A metrology system according to clause 10, wherein at least one location distribution comprises at least one difference distribution having representative location values ​​and a corrected location distribution. 14. The metrologic system of Clause 13, wherein the result of minimization is a measurement correction distribution for each target, and the processing unit is further capable of determining the measurement correction for each target from each respective correction distribution for each target. 15. The metrologic system of Clause 14, wherein the processing unit is further capable of determining the measurement correction for each target as the average of each respective correction distribution for each target. 16. A variability metric is a metrologic system of any of the clauses 10 to 15, comprising variability or dispersion within and / or relative to the nominal target. 17. A metrologic system according to any of clauses 10 to 12, wherein the processor is operable to constrain the sum of any weighting coefficients assigned to at least one location distribution to equal 1. 18. A metrology system according to any of clauses 10 to 17, wherein the weighting coefficient for at least one of at least two parameter distributions depends on the position within the target and / or within the image of the target. 19. A metrologic system according to any of clauses 10 to 18, wherein the processor is further capable of determining separate weighting coefficients for each of the parameter distributions. 20. A metrology system according to any of clauses 9 to 19, wherein at least two parameter distributions comprise at least two positional distributions, each relating to a different measurement setting. 21. A metrologic system according to any of the clauses 9 to 20, wherein at least two parameter distributions include at least one non-locative parameter distribution that describes variations in non-locative parameter values ​​over at least a portion of at least one target. 22. A metrology system according to Clause 21, wherein the non-positional parameters include one or more of the following: intensity asymmetry between complementary diffraction orders, fringe visibility of the pattern in the target image, local intensity, wafer quality, and amplitude of the pattern in the target image. 23. A metrology system according to clause 21 or 22, wherein at least one non-positional parameter distribution comprises multiple non-positional parameter distributions, each relating to a different measurement setting. 24. A metrology system according to any of clauses 1 to 23, comprising alignment correction for correcting alignment measurements performed by alignment sensors. 25. A metrology system according to any of clauses 1 to 23, wherein measurement correction is performed using an alignment sensor and includes correction of parameters of interest other than alignment. 26. A metrology system of clause 25, with an overlay for the parameters of interest. 27. A metrology system according to any of Clauses 1 to 26, wherein the pre-alignment metrology tool is configured to generate a measurement illumination comprising multiple illumination beams of measurement illumination, each of which illumination beams is spatially incoherent or pseudospatially incoherent and has multiple pupil points in the illumination pupil of the metrology device, and for at least the illumination beam corresponding to each measurement direction under consideration, each pupil point of each of the multiple illumination beams has a corresponding pupil point in the other illumination beams of the multiple illumination beams, thereby defining multiple sets of corresponding pupil points, and the pupil points of each set of corresponding pupil points are spatially coherent with respect to one another. 28. Each pupil is substantially spatially incoherent with respect to all other pupils of the same illumination beam. The metrologic system of Clause 27, wherein each set of pupils is the geometric parallel motion of all other sets of pupils in its illuminating pupil, with respect to at least the illumination beam corresponding to the measurement direction under consideration. 29. A pre-alignment metrology tool is a metrology system of Clause 27 or 28, comprising an off-axis illumination generator for generating multiple illumination beams of measurement illumination from a single beam of incoherent radiation. 30. Off-axis lighting generators are Phase grid or 2D phase grid for each measurement direction, A pair of phase gratings or 2D phase gratings, a pair of lenses, and a pair of optical wedges in the Fourier plane defined by one of the lenses, arranged such that various wavelengths within each illumination beam have a common incident illumination angle, or Multiple beam splitter and reflector components arranged to generate four identical illumination beams from a single beam of incoherent radiation, and so that the various wavelengths within each illumination beam have a common incident illumination angle. A metrologic system of Clause 29, comprising one of the following: 31. A metrology system according to any of the clauses 27 to 30, in which each illumination beam is positioned in the illumination pupil, thereby capturing the corresponding higher order diffraction for each illumination beam in the detection pupil of the metrology device after scattering of the measurement illumination by the target. 32. The metrology system of Clause 31, wherein the multiple illumination beams comprise one pair of illumination beams for each measurement direction under consideration, and the corresponding higher-order diffraction orders captured are complementary for each direction. 33. The pupils of each set of corresponding pupils are spatially coherent with respect to all of the multiple illumination beams, or The pupils of each corresponding set of pupils are spatially coherent with respect to each other only for each pair of illumination beams corresponding to one of the measurement directions under consideration. Metrology system under Clause 32. 34. A metrology device capable of operating in a dark-field configuration so as not to detect zero-order scattered radiation, as a metrology system of Clause 32 or 33. 35. Metrology system under Article 24, An alignment sensor capable of measuring multiple targets and acquiring alignment data, It is equipped with, A lithography system in which the processing unit is capable of applying alignment correction to alignment data and acquiring corrected alignment data. 36. The lithography system according to Clause 35, comprising a lithography exposure station operable to use corrected alignment data when positioning a substrate having multiple targets for a lithography exposure process.

Claims

1. A pre-alignment metrology tool capable of operating to measure multiple targets on a substrate in order to acquire measurement data, A processing unit, The measurement data is processed to determine, for each target, at least one positional distribution that describes the variation in the positional value over at least a portion of the target, and A processing unit is configured to determine a measurement correction that corrects for intra-target variation in each of the targets from the at least one position distribution, and the measurement correction for correcting the measurement is performed by an alignment sensor. A metrologic system equipped with [a specific feature / feature].

2. The metrology system according to claim 1, wherein the measurement correction comprises at least one independent measurement correction for each target.

3. The metrology system according to claim 1 or 2, wherein the measurement correction comprises a plurality of independent measurement corrections for each target or a subset thereof.

4. The metrology system according to claim 3, wherein each of the plurality of independent measurement corrections for each target corresponds to its respective measurement setting.

5. The metrology system according to any one of claims 1 to 4, wherein the processing unit is operable to determine the measurement correction as, for each target, the difference or comparison between at least a representative position value that has not been corrected for intra-target variation and a corrected position value that has been corrected for intra-target variation.

6. The metrology system according to any one of claims 1 to 5, wherein the processing unit is operable to process the measurement data and determine at least two parameter distributions, including the at least one position distribution.

7. The metrology system according to claim 6, wherein the processing unit is operable to determine, for each target, at least one weighting coefficient for at least one of at least two parameter distributions, and to obtain a corresponding corrected position distribution comprising the combination of the at least two parameter distributions to which the at least one weighting coefficient applies, the at least one weighting coefficient minimizes the variation metric in the corrected position distribution.

8. The metrologic system according to claim 6 or 7, wherein the at least two parameter distributions include at least one non-positional parameter distribution that describes the variation of the non-positional parameter value over at least a portion of the at least one target.

9. The metrology system according to claim 8, wherein the non-positional parameters include one or more of the following: intensity asymmetry between complementary diffraction orders, fringe visibility of the pattern in the target image, local intensity, wafer quality, and amplitude of the pattern in the target image.

10. The metrology system according to any one of claims 1 to 9, wherein the measurement correction comprises alignment correction for correcting alignment measurements performed by the alignment sensor.

11. The metrology system according to any one of claims 1 to 10, wherein the measurement correction comprises correction of parameters of interest other than alignment, performed using the alignment sensor.

12. The metrologic system according to claim 11, wherein the parameters of interest are overlaid.

13. The metrology system according to any one of claims 1 to 12, wherein the pre-alignment metrology tool is configured to generate a measurement illumination comprising a plurality of illumination beams of measurement illumination, each of the illumination beams being spatially incoherent or pseudospatially incoherent and having a plurality of pupil points in the illumination pupil of the metrology device, and for at least the illumination beam corresponding to each measurement direction under consideration, each pupil point of each of the plurality of illumination beams has a corresponding pupil point in the other illumination beam of the plurality of illumination beams, thereby defining a plurality of sets of corresponding pupil points, and the pupil points of each set of corresponding pupil points are spatially coherent with respect to one another.

14. The metrology system according to claim 10, The system includes an alignment sensor capable of measuring the plurality of targets and acquiring alignment data, A lithography system in which the processing unit is operable to apply the alignment correction to the alignment data and acquire the corrected alignment data.

15. The lithography system according to claim 14, further comprising a lithography exposure station operable to use the corrected alignment data when positioning the substrate having the plurality of targets for a lithography exposure process.

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