Alignment method and associated alignment and lithographic apparatus

Abstract

A method for determining or correcting a stage position in a lithographic process is disclosed. The method comprises obtaining transport data describing the transport of alignment radiation onto the substrate; obtaining position data relating to a stage position of the stage and / or a sensor position of the sensor. A weighting is determined for the position data based on the transport data. The position is based on the transport data, position data and weighting.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European application 19213963.2, filed on 5 December 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to methods and apparatus for use in device fabrication, such as by photolithography, and to methods for fabricating devices using said photolithography. The invention also relates to metrology apparatus, and more specifically to metrology apparatus for measuring the position of objects such as alignment sensors and photolithography apparatus having such alignment sensors. Background Technology

[0004] A photolithography apparatus is a machine that applies a desired pattern onto a substrate (typically a target portion of the substrate). Photolithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning apparatus, alternatively called a mask or photomask, can be used to generate a circuit pattern to be formed on a single layer of the IC. This pattern can then be transferred onto a target portion (e.g., a portion of a die, one or more dies) on a substrate (e.g., a silicon wafer). Typically, the pattern is transferred by imaging the pattern onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a grid of adjacent target portions that are patterned sequentially. These target portions are often referred to as "fields".

[0005] In the fabrication of complex devices, numerous photolithographic patterning steps are typically performed, thereby forming functional features in successive layers on the substrate. Therefore, a crucial aspect of the performance of a photolithography apparatus is its ability to correctly and accurately place the applied pattern relative to features set in previous layers (by the same or different photolithography apparatuses). For this purpose, the substrate has one or more sets of alignment marks. Each mark is structured such that its position can be measured later using a position sensor (typically an optical position sensor). The photolithography apparatus includes one or more alignment sensors by which the position of the marks on the substrate can be accurately measured. Different types of marks and different types of alignment sensors are known from different manufacturers and from different products of the same manufacturer.

[0006] In other applications, measurement sensors are used to measure exposed structures on a substrate (after resist neutralization and / or etching). A fast and non-invasive form of specialized inspection tool is a scatterometer in which a radiation beam is directed onto a target on the surface of the substrate, and the properties of the scattered or reflected beam are measured. Examples of known scatterometers include angle-resolved scatterometers of the type described in US2006033921A1 and US2010201963A1. In addition to measuring characteristic shapes via reconstruction, such devices can also be used to measure diffraction-based overlap, as described in published patent application US2006066855A1. Diffraction-based overlap measurement using dark-field imaging with diffraction orders enables overlap measurements of smaller targets. Examples of dark-field imaging measurements can be found in international patent applications WO2009 / 078708 and WO2009 / 106279, the entire contents of which are hereby incorporated by reference. Further developments in the technology have been described in published patent publications US20110027704A, US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A, and WO2013178422A1. These targets can be smaller than the illumination spot and can be surrounded by the product structure on the wafer. Using composite grating targets, multiple gratings can be measured in a single image. The contents of all these applications are also incorporated herein by reference.

[0007] In some metrology applications, such as position measurement using alignment sensors, a complementary platform position monitoring (SPM) subsystem operates complementaryly to the alignment sensor. Such an SPM subsystem monitors the positional difference between the platform (wafer platform / substrate platform and / or mask platform) and the sensor and determines corrections for the positioning and / or movement of the platform. Such an SPM subsystem can monitor the position of the platform, the position of the sensor (or any specific component of the sensor), and combinations thereof. It is desirable to provide or adapt such an SPM subsystem for other types of alignment sensors. Summary of the Invention

[0008] The present invention provides, in a first aspect, a method for determining the position of a target structure on a substrate supported by a platform during an alignment process using a sensor; comprising: obtaining transmission data describing the transmission of alignment radiation onto the substrate; obtaining position data relating to the platform position and / or the sensor position of the sensor; determining a weighted average of the position data based on the transmission data; and determining the position based on the transmission data, the position data, and the weighted average.

[0009] In a second aspect, the present invention provides a method for determining the position of a target structure on a substrate supported by a platform during an alignment process using a sensor; comprising: obtaining transmission data describing the transmission of alignment radiation onto the substrate; obtaining position data relating to the platform position and / or the sensor position of the sensor; tuning the spectral characteristics of the transmission of the alignment radiation such that the transmission of the alignment radiation has improved spectral characteristics relative to the spectral characteristics of the position data; and determining the position based on the position data.

[0010] It also discloses computer programs, measuring devices, and lithography equipment capable of operating to perform the methods of the first aspect and / or the second aspect.

[0011] The above and other aspects of the invention will be understood in light of the considerations given in the examples described below. Attached Figure Description

[0012] Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

[0013] Figure 1 The photolithography equipment is described;

[0014] Figure 2 schematic diagram Figure 1 The measurement and exposure processes in the equipment;

[0015] Figure 3 This is a schematic diagram of a first alignment sensor that can be adjusted according to an embodiment;

[0016] Figure 4 This is a schematic diagram of a second alignment sensor that can be adjusted according to an embodiment;

[0017] Figure 5 This is a schematic diagram of an alternative measuring device that can also be used for alignment and can be adjusted according to the embodiments;

[0018] Figure 6 Includes: (a) an image of the pupil of the incident radiation; (b) a diagram showing... Figure 5 The operating principle of the measuring device is illustrated in the pupil image of the off-axis illumination beam; and (c) shows the figure. Figure 5 Another operating principle of the measuring device is the pupil image of the off-axis illumination beam;

[0019] Figure 7 It is used for, for example Figure 5 The exemplary illumination source arrangement of the measuring device shown in the figure; and

[0020] Figure 8The time curves include: (a) platform position monitoring signals; and (b) a weighting function for the platform position monitoring signals according to an embodiment; and

[0021] Figure 9 It includes: (a) a time curve of the platform position monitoring signal; (b) a corresponding spectral curve of the platform position monitoring signal; (c) a time curve of the transmission characteristics of the measuring device; and (d) a corresponding spectral curve of the transmission characteristics. Detailed Implementation

[0022] Before describing the embodiments of the present invention in detail, it is helpful to provide example environments in which the embodiments of the present invention can be implemented.

[0023] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus includes: an irradiation system (irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation or DUV radiation); a patterning apparatus support or support structure (e.g., a mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning apparatus according to certain parameters; two substrate stages (e.g., wafer stages) WTa and WTb, each substrate stage configured to hold a substrate (e.g., a wafer coated with resist) W, and each substrate stage connected to a second positioner PW configured to accurately position the substrate according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the radiation beam B by the patterning apparatus MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. The reference frame RF connects various components and serves as a reference or benchmark for setting and measuring the positions of the patterning apparatus and the substrate, as well as the positions of features on the patterning apparatus and the substrate.

[0024] The irradiation 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 guiding, shaping, or controlling radiation.

[0025] The patterning apparatus MT holds the patterning apparatus in a manner dependent on the orientation of the patterning apparatus, the design of the lithography equipment, and other conditions such as whether the patterning apparatus is kept in a vacuum environment. The patterning apparatus support MT can employ mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning apparatus. The patterning apparatus support MT can be a frame or a table; for example, it can be fixed or movable as needed. The patterning apparatus support ensures that the patterning apparatus (e.g., relative to the projection system) is positioned as desired.

[0026] As used herein, the term "patterning apparatus" should be interpreted broadly as any apparatus that can be used to impart a pattern to the cross-section of a radiation beam in order to generate a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not correspond precisely to the desired pattern in the target portion of the substrate (e.g., if the pattern includes phase-shifting features or so-called auxiliary features). Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in a device (such as an integrated circuit) generated in the target portion.

[0027] As described herein, the apparatus is of the transmissive type (e.g., employing a transmissive patterning apparatus). Alternatively, the apparatus may be of the reflective type (e.g., using a programmable mirror array of the type mentioned above, or using a reflective mask). Examples of patterning apparatuses include masks, programmable mirror arrays, and programmable LCD (liquid crystal display) panels. Any term “mask” or “mask” used herein may be considered synonymous with the more general term “patterning apparatus.” The term “patterning apparatus” may also be interpreted as a means of storing pattern information in digital form for use in controlling such a programmable patterning apparatus.

[0028] As used herein, the term "projection system" should be interpreted broadly to include any type of projection system, including refractive, reflective, reflective-refractive, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation used or other factors such as the use of immersion liquids or vacuum. Any term "projection lens" used herein may be considered synonymous with the more general term "projection system."

[0029] The photolithography apparatus may also be of the type in which at least a portion of the substrate is covered by a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces within the photolithography apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system.

[0030] In operation, the irradiator IL receives a radiation beam from a radiation source SO. The source and the lithography apparatus can be separate entities, for example, when the source is an excimer laser. In such cases, the source is not considered part of the lithography apparatus, and the radiation beam is delivered from the source SO to the irradiator IL by means of a beam delivery system BD comprising, for example, suitable directional mirrors and / or beam expanders. In other cases, the source can be an integral part of the lithography apparatus (e.g., when the source is a mercury lamp). The source SO, the irradiator IL, and the beam delivery system BD, provided as needed, can be collectively referred to as the radiation system.

[0031] The irradiator IL may, for example, include an adjuster AD, an integrator IN, and a concentrator CO for adjusting the angular intensity distribution of the radiation beam. The irradiator can be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0032] The radiation beam B is incident on the patterning apparatus MA held on the patterning apparatus support MT and patterned by the patterning apparatus. After traversing the patterning apparatus (e.g., mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto the target portion C of the substrate W. The substrate stage WTa or WTb can be precisely moved, for example, to position different target portions C within the path of the radiation beam B, by means of the second positioner PW and the position sensor IF (e.g., interferometric measurement device, linear encoder, 2D encoder, or capacitive sensor). Similarly, the first positioner PM and another position sensor (…) can be moved, for example, after mechanical retrieval from a mask library or during scanning. Figure 1 (Not explicitly shown) for accurately positioning the pattern forming apparatus (e.g., mask) MA relative to the path of the radiation beam B.

[0033] The patterning apparatus (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks occupy dedicated target portions, they can be located in the space between multiple target portions (these are referred to as scribing alignment marks). Similarly, when more than one die is disposed on the patterning apparatus (e.g., mask) MA, the mask alignment marks can be located between the dies. Small alignment marks can also be included within the dies, between device features, in which case it is desirable that the markings be as small as possible and do not require any imaging or process conditions different from adjacent features. An alignment system for detecting these alignment marks is further described below.

[0034] The depicted apparatus can be used in various modes. In scanning mode, the pattern forming apparatus support (e.g., mask stage) MT and the substrate stage WT are scanned simultaneously while the pattern to be applied to the radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The speed and direction of the substrate stage WT relative to the pattern forming apparatus support (e.g., mask stage) MT can be determined by the magnification (reduction) and image inversion characteristics of the projection system PS. In scanning mode, the maximum size of the exposure field limits the width of the target portion (along the non-scanning direction) in a single dynamic exposure, while the length of the scanning motion determines the height of the target portion C (along the scanning direction). Other types of lithography apparatus and operating modes are possible, as is known in the art. For example, stepping mode is known. In so-called "maskless" lithography, the programmable pattern forming apparatus is kept stationary but has a changing pattern, and the substrate stage WT is moved or scanned.

[0035] Alternatively, combinations and / or variations of the usage patterns described above, or entirely different usage patterns, may be used.

[0036] The lithography apparatus LA is a so-called dual-platform type, featuring two substrate stages WTa and WTb, and two stations—an exposure station EXP and a measurement station MEA—where the substrate stages can be exchanged. While a substrate on one stage is being exposed at the exposure station, another substrate can be loaded onto the other substrate stage at the measurement station, and various preparatory steps can be performed. This enables a significant increase in the apparatus's throughput. The preparatory steps may include mapping or plotting the surface height profile of the substrate using a level sensor LS and measuring the position of alignment marks on the substrate using an alignment sensor AS. If the position sensor IF cannot measure the position of the substrate stage simultaneously at both the measurement and exposure stations, a second position sensor can be provided to enable tracking of the substrate stage's position relative to the reference frame RF at both stations. Other arrangements are known and available instead of the illustrated dual-platform arrangement. For example, other lithography apparatuses in which substrate stages and measurement stages are arranged are known. These substrate stages and measurement stages are mated together during preparatory measurements and then dismounted during exposure.

[0037] Figure 2 The diagram illustrates exposing a target portion (e.g., a die) to... Figure 1 The steps on substrate W in the dual-platform apparatus are shown. The steps on the left-hand side (within the dashed box) are performed at the measurement station MEA, while the steps on the right-hand side are performed at the exposure station EXP. Typically, one of the substrate stages WTa and WTb will be located at the exposure station, while the other substrate stage will be located at the measurement station, as described above. For the purposes of this description, it is assumed that substrate W has already been loaded into the exposure station. At step 200, a new substrate W' is loaded into the apparatus via a mechanism not shown. Both substrates are processed in parallel to increase the throughput of the lithography apparatus.

[0038] First, consider the newly loaded substrate W'. This substrate can be a previously untreated substrate, prepared with a new photoresist for the first exposure in the apparatus. However, typically, the described lithography process will only be one step in a series of exposure and processing steps, such that the substrate W' has already passed through this apparatus and / or other lithography apparatuses several times, and may undergo subsequent processes. In particular, to address the issue of improving overlap performance, the task will be to ensure that the new pattern is correctly applied to the correct position on the substrate that has already undergone one or more cycles of patterning and processing. These processing steps gradually introduce deformations into the substrate, which must be measured and corrected to achieve satisfactory overlap performance.

[0039] Pre- and / or subsequent patterning steps (as just mentioned) can be performed in other lithography equipment, and even in different types of lithography equipment. For example, in device fabrication, some layers with very high requirements for parameters such as resolution and overlap can be processed in more advanced lithography tools compared to other layers with less stringent requirements. Therefore, some layers can be exposed in immersion lithography tools, while others are exposed in "dry" tools. Some layers can be exposed in tools operating at DUV wavelengths, while others are exposed using EUV wavelength radiation.

[0040] At point 202, alignment measurements using the substrate marker P1 and an image sensor (not shown) are used to measure and record the alignment of the substrate relative to the substrate stage WTa / WTb. Furthermore, an alignment sensor AS is used to measure several alignment marks spanning the entire substrate W'. In one embodiment, these measurements are used to establish a "wafer grid" that maps the distribution of the marks across the entire substrate very accurately, including any distortions relative to the nominal rectangular grid.

[0041] At step 204, the horizontal sensor LS is also used to measure a graph of the wafer height (Z) relative to the XY position. Typically, height mapping is used only to achieve accurate focusing of the exposed pattern. Height maps or height mappings can be used for other purposes.

[0042] When substrate W' is loaded, configuration data 206 is received, which defines the exposure to be performed and also defines the properties of the wafer, the pattern previously fabricated on the wafer, and the pattern to be fabricated on the wafer. Measurements of wafer position, wafer grid, and height mapping performed at 202 and 204 are added to this configuration data, allowing a complete set of configurations and measurement data 208 to 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 the product pattern (which is the product of the lithography process). This alignment data, acquired just before exposure, is used to generate an alignment model with parameters that fit the model to the data. These parameters and the alignment model are used during the exposure operation to correct the position of the pattern applied in the current lithography step. The model used interpolates positional deviations between the measured positions. A typical alignment model may include four, five, or six parameters that together define the translation, rotation, and scaling of the "ideal" grid in different dimensions. A high-level model using more parameters is known.

[0043] At 210, wafers W' and W are swapped so that the substrate W' being measured becomes the substrate W entering the exposure station EX. Figure 1 In the example apparatus, this interchange is performed by swapping the supports WTa and WTb within the apparatus, ensuring that the substrates W and W' remain accurately clamped and positioned on those supports to maintain relative alignment between the substrate stage and the substrate itself. Therefore, once the stage has been interchanged, determining the relative position between the projection system PS and the substrate stage WTb (formerly WTa) is necessary to control the exposure steps using measurement information 202, 204 of the substrate W (formerly W'). At step 212, mask alignment is performed using the mask alignment marks M1, M2. In steps 214, 216, 218, scanning motion and radiation pulses are applied to continuous target areas across the entire substrate W to complete the exposure of multiple patterns.

[0044] By using the alignment data and height mapping obtained at the measuring station during the execution of the exposure step, these patterns are accurately aligned relative to the desired locations, and specifically, accurately aligned relative to features previously placed on the same substrate. At step 220, the exposed substrate, now labeled "W", unloaded from the equipment, undergoes etching or other processes according to the exposed pattern.

[0045] Those skilled in the art will recognize that the above description is a simplified overview of many very detailed steps involved in an example of a real manufacturing scenario. For instance, instead of measuring alignment in a single stroke or during a single process, there will often be multiple separate stages of coarse and fine measurements using the same or different markings. The coarse alignment measurement steps and / or fine alignment measurement steps can be performed before or after the height measurement, or interleaved with the height measurement.

[0046] In the fabrication of complex devices, numerous photolithographic patterning steps are typically performed, thereby forming functional features in successive layers on the substrate. Therefore, a crucial aspect of the performance of the photolithography apparatus is its ability to correctly and accurately place the applied pattern relative to features set in previous layers (by the same or different photolithography apparatus). For this purpose, the substrate has one or more sets of markers. Each marker is structured such that its position can be measured later using a position sensor (typically an optical position sensor). The position sensor may be referred to as an "alignment sensor," and the marker may be referred to as an "alignment marker."

[0047] Photolithography apparatuses may include one or more alignment sensors that can accurately measure the position of alignment marks set on a substrate. Alignment sensors (or position sensors) can use optical phenomena such as diffraction and interference to obtain positional information from the alignment marks formed on the substrate. Examples of alignment sensors used in current photolithography apparatuses are based on self-reference interferometers as described in US6961116. Various improvements and modifications to these position sensors have been developed, such as those disclosed in US2015261097A1. All of these disclosures are incorporated herein by reference.

[0048] The markings or alignment marks may comprise a series of gratings formed on or within a layer disposed on the substrate, or (directly) formed in the substrate. These gratings are regularly spaced and act as grating lines, such that the markings can be considered as diffraction gratings with a well-known spatial period (spacing). Depending on the orientation of these grating lines, the markings can be designed to allow measurements along the x-axis or along the y-axis (with the y-axis oriented approximately perpendicular to the x-axis). Markings comprising gratings arranged at +45 degrees and / or -45 degrees relative to both the x-axis and y-axis allow for combined x- and y-measurements using techniques as described in US2009 / 195768A (which is incorporated herein by reference).

[0049] The alignment sensor can optically scan each mark using a radiation spot to obtain a periodically changing signal, such as a sine wave. The phase of this signal is analyzed to determine the position of the mark, and thus the position of the substrate relative to the alignment sensor, which is subsequently fixed relative to the reference frame of the photolithography apparatus. So-called coarse and fine marks involving different (coarse and fine) mark sizes can be configured so that the alignment sensor can distinguish different periods of the periodic signal and, more precisely, the exact position (phase) within a period. Marks with different spacing can also be used for this purpose.

[0050] Measuring the position of the markings, which are provided on the substrate, for example, in the form of a wafer grid, can also provide information about the deformation of the substrate. Deformation of the substrate may occur, for example, by electrostatically clamping the substrate to the substrate stage and / or by heating the substrate when it is exposed to radiation.

[0051] Figure 3This is a schematic block diagram of a known alignment sensor AS. A radiation source RSO provides a beam RB having one or more wavelengths, which is directed by a steering optics onto a marker (such as a marker AM located on a substrate W) as an illumination spot SP. In this example, the steering optics include a spot mirror SM and an objective lens OL. The diameter of the illumination spot SP (on which the marker AM is illuminated) can be slightly smaller than the width of the marker itself.

[0052] Radiation diffracted by the marker AM (in this example, via the objective lens OL) is collimated into the information-carrying beam IB. The term "diffraction" is intended to include zero-order diffraction from the marker (which may be referred to as reflection). A self-referenced interferometer SRI (e.g., of the type disclosed in US6961116 mentioned above) causes the beam IB to interfere with itself, after which the beam is received by a photodetector PD. In cases where more than one wavelength is generated by the radiation source RSO, additional optics (not shown) may be included to provide multiple separate, i.e., individual beams. The photodetector may be a single element, or it may include multiple pixels (if desired). The photodetector may include a sensor array.

[0053] The steering optics (which in this example includes the speckle mirror SM) can also be used to block the zero-order radiation reflected from the marker, so that the information-carrying beam IB only includes higher-order diffraction radiation from the marker AM (this is not necessary for measurement, but improves the signal-to-noise ratio).

[0054] The intensity signal SI is supplied to the processing unit PU. Through a combination of optical processing in the frame SRI and computational processing in the unit PU, the values ​​of the X and Y positions on the substrate relative to the reference frame are output.

[0055] A single measurement of the type illustrated only fixes the position of the mark within a certain range corresponding to a spacing of the mark. Coarser measurement techniques can be used in conjunction with this to identify which period of the sine wave contains the marked position. To increase accuracy (precision) and / or to robustly detect the mark, regardless of the material on which the mark is made and on or below it, the same process can be repeated at different wavelengths at coarser and / or finer levels.

[0056] A platform position monitoring subsystem (SPM) is configured to monitor the position and / or motion of the platform or wafer stage (WT) relative to a desired position and / or motion. The SPM may, for example, include sensors or encoders on the system's measurement frame for measuring the platform position. The SPM subsystem will be described in more detail below.

[0057] Figure 4 The figure illustrates a schematic cross-sectional view of another known alignment device 400. In this example embodiment, the alignment device 400 can be configured to align a substrate (e.g., substrate W) relative to a patterning apparatus (e.g., patterning apparatus MA). The alignment device 400 can also be configured to detect the position of alignment marks on the substrate and use the detected position of the alignment marks to align the substrate relative to the patterning apparatus or other components of the photolithography apparatus 100 or 100'. Such alignment of the substrate ensures accurate exposure of one or more patterns on the substrate.

[0058] According to an embodiment, the alignment device 400 may include an illumination system 402, a beam splitter 414, an interferometer 426, a detector 428, and a signal analyzer 430, as exemplified in this embodiment. The illumination system 402 may be configured to provide a narrow-band electromagnetic radiation beam 404 having one or more passbands. In one example, the one or more passbands may be within a wavelength spectrum between about 400 nm and about 2.0 μm. In another example, the one or more passbands may be discrete narrow passbands within a wavelength spectrum between about 400 nm and about 2.0 μm.

[0059] Beam splitter 414 can be configured to receive radiation beam 404 and guide sub-radiation beam 415 onto substrate 420 placed on platform 422. In one example, platform 422 is movable along direction 424. Sub-radiation beam 415 can be configured to illuminate alignment mark or target 418 located on substrate 420. In this embodiment, alignment mark or target 418 can be coated with a radiation-sensitive film. In another example, alignment mark or target 418 can have 180° symmetry. That is, when alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to the plane of alignment mark or target 418, the rotated alignment mark or target 418 can be substantially identical to the unrotated alignment mark or target 418. The target 418 on the substrate 420 may be: (a) a resist layer grating, comprising grating strips formed by solid resist lines; or (b) a product layer grating; or (c) a composite grating stack in an overlapping target structure, comprising resist gratings overlapping or interleaved on the product layer grating. The grating strips may alternatively be etched into the substrate.

[0060] According to an embodiment, the beam splitter 414 may also be configured to receive the diffracted radiation beam 419 and guide the diffracted radiation sub-beams 429 toward the interferometer 426.

[0061] In an example embodiment, the diffracted sub-beam 429 may be at least a portion of the sub-beam 415 that can be reflected from the alignment mark or target 418. In this example embodiment, the interferometer 426 includes any suitable group of optical elements, such as a prism combination that can be configured to form two images of the alignment mark or target 418 based on the received diffracted sub-beam 429. The interferometer 426 may also be configured to rotate one of the two images by 180° relative to the other image and to interferometrically recombine the rotated and unrotated images. In some embodiments, the interferometer 426 may be a self-reference interferometer (SRI) disclosed in U.S. Patent No. 6,628,406 (Kreuzer), the entirety of which is incorporated herein by reference.

[0062] In an embodiment, detector 428 may be configured to receive the recombined image via interferometer signal 427 when the alignment axis 421 of alignment device 400 passes through the center of symmetry (not shown) of alignment mark or target 418, and to detect interference resulting from the recombined image. This interference may be due to the alignment mark or target 418 being 180° symmetrical, and according to an example embodiment, the recombined image interferes constructively or destructively. Based on the detected interference, detector 428 may also be configured to determine the position of the center of symmetry of alignment mark or target 418 and thus detect the position of substrate 420. According to an example, alignment axis 421 may be aligned with an optical beam perpendicular to substrate 420 and passing through the center of image rotation interferometer 426. Detector 428 may also be configured to estimate the position of alignment mark or target 418 by implementing sensor characteristics and interacting with changes in the wafer marking process.

[0063] like Figure 3 As in the alignment sensor, the platform position monitoring subsystem 435 is configured to monitor the position and / or movement of the platform 422 relative to the desired position and / or movement.

[0064] Another type of measurement sensor, applicable to both alignment and product / process monitoring measurement applications, has recently been described in European applications EP18195488.4 and EP19150245.9, which are incorporated herein by reference. This describes a measurement device with optimized coherence. More specifically, the measurement device is configured to generate multiple spatially incoherent beams of measurement illumination, each beam (or two beams of a measurement pair, each measurement pair corresponding to a measurement direction) having corresponding regions within their cross-sections where the phase relationship between the beams is known; that is, the corresponding regions exhibit mutual spatial coherence.

[0065] Such a measurement device is capable of measuring small-pitch targets with acceptable (minimal) interference artifacts (speckles) and will also be capable of operating in dark-field mode. Such a measurement device can be used as a position or alignment sensor for measuring substrate position (e.g., measuring the position of periodic structures or alignment marks relative to a fixed reference position). However, the measurement device can also be used for overlapping measurements (e.g., in the case of stitching marks, measuring the relative positions of periodic structures in different layers, or even in the same layer). The measurement device is also capable of measuring the asymmetry of periodic structures and can therefore be used to measure any parameter based on the target asymmetry measurement results (e.g., using diffraction-based overlap (DBO) techniques or focusing using diffraction-based focusing (DBF) techniques).

[0066] Figure 5 This illustrates a possible implementation of such a measurement device. The device essentially operates as a standard microscope and features a novel illumination mode. The measurement device 500 includes an optical module 505 containing the main components of the device. An illumination source 510 (which may be located outside the module 505 and optically coupled to the module 505 by a multimode fiber 515) provides a spatially incoherent radiation beam 520 to the optical module 505. An optical component 517 transmits the spatially incoherent radiation beam 520 to a coherent off-axis illumination generator 525. This component is particularly important to the concept herein and will be described in more detail. The coherent off-axis illumination generator 525 generates multiple (e.g., four) off-axis beams 530 from the spatially incoherent radiation beam 520. The characteristics of these off-axis beams 530 will be described in further detail below. The zero-order of the illumination generator can be blocked by an illumination zero-order blocking element 575. This zeroth order will only be presented for some examples of coherent off-axis illumination generators described in this document (e.g., phase grating-based illumination generators), and therefore can be omitted when no such zeroth order illumination is generated. The off-axis beam 530 (via optics 535 and spot mirror 540) is passed to (e.g., high NA) objective 545. The objective focuses the off-axis beam 530 onto a sample (e.g., periodic structure / alignment mark) located on a substrate 550, where the off-axis beam 530 is scattered and diffracted. The scattered higher diffraction orders 555+, 555 (e.g., +1 and -1 orders, respectively) propagate back via the spot mirror 540 and are focused by optics 560 onto a sensor or camera 565, where the scattered higher diffraction orders 555+, 555- interfere to form an interference pattern. Then, the processor 580, running appropriate software, can process one or more images of the interference pattern captured by the camera 565.

[0067] The zero-order diffracted (specularly reflected) radiation is blocked at appropriate locations in the detection branch by, for example, the speckled mirror 540 and / or separate detection zero-order blocking elements. It should be noted that there is a zero-order reflection for each off-axis illumination beam, i.e., a total of four zero-order reflections exist in this current embodiment. Thus, the measurement device operates as a "dark field" measurement device.

[0068] In this measurement apparatus, spatial coherence is induced in the measurement illumination only when necessary. More specifically, spatial coherence is induced between corresponding sets of pupil points in each of the off-axis beams 530. More specifically, a set of pupil points comprises a corresponding single pupil point in each of the off-axis beams, the sets of pupil points being spatially coherent with each other, but wherein each pupil point is incoherent with respect to all other pupil points in the same beam. By optimizing the coherence of the measurement illumination in this way, performing dark-field off-axis illumination on small-pitch targets becomes feasible, but with minimal speckle artifacts, because each off-axis beam 530 is spatially incoherent.

[0069] Figure 6 Three pupil images are shown to illustrate the concept described. Figure 6 (a) shows the relationship with Figure 5 The first pupil image related to the pupil plane P1 in the image, and Figure 6 (b) and Figure 6 (c) Each is shown with Figure 5 The second pupil image related to the pupil plane P2 in the image. Figure 6 (a) (in cross-section) shows the spatially incoherent radiation beam 520, and Figure 6 (b) and Figure 6 (c) (in cross-section) shows the off-axis beam 530 generated by the coherent off-axis illumination generator 525 in two different embodiments. In each case, the range of the outer circle 595 corresponds to the maximum detection NA of the microscope objective; this can be 0.95 NA (by way of example only).

[0070] In each of the pupils, triangle 600 indicates a set of pupil points that are spatially coherent with respect to each other. Similarly, cross 605 indicates another set of pupil points that are spatially coherent with respect to each other. The triangles are spatially incoherent with respect to the cross and all other pupil points corresponding to beam propagation. (In Figure 6 (b) shows the example. The general principle is that each set of pupil points that is spatially coherent (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.

[0071] exist Figure 6 In (b), the spacing between each pupil point of the first set of coherent points represented by triangle 600 must be equal to the spacing between each pupil point of the set of coherent points represented by cross 605. The “spacing” in this context is directional; that is, the cross set (the second set of points) is not allowed to rotate relative to the triangle set (the first set of points). Thus, each off-axis bundle 530 comprises incoherent radiation on its own; however, the off-axis bundles 530 together comprise the same bundle having corresponding sets of points within their cross-sections and having a known phase relationship (spatial coherence). It should be noted that the points in each set of points need not be equally spaced (e.g., the spacing between the four triangles 605 in this example does not need to be equal). Thus, the off-axis bundles 530 need not be arranged symmetrically within the pupils.

[0072] Figure 6 (c) shows that this basic concept can be extended to provide mutual spatial coherence only between bundles corresponding to a single measurement direction, where bundle 530X corresponds to a first direction (X direction) and bundle 530Y corresponds to a second direction (Y direction). In this example, the square and the plus sign each indicate a set of pupil points that correspond to, but are not necessarily spatially coherent with, the set of pupil points represented by the triangle and the cross. However, the cross is spatially coherent with each other, as is the plus sign, and the cross is a geometric translation within the pupil of the plus sign. Thus, in Figure 6 In (c), the off-axis bundles are only paired coherent.

[0073] In this embodiment, the off-axis beams are considered separately / individually by direction (e.g., X-direction 530X and Y-direction 530Y). The beam pair 530X that produces the captured X-direction diffraction order only needs to be coherent with each other (such that point pair 600X is coherent with each other, as is point pair 605X). Similarly, the beam pair 530Y that produces the captured Y-direction diffraction order only needs to be coherent with each other (such that point pair 600Y is coherent with each other, as is point pair 605Y). However, point pairs 600X and 600Y do not need to be coherent with each other, nor do point pairs 605X and 605Y. Thus, there exist coherent point pairs contained within the pair of off-axis beams corresponding to each considered measurement direction. As previously stated, for each beam pair corresponding to the measurement direction, each coherent point pair is a geometric translation within the pupil of all other coherent point pairs.

[0074] In some devices (such as) Figure 5In the measurement apparatus illustrated in the figure, single-mode and multi-mode coherent light sources cannot be used for illumination because they produce highly non-uniform illumination. However, coherent sources have the advantage of often being very bright. Therefore, incoherent sources for such a measurement apparatus may include coherent sources and a coherence scrambling arrangement for disrupting the output of the coherent sources.

[0075] Figure 7 This paper illustrates a coherence scrambling arrangement suitable for converting the output of a spatially coherent source into a spatially incoherent (or pseudo-incoherent) source. The main principle involves moving the focusing spot FS from the coherent source CS on the core input facet InF of a multimode fiber MF. Figure 7 (a) shows a simplified schematic diagram of this arrangement, and Figure 7 (b) A planar representation of the input facet InF of a multimode fiber MF is shown; the input facet InF includes the core facet CF (a brighter shaded circle) and the fiber cladding CL outside the core facet CF, as well as the surrounding ferrule or other coating (a darker shaded area).

[0076] The specific arrangement illustrates a single-mode fiber (SMF) transmitting radiation from an incoherent light source (IS). Intervention optics transmit this radiation to the multimode fiber (MMF) via a scanning mirror (SM), a spatial light modulator (SLM), or other scanning components. In the illustrated specific arrangement, the intervention optics include a fiber collimator (FC) for transmitting the beam from the single-mode fiber (SMF) to the scanning mirror (SM). SM And imaging systems (e.g., 4f imaging systems) 4f SM and a similar arrangement FC for transmitting the bundle to the multimode fiber MMF. MM 4f MM .

[0077] With this arrangement, coherence disturbances can be controlled by focusing the output of the coherent source CS onto the facet InF of the multimode fiber MMF and scanning across the spot FS on the input facet InF, so that the scanning mirror SM or other scanning device capable of scanning the focused spot can be used to scan across the fiber core facet CF. Figure 7 (b) shows an exemplary beam path BP of the focused spot FS, wherein the spot FS is scanned on the input facet InF according to a zigzag or meandering pattern.

[0078] The NA of the multimode fiber (MMF) can be matched with the illumination NA output by the coherence disruptor, and the entire core of the fiber can be uniformly scanned during the single-frame integration time of the system's camera (not shown). In this way, during this uniform scan, all fiber modes are treated equally, and speckle contrast is minimized for a given fiber.

[0079] The lithography apparatus may include a complementary platform position monitoring (SPM) subsystem that operates complementaryly to the alignment sensor. Such an SPM subsystem monitors the position of the platform (wafer platform / substrate platform and / or mask platform) and determines corrections for the platform's positioning and / or movement relative to the platform's expected position and / or movement (sensor feedback during movement). This correction takes into account the fact that the platform, when set to rest at a specific location or moving at a certain speed, will not necessarily precisely follow the required position / movement (e.g., as determined by the alignment sensor using alignment marks measured on the wafer); instead, there will be some variation around the set value. This variation can be measured, for example, by an SPM encoder (or other sensor) on the system's measurement frame. The obtained variation data is fed into the alignment position algorithm to improve the alignment accuracy.

[0080] Additionally, the alignment sensor itself is not completely stationary, which can also affect the measured alignment position. An ARA (Alignment Reference Axis) sensor can be configured to measure the alignment sensor position, and this information is combined into the SPM correction.

[0081] Thus, the location data in the context of this disclosure may include platform location (e.g., as measured by the SPM subsystem) and / or sensor location data (e.g., as measured by ARA); this may include any combination of platform location data or sensor location data. The location data may describe the relative positional differences between the sensors and the platform.

[0082] The SPM subsystem described has been developed for measuring or aligning sensors, such as Figure 3 and Figure 4 The measurement or alignment sensors shown in the diagram. However, for (such as) Figure 5 The optimized coherence measurement system (illustrated in the diagram) using an equivalent SPM subsystem requires a different calibration strategy than currently used. Additionally, for other sensor arrangements (e.g., Figure 3 and Figure 4 The current SPM calibration scheme developed may not be suitable for optimized coherence measurement systems due to significant differences between sensors, especially the differences in the operation of their respective sources.

[0083] As already described, incoherent measurement systems can use incoherent sources, and this incoherence can be obtained by perturbing the coherence of coherent illumination; for example, by using, for example, Figure 7 The source layout is shown in the diagram. Return to reference. Figure 7 (b) When the laser spot FS is incident on the fiber core CF, the laser spot FS will be transmitted efficiently through the fiber. When the spot is incident on the outside of the core (e.g., on the fiber cladding / tube CL), the transmission will be much lower or even zero. This means that alignment measurements will be sensitive only to the portion of the SPM data corresponding to the spot FS incident on the fiber core CF; that is, the SPM data captured during the time when the laser spot is on the fiber core (or close enough to the fiber core for good transmission), such that light from the source reaches and subsequently reaches the camera / detector.

[0084] Therefore, consideration is proposed for the source behavior of the measurement or alignment sensor to provide improved SPM correction. This may include considering the time during which the alignment sensor transmits little or no light to the wafer. Such an approach may include weighting the SPM data (data from the SPM sensor and / or output data from the SPM algorithm) depending on the transmission of light from the alignment sensor source to the wafer. This can be achieved by weighting the SPM data using a weighted source function. The weighted source function can be largely binary in nature; for example, switching between 0% and 100% weight depending on whether illumination is being transmitted. Alternatively, other weighting functions may be used, for example, with some gradient between 0% and 100% weight to correspond to the case where partial illumination transmission occurs as the spot transitions from being incident on the core to being incident on the surroundings (and vice versa). These are just two examples of weighting functions, and other weighting functions are possible.

[0085] Figure 8 (a) An exemplary SPM data trace SPM is shown, where there are arbitrary units on the y-axis and time t on the x-axis. The SPM data can be SPM sensor data (e.g., intensity values) from one or more sensors (e.g., encoders), or SPM control data (e.g., setpoint position or velocity values) determined by an SPM algorithm based on the SPM sensor data. Time t (through shading) is broken down into the duration ti of the alignment sensor transmitting illumination to the wafer (corresponding to the focused spot FS being incident on the core CF). tAnd the duration t during which little or no irradiation is transmitted to the wafer (corresponding to the focused spot FS being incident on the cladding CL). n . Figure 8 (b) shows the trace of an exemplary weighted source function WF, where the y-axis represents the weighting (0 to 100%) and the x-axis represents time. The time axis is further divided into the same duration t during which the alignment sensor is transmitting illumination to the wafer. t and the duration t during which no transmission occurs (or transmission is very low). n Such a weighted source function WF can be used for... Figure 8 The SPM data traces shown in (a) are weighted (weighting can be used, for example, to calculate the average position). In this way, the SPM correction is determined primarily (or entirely) from the SPM data corresponding to the period during which the wafer is receiving alignment illumination, wherein SPM data recorded outside of these time periods is either weighted or discarded entirely.

[0086] The weighted source function WF can be determined, for example, using one or more of the following measurements or methods (this list is not exhaustive):

[0087] 1) The weighted source function can be determined by simulation; for example, by using a light source model that simulates the radiation characteristics (e.g., transmission / reflection) from the source.

[0088] 2) In the light source module, reflection from the fiber facet can be measured. Therefore, one such embodiment may include determining that reflection from the fiber facet is low (indicating light is being transmitted to the alignment optics module); or that reflection is high (indicating light is not being transmitted to the alignment optics module).

[0089] 3) Fiber optic bundle splitters or other optical taps and associated detectors (e.g., photodiodes) can be configured to generate power / intensity sensors (pick-off) on individual detectors. In this way, the amount of light being transmitted into the multimode fiber can be measured directly.

[0090] 4) Since it is desirable to operate the light source module in a repeatable manner (repeating the same scan path), the weighted source function (WF) can be measured offline (e.g., in a single scan or by averaging multiple scans) at the end of the fiber before it is connected to the optical module (e.g., during calibration). This method has a slight drawback compared to other methods: it cannot account for changes in source power over time.

[0091] 5) The sensor branch can be located within the alignment sensor (e.g., at the output, i.e., the emitting end, of the multimode fiber); for example, it includes a dedicated detector (e.g., a photodiode). In this way, the amount of light transmitted from the multimode fiber to the alignment sensor can be measured directly.

[0092] For embodiments that measure intensity online (e.g., embodiments 3 and 5 in the previous paragraph), another advantage of this concept is that the weighted source function can account for and mitigate variations / fluctuations in light source intensity. Thus, the proposed algorithm for determining the weighted source function can take into account the light source intensity variation / fluctuation data (if available).

[0093] Further embodiments, which may be implemented independently or in combination with the embodiments described above, may include active or non-active tuning of existing components, or the addition of tunable elements to the source or sensor, to alter the spectral characteristics of the alignment signal (or the alignment source signal) so that the alignment signal has improved spectral characteristics relative to the SPM signal. It has been observed that the SPM signal is often dominated by one or more spectral frequencies. To address this, periodic or quasi-periodic modulators may be used to modify the spectral content of the alignment signal to reduce crosstalk with the SPM signal, and / or match the signal so that the alignment signal is "locked" to the SPM signal, depending on the specific application.

[0094] The spectral content of the alignment signal can be modified, for example by adding one or more periodic modulators along the optical path (hardware modification), and / or by tuning the scanning speed of the laser on the core facet of the coherence disruptor, i.e., the phase interference frequency generator (no hardware modification required, but not a precisely periodic signal).

[0095] In one embodiment, it is proposed to ensure that the dominant spectral frequency of the on / off time illumination signal is consistent with the dominant spectral frequency of the SPM. In this way, the camera should receive light in phase with a specific location on the platform. Figure 9 Conceptual maps illustrate this situation. Figure 9 (a) is a graph of the SPM (e.g., control or correction) signal versus time t, and Figure 9 (b) is the corresponding spectrum curve (x-axis is frequency f). Figure 9 (c) is the corresponding transmission signal curve (i.e., the intensity I transmitted to the wafer relative to time t), and Figure 9 (d) is the corresponding spectrum curve.

[0096] Effectively, the modulator or the coherence disruptor, i.e., the phase interference frequency converter, is being used for "lock-in" on the SPM signal. This technique can significantly reduce the impact of SPM on reproduction because instead of averaging over the entire SPM variation, averaging is performed on a smaller subrange of this variation (by...). Figure 9 (a) The interval Δ is illustrated in the example.

[0097] Other aspects of the invention are described as follows: as indicated by the following numbered aspects.

[0098] 1. A method for determining the position of a target structure on a substrate supported by a platform during alignment using sensors; the method comprising:

[0099] Obtain transmission data describing the transmission of aligned radiation onto the substrate;

[0100] Obtain location data related to the platform position and / or the sensor position of the sensor;

[0101] Determine the weighting of the location data based on the transmitted data; and

[0102] The location is determined based on the transmitted data, location data, and weighted average.

[0103] 2. The method according to aspect 1, wherein the position data relates to the correction of the positioning and / or movement of the platform relative to the desired position and / or movement.

[0104] 3. The method according to aspect 2, wherein the desired position and / or movement is determined during the alignment process.

[0105] 4. The method according to any one of the foregoing aspects, wherein the weighting is relative to the position data corresponding to the time period during which alignment radiation is not transmitted to the substrate.

[0106] 5. The method according to any one of the foregoing aspects, wherein aligned radiation is transmitted to the substrate via a multimode fiber by scanning a focused radiation beam across the input facet of the multimode fiber to disrupt the spatial coherence of the radiation beam, the scanning comprising a period in which the focused radiation beam is incident outside the core region of the input facet.

[0107] 6. The method according to aspect 5, wherein obtaining the transmission data includes determining the transmission data via simulation using the light source model of the aligned radiation.

[0108] 7. The method according to aspect 5, wherein obtaining the transmission data includes directly measuring the amount of light transmitted through and / or reflected from the optical fiber using a detector.

[0109] 8. The method according to aspect 7, wherein the direct measurement is performed via an optical splitter in the multimode fiber.

[0110] 9. The method according to aspect 7, wherein the direct measurement is performed via a branch located downstream of the output of the multimode fiber.

[0111] 10. The method according to aspect 7, 8 or 9, including taking into account source strength variations when determining the weighting.

[0112] 11. The method according to aspect 5, wherein obtaining the transmission data comprises: measuring the transmission data offline by measuring the transmission at the output of the multimode fiber when the multimode fiber is not connected.

[0113] 12. The method according to any one of aspects 5 to 11 further includes tuning the spectral characteristics of the transmission of the alignment radiation such that the transmission of the alignment radiation has spectral characteristics that are improved relative to the spectral characteristics of the position data.

[0114] 13. The method according to aspect 12, wherein the spectral characteristics of the alignment radiation are tuned such that the main spectral frequency of the transmission of the alignment radiation is better matched with the main spectral frequency of the position data.

[0115] 14. The method according to aspect 12 or 13, wherein the tuning includes modulating the alignment radiation using one or more modulators located within the path of the alignment radiation.

[0116] 15. The method according to aspect 12 or 13, wherein the tuning includes tuning the scanning speed of the focused radiation beam on the input facet.

[0117] 16. The method according to aspect 15, comprising correcting for an accuracy error in the tuning derived from the phase difference between the position data and the scanning speed.

[0118] 17. A method for determining the position of a target structure on a substrate supported by a platform during alignment using sensors; the method comprising:

[0119] Obtain transmission data describing the transmission of aligned radiation onto the substrate;

[0120] Obtain location data related to the platform position and / or the sensor position of the sensor;

[0121] The spectral characteristics of the transmission of the alignment radiation are tuned so that the transmission of the alignment radiation has improved spectral characteristics relative to the spectral characteristics of the position data; and

[0122] The location is determined based on the location data.

[0123] 18. The method according to aspect 17, wherein the spectral characteristics of the alignment radiation are tuned such that the main spectral frequency of the transmission of the alignment radiation is better matched with the main spectral frequency of the position data.

[0124] 19. The method according to aspect 17 or 18, wherein the tuning includes modulating the alignment radiation using one or more modulators located within the path of the alignment radiation.

[0125] 20. The method according to aspects 17, 18 or 19, wherein aligned radiation is transmitted to the substrate via a multimode fiber by scanning a focused radiation beam across the input facet of the multimode fiber to disrupt the spatial coherence of the radiation beam, the scanning comprising a period in which the focused radiation beam is incident outside the core region of the input facet.

[0126] 21. The method according to aspect 20, wherein the tuning includes tuning the scanning speed of the focused radiation beam on the input facet.

[0127] 22. The method according to aspect 21, comprising correcting for an accuracy error in the tuning derived from the phase difference between the position data and the scanning speed.

[0128] 23. A computer program comprising computer-readable instructions operable to perform the method according to any of the foregoing aspects.

[0129] 24. A processor and an associated storage medium, the storage medium comprising a computer program according to aspect 23, enabling the processor to operate to perform the method according to any one of aspects 1 to 22.

[0130] 25. A measuring device comprising a processor according to aspect 24 and an associated storage medium to be operable to perform the method according to any one of aspects 1 to 22.

[0131] 26. The measuring apparatus according to aspect 25, comprising a radiation source arrangement for providing alignment radiation, the radiation source arrangement comprising:

[0132] A coherent radiation source, which is operable to emit a coherent radiation beam;

[0133] Multimode fiber, the multimode fiber being used to transmit the alignment radiation to the measuring device; and

[0134] A scanning component operable to scan the coherent radiation beam across the input facet of the multimode fiber to disrupt the spatial coherence of the radiation beam.

[0135] 27. A photolithography apparatus, comprising:

[0136] A pattern forming apparatus stage for supporting the pattern forming apparatus;

[0137] Substrate stage, used to support the substrate;

[0138] A first measuring device, comprising the measuring device according to aspect 25 or 26 and operable to determine the alignment position of one or both of the pattern forming apparatus support and the substrate support; and

[0139] A second measuring device is used to measure the position of one or both of the pattern forming apparatus platform or the substrate platform.

[0140] Depending on the phase difference between the SPM and the coherent disruptor scan, such a method may introduce accuracy errors. It is desirable that these errors remain constant over time intervals on the order of the inverse of the SPM bandwidth. It is also desirable that these accuracy errors be correctable, and can be corrected, for example, by the following terms:

[0141] 1) Depending on the phase stability and bandwidth of the SPM signal, standard calibration of the reference or different gratings may be sufficient to calibrate and eliminate the error.

[0142] 2) The phase of the coherence disruptor scanning mechanism can be kept synchronized with the phase of the SPM.

[0143] 3) The start time of the image acquisition process can be kept synchronized with the SPM signal.

[0144] 4) The constant calibration error can be corrected using the data recorded by the SPM obtained using the method of the first embodiment described above. Due to technological lock-in, this correction does not need to be repeated for each image acquisition, but only needs to be repeated at intervals on the order of 1 / (SPM bandwidth).

[0145] Although the above methods are described for Figure 5The measurement apparatus illustrated in the figure is described above, but the method can be used with any other suitable measurement apparatus that only has periodic transmission of alignment radiation, such as measurement apparatus including coherence disturbance arrangements as described herein. Thus, any reference to alignment markings can be used to cover and relate to any target structure being measured, whether it is a dedicated measurement / alignment structure formed for measurement purposes or a product structure with characteristics suitable for use in measurement.

[0146] Although specific embodiments of the invention have been described above, it will be understood that the invention may be practiced in ways different from those described.

[0147] While embodiments of the invention have been described above in the context of optical lithography, it should be understood that these embodiments can be used in other applications, such as imprint lithography, and are not limited to optical lithography where circumstances permit. In imprint lithography, the morphology in the patterning apparatus defines a pattern formed on a substrate. The morphology of the patterning apparatus can be imprinted onto a resist layer supplied to the substrate, whereby the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning apparatus is removed from the resist, thereby leaving a pattern therein.

[0148] The terms “radiation” and “beam” as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having wavelengths of 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having wavelengths in the range of 1 nm to 100 nm), as well as particle beams, such as ion beams or electron beams.

[0149] Where context permits, the terms "lens" and "objective" can refer to any one or a combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components. Reflective components are likely to be used in equipment operating in the UV and / or EUV range.

[0150] The breadth and scope of this invention should not be limited by any of the exemplary embodiments described above, but should be defined only by the appended claims and their equivalents.

Claims

1. A method for using an alignment sensor to correct platform position measurements of a target structure on a substrate supported by a platform during alignment; The method includes: Transmission data describing the transmission of alignment radiation toward the platform supporting the substrate is obtained, the transmission data including: the duration during which the alignment sensor is transmitting irradiation to the substrate, and the duration during which little or no irradiation is transmitted to the substrate. Obtain position data relating to the platform position and / or the sensor position of the alignment sensor; Determine the weighting of the location data based on the transmitted data; and The corrected platform position measurement is determined based on the transmitted data, location data, and weighting.

2. The method according to claim 1, wherein, The location data relates to the correction of the platform's positioning and / or motion relative to the desired position and / or motion.

3. The method according to claim 2, wherein, The desired position and / or movement are determined during the alignment process.

4. The method according to any one of the preceding claims, wherein, The weighting is applied relative to the position data corresponding to the time period during which alignment radiation was not transmitted to the substrate.

5. The method according to claim 1, wherein, Aligned radiation is transmitted to the substrate via a multimode fiber by scanning a focused radiation beam across the input facet of the multimode fiber to disrupt the spatial coherence of the radiation beam, the scanning including a period in which the focused radiation beam is incident outside the core region of the input facet.

6. The method according to claim 5, wherein, The acquisition of transmission data includes determining the transmission data via simulation using the light source model of the aligned radiation.

7. The method according to claim 5, wherein, The acquisition of transmission data includes directly measuring the amount of light transmitted through and / or reflected from the multimode fiber using a detector.

8. The method according to claim 7, wherein, The direct measurement is performed via an optical splitter in the multimode fiber.

9. The method according to claim 7, wherein, The direct measurement is performed via a branch located downstream of the output of the multimode fiber.

10. The method of claim 7, 8 or 9, comprising taking source strength variations into account when determining the weighting.

11. The method according to claim 5, wherein, The acquisition of transmission data includes: measuring the transmission data offline by measuring the transmission at the output of the multimode fiber when the multimode fiber is not connected.

12. The method of claim 5, further comprising tuning the spectral characteristics of the transmission of the alignment radiation such that the transmission of the alignment radiation has improved spectral characteristics relative to the spectral characteristics of the position data.

13. The method according to claim 12, wherein, The spectral characteristics of the alignment radiation are tuned so that the main spectral frequency of the transmitted alignment radiation is better matched with the main spectral frequency of the position data.

14. The method according to claim 12 or 13, wherein, The tuning includes modulating the alignment radiation using one or more modulators located within the path of the alignment radiation.

15. The method according to claim 12 or 13, wherein, The tuning includes tuning the scanning speed of the focused radiation beam on the input facet.

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