Vibration correction for interferometric or holographic metrology

Abstract

Interferometric or holographic metrology systems may be used to determine overlay, alignment, and / or other metrics. Light scattered into different diffraction orders is detected by a first radiation sensor, together with two reference beams. The reference beams are carefully matched to two illumination paths from the two sources, such that a total interference pattern forms a hologram that encodes measurement information. Computational processing of the hologram determines metrology values. However, vibrations from metrology system stage settling and / or other sources cause path length shifts in the diffracted radiation. This negatively affects sensor performance. Advantageously, a second radiation sensor having a relatively higher frame rate is used to measure a phase shift from vibrations in near-real-time and make corrections for the vibrations.

Description

VIBRATION CORRECTION FOR INTERFEROMETRIC OR HOLOGRAPHIC METROLOGYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 649,665 which was filed on May 20, 2024 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] This description relates generally to vibration correction for interferometric or holographic metrology.BACKGROUND

[0003] A lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A patterning device (e.g., a mask) may include or provide a pattern corresponding to an individual layer of the IC (“design layout”), and this pattern can be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g., silicon wafer) that has been coated with a layer of radiation-sensitive material (“resist”), by methods such as irradiating the target portion through the pattern on the patterning device. In general, a single substrate includes a plurality of adjacent target portions to which the pattern is transferred successively by the lithographic projection apparatus, one target portion at a time. In one type of lithographic projection apparatus, the pattern on the entire patterning device is transferred onto one target portion in one operation. Such an apparatus is commonly referred to as a stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, a projection beam scans over the patterning device in a given reference direction (the “scanning” direction) while synchronously moving the substrate parallel or anti-parallel to this reference direction. Different portions of the pattern on the patterning device are transferred to one target portion progressively.

[0004] Prior to transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures, such as priming, resist coating, and a soft bake. After exposure, the substrate may be subjected to other procedures (“post-exposure procedures”), such as a post-exposure bake (PEB), development, a hard bake and measurement / inspection of the transferred pattern. This array of procedures is used as a basis to make an individual layer of a device, e.g., an IC. The substrate may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, deposition, chemo-mechanical polishing, etc., all intended to finish the individual layer of the device. If several layers are required in the device, then the whole procedure, or a variant thereof, is repeated for each layer. Eventually, a device will be present in each target portion on the substrate. These devices are then separated from one another by a technique such as dicing or sawing, such that the individual devices can be mounted on a carrier, connected to pins, etc.

[0005] Thus, manufacturing devices, such as semiconductor devices, typically involves processing a substrate (e.g., a semiconductor wafer) using a number of fabrication processes to form various features and multiple layers of the devices. Such layers and features are typically manufactured and processed using, e.g., deposition, lithography, etch, deposition, chemical-mechanical polishing, and ion implantation. Multiple devices may be fabricated on a plurality of dies on a substrate and then separated into individual devices. This device manufacturing process may be considered a patterning process. A patterning process involves a patterning step, such as optical and / or nanoimprint lithography using a patterning device in a lithographic apparatus, to transfer a pattern on the patterning device to a substrate and typically, but optionally, involves one or more related pattern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the pattern using an etch apparatus, deposition, etc.

[0006] Lithography is a central step in the manufacturing of devices such as ICs, where patterns formed on substrates define functional elements of the devices, such as microprocessors, memory chips, etc. Similar lithographic techniques are also used in the formation of flat panel displays, micro-electro mechanical systems (MEMS) and other devices.

[0007] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements have continually been reduced while the number of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as “Moore’s law”. At the current state of technology, layers of devices are manufactured using lithographic projection apparatuses that project a design layout onto a substrate using illumination from a deep-ultraviolet or extreme ultraviolet illumination source, creating individual functional elements having dimensions well below 100 nm, i.e. less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source).

[0008] This process in which features with dimensions smaller than the classical resolution limit of a lithographic projection apparatus are printed, is commonly known as low-ki lithography, according to the resolution formula CD = kjxk / NA, where I is the wavelength of radiation employed, NA is the numerical aperture of projection optics in the lithographic projection apparatus, CD is the “critical dimension’ -generally the smallest feature size printed-and ki is an empirical resolution factor. In general, the smaller ki the more difficult it becomes to reproduce a pattern on the substrate that resembles the shape and dimensions planned by a designer in order to achieve particular electrical functionality and performance. To overcome these difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, for example, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, use of phase shifting patterning devices, optical proximity correction (OPC, sometimes also referred to as “optical and process correction”) in the design layout, or other methods generally defined as “resolution enhancement techniques” (RET).

[0009] Accurate metrology is critical for these and / or other operations.SUMMARY

[0010] Interferometric or holographic metrology systems may be used to determine overlay, alignment, and / or other metrics. Light scattered into different diffraction orders by a metrology target is detected by a first radiation sensor, together with two reference beams. The reference beams are carefully matched to two illumination paths from the two sources, such that a total interference pattern forms a first metrology signal (e.g., a hologram) with encoded measurement information. Computational processing of the metrology signal determines metrology values. However, vibrations from metrology system stage settling and / or other sources cause path length shifts in the diffracted radiation. This negatively affects sensor performance. Advantageously, a second radiation sensor having a relatively higher frame rate is used to measure a phase shift from vibrations in near-real-time, so that corrections can be made for the vibrations.

[0011] According to an embodiment, a metrology system is provided. The system comprises a first radiation sensor configured to generate a first metrology signal based on diffracted radiation received from a metrology target in a patterned substrate. The first metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation. The system comprises a second radiation sensor having a relatively higher frame rate compared to the first radiation sensor, such that the second radiation sensor is configured to generate a second metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system. The system comprises one or more processors operatively coupled to the first radiation sensor and the second radiation sensor. The one or more processors are configured to adjust the first metrology signal based on the second metrology signal.

[0012] In some embodiments, generating the first metrology signal comprises performing interferometry or holography using the diffracted radiation in combination with secondary reference illumination that interferes with the diffracted radiation, to produce fringes in the intensity modulated fringe pattern.

[0013] In some embodiments, the one or more processors are configured to adjust the first metrology signal based on the second metrology signal to compensate for the vibration in the metrology system. Adjusting the first metrology signal based on the second metrology signal may comprise computationally correcting the first metrology signal by calculating and applying a correction factor. In some embodiments, the one or more processors are configured to perform a feedthrough operation, by using a computationally corrected first metrology signal to adjust a stage in the metrology system to compensate for vibrations in real-time. In some embodiments, adjusting the first metrology signal based on the second metrology signal comprises a post processing operation performed after the diffracted radiation impinges on the first radiation sensor and the second radiation sensor.

[0014] In some embodiments, the one or more processors are configured such that adjusting the first metrology signal based on the second metrology signal comprises determining phases of the diffracted radiation used to generate the first metrology signal as a function of time; and adjusting the firstmetrology signal based on an aggregation of the phases.

[0015] In some embodiments, the one or more processors are further configured to: determine phases of the diffracted radiation used to generate the first metrology signal as a function of time; determine path length differences based on the determined phases; and adjust a fast moving mirror associated with a stage in the metrology system to compensate for vibrations, based on an aggregation of the path length differences.

[0016] In some embodiments, the second radiation sensor comprises a line scan camera, a photodiode array, or a two dimensional camera with the relatively higher frame rate compared to the first radiation sensor. The frame rate of the second radiation sensor may be two or more times faster than a vibration frequency in the metrology system, for example. In some embodiments, the second radiation sensor need only detect one or more pixel or diode lines of the intensity modulated fringe pattern for the diffracted radiation.

[0017] In some embodiments, the second radiation sensor is positioned at an angle relative to the diffracted radiation such that the second metrology signal indicates phase shifts in two or more different orders of the diffracted radiation.

[0018] In some embodiments, the metrology system comprises a third radiation sensor. The third radiation sensor has the relatively higher frame rate compared to the first radiation sensor and is configured to generate a third metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system. The one or more processors are operatively coupled to the first radiation sensor, the second radiation sensor, and the third radiation sensor, and are configured to adjust the first metrology signal based on the second metrology signal and the third metrology signal to compensate for the vibration in the metrology system.

[0019] In some embodiments, the second radiation sensor is positioned at an angle relative to the diffracted radiation such that the second metrology signal indicates phase shifts in a first order of the diffracted radiation; and the third radiation sensor is positioned at a different angle relative to the diffracted radiation such that the third metrology signal indicates phase shifts in another order of the diffracted radiation. In some embodiments, the second radiation sensor is positioned at a first perpendicular angle relative to fringes in the intensity modulated fringe pattern, and the third radiation sensor is positioned at a different perpendicular angle relative to the fringes.

[0020] In some embodiments, the second and third radiation sensors comprise: two separate line scan cameras, photodiode arrays, or two dimensional cameras with the relatively higher frame rate compared to the first radiation sensor; or a single sensor comprising one or more chips configured to sense diffracted radiation in two different orientations. In some embodiments, the second and third radiation sensors comprise visible radiation sensors and / or infrared radiation sensors.

[0021] In some embodiments, the metrology system comprises first and / or second optical modules configured to direct first, second, and / or third portions of the diffracted radiation from the metrology target toward the first radiation sensor, the second radiation sensor, and / or the third radiation sensor,respectively, such that a same phase of the diffracted radiation impinges on the first radiation sensor, the second radiation sensor, and / or the third radiation sensor. The first and / or second optical modules each may comprise a beam splitter, for example.

[0022] In some embodiments, the first radiation sensor comprises an interferometer. In some embodiments, the first radiation sensor comprises a camera configured to generate a two dimensional intensity modulated fringe pattern. In some embodiments, the first radiation sensor comprises two or more cameras, each camera being configured for a different radiation wavelength range. The different radiation wavelength ranges may comprise a visible wavelength range and a short wave infrared wavelength range, for example.

[0023] In some embodiments, the first radiation sensor is configured such that the intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the metrology target and one or more reference radiation sources. The metrology system may comprise two reference radiation sources, and two illumination radiation sources oriented in two illumination directions configured to project radiation onto the metrology target, such that: illumination radiation is diffracted by the metrology target into at least +lst order diffracted radiation from one illumination radiation source and -1st order diffracted radiation from the other of the two illumination radiation sources; and the at least -4-lst and -1st order diffracted radiation is directed toward the first radiation sensor, together with two reference beams of radiation, with the reference beams of radiation matched to two illumination paths for the illumination radiation, such that an interference pattern impinging on the first radiation sensor forms a hologram that encodes information from the two illumination directions.

[0024] In some embodiments, the one or more processors are further configured to determine one or more amplitudes of fringes in the intensity modulated fringe pattern after an adjustment; and determine a metrology value based on the one or more amplitudes.

[0025] In some embodiments, the metrology value is overlay of a layer of the patterned substrate. In some embodiments, the metrology target comprises a diffraction-based overlay metrology target. In some embodiments, the metrology target comprises a diffraction-based alignment metrology target.

[0026] In some embodiments, the metrology system is configured to be used to measure overlay and / or alignment on a patterned semiconductor wafer as part of a semiconductor manufacturing process. In some embodiments, the adjusted first metrology signal is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.

[0027] According to another embodiment, a metrology method comprising one or more of the operations described above is provided.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above aspects and other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction withthe accompanying figures.Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.Fig. 3 schematically depicts an example metrology system, according to an embodiment.Fig. 4 schematically depicts an example metrology technique, according to an embodiment.Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.Fig. 6 illustrates a metrology method, according to an embodiment.Fig. 7 schematically depicts another example metrology system, according to an embodiment.Fig. 8 schematically depicts yet another example metrology system, according to an embodiment.Fig. 9 illustrates an example of a fringe pattern, which can be used to determine overlay and / or other metrics, according to an embodiment.Fig. 10 illustrates a metrology target, according to an embodiment.Fig. 11 illustrates an example of a radiation sensor (e.g., second radiation sensor shown in Fig. 7 or Fig. 8) that is positioned at an angle relative to diffracted radiation such that a second metrology signal indicates phase shifts in two or more different orders of the diffracted radiation, according to an embodiment.Fig. 12 illustrates an example of two radiation sensors (e.g. , second and third radiation sensors shown in Fig. 8) that are positioned at angles relative to diffracted radiation such that second and third metrology signals indicate phase shifts in two or more different orders of the diffracted radiation, according to an embodiment.Fig. 13 illustrates using multiple lines of a camera to implement 4-step phase shifted interferometry, according to an embodiment.Fig. 14 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0029] As introduced above, interferometric or holographic metrology systems may be used to determine overlay, alignment, and / or other metrics. In these systems, illumination radiation sources are used to project radiation onto a metrology target. Light scattered into at least +lst (from one source) and -1st (from another source) diffraction orders is detected by a first radiation sensor, together with reference beams. The reference beams are carefully matched to the illumination paths from the sources, such that a total interference pattern forms a metrology signal (e.g., a hologram), with encoded information from different illumination directions. Computational processing of the metrology signal determines metrology values.

[0030] However, vibrations from metrology system stage settling and / or other sources cause pathlength shifts in the diffracted radiation at the relevant timescales. Loss of fringe contrast from motion affects sensor performance. Large motions during acquisition reduce the effective signal level, which worsens the signal-to-noise ratio. If loss of fringe contrast varies, a tool-induced asymmetry is perceived. This causes a registration error that, due to the stochastic nature of vibrations, cannot be calibrated out.

[0031] Advantageously, a second radiation sensor having a relatively higher frame rate is used to measure the phase shift from vibrations in near-real-time and adjust for them. Fringes associated with the signal from the first radiation sensor serve as an optical measurement of the phase of the signal and the movement of the fringes back-and-forth as detected by the second radiation sensor provides a measurement of the phase shift, like an optical encoder. The second radiation sensor can be added with a beamsplitter, so it measures the same phase as the first radiation sensor.

[0032] By way of a brief introduction, the following description relates generally to semiconductor device manufacturing and patterning processes. More particularly, the following paragraphs describe several components of a system and / or related systems. As described above these systems and methods may be used for measuring overlay in a semiconductor device manufacturing process, for example, or for other operations.

[0033] Although specific reference may be made in this text to the measurement of overlay and / or alignment, and the manufacture of integrated circuits (ICs) for semiconductor devices, it should be understood that the description has many other possible applications. For example, it may be employed in the measurement of other parameters. It may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle”, “wafer” or “die” in this text should be considered as interchangeable with the more general terms “mask”, “substrate” and “target portion”, respectively.

[0034] Fig. 1 schematically depicts an embodiment of a lithographic apparatus LA. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation, or EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT (e.g., WTa, WTb or both) configured to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies and often referred to as fields) of the substrate W. The projection system is supported on a reference frame RF. As depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array, or employing a reflective mask).

[0035] The illuminator IL receives a beam of radiation from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising for example suitable directing mirrors and / or a beam expander. In other cases, the source may be an integral part of the apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0036] The illuminator IL may alter the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution is non-zero within an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the distribution of the beam in the pupil plane such that the intensity distribution is non-zero in a plurality of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in a pupil plane of the illuminator IL may be referred to as an illumination mode.

[0037] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial extent (commonly referred to as o-outer and o-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane where the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multi-pole distribution such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, e.g., by inserting an optic which provides that illumination mode into the illuminator IL or using a spatial light modulator.

[0038] The illuminator IL may be operable to alter the polarization of the beam and may be operable to adjust the polarization using adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as a polarization mode. The use of different polarization modes may allow greater contrast to be achieved in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across a pupil plane of the illuminator IL. The polarization direction of radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen in dependence on the illumination mode. For multi-pole illumination modes, the polarization of each pole of the radiation beam may be generally perpendicular to the position vector of that pole in the pupil plane of theilluminator IL. For example, for a dipole illumination mode, the radiation may be linearly polarized in a direction that is substantially perpendicular to a line that bisects the two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as X-polarized and Y-polarized states. For a quadrupole illumination mode, the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as XY polarization. Similarly, for a hexapole illumination mode the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as TE polarization.

[0039] In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0040] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” may be considered synonymous with the more general term “patterning device.”

[0041] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a pattern in a target portion of the substrate. In an embodiment, a patterning device is any device that can be used to impart a radiation beam with a pattern in its cross-section to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in a target portion of the device, such as an integrated circuit.

[0042] A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflectedby the mirror matrix.

[0043] The term “projection system” should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” may be considered as synonymous with the more general term “projection system”.

[0044] The projection system PS may comprise a plurality of optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of the optical elements to correct for aberrations (phase variations across the pupil plane throughout the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system where its optical axis extends in the z direction. The adjustment mechanism may be operable to do any combination of the following: displace one or more optical elements; tilt one or more optical elements; and / or deform one or more optical elements. Displacement of an optical element may be in any direction (x, y, z, or a combination thereof). Tilting of an optical element is typically out of a plane perpendicular to the optical axis, by rotating about an axis in the x and / or y directions although a rotation about the z axis may be used for a non-rotationally symmetric aspherical optical element. Deformation of an optical element may include a low frequency shape (e.g. astigmatic) and / or a high frequency shape (e.g. free form aspheres). Deformation of an optical element may be performed for example by using one or more actuators to exert force on one or more sides of the optical element and / or by using one or more heating elements to heat one or more selected regions of the optical element. In general, it may not be possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). The transmission map of a projection system PS may be used when designing a patterning device (e.g., mask) MA for the lithography apparatus LA. Using a computational lithography technique, the patterning device MA may be designed to at least partially correct for apodization.

[0045] The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g., two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system without a substrate that is dedicated to, for example, facilitating measurement, and / or cleaning, etc.). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using an alignment sensor AS and / or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0046] In operation of the lithographic apparatus, a radiation beam is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device.Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a shortstroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0047] The depicted apparatus may be used in at least one of the following modes. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while a pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

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

[0049] The substrate may be processed, before or after exposure, in for example a back (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multilayer IC, so that the term substrate may also refer to a substrate that already includes multiple processed layers.

[0050] The terms “radiation” and “beam” used with respect to lithography encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0051] Various patterns on or provided by a patterning device may have different process windows, i.e., a space of processing variables under which a pattern will be produced within specification. Examples of pattern specifications that relate to potential systematic defects include checks for necking, line pull back, line thinning, CD, edge placement, overlapping, resist top loss, resist undercut and / or bridging. The process window of the patterns on a patterning device or an area thereof may be obtained by merging (e.g., overlapping) process windows of each individual pattern. The boundary of the process window of a group of patterns comprises boundaries of process windows of some of the individual patterns. In other words, these individual patterns limit the process window of the group of patterns.

[0052] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to as a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input / output port I / Ol, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0053] In order that a substrate that is exposed by the lithographic apparatus is exposed correctly and consistently and / or in order to monitor a part of the patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., an optical lithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties such as alignment, overlay (which can be, for example, between structures in overlying layers or between structures in a same layer that have been provided separately to the layer by, for example, a double patterning process),line thickness, critical dimension (CD), focus offset, a material property, etc. Accordingly, a manufacturing facility in which lithocell LC is located also typically includes a metrology system that measures some or all of the substrates W (Fig. 1) that have been processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithocell LC, for example it may be part of the lithographic apparatus LA (such as alignment sensor AS (Fig. 1)).

[0054] The one or more measured parameters may include, for example, overlay between successive layers formed in or on the patterned substrate, alignment, critical dimension (CD) (e.g., critical linewidth) of, for example, features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. This measurement is often performed on a dedicated metrology target provided on the substrate. The measurement can be performed after-development of a resist but before etching, after-etching, after deposition, and / or at other times.

[0055] There are various techniques for making measurements of the structures formed in the patterning process, including the use of a scanning electron microscope, an image -based measurement tool and / or various specialized tools. A fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted / reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this may be termed diffraction-based metrology. One such application of this diffractionbased metrology is in the measurement of overlay (e.g., as described below).

[0056] Thus, in a device fabrication process (e.g., a patterning process or a lithography process), a substrate or other objects may be subjected to various types of measurement during or after the process. The measurement may determine whether a particular substrate is defective, may establish adjustments to the process and apparatuses used in the process (e.g., aligning two or more layers on the substrate or aligning the patterning device to the substrate), may measure the performance of the process and the apparatuses, or may be for other purposes. Examples of measurement include optical imaging (e.g., optical microscope), non-imaging optical measurement (e.g., measurement based on diffraction such as the ASML YieldStar metrology tool, the ASML SMASH metrology system), mechanical measurement (e.g., profiling using a stylus, atomic force microscopy (AFM)), and / or non-optical imaging (e.g., scanning electron microscopy (SEM)).

[0057] Metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, an adjustment may be made to exposure of a subsequent substrate (especially if the inspection can be done soon and fast enough that one or more other substrates of the batch are still to be exposed) and / or to subsequent exposure of the exposed substrate. Also, an already exposed substrate may be stripped and reworked to improve yield, or discarded, thereby avoiding performing further processing on a substrate known to be faulty. In a case where only some target portions of a substrate are faulty, further exposures may be performed only on those target portionswhich meet specifications. Other manufacturing process adjustments are contemplated.

[0058] A metrology system may be used to determine one or more properties of the substrate structure, and in particular, how one or more properties of different substrate structures vary, or different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithographic apparatus LA or the lithocell LC, or may be a stand-alone device.

[0059] To enable metrology, often one or more targets are specifically provided on the substrate. A target may include an overlay target, for example, an alignment mark, and / or other targets. Typically, the target is specially designed and may comprise one or more periodic structures. For example, the target on a substrate may comprise one or more 1-D periodic structures (e.g., geometric features such as gratings) in one or more layers of the substrate, which are printed such that after development, the periodic structural features are formed of solid resist lines. As another example, the target may comprise one or more 2-D periodic structures (e.g., gratings) in one or more layers, which are printed such that after development, the one or more periodic structures are formed of solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0060] Fig. 3 depicts an example inspection (metrology) system 10 that may be used to detect overlay, alignment, and / or perform other metrology operations. It comprises a radiation source 2 which projects or otherwise irradiates radiation onto a substrate W. Substrate W may typically include a metrology target 30 such as an overlay target, an alignment mark, and / or other structures. The redirected radiation is passed to a radiation sensor such as a spectrometer detector 4 and / or other sensors, which measures a spectrum (intensity as a function of wavelength) of the specular reflected and / or diffracted radiation, as shown, e.g., in the graph on the left of Fig. 4. The sensor may generate a metrology signal conveying overlay data, alignment data, and / or other data indicative of properties of the reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in Fig. 4, or by other operations. Note that these are generalized examples. Often, illumination of a target such as overlay target and / or an alignment mark is done orthogonal to the target and / or mark, and not at an angle as shown in Fig. 3.

[0061] As in the lithographic apparatus LA in Fig. 1, one or more substrate tables or stages (not shown in Fig. 3 or 4) may be provided to hold the substrate W during metrology operations. The one or more substrate tables or stages may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Fig. 1. In an example where system 10 is integrated with the lithographic apparatus, they may even be the same substrate table or stage. Coarse and fine positioners may be provided and configured to accurately position the substrate in relation to a measurement optical system. Various sensors and actuators are provided, for example, to acquire the position of a target portion of interest of a structure (e.g., an overlay target and / or an alignment mark), and to bring it into position under an objective lens. Typically, many measurements will be made on target portions of a structure at differentlocations across the substrate W. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the target portion relative to the focus of the optical system. It is convenient to think and describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves. Provided the relative position of the substrate and the optical system is correct, it does not matter in principle which one of those is moving, or if both are moving, or a combination of a part of the optical system is moving (e.g., in the Z and / or tilt direction) with the remainder of the optical system being stationary and the substrate is moving (e.g., in the X and Y directions, but also optionally in the Z and / or tilt direction).

[0062] For typical metrology measurements, a target 30 on substrate W may be a 1-D grating, which is printed such that after development, the bars are formed of solid resist lines (e.g., which may be covered by a deposition layer), and / or other materials. Or the target 30 may be a 2-D grating, which is printed such that after development, the grating is formed of solid resist pillars, and / or other features in the resist. The bars, pillars, vias, and / or other features may be etched into or on the substrate (e.g., into one or more layers on the substrate), deposited on a substrate, covered by a deposition layer, and / or have other properties. Target 30 (e.g., of bars, pillars, vias, etc.) is sensitive to changes in processing in the patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in target 30. Accordingly, the measured data from target 30 may be used to determine an adjustment for one or more of the manufacturing processes, and / or used as a basis for making the actual adjustment. Note that in this example, target 30 may represent one or more layers comprising one or more metrology marks (e.g., with one or more gratings per mark).

[0063] For example, the measured data from target 30 may indicate overlay for layers of a semiconductor device, alignment, and / or other information. The measured data from target 30 may be used (e.g., by the one or more processors) for determining one or more semiconductor device manufacturing process parameters based the alignment, overlay, and / or other information, and / or determining an adjustment for a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may comprise a stage position adjustment, for example, or this may include determining an adjustment for a mask design, a metrology target (e.g., an overlay target and / or an alignment mark) design, a semiconductor device design, an intensity of the radiation, an incident angle of the radiation, a wavelength of the radiation, a pupil size and / or shape, a resist material, and / or other process parameters.

[0064] Fig. 5 illustrates a plan view of a typical target 30 (e.g., an overlay target, an alignment mark, etc.), and the extent of a radiation illumination spot S in the system of Fig. 4. Typically, to obtain a diffraction spectrum that is free of interference from surrounding structures, the target 30, in an embodiment, comprises one or more periodic structures (e.g., gratings) larger than the width (e.g.,diameter) of the illumination spot S. The width of spot S may be smaller than the width and length of the target 30. The target 30, in other words, is ‘underfilled’ by the illumination, and the diffraction signal is essentially free from any signals from product features and the like outside the target itself. The illumination arrangement may be configured to provide illumination of a uniform intensity across a back focal plane of an objective, for example. Alternatively, by, for example, including an aperture in the illumination path, illumination may be restricted to on axis or off axis directions.

[0065] Fig. 6 illustrates a metrology method 600. In some embodiments, method 600 is performed as part of a semiconductor device manufacturing process. In some embodiments, one or more operations of method 600 may be implemented in or by system 10 illustrated in Fig. 3 and 4 (and / or system 700 shown in Fig. 7, and / or system 800 shown in Fig. 8 and described below), a computer system (e.g., as illustrated in Fig. 14 and described below), and / or in or by other systems, for example. In some embodiments, method 600 comprises irradiating (operation 602) a metrology target in a patterned substrate (such as a semiconductor wafer) with radiation, generating (operation 604) a first metrology signal based on diffracted radiation received radiation from the metrology target, generating (operation 606) a second metrology signal based on the diffracted radiation using a radiation sensor with a higher frame rate, adjusting (operation 608) the first metrology signal based on the second metrology signal, performing (operation 610) a feedthrough operation, determining (operation 612) a metrology value, and / or other operations. As described above, mitigation of vibrations (e.g., stage and / or other vibrations) in a metrology system is a problem. In some embodiments, adjusting the first metrology signal based on the second metrology signal, performing the feedthrough operation, and / or other operations are configured to compensate for vibrations in the metrology system so that an accurate metrology value can be determined.

[0066] Method 600 is described below in the context of a metrology value such as overlay, but this is not intended to be limiting. Method 600 may be generally applied to a number of different processes (e.g., alignment determination, etc.). For example, in some embodiments, the metrology value is overlay of a layer of the patterned substrate. In some embodiments, the metrology target comprises a diffraction-based overlay metrology target. In some embodiments, the metrology value is an alignment measurement, and the metrology target comprises a diffraction-based alignment metrology target.

[0067] The operations of method 600 presented below are intended to be illustrative. In some embodiments, method 600 may be accomplished with one or more additional operations not described, and / or without one or more of the operations discussed. For example, in some embodiments, method 600 may include an additional operation comprising determining an adjustment for a semiconductor device manufacturing process. Additionally, the order in which the operations of method 600 are illustrated in Fig. 6 and described below is not intended to be limiting.

[0068] In some embodiments, one or more portions of method 600 may be implemented in and / or controlled by one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a statemachine, and / or other mechanisms for electronically processing information - see the description of processors PRO). The one or more processing devices may include one or more devices executing some or all of the operations of method 600 in response to (machine readable) instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and / or software to be specifically designed for execution of one or more of the operations of method 600 (e.g., see discussion related to Fig. 14 below).

[0069] Operation 602 comprises irradiating a metrology target in a patterned substrate with radiation. In some embodiments, a metrology target comprises metrology marks in different layers of the patterned substrate, and / or other features. In some embodiments, the metrology target is associated with an overlay measurement for the patterned substrate. For example, a metrology target may be or include a dedicated overlay target comprising diffraction gratings in the different layers. The radiation may be diffracted by the diffraction grating(s). In some embodiments, a metrology target comprises one or more structures in the patterned substrate capable of providing a diffraction signal (e.g., a metrology target or some other structure(s)). In some embodiments, a metrology target can be any structure in a pattern design layout capable of generating a wide angle diffraction signal.

[0070] In some embodiments, a metrology target may be included in two or more layers of a substrate in a semiconductor device structure, for example. In some embodiments, a metrology target comprises one or more geometric features such as ID or 2D features, and / or other geometric features. By way of several non-limiting examples, a metrology target may comprise a line, an edge, a fine -pitched series of lines and / or edges, a set of multiple fine -pitched series of lines and / or edges, and / or other features.

[0071] In some embodiments, the metrology mark comprises a diffraction-based overlay metrology mark comprising multiple gratings and / or other metrology marks. The gratings may have the same pitch, different pitches, and / or other features. In some embodiments, gratings in different layers form a Micro Diffraction Based Overlay (pDBO) target, with gratings formed on top of each other in the different layers, but shifted by a known bias amount (which can be zero).

[0072] At operation 602, two reference radiation sources, and two illumination radiation sources oriented in two illumination directions are configured to project radiation onto the metrology target. The illumination radiation is diffracted by the metrology target into at least -4-lst order diffracted radiation from one illumination radiation source and -1st order diffracted radiation from the other of the two illumination radiation sources. The at least 4-lst and -1st order diffracted radiation is directed toward the first radiation sensor (see operation 604), together with two reference beams of radiation. The reference beams of radiation are matched to two illumination paths for the illumination radiation, such that an interference pattern impinging on the first radiation sensor forms a hologram that encodes information from the two illumination directions. These principles can be applied to diffracted radiation of any order (e.g., more than just + / - 1st), provided the first radiation sensor (e.g., a line scan camera) is positioned such that each diffraction order is resolvable in the Fourier domain.

[0073] The radiation may have a target wavelength and / or wavelength range, a target intensity,and / or other characteristics. The target wavelength and / or wavelength range, the target intensity, etc., may be entered and / or selected by a user, determined by the system based on previous metrology measurements, and / or determined in other ways. In some embodiments, the radiation comprises light and / or other radiation. In some embodiments, the light comprises visible light, infrared light, near infrared light, extreme ultraviolet (EUV) light, soft-X-ray light and / or any other light. In some embodiments, the radiation may be any radiation appropriate for interferometry.

[0074] In some embodiments, the radiation may be directed by the two reference radiation sources, and the two illumination radiation sources (e.g., by way of one or more lenses, a modulator, and / or other components) onto a metrology target, sub-portions (e.g., something less than the whole) of a metrology target, multiple metrology targets either sequentially or in a single acquisition shot, and / or onto a patterned substrate in other ways. Conjugate diffracted orders that can interfere with each other are desired.

[0075] For example, Fig. 7 illustrates a possible embodiment of a metrology system 700 configured to perform operation 602 and / or other operations of method 600. System 700 is the same as or similar to system 10 described above with respect to Fig. 3, with one or more components of system 700 being similar to and / or the same as one or more components of system 10 (and Fig. 7 illustrating additional possible components of the system). In some embodiments, one or more components of system 700 may replace, be used with, and / or otherwise augment one or more components of system 10. In Fig. 7, illumination radiation 702 may be generated and directed to a metrology target (e.g., target 30) by illumination radiation sources 2A and 2B (similar to and / or the same as source 2 shown in Fig. 3) - lasers in this example. Illumination radiation sources 2 A and 2B are oriented such that radiation 702 impinges on target 30 from two example illumination directions 701 and 703.

[0076] Illumination radiation 702 is diffracted by metrology target 30 into + 1 st order (in this example) diffracted radiation from one illumination radiation source 2A, and -1st order diffracted radiation from the other of the two illumination radiation sources 2B. The at least -4-lst and -1st order diffracted radiation is directed toward a first radiation sensor 710 (see operation 604), together with two reference beams of radiation 704 (generated by reference radiation sources 706 and 708). Note that first radiation sensor 710 may be similar to and / or the same as sensor 4 shown in Fig. 3, for example. The reference beams of radiation 704 are matched (e.g., as shown in Fig. 7) to two illumination paths for the illumination radiation 702, such that an interference pattern impinging on first radiation sensor 710 forms a hologram.

[0077] In Fig. 7, metrology target 30 on substrate W comprises gratings in multiple layers of substrate W. A grating may be formed of solid resist pillars, bars, vias, and / or other features, for example. Metrology target 30 may be sensitive to changes in processing in a patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in metrology target 30. Accordingly, the measured data from metrology target 30 may be used to determine an overlay value,and / or an adjustment based on the overlay value for one or more manufacturing processes, and / or used as a basis for making the actual adjustment. Again note that in this example, metrology target 30 may represent multiple layers comprising multiple metrology gratings and / or other marks. Fig. 7 also illustrates one or more lenses 720, optical modules 730, and / or other components configured to direct (and / or are otherwise associated with directing) radiation 702 from sources 2A and 2B to metrology target 30, and directing the diffracted radiation from metrology target 30 toward first radiation sensor 710, and a second radiation sensor 750 (as described below - see operation 606).

[0078] Fig. 8 illustrates another example embodiment of a metrology system 800 configured to perform one or more operations of method 600. System 800 is the same as or similar to system 10 described above with respect to Fig. 3, and / or system 700 described in Fig. 7, with one or more components of system 800 being similar to and / or the same as one or more components of system 10 and / or system 700 (and Fig. 8 illustrating additional possible components of the system). In some embodiments, one or more components of system 800 may replace, be used with, and / or otherwise augment one or more components of system 10 and / or system 700.

[0079] Illumination radiation 702 is again diffracted by metrology target 30 into at least +1 st order diffracted radiation from one illumination radiation source 2A and -1st order diffracted radiation from the other of the two illumination radiation sources 2B. The at least -4-lst and -1st order diffracted radiation is directed toward a first radiation sensor 710 (see operation 604), together with two reference beams of radiation 704 (generated by reference radiation sources 706 and 708). The reference beams of radiation 704 are matched (e.g., as shown in Fig. 7 and Fig. 8) to two illumination paths for the illumination radiation 702, such that an interference pattern impinging on first radiation sensor 710 forms a hologram. Fig. 8 also illustrates one or more lenses 720, optical modules 730A and 730B, and / or other components configured to direct (and / or are otherwise associated with directing) radiation from sources 2A and 2B to metrology target 30, and direct the diffracted radiation from metrology target 30 toward first radiation sensor 710, a second radiation sensor 750A, and a third radiation sensor 750B (as described below - see operation 608).

[0080] For example, in some embodiments, metrology system 800 comprises first and second optical modules such as modules 730A and / or 730B shown in Fig. 8 configured to direct first, second, and / or third portions of the diffracted radiation from metrology target 30 toward first radiation sensor 710, the second radiation sensor (e.g., 750 in Fig. 7, or 750A or 750B in Fig. 8), and / or the third radiation sensor (e.g., the other one of 750A or 750B in Fig. 8), respectively, such that a same phase of the diffracted radiation impinges on the first radiation sensor, the second radiation sensor, and / or the third radiation sensor. The first and / or second optical modules each may comprise a beam splitter, a lens, a mirror, and / or other components, for example.

[0081] Returning to Fig. 6, operation 604 comprises detecting reflected and / or transmitted radiation from the metrology target, and generating a first metrology signal based on diffracted radiation received from the metrology target (e.g., from metrology target 30 shown in Fig. 7), in a patterned substrate (e.g.,W shown in Fig. 7) and / or other information. The first metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation. The first metrology signal may be generated by a first radiation sensor (e.g., such as first radiation sensor 710 shown in Fig. 7 and Fig. 8, and / or sensor detector 4 shown in 3) and / or other components. In some embodiments, the first radiation sensor may comprise a camera, an interferometer, an interferometric microscopy detector, and / or other components. In some embodiments, the first radiation sensor comprises two or more cameras, each camera being configured for a different radiation wavelength range. The different radiation wavelength ranges may comprise a visible wavelength range and a short wave infrared wavelength range, for example.

[0082] In some embodiments, the first radiation sensor comprises a camera configured to generate a two dimensional intensity modulated fringe pattern. In some embodiments, generating the first metrology signal comprises performing interferometry or holography using the diffracted radiation in combination with secondary reference illumination that interferes with the diffracted radiation (e.g., as shown in Fig. 7 and Fig. 8 and described above), to produce fringes in the two dimensional intensity modulated fringe pattern. In some embodiments, the first radiation sensor is configured such that the intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the metrology target and the one or more reference radiation sources (e.g., as shown in Fig. 7 and Fig. 8 and described above). The reference beams of radiation may be matched to two illumination paths for the illumination radiation, such that an interference pattern impinging on the first radiation sensor forms a hologram that encodes information from the two illumination directions.

[0083] Detecting such radiation comprises detecting intensity (amplitude) and / or phase information of (diffracted) radiation received from one or more geometric features. The amplitude and / or phase information corresponds to one or more dimensions of a feature. For example, the phase and / or amplitude of reflected radiation from one side of a feature is different relative to the phase and / or amplitude of reflected radiation from another side of the feature. The radiation from a specific area of a mark may comprise a sinusoidal waveform having a certain phase and / or amplitude. The radiation from a different area of the mark may also comprise a sinusoidal waveform, but one with a different phase and / or amplitude. Detecting radiation also comprises measuring a phase and / or amplitude difference in radiation of different diffraction orders. This may be performed using Fourier transformations, Hilbert transformations, for example, and / or other techniques. Interferometry techniques and / or other operations may be used to measure phase and / or amplitude differences in reflected radiation of different diffraction orders. Vibrations in a metrology system can disrupt and / or otherwise decrease the accuracy of these determinations.

[0084] The first metrology signal (e.g., from first radiation sensor 710 shown in Fig. 7 and Fig. 8) comprises an electronic signal that represents and / or otherwise corresponds to the radiation from the metrology target (e.g., metrology target 30 shown in Fig. 7 and Fig. 8). The metrology signal may indicate an overlay value for one or more layers, for example, an alignment value, and / or otherinformation. Generating the metrology signal comprises sensing the radiation and converting the sensed radiation into the electronic signal. In some embodiments, generating the metrology signal comprises sensing different portions of the radiation from different portions and / or different geometries of the metrology target (e.g., different gratings in different layers), or metrology targets, and combining the different portions of the sensed radiation to form the metrology signal. This sensing and converting may be performed by components similar to and / or the same as radiation sensor detector 4, first radiation sensor 710 shown in Fig. 7 and Fig. 8, and / or processors PRO shown in Fig. 3, Fig. 4, Fig. 7, Fig, 8, and Fig. 14, and / or other components.

[0085] As described above, the metrology target is configured to diffract radiation from the radiation source(s). The radiation received by the radiation sensors comprises diffracted radiation. The first metrology signal comprises an intensity modulated fringe pattern for diffracted radiation received from the metrology target. In some embodiments, the intensity modulated fringe pattern comprises a one or more dimensional interference pattern. In some embodiments, the first radiation sensor is configured such that the intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from a first grating in a first layer, and a second grating in a second layer in the metrology target. For example, in some embodiments, the first radiation sensor is configured such that the intensity modulated fringe pattern for the diffracted radiation comprises a two beam interference pattern between two 1st order diffracted beams, generated based on diffracted radiation from at least one segment or pad of both a first grating and a second grating, in a metrology target.

[0086] For overlay, as an example, two illuminators (e.g., illumination radiation sources 2A and 2B shown in Fig. 7 and Fig. 8) may be used to project light (e.g., radiation 702) onto an overlay target (e.g., metrology target 3). Light scattered into + 1 st (from one illuminator) and -1st (from the other illuminator) grating diffraction orders may be captured with an objective lens (e.g., a lens 720 shown in Fig. 7 and Fig. 8) and projected onto a camera (e.g., first radiation sensor 710 shown in Fig. 7 and Fig. 8), together with two reference beams (e.g., reference beams of radiation 704). These reference beams are carefully matched to the two illumination paths, such that the total interference pattern forms a hologram that encodes information from both illumination directions. Computational processing of the hologram reveals high-quality information about the target. On the camera, object beams scattered from the overlay target interfere with reference beams. One object / reference pair exists for a positive grating diffraction order and one exists for the negative grating diffraction order, corresponding to illumination from left and right in the examples shown in Fig. 7 and Fig. 8. The interference pattern, known as a hologram, comprises fringes, as described herein. In subsequent computational processing, the amplitude of these fringes may be interpreted as a signal level and used to determine overlay. Overlay determination is an asymmetry determination. Ignoring vibrations for now, in a symmetric, static sensor, overlay error in the metrology target is the (only) source of asymmetry between the signals from the two sides (left and right). Therefore, overlay may be calculated based on differences between the signallevels from each side.

[0087] Fig. 9 illustrates an example of an intensity modulated fringe pattern 900, which can be used to determine a metrology value such as overlay, as described herein. Fringe pattern 900 may be generated based on radiation diffracted by a metrology target (e.g., target 30 shown in other figures). For example, radiation received by a first radiation sensor (e.g., sensor 4 shown in Fig. 3, sensor 710 shown in Fig. 7 and Fig. 8) comprises diffracted radiation. The first radiation sensor (and / or one or more processors PRO operatively coupled to the first radiation sensor - see Fig. 3, Fig. 7, Fig. 8, and Fig. 14) is configured to generate a metrology signal, which comprises an intensity modulated fringe pattern such as fringe pattern 900. In Fig. 9 and fringe pattern 900, the darker and lighter lines that run at an angle through each rectangle are fringes. Intensity modulation comprises variation in the intensity of radiation reflected by target 30 and received by the first radiation sensor (e.g., sensor 4, sensor 710) from across a grating. In Fig. 9, intensity modulation is illustrated by how dark or how light the varying darker and lighter lines are. The intensity modulated fringe pattern 900 may comprise a two or more dimensional interference pattern, for example.

[0088] Fig. 10 illustrates an example of a metrology target 30. In this example, metrology target 30 comprises pads 1002, 1004, 1006, and 1008. Each pad comprises two gratings (an upper grating and a lower grating), with a first grating in a first layer of a patterned substrate shifted relative to a second grating, which is in a second layer of the patterned substrate, by a known bias (+ / - x and / or y in this example) amount (which can be zero).

[0089] Returning to Fig. 6, at operation 606, a second radiation sensor (e.g., second radiation sensor 750 shown in Fig. 7, or sensor 750A or 750B in Fig. 8) having a relatively higher frame rate compared to the first radiation sensor (e.g., first radiation sensor 710 shown in Fig. 7) is configured to generate a second metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system (e.g., system 700). In some embodiments, also at operation 606, a third radiation sensor (e.g., sensor 750B shown in Fig. 8, with the second radiation sensor formed by sensor 750A, and the first radiation sensor formed by sensor 710) that also has the relatively higher frame rate compared to the first radiation sensor, is configured to generate a third metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system (e.g., system 800 in this example).

[0090] Continuing with the overlay example described above, since signal level is indicated by fringe contrast, effects that erode fringe contrast reduce a perceived signal level. For example, path length shifts between a diffracted radiation beam from the metrology target and a reference beam (e.g., a reference beam of radiation 704 shown in Fig. 8 and Fig. 8) cause the fringes in the intensity modulated fringe patter or hologram to shift. This leads to fringe contrast reduction and loss of signal. Path length shifts at the relevant (sub-)millisecond timescales are often caused by metrology system stage settling, random vibrations, and / or have other causes. Motion in the metrology system is unavoidable, as a patterned substrate such as a semiconductor wafer, and / or a radiation sensor itself, has to move as part of metrology operations.

[0091] Loss of fringe contrast from vibrations affects radiation sensor (e.g., first radiation sensor 710 shown in Fig. 7 and Fig. 8) performance in two primary ways: large vibrations during acquisition of diffracted radiation by first radiation sensor 710 reduce the effective signal level, which worsens the signal-to-noise ratio; and if loss of fringe contrast is different between the left and right (in the examples shown in Fig. 7 and Fig. 8), a tool-induced asymmetry is perceived. This causes an overlay registration error that, due to the stochastic nature of vibrations, cannot be calibrated out. Since overlay measurement is highly precise, the latter effect causes errors even for small vibrations, on the scale of more than a few nanometers.

[0092] The second radiation sensor (e.g., second radiation sensor 750 shown in Fig. 7, or sensor 750A or 750B in Fig. 8) may be a relatively fast camera or fast photodiode array (with the relatively higher frame rate) whose output is used to measure the phase shifts caused by vibrations in near-real- time and facilitate correction. The fringes in the intensity modulated fringe pattern (e.g., the hologram) function as an optical measurement of the phase of the signal and the movement of the fringes back- and-forth on the fast camera functions as a measurement of the phase shift, like an optical encoder. The fast camera (e.g., the second and / or third radiation sensors described herein) can be added to the metrology system (e.g., system 700 shown in Fig. 7 and / or system 800 shown in Fig. 8) with a beamsplitter and / or other components, as described above, so the exact same phase is measured by the radiation sensors. The fast camera (e.g., the second and / or third radiation sensors) provide a fast measurement of the phase that can be used to correct for vibrations, while a main camera (e.g., first radiation sensor 710) provides a relatively slower, precise measurement of intensity that is used to measure overlay.

[0093] In some embodiments, the second radiation sensor and / or the third radiation sensor comprises a line scan camera, a photodiode array, or a two dimensional camera with the relatively higher frame rate compared to the first radiation sensor, and / or other components. The frame rate of the second radiation sensor and / or the third radiation sensor may be two or more times faster than a vibration frequency in the metrology system (e.g., system 700 shown in Fig. 7), for example. In some embodiments, the second and / or third radiation sensors need only detect one or more pixel or diode lines of the intensity modulated fringe pattern for the diffracted radiation. In some embodiments, the second and third radiation sensors comprise: two separate line scan cameras, photodiode arrays, or two dimensional cameras with the relatively higher frame rate compared to the first radiation sensor; or a single sensor comprising one or more chips configured to sense diffracted radiation in two different orientations. In some embodiments, the second and third radiation sensors comprise visible radiation sensors and / or infrared radiation sensors.

[0094] In some embodiments, as shown in Fig. 11 (and in the example of system 700 shown in Fig. 7), the second radiation sensor (e.g., second radiation sensor 750 in this example) is positioned at an angle 1100 relative to the diffracted radiation such that the second metrology signal indicates phase shifts in two or more different orders of the diffracted radiation. Fig. 11 illustrates an example of sucha second sensor 750. In Fig. 11, sensor 750 is a line scan camera with the relatively higher frame rate compared to the first radiation sensor (e.g., sensor 710 shown in Fig. 7 and Fig. 8). A line scan camera or photodiode array may be ideal for this application because they can read at extremely high frame rates. Additionally, only one line of information is required to measure the phase for each diffraction order, so measuring with just one line is sufficient.

[0095] The frame rate (e.g., about 10kHz or higher) of (the second) radiation sensor 750 is two or more times faster than a vibration frequency (e.g., 2kHz or lower) in the metrology system (e.g., system 700 shown in Fig. 7), for example. Sensor 750 in Fig. 11 need only detect one or more pixel or diode lines of the intensity modulated fringe pattern 1102 for the diffracted radiation. In the example shown in Fig. 11, a single line scan camera is positioned at an angle to the fringes so that both +1 and -1 diffraction orders are captured with their fringes at different spatial frequencies on the line scan camera. As one example, a line scan camera at an angle 1100 of 18.4 degrees may measure both diffraction orders and separate them evenly in spatial frequency. One order will be measured at 0.45 times the maximum spatial frequency and the other at 0.9 times the maximum spatial frequency. The two diffraction orders may be separated with a simple Fourier transform.

[0096] In some embodiments, as shown in Fig. 12 (and as in the example of system 800 shown in Fig. 8), the second radiation sensor (e.g., second radiation sensor 750A in this example) is positioned at an angle 1200 relative to the diffracted radiation such that the second metrology signal indicates phase shifts in a first order of the diffracted radiation; and the third radiation sensor (e.g., third radiation sensor 750B in this example) is positioned at a different angle 1202 relative to the diffracted radiation such that the third metrology signal indicates phase shifts in another order of the diffracted radiation. In some embodiments, the second radiation sensor (e.g., second radiation sensor 750A) is positioned at a first perpendicular angle relative to fringes in an intensity modulated fringe pattern 1204, and the third radiation sensor (e.g., third radiation sensor 750B) is positioned at a different perpendicular angle relative to the fringes. In this example, the second and / or third radiation sensors may again be line scan cameras or photodiode arrays, for example. Either of these types of sensors can be placed perpendicular to the fringes generated by one diffraction order for maximum signal, and a second sensor can be configured to measure the phase for the second diffraction order. In some embodiments, relevant overlay targets have two or more pads (see Fig. 10), which are often predictably imaged in a top half and a bottom half of a field of view (or left and right halves). One line scan camera or photodiode array may use the bottom (or left) half of the field of view and monitor one fringe direction, and another could use the other half and the other fringe direction.

[0097] Returning to Fig. 6, at operation 608, the first metrology signal may be adjusted based on the second metrology signal, the third metrology signal, and / or other information. The one or more processors PRO are operatively coupled to the first radiation sensor, the second radiation sensor, and / or the third radiation sensor, and are configured to adjust the first metrology signal based on the second metrology signal and / or the third metrology signal to compensate for the vibration in the metrologysystem.

[0098] The adjusting may be performed by one or more processors PRO (e.g., shown in Fig. 3, Fig. 7, Fig. 14) and / or other components described herein. Adjusting the first metrology signal based on the second metrology signal and / or the third metrology signal may comprise computationally correcting the first metrology signal by calculating and applying a correction factor. In some embodiments, the one or more processors are configured such that adjusting the first metrology signal based on the second metrology signal and / or the third metrology signal comprises determining phases of the diffracted radiation used to generate the first metrology signal as a function of time; and adjusting the first metrology signal based on an aggregation of the phases.

[0099] In some embodiments, adjusting the first metrology signal based on the second metrology signal and / or the third metrology signal comprises a post processing operation performed after the diffracted radiation impinges on the first radiation sensor and the second radiation sensor.

[0100] At operation 610, a feedthrough operation may be performed. The one or more processors PRO (Fig. 3, Fig. 7, Fig. 14) may perform the feedthrough operation by using a computationally corrected first metrology signal to adjust a stage in the metrology system (e.g., system 10 shown in Fig. 3, system 700 shown in Fig. 7, and / or system 800 shown in Fig. 8) to compensate for vibrations in realtime. For example, in some embodiments, the one or more processors are configured to determine phases of the diffracted radiation used to generate the first metrology signal as a function of time; determine path length differences based on the determined phases; and adjust a fast moving mirror associated with a stage in the metrology system to compensate for vibrations, based on an aggregation of the path length differences (described above), and / or other information.

[0101] For example, the second radiation sensor (e.g., second radiation sensor 750 shown in Fig. 7, or sensor 750A or 750B in Fig. 8) and / or third radiation sensor (e.g., sensor 750B shown in Fig. 8, with the second radiation sensor formed by sensor 750A, and the first radiation sensor formed by sensor 710) that have the relatively higher frame rate compared to the first radiation sensor, is configured to generate a metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system (e.g., system 800 in this example). This signal may comprise the phase as a function of time (<p(t)). Any known algorithm to extract the phase may be used. The algorithm to extract the phase can be relatively simple, as we are only phase differences over time are of interest, the full phase as a function of position across a radiation sensor is not needed. The fringe contrast in the intensity modulated fringe pattern from the first radiation sensor is reduced by vibrations according to the equation:where C is the desired fringe contrast that gives the intensity signal used to calculate overlay. Cvibis the actual fringe contrast measured on the first radiation sensor due to vibrations, <p(t) is the phase shift due to vibration as a function of time, <pQis the average phase during an acquisition, and the brackets <> indicate a time average over the integration time of the first radiation sensor. Without mitigation, vibrations with magnitudes of a few nanometers are expected to decrease the measured fringe contrast and cause unacceptable overlay error. From this expression, it is easy to see that if the phase can be measured, the correct fringe contrast can be determined based on the equation.

[0102] The effectiveness of this correction is limited by how precisely <p(t) can be determined. Errors that may be considered include: (1) error in <p(t) caused by noise; (2) slow sampling frequency of <p(t) which does not collect information about fast vibrations; and (3) timing jitter of <p(t) acquisition. Errors (2) and (3) are easily mitigated by using a line scan camera (or photodiode array) with a fast frame rate, for example. The highest frequency vibration observed in current metrology system data is about 800 Hz. As a general rule of thumb, measurements 10X faster than that are needed to facilitate corrections - i.e., 8 kHz. Line scan cameras (and / or photodiode arrays) can easily measure at 10’s of kHz, with some models measuring at 300 kHz (e.g., a Teledyne Linea ML / linea-ml). In this line scan camera, the timing jitter is negligibly small as long as the exposure time of the camera is less than the line period. Therefore, the error caused by incorrect measurement of <p(t) will dominate current system measurements.

[0103] The phase noise in a given measurement may be normally distributed with a standard deviation, for example:1 <p ! — 7 2 SNR where SNR is the signal-to-noise ratio of the line scan camera or photodiode array. If the camera is exposed for a shorter time to acquire at high frame rate, the SNR will decrease and there will be more error in the phase measurement. Simulations indicate that for an overlay specification of about 0.05 nm, phase measurement to three milliradian (mrad) precision is required, as one possible example of many.

[0104] There are two primary factors that make accurate phase measurement possible at the much faster acquisition rates described herein. First, much less SNR is needed for phase measurement compared to overlay measurement. Error in overlay scales aswhere d is the bias on the gratings of a metrology target, and S is a stack sensitivity. To measure overlay correctly to -0.05 nm, an SNR of 104 in this example. In contrast, an SNR of 2 x 102is needed to measure phase to the 3 mrad precision described above. The SNR can be enhanced by using a cylindrical lens to focus the fringes onto a line scan camera, for example. Second, a heterodyne gain (i.e., coherent amplification - using a reference beam that is brighter than the diffracted radiation, and interfering them, thus obtaining an enhanced signal) from the diffraction based metrology operations described herein provides better SNR than a normal dark field measurement for low light levels. The SNR obtained from the diffraction based metrology operations described herein scales like N0NrSNRDHM / / Vo+ Nr' where Nois the number of signal photons collected, Nris the number of reference photons collected, and there is an extra in the denominator because the shot noise variance is doubled by the two diffraction orders on the camera simultaneously.

[0105] An adjusted first metrology signal may be used for opto-mechatronic correction and / or other purposes. For example, a phase signal from a line scan camera may be fed back to a wafer stage or a delay line to provide real time opto-mechatronic corrections and provide even more vibration correction as needed.

[0106] The SNR may also and / or instead be enhanced by adding another light source to the metrology system (e.g., system 700 shown in Fig. 7 and / or system 800 shown in Fig. 8) specifically for phase measurement. The secondary light source may be separated from the illumination radiation 702 (Fig. 7, Fig. 8) signal light by a beamsplitter or dichroic mirror and be directed to a line scan camera or photodiode array (e.g., a second and / or third radiation sensor). Because this secondary light source is not required to support full wavelength and polarization functionality, the secondary light source may be configured to be stronger to provide better SNR. To support the full lambda / pitch range of one or more of the radiation sensors, the secondary light source may be configured to generate different wavelengths (for example 600 nm, 1000 nm, and 1400 nm) of radiation, and a radiation sensor may detect a first diffraction order or one single short wavelength, below the shortest wavelength supported for overlay measurement (for example 390 nm), and collect any diffraction order that falls within a numerical aperture (NA) of an objective lens of the metrology system.

[0107] Fig. 13 illustrates using multiple lines 1300 of a camera to implement 4-step phase shifted interferometry 1302. This technique is the basis of Heidenhain encoders 1304 illustrated in Fig. 13. For example, in some embodiments, a sufficiently fast 2D camera may be used as the second and / or thirdradiation sensors, as described above. The full 2D information provides an enhanced SNR compared to a line scan camera and / or photodiode array, as well as enabling more complex algorithms. For example, a 4-step phase shifted interferometry algorithm may be applied using four lines 1300 of the camera as shown in Figure 13. Phase shifting interferometry is mature and has computationally simple and robust algorithms that enable read-time feedback.

[0108] Returning to Fig. 6, in some embodiments, operation 612 comprises determining a metrology value based on the adjusted first metrology signal and / or other information. The metrology value may be overlay for two or more layers of the semiconductor layer structure, alignment, and / or other metrology values. The metrology value may be determined using principles of interferometry and / or other principles. The first metrology signal comprises measurement information pertaining to the metrology target. For example, the metrology signal may be an overlay signal comprising overlay measurement information, and / or other metrology signals.

[0109] In some embodiments, operation 612 includes determining an adjustment for a semiconductor device manufacturing process. In some embodiments, operation 612 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on an overlay value indicated by the adjusted first metrology signal, and / or other information. The one or more semiconductor device manufacturing process parameters may include a parameter of the radiation (the radiation used for determining overlay), an overlay inspection location on a layer of a semiconductor device structure, an overlay value, and / or other parameters. In some embodiments, semiconductor device manufacturing process parameters can be interpreted broadly to include a stage position, a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation (used for exposing resist, etc.), an incident angle of the radiation (used for exposing resist, etc.), a wavelength of the radiation (used for exposing resist, etc.), a pupil size and / or shape, a resist material, and / or other parameters.

[0110] A parameter of the radiation used for determining overlay, for example, may include a wavelength, an intensity, an angle of incidence, and / or parameters of the radiation. These parameters may be adjusted to better measure features with specific shapes, enhance the intensity of reflected radiation, increase and / or otherwise enhance (e.g., maximize) the phase and / or amplitude shifts (if any) in reflected radiation from one area of a feature to the next, and / or for other purposes. This may enable and / or enhance detection of more subtle deviations, make the phase and / or amplitude shifts easier to detect, and / or have other advantages.

[0111] In some embodiments, operation 610 includes determining a process adjustment based on the one or more determined semiconductor device manufacturing process parameters, adjusting a semiconductor device manufacturing apparatus based on the determined adjustment, and / or other operations. For example, based on a measured overlay value, a lithography exposure may be corrected. As another example, if a determined overlay value is not within process tolerances, the misalignment may be caused by one or more manufacturing processes whose process parameters have drifted and / orotherwise changed so that the process is no longer producing acceptable devices (e.g., overlay measurements may breach a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the overlay determination. The new or adjusted process parameters may be configured to cause a manufacturing process to again produce acceptable devices. For example, a new or adjusted process parameter may cause a previously unacceptable overlay value to be adjusted back into an acceptable range. The new or adjusted process parameters may be compared to existing parameters for a given process. If there is a difference, that difference may be used to determine an adjustment for an apparatus that is used to produce the devices (e.g., parameter “x” should be increased / decreased / changed so that it matches the new or adjusted version of parameter “x” determined as part of operation 610), for example. In some embodiments, operation 604 may include electronically adjusting an apparatus (e.g. , based on the determined process parameters) . Electronically adjusting an apparatus may include sending an electronic signal, and / or other communications to the apparatus, for example, which causes a change in the apparatus. The electronic adjustment may include changing a setting on the apparatus, for example, and / or other adjustments.

[0112] Fig. 14 is a diagram of an example computer system CS that may be used for one or more of the operations described herein. Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0113] Computer system CS may be coupled via bus BS to a display DS, such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor PRO and for controlling cursor movement on display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

[0114] In some embodiments, portions of one or more methods may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from anothercomputer-readable medium, such as storage device SD. Execution of the sequences of instructions included in main memory MM causes processor PRO to perform the process steps (operations). One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, this description is not limited to any specific combination of hardware circuitry and software.

[0115] The term “computer-readable medium” or “machine-readable medium” refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-transitory, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non- transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the operations described. Transitory computer-readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[0116] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[0117] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interfaceCI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0118] Network link NDL typically provides data communication through one or more networks to other data devices. For example, network link NDL may provide a connection through local network LAN to a host computer HC. This can include data communication services provided through the worldwide packet data communication network, now commonly referred to as the “Internet” INT. Local network LAN (Internet) may use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network data link NDL and through communication interface CI, which carry the digital data to and from computer system CS, are exemplary forms of carrier waves transporting the information.

[0119] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN, and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other non-volatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0120] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:1. A metrology system, comprising: a first radiation sensor configured to generate a first metrology signal based on diffracted radiation received from a metrology target in a patterned substrate, the first metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation; a second radiation sensor having a relatively higher frame rate compared to the first radiation sensor, such that the second radiation sensor is configured to generate a second metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system; and one or more processors operatively coupled to the first radiation sensor and the second radiation sensor, the one or more processors configured to adjust the first metrology signal based on the second metrology signal.2. The system of clause 1, wherein the one or more processors are configured to adjust the first metrology signal based on the second metrology signal to compensate for the vibration in the metrology system.3. The system of any of the previous clauses, wherein generating the first metrology signal comprises performing interferometry or holography using the diffracted radiation in combination with secondary reference illumination that interferes with the diffracted radiation, to produce fringes in the intensity modulated fringe pattern.4. The system of any of clauses 1-3, wherein adjusting the first metrology signal based on the second metrology signal comprises computationally correcting the first metrology signal by calculating andapplying a correction factor.5. The system of any of the previous clauses, where the one or more processors are further configured to perform a feedthrough operation, by using a computationally corrected first metrology signal to adjust a stage in the metrology system to compensate for vibrations in real-time.6. The system of any of the previous clauses, wherein adjusting the first metrology signal based on the second metrology signal comprises a post processing operation performed after the diffracted radiation impinges on the first radiation sensor and the second radiation sensor.7. The system of any of the previous clauses, wherein the second radiation sensor comprises a line scan camera, a photodiode array, or a two dimensional camera with the relatively higher frame rate compared to the first radiation sensor.8. The system of any of the previous clauses, wherein the frame rate of the second radiation sensor is two or more times faster than a vibration frequency in the metrology system.9. The system of any of the previous clauses, wherein the second radiation sensor need only detect one or more pixel or diode lines of the intensity modulated fringe pattern for the diffracted radiation.10. The system of any of the previous clauses, wherein the one or more processors are configured such that adjusting the first metrology signal based on the second metrology signal comprises determining phases of the diffracted radiation used to generate the first metrology signal as a function of time; and adjusting the first metrology signal based on an aggregation of the phases.11. The system of any of the previous clauses, wherein the one or more processors are further configured to: determine phases of the diffracted radiation used to generate the first metrology signal as a function of time; determine path length differences based on the determined phases; and adjust a fast moving mirror associated with a stage in the metrology system to compensate for vibrations, based on an aggregation of the path length differences.12. The system of any of the previous clauses, wherein the second radiation sensor is positioned at an angle relative to the diffracted radiation such that the second metrology signal indicates phase shifts in two or more different orders of the diffracted radiation.13. The system of any of the previous clauses, further comprising a third radiation sensor, the third radiation sensor having the relatively higher frame rate compared to the first radiation sensor and being configured to generate a third metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system, wherein: the one or more processors are operatively coupled to the first radiation sensor, the second radiation sensor, and the third radiation sensor, and are configured to adjust the first metrology signal based on the second metrology signal and the third metrology signal to compensate for the vibration in the metrology system.14. The system of any of the previous clauses, wherein the second radiation sensor is positioned at an angle relative to the diffracted radiation such that the second metrology signal indicates phase shifts in a first order of the diffracted radiation; and the third radiation sensor is positioned at a different angle relative to the diffracted radiation such that the third metrology signal indicates phase shifts in anotherorder of the diffracted radiation.15. The system of any of the previous clauses, wherein the second radiation sensor is positioned at a first perpendicular angle relative to fringes in the intensity modulated fringe pattern, and the third radiation sensor is positioned at a different perpendicular angle relative to the fringes.16. The system of any of the previous clauses, wherein the second and third radiation sensors comprise: two separate line scan cameras, photodiode arrays, or two dimensional cameras with the relatively higher frame rate compared to the first radiation sensor; or a single sensor comprising one or more chips configured to sense diffracted radiation in two different orientations.17. The system of any of the previous clauses, wherein the second and third radiation sensors comprise visible radiation sensors and / or infrared radiation sensors.18. The system of any of the previous clauses, further comprising first and / or second optical modules configured to direct first, second, and / or third portions of the diffracted radiation from the metrology target toward the first radiation sensor, the second radiation sensor, and / or the third radiation sensor, respectively, such that a same phase of the diffracted radiation impinges on the first radiation sensor, the second radiation sensor, and / or the third radiation sensor.19. The system of any of the previous clauses, wherein the first and / or second optical modules each comprises a beam splitter.20. The system of any of the previous clauses, wherein the first radiation sensor comprises an interferometer.21. The system of any of the previous clauses, wherein the first radiation sensor comprises a camera configured to generate a two dimensional intensity modulated fringe pattern.22. The system of any of the previous clauses, wherein the first radiation sensor comprises two or more cameras, each camera being configured for a different radiation wavelength range.23. The system of any of the previous clauses, wherein the different radiation wavelength ranges comprise a visible wavelength range and a short wave infrared wavelength range.24. The system of any of the previous clauses, wherein the first radiation sensor is configured such that the intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the metrology target and one or more reference radiation sources.25. The system of any of the previous clauses, further comprising two reference radiation sources, and two illumination radiation sources oriented in two illumination directions configured to project radiation onto the metrology target, such that: illumination radiation is diffracted by the metrology target into at least +lst order diffracted radiation from one illumination radiation source and -1st order diffracted radiation from the other of the two illumination radiation sources; and the at least -4-lst and -1st order diffracted radiation is directed toward the first radiation sensor, together with two reference beams of radiation, with the reference beams of radiation matched to two illumination paths for the illumination radiation, such that an interference pattern impinging on the first radiation sensor forms a hologram thatencodes information from the two illumination directions.26. The system of any of the previous clauses, wherein the one or more processors are further configured to determine one or more amplitudes of fringes in the intensity modulated fringe pattern after an adjustment; and determine a metrology value based on the one or more amplitudes.27. The system of any of the previous clauses, wherein the metrology value is overlay of a layer of the patterned substrate.28. The system of any of the previous clauses, wherein the metrology target comprises a diffractionbased overlay metrology target.29. The system of any of the previous clauses, wherein the metrology target comprises a diffractionbased alignment metrology target.30. The system of any of the previous clauses, wherein the metrology system is configured to be used to measure overlay and / or alignment on a patterned semiconductor wafer as part of a semiconductor manufacturing process.31. A metrology method, comprising: generating, with a first radiation sensor of a metrology system, a first metrology signal based on diffracted radiation received from a metrology target in a patterned substrate, the first metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation; generating, with a second radiation sensor of the metrology system having a relatively higher frame rate compared to the first radiation sensor, a second metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system; and adjusting, with one or more processors operatively coupled to the first radiation sensor and the second radiation sensor, the first metrology signal based on the second metrology signal.32. The method of clause 31, wherein the one or more processors are configured to adjust the first metrology signal based on the second metrology signal to compensate for the vibration in the metrology system.33. The method of any of the previous clauses, wherein generating the first metrology signal comprises performing interferometry or holography using the diffracted radiation in combination with secondary reference illumination that interferes with the diffracted radiation, to produce fringes in the intensity modulated fringe pattern.34. The method of any of the previous clauses, wherein adjusting the first metrology signal based on the second metrology signal comprises computationally correcting the first metrology signal by calculating and applying a correction factor.35. The method of any of the previous clauses, further comprising performing, with the one or more processors, a feedthrough operation, by using a computationally corrected first metrology signal to adjust a stage in the metrology system to compensate for vibrations in real-time.36. The method of any of the previous clauses, wherein adjusting the first metrology signal based on the second metrology signal comprises a post processing operation performed after the diffracted radiation impinges on the first radiation sensor and the second radiation sensor.37. The method of any of the previous clauses, wherein the second radiation sensor comprises a line scan camera, a photodiode array, or a two dimensional camera with the relatively higher frame rate compared to the first radiation sensor.38. The method of any of the previous clauses, wherein the frame rate of the second radiation sensor is two or more times faster than a vibration frequency in the metrology system.39. The method of any of the previous clauses, wherein the second radiation sensor need only detect one or more pixel or diode lines of the intensity modulated fringe pattern for the diffracted radiation.40. The method of any of the previous clauses, wherein the one or more processors are configured such that adjusting the first metrology signal based on the second metrology signal comprises determining phases of the diffracted radiation used to generate the first metrology signal as a function of time; and adjusting the first metrology signal based on an aggregation of the phases.41. The method of any of the previous clauses, further comprising determining, with the one or more processors, phases of the diffracted radiation used to generate the first metrology signal as a function of time; determining, with the one or more processors, path length differences based on the determined phases; and adjusting, with the one or more processors, a fast moving mirror associated with a stage in the metrology system to compensate for vibrations, based on an aggregation of the path length differences.42. The method of any of the previous clauses, wherein the second radiation sensor is positioned at an angle relative to the diffracted radiation such that the second metrology signal indicates phase shifts in two or more different orders of the diffracted radiation.43. The method of any of the previous clauses, further comprising generating, with a third radiation sensor, the third radiation sensor having the relatively higher frame rate compared to the first radiation sensor, a third metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system, wherein: the one or more processors are operatively coupled to the first radiation sensor, the second radiation sensor, and the third radiation sensor, and are configured to adjust the first metrology signal based on the second metrology signal and the third metrology signal to compensate for the vibration in the metrology system.44. The method of any of the previous clauses, wherein the second radiation sensor is positioned at an angle relative to the diffracted radiation such that the second metrology signal indicates phase shifts in a first order of the diffracted radiation; and the third radiation sensor is positioned at a different angle relative to the diffracted radiation such that the third metrology signal indicates phase shifts in another order of the diffracted radiation.45. The method of any of the previous clauses, wherein the second radiation sensor is positioned at a first perpendicular angle relative to fringes in the intensity modulated fringe pattern, and the third radiation sensor is positioned at a different perpendicular angle relative to the fringes.46. The method of any of the previous clauses, wherein the second and third radiation sensors comprise: two separate line scan cameras, photodiode arrays, or two dimensional cameras with the relativelyhigher frame rate compared to the first radiation sensor; or a single sensor comprising one or more chips configured to sense diffracted radiation in two different orientations.47. The method of any of the previous clauses, wherein the second and third radiation sensors comprise visible radiation sensors and / or infrared radiation sensors.48. The method of any of the previous clauses, further comprising directing, with first and / or second optical modules, first, second, and / or third portions of the diffracted radiation from the metrology target toward the first radiation sensor, the second radiation sensor, and / or the third radiation sensor, respectively, such that a same phase of the diffracted radiation impinges on the first radiation sensor, the second radiation sensor, and / or the third radiation sensor.49. The method of any of the previous clauses, wherein the first and / or second optical modules each comprises a beam splitter.50. The method of any of the previous clauses, wherein the first radiation sensor comprises an interferometer.51. The method of any of the previous clauses, wherein the first radiation sensor comprises a camera configured to generate a two dimensional intensity modulated fringe pattern.52. The method of any of the previous clauses, wherein the first radiation sensor comprises two or more cameras, each camera being configured for a different radiation wavelength range.53. The method of any of the previous clauses, wherein the different radiation wavelength ranges comprise a visible wavelength range and a short wave infrared wavelength range.54. The method of any of the previous clauses, wherein the first radiation sensor is configured such that the intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the metrology target and one or more reference radiation sources.55. The method of any of the previous clauses, further comprising projecting, with two reference radiation sources, and two illumination radiation sources oriented in two illumination directions, radiation onto the metrology target, such that: illumination radiation is diffracted by the metrology target into at least +1 st order diffracted radiation from one illumination radiation source and -1st order diffracted radiation from the other of the two illumination radiation sources; and the at least +1 st and - 1st order diffracted radiation is directed toward the first radiation sensor, together with two reference beams of radiation, with the reference beams of radiation matched to two illumination paths for the illumination radiation, such that an interference pattern impinging on the first radiation sensor forms a hologram that encodes information from the two illumination directions.56. The method of any of the previous clauses, further comprising determining, with the one or more processors, one or more amplitudes of fringes in the intensity modulated fringe pattern after an adjustment; and determining a metrology value based on the one or more amplitudes.57. The method of any of the previous clauses, wherein the metrology value is overlay of a layer of the patterned substrate.58. The method of any of the previous clauses, wherein the metrology target comprises a diffractionbased overlay metrology target.59. The method of any of the previous clauses, wherein the metrology target comprises a diffractionbased alignment metrology target. 60. The method of any of the previous clauses, further comprising using the metrology system to measure overlay and / or alignment on a patterned semiconductor wafer as part of a semiconductor manufacturing process.

[0121] The concepts disclosed herein may be associated with any generic metrology and / or imaging system for measuring and / or imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths.

[0122] While the concepts disclosed herein may be used for metrology and / or imaging on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of metrology and / or imaging systems, e.g., those used for metrology and / or imaging on substrates other than silicon wafers. In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments.

[0123] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A metrology system, comprising: a first radiation sensor configured to generate a first metrology signal based on diffracted radiation received from a metrology target in a patterned substrate, the first metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation; a second radiation sensor having a relatively higher frame rate compared to the first radiation sensor, such that the second radiation sensor is configured to generate a second metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system; and one or more processors operatively coupled to the first radiation sensor and the second radiation sensor, the one or more processors configured to adjust the first metrology signal based on the second metrology signal.

2. The system of claim 1 , wherein the one or more processors are configured to adjust the first metrology signal based on the second metrology signal to compensate for the vibration in the metrology system.

3. The system of claim 1 or 2, wherein generating the first metrology signal comprises performing interferometry or holography using the diffracted radiation in combination with secondary reference illumination that interferes with the diffracted radiation, to produce fringes in the intensity modulated fringe pattern.

4. The system of any of claims 1-3, wherein adjusting the first metrology signal based on the second metrology signal comprises computationally correcting the first metrology signal by calculating and applying a correction factor.

5. The system of claim 4, where the one or more processors are further configured to perform a feedthrough operation, by using a computationally corrected first metrology signal to adjust a stage in the metrology system to compensate for vibrations in real-time.

6. The system of any of claims 1-5, wherein adjusting the first metrology signal based on the second metrology signal comprises a post processing operation performed after the diffracted radiation impinges on the first radiation sensor and the second radiation sensor.

7. The system of any of claims 1-6, wherein the second radiation sensor comprises a line scan camera, a photodiode array, or a two dimensional camera with the relatively higher frame rate compared to the first radiation sensor.

8. The system of any of claims 1-7, wherein the frame rate of the second radiation sensor is two or more times faster than a vibration frequency in the metrology system.

9. The system of any of claims 1-8, wherein the second radiation sensor need only detect one or more pixel or diode lines of the intensity modulated fringe pattern for the diffracted radiation.

10. The system of any of claims 1-9, wherein the one or more processors are configured such that adjusting the first metrology signal based on the second metrology signal comprises determining phases of the diffracted radiation used to generate the first metrology signal as a function of time; and adjusting the first metrology signal based on an aggregation of the phases.

11. The system of any of claims 1-10, wherein the one or more processors are further configured to: determine phases of the diffracted radiation used to generate the first metrology signal as a function of time; determine path length differences based on the determined phases; and adjust a fast moving mirror associated with a stage in the metrology system to compensate for vibrations, based on an aggregation of the path length differences.

12. The system of any of claims 1-11, wherein the second radiation sensor is positioned at an angle relative to the diffracted radiation such that the second metrology signal indicates phase shifts in two or more different orders of the diffracted radiation.

13. The system of any of claims 1-11, further comprising a third radiation sensor, the third radiation sensor having the relatively higher frame rate compared to the first radiation sensor and being configured to generate a third metrology signal indicating phase shifts in the diffracted radiation caused by vibration in the metrology system, wherein: the one or more processors are operatively coupled to the first radiation sensor, the second radiation sensor, and the third radiation sensor, and are configured to adjust the first metrology signal based on the second metrology signal and the third metrology signal to compensate for the vibration in the metrology system.

14. The system of claim 13, wherein the second radiation sensor is positioned at an angle relative to the diffracted radiation such that the second metrology signal indicates phase shifts in a first order of the diffracted radiation; and the third radiation sensor is positioned at a different angle relative to thediffracted radiation such that the third metrology signal indicates phase shifts in another order of the diffracted radiation.

15. The system of claim 14, wherein the second radiation sensor is positioned at a first perpendicular angle relative to fringes in the intensity modulated fringe pattern, and the third radiation sensor is positioned at a different perpendicular angle relative to the fringes.

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