Reference grating for semiconductor metrology systems and methods

Abstract

A reference grating for a semiconductor metrology system is described. The reference grating has a changeable pitch, which is changed to match the pitch of a metrology target in a semiconductor wafer. The reference grating is configured to receive radiation simultaneously with the target grating, and a radiation sensor is configured to generate a metrology signal (e.g., an alignment signal) based on diffracted radiation received from the target grating and the reference grating. The reference grating comprises an actuator and a reflective grating mask. The reflective grating mask comprises various gratings with different layouts and / or pitches configured to match various different target gratings in the wafer. The actuator is configured to move the reflective grating mask such that the reference grating is in a physical position to receive the radiation from the radiation source simultaneously with the target grating; and diffract radiation back toward the radiation sensor.

Description

REFERENCE GRATING FOR SEMICONDUCTOR METROLOGY SYSTEMS AND METHODSCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Application No. 63 / 528,872, filed July 25, 2023, and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] This description relates to a reference grating for semiconductor metrology systems and methods.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. Since, in general, the lithographic projection apparatus will have a reduction ratio M (e.g., 4), the speed F at which the substrate is moved will be 1 / M times that at which the projection beam scans the patterning device.

[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 targetportion 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] Various 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 device 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, microelectro 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 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 (currently in most cases 248nm or 193nm), 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). Various metrology systems and methods are typically required for these fine tuning steps.SUMMARY

[0009] A reference grating for a semiconductor metrology system is described. The reference grating has a changeable pitch, which is changed to match the pitch of a metrology target in a semiconductor wafer. The reference grating is configured to receive radiation simultaneously with the target grating, and a radiation sensor is configured to generate a metrology signal (e.g., an alignment signal) based on diffracted radiation received from the target grating and the reference grating. The reference grating comprises an actuator and a reflective grating mask. The reflective grating mask comprises various gratings with different layouts and / or pitches configured to match various different target gratings in the wafer. The actuator is configured to move the reflective grating mask such that the reference grating is in a physical position to receive the radiation from the radiation source simultaneously with the target grating; and diffract radiation back toward the radiation sensor. This may provide a compact and cheaper alternative compared to prior systems for dual polarization, same pitch range, and same mark type applications, with half the channels, among other advantages.

[0010] According to an embodiment, a metrology system is provided. The metrology system comprises a multi wavelength radiation source configured to irradiate a target grating in a patterned substrate with radiation. The target grating has a target pitch. The metrology system comprises a reference grating. The reference grating has a changeable pitch. The changeable pitch is configured to be changed to match the target pitch. The reference grating is configured to receive radiation from the radiation source simultaneously with the target grating. The metrology system comprises a radiation sensor configured to generate a metrology signal based on diffracted radiation received from the target grating and the reference grating. The metrology signal comprises measurement information pertaining to the target grating.

[0011] In some embodiments, the metrology signal is an alignment signal comprising alignment measurement information for a layer of the patterned substrate that includes the target grating.

[0012] In some embodiments, a path length of a target branch and a reference branch of the metrology system are matched to within a coherence length of the radiation source.

[0013] In some embodiments, the alignment signal has a period equal to the pitch of the target and reference grating pitches when the target and the reference grating have the same pitch.

[0014] In some embodiments, the reference grating is physically separate from the patterned substrate and located along a different optical path than the target grating.

[0015] In some embodiments, the system further comprises an optical element with transmissive and reflective regions. The optical element is positioned in a pupil plane of the system. The optical element configured to: receive the radiation from the radiation source and transmit portions of the radiation toward the target grating target along a first optical path, and toward the reference grating along a second optical path. The optical element is configured to transmit the diffracted radiation from the target grating and the reference grating toward the radiation sensor.

[0016] In some embodiments, different orders of the diffracted radiation from the target grating and the reference grating overlap in the pupil plane and are combined for the radiation sensor, thus providing an intensity interference within a coherence length of the radiation source versus position alignment signal.

[0017] In some embodiments, a plus diffraction order from the reference grating overlaps with a minus diffraction order from the target grating, and a minus diffraction order from the reference grating overlaps with a plus diffraction order form the target grating, in the pupil plane. In some embodiments, a plus diffraction order from the reference grating overlaps with a plus diffraction order from the target grating.

[0018] In some embodiments, the system comprises a second optical element positioned between the optical element and the radiation sensor. The second optical element is configured to split combined overlapping diffracted radiation into an aligned position y polarization (or p polarization) component and an aligned position x polarization (or s polarization) component. In some embodiments, the second optical element comprises separate third and fourth optical elements. The third optical element is configured to split the combined overlapping diffracted radiation into an aligned position minus y polarization component and the aligned position x polarization component. The fourth optical element is configured to split the combined overlapping diffracted radiation into an aligned position plus y polarization component and a second aligned position x polarization component.

[0019] In some embodiments, the aligned position minus y polarization component, the aligned position x polarization component, the aligned position plus y polarization component, and the second aligned position x polarization component are combined to generate the intensity versus position alignment signal.

[0020] In some embodiments, the measurement information in the metrology signal comprises an alignment position. The alignment position is determined based on a weighted sum of aligned positions over x and y polarizations, wavelengths, and plus and minus channels.

[0021] In some embodiments, the reference grating comprises an actuator and a reflective grating mask. In some embodiments, the actuator comprises a motor (e.g., a dual axis motor, a rotation motor, etc.), an ultrasonic piezoelectric motor, or a liquid crystal based spatial light modulator. In some embodiments, the reflective grating mask comprises various gratings with different layouts and / or pitches configured to match various different target gratings in the patterned substrate, wherein the reference grating is one the various gratings having a broad range of reflectivity with different layouts. In some embodiments, the actuator is configured to move the reflective grating mask such that the reference grating is in a physical position to receive the radiation from the radiation source simultaneously with the target grating; and diffract radiation back toward the radiation sensor.

[0022] In some embodiments, the system comprises a selective order blocker mask located in a pupil plane of the system. The selective order blocker mask is configured to block non-scanning direction spots of radiation from the reference grating.

[0023] In some embodiments, the reference grating comprises a bi-directional reference grating configured to correspond to a type of the target grating.

[0024] In some embodiments, the system comprises a wedge and / or a mask configured to separate orthogonal direction diffraction spots.

[0025] In some embodiments, the radiation comprises off axis radiation relative to the target grating and / or the reference grating.

[0026] In some embodiments, the system comprises one or more attenuators, compensators, and / or beam shifting elements for thick / wedge resists on the target grating.

[0027] In some embodiments, the metrology system is an alignment sensor, the alignment sensor is configured for a semiconductor wafer, and the alignment sensor is used in a semiconductor manufacturing process.

[0028] According to another embodiment, a metrology method comprising one or more of the operations described above is provided.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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 with the accompanying figures.

[0030] Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.

[0031] Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.

[0032] Fig. 3 schematically depicts an example inspection system, according to an embodiment.

[0033] Fig. 4 schematically depicts an example metrology technique, according to an embodiment.

[0034] Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.

[0035] Fig. 6 illustrates a semiconductor metrology system comprising a reference grating, among other components, according to an embodiment.

[0036] Fig. 7 illustrates an example mask that may be included in the metrology system and used to separate orthogonal direction diffraction spots, according to an embodiment.

[0037] Fig. 8 illustrates an example of providing off axis radiation relative to a target grating and a reference grating, according to an embodiment.

[0038] Fig. 9 illustrates a metrology method, according to an embodiment.

[0039] Fig. 10 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0040] In semiconductor device manufacturing, metrology operations typically include determining the position of a metrology mark (or marks) and / or other target in a layer of a semiconductor devicestructure in a substrate such as a wafer. This position is typically determined by irradiating a metrology mark with radiation and comparing characteristics of different diffraction orders of radiation reflected from the metrology mark. Such techniques are used to measure overlay, alignment, and / or other parameters.

[0041] Alignment sensors often provide wafer alignment capability using a self-referencing interferometer for a variety of periodic, oblique, and bi-directional marks with a range of pitches. Some of these sensors may provide intensity channel measurements which address target mark asymmetry quantification. These intensity channel measurements are DC signals as opposed to modulating alignment signals from other sensors. The costs associated with these sensors, combined with the number of channels they provide, and their form factor, make scalability for parallelization of alignment mark measurements challenging.

[0042] The present systems and methods provide a compact and cheaper alternative compared to prior systems for dual polarization, same pitch range, and same mark type applications, with half the channels, among other advantages. In the present systems and methods, a reference grating with the same mark type and pitch as a target mark is irradiated along with the target mark. The radiation is split into two paths - one portion of the radiation is focused on the target mark at the wafer plane; while the other portion is focused onto the reference grating. The diffracted orders from the target mark and the reference grating overlap in the pupil plane and are combined and output to a radiation detector, thus providing an intensity versus position alignment signal.

[0043] By way of a brief introduction, the description below relates to semiconductor device manufacturing and patterning processes. The following paragraphs also describe several components of systems and / or methods for semiconductor device metrology. These systems and methods may be used for measuring overlay, alignment, etc., in a semiconductor device manufacturing process, for example, or for other operations.

[0044] Although specific reference may be made in this text to the measurement of alignment, or other parameters, and the manufacture of integrated circuits (ICs) for semiconductor devices, it should be understood that the description herein has many other possible applications. For example, 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.

[0045] The term “projection optics” should be broadly interpreted as encompassing various types of optical systems, including refractive optics, reflective optics, apertures and catadioptric optics, for example. The term “projection optics” may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, collectively or singularly. The term “projection optics” may include any optical component in the lithographicprojection apparatus, no matter where the optical component is located on an optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, adjusting and / or projecting radiation from the source before the radiation passes the patterning device, and / or optical components for shaping, adjusting and / or projecting the radiation after the radiation passes the patterning device. The projection optics generally exclude the source and the patterning device.

[0046] 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).

[0047] 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.

[0048] 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.

[0049] 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 theilluminator 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 wherein 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.

[0050] 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 the illuminator 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.

[0051] 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.

[0052] 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. Thesupport 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” herein may be considered synonymous with the more general term “patterning device.”

[0053] The term “patterning device” used herein 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 crosssection 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.

[0054] 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 phaseshift, 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 reflected by the mirror matrix.

[0055] 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” herein may be considered as synonymous with the more general term “projection system.”

[0056] 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 wherein 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 symmetricaspherical 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.

[0057] 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 conducted 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.

[0058] The lithographic apparatus may also be of a type where at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0059] 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 (finepositioning), 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 short-stroke 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.

[0060] 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.

[0061] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0062] The substrate may be processed, before or after exposure, in for example a track (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 herein 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 multi-layer IC, so that the term substrate used herein may also refer to a substrate that already includes multiple processed layers.

[0063] The terms “radiation” and “beam” used herein 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.

[0064] 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.

[0065] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to 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.

[0066] 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)).

[0067] The one or more measured parameters may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, 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 one or more dedicated metrology targets 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.

[0068] 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. Applications of this diffraction-based metrology include the measurement of overlay, alignment, etc. For example, overlay and / or alignment can be measured by comparing parts of the diffraction spectrum (for example, comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0069] 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 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)).

[0070] 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 portions which meet specifications. Other manufacturing process adjustments are contemplated.

[0071] 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, ordifferent 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.

[0072] To enable the metrology, often one or more targets are specifically provided on the substrate. Typically, the target is specially designed and may comprise a periodic structure. For example, the target on a substrate may comprise one or more 1-D periodic structures (e.g., geometric features such as gratings), 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), 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).

[0073] Fig. 3 depicts an example metrology (inspection) system 10 that may be used to detect overlay, alignment, and / or perform other metrology operations. It comprises a radiation or illumination source 2 which projects or otherwise irradiates radiation onto a substrate W (e.g., which may typically include a metrology mark). The redirected radiation is passed to a radiation sensor 4 such as a spectrometer detector 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 metrology 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.

[0074] As in the lithographic apparatus LA in Fig. 1 , one or more substrate tables (not shown in Fig.4) may be provided to hold the substrate W during measurement operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Fig. 1. In an example where inspection system 10 is integrated with the lithographic apparatus, they may even be the same substrate table. 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., a metrology mark), and to bring it into position under an objective lens. Typically, many measurements will be made on target portions of a structure at different locations 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).

[0075] For typical metrology measurements, a target grating 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 grating 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.

[0076] 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 grating 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 grating 30. Accordingly, the measured data from target grating 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.

[0077] For example, the measured data from target grating 30 may indicate alignment for a layer of a semiconductor device. The measured data from target grating 30 may be used (e.g., by the one or more processors PRO and / or other processors) for determining one or more semiconductor device manufacturing process parameters based the alignment and 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 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.

[0078] Fig. 5 illustrates a plan view of a typical target grating 30, and the extent of a typical 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 grating 30, in an embodiment, is a periodic structure (e.g., grating) 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. The target, 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.

[0079] Fig. 6 illustrates a semiconductor metrology system 600 that includes a reference grating 602, among other components. Fig. 6 illustrates two different example embodiments of system 600 (seethe upper and lower images in Fig. 6), each of which are described below. System 600 may form a portion of system 10 described above with respect to Fig. 3. System 600 may be a subsystem of system 10, for example. In some embodiments, one or more components of system 600 may be similar to and / or the same as one or more components of system 10. In some embodiments, one or more components of system 600 may replace, be used with, and / or otherwise augment one or more components of system 10. System 600 is configured for generating (e.g., with source 2 shown in Fig. 3) one or more spots of radiation 604 configured to be directed at one or more metrology targets 30 (shown in substrate W as in Fig. 3) such as one or more diffraction grating targets, reference grating 602, and / or other components. Radiation 604 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 (e.g., system 10 shown in Fig. 3) based on previous 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, and / or other light. In some embodiments, the radiation may be any radiation appropriate for interferometry.

[0080] Diffracted radiation from target 30 and / or reference grating 602 may be used (e.g., by radiation sensor 4 shown in Fig. 3) to obtain images of the metrology target(s) and / or reference grating 602, and / or for other uses. A target 30 may comprise one or more metrology marks, such as diffraction gratings, formed in a substrate W such as a semiconductor wafer, for example. In some embodiments, target 30 may comprise one or more structures in the patterned substrate capable of providing a diffraction signal. One or more targets 30 may be included in a layer of a substrate in a semiconductor device structure, for example. In some embodiments, the feature comprises a geometric feature such as a ID or 2D feature, and / or other geometric features. By way of several non-limiting examples, the feature may comprise a grating, a line, an edge, a fine -pitched series of lines and / or edges, and / or other features.

[0081] In some embodiments, system 600 may comprise one or more attenuators, compensators, beam shifting elements, and / or other components configured for thick / wedge resists on the target 30 grating and / or for other purposes. In order to account for wedge resists on target gratings, a corresponding portion of the reference grating substrate can have gratings such that the diffraction spots in the pupil can be biased by a typical ~ um offset from nominal to get an overlap of the diffraction spots between the two paths to retrieve the depth of modulation of the signal.

[0082] Reference grating 602 has a changeable pitch, which is changed to match the pitch of a grating of metrology target 30 in substrate W (e.g., a semiconductor wafer). As described in more detail below, changing the pitch may including moving the pitch, adjusting the pitch, tilting the pitch, tuning the pitch, some combination of these operations, and / or other operations performed on or with the pitch to cause the pitch of the reference grating to match the target pitch. System 600 is configured such that reference grating 602 is configured to receive radiation 604 simultaneously with the gratingof target 30, and radiation sensor 4 (Fig. 3) is configured to generate a metrology signal (e.g., an alignment signal) based on diffracted radiation received from the target 30 grating and reference grating 602. In some embodiments, reference grating 602 may comprise an actuator 610, a reflective grating mask 612, and / or other components. The reflective grating mask 612 comprises various gratings with different layouts and / or pitches configured to match various different target gratings (e.g., various targets 30) in the wafer (substrate W). In this embodiment, actuator 610 is configured to move reflective grating mask 612 such that the reference grating is in a physical position to receive radiation 604 from the radiation source (e.g., source 2 shown in Fig. 3) simultaneously with grating of target 30; and diffract radiation back toward radiation sensor 4. This may provide a compact and cheaper alternative compared to prior systems for dual polarization, same pitch range, and same mark type applications, with half the channels, among other advantages.

[0083] The radiation source (e.g., source 2 shown in Fig. 3) may be a multi wavelength radiation source of metrology system 600 configured to irradiate the grating of target 30 in patterned substrate W with radiation 604. In some embodiments, radiation 604 comprises off axis radiation relative to the target 30 grating and / or reference grating 602 (see Fig. 9 and discussion below). The target 30 grating may have a target pitch. Radiation 604 may be directed by the radiation source onto the target pitch, multiple pitches of multiple targets, sub-portions (e.g., something less than the whole) of the target pitch, and / or onto substrate W in other ways. Radiation 604 may also be directed by the radiation source onto the reference grating 602, multiple pitches of multiple reference gratings 602, sub-portions (e.g., something less than the whole) of the reference grating 602, and / or onto other corresponding reference components. In some embodiments, radiation 604 may be directed by the radiation source onto the target 30 grating and / or reference grating 602 in a time varying manner. For example, radiation 604 may be rastered over a target 30 (e.g., by moving the target 30 under the radiation) grating and / or reference grating 602 such that different portions of the target pitch and / or the pitch of reference grating 602 are irradiated at different times. As another example, characteristics of radiation 604 (e.g., wavelength, intensity, etc.) may be varied. This may create time varying data envelopes, or windows, for analysis. The data envelopes may facilitate analysis of individual subportions of a target pitch, comparison of one portion of a target 30 to another and / or to other targets (e.g., in other layers), and / or reference grating 602, and / or other analysis.

[0084] The changeable pitch of reference grating 602 is configured to be changed to match the target pitch of the grating of target 30. Changing the pitch of reference grating 602 may include moving the pitch, adjusting the pitch, tilting the pitch, and / or other operations as mentioned above performed on or with the pitch of reference grating 602 to cause the pitch of reference grating 602 to match the target pitch (e.g., the pitch of grating of target 30). As shown in Fig. 6, reference grating 602 is configured to receive radiation 604 from the radiation source (e.g., source 2 shown in Fig. 3) simultaneously with the target 30 grating. In some embodiments, reference grating 602 comprises a bi-directional reference grating 602 configured to correspond to a type of the target 30 grating. Asdescribed above, in some embodiments, reference grating 602 comprises actuator 610, reflective grating mask 612, and / or other components. Actuator 610 may comprise a motor, an ultrasonic piezoelectric motor, a liquid crystal based spatial light modulator, and / or other actuators, for example. In some embodiments, reflective grating mask 612 comprises various gratings with different layouts and / or pitches configured to match various different target 30 gratings in the patterned substrate W. Reference grating 602 may be one the various gratings having a broad range of reflectivity with different layouts. Actuator 610 is configured to move the reflective grating mask 612 such that reference grating 602 is in a physical position to receive radiation 604 from the radiation source simultaneously with the target 30 grating; and diffract radiation back toward the radiation sensor (e.g., radiation sensor 4), as shown by the various arrows in Fig. 6. Movement may comprise rotation, translation, tilting, and / or other movement, for example. In some embodiments, a spatial light modulator (SLM) and / or other components can be used to adjust the pitch of reference grating 602.

[0085] As shown in Fig. 6, reference grating 602 is physically separate from the patterned substrate W and located along a different optical path (see optical path 640 versus optical path 642) than the target 30 grating in system 600. System 600 includes an optical element 650 having transmissive and reflective regions, which is positioned in a pupil plane 652 of system 600. Radiation 604 from the radiation source and transmitting portions of optical element 650 transmit radiation 604 toward the target 30 grating target along a first optical path 640, and toward the reference grating 602 along a second optical path 642. Optical element 650 is also configured to transmit diffracted radiation from the target 30 grating and the reference grating 602 toward the radiation sensor (e.g., as indicated by the various arrows in Fig. 6). In some embodiments, path lengths (e.g., the lengths of optical paths 640 and 642) of a target branch 630 and a reference branch 632 of system 600 are matched to within a coherence length of the radiation source (e.g., source 2 shown in Fig. 3).

[0086] In order to obtain an aligned position, the phase of the signal needs to be detected. The phase of the signal is generated due to the interference signal from the reference and the target branches. In order for interference to occur, the two beams should be within the coherence length of the laser. Otherwise, the two signals will add incoherently and just the sum of the intensities of the two signals will be detected and not the phase. In some embodiments, one or more components of system 600 (e.g., a selective order blocker mask located in the pupil plane of the system) are configured for blocking non-scanning direction spots of radiation 604 from reference grating 602. Blocking the nonscanning direction spots is important to retain the full depth of modulation. The leakage of the nonscanning direction spots, adds a DC (non-interfering, as there is no phase change for the non-scanning direction spots) signal to the resultant signal thus lowering the phase carrying modulated signal. System 600 may also include other various lenses, reflectors, and other optical components, and / or other components.

[0087] Radiation sensor 4 (Fig. 3) is configured to generate a metrology signal based on diffracted radiation received from the target 30 grating and reference grating 602, and / or other information. Themetrology signal comprises measurement information pertaining to the target 30 grating and / or other information. For example, the metrology signal may be an alignment signal comprising alignment measurement information, and / or other metrology signals. The metrology signal may be an alignment signal comprising alignment measurement information for a layer of the patterned substrate W that includes the target 30 grating, for example. In some embodiments, the alignment signal has a period equal to the pitch of the target 30 and reference grating 602 pitches when the target 30 and the reference grating 602 have the same pitch. The pitch matching ensures full depth of modulation of the modulated signal. A mismatch in the pitch leads to a reduced overlap in the pupil plane, thus the amount of interfering signal is reduced. A pitch mismatch leads to loss of depth of modulation and having to deal with higher amount of DC signal as compared to the case of perfect match of pitch among target and reference grating.

[0088] As shown in Fig. 6 and described above, radiation 604 is split into two paths 640 and 642 - one portion of radiation 604 is focused on the target 30 mark at the wafer plane; while the other portion is focused onto the reference grating 602. The diffracted orders of radiation 604 from the target 30 grating and reference grating 602 overlap in the pupil plane 652 (see the different corresponding arrow styles / shades in Fig. 6) and are combined and output to radiation sensor 4 (Fig. 3), thus providing an intensity versus position alignment signal. In some embodiments, different orders of the diffracted radiation from the target 30 grating and reference grating 602 overlap in the pupil plane 652 and are combined for the radiation sensor, thus providing an intensity interference within a coherence length of the radiation source versus position alignment signal. The matching of the mark pitches in the reference and the target grating branches ensures overlap in the pupil plane for an aligned optical system. In some embodiments, a plus diffraction order from the reference grating 602 overlaps with a minus diffraction order from the target 30 grating, and a minus diffraction order from the reference grating 602 overlaps with a plus diffraction order form the target 30 grating, in the pupil plane 652. In some embodiments, a plus diffraction order from the reference grating 602 overlaps with a plus diffraction order from the target 30 grating. In some embodiments, system 600 comprises one or more components, such as a wedge and / or a mask, configured to separate orthogonal direction diffraction spots (see Fig. 8 discussed below).

[0089] In some embodiments, system 600 comprises a second optical element 680 (see the top image in Fig. 6) positioned between optical element 650 and the radiation sensor. Second optical element 680 is configured to split the combined overlapping diffracted radiation into an aligned position y polarization (or p polarization) component 682 and an aligned position x polarization (or s polarization) component 684. In some embodiments, the second optical element 680 comprises separate third and fourth optical elements 690 and 692 (see the bottom image in Fig. 6), and / or other components. The third optical element 690 may be configured to split the combined overlapping diffracted radiation into an aligned position minus y polarization component 694 and the aligned position x polarization component 684. The fourth optical element 692 may be configured to split thecombined overlapping diffracted radiation into an aligned position plus y polarization component 698 and a second aligned position x polarization component 684. The aligned position minus y polarization component 694, the aligned position x polarization component 684, the aligned position plus y polarization component 698, and the second aligned position x polarization component 684 may be combined (e.g., at an output fiber) to generate the intensity versus position alignment signal. In some embodiments, an alignment position and / or value may be determined based on a weighted sum of aligned positions over x and y polarizations, wavelengths, plus and minus channels, and / or other information.

[0090] Example actuators configured to change the pitch of a reference grating (e.g., reference grating 602 shown in Fig. 6) may be relatively small (e.g., less than 20mm in diameter and less than 10mm in height), be vacuum compatible, have a low thermal and / or vibrational impact, have a long lifetime (e.g., 20 million plus moves), be able to move quickly (e.g., a 90 degree move in less than 200 milliseconds), and / or other properties. An example actuator may be or include a piezoelectric actuator, and / or may include and / or be coupled to various components such as a grating, one or more sensors, a runner, structural components, a preload component, a piezoelectric material, a coupling element, etc. In this example, a piezoelectric material may be configured to move and / or otherwise actuate a grating via a coupling element and runner. The movement may be in response to a signal from a sensor, for example, and / or other information. An actuator may comprise a motor, a rotatable stage, and / or other components. In this example, the actuator may be configured to move (e.g., rotate in this example) a reflective grating mask such that a reference grating is in a physical position to receive radiation from a radiation source simultaneously with a target grating; and diffract radiation back toward a radiation sensor.

[0091] In some embodiments, actuation may be controlled electronically by a processor, such as processor PRO shown in Fig. 3 (and also in Fig. 10 discussed below). Processor PRO may be included in a computing system CS (Fig. 10) and may operate based on computer or machine readable instructions MRI (e.g., as described below related to Fig. 10). Electronic communication may occur by transmitting electronic signals between separate components and / or other communication. The components of system 10 (Fig. 3) and / or 600 (Fig. 6), and / or actuators, may communicate via wires or wirelessly via a network, such as the Internet or the Internet in combination with various other networks, like local area networks, cellular networks, or personal area networks, internal organizational networks, and / or other networks.

[0092] In some embodiments, one or more actuators may be coupled to and configured to move reference grating 602 (e.g., which may be included in a reflective grating mask as described above) and / or other components of system 600. The actuators may be coupled to one or more components of system 600 by adhesive, clips, clamps, screws, a collar, and / or other mechanisms. The actuators may be configured to be controlled electronically. Individual actuators may be configured to convert an electrical signal into mechanical displacement. The mechanical displacement is configured to movereference grating 602. One or more processors PRO (Fig. 3, Fig. 10) may be configured to control the actuators.

[0093] As mentioned above, in some embodiments, system 600 (Fig. 6) comprises one or more components, such as a wedge and / or a mask, configured to separate orthogonal direction diffraction spots (see spots 702 in Fig. 7). Fig. 7 illustrates an example mask 700 that may be used to separate orthogonal direction diffraction spots. In some embodiments, mask 700 comprises a higher or selective order blocker mask located in a pupil plane of the system. The selective order blocker mask is configured to block non-scanning direction spots of radiation from the reference grating. Mask 700 may be located in the reference grating 602 pupil plane. Mask 700 is designed such that the nonscanning direction spots can be blocked for 2d diffraction gratings. This is done to improve the depth of modulation, for example. The illustration of mask 700 in Fig. 7 is one possible example of many. The exact shape of mask 700 shown in Fig. 7 is not intended to be limiting. Other shapes are contemplated. For example, Fig. 7 also illustrates a second potential embodiment 710. Embodiment 710 is a blocker design that may provide for quicker X-Y translation, for example, and / or have other advantages. Alternatively, algorithms can be used to account for the additional DC signal arising from the orthogonal diffraction spots. In a parallel, miniaturized scenario, sensors can be synchronized such that orthogonal scans are aligned using other sensors in a sensor array.

[0094] Another way to enhance reproducibility of the reference grating is to underfill the marks (mark footprint > spot size at the reference grating branch). This may address any reproducibility effects due to lateral scan offsets. Lateral scan offsets in the reference grating arising due to drifts / reproduction of reference grating actuation can be calibrated using fiducial marks. As described above, the reference grating assemblies can be realized using a variety of technologies, such as a reticle on a compact linear XY stage, a reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM). In some embodiments, the reference grating branch (of system 600 shown in Fig. 6) may be magnified compared to the target branch, which may ensure that a depth of modulation is retrieved due to lack of overlap due to wedge resists.

[0095] Also as mentioned above, in some embodiments, radiation 604 (Fig. 6) comprises off axis radiation relative to the target 30 grating (Fig. 6) and / or reference grating 602 (Fig. 6). Fig. 8 illustrates an example of providing off axis radiation 801 (which may be similar to and / or the same as radiation 604 described above) relative to a target grating 800 (which may be similar to and or the same as the grating of target 30 described above) and a reference grating 802 (which may be similar to and / or the same as reference grating 602 described above). Radiation 801 is generated by a source 810 (which may be similar to and / or the same as source 2 described above) and a splitter 850 (which may be similar to and / or the same as optical element 650 (e.g., a splitter) described above). Various lenses 860, 870, a partial spot mirror 880, and / or other components, may also be utilized. Splitter 850, lens 860, lens 870, partial spot mirror 880, and / or other components may have transmissive and / or reflective portions (e.g., see the darkened rectangles in splitter 850 and / or the darker smallcircles in spot mirror 880) configured to create and / or direct off axis radiation 801. Off axis radiation 801 (or illumination) allows the measurement of “finer” pitches; or pitches that are similar in comparison to the wavelength of light. This mitigates the need of having really high numerical aperture objectives to detect the diffracted signals. Finer pitches are more robust to wafer processing and also allow to print smaller marks thus taking less real estate on the wafer for these target alignment marks and facilitating more real estate for the product.

[0096] Fig. 9 illustrates a metrology method 900. In some embodiments, method 900 is performed as part of an alignment sensing operation in a semiconductor device manufacturing process, for example. In some embodiments, one or more operations of method 900 may be implemented in or by system 600 illustrated in Fig. 6, system 10 illustrated in Fig. 3, a computer system (e.g., as illustrated in Fig. 10 and described below), and / or in or by other systems, for example. In some embodiments, method 900 comprises irradiating (operation 902) a target grating in a patterned substrate with radiation, changing (operation 904) a changeable pitch of a reference grating to match the pitch of the target grating, generating (operation 906) a metrology signal based on reflected diffracted radiation from the target grating and the reference grating, and / or other operations.

[0097] The operations of method 900 are intended to be illustrative. In some embodiments, method 900 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 900 may include an additional operation comprising determining an adjustment for a semiconductor device manufacturing process. Additionally, the order in which the operations of method 900 are illustrated in Fig. 9 and described herein is not intended to be limiting.

[0098] In some embodiments, one or more portions of method 900 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 state machine, and / or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices executing some or all of the operations of method 900 in response to 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 900 (e.g., see discussion related to Fig. 10 below).

[0099] At operation 902, a multi wavelength radiation source of a metrology system irradiates a target grating in a patterned substrate with radiation. The radiation comprises light and / or other radiation. In some embodiments, the radiation comprises off axis radiation relative to the target grating and / or the reference grating. The target grating has a target pitch. In some embodiments, the radiation source is the same as or similar to source 2 (of system 10) shown in Fig. 3 and described above. The target grating may be similar and / or the same as target 30 shown in Fig. 3, Fig. 6, etc., and described above. In some embodiments, the metrology system may comprise one or more attenuators,compensators, beam shifting elements, and / or other components configured for thick / wedge resists on the target grating.

[0100] The radiation may be directed by the radiation source onto multiple targes, a single target, sub-portions (e.g., something less than the whole) of a target, and / or onto a substrate in other ways. In some embodiments, the radiation may be directed by the radiation source onto the target in a time varying manner. For example, the radiation may be rastered over a target (e.g., by moving the target under the radiation) such that different portions of the target are irradiated at different times. As another example, characteristics of the radiation (e.g., wavelength, intensity, etc.) may be varied. This may create time varying data envelopes, or windows, for analysis. The data envelopes may facilitate analysis of individual sub-portions of a target, comparison of one portion of a target to another and / or to other targets (e.g., in other layers), and / or other analysis.

[0101] At operation 904, a changeable pitch of a reference grating of the metrology system is changed to match the target pitch. Changing the pitch may including moving the pitch, adjusting the pitch, and / or other operations performed on or with the pitch to cause the pitch of the reference grating to match the target pitch. The reference grating is configured to receive radiation from the radiation source simultaneously with the target grating. In some embodiments, the reference grating comprises a bi-directional reference grating configured to correspond to a type of the target grating. In some embodiments, the reference grating comprises an actuator and a reflective grating mask. The actuator may comprise a motor, an ultrasonic piezoelectric motor, a liquid crystal based spatial light modulator, and / or other actuators. In some embodiments, the reflective grating mask comprises various gratings with different layouts and / or pitches configured to match various different target gratings in the patterned substrate. The reference grating may be one the various gratings having a broad range of reflectivity with different layouts. Operation 904 may comprise moving, with the actuator, the reflective grating mask such that the reference grating is in a physical position to receive the radiation from the radiation source simultaneously with the target grating; and diffract radiation back toward the radiation sensor. In some embodiments, a spatial light modulator (SLM) and / or other components can be used to adjust the pitch. In some embodiments, the reference grating may be similar to and / or the same as reference grating 602 shown in Fig. 6.

[0102] In some embodiments, a path length of a target branch and a reference branch of the metrology system are matched to within a coherence length of the radiation source. For example, the reference grating is physically separate from the patterned substrate and located along a different optical path than the target grating in the metrology system. Operation 904 may include receiving, with an optical element having transmissive and reflective regions and positioned in a pupil plane of the metrology system, the radiation from the radiation source and transmitting portions of the radiation toward the target grating target along a first optical path, and toward the reference grating along a second optical path. Operation 904 may also include transmitting, with the optical element, the diffracted radiation from the target grating and the reference grating toward the radiation sensor.In some embodiments, operation 904 comprises blocking, with a selective order blocker mask located in a pupil plane of the system, non-scanning direction spots of radiation from the reference grating.

[0103] At operation 906, a metrology signal is generated. The metrology signal is generated with a radiation sensor of the metrology system. The radiation sensor may be similar to and / or the same as sensor (detector) 4 and / or processor PRO shown in Fig. 3 and described above. The metrology signal is generated based on diffracted radiation received from the target grating and the reference grating, and / or other information. The metrology signal comprises measurement information pertaining to the target grating and / or other information. For example, the metrology signal may be an alignment signal comprising alignment measurement information, and / or other metrology signals. The metrology signal may be an alignment signal comprising alignment measurement information for a layer of the patterned substrate that includes the target grating. In some embodiments, the alignment signal has a period equal to the pitch of the target and reference grating pitches when the target and the reference grating have the same pitch.

[0104] In some embodiments, different orders of the diffracted radiation from the target grating and the reference grating overlap in the pupil plane and are combined for the radiation sensor, thus providing an intensity interference within a coherence length of the radiation source versus position alignment signal. In some embodiments, a plus diffraction order from the reference grating overlaps with a minus diffraction order from the target grating, and a minus diffraction order from the reference grating overlaps with a plus diffraction order form the target grating, in the pupil plane. In some embodiments, a plus diffraction order from the reference grating overlaps with a plus diffraction order from the target grating. In some embodiments, operation 906 comprises separating, with a wedge and / or a mask, orthogonal direction diffraction spots.

[0105] The measurement information (e.g., an alignment value, and / or other information) may be determined using principles of interferometry and / or other principles. The metrology signal comprises an electronic signal that represents and / or otherwise corresponds to the radiation reflected from the target(s) and / or reference grating. The metrology signal may indicate a metrology value associated with a diffraction grating target, for example, and / or other information. Generating the metrology signal comprises sensing the reflected radiation and converting the sensed reflected radiation into the electronic signal. In some embodiments, generating the metrology signal comprises sensing different portions of the reflected radiation from different areas and / or different geometries of the target, multiple targets, and / or the reference grating, and combining the different portions of the reflected radiation to form the metrology signal. This may include generating and / or analyzing one or more images of a target and / or the reference grating, using the radiation described herein.

[0106] In some embodiments, operation 906 comprises splitting, with a second optical element positioned between the optical element and the radiation sensor, combined overlapping diffracted radiation into an aligned position y polarization (or p polarization) component and an aligned position x polarization (or s polarization) component. In some embodiments, the second optical elementcomprises separate third and fourth optical elements, and / or other components. The third optical element may be configured to split the combined overlapping diffracted radiation into an aligned position minus y polarization component and the aligned position x polarization component. The fourth optical element may be configured to split the combined overlapping diffracted radiation into an aligned position plus y polarization component and a second aligned position x polarization component. The aligned position minus y polarization component, the aligned position x polarization component, the aligned position plus y polarization component, and the second aligned position x polarization component may be combined to generate the intensity versus position alignment signal. In some embodiments, an alignment position and / or value may be determined based on a weighted sum of aligned positions over x and y polarizations, wavelengths, and plus and minus channels.

[0107] As described above, in some embodiments, operation 906 comprises detecting reflected radiation from one or more diffraction grating targets, the reference grating, and / or other structures. Detecting reflected radiation comprises detecting one or more phase and / or amplitude (intensity) shifts in reflected radiation from one or more geometric features of the target(s) and / or reference grating. The one or more phase and / or amplitude shifts correspond to one or more dimensions of a target and / or the reference grating. For example, the phase and / or amplitude of reflected radiation from one side of a target and / or reference grating is different relative to the phase and / or amplitude of reflected radiation from another side of the target and / or reference grating.

[0108] Detecting the one or more phase and / or amplitude (intensity) shifts in the reflected radiation comprises measuring local phase shifts (e.g., local phase deltas) and / or amplitude variations that correspond to different portions of a target and / or the reference grating. For example, the reflected radiation from a specific area of a target and / or reference grating may comprise a sinusoidal waveform having a certain phase and / or amplitude. The reflected radiation from a different area of the target (or a target in a different layer) and / or reference grating may also comprise a sinusoidal waveform, but one with a different phase and / or amplitude. Detected reflected radiation also comprises measuring a phase and / or amplitude difference in reflected radiation of different diffraction orders. Detecting the one or more local phase and / or amplitude shifts may be performed using 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.

[0109] In some embodiments, method 900 comprises determining an adjustment for a semiconductor device manufacturing process. In some embodiments, method 900 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on one or more detected phase and / or amplitude variations, an alignment value indicated by the metrology signal, and / or other similar systems, and / or other information. The one or more parameters may include a parameter of the radiation (the radiation used for metrology), an alignment value, a metrology inspection location on alayer of a semiconductor device structure, a radiation beam trajectory across a target, and / or other parameters. In some embodiments, 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] In some embodiments, method 900 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, if a determined metrology measurement is not within process tolerances, the out of tolerance measurement may be caused by one or more manufacturing processes whose process parameters have drifted and / or otherwise changed so that the process is no longer producing acceptable devices (e.g., measurements may breach a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the measurement determination. The new or adjusted process parameters may be configured to cause a manufacturing process to again produce acceptable devices.

[0111] For example, a new or adjusted process parameter may cause a previously unacceptable measurement 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 method 900), for example. In some embodiments, method 900 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] Figure 10 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 similar to and / or the same as processor PRO shown in Fig. 3) 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 amagnetic 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 flat panel or touch panel display or a cathode ray tube (CRT) 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, all or some of one or more operations described herein 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 another computer-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) described herein. 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, the description herein is not limited to any specific combination of hardware circuitry and software.

[0115] The term “computer-readable medium” or “machine-readable medium” as used herein 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 herein. 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 interface CI 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 nonvolatile 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. In the following, further features, characteristics, and exemplary technicalsolutions of the present disclosure will be described in terms of clauses that may be optionally claimed in any combination:1. A metrology system, comprising: a multi wavelength radiation source configured to irradiate a target grating in a patterned substrate with radiation, the target grating having a target pitch; a reference grating, the reference grating having a changeable pitch, the changeable pitch being changed to match the target pitch, the reference grating configured to receive radiation from the radiation source simultaneously with the target grating; and a radiation sensor configured to generate a metrology signal based on diffracted radiation received from the target grating and the reference grating, the metrology signal comprising measurement information pertaining to the target grating.2. The system of clause 1 , wherein the metrology signal is an alignment signal comprising alignment measurement information for a layer of the patterned substrate that includes the target grating.3. The system of any of the previous clauses, wherein a path length of a target branch and a reference branch of the metrology system are matched to within a coherence length of the radiation source; and wherein the alignment signal has a period equal to the pitch of the target and reference grating pitches when the target and the reference grating have the same pitch.4. The system of any of the previous clauses, wherein the reference grating is physically separate from the patterned substrate and located along a different optical path than the target grating, the system further comprising an optical element with transmissive and reflective regions, the optical element positioned in a pupil plane of the system, the optical element configured to: receive the radiation from the radiation source and transmit portions of the radiation toward the target grating target along a first optical path, and toward the reference grating along a second optical path; and transmit the diffracted radiation from the target grating and the reference grating toward the radiation sensor.5. The system of any of the previous clauses, wherein different orders of the diffracted radiation from the target grating and the reference grating overlap in the pupil plane and are combined for the radiation sensor, thus providing an intensity interference within a coherence length of the radiation source versus position alignment signal.6. The system of any of the previous clauses, wherein a plus diffraction order from the reference grating overlaps with a minus diffraction order from the target grating, and a minus diffraction order from the reference grating overlaps with a plus diffraction order form the target grating, in the pupil plane; and / or wherein a plus diffraction order from the reference grating overlaps with a plus diffraction order from the target grating.7. The system of any of the previous clauses, further comprising a second optical element positioned between the optical element and the radiation sensor, the second optical element configured to split combined overlapping diffracted radiation into an aligned position y polarization (or p polarization) component and an aligned position x polarization (or s polarization) component.8. The system of any of the previous clauses, wherein the second optical element comprises separate third and fourth optical elements, the third optical element configured to split the combined overlapping diffracted radiation into an aligned position minus y polarization component and the aligned position x polarization component; and the fourth optical element configured to split the combined overlapping diffracted radiation into an aligned position plus y polarization component and a second aligned position x polarization component.9. The system of any of the previous clauses, wherein the aligned position minus y polarization component, the aligned position x polarization component, the aligned position plus y polarization component, and the second aligned position x polarization component are combined to generate the intensity versus position alignment signal.10. The system of any of the previous clauses, wherein the measurement information in the metrology signal comprises an alignment position, the alignment position determined based on a weighted sum of aligned positions over x and y polarizations, wavelengths, and plus and minus channels.11. The system of any of the previous clauses, wherein the reference grating comprises an actuator and a reflective grating mask.12. The system of any of the previous clauses, wherein the actuator comprises a motor, an ultrasonic piezoelectric motor, or a liquid crystal based spatial light modulator.13. The system of any of the previous clauses, wherein the reflective grating mask comprises various gratings with different layouts and / or pitches configured to match various different target gratings in the patterned substrate, wherein the reference grating is one the various gratings having a broad range of reflectivity with different layouts.14. The system of any of the previous clauses, wherein the actuator is configured to move the reflective grating mask such that the reference grating is in a physical position to receive the radiation from the radiation source simultaneously with the target grating; and diffract radiation back toward the radiation sensor.15. The system of any of the previous clauses, further comprising a selective order blocker mask located in a pupil plane of the system, the selective order blocker mask configured to block nonscanning direction spots of radiation from the reference grating.16. The system of any of the previous clauses, wherein the reference grating comprises a bidirectional reference grating configured to correspond to a type of the target grating.17. The system of any of the previous clauses, further comprising a wedge and / or a mask configured to separate orthogonal direction diffraction spots.18. The system of any of the previous clauses, wherein the radiation comprises off axis radiation relative to the target grating and / or the reference grating.19. The system of any of the previous clauses, further comprising one or more attenuators, compensators, and / or beam shifting elements for thick / wedge resists on the target grating.20. The system of any of the previous clauses, wherein the metrology system is an alignment sensor, the alignment sensor is configured for a semiconductor wafer, and the alignment sensor is used in a semiconductor manufacturing process.21. A metrology method, comprising: irradiating, with a multi wavelength radiation source of a metrology system, a target grating in a patterned substrate with radiation, the target grating having a target pitch; changing a changeable pitch of a reference grating of the metrology system to match the target pitch, the reference grating configured to receive radiation from the radiation source simultaneously with the target grating; and generating, with a radiation sensor of the metrology system, a metrology signal based on diffracted radiation received from the target grating and the reference grating, the metrology signal comprising measurement information pertaining to the target grating.22. The method of clause 21, wherein the metrology signal is an alignment signal comprising alignment measurement information for a layer of the patterned substrate that includes the target grating.23. The method of any of the previous clauses, wherein a path length of a target branch and a reference branch of the metrology system are matched to within a coherence length of the radiation source; and wherein the alignment signal has a period equal to the pitch of the target and reference grating pitches when the target and the reference grating have the same pitch.24. The method of any of the previous clauses, wherein the reference grating is physically separate from the patterned substrate and located along a different optical path than the target grating, the method further comprising: receiving, with an optical element having transmissive and reflective regions and positioned in a pupil plane of the metrology system, the radiation from the radiation source and transmitting portions of the radiation toward the target grating target along a first optical path, and toward the reference grating along a second optical path; and transmitting, with the optical element, the diffracted radiation from the target grating and the reference grating toward the radiation sensor.25. The method of any of the previous clauses, wherein different orders of the diffracted radiation from the target grating and the reference grating overlap in the pupil plane and are combined for the radiation sensor, thus providing an intensity interference within a coherence length of the radiation source versus position alignment signal.26. The method of any of the previous clauses, wherein a plus diffraction order from the reference grating overlaps with a minus diffraction order from the target grating, and a minus diffraction order from the reference grating overlaps with a plus diffraction order form the target grating, in the pupil plane; and / or wherein a plus diffraction order from the reference grating overlaps with a plus diffraction order from the target grating.27. The method of any of the previous clauses, further comprising splitting, with a second optical element positioned between the optical element and the radiation sensor, combined overlappingdiffracted radiation into an aligned position y polarization (or p polarization) component and an aligned position x polarization (or s polarization) component.28. The method of any of the previous clauses, wherein the second optical element comprises separate third and fourth optical elements, the third optical element configured to split the combined overlapping diffracted radiation into an aligned position minus y polarization component and the aligned position x polarization component; and the fourth optical element configured to split the combined overlapping diffracted radiation into an aligned position plus y polarization component and a second aligned position x polarization component.29. The method of any of the previous clauses, wherein the aligned position minus y polarization component, the aligned position x polarization component, the aligned position plus y polarization component, and the second aligned position x polarization component are combined to generate the intensity versus position alignment signal.30. The method of any of the previous clauses, wherein the measurement information in the metrology signal comprises an alignment position, the alignment position determined based on a weighted sum of aligned positions over x and y polarizations, wavelengths, and plus and minus channels.31. The method of any of the previous clauses, wherein the reference grating comprises an actuator and a reflective grating mask.32. The method of any of the previous clauses, wherein the actuator comprises a motor, an ultrasonic piezoelectric motor, or a liquid crystal based spatial light modulator.33. The method of any of the previous clauses, wherein the reflective grating mask comprises various gratings with different layouts and / or pitches configured to match various different target gratings in the patterned substrate, wherein the reference grating is one the various gratings having a broad range of reflectivity with different layouts.34. The method of any of the previous clauses, further comprising moving, with the actuator, the reflective grating mask such that the reference grating is in a physical position to receive the radiation from the radiation source simultaneously with the target grating; and diffract radiation back toward the radiation sensor.35. The method of any of clauses 31-34, further comprising blocking, with a selective order blocker mask located in a pupil plane of the system, non-scanning direction spots of radiation from the reference grating.36. The method of any of the previous clauses, wherein the reference grating comprises a bidirectional reference grating configured to correspond to a type of the target grating.37. The method of any of the previous clauses, further comprising separating, with a wedge and / or a mask, orthogonal direction diffraction spots.38. The method of any of the previous clauses, wherein the radiation comprises off axis radiation relative to the target grating and / or the reference grating.39. The method of any of the previous clauses, the metrology system further comprising one or more attenuators, compensators, and / or beam shifting elements for thick / wedge resists on the target grating.40. The method of any of the previous clauses, wherein the metrology system is an alignment sensor, the alignment sensor is configured for a semiconductor wafer, and the alignment sensor is used in a semiconductor manufacturing process.

[0121] The concepts disclosed herein may be associated with any generic imaging system for imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths. Emerging technologies already in use include EUV (extreme ultra violet), DUV lithography that is capable of producing a 193nm wavelength with the use of an ArF laser, and even a 157nm wavelength with the use of a Fluorine laser. Moreover, EUV lithography is capable of producing wavelengths within a range of 20-5nm by using a synchrotron or by hitting a material (either solid or a plasma) with high energy electrons in order to produce photons within this range.

[0122] While the concepts disclosed herein may be used for imaging on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of lithographic imaging systems, e.g., those used for 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 multi wavelength radiation source configured to irradiate a target grating in a patterned substrate with radiation, the target grating having a target pitch; a reference grating, the reference grating having a changeable pitch, the changeable pitch being changed to match the target pitch, the reference grating configured to receive radiation from the radiation source simultaneously with the target grating; and a radiation sensor configured to generate a metrology signal based on diffracted radiation received from the target grating and the reference grating, the metrology signal comprising measurement information pertaining to the target grating.

2. The system of claim 1 , wherein the metrology signal is an alignment signal comprising alignment measurement information for a layer of the patterned substrate that includes the target grating.

3. The system of claim 2, wherein a path length of a target branch and a reference branch of the metrology system are matched to within a coherence length of the radiation source; and wherein the alignment signal has a period equal to the pitch of the target and reference grating pitches when the target and the reference grating have the same pitch.

4. The system of any of claims 1-3, wherein the reference grating is physically separate from the patterned substrate and located along a different optical path than the target grating, the system further comprising an optical element with transmissive and reflective regions, the optical element positioned in a pupil plane of the system, the optical element configured to: receive the radiation from the radiation source and transmit portions of the radiation toward the target grating target along a first optical path, and toward the reference grating along a second optical path; and transmit the diffracted radiation from the target grating and the reference grating toward the radiation sensor.

5. The system of claim 4, wherein different orders of the diffracted radiation from the target grating and the reference grating overlap in the pupil plane and are combined for the radiation sensor, thus providing an intensity interference within a coherence length of the radiation source versus position alignment signal.

6. The system of claim 5, wherein a plus diffraction order from the reference grating overlaps with a minus diffraction order from the target grating, and a minus diffraction order from the referencegrating overlaps with a plus diffraction order form the target grating, in the pupil plane; and / or wherein a plus diffraction order from the reference grating overlaps with a plus diffraction order from the target grating.

7. The system of claim 6, further comprising a second optical element positioned between the optical element and the radiation sensor, the second optical element configured to split combined overlapping diffracted radiation into an aligned position y polarization (or p polarization) component and an aligned position x polarization (or s polarization) component.

8. The system of claim 7, wherein the second optical element comprises separate third and fourth optical elements, the third optical element configured to split the combined overlapping diffracted radiation into an aligned position minus y polarization component and the aligned position x polarization component; and the fourth optical element configured to split the combined overlapping diffracted radiation into an aligned position plus y polarization component and a second aligned position x polarization component.

9. The system of claim 8, wherein the aligned position minus y polarization component, the aligned position x polarization component, the aligned position plus y polarization component, and the second aligned position x polarization component are combined to generate the intensity versus position alignment signal.

10. The system of claim 9, wherein the measurement information in the metrology signal comprises an alignment position, the alignment position determined based on a weighted sum of aligned positions over x and y polarizations, wavelengths, and plus and minus channels.

11. The system of any of claims 1-10, wherein the reference grating comprises an actuator and a reflective grating mask.

12. The system of claim 11, wherein the actuator comprises a motor, an ultrasonic piezoelectric motor, or a liquid crystal based spatial light modulator.

13. The system of claim 11 or 12, wherein the reflective grating mask comprises various gratings with different layouts and / or pitches configured to match various different target gratings in the patterned substrate, wherein the reference grating is one the various gratings having a broad range of reflectivity with different layouts.

14. The system of claim 13, wherein the actuator is configured to move the reflective grating mask such that the reference grating is in a physical position to receive the radiation from the radiation source simultaneously with the target grating; and diffract radiation back toward the radiation sensor.

15. The system of any of claims 1-14, further comprising a selective order blocker mask located in a pupil plane of the system, the selective order blocker mask configured to block non-scanning direction spots of radiation from the reference grating.

Images