Beam splitting systems and methods for semiconductor metrology

Abstract

Achromatic polarization insensitive beam splitting systems and methods for semiconductor metrology are described. One or more mirrors are positioned in different parts of the path of a radiation beam. The mirrors are configured to achromatically reflect different portions of the radiation beam to form constituent output beams. The mirrors provide polarization insensitive balanced spectral splitting of the radiation beam into the constituent output beams, such that the different constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors. An optical switch may be used to selectively pass or block the constituent output beams once coupled into the different single mode light guides.

Description

BEAM SPLITTING SYSTEMS AND METHODS FOR SEMICONDUCTOR METROLOGYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 683,616 which was filed on August 15, 2024 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] This description relates to beam splitting systems and methods for semiconductor metrology.BACKGROUND

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

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

[0005] This device manufacturing process may be considered a patterning process. A patterningprocess involves a paterning step, such as optical and / or nanoimprint lithography using a paterning device in a lithographic apparatus, to transfer a patern on the paterning device to a substrate and typically, but optionally, involves one or more related patern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the patern using an etch apparatus, deposition, etc.

[0006] 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.

[0007] 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 = ki A. / N A, 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 patern 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 paterning device. These include, for example, but are not limited to, optimization of NA and optical coherence setings, customized illumination schemes, use of phase shifting paterning 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). Metrology is an integral part of these fine-tuning steps.SUMMARY

[0008] Achromatic (without separation into colors) polarization insensitive beam spliting systems and methods for semiconductor metrology are described. One or more mirrors are positioned in different parts of the path of a radiation beam. The mirrors are configured to achromatically reflect different portions of the radiation beam to form constituent output beams. The mirrors provide polarization insensitive balanced spectral spliting of the radiation beam into the constituent output beams, such that the different constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors. An optical switch may be used to selectively pass or block the constituent output beams once coupled into the differentsingle mode light guides.

[0009] According to an embodiment, a system configured to achromatically reflect a portion of a radiation beam to form constituent output beams for different semiconductor metrology sensors is provided. The system comprises a radiation source configured to generate the radiation beam. The radiation beam has an intensity, and is directed along a path. The system comprises a mirror positioned in a part of the path and configured to achromatically reflect the portion of the radiation beam to form a first constituent output beam and a second constituent output beam. The mirror provides balanced spectral splitting of the radiation beam into the first and second constituent output beams, such that the first and second constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors.

[0010] According to another embodiment, a system configured to achromatically reflect portions of a radiation beam to form constituent output beams for different semiconductor metrology sensors is provided. The system comprises a radiation source configured to generate the radiation beam. The radiation beam has an intensity, and is directed along a path. The system comprises a first mirror positioned in a first part of the path and configured to achromatically reflect a first portion of the radiation beam to form a first constituent output beam. The system comprises a second mirror positioned in a second part of the path and configured to achromatically reflect a second portion of the radiation beam to form a second constituent output beam. The first mirror and the second mirror provide balanced spectral splitting of the radiation beam into the first and second constituent output beams, such that the first and second constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors.

[0011] In some embodiments, the first mirror is configured to achromatically reflect the first portion of the radiation beam through a first branch of the system to form the first constituent output beam. The second mirror is configured to achromatically reflect the second portion of the radiation beam through a second branch of the system to form the second constituent output beam. The first and second constituent output beams have smaller sizes compared to the radiation beam, and the same or different intensities depending on downstream semiconductor metrology sensor requirements.

[0012] In some embodiments, the system comprises one or more additional mirrors configured to achromatically reflect additional portions of the radiation beam through additional branches of the system to form n additional output beams, with n representing a target number of output beams for a target number of different semiconductor metrology sensors.

[0013] In some embodiments, the first and second mirrors, and the one or more additional mirrors, are polarization insensitive. In some embodiments, the first and second mirrors comprise D-mirrors, pupil dividing mirrors, and / or aperture mirrors, for example.

[0014] In some embodiments, the radiation source comprises a white light laser. In some embodiments, the radiation beam comprises white light. In some embodiments, the radiation beamcomprises wavelengths from about 500nm to about 1 lOOnm.

[0015] In some embodiments, the system comprises an optical expansion system configured to expand the radiation beam from the radiation source such that: (1) a required alignment sensitivity of downstream mirrors is reduced, and / or (2) the etendue of the system facilitates maximum coupling efficiency between constituent output beams and the different single mode light guides, with the etendue of the optical expansion system within an acceptance etendue of the different single mode light guides.

[0016] In some embodiments, the system comprises beam shaping elements associated with each constituent output beam. The beam shaping elements are configured to shape each constituent output beam into a Gaussian beam and mitigate coupling efficiency losses due to mirror edge diffraction effects. In some embodiments, the beam shaping elements comprise spatial light modulators, diffractive optical elements, and / or refractive optical elements.

[0017] In some embodiments, the system comprises different single mode lightguides. The different single mode light guides are configured to provide optical pathways for constituent output beams to the different semiconductor metrology sensors. In some embodiments, each single mode light guide comprises a photonic crystal fiber.

[0018] In some embodiments, the system comprises free space optical components configured to provide optical pathways to optically couple the constituent output beams into the different single mode light guides.

[0019] In some embodiments, the constituent output beams are configured to be coupled to the different single mode light guides for conduction to the different semiconductor metrology sensors in parallel. The different semiconductor metrology sensors are configured to be used in parallel to determine alignment of a layer in a patterned substrate, for example.

[0020] In some embodiments, the system comprises an optical switch configured to selectively pass or block the constituent output beams once coupled into the different single mode light guides. In some embodiments, the optical switch is a micro electrical mechanical system. In some embodiments, the micro electrical mechanical system is analog or digitally based.

[0021] In some embodiments, the optical switch comprises switching mirrors that correspond to each constituent output beam and single mode light guide combination, with each switching mirror configured to be selectively actuated to pass or block a given constituent output beam in its single mode light guide. In some embodiments, the optical switch comprises a switching mirror configured to be selectively actuated to pass or block a given constituent output beam in a target single mode light guide .

[0022] According to another embodiment, a method for achromatically reflecting portions of a radiation beam to form constituent output beams for different semiconductor metrology sensors is provided. The method comprises one or more operations performed by the system(s) described above.

[0023] According to another embodiment, a system configured to facilitate selective switching of radiation for different semiconductor metrology sensors is provided. The system comprises a radiationsource configured to generate a radiation beam; a plurality of single mode light guides configured to output the radiation beam to the different semiconductor metrology sensors; and an optical switch configured to selectively pass or block constituent output beams of radiation once coupled into the different single mode light guides. In some embodiments, the optical switch has a switching speed of at least about 0.5ms.

[0024] According to another embodiment, a method to facilitate selective switching of radiation for different semiconductor metrology sensors is provided. The method comprises one or more operations performed by the system(s) described above.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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.Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.Fig. 3 schematically depicts an example inspection system, according to an embodiment.Fig. 4 schematically depicts an example metrology technique, according to an embodiment.Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.Fig. 6 illustrates a first example embodiment of a system with mirrors configured to achromatically reflect portions of a radiation beam to form constituent output beams for different semiconductor metrology sensors (e.g., multiple sensors similar to and / or the same as the sensor shown in Fig. 3), according to an embodiment.Fig. 7 illustrates a second example embodiment of the system shown in Fig. 6, with additional mirrors used to form additional constituent output beams, according to an embodiment.Fig. 8 illustrates intensity profiles of a clipped constituent output beam and a reshaped constituent output beam, according to an embodiment.Fig. 9 illustrates another embodiment of the system that is similar to the embodiment shown in Fig. 7, but with beam shaping elements included in system, according to an embodiment.Fig. 10 illustrates an optical switch, according to an embodiment. -Fig. 11 illustrates a method for achromatically reflecting portions of a radiation beam to form constituent output beams for different semiconductor metrology sensors, according to an embodiment.Fig. 12 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0026] 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 device structure. 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. These techniques are used to measure alignment, for example, and / or other parameters.

[0027] To meet future throughput requirements, metrology systems have been proposed that utilize multiple light sources, or divide a single light source into multiple illumination beams for parallel measurement of multiple metrology marks. Parallel measurement of multiple metrology marks simultaneously is desired, but difficult. Prior systems that have multiple radiation sources are often relatively more expensive and complex compared to other systems. Optical splitting of radiation from a single source is a known approach to provide output for multiple parallel metrology sensors (from that single radiation source). However, spectral splitting characteristics for a typical optical splitter often produce differences in output intensities, splitting differences that change with wavelength, and differences for differently polarized radiation, among other difficulties. For example, spectral splitting characteristics often change based on wavelength and polarization of the input radiation. Thus, a target range of outputs can become a problem if a wider wavelength range is desired, or if the polarization of the input radiation must be preserved.

[0028] Advantageously, achromatic polarization insensitive beam splitting systems and methods for semiconductor metrology are described. A (e.g., white light) radiation beam is achromatically split into constituent beams (e.g., output channels) without significant impacts on (1) wavelength-splitting intensity balance, (2) polarization, or (3) throughput efficiency. This is done with a series of mirrors positioned in different parts of the path of a radiation beam. The mirrors are configured to achromatically reflect different portions of the radiation beam to form the constituent output beams. The mirrors provide polarization insensitive balanced spectral splitting of the radiation beam into the constituent output beams, such that the different constituent output beams are configured to be coupled to different single mode light guides (e.g., fibers) for conduction to different semiconductor metrology sensors (so that measurements can be performed in parallel) . Any number of mirrors may be configured to achromatically reflect additional portions of the radiation beam through additional branches of the system to form any number of additional output beams (any number of output channels). Beam shaping optics may be used to increase coupling efficiency into single mode light guides. In addition, an optical switch may be used to selectively pass or block the constituent output beams once coupled into the different single mode light guides.

[0029] Note that measurement of alignment is discussed throughout this document as one example application for the described systems and methods, but many other applications are contemplated.

[0030] By way of a brief introduction, the description below relates to semiconductor device manufacturing and patterning processes. The following paragraphs also describe several componentsof systems and / or methods for semiconductor device metrology. These systems and methods may be used for measuring alignment in a semiconductor device manufacturing process, for example, or for other operations.

[0031] Although specific reference may be made to the manufacture of integrated circuits (ICs) for semiconductor devices, it should be understood that the description has many other possible applications. For example, it may be employed in the 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.

[0032] 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 lithographic projection 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.

[0033] 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).

[0034] 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.

[0035] 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.

[0036] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial extent (commonly referred to as o-outer and o-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane 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.

[0037] 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 ina 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.

[0038] 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.

[0039] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

[0040] 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.

[0041] A patterning device may be transmissive or reflective . Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflectedby the mirror matrix.

[0042] 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.”

[0043] 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 symmetric aspherical optical element. Deformation of an optical element may include a low frequency shape (e.g. astigmatic) and / or a high frequency shape (e.g. free form aspheres). Deformation of an optical element may be performed for example by using one or more actuators to exert force on one or more sides of the optical element and / or by using one or more heating elements to heat one or more selected regions of the optical element. In general, it may not be possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). The transmission map of a projection system PS may be used when designing a patterning device (e.g., mask) MA for the lithography apparatus LA. Using a computational lithography technique, the patterning device MA may be designed to at least partially correct for apodization.

[0044] 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.

[0045] The lithographic apparatus may also be of a type wherein 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 betweenthe 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.

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

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

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

[0049] The substrate may be processed, before or after exposure, in for example a 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.

[0050] 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.

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

[0052] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to as a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler, or robot, RO picks up one or moresubstrates from input / output port I / O 1 , 1 / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

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

[0054] The one or more measured parameters may include, for example, 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.

[0055] There are various techniques for making measurements of the structures formed in the patterning process, including the use of a scanning electron microscope, an image-based measurement tool and / or various specialized tools. A fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted / reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this may be termed diffraction-based metrology. Applications of this diffraction-based metrology include the measurement of alignment, overlay, etc. For example, alignment and / or overlay can be measured by comparing parts of the diffraction spectrum (for example, comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0056] Thus, in a device fabrication process (e.g., a patterning process or a lithography process), a substrate or other objects may be subjected to various types of measurement during or after the process.The measurement may determine whether a particular substrate is defective, may establish adjustments to the process and apparatuses used in the process (e.g., aligning two 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 Orion metrology tool, the ASML YieldStar metrology tool, the ASML SMASH metrology system), mechanical measurement (e.g., profding using a stylus, atomic force microscopy (AFM)), and / or non-optical imaging (e.g., scanning electron microscopy (SEM)).

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

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

[0059] To enable 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).

[0060] Fig. 3 depicts an example metrology (inspection) system 300 that may be used to detect alignment and / or perform other metrology operations. It comprises a radiation or illumination source 302 which projects or otherwise irradiates radiation onto a substrate W (e.g., which may typically include a plurality of metrology targets 301). Redirected radiation is passed to a sensor such as a spectrometer detector (sensor 304) 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 detectedspectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in Fig. 4, or by other operations.

[0061] 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 300 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, 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, often in parallel. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the target portion relative to the focus of the optical system. It is convenient to think and describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves. Provided the relative position of the substrate and the optical system is correct, it does not matter in principle which one of those is moving, or if both are moving, or a combination of a part of the optical system is moving (e.g., in the Z and / or tilt direction) with the remainder of the optical system being stationary and the substrate is moving (e.g., in the X and Y directions, but also optionally in the Z and / or tilt direction).

[0062] For typical metrology measurements, a target 301 on substrate W (remember there may be a plurality of targets 301 measured in parallel) 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 301 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.

[0063] 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 301 (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 301. Accordingly, the measured data from target 301 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.

[0064] For example, the measured data from target 301 may indicate alignment for a layer of a semiconductor device. The measured data from target 301 may be used (e.g., by the one or more processors PRO and / or other processors) for determining one or more semiconductor devicemanufacturing 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.

[0065] Fig. 5 illustrates a plan view of a typical target 301, and the extent of a typical radiation illumination spot S in the system of Fig. 3. Typically, to obtain a diffraction spectrum that is free of interference from surrounding structures, the target 301, 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 aback 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.

[0066] Fig. 6 illustrates a first example embodiment of a system 600 with a mirror 602 configured to achromatically reflect a portion of a radiation beam 604 to form constituent output beams 606 (two in this example) for different semiconductor metrology sensors (e.g., multiple sensors similar to and / or the same as sensor 304 shown in Fig. 3 and described above). Fig. 7 illustrates a second example embodiment of system 600, with additional mirrors 700 used to form additional constituent output beams 702 (six in this example). Note that Fig. 6 and Fig. 7 illustrate just two of many possible embodiments of system 600. System 600 may comprise any number of mirrors (e.g., mirror 602 shown in Fig. 6 and / or mirrors 700 shown in Fig. 7) configured to achromatically reflect portions of radiation beam 604 through one or more branches of system 600 to form n additional output beams (e.g., beams 606 in Fig. 6 and / or beams 702 shown in Fig. 7), where n represents a target number of output beams for a target number of different semiconductor metrology sensors. The target number of semiconductor metrology sensors may be the number of sensors in a particular metrology system configured to measure several different metrology targets in parallel (e.g., parallel measurement of several alignment targets). The metrology sensors (e.g., similar and / or the same as sensor 304 shown in Fig. 3) may use photodetectors for converting output optical signals (the output beams) into electrical signals, for example. In some embodiments, a sensor comprises a multichannel circuit board which uses one or more photodetectors configured to convert optical signals into electrical signals, an array of photodetectors or camera devices, and / or other components.

[0067] Phrased another way, system 600 comprises an optical pupil dividing system which dividesa radiation (e.g., laser) beam pupil into any number of constituent output beams which are required. This division is performed by picking off a portion of the laser beam with a mirror, and subsequently picking off additional portions of the radiation beam into individual branches of the system as needed. This allows for balanced spectral splitting into the constituent beams, which then can be coupled into fibers and / or other single mode light guides for any number of metrology sensors. The target number of outputs changes how the pick-offs are oriented. For example, Fig. 6 shows a l-to-2 beam splitting system. Fig. 7 shows a l-to-6 beam splitting system. The input radiation beam 604 may be expanded to reduce sensitivity to mirror 602 and / or 700 alignment errors. A beam expander (described below) is optically designed such that the alignment sensitivity of the mirrors is reduced, and the etendue of system 600 facilitates maximum coupling efficiency into the fibers without additional loss. Beam shaping optics, such as diffractive optical elements, spatial light modulators, etc., can be used to mitigate coupling efficiency losses due to edge diffraction effect from the mirrors. System 600 may be useful for parallel scanning with any alignment sensor, for example, where one radiation source is divided into several constituent beams, balanced in intensity across all wavelengths (for example 500-900nm, and / or up to 1 lOOnm or more).

[0068] Achromatically reflecting portions of radiation beam 604 to form constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7) provides multiple output channels 608 (shown in Fig. 6) and / or 710 (shown in Fig. 7). The multiple output channels 608 and / or 710 output constituent output beams 606 and / or 702 that are configured to be coupled to different single mode light guides 610 (Fig. 6) and / or 712 (Fig. 7) for conduction to the different semiconductor metrology sensors (e.g., two sensors in Fig. 6, and six sensors in Fig. 7) in parallel. The different semiconductor metrology sensors may be configured to be used in parallel to determine alignment of a layer in a patterned substrate such as a semiconductor wafer, as one practical example. System 600 comprises a radiation source 620, an optical expansion system 622, the one or more mirrors 602 (Fig. 6) and / or 700 (Fig. 7), the single mode light guides 610 (Fig. 6) and / or 712 (Fig. 7), free space optical components 630, and / or other components.

[0069] Radiation source 620 is configured to generate radiation beam 604. Radiation beam 604 has a certain wavelength range, an intensity, may be polarized and / or not polarized, and / or have other characteristics. For example, in some embodiments, radiation beam 604 comprises wavelengths from about 500nm (e.g., visible light) to about 1 lOOnm (e.g., infrared light). Radiation beam 604 may comprise visible light, infrared light, near infrared light, and / or other radiation. In some embodiments, radiation source 620 comprises a white light laser, and radiation beam 604 comprises white light.

[0070] Optical expansion system 622 is configured to expand radiation beam 604 from a first diameter DI to a second, larger diameter, D2. Optical expansion system 622 may be configured to expand the diameter of radiation beam 604 by 200%, 500%, or more. For example, first diameter DI may be about 0.5mm, 1mm, 2mm, and / or other diameters. Second diameter D2 may be about 10mm,15mm, 50mm, and / or other diameters. Optical expansion system 622 may comprise one or more lenses 652 and / or other components. The lenses may be concave, convex, partially concave and / or convex, parabolic, and / or have other shapes. Optical expansion system 622 may have any type and / or number of components, in any shapes, orientations, and / or arrangements, which allow optical expansion system 622 to function as described.

[0071] Optical expansion system 622 is configured to expand radiation beam 604 from radiation source 620 such that a required alignment sensitivity of downstream mirrors 602 (Fig. 6) and / or 700 (Fig. 7) is reduced. For example, as described herein, mirrors 602 (Fig. 6) and / or 700 (Fig. 7) are placed in portions of the path of radiation beam 604. Accurately placing a mirror in only a portion of the path of a beam that is 1mm in diameter is much more difficult than placing that same mirror in a portion of the path of a beam that is 10mm, 20mm, or more in diameter. There is more room for error with the larger diameter beam. Optical expansion system 622 is also configured to expand radiation beam 604 from radiation source 620 to ensure that the etendue (a measure of the spread - in area and angle - of radiation beam 604) of system 600 facilitates maximum coupling efficiency between constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7) and the different single mode light guides 610 (Fig. 6) and / or 712 (Fig. 7), with the etendue of optical expansion system 622 within an acceptance etendue of the different single mode light guides.

[0072] Radiation beam 604 is directed along a path 650 (before and / or after expansion). Path 650 is shown as a single horizontal arrow in Fig. 6 and Fig. 7, but path 650 continues through the branches of system 600 (two branches in Fig. 6, and multiple branches in Fig. 7). One or more mirrors 602 (Fig. 6) and / or 700 (Fig. 7) are positioned in one or more parts of path 650 to achromatically reflect different portions of radiation beam 604 to form the different constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7). In Fig. 6 and Fig. 7, the different portions of radiation beam 604 reflected by each mirror 602 (Fig. 6) and / or 700 (Fig. 7) are illustrated by the pie shaped indicators 675 located near each mirror 602 and / or 700.

[0073] By way of a non-limiting example, a first mirror 602 (Fig. 6) positioned in a first part of path 650 may be configured to achromatically reflect a first portion (e.g., the left side pie shape shown in corresponding indicator 675) of radiation beam 604 to form a first constituent output beam 606. In Fig. 6, the remaining portion (e.g., the leftover right hand side of the pie shape shown in the other corresponding indicator 675) of radiation beam 604 forms a second constituent output beam 606. In Fig. 7, a second (and a third, fourth, fifth, sixth, etc.) mirror 700 positioned in a second (and a third, fourth, fifth, sixth, etc.) part of path 650 is configured to achromatically reflect a second (and a third, fourth, fifth, sixth, etc.) - as indicated in the different pie shaped indicators 675 for the different mirrors 700) portion of radiation beam 604 to form a second (and a third, fourth, fifth, and sixth, in this example) constituent output beam 702. The mirrors 602 (Fig. 6) and / or 700 (Fig.7) provide balanced spectral splitting of radiation beam 604 into first, second, third, fourth, fifth, sixth, and / or more constituentoutput beams 606 (Fig. 6) and / or 702 (Fig. 7), such that the constituent output beams are configured to be coupled to different single mode light guides 610 (Fig. 6) and / or 712 (Fig. 7) for conduction to the different semiconductor metrology sensors (e.g., sensors similar to and / orthe same as sensor 304 shown in Fig. 3).

[0074] The achromatically reflected portions of radiation beam 604 may be reflected through different (e.g., first, second, third, fourth, etc.) branches of system 600 to form the different constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7). The different (e.g., first, second, third, fourth, fifth, and / or sixth in these two figures) constituent output beams have smaller sizes compared to radiation beam 604, and the same or different intensities depending on downstream semiconductor metrology sensor requirements.

[0075] Mirrors 602 (Fig. 6) and / or 700 (Fig. 7) are polarization insensitive (e.g., if non-polarized light comes in, non-polarized light goes out; or if polarized light comes in, polarized light goes out). For example, mirrors 602 and / or 700 may be broadband metallic coated mirrors (other examples are contemplated). One or more mirrors 602 and / or 700 may comprise D-mirrors as shown in Fig. 6 and Fig. 7, and / or have other shapes. Mirrors 602 and / or 700 may comprise pupil dividing mirrors, aperture mirrors, and / or any other mirrors that allow them to function as described.

[0076] The different single mode light guides 610 (Fig. 6) and / or 712 (Fig. 7) are configured to provide optical pathways for constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7) to the different semiconductor metrology sensors (see Fig. 3 and discussion above). The different single mode light guides may comprise optical fibers configured to provide these optical pathways. In some embodiments, each single mode light guide 610 and / or 712 comprises a photonic crystal fiber (PCF) and / or other structures.

[0077] Constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7) are configured to be coupled to the different single mode light guides 610 and / or 712 for conduction to the different semiconductor metrology sensors (Fig. 3) in parallel. The different semiconductor metrology sensors may be configured to be used in parallel to determine alignment of a layer in a patterned substrate, for example. In some embodiments, constituent output beams 606 and / or 702 may be directly coupled (e.g., without any intervening lenses and / or other components) to corresponding single mode light guides 610 and / or 712. In some embodiments, system 600 comprises free space optical components 630 configured to optically couple the constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7) into the different single mode light guides. Free space optical components 630 may comprise one or more lenses and / or other components. The lenses may be concave, convex, partially concave and / or convex, parabolic, and / or have other shapes. Free space optical components 630 may have any type and / or number of components, in any shapes, that allow optical free space optical components 630 to function as described.

[0078] The different single mode light guides 610 and / or 712 generally only accept Gaussian constituent output beams for maximum coupling efficiency. However, the constituent output beamsmay be clipped (e.g., when only half, or a third, or a fourth, etc., of a beam is reflected by a given mirror) when reflected by the mirrors of system 600. Decomposing a Gaussian beam clipped by 50% (and / or other amounts) will cause edge diffraction effects. This optical problem can be analyzed by ID Fourier decomposition, where a Gaussian beam is convolved with a shifted rect function to clip 50% of the Gaussian beam, where the rect function behaves as a clipping aperture window. When taking the Fourier transform of these beams, which represent the beam profile at a Fourier plane (focused), this results in the original Gaussian beam multiplied by a sine function with a phase shift. If there are concerning coupling efficiency losses into the different single mode light guides, beam shaping elements may be included in system 600 which may be designed by the described Fourier decomposition example above. These beam shaping elements may be used to reshape the constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7) into Gaussian beams to maximize coupling efficiency.

[0079] For example, Fig. 8 illustrates intensity profiles 800 and 802 (in a two dimensional x - y plane) of a clipped constituent output beam and a reshaped constituent output beam, respectively. Intensity profile 800 shows edge diffraction effects that show as color variations in the clipped constituent output beam. In contrast, intensity profile 802 shows a reshaped constituent output beam with symmetric coloration, radiating out from a center of intensity profile 802. Beam shaping elements may be used to reshape a clipped constituent output beam with intensity profile 800 back into a reshaped constituent output beam with intensity profile 802. Beam shaping elements may be associated with each constituent output beam. The beam shaping elements may be configured to shape each constituent output beam into a Gaussian beam and mitigate coupling efficiency losses due to mirror edge diffraction effects. The beam shaping elements may comprise spatial light modulators, diffractive optical elements, refractive optical elements, and / or other components. For example, a diffractive optical element such as a computer generated hologram may be used.

[0080] Fig. 9 illustrates another embodiment of system 600 that is similar to the embodiment shown in Fig. 7, but with beam shaping elements 900 included in system 600. As shown in Fig. 9, beam shaping elements 900 are associated with each constituent output beam 702. Beam shaping elements 900 are configured to shape each constituent output beam 702 into a Gaussian beam 902 and mitigate coupling efficiency losses due to mirror edge diffraction effects. As described above, beam shaping elements 900 may comprise spatial light modulators, diffractive optical elements, refractive optical elements, and / or other components.

[0081] Fig. 10 illustrates an optical switch 1000. Optical switch 1000 is configured to selectively pass or block the constituent output beams 606 (Fig. 6) and / or 702 (Fig. 7 and Fig. 9) once coupled into the different single mode light guides 610 (Fig. 6) and / or 712 (Fig. 7 and Fig. 9). In this design the illumination power can be directed out a single output (or any select number of outputs) if needed, and not permanently split across multiple outputs.

[0082] For example, as described above, in prior systems with a single, shared radiation source, eachoutput (e.g., each objective in a metrology system) illuminates a substrate such as a wafer simultaneously, resulting in diffraction / reflection crosstalk from the other outputs. With these prior systems the intensity of the radiation on a given metrology target is split and shared by the number of outputs using non-polarizing beam splitters. In addition, simultaneous illumination often results in crosstalk between different outputs. Reflected and diffracted light from metrology targets, first order reflections, and other contributors can pollute the final measured signal for both phase and intensity channels for a given output (e.g., for alignment measurements).

[0083] Multiple-illumination using optical switch 1000 (e.g., a broadband single-mode photoniccrystal fiber optical switch) can be configured to output radiation from a single output (or multiple selected outputs that are not in proximity to each other) at a time, reducing or removing crosstalk without increasing a required number of radiation sources. In addition, this design utilizes passive optics, avoiding potential problems with mechanically-controlled, alignment-sensitive optical components inside the metrology system.

[0084] Optical switch 1000 may be a micro electrical mechanical system and / or may be formed by other structures, such as a bistable micro electrical mechanical system. The optical switch system may be analog or digitally based. In some embodiments (e.g., as shown in the right side of Fig. 10), optical switch 1000 comprises switching mirrors 1002 that correspond to each constituent output beam 606 and / or 702 and single mode light guide 610 and / or 712 combination, with each switching mirror 1002 configured to be selectively actuated to pass or block a given constituent output beam 606 and / or 702 in its single mode light guide 610 and / or 712.

[0085] In some embodiments, optical switch 1000 comprises a switching mirror 1004 (left side of Fig. 10) configured to be selectively actuated to pass or block a given constituent output beam 606 and / or 702 in a target single mode light guide 610 and / or 712. In some embodiments, optical switch 1000 has a switching speed of at least about 0.5ms, for example. Fig. 10 also provides an example illustration 1010 of where optical switch 1000 may be incorporated into the larger structure of system 600 (though this is just a simplified representative example). In illustration 1010, multiple output channels 710 may correspond to one or more sensors, for example.

[0086] Fig. 11 illustrates a method 1100 for achromatically reflecting portions of a radiation beam to form constituent output beams for different semiconductor metrology sensors. In some embodiments, one or more operations of method 1100 may be implemented in or by system 600 illustrated in Figs. 6, 7, 9, and 10 respectively; system 300 illustrated in Fig. 3; a computer system (e.g., as illustrated in Fig. 12 and described below), and / or in or by other systems, for example. In some embodiments, method 1100 comprises generating (operation 1102) a radiation beam, expanding (operation 1104) the radiation beam, achromatically reflecting (operation 1106) one or more portions of the radiation beam, shaping (operation 1108) constituent output beams, providing (operation 1110) optical pathways to conduct the constituent output beams to different semiconductor metrology sensors, selectively passing or blocking(operation 1112) the constituent output beams, and / or other operations.

[0087] The operations of method 1100 are intended to be illustrative. In some embodiments, method 1100 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 1100 may include additional operations related to determining alignment of a layer of a semiconductor wafer. Additionally, the order in which the operations of method 1100 are illustrated in Fig. 11 and described herein is not intended to be limiting.

[0088] In some embodiments, one or more portions of method 1100 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 1100 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 1100 (e.g., see discussion related to Fig. 12 below).

[0089] At operation 1102, a radiation beam is generated with a radiation source. The radiation may have a target wavelength and / or wavelength range, a target intensity, and / or other characteristics. The target wavelength and / or wavelength range, the target intensity, etc., may be entered and / or selected by a user, determined by the system (e.g., system 300 shown in Fig. 3, and / or system 600 shown in Fig. 6, 7, and 9) based on previous measurements, and / or determined in other ways. In some embodiments, the radiation beam 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. In some embodiments, the input radiation has a wavelength (or wavelengths) between about 500nm and about HOOnm. As one example, the input radiation may be considered to be visible light. In some embodiments, the input radiation is generated by a single source configured to generate the radiation along a path. In some embodiments, the radiation source is a white light laser, and the radiation beam is white light. In some embodiments, operation 1102 is performed by a radiation source similar to and / or the same as source 620 shown in Fig. 6, 7, and 9).

[0090] At operation 1104, the radiation beam from the radiation source is expanded with an optical expansion system. The radiation beam from the radiation source is expanded such that: (1) a required alignment sensitivity of downstream mirrors is reduced, and / or (2) the etendue of the system facilitates maximum coupling efficiency between constituent output beams and the different single mode light guides, with the etendue of the optical expansion system within an acceptance etendue of the different single mode light guides. In some embodiments, operation 1104 is performed by an optical expansionsystem that is the same as or similar to optical expansion system 622 shown in Fig. 6. 7, and 9, and described above.

[0091] At operation 1106, one or more portions of the radiation beam are achromatically reflected with one or more mirrors. For example, a first mirror positioned in a first part of the path of the radiation beam may achromatically reflect a first portion of the radiation beam to form a first constituent output beam. A second mirror positioned in a second part of the path may achromatically reflect a second portion of the radiation beam to form a second constituent output beam. The first mirror and the second mirror provide balanced spectral splitting of the radiation beam into the first and second constituent output beams, such that the first and second constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors. In some embodiments, the first mirror is configured to achromatically reflect the first portion of the radiation beam through a first branch of the system (e.g., system 600 described above) to form the first constituent output beam; and the second mirror is configured to achromatically reflect the second portion of the radiation beam through a second branch of the system to form the second constituent output beam, such that the first and second constituent output beams have smaller sizes compared to the radiation beam, and the same or different intensities depending on downstream semiconductor metrology sensor requirements. In some embodiments, operation 1106 comprises achromatically reflecting, with one or more additional mirrors, additional portions of the radiation beam through additional branches of the system to form n additional output beams, where n represents a target number of output beams for a target number of different semiconductor metrology sensors. The mirrors may be polarization insensitive and / or have other characteristics. The mirrors may comprise D-mirrors, pupil dividing mirrors, aperture mirrors, and / or other mirrors. In some embodiments, operation 1106 is performed with one or more mirrors similar to and / or the same as mirrors 602 and / or 700 shown in Fig. 6, 7, and 9 and described above.

[0092] At operation 1108, each constituent output beam is shaped into a Gaussian beam to mitigate coupling efficiency losses due to mirror edge diffraction and / or other effects. The shaping may be performed with beam shaping elements associated with each constituent output beam. The beam shaping elements may include spatial light modulators, diffractive optical elements, refractive optical elements, and / or other beam shaping elements. The beam shaping elements may be similar to and / or the same as beam shaping elements 900 shown in Fig. 9 and described above.

[0093] At operation 1110, different single mode light guides are provided to conduct the constituent output beams to different semiconductor metrology sensors. The different single mode light guides are configured to provide optical pathways for constituent output beams to the different semiconductor metrology sensors. Each single mode light guide may comprise a photonic crystal fiber and / or other components. In some embodiments, free space optical components may be used to provide optical pathways to optically couple the constituent output beams into the different single mode light guides.The constituent output beams may be coupled to the different single mode light guides for conduction to the different semiconductor metrology sensors in parallel. The different semiconductor metrology sensors may be configured to be used in parallel to determine alignment of a layer in a patterned substrate, for example. However, again note that using the constituent output beams to determine alignment of a layer of a semiconductor wafer is one example application for a radiation beam that is split as described. Other example applications are contemplated. In some embodiments, the different single mode light guides are similar to and / or the same as single more light guides 610 and / or 712 shown in Fig. 6, 7, and 9, and described above. In some embodiments, the free space optical components are similar to and / or the same as free space optical components 630 shown in Fig. 6, 7, and 9, and described above.

[0094] At operation 1112, the constituent output beams are selectively passed or blocked in the single mode light guides. Operation 1112 comprises selectively, with an optical switch, passing or blocking the constituent output beams once coupled into the different single mode light guides. The optical switch may have a switching speed of at least about 0.5ms. The optical switch may be a micro electrical mechanical system. The micro electrical mechanical system may be analog or digitally based. In some embodiments, the optical switch comprises switching mirrors that correspond to each constituent output beam and single mode light guide combination, with each switching mirror configured to be selectively actuated to pass or block a given constituent output beam in its single mode light guide. In some embodiments, the optical switch comprises a switching mirror configured to be selectively actuated to pass or block a given constituent output beam in a target single mode light guide . In some embodiments, the optical switch may be similar to and / or the same as optical switch 1000 shown in Fig. 10 and described above.

[0095] Note that in some embodiments, operation 1112 may form its own standalone method for optically switching radiation in different single mode light guides, without a need for the mirrors and / or other components that split the radiation beam into constituent output beams. For example, if radiation source 620 (Fig. 6) is unable to provide sufficient radiation power to the multiple parallel metrology sensors simultaneously, but provides sufficient energy to at least one metrology sensor, operation 1112 could be used as a standalone method to sequentially provide light to the multiple metrology sensors. Additionally, an optical switch could be part of system 600 described above, or it could be used in a prior system with a beam splitter.

[0096] In some embodiments, method 1100 comprises performing metrology with the constituent output beams of radiation. In some embodiments, metrology is performed by various components of a system such as system 300 illustrated in Fig. 3, e.g., including sensor 304 and processor PRO, etc.; and / or a system such as system 600 shown in Fig. 6, 7, and 9. In some embodiments, alignment and / or other measurements may be determined as part of method 1100. Alignment may be determined based on reflected diffracted radiation from a diffraction grating target and / or other information. For example,in some embodiments, method 1100 includes illuminating (and / or otherwise irradiating) one or more targets (e.g., target 301 shown in Fig. 3) in apattemed substrate with radiation in parallel. The radiation may be generated by a radiation source (as described above). In some embodiments, the radiation may be directed onto multiple targets, 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 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 via the calibrated detector. 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.

[0097] In some embodiments, method 1100 comprises generating a metrology signal based on the detected reflected radiation from diffraction grating target(s). The metrology signal is generated by one or more calibrated sensors (such as sensor 304 in Fig. 3 and / or other sensors) based on radiation received by the sensor. The metrology signal comprises measurement information pertaining to the target(s). For example, the metrology signal may be an alignment signal comprising alignment measurement information, and / or other metrology signals. The measurement information (e.g., an alignment value and / or other information) may be determined using principles of interferometry and / or other principles.

[0098] The metrology signal comprises an electronic signal that represents and / or otherwise corresponds to the radiation reflected from the target(s). 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, and / or multiple targets, 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, using the radiation described herein. This sensing and converting may be performed by components similar to and / or the same as sensor 304 and / or processors PRO shown in Fig. 3, and / or other components.

[0099] In some embodiments, method 1100 comprises determining an adjustment for a semiconductor device manufacturing process. In some embodiments, method 1100 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on an alignment value indicated by the metrology signal 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 a layer of a semiconductor device structure, a radiation beam trajectory across atarget, and / or other parameters. In some embodiments, 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.

[0100] In some embodiments, method 1100 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.

[0101] 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 1100), for example. In some embodiments, method 1100 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.

[0102] Fig. 12 is a diagram of an example computer system CS that may be used for and / or to control one or more of the operations described herein (e.g., controlling the radiation source, controlling the optical switch, etc.). 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 staticinformation and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0103] Computer system CS may be coupled via bus BS to a display DS, such as a flat panel or touch panel display for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor PRO and for controlling cursor movement on display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

[0104] In some embodiments, all or some of one or more operations described herein may be performed and / or otherwise caused or controlled 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, this description is not limited to any specific combination of hardware circuitry and software.

[0105] The term “computer-readable medium” or “machine -readable medium” refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-transitory, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non- transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the operations described herein. Transitory computer- readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[0106] Various forms of computer readable media may be involved in carrying one or moresequences 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 network. A communication interface CI coupled to bus BS can receive the data carried in a 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.

[0107] 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 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.

[0108] 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.

[0109] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN, and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other non-volatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0110] 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 technical solutions of the present disclosure will be described in terms of clauses that may be optionally claimed in any combination.1. A system configured to achromatically reflect portions of a radiation beam to form constituent output beams for different semiconductor metrology sensors, the system comprising: a radiation source configured to generate the radiation beam, wherein the radiation beam has anintensity and a polarization state, and is directed along a path; a first mirror positioned in a first part of the path and configured to achromatically reflect a first portion of the radiation beam to form a first constituent output beam; and a second mirror positioned in a second part of the path and configured to achromatically reflect a second portion of the radiation beam to form a second constituent output beam; wherein the first mirror and the second mirror provide balanced spectral splitting of the radiation beam into the first and second constituent output beams, such that the first and second constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors.2. The system of clause 1, wherein the first mirror is configured to achromatically reflect the first portion of the radiation beam through a first branch of the system to form the first constituent output beam; and the second mirror is configured to achromatically reflect the second portion of the radiation beam through a second branch of the system to form the second constituent output beam, such that the first and second constituent output beams have smaller sizes compared to the radiation beam, and the same or different intensities depending on downstream semiconductor metrology sensor requirements.3. The system of any of the previous clauses, further comprising one or more additional mirrors configured to achromatically reflect additional portions of the radiation beam through additional branches of the system to form n additional output beams, wherein n represents a target number of output beams for a target number of different semiconductor metrology sensors.4. The system of any of the previous clauses, wherein the first and second mirrors, and the one or more additional mirrors, are polarization insensitive.5. The system of any of the previous clauses, wherein the first and second mirrors comprise D- mirrors, pupil dividing mirrors, and / or aperture mirrors.6. The system of any of the previous clauses, wherein the radiation source comprises a white light laser.7. The system of any of the previous clauses, wherein the radiation beam comprises white light.8. The system of any of the previous clauses, wherein the radiation beam comprises wavelengths from about 500nm to about 1 lOOnm.9. The system of any of the previous clauses, further comprising an optical expansion system configured to expand the radiation beam from the radiation source such that: (1) a required alignment sensitivity of downstream mirrors is reduced, and / or (2) an etendue of the system facilitates maximum coupling efficiency between constituent output beams and the different single mode light guides, with an etendue of the optical expansion system within an acceptance etendue of the different single mode light guides.10. The system of any of the previous clauses, further comprising beam shaping elements associated with each constituent output beam, the beam shaping elements configured to shape each constituent output beam into a Gaussian beam and mitigate coupling efficiency losses due to mirroredge diffraction effects.11. The system of any of the previous clauses, wherein the beam shaping elements comprise spatial light modulators, diffractive optical elements, and / or refractive optical elements.12. The system of any of the previous clauses, further comprising the different single mode light guides, the different single mode light guides configured to provide optical pathways for constituent output beams to the different semiconductor metrology sensors.13. The system of any of the previous clauses, wherein each single mode light guide comprises a photonic crystal fiber.14. The system of any of the previous clauses, further comprising free space optical components configured to provide optical pathways to optically couple the constituent output beams into the different single mode light guides.15. The system of any of the previous clauses, wherein the constituent output beams are configured to be coupled to the different single mode light guides for conduction to the different semiconductor metrology sensors in parallel, and the different semiconductor metrology sensors are configured to be used in parallel to determine alignment of a layer in a patterned substrate.16. The system of any of the previous clauses, further comprising an optical switch configured to selectively pass or block the constituent output beams once coupled into the different single mode light guides.17. The system of any of the previous clauses, wherein the optical switch is a micro electrical mechanical system.18. The system of any of the previous clauses, wherein the micro electrical mechanical system is analog or digitally based.19. The system of any of the previous clauses, wherein the optical switch comprises switching mirrors that correspond to each constituent output beam and single mode light guide combination, with each switching mirror configured to be selectively actuated to pass or block a given constituent output beam in its single mode light guide.20. The system of any of the previous clauses, wherein the optical switch comprises a switching mirror configured to be selectively actuated to pass or block a given constituent output beam in a target single mode light guide.21. A system configured to facilitate selective switching of radiation for different semiconductor metrology sensors, the system comprising: a radiation source configured to generate a radiation beam; a plurality of single mode light guides configured to output the radiation beam to the different semiconductor metrology sensors; and an optical switch configured to selectively pass or block constituent output beams of radiation once coupled into the different single mode light guides.22. The system of any of the previous clauses, wherein the optical switch is a micro electrical mechanical system.23. The system of any of the previous clauses, wherein the micro electrical mechanical system is analog or digitally based.24. The system of any of the previous clauses, wherein the optical switch comprises switching mirrors that correspond to each constituent output beam and single mode light guide combination, with each switching mirror configured to be selectively actuated to pass or block a given constituent output beam in its single mode light guide.25. The system of any of the previous clauses, wherein the optical switch comprises a switching mirror configured to be selectively actuated to pass or block a given constituent output beam in a target single mode light guide.26. The system of any of the previous clauses, further comprising different single mode light guides for each different semiconductor metrology sensor, the different single mode light guides configured to provide optical pathways to output the radiation beam to the different semiconductor metrology sensors.27. The system of any of the previous clauses, wherein each single mode light guide comprises a photonic crystal fiber.28. The system of any of the previous clauses, further comprising free space optical components configured to provide optical pathways to optically couple the radiation beam into one of the single mode light guides.29. The system of any of the previous clauses, wherein the optical switch has a switching speed of at least about 0.5ms.30. The system of any of the previous clauses, wherein the different semiconductor metrology sensors are configured to be used to determine alignment of a layer in a patterned substrate.31. A method for achromatically reflecting portions of a radiation beam to form constituent output beams for different semiconductor metrology sensors, the method comprising: generating the radiation beam with a radiation source, wherein the radiation beam has an intensity and a polarization state, and is directed along a path; achromatically reflecting, with a first mirror positioned in a first part of the path, a first portion of the radiation beam to form a first constituent output beam; and achromatically reflecting, with a second mirror positioned in a second part of the path, a second portion of the radiation beam to form a second constituent output beam; wherein the first mirror and the second mirror provide balanced spectral splitting of the radiation beam into the first and second constituent output beams, such that the first and second constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors.32. The method of clause 31, wherein the first mirror is configured to achromatically reflect the first portion of the radiation beam through a first branch to form the first constituent output beam; and the second mirror is configured to achromatically reflect the second portion of the radiation beam through a second branch to form the second constituent output beam, such that the first and secondconstituent output beams have smaller sizes compared to the radiation beam, and the same or different intensities depending on downstream semiconductor metrology sensor requirements.33. The method of any of the previous clauses, further comprising achromatically reflecting, with one or more additional mirrors, additional portions of the radiation beam through additional branches to form n additional output beams, wherein n represents a target number of output beams for a target number of different semiconductor metrology sensors.34. The method of any of the previous clauses, wherein the first and second mirrors, and the one or more additional mirrors, are polarization insensitive.35. The method of any of the previous clauses, wherein the first and second mirrors comprise D- mirrors, pupil dividing mirrors, and / or aperture mirrors.36. The method of any of the previous clauses, wherein the radiation source comprises a white light laser.37. The method of any of the previous clauses, wherein the radiation beam comprises white light.38. The method of any of the previous clauses, wherein the radiation beam comprises wavelengths from about 500nm to about 1 lOOnm.39. The method of any of the previous clauses, further comprising expanding, with an optical expansion system, the radiation beam from the radiation source such that: (1) a required alignment sensitivity of downstream mirrors is reduced, and / or (2) an etendue of the system facilitates maximum coupling efficiency between constituent output beams and the different single mode light guides, with an etendue of the optical expansion system within an acceptance etendue of the different single mode light guides.40. The method of any of the previous clauses, further comprising shaping, with beam shaping elements associated with each constituent output beam, each constituent output beam into a Gaussian beam and mitigating coupling efficiency losses due to mirror edge diffraction effects.41. The method of any of the previous clauses, wherein the beam shaping elements comprise spatial light modulators, diffractive optical elements, and / or refractive optical elements.42. The method of any of the previous clauses, further comprising providing the different single mode light guides, the different single mode light guides configured to provide optical pathways for constituent output beams to the different semiconductor metrology sensors.43. The method of any of the previous clauses, wherein each single mode light guide comprises a photonic crystal fiber.44. The method of any of the previous clauses, further comprising providing, with free space optical components, optical pathways to optically couple the constituent output beams into the different single mode light guides.45. The method of any of the previous clauses, wherein the constituent output beams are configured to be coupled to the different single mode light guides for conduction to the differentsemiconductor metrology sensors in parallel, and the different semiconductor metrology sensors are configured to be used in parallel to determine alignment of a layer in a patterned substrate.46. The method of any of the previous clauses, further comprising selectively, with an optical switch, passing or blocking the constituent output beams once coupled into the different single mode light guides.47. The method of any of the previous clauses, wherein the optical switch is a micro electrical mechanical system.48. The method of any of the previous clauses, wherein the micro electrical mechanical system is analog or digitally based.49. The method of any of the previous clauses, wherein the optical switch comprises switching mirrors that correspond to each constituent output beam and single mode light guide combination, with each switching mirror configured to be selectively actuated to pass or block a given constituent output beam in its single mode light guide.50. The method of any of the previous clauses, wherein the optical switch comprises a switching mirror configured to be selectively actuated to pass or block a given constituent output beam in a target single mode light guide.51. A method for facilitating selective switching of radiation for different semiconductor metrology sensors, the method comprising: generating a radiation beam with a radiation source; outputting, with a plurality of single mode light guides, the radiation beam to the different semiconductor metrology sensors; and selectively, with an optical switch, passing or blocking constituent output beams of radiation once coupled into the different single mode light guides.52. The method of any of the previous clauses, wherein the optical switch is a micro electrical mechanical system.53. The method of any of the previous clauses, wherein the micro electrical mechanical system is analog or digitally based.54. The method of any of the previous clauses, wherein the optical switch comprises switching mirrors that correspond to each constituent output beam and single mode light guide combination, with each switching mirror configured to be selectively actuated to direct a given constituent output beam to its single mode light guide.55. The method of any of the previous clauses, wherein the optical switch comprises a switching mirror configured to be selectively actuated to direct a given constituent output beam to a target single mode light guide.56. The method of any of claims 51-55, further comprising providing different single mode light guides for each different semiconductor metrology sensor, the different single mode light guides configured to provide optical pathways to output the radiation beam to the different semiconductor metrology sensors.57. The method of any of the previous clauses, wherein each single mode light guide comprises a photonic crystal fiber.58. The method of any of the previous clauses, further comprising providing, with free space optical components, optical pathways to optically couple the radiation beam into one of the single mode light guides.59. The method of any of the previous clauses, wherein the optical switch has a switching speed of at least about 0.5ms.60. The method of any of the previous clauses, wherein the different semiconductor metrology sensors are configured to be used to determine alignment of a layer in a patterned substrate.61. A system configured to achromatically reflect a portion of a radiation beam to form constituent output beams for different semiconductor metrology sensors, the system comprising: a radiation source configured to generate the radiation beam, wherein the radiation beam has an intensity and a polarization state, and is directed along a path; and a mirror positioned in a part of the path and configured to achromatically reflect the portion of the radiation beam to form a first constituent output beam and a second constituent output beam; wherein the mirror provides balanced spectral splitting of the radiation beam into the first and second constituent output beams, such that the first and second constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors.62. A method for achromatically reflecting a portion of a radiation beam to form constituent output beams for different semiconductor metrology sensors, the method comprising: generating the radiation beam with a radiation source, wherein the radiation beam has an intensity and a polarization state, and is directed along a path; and positioning a mirror in a part of the path, the mirror configured to achromatically reflect the portion of the radiation beam to form a first constituent output beam and a second constituent output beam; wherein the mirror provides balanced spectral splitting of the radiation beam into the first and second constituent output beams, such that the first and second constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors.63. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; directing patterning radiation from a radiation source of a lithography apparatus to transfer a pattern from a mask onto the photoresist layer; removing a portion the photoresist layer to form the pattern over the substrate; and generating radiation for determining a metrology value associated with the pattern by: generating a radiation beam with a radiation source; achromatically reflecting a first portion of the radiation beam with a first mirror to form a first constituent output beam; and achromatically reflecting a second portion of the radiation beam with a second mirror to form a second constituent output beam; wherein the first mirror and the second mirror provide balanced spectral splitting of the radiation beam into the first and second constituent output beams, which areeach configured to be coupled to different single mode light guides for conduction to different semiconductor metrology sensors.

[0111] The concepts disclosed herein may be associated with any generic imaging and / or metrology system for imaging sub wavelength features, and may be especially useful with emerging imaging and / or metrology technologies capable of producing and / or measuring 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.

[0112] While the concepts disclosed herein may be used for imaging and / or metrology 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 and / or metrology systems, e.g., those used for imaging and / or metrology on substrates other than silicon wafers. In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments.

[0113] 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

1. CLAIMS1. A system configured to achromatically reflect portions of a radiation beam to form constituent output beams for different semiconductor metrology sensors, the system comprising: a radiation source configured to generate the radiation beam, wherein the radiation beam has an intensity and a polarization state, and is directed along a path; a first mirror positioned in a first part of the path and configured to achromatically reflect a first portion of the radiation beam to form a first constituent output beam; and a second mirror positioned in a second part of the path and configured to achromatically reflect a second portion of the radiation beam to form a second constituent output beam; wherein the first mirror and the second mirror provide balanced spectral splitting of the radiation beam into the first and second constituent output beams, such that the first and second constituent output beams are configured to be coupled to different single mode light guides for conduction to the different semiconductor metrology sensors.

2. The system of claim 1, wherein the first mirror is configured to achromatically reflect the first portion of the radiation beam through a first branch of the system to form the first constituent output beam; and the second mirror is configured to achromatically reflect the second portion of the radiation beam through a second branch of the system to form the second constituent output beam, such that the first and second constituent output beams have smaller sizes compared to the radiation beam, and the same or different intensities depending on downstream semiconductor metrology sensor requirements.

3. The system of claim 1 or 2, further comprising one or more additional mirrors configured to achromatically reflect additional portions of the radiation beam through additional branches of the system to form n additional output beams, wherein n represents a target number of output beams for a target number of different semiconductor metrology sensors.

4. The system of claim 3, wherein the first and second mirrors, and the one or more additional mirrors, are polarization insensitive.

5. The system of any of claims 1-4, wherein the first and second mirrors comprise D-mirrors, pupil dividing mirrors, and / or aperture mirrors.

6. The system of any of claims 1-5, wherein the radiation source comprises a white light laser.

7. The system of any of claims 1-6, wherein the radiation beam comprises white light.

8. The system of any of claims 1-7, wherein the radiation beam comprises wavelengths from about 500nm to about 1 lOOnm.

9. The system of any of claims 1-8, further comprising an optical expansion system configured to expand the radiation beam from the radiation source such that:(1) a required alignment sensitivity of downstream mirrors is reduced, and / or(2) an etendue of the system facilitates maximum coupling efficiency between constituent output beams and the different single mode light guides, with an etendue of the optical expansion system within an acceptance etendue of the different single mode light guides.

10. The system of any of claims 1-9, further comprising beam shaping elements associated with each constituent output beam, the beam shaping elements configured to shape each constituent output beam into a Gaussian beam and mitigate coupling efficiency losses due to mirror edge diffraction effects.

11. The system of claim 10, wherein the beam shaping elements comprise spatial light modulators, diffractive optical elements, and / or refractive optical elements.

12. The system of any of claims 1-11, further comprising the different single mode light guides, the different single mode light guides configured to provide optical pathways for constituent output beams to the different semiconductor metrology sensors.

13. The system of claim 12, wherein each single mode light guide comprises a photonic crystal fiber.

14. The system of claim 12 or 13, further comprising free space optical components configured to provide optical pathways to optically couple the constituent output beams into the different single mode light guides.

15. The system of any of claims 1-14, wherein the constituent output beams are configured to be coupled to the different single mode light guides for conduction to the different semiconductor metrology sensors in parallel, and the different semiconductor metrology sensors are configured to be used in parallel to determine alignment of a layer in a patterned substrate.

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