Stable light source systems and methods

Abstract

A stable light source is described, which is configured for multi-output spectrally matched and equivalent intensity radiation. The source includes a first splitter configured to receive and split input radiation into first transmissive and reflective portions; second splitters configured to receive and further split each of the first transmissive and reflective portions into second transmissive and reflective portions; and combiners configured to combine the second transmissive and reflective portions into different outputs with mixed transmissive and reflective portions. The mixed transmissive and reflective portions are configured such that outputs together form the spectrally matched and equivalent intensity radiation. This may be used to calibrate highly accurate detectors, for example, and / or for other purposes. An integrating sphere may be included (e.g., instead of and / or in addition to the splitter(s) and combiner(s)).

Description

STABLE LIGHT SOURCE SYSTEMS AND METHODSCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Application No. 63 / 531,536, filed August 8, 2023, and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] This description relates to stable light source systems and methods.BACKGROUND

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

[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 patterning process involves a patterning step, such as optical and / or nanoimprint lithography using a patterningdevice in a lithographic apparatus, to transfer a pattern on the patterning device to a substrate and typically, but optionally, involves one or more related pattern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the pattern using an etch apparatus, deposition, etc.

[0006] 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 = kjxk / NA, where I is the wavelength of radiation employed (currently in most cases 248nm or 193nm), NA is the numerical aperture of projection optics in the lithographic projection apparatus, CD is the “critical dimension’ -generally the smallest feature size printed-and ki is an empirical resolution factor. In general, the smaller ki the more difficult it becomes to reproduce a pattern on the substrate that resembles the shape and dimensions planned by a designer in order to achieve particular electrical functionality and performance. To overcome these difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, for example, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, use of phase shifting patterning devices, optical proximity correction (OPC, sometimes also referred to as “optical and process correction”) in the design layout, or other methods generally defined as “resolution enhancement techniques” (RET). Metrology is an integral part of these fine-tuning steps.SUMMARY

[0008] A stable light source system is described. The system is configured to output spectrally matched and equivalent intensity radiation. In some embodiments, the system is configured for multioutput spectrally matched and equivalent intensity radiation. The system includes a first splitter configured to receive and split input radiation into first transmissive and reflective portions; second splitters configured to receive and further split each of the first transmissive and reflective portions into second transmissive and reflective portions; and one or more combiners configured to combine the second transmissive and reflective portions into different outputs with mixed transmissive and reflective portions. The mixed transmissive and reflective portions are configured such that outputs together form the spectrally matched and equivalent intensity radiation. This spectrally matched andequivalent intensity radiation (e.g., more stable radiation) may be used to calibrate highly accurate detectors and / or for other purposes. As one example, the highly accurate detectors may be used in alignment sensors for semiconductor manufacturing, and / or for other purposes. In some embodiments, an integrating sphere may be included (e.g., instead of and / or in addition to the splitter(s) and combiner(s)).

[0009] According to an embodiment, a system configured to output spectrally matched and equivalent intensity radiation is provided. The system comprises a first splitter configured to receive and split input radiation into first transmissive and reflective portions. The system comprises second splitters configured to receive and further split each of the first transmissive and reflective portions into second transmissive and reflective portions. The system comprises one or more combiners configured to combine the second transmissive and reflective portions into different outputs with mixed transmissive and reflective portions. The mixed transmissive and reflective portions are configured such that outputs from the system together form the spectrally matched and equivalent intensity radiation.

[0010] In some embodiments, the system further comprises optical fibers configured to provide optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners. In some embodiments, the system further comprises free space optical components configured to provide optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners. In some embodiments, the optical pathways have the same optical path length and are spectrally matched.

[0011] In some embodiments, the different outputs with the mixed transmissive and reflective portions collectively comprise an equal number of transmissive and reflective portions. In some embodiments, different outputs comprise different mixtures of transmissive and reflective portions.

[0012] In some embodiments, a combiner of the one or more combiners comprises a 2 x 2 optical coupler. In some embodiments, the first splitter comprises a 1 x2 optical splitter. In some embodiments, the second splitters each comprise a 1 x 2 optical splitter. In some embodiments, the second splitters comprise two 1 x2 optical splitters. In some embodiments, the second splitters comprise three 1 x 2 optical splitters. In some embodiments, the second splitters comprise 10 1 x2 optical splitters.

[0013] In some embodiments, the system further comprises a radiation source configured to generate the input radiation. In some embodiments, the system further comprises one or more isolators configured to receive the input radiation from the radiation source and ensure photons propagate only in one direction, reducing back reflection. In some embodiments, the system further comprises one or more variable optical attenuators and / or neutral density filters configured to reduce a power level of the input radiation before the input radiation is provided to the first splitter.

[0014] In some embodiments, the input radiation: has a wavelength between about 400nm and about 1600nm; and comprises visible light; or comprises infrared light.

[0015] In some embodiments, the output spectrally matched and equivalent intensity radiation is configured to be used to calibrate a detector. In some embodiments, the detector comprises a multichannel circuit board which uses one or more photodetectors configured to convert intensity channel optical signals into electrical signals. In some embodiments, the detector is associated with semiconductor metrology.

[0016] In some embodiments, the output spectrally matched and equivalent intensity radiation is configured for lithography, alignment metrology, and / or overlay metrology associated with a semiconductor manufacturing process.

[0017] According to another embodiment, a system configured to output spectrally matched and equivalent intensity radiation is provided. The system comprises a radiation source configured to generate radiation and an integrating sphere. The integrating sphere is configured to receive the radiation from the radiation source and flatten an intensity profile of the radiation, such that one or more outputs from the integrating sphere together have mixed transmissive and reflective portions configured to form spectrally matched and equivalent intensity radiation.

[0018] In some embodiments, the system comprises a filter configured to filter an infrared (IR) portion of the radiation from the radiation source to decrease or eliminate thermal heating of the system.

[0019] In some embodiments, the radiation source comprises a 500-900nm white light source.

[0020] In some embodiments, the one or more outputs comprise multiple output ports, with each output port comprising a 200pm multi-mode fiber (as one example of many possible examples). In some embodiments, the multiple output ports comprise eight output ports. In some embodiments, each multi-mode fiber has a numerical aperture equal to 0.22 (again as one possible example of many).

[0021] In some embodiments, the radiation source comprises an attenuator configured to be adjusted to achieve different powers at the multi-mode fiber output ports.

[0022] In some embodiments, the radiation source comprises a spectral filter configured to filter the radiation to provide a specific spectrum of the radiation to the integrating sphere.

[0023] In some embodiments, the integrating sphere comprises one or more baffles inside the integrating sphere. The one or more baffles are configured to prevent direct line of sight paths from an input to the integrating sphere to the one or more outputs.

[0024] In some embodiments, a photonic crystal fiber is configured to conduct the radiation from the radiation source to the integrating sphere.

[0025] According to another embodiment, one or more methods for outputting spectrally matched and equivalent intensity are provided. The one or more methods comprise one or more operations performed by the system(s) described above.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.

[0028] Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.

[0029] Fig. 3 schematically depicts an example inspection system, according to an embodiment.

[0030] Fig. 4 schematically depicts an example metrology technique, according to an embodiment.

[0031] Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.

[0032] Fig. 6 illustrates optical splitting of radiation from a single radiation source to provide multiple output channels that may be used to calibrate a detector, and a graph showing transmission as a function of input light wavelength for the splitting, according to an embodiment.

[0033] Fig. 7 illustrates an example embodiment of a system configured to output spectrally matched and equivalent intensity radiation, according to an embodiment.

[0034] Fig. 8 illustrates another example embodiment of a system configured to output spectrally matched and equivalent intensity radiation, according to an embodiment.

[0035] Fig. 9 illustrates yet another example embodiment of a system configured to output spectrally matched and equivalent intensity radiation, according to an embodiment.

[0036] Fig. 10 shows an equation that defines radiation source stability, according to an embodiment.

[0037] Fig. 11 illustrates still another example embodiment of a system configured to output spectrally matched and equivalent intensity radiation, according to an embodiment.

[0038] Fig. 12 illustrates a method for outputting spectrally matched and equivalent intensity radiation, according to an embodiment.

[0039] Fig. 13 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0040] In semiconductor device manufacturing, metrology operations typically include determining the position of a metrology mark (or marks) and / or other target in a layer of a semiconductor 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, overlay, and / or other parameters, and require highly accurate, precisely calibrated detectors.

[0041] Different radiation phase channels in combination with extracted intensity channel information are used to characterize mark asymmetry. Radiation intensity channel signals are steady state, and are not modulated. To be able to measure mark asymmetry with these intensity channelsignals, very small intensity differences must be detectable. This means that detectors need to be calibrated at different gain settings using a very stable optical source.

[0042] Optical splitting of radiation from a source is a known approach to provide output to multiple channels form a single radiation source. However, spectral splitting characteristics for a typical 1x4 optical splitter produce differences in output power splitting percentages, for example outputs ranging between 20-30% across four outputs, rather than the preferred 25% for each output (for a given wavelength). The range of outputs can become even more of a problem if a wider wavelength is desired.

[0043] Advantageously, the present systems and methods use strategic splice or splitting points, and strategic recombination, to spectrally flatten (e.g., in terms of power and wavelength) input radiation from a radiation source, and incorporate additional fiber optics (e.g., isolators, variable optical attenuators, and / or neutral density filters), free space optics, and / or other components, as needed to achieve extremely stable outputs across a desired output dynamic range. This technique is able to produce a wide dynamic range of outputs with channel-to-channel power ratio stability less than ±100ppm over four hours needed for calibration. Note that calibration is discussed throughout this document as one example application for the described systems and methods, but many other applications where a stable light source is desirable are contemplated.

[0044] By way of a brief introduction, the description below relates to semiconductor device manufacturing and patterning processes. The following paragraphs also describe several components of systems and / or methods for semiconductor device metrology. These systems and methods may be used for measuring alignment, overlay, etc., in a semiconductor device manufacturing process, for example, or for other operations.

[0045] 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.

[0046] 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.

[0047] 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).

[0048] 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.

[0049] 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.

[0050] 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, ofsectors 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.

[0051] The illuminator IL may be operable to alter the polarization of the beam and may be operable to adjust the polarization using adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as a polarization mode. The use of different polarization modes may allow greater contrast to be achieved in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across a pupil plane of the illuminator IL. The polarization direction of radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen in dependence on the illumination mode. For multi-pole illumination modes, the polarization of each pole of the radiation beam may be generally perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, for a dipole illumination mode, the radiation may be linearly polarized in a direction that is substantially perpendicular to a line that bisects the two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as X-polarized and Y-polarized states. For a quadrupole illumination mode, the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as XY polarization. Similarly, for a hexapole illumination mode the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as TE polarization.

[0052] 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.

[0053] 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 fixedor 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.”

[0054] 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.

[0055] A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phaseshift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.

[0056] 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.”

[0057] 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 opticalelement 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.

[0058] 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.

[0059] 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 between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0060] 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 thesecond positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0061] The depicted apparatus may be used in at least one of the following modes. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while a pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

[0062] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input / output port I / Ol, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0067] 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)).

[0068] 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 anoptical 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.

[0069] 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).

[0070] 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., profiling using a stylus, atomic force microscopy (AFM)), and / or non-optical imaging (e.g., scanning electron microscopy (SEM)).

[0071] 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.

[0072] 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.

[0073] 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, thetarget 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).

[0074] Fig. 3 depicts an example metrology (inspection) system 10 that may be used to detect alignment, overlay, and / or perform other metrology operations. It comprises a radiation or illumination source 2 which projects or otherwise irradiates radiation onto a substrate W (e.g., which may typically include a metrology mark). Redirected radiation is passed to a sensor such as a spectrometer detector 4 and / or other sensors, which measures a spectrum (intensity as a function of wavelength) of the specular reflected and / or diffracted radiation, as shown, e.g., in the graph on the left of Fig. 4. The sensor may generate a metrology signal conveying metrology data indicative of properties of the reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in Fig. 4, or by other operations.

[0075] As in the lithographic apparatus LA in Fig. 1 , one or more substrate tables (not shown in Fig.4) may be provided to hold the substrate W during measurement operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Fig. 1. In an example where inspection system 10 is integrated with the lithographic apparatus, they may even be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate in relation to a measurement optical system. Various sensors and actuators are provided, for example, to acquire the position of a target portion of interest of a structure (e.g., a metrology mark), and to bring it into position under an objective lens. Typically, many measurements will be made on target portions of a structure at different locations across the substrate W. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the target portion relative to the focus of the optical system. It is convenient to think and describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves. Provided the relative position of the substrate and the optical system is correct, it does not matter in principle which one of those is moving, or if both are moving, or a combination of a part of the optical system is moving (e.g., in the Z and / or tilt direction) with the remainder of the optical system being stationary and the substrate is moving (e.g., in the X and Y directions, but also optionally in the Z and / or tilt direction).

[0076] For typical metrology measurements, a target (portion) 30 on substrate W may be a 1-D grating, which is printed such that after development, the bars are formed of solid resist lines (e.g.,which may be covered by a deposition layer), and / or other materials. Or the target 30 may be a 2-D grating, which is printed such that after development, the grating is formed of solid resist pillars, and / or other features in the resist.

[0077] 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 (portion) 30 (e.g., of bars, pillars, vias, etc.) is sensitive to changes in processing in the patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in target 30. Accordingly, the measured data from target 30 may be used to determine an adjustment for one or more of the manufacturing processes, and / or used as a basis for making the actual adjustment.

[0078] For example, the measured data from target 30 may indicate alignment for a layer of a semiconductor device. The measured data from target 30 may be used (e.g., by the one or more processors PRO and / or other processors) for determining one or more semiconductor device manufacturing process parameters based the alignment, and determining an adjustment for a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may comprise a stage position adjustment, for example, or this may include determining an adjustment for a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation, an incident angle of the radiation, a wavelength of the radiation, a pupil size and / or shape, a resist material, and / or other process parameters.

[0079] Fig. 5 illustrates a plan view of a typical target (e.g., metrology mark) 30, and the extent of a typical radiation illumination spot S in the system of Fig. 4. Typically, to obtain a diffraction spectrum that is free of interference from surrounding structures, the target 30, in an embodiment, is a periodic structure (e.g., grating) larger than the width (e.g., diameter) of the illumination spot S. The width of spot S may be smaller than the width and length of the target. The target, in other words, is ‘underfilled’ by the illumination, and the diffraction signal is essentially free from any signals from product features and the like outside the target itself. The illumination arrangement may be configured to provide illumination of a uniform intensity across a back focal plane of an objective, for example. Alternatively, by, for example, including an aperture in the illumination path, illumination may be restricted to on axis or off axis directions.

[0080] Fig. 6 illustrates optical splitting 600 of radiation 601 from a single radiation source 602 to provide multiple output channels 604, 606, 608, 610. The multiple output channels may be used to calibrate a detector such as detector 4 shown in Fig. 3, for example. Splitting 600 is accomplished with a series of 1x2 optical splitters 620, which together comprise a 1x4 optical splitter (one radiation 601 input is split into the four output channels 604-610 by a cascade of 1x2 splitters). However, spectral splitting characteristics for a typical 1x4 optical splitter produce differences in output powersplitting percentages, for example outputs ranging between 20-30% across four outputs, rather than the preferred 25% for each output. Spectral splitting characteristics also often change based on wavelength of the input radiation from 602. Thus, the range of outputs can become even more of a problem if a wider wavelength is desired. In addition, splitting 600 may be based on free-spaced splitting of a super luminescent diode (SLD) beam onto four multimode fibers housed in a fiber bundle. Such a solution is not only difficult to set up but is highly sensitive to environmental variables such as temperature, relative humidity, air pressure, vibration, etc. Fig. 6 also illustrates a graph 650 showing transmission (power) 652 as a function of input light wavelength 654 for splitting 600. Graph 650 shows a nonuniform splitter ratio ranging from 26% to 24% (for output channels 604, 606, 608, 610) as a function input wavelength ranges across 850nm + / -10nm.

[0081] Fig. 7 illustrates an example embodiment of a system 700 configured to output spectrally matched and equivalent intensity radiation 701. As shown in Fig. 7, system 700 is configured for multi-output spectrally matched and equivalent intensity radiation. System 700 provides a new optical design architecture. System 700 comprises a first splitter 702 configured to receive and split input radiation 703 from a radiation source 705 into first transmissive and reflective portions 710 and 712, respectively. Input radiation 703 may have a wavelength between about 400nm and about 1600nm, for example. Input radiation 703 may comprise visible light, infrared light, near infrared light, and / or other radiation.

[0082] System 700 comprises second splitters 704 configured to receive and further split each of the first transmissive and reflective portions 710 and 712 into second transmissive and reflective portions 714, 716, 718, and 720. System 700 comprises one or more combiners 706 configured to combine the second transmissive and reflective portions 714-720 into different outputs 730, 732, 734, 736 with mixed transmissive and reflective portions. Four outputs (channels) are shown in Fig. 7 as an example. More or less outputs are possible. The mixed transmissive and reflective portions are configured such that outputs 730-736 from system 700 together form the spectrally matched and equivalent intensity radiation. For example, the spectrally matched and equivalent intensity radiation may have a wavelength of about 850nm, and the intensity of the radiation from each output 730-736 may be about the same.

[0083] In some embodiments, as in the example shown in Fig. 7, a combiner 706 (or mixer) of the one or more combiners comprises a 2x2 optical coupler. The first splitter 702 may comprise a 1x2 optical splitter. The second splitters 704 may each comprise a 1x2 optical splitter. Here, the second splitters comprise two 1x2 optical splitters. Note that in some embodiments, the splitter(s) and combiner(s) described herein comprise multiple instances of the same (or similar) products, such as 1x2 or 2x2 fiber couplers.) The splitters and / or couplers may comprise a fiber fused coupler / splitter, such as fused fiber couplers / splitters that include two fibers which are essentially fused into one, resulting in a 1x2 coupler, and / or other splitter s / couplers. This can be thought of as being the fiberequivalent of a free-spaced non-polarizing beam splitter, for example, or the whole scheme may be implemented in integrated optical devices.

[0084] In some embodiments, the spectrally matched and equivalent intensity radiation may be used to calibrate detectors (such as detector 4 shown in Fig. 4) which use photodetectors for converting intensity channel optical signals into electrical signals, for example. In some embodiments, a detector comprises a multichannel circuit board which uses one or more photodetectors configured to convert intensity channel optical signals into electrical signals, an array of photodetectors or camera devices, and / or other components. Other uses for the spectrally matched and equivalent intensity radiation are contemplated.

[0085] Fig. 7 also illustrates a graph 750 showing transmission (power) 752 as a function of input light wavelength 754 for system 700. Graph 750 shows a reduced nonuniform splitter ratio ranging from just above to just below 25% (for outputs 730, 732, 734, and 736) as a function input wavelength ranges across 850nm + / -10nm. As shown in graph 750, system 700 expands a flatter portion of transmission (power) 752 over 850 + / -10nm that is within a range of 24.99% to 25.03%, compared to 24-26% as shown in Fig. 6.

[0086] Fig. 8 illustrates another example embodiment of a system 800 configured to output spectrally matched and equivalent intensity radiation 801. As shown in Fig. 8, system 800 is configured for multi-output spectrally matched and equivalent intensity radiation. System 800 may be similar to and / or the same as system 700 in one or more aspects, such that similar or equivalent components share similar or equivalent characteristics. For example, system 800 comprises a first splitter 802 configured to receive and split input radiation 803 from a radiation source 805 into first transmissive and reflective portions 810 (T stands for transmissive) and 812 (R stands for reflective), respectively. System 700 comprises second splitters 804 configured to receive and further split each of the first transmissive and reflective portions 810 and 812 into second transmissive and reflective portions 814, 816, 818, 820, 822, and 824 (see the various T’s and R’s). In this example, the second splitters comprise three 1x2 optical splitters.

[0087] System 800 comprises one or more combiners 806 configured to combine the second transmissive and reflective portions 814-824 into different outputs 830, 832, 834, 836 (again four in this example) with mixed transmissive and reflective portions. For example, tracing the various T’s and R’s through the different branches of system 800, output 830 comprises T*R. Output 832 comprises (T*T*T)+(R*R*T). Output 834 comprises (T*T*R)+(R*R*R). Output 836 comprises R*T. The mixed transmissive and reflective portions (T’s and R’s) are configured such that outputs 830-836 from system 800 together form the spectrally matched and equivalent intensity radiation.

[0088] In some embodiments, the different outputs 830-836 with the mixed transmissive and reflective portions collectively comprise an equal number of transmissive and reflective portions. For example, counting the total number of T’s, and the total number of R’s in output 830-836 shows thatthey are the same. However, different outputs 830-836 comprise different mixtures of transmissive and reflective portions.

[0089] In some embodiments, system 800 (and / or any other embodiment of a system described herein) may comprise optical fibers 850 configured to provide optical pathways 852 to optically couple the first splitter 802, the second splitters 804, and the one or more combiners 806. In some embodiments, optical pathways 852 may be directly coupled (e.g., without any intervening air or lens space) to corresponding splitters, combiners, and / or other components. Each optical pathway may comprise a waveguide and / or other structures, for example. In some embodiments, system 800 comprises free space optical components 854 configured to provide optical pathways 852. In this example, optical pathways 852 may not be directed coupled to any other components of system 800. In some embodiments, optical pathways 852 are the same optical path length and the intensity of radiation 801 is spectrally matched.

[0090] In some embodiments, system 800 (and / or any other embodiment of a system described herein) may comprise one or more isolators 880 (two are shown in this example) configured to receive input radiation 803 from radiation source 805 and ensure photons propagate only in one direction, reducing back reflection. System 800 may also include one or more variable optical attenuators 882 (again two are shown in this example), neutral density filters, and / or other components configured to reduce a power level of input radiation 803 before input radiation 803 is provided to first splitter 802.

[0091] Fig. 9 illustrates yet another example embodiment of a system 900 configured to output spectrally matched and equivalent intensity radiation. As shown in Fig. 9, system 900 is configured for multi-output spectrally matched and equivalent intensity radiation. System 900 may be similar to and / or the same as system 700 and / or system 800 in one or more aspects, such that similar or equivalent components share similar or equivalent characteristics. For example, system 900 comprises a first splitter 902 configured to receive and split input radiation 903 from a radiation source 905 into first transmissive and reflective portions 910 and 912, respectively. System 900 comprises second splitters 904 configured to receive and further split each of the first transmissive and reflective portions 910 and 912 into second transmissive and reflective portions 914-952. In this example, the second splitters comprise instances of the same (or similar) products, such as 1x2 or 2x2 fiber couplers. In some embodiments, second splitters 904 may comprise up to 10 or more 1x2 and / or 2x2 optical splitters, for example.

[0092] System 900 comprises one or more combiners 906 configured to combine the second transmissive and reflective portions 914-952 into different outputs 960, 962, 964, 966, 968, 970, 972, and 974 (eight in this example) with mixed transmissive and reflective portions. The mixed transmissive and reflective portions are configured such that outputs 960-974 from system 900 together form the spectrally matched and equivalent intensity radiation. Again here, system 900 (and / or any other embodiment of a system described herein) may comprise optical fibers, free spaceoptical components, and / or other components (all unlabeled in Fig. 9) configured to provide optical pathways (unlabeled in Fig. 9 for available space reasons) to optically couple the first splitter 902, the second splitters 904, and the one or more combiners 906.

[0093] System 900 (and / or any other embodiment of a system described herein) may also comprise one or more isolators 980 (two are shown in this example) configured to receive input radiation 903 from radiation source 905, one or more variable optical attenuators 982 (again two are shown in this example), neutral density filters, and / or other components configured to reduce a power level of input radiation 903 before input radiation 903 is provided to first splitter 902, and / or other components. Note that one or more isolators 980, radiation 903, radiation source 905, and / or variable optical attenuators 982 may be similar to and or the same as the corresponding components of Fig. 8 (i.e., one or more isolators 880, radiation 803, radiation source 805, and / or variable optical attenuators 882). The different numbering in Fig. 9 is merely meant to indicate that any of these such components (and / or any other components described herein) may be used equivalently in more than one of the described embodiments.

[0094] Tests with one or more of the systems described above (e.g., systems 700, 800, and 900) on four independent detectors (each similar to and / or the same as detector 4 shown in Fig. 3 and described above) with impinging power varying between lOOpW to InW (this is just one example range and should not be considered limiting), showed excellent stability (~ lOOppm (parts per million) over 4 hours) across all output channel combinations. Intensity = power / area (Watts / Area). Power = energy (W).

[0095] Fig. 10 shows an equation 1000 that defines this stability. Equation 1000 defines a stability of one channel (Ch) or output (e.g., as described relative to Fig. 7-9 above) relative to another (i.e., Chl / Ch2) - e.g., similar to the power percentage outputs for each channel shown in Fig. 6 or Fig. 7 (the Y axis in each graph). As shown in Fig. 10, equation 1000 a maximum - minimum range term for a ratio of two channels (this term gives the largest difference of the Chl / Ch2 ratio) is multiplied by le6 / 2 (converted into ppm, the / 2 is for + / -; in the end, it is ppm. That whole product is divided by two times an average of the ratio (the midrange of the Chl / Ch2 ratio).

[0096] Fig. 11 illustrates another example embodiment of a system 1100 configured to output spectrally matched and equivalent intensity radiation 1101 (e.g., which can be used for calibration and / or other purposes as described herein). As shown in Fig. 11, system 1100 is configured for multioutput spectrally matched and equivalent intensity radiation. System 1100 comprises a radiation source 1102 (e.g., which may be similar to and / or the same as one or more of the other radiation sources described herein), an integrating sphere 1104, and / or other components. Radiation source 1102 is configured to generate radiation 1103. Integrating sphere 1104 is configured to receive radiation 1103 from radiation source 1102 and flatten an intensity profile of radiation 1103.Integrating sphere 1104 is configured such that, at the circumference of the sphere, there is sufficient random scattering such that at the given output port of the sphere, each unit of integrated area receivesthe same radiance / flux of light. In some embodiments, a filter 1110 is configured to filter an infrared (IR) portion of radiation 1103 from radiation source 1102 to decrease or eliminate thermal heating of system 1100 and / or for other purposes. In some embodiments, filter 1110 is configured to filter radiation 1103 to provide a specific spectrum of radiation 1103 to integrating sphere 1104.

[0097] In some embodiments, radiation source 1102 comprises a 500-900nm white light source, for example. In some embodiments, integrating sphere 1104 facilitates expansion of wavelengths even further, going from 400-2200nm, for example (note: this wavelength range is a limitation of the optical fiber itself, not the splitting mechanism of the integrating sphere). The one or more outputs 1106 comprise multiple output ports 1107, with each output port 1107 comprising a 200pm multimode fiber and / or other components. In some embodiments, the multiple output ports 1107 comprise up to eight or more output ports 1107 (though only three are shown for example in Fig. 11). In some embodiments, each multi-mode fiber has a numerical aperture equal to 0.22 and / or other properties. In some embodiments, radiation source 1102 comprises an attenuator 1120 configured to be adjusted to achieve different powers at the multi-mode fiber output ports 1107. In some embodiments, a photonic crystal fiber is configured to conduct radiation 1103 from radiation source 1102 to integrating sphere 1104.

[0098] In some embodiments, integrating sphere 1104 comprises one or more baffles 1130 inside integrating sphere 1104. The one or more baffles 1130 are configured to prevent direct line of sight paths from an input to integrating sphere 1104 to the one or more outputs 1106 (or output ports 1107), for example.

[0099] Fig. 12 illustrates a method 1200 for outputting spectrally matched and equivalent intensity radiation. In some embodiments, one or more operations of method 1200 may be implemented in or by systems 700, 800, and / or 900 illustrated in Figs. 7, 8, and 9 respectively; system 10 illustrated in Fig. 3; a computer system (e.g., as illustrated in Fig. 13 and described below), and / or in or by other systems, for example. In some embodiments, method 1200 comprises generating (operation 1202) input radiation, receiving and splitting (operation 1204) the input radiation into first transmissive and reflective portions, receiving and further splitting (operation 1206) each of the first transmissive and reflective portions into second transmissive and reflective portions, combining (operation 1208) the second transmissive and reflective portions into different outputs with mixed transmissive and reflective portions, calibrating (operation 1210) a detector, and / or other operations. Again note that calibrating a detector (operation 1210) is one example use for the spectrally matched and equivalent intensity radiation. Other example uses are contemplated and could augment and / or replace calibration in operation 1210, for example.

[0100] The operations of method 1200 are intended to be illustrative. In some embodiments, method 1200 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 1200 may include additional operations related to determining an adjustment for a metrology detector. Additionally, theorder in which the operations of method 1200 are illustrated in Fig. 12 and described herein is not intended to be limiting.

[0101] In some embodiments, one or more portions of method 1200 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 1200 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 1200 (e.g., see discussion related to Fig. 13 below).

[0102] At operation 1202, input radiation is generated. 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 10 shown in Fig. 3) based on previous measurements, and / or determined in other ways. In some embodiments, the radiation comprises light and / or other radiation. In some embodiments, the light comprises visible light, infrared light, near infrared light, and / or other light. In some embodiments, the radiation may be any radiation appropriate for interferometry. In some embodiments, the input radiation has a wavelength (or wavelengths) between about 400nm and about 1600nm. 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 first axis. In some embodiments, operation 1202 is performed by a radiation source similar to and / or the same as source 2 shown in Fig. 3).

[0103] In some embodiments, operation 1202 comprises receiving, with one or more isolators, the input radiation from the radiation source, and ensuring photons propagate only in one direction, reducing back reflection. Operation 1202 may also include reducing, with one or more variable optical attenuators and / or neutral density filters, a power level of the input radiation before the input radiation is provided to the first splitter.

[0104] At operation 1204, the input radiation is received (e.g., from the radiation source optionally via the one or more isolators, variable optical attenuators, and / or neutral density filters) and split, with a first splitter, into first transmissive and reflective portions (or channels). In some embodiments, the input radiation is split into two or more portions, for example. In some embodiments, operation 1204 is performed by a splitter that is the same as or similar to splitters 702, 802, and / or 902 shown in Fig. 7, 8, and 9, respectively, and described above. For example, in some embodiments, the first splitter comprises a 1x2 optical splitter.

[0105] At an operation 1206, each of the first transmissive and reflective portions are received and further split, with second splitters, into second transmissive and reflective portions. In someembodiments, the second splitters are similar to and / or the same as splitters 704, 804, and / or 904 shown in Fig. 7, 8, and 9, respectively, and described above. For example, in some embodiments, the second splitters each comprise a 1x2 optical splitter. In some embodiments, the second splitters comprise two 1x2 optical splitters. In some embodiments, the second splitters comprise three 1x2 optical splitters. In some embodiments, the second splitters comprise up to 10 or more 1x2 optical splitters.

[0106] At an operation 1208, the second transmissive and reflective portions are combined, with one or more combiners, into different outputs with mixed transmissive and reflective portions. The mixed transmissive and reflective portions are configured such that outputs together form spectrally matched and equivalent intensity radiation. In some embodiments, the different outputs with the mixed transmissive and reflective portions collectively comprise an equal number of transmissive and reflective portions. In some embodiments, the different outputs comprise different mixtures of transmissive and reflective portions. In some embodiments, operation 1108 is performed by one or more combiners that re the same as or similar to combiners 706, 806, and / or 906 shown in Fig. 7, 8, and 9, respectively, and described above. For example, in some embodiments, a combiner of the one or more combiners comprises a 2x2 optical coupler.

[0107] In some embodiments, the splitter(s) and combiner(s) described above comprise multiple instances of the same (or similar) products such as 1x2 or 2x2 fiber couplers.

[0108] In some embodiments, operations 1202, 1204, and / or 1206 include providing, with optical fibers, optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners. In some embodiments, the optical pathways may be provided with free space optical components. The optical pathways have the same optical path length and are spectrally matched., for example.

[0109] In some embodiments, instead of and / or in addition to operations 1204-1208, method 1200 comprises receiving and flattening, with an integrating sphere, the radiation from the radiation source, such that one or more outputs from the integrating sphere together have mixed transmissive and reflective portions configured to form spectrally matched and equivalent intensity radiation (e.g., see Fig. 11 and system 1100 described above). This may include filtering, with a filter, an infrared (IR) portion of the radiation from the radiation source to decrease or eliminate thermal heating of the system, adjusting an attenuator to achieve different powers at the (e.g. multi-mode fiber) outputs (e.g., ports), filtering the radiation with a spectral filter to provide a specific spectrum of the radiation to the integrating sphere, and / or other operations. In some embodiments, the integrating sphere comprises one or more baffles inside the integrating sphere, configured to prevent direct line of sight paths from an input to the integrating sphere to the one or more outputs. In this embodiment, radiation may be conducted from the source to the integrating sphere with a photonic crystal fiber, for example.

[0110] At operation 1210, a detector (e.g., detector 4 shown in Fig. 3) is calibrated using the spectrally matched and equivalent intensity radiation. The detector may be associated withsemiconductor metrology, for example. In some embodiments, the detector comprises a multichannel circuit board which uses one or more photodetectors configured to convert intensity channel optical signals into electrical signals.

[0111] In some embodiments, operation 1210 comprises performing metrology with the calibrated detector. In some embodiments, operation 1210 is performed by various components of a system such as system 10 illustrated in Fig. 3, e.g., including detector 4 and processor PRO, etc. In some embodiments, alignment and / or overlay and / or other measurements may be determined at operation 1210. Alignment and / or overlay may be determined based on reflected diffracted radiation from a diffraction grating target and / or other information. For example, in some embodiments, operation 1210 includes illuminating (and / or otherwise irradiating) one or more targets (e.g., target 30 shown in Fig. 3) in a patterned substrate with radiation. The radiation may be generated by a radiation source (e.g., source 2 shown in Fig. 3 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.

[0112] In some embodiments, operation 1210 comprises generating a metrology signal based on the detected reflected radiation from diffraction grating target(s), as described above with the calibrated detector. The metrology signal is generated by a calibrated detector (such as detector 4 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 and / or overlay signal comprising alignment and / or overlay measurement information, and / or other metrology signals. The measurement information (e.g, an alignment value, an overlay value, and / or other information) may be determined using principles of interferometry and / or other principles.

[0113] 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 reflectedradiation 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 detector 4 (e.g., calibrated as part of operation 1110) and / or processors PRO shown in Fig. 3, and / or other components.

[0114] In some embodiments, method 1200 comprises determining an adjustment for a semiconductor device manufacturing process. In some embodiments, method 1200 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on one or more detected phase and / or amplitude variations, an overlay and / or alignment value indicated by the metrology signal, and / or other similar systems, and / or other information. The one or more parameters may include a parameter of the radiation (the radiation used for metrology), an overlay value, an alignment value, a metrology inspection location on a layer of a semiconductor device structure, a radiation beam trajectory across a target, and / or other parameters. In some embodiments, process parameters can be interpreted broadly to include a stage position, a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation (used for exposing resist, etc.), an incident angle of the radiation (used for exposing resist, etc.), a wavelength of the radiation (used for exposing resist, etc.), a pupil size and / or shape, a resist material, and / or other parameters.

[0115] In some embodiments, method 1200 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.

[0116] 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 1200), 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 changein the apparatus. The electronic adjustment may include changing a setting on the apparatus, for example, and / or other adjustments.

[0117] Fig. 13 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. Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors similar to and / or the same as processor PRO shown in Fig. 3) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0118] Computer system CS may be coupled via bus BS to a display DS, such as a flat panel or touch panel display or a cathode ray tube (CRT) for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor PRO and for controlling cursor movement on display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

[0119] In some embodiments, all or some of one or more operations described herein may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions included in main memory MM causes processor PRO to perform the process steps (operations) described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0120] The term “computer-readable medium” or “machine-readable medium” as used herein refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such asstorage 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.

[0121] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a 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.

[0122] Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0123] 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.

[0124] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example,host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN, and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other nonvolatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0125] 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 output spectrally matched and equivalent intensity radiation, the system comprising: a first splitter configured to receive and split input radiation into first transmissive and reflective portions; second splitters configured to receive and further split each of the first transmissive and reflective portions into second transmissive and reflective portions; and one or more combiners configured to combine the second transmissive and reflective portions into different outputs with mixed transmissive and reflective portions, the mixed transmissive and reflective portions configured such that outputs from the system together form the spectrally matched and equivalent intensity radiation.2. The system of clause 1 , further comprising optical fibers configured to provide optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners.3. The system of any of the previous clauses, further comprising free space optical components configured to provide optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners.4. The system of any of the previous clauses, wherein the optical pathways have the same optical path length and are spectrally matched.5. The system of any of clauses 1-4, wherein the different outputs with the mixed transmissive and reflective portions collectively comprise an equal number of transmissive and reflective portions.6. The system of any of the previous clauses, wherein different outputs comprise different mixtures of transmissive and reflective portions.7. The system of any of the previous clauses, wherein a combiner of the one or more combiners comprises a 2x2 optical coupler.8. The system of any of the previous clauses, wherein the first splitter comprises a 1x2 optical splitter.9. The system of any of the previous clauses, wherein the second splitters each comprise a 1x2 optical splitter.10. The system of any of the previous clauses, wherein the second splitters comprise two 1x2 optical splitters.11. The system of any of the previous clauses, wherein the second splitters comprise three 1x2 optical splitters.12. The system of any of the previous clauses, wherein the second splitters comprise 10 1x2 optical splitters.13. The system of any of the previous clauses, further comprising a radiation source configured to generate the input radiation.14. The system of any of the previous clauses, further comprising one or more isolators configured to receive the input radiation from the radiation source and ensure photons propagate only in one direction, reducing back reflection.15. The system of any of the previous clauses, further comprising one or more variable optical attenuators and / or neutral density filters configured to reduce a power level of the input radiation before the input radiation is provided to the first splitter.16. The system of any of the previous clauses, wherein the input radiation: has a wavelength between about 400nm and about 1600nm; and comprises visible light; or comprises infrared light.17. The system of any of the previous clauses, wherein the output spectrally matched and equivalent intensity radiation is configured to be used to calibrate a detector.18. The system of any of the previous clauses, wherein the detector comprises a multichannel circuit board which uses one or more photodetectors configured to convert intensity channel optical signals into electrical signals.19. The system of any of the previous clauses, wherein the detector is associated with semiconductor metrology.20. The system of any of the previous clauses, wherein the output spectrally matched and equivalent intensity radiation is configured for lithography, alignment metrology, and / or overlay metrology associated with a semiconductor manufacturing process.21. A method for outputting spectrally matched and equivalent intensity radiation, the method comprising: receiving and splitting, with a first splitter, input radiation into first transmissive and reflective portions; receiving and further splitting, with second splitters, each of the first transmissive and reflective portions into second transmissive and reflective portions; and combining, with one or more combiners the second transmissive and reflective portions into different outputs with mixed transmissive and reflective portions, the mixed transmissive and reflective portions configured such that outputs together form the spectrally matched and equivalent intensity radiation.22. The method of clause 21, further comprising providing, with optical fibers, optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners.23. The method of any of the previous clauses, further comprising providing, with free space optical components, optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners.24. The method of any of the previous clauses, wherein the optical pathways have the same optical path length and are spectrally matched.25. The method of any of the previous clauses, wherein the different outputs with the mixed transmissive and reflective portions collectively comprise an equal number of transmissive and reflective portions.26. The method of any of the previous clauses, wherein different outputs comprise different mixtures of transmissive and reflective portions.27. The method of any of the previous clauses, wherein a combiner of the one or more combiners comprises a 2x2 optical coupler.28. The method of any of the previous clauses, wherein the first splitter comprises a 1x2 optical splitter.29. The method of any of the previous clauses, wherein the second splitters each comprise a 1x2 optical splitter.30. The method of any of the previous clauses, wherein the second splitters comprise two 1x2 optical splitters.31. The method of any of the previous clauses, wherein the second splitters comprise three 1x2 optical splitters.32. The method of any of the previous clauses, wherein the second splitters comprise 10 1x2 optical splitters.33. The method of any of the previous clauses, further comprising generating, with a radiation source, the input radiation.34. The method of any of the previous clauses, further comprising receiving, with one or more isolators, the input radiation from the radiation source, and ensuring photons propagate only in one direction, reducing back reflection.35. The method of any of the previous clauses, further comprising reducing, with one or more variable optical attenuators and / or neutral density filters, a power level of the input radiation before the input radiation is provided to the first splitter.36. The method of any of the previous clauses, wherein the input radiation: has a wavelength between about 400nm and about 1600nm; and comprises visible light; or comprises infrared light.37. The method of any of the previous clauses, further comprising calibrating a detector with the output spectrally matched and equivalent intensity radiation.38. The method of any of the previous clauses, wherein the detector comprises a multichannel circuit board which uses one or more photodetectors configured to convert intensity channel optical signals into electrical signals.39. The method of any of the previous clauses, wherein the detector is associated with semiconductor metrology.40. The method of any of the previous clauses, further comprising performing lithography, alignment metrology, and / or overlay metrology associated with a semiconductor manufacturing process with the output spectrally matched and equivalent intensity radiation.41. A system configured to output spectrally matched and equivalent intensity radiation, the system comprising: a radiation source configured to generate radiation; and an integrating sphere configured to receive the radiation from the radiation source and flatten an intensity profile of the radiation, such that one or more outputs from the integrating sphere together have mixed transmissive and reflective portions configured to form spectrally matched and equivalent intensity radiation.42. The system of clause 41, further comprising a filter configured to filter an infrared (IR) portion of the radiation from the radiation source to decrease or eliminate thermal heating of the system.43. The system of any of the previous clauses, wherein the radiation source comprises a 500-900nm white light source.44. The system of any of the previous clauses, wherein the one or more outputs comprise multiple output ports, each output port comprising a 200pm multi-mode fiber.45. The system of any of the previous clauses, wherein the multiple output ports comprise eight output ports.46. The system of any of the previous clauses, wherein each multi-mode fiber has a numerical aperture equal to 0.22.47. The system of any of the previous clauses, wherein the radiation source comprises an attenuator configured to be adjusted to achieve different powers at the multi-mode fiber output ports.48. The system of any of the previous clauses, wherein the radiation source comprises a spectral filter configured to filter the radiation to provide a specific spectrum of the radiation to the integrating sphere.49. The system of any of the previous clauses, wherein the integrating sphere comprises one or more baffles inside the integrating sphere, the one or more baffles configured to prevent direct line of sight paths from an input to the integrating sphere to the one or more outputs.50. The system of any of the previous clauses, further comprising a photonic crystal fiber configured to conduct the radiation from the radiation source to the integrating sphere.51. A method for outputting spectrally matched and equivalent intensity radiation, the method comprising: generating radiation with a radiation source; and receiving and flattening, with an integrating sphere, the radiation from the radiation source, such that one or more outputs from the integrating sphere together have mixed transmissive and reflective portions configured to form spectrally matched and equivalent intensity radiation.52. The method of clause 51, further comprising filtering, with a filter, an infrared (IR) portion of the radiation from the radiation source to decrease or eliminate thermal heating of the system.53. The method of any of the previous clauses, wherein the radiation source comprises a 500-900nm white light source.54. The method of any of the previous clauses, wherein the one or more outputs comprise multiple output ports, each output port comprising a 200pm multi-mode fiber.55. The method of any of the previous clauses, wherein the multiple output ports comprise eight output ports.56. The method of any of the previous clauses, wherein each multi-mode fiber has a numerical aperture equal to 0.22.57. The method of any of the previous clauses, wherein the radiation source comprises an attenuator configured to be adjusted to achieve different powers at the multi-mode fiber output ports.58. The method of any of the previous clauses, wherein the radiation source comprises a spectral filter configured to filter the radiation to provide a specific spectrum of the radiation to the integrating sphere.59. The method of any of the previous clauses, wherein the integrating sphere comprises one or more baffles inside the integrating sphere, the one or more baffles configured to prevent direct line of sight paths from an input to the integrating sphere to the one or more outputs.60. The method of any of the previous clauses, further comprising conducting, with a photonic crystal fiber, the radiation from the radiation source to the integrating sphere.

[0126] 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.

[0127] 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.

[0128] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A system configured to output spectrally matched and equivalent intensity radiation, the system comprising: a first splitter configured to receive and split input radiation into first transmissive and reflective portions; second splitters configured to receive and further split each of the first transmissive and reflective portions into second transmissive and reflective portions; and one or more combiners configured to combine the second transmissive and reflective portions into different outputs with mixed transmissive and reflective portions, the mixed transmissive and reflective portions configured such that outputs from the system together form the spectrally matched and equivalent intensity radiation.

2. The system of claim 1 , further comprising optical fibers configured to provide optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners.

3. The system of claim 1, further comprising free space optical components configured to provide optical pathways to optically couple the first splitter, the second splitters, and the one or more combiners.

4. The system of claim 2 or 3, wherein the optical pathways have the same optical path length and are spectrally matched.

5. The system of any of claims 1-4, wherein the different outputs with the mixed transmissive and reflective portions collectively comprise an equal number of transmissive and reflective portions.

6. The system of claim 5, wherein different outputs comprise different mixtures of transmissive and reflective portions.

7. The system of any of claims 1-6, wherein a combiner of the one or more combiners comprises a 2x2 optical coupler.

8. The system of any of claims 1-7, wherein the first splitter comprises a 1x2 optical splitter.

9. The system of any of claims 1-8, wherein the second splitters each comprise a 1x2 optical splitter.

10. The system of claim 9, wherein the second splitters comprise two 1x2 optical splitters.

11. The system of claim 9, wherein the second splitters comprise three 1x2 optical splitters.

12. The system of claim 9, wherein the second splitters comprise 10 1x2 optical splitters.

13. The system of any of claims 1-12, further comprising a radiation source configured to generate the input radiation.

14. The system of claim 13, further comprising one or more isolators configured to receive the input radiation from the radiation source and ensure photons propagate only in one direction, reducing back reflection.

15. The system of claims 13 or 14, further comprising one or more variable optical attenuators and / or neutral density filters configured to reduce a power level of the input radiation before the input radiation is provided to the first splitter.

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