Field splitting optical configuration for level sensing systems and methods

Abstract

A level sensor is an optical sensor that measures the height of a substrate surface. The field of view of a level sensor limits the sensor's per substrate measurement time (e.g., throughput). An enhanced level sensor with a larger field of view and faster throughput is described. The enhanced level sensor incorporates a projection grating comprising sub-fields configured to separately pattern different portions of radiation that is projected onto the substrate surface. Projection optics comprising a series of mirrors direct the different portions of the radiation onto the substrate surface in a colinear arrangement or a parallel arrangement. This doubles the size of the field of view of the level sensing system compared to prior systems, significantly reduces a total required measurement time for each substrate, and / or has other advantages.

Description

FIELD SPLITTING OPTICAL CONFIGURATION FOR LEVEL SENSING SYSTEMS AND METHODSCROSS-REFERENCE TO RELATED APPLICATION

[0001] The Application claims priority of US provisional application number 63 / 691,283 which was filed on 5 September, 2024 and which is incorporated herein its entirety by reference.TECHNICAL FIELD

[0002] This description relates to level sensing systems and methods for semiconductor manufacturing.BACKGROUND

[0003] A lithographic proj ection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A patterning device (e.g., a reticle or mask) may include or provide a pattern corresponding to an individual layer of the IC (“design layout”). 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 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. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate..

[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 devicesare 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] Accurate efficient metrology, including level sensing and / or other metrology, is important for these operations.SUMMARY

[0006] A level sensor is an optical sensor that measures the level (e.g., height) of a substrate surface. The field of view of a level sensor limits the sensor’s per substrate measurement time (e.g., throughput). An enhanced level sensor with a larger field of view and faster throughput is described. The enhanced level sensor incorporates a projection grating comprising sub-fields configured to separately pattern different portions of radiation that is projected onto the substrate surface. Projection optics comprising a series of mirrors direct the different portions of the radiation onto the substrate surface in a colinear arrangement or a parallel arrangement. This doubles the size of the field of view of the level sensing system compared to prior systems, significantly reduces a total required measurement time for each substrate, and / or has other advantages.

[0007] According to an embodiment, a level sensing system is provided. The system comprises a radiation source configured to generate radiation configured to be projected onto a substrate surface. The system comprises a projection grating comprising sub-fields configured to separately pattern different portions of the radiation. The system comprises projection optics configured to project the different portions of the radiation onto the substrate surface. The projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement. The system comprises a detector configured to determine a level of the substrate surface based on the different portions of the radiation that have been reflected from the substrate surface and received by the detector.

[0008] In some embodiments, the field optics are configured such that the different portions of the radiation directed onto the surface of the substrate are incident simultaneously across an entire width of the substrate surface.

[0009] In some embodiments, the field optics comprise at least one mirror associated with each of the portions of radiation. In some embodiments, the at least one mirror comprises two field splitting mirrors per different portion of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement. In some embodiments, the at least one mirror comprises folding mirrors associated with each of the different portions of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the parallel arrangement.

[0010] In some embodiments, the sub-fields comprise different physical areas of the projectiongrating. In some embodiments, the sub-fields comprise different separate individual projection gratings which together comprise the projection grating. In some embodiments, the projection grating comprises two, three, four, or more sub-fields configured to separately pattern two, three, four, or more different portions of the radiation.

[0011] In some embodiments, the colinear arrangement comprises the different portions of the radiation arranged end to end adjacent to each other to form a continuous line of radiation.

[0012] In some embodiments, the parallel arrangement comprises the different portions of the radiation arranged side by side, with a target amount of separation space between them.

[0013] In some embodiments, directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement enhances a field of view of the level sensing system on the substrate surface. In some embodiments, the enhanced field of view has a dimension of about 150-300mm, for example. In some embodiments, directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement at least doubles a size of the field of view of the level sensing system on the substrate surface compared to prior level sensing systems. In some embodiments, enhancing the field of view of the level sensing system reduces a total required measurement time for the substrate surface compared to prior level sensing systems.

[0014] In some embodiments, a shape of each of the different portions of the radiation directed onto the substrate surface is linear.

[0015] In some embodiments, a footprint of the different portions of the radiation on a primary mirror of the mirror relay covers less than half of an area of the primary mirror. In some embodiments, the footprint is less than about 70mm x 150mm.

[0016] In some embodiments, determining the level comprises constructing a height map for the substrate surface. In some embodiments, the level comprises height, topography, position, and / or tilt.

[0017] In some embodiments, the level sensing system forms a portion of an exposure apparatus. In some embodiments, the level sensing system forms a portion of a lithography apparatus. In some embodiments, the level sensing system may be used in an exposure apparatus, a lithography apparatus, and / or similar apparatuses. The exposure apparatus and / or the lithography apparatus may be used for semiconductor manufacturing, for example. In some embodiments, the level sensing system is configured to determine the level of the substrate surface as part of semiconductor manufacturing operations performed by the exposure apparatus, the lithography apparatus, and / or other apparatuses.

[0018] The substrate may be a semiconductor wafer, a carrier wafer (e.g., with semiconductor chips in a molding material), and / or other substrates.

[0019] According to another embodiment, there is provided a corresponding level sensing method comprising one or more of the operations described above.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Fig. 1 illustrates a lithography apparatus, according to an embodiment.

[0022] Fig. 2 illustrates a base example level sensing system, according to an embodiment.

[0023] Fig. 3 illustrates another base example level sensing system, according to an embodiment.

[0024] Fig. 4 illustrates an enhanced level sensor or level sensing system with a larger field of view and faster throughput compared to the system shown in Fig. 3, according to an embodiment.

[0025] Fig. 5 illustrates a view of projection optics of the system in Fig. 4, comprising a series of mirrors configured to direct different portions of radiation onto a substrate surface in a colinear arrangement, according to an embodiment.

[0026] Fig. 6 illustrates a view of projection optics of the system in Fig. 4, comprising a series of mirrors configured to direct different portions of radiation onto a substrate surface in a parallel arrangement, according to an embodiment.

[0027] Fig. 7 illustrates one example of how the system of Fig. 4-6 remains well within the physical volume constraints of typical level sensing systems, according to an embodiment.

[0028] Fig. 8 illustrates a level sensing method, according to an embodiment.

[0029] Fig. 9 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0030] As described above, a level sensor (LS) is an optical sensor that measures the level (e.g., a height) of a surface of a substrate, or a layer on said substrate. Current level sensors use broadband (or multi-color) light, a projection grating, a detection grating, and imaging optics between these gratings and the substrate. The level is determined based on a position shift of an image of the projection grating with respect to the detection grating. The field of view of a level sensor (a byproduct of the projection grating and the imaging optics) limits the sensor’s per substrate measurement time (e.g., throughput).

[0031] An enhanced level sensor with a larger field of view and faster throughput is described. The larger field of view facilitates increased level sensor throughput, and more substrate measurements. For example, a substrate surface may be measured in about six strokes using prior level sensing systems. The present systems and methods facilitate measurement in one or two strokes, as described below. Simply enlarging the size of the imaging optics to increase the field of view of prior level sensing systems (thereby decreasing the number of required strokes) is difficult or impossible because of physical volume (and cost) constraints in these systems.

[0032] Advantageously, the present systems and methods utilize multi-subfield splitting techniques between the projection grating and the detection grating. A projection grating comprising sub-fields isconfigured to separately pattern different portions of radiation that is proj ected onto the substrate surface . Projection optics comprising a series of mirrors direct the different portions of the radiation onto the substrate surface in a colinear arrangement or a parallel arrangement, while remaining well within physical volume constraints. This at least doubles the size of the field of view of the level sensing system compared to prior systems (reducing the number of required strokes by at least half), significantly reduces a total required measurement time for each substrate (which reduces the cost associated with each substrate), and / or has other advantages.

[0033] 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.

[0034] Although specific reference may be made to the measurement of a level or height of a substrate surface, or other parameters, and the manufacture of integrated circuits (ICs) for semiconductor devices, it should be understood that this 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.

[0035] In the following discussion, the term “optics” and / or “optical components” should be broadly interpreted as encompassing various types of optical systems, including refractive optics, reflective optics, apertures and catadioptric optics, for example. These terms may also include components operating according to any of these design types for directing, shaping or controlling beams of radiation, collectively or singularly. This may include any optical component in the lithographic apparatus, no matter where the optical component is located on an optical path of the lithographic apparatus. Optics may include optical components for shaping, adjusting and / or projecting radiation from a radiation source before the radiation passes and / or reflects off of the patterning device and / or substrate, and / or optical components for shaping, adjusting and / or projecting radiation after the radiation passes and / or reflects off of the patterning device and / or substrate.

[0036] 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 configuredto 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).

[0037] 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.

[0038] 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.

[0039] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial extent (commonly referred to as o-outer and o-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane wherein the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multi-pole distribution such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, e.g., by inserting an optic which provides that illumination mode into the illuminator IL or using a spatial light modulator.

[0040] 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 radiationbeam 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.

[0041] 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.

[0042] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

[0043] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a pattern in a target portion of the substrate. In an embodiment, a patterning device is any device that can be used to impart a radiation beam with a pattern in its cross-section to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in a targetportion of the device, such as an integrated circuit.

[0044] A patterning device may be transmissive or reflective . Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.

[0045] The projection system PS may comprise a plurality of optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of the optical elements to correct for aberrations (phase variations across the pupil plane throughout the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system wherein its optical axis extends in the z direction. The adjustment mechanism may be operable to do any combination of the following: displace one or more optical elements; tilt one or more optical elements; and / or deform one or more optical elements. Displacement of an optical element may be in any direction (x, y, z, or a combination thereof). Tilting of an optical element is typically out of a plane perpendicular to the optical axis, by rotating about an axis in the x and / or y directions although a rotation about the z axis may be used for a non-rotationally symmetric aspherical optical element. Deformation of an optical element may include a low frequency shape (e.g. astigmatic) and / or a high frequency shape (e.g. free form aspheres). Deformation of an optical element may be performed for example by using one or more actuators to exert force on one or more sides of the optical element and / or by using one or more heating elements to heat one or more selected regions of the optical element. In general, it may not be possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). The transmission map of a projection system PS may be used when designing a patterning device (e.g., mask) MA for the lithography apparatus LA. Using a computational lithography technique, the patterning device MA may be designed to at least partially correct for apodization.

[0046] 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. Lor example, alignment measurements using an alignment sensor AS and / or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0047] In operation of the lithographic apparatus, a radiation beam B is conditioned and provided bythe illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a shortstroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0048] Lithographic apparatus LA 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 eachmovement 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.

[0049] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0050] 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.

[0051] 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.

[0052] 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.

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

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

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

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

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

[0058] A metrology system may be used to determine one or more properties of the substratestructure, 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. Metrology data may be used for determining one or more semiconductor device manufacturing process parameters, 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.

[0059] Fig. 2 illustrates a base example level sensing system, or level sensor LS (also see LS in Fig. 1). Level sensor LS is a topography measurement system, level sensor, or height sensor which may be integrated in the lithographic apparatus (e.g., LA in Fig. 1). Level sensor LS is configured to measure the topography of a top surface of a substrate (or wafer) W. A map of the topography of the substrate, also referred to as height map, may be generated from these measurements indicating a height of the substrate as a function of the position on the substrate. This height map may subsequently be used to correct the position of the substrate during transfer of the pattern on the substrate, in order to provide an aerial image of the patterning device in a properly focus position on the substrate. It will be understood that “height” in this context refers to a dimension broadly out of the plane to the substrate (also referred to as the Z-axis). Typically, the level or height sensor performs measurements at a fixed location (relative to its own optical system) and a relative movement between the substrate and the optical system of the level or height sensor results in height measurements at locations across the substrate.

[0060] The example level or height sensor LS shown in Fig. 2 illustrates principles of operation. In this example, the level sensor comprises an optical system, which includes a projection unit LSP and a detection unit LSD. The projection unit LSP comprises a radiation source LSO providing a beam of radiation LSB to which a pattern is imparted by an object or projection grating PGR of the projection unit LSP. The radiation source LSO may be, for example, a narrowband or broadband radiation source, such as a supercontinuum light source, polarized or non-polarized, pulsed or continuous, such as a polarized or non-polarized laser beam. The radiation source LSO may include a plurality of radiation sources having different colors, or wavelength ranges, such as a plurality of LEDs. The radiation source LSO of the level sensor LS is not restricted to visible radiation, but may additionally or alternatively encompass UV and / or IR radiation and any range of wavelengths suitable to reflect from a surface of a substrate (e.g., W).

[0061] The object or projection grating PGR is a periodic grating comprising a periodic structure configured to produce a beam of radiation BE1 having a periodically varying intensity. The beam ofradiation BE1 with the periodically varying intensity is directed towards a measurement location MLO on a substrate W having an angle of incidence ANG with respect to an axis perpendicular (Z-axis) to the incident substrate surface between 0 degrees and 90 degrees, typically between 70 degrees and 80 degrees. At the measurement location MLO, the patterned beam of radiation BE1 is reflected by the substrate W (indicated by arrows BE2) and directed towards the detection unit LSD.

[0062] In order to determine the height level at the measurement location MLO, the level sensor further comprises a detection system comprising a detection grating DGR, a detector DET and a processing unit (not shown) for processing an output signal of the detector DET. The detection grating DGR may be identical to the projection grating PGR. The detector DET produces a detector output signal indicative of the light received, for example indicative of the intensity of the light received, such as a photodetector, or representative of a spatial distribution of the intensity received, such as a camera. The detector DET may comprise any combination of one or more detector types.

[0063] By means of triangulation techniques, the height level at the measurement location MLO can be determined. The detected height level is typically related to the signal strength as measured by the detector DET, the signal strength having a periodicity that depends, amongst others, on the design of the projection grating PGR and the (oblique) angle of incidence ANG.

[0064] The projection unit LSP and / or the detection unit LSD may include further optical elements, such as lenses and / or mirrors, along the path of the patterned beam of radiation between the projection grating PGR and the detection grating DGR (not shown).

[0065] In order to cover the surface of the substrate W effectively, a level sensor LS may be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating an array of measurement areas MLO or spots covering a larger measurement range.

[0066] Various height sensors of a general type are disclosed for example in US7265364 and US7646471, both incorporated by reference. A height sensor using UV radiation instead of visible or infrared radiation is disclosed in US2010233600A1, incorporated by reference. In W02016102127A1, incorporated by reference, a compact height sensor is described which uses a multi -element detector to detect and recognize the position of a grating image, without needing a detection grating.

[0067] Fig. 3 illustrates another base example level sensing system 300, or level sensor LS (also see LS in Fig. 1 and Fig. 2). Fig. 3 illustrates additional potential aspects of the base example level sensing system shown in Fig. 2. In some embodiments, level sensing system 300 forms a portion of a lithography apparatus (such as lithography apparatus LA shown in Fig. 1) used for semiconductor manufacturing, and / or another exposure apparatus. In some embodiments, level sensing system 300 is configured for use in such apparatuses. System 300 comprises a radiation source 302 (similar to and / or the same as LSO shown in Fig. 2), projection grating 320 (similar to and / or the same as PGR in Fig. 2), a detection grating 322 (similar to and / or the same as DGR in Fig. 2), a detector 310 (similar to and / or the same as DET in Fig. 2), one or more processors 311, various optical components 312 (e.g.,projection optics and / or other optical components), and / or other components. Each of these elements are described below.

[0068] Radiation source 302 is configured to irradiate substrate 303 (similar to and / or the same as W in Fig. 2) surface 305 with radiation 324 (similar to and / or the same as BE1 in Fig. 2). Radiation source 302 comprises a generator 326, collection optics 328, a light guide 330, a reflector 334, and / or other components.

[0069] Generator 326 is configured to generate radiation 324. Generator 326 may be and / or include a lamp, for example, and / or other sources of radiation. Radiation 324 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 system 300 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 ultraviolet light, visible light, and / or other light. In some embodiments, the radiation may be any radiation appropriate for interferometry.

[0070] Collection optics 328 may comprise one or more lenses and / or other optical components configured to collect radiation 324 from generator 326 and guide radiation 324 into light guide 330. Light guide 330 may comprise a tube, a channel, a light pipe, and / or other structures configured to guide radiation 324 toward substrate 303 and / or other components of system 300.

[0071] In system 300, radiation 324 is guided toward projection grating 320 and substrate 303 surface 305, and reflected radiation 324 (similar to and / or the same as BE2 in Fig. 2) is guided from substrate 303 surface 305 toward detection grating 322 and detector 310 by optical components 312 (e.g., which may include various lenses 333, reflectors 334 and 336 (e.g., flat or curved mirrors), etc., as described below). Various optical components are configured to receive, transmit, reflect, focus, and / or perform other operations on radiation 324. These components may comprise any type of lens, reflector, conduit, wedge, splitter, and / or other optical component configured to allow system 300 to function as described.

[0072] As shown in Fig. 3, optical components 312 include a mirror relay 350. Mirror relay 350 comprises a primary mirror 352, a secondary mirror 354, and folding mirrors 356 and 358. These optics facilitate projection of patterned radiation 324 from projection grating 320 onto the substrate 303 surface 305. As shown in Fig. 3, with the field of view 370 that results from projection grating 320 and mirror relay 350, several scans 372 of a given stroke size 374 must be made in order to cover the whole substrate 303 surface 305 and obtain a corresponding heigh map (e.g., level determinations). Fig. 3 shows three scans 372 (or strokes), with three more likely required to cover all of substrate 303 surface 305. It is desirable to enhance system 300 to enlarge field of view 370 (i.e. the stroke size 374) to reduce measurement time, and achieve an increased throughput. As described above, simply enlarging the size of primary mirror 352, secondary mirror 354, and folding mirrors 356 and 358 in mirror relay350 to increase the size of field of view 370 (thereby decreasing the number of required strokes) is difficult or impossible because of physical volume (and cost) constraints in system 300.

[0073] For a relatively large field of view (e.g., 150mm, 300mm, or more), the design of mirror relay 350 would need to be adjusted to increase the size of the optics, and thus be likely to encounter volume constraints because a surface radius of primary mirror 352 and secondary mirror 354, and the optical path lengths from a primary lens and a secondary lens, would need to be significantly increased. Therefore, the standard Offner relay design may not work because of the volume contains. Also, aberration corrections to achieve the required optical performance requirements may be necessary in such adjusted components.

[0074] Fig. 4 illustrates an enhanced level sensor or level sensing system 400 with a larger field of view and faster throughput compared to prior systems. Like system 300 shown in Fig. 3, level sensing system 400 may form a portion of a lithography apparatus (such as level sensor LS in lithography apparatus LA shown in Fig. 1) used for semiconductor manufacturing. As described above, in some embodiments, level sensing system 400 forms a portion of an exposure apparatus. In some embodiments, level sensing system 400 may be used in an exposure apparatus, a lithography apparatus (which may be one possible example of an exposure apparatus), and / or similar apparatuses. The exposure apparatus and / or the lithography apparatus may be used for semiconductor manufacturing, for example. In some embodiments, level sensing system 400 is configured to determine the level of the substrate surface as part of semiconductor manufacturing operations performed by an exposure apparatus, a lithography apparatus, and / or other apparatuses.

[0075] Various components of system 400 may be similar to and / or the same as components in system 300 shown in Fig. 2 (and / or level sensor LS shown in Fig. 2). However, system 400 includes a projection grating 420 comprising sub-fields 421 and 423 (two in this example - more sub-fields are possible) configured to separately pattern different portions 425 and 427 (two portions that correspond to the two sub-fields - again more are possible) of radiation 424 that is projected onto a substrate 403 surface 405 (e.g., the surface of a semiconductor wafer, a carrier wafer, and / or other substrates). The shape of each of the different portions 425 and 427 (in this example) of radiation 424 directed onto substrate 403 surface 405 may be linear (as in Fig. 4), arcuate, and / or have other shapes. System 400 also includes projection optics 450 comprising a series of mirrors 455 configured to direct the different portions 425 and 427 of radiation 424 onto the substrate 403 surface 405 in a colinear arrangement 460 or a parallel arrangement 462 (also see Fig. 5 and Fig. 6). Mirrors 455 direct the different portions 425 and 427 of radiation 424 onto the substrate 403 surface 405 in colinear arrangement 460 or parallel arrangement 462, while remaining well within physical volume constraints of system 400. This arrangement is space efficient, doubles the size of the field of view of level sensing system 400 compared to prior systems, significantly reduces a total required measurement time for each substrate 403, facilitates increased throughput by system 400, reduces the cost associated with each substrate 403,and / or has other advantages.

[0076] For example, as shown in Fig. 4, in some embodiments, mirrors 455 are configured such that (e.g., for colinear arrangement 460) the resulting field of view 470 is larger (compared to field of view 370 shown in Fig. 3) which facilitates fewer scans 472 with a larger stroke size 474 to cover the whole substrate 403 surface 405 and obtain a corresponding heigh map (e.g., make level determinations). In some embodiments, mirrors 455 are configured such that scans 473 (in parallel arrangement 462) require much less movement (e.g., half or less of the amount of movement required in prior systems). In scans 473, because portions 425 and 427 are arranged in parallel (with a target amount of separation space 481 between them), portion 425 can remain on the right side of surface 405, and portion 427 can remain on the left, so that the distance covered by a give scan 473 only needs to cover about half of the width of surface 405. Target amount of separation space 481 may be determined based on substrate 403 dimensions, system 400 characteristics, process tolerances, throughput requirements, and / or other information, for example.

[0077] Fig. 5 and Fig. 6 illustrate enlarged views of embodiments 500 (Fig. 5) and 600 (Fig. 6) of projection optics 450 comprising the series of mirrors 455 configured to direct the different portions 425 and 427 of radiation 424 onto the substrate 403 surface 405 in colinear arrangement 460 (Fig. 5) or parallel arrangement 462 (Fig. 6). As described above, a radiation source (e.g., source 402 shown in Fig. 4) is configured to generate radiation 424 configured to be projected onto a substrate surface (e.g., surface 405 of substrate 403 shown in Fig. 4). A detector (e.g., detector 410 in Fig. 4) is configured to determine a level of the substrate surface based on the different portions 425 and 427 of radiation 424 that have been reflected from the substrate surface and received by the detector.

[0078] Projection grating 420 sub-fields 421 and 423 are configured to separately pattern different portions 425 and 427 of radiation 424. Sub-fields 421 and 423 may comprise different physical areas of projection grating 420. In some embodiments, sub-fields 421 and 423 comprise different separate individual projection gratings (e.g., as shown in Fig, 4, 5, and 6) which together comprise projection grating 420. Note that projection grating 420 may comprise two (e.g., as shown in Fig. 4, Fig. 5, and Fig. 6), three, four, or more sub-fields configured to separately pattern two, three, four, or more different portions of radiation 424. The present discussion focuses on two portions 425 and 427, but this is not intended to be limiting.

[0079] Projection optics 450 are configured to project the different portions 425 and 427 of radiation424 onto the substrate surface. Projection optics 450 comprise mirrors 455 arranged in a mirror relay 457, with at least one folding mirror 459 configured to direct the different portions 425 and 427 of radiation 424 toward mirror relay 457, and field optics 461 configured to direct the different portions425 and 427 of radiation 424 from mirror relay 457 onto the substrate surface in colinear arrangement 460 (Fig. 5) or parallel arrangement 462 (Fig. 6). This projection of sub-fields is either parallel in a transverse direction on the surface of the wafer (parallel arrangement 462), or adjacent in a lateraldirection, side-by-side (colinear arrangement 460) to enable to field of view across the width of the wafer.

[0080] Mirror relay 457 comprises a primary mirror 490, a secondary mirror 492, and / or other components. As shown in Fig. 5, colinear arrangement 460 comprises the different portions 425 and 427 of radiation 424 arranged end to end adjacent to each other to form a continuous line of radiation 424. As shown in Fig. 6, parallel arrangement 462 comprises the different portions 425 and 427 of radiation 424 arranged side by side, with a target amount of separation space 481 space between them.

[0081] In some embodiments, field optics 461 are configured such that the different portions 425 and 427 of radiation 424 directed onto the surface of the substrate are incident simultaneously across an entire width of the substrate surface. In some embodiments, field optics 461 are configured such that the different portions 425 and 427 of radiation 424 directed onto the surface of the substrate are incident simultaneously across one quarter, one third, one half (e.g., as shown in Fig. 4), or more of the entire width of the substrate surface. In some embodiments, field optics 461 comprise at least one mirror associated with each of the portions (e.g., 425 and 427) of radiation 424. For example, in some embodiments, this at least one mirror may comprise two field splitting mirrors 465 per different portion 425 and 427 of radiation 424 configured to direct the different portions 425 and 427 of radiation 424 from mirror relay 457 onto the substrate surface in colinear arrangement 460 (Fig. 5). In some embodiments, the at least one mirror comprises folding mirrors 467 associated with each of the different portions 425 and 427 of radiation 424 configured to direct the different portions 425 and 427 of radiation424 from mirror relay 457 onto the substrate surface in parallel arrangement 462 (Fig. 6).

[0082] Directing the different portions 425 and 427 of radiation 424 from mirror relay 457 onto the substrate surface in colinear arrangement 460 or parallel arrangement 462 enhances field of view 470 (Fig. 4) of level sensing system 400 on the substrate surface (e.g., as shown in Fig. 4 and described above). In some embodiments, field of view 470 (Fig. 4) has a dimension of about 150-300mm (e.g., in total between portions 425 and 427). In some embodiments, directing different portions 425 and 427 of radiation 424 from mirror relay 457 onto the substrate surface in colinear arrangement 460 or parallel arrangement 462 at least doubles a size of field of view 470 on the substrate surface compared to prior level sensing systems.

[0083] Fig. 7 illustrates one example of how projection grating 420 (Fig. 4-6) comprising sub-fields (e.g., 421 and 423 shown in Fig. 4-6) configured to separately pattern different portions (e.g., 425 and 427) of radiation that is projected onto substrate surface, used in conjunction with projection optics 450 (Fig. 4-6) comprising a series of mirrors 455 (Fig. 4-6) to direct the different portions of the radiation onto the substrate surface in a colinear arrangement or a parallel arrangement, remains well within the physical volume constraints of system 400. Fig. 7 illustrates a footprint 700 of the different portions425 and 427 of radiation 424 (Fig. 4-6) on primary mirror 490 of mirror relay 457 (Fig. 4-6). Footprint 700 only covers less than half of an area 702 of primary mirror 490 in this example. As shown in Fig.7, footprint 700 may be less than about 70mm x 150mm, for example.

[0084] Returning to Fig. 4, for completeness, system 400 comprises a radiation source 402 (similar to and / or the same as radiation source 302 shown in Fig. 3, and / or LSO shown in Fig. 2), projection grating 420 (as described above), a detection grating 422 (similar to and / or the same as detection grating 322 shown in Fig. 3 and / or DGR in Fig. 2), a detector 410 (similar to and / or the same as detector 310 shown in Fig. 3 and / or DET in Fig. 2), one or more processors 411 (similar to and / or the same as processor(s) 311 shown in Fig. 3 and / or processor(s) PRO described below with respect to Fig. 9), various optical components 412 (e.g., projection optics as described herein and / or other optical components), and / or other components.

[0085] Radiation source 402 is configured to irradiate substrate 403 (e.g., a semiconductor wafer, a carrier wafer, and / or other substrates) surface 405 with radiation 424. Radiation source 402 comprises a generator 426, collection optics 428, a light guide 430, a reflector 434, and / or other components. Generator 426 is configured to generate radiation 424. Generator 426 may be and / or include a lamp, for example, and / or other sources of radiation. Radiation 424 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 system 400 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 ultraviolet light, visible light, and / or other light. In some embodiments, the radiation may be any radiation appropriate for interferometry. Collection optics 428 may comprise one or more lenses and / or other optical components configured to collect radiation 424 from generator 426 and guide radiation 424 into light guide 430. Light guide 430 may comprise a tube, a channel, a light pipe, and / or other structures configured to guide radiation 424 toward substrate 403 and / or other components of system 400.

[0086] In system 400, radiation 424 is guided toward projection grating 420 and substrate 403 surface 405, and reflected radiation 424 is guided from substrate 403 surface 405 toward detection grating 422 and detector 410 by optical components 412 (e.g., which may include various lenses 433, reflectors 434 and 436, etc.). Detector 410 is configured to determine the level of substrate 403 surface 405. Determining the level comprises constructing a height map for the substrate 403 surface 405 and / or other operations. In some embodiments, the level comprises height, topography, position, and / or tilt, for example.

[0087] Various optical components are configured to receive, transmit, reflect, focus, and / or perform other operations on radiation 424. These components may comprise any type of lens, reflector, conduit, wedge, splitter, and / or other optical component configured to allow system 400 to function as described. The various components may be positioned in any location and / or at any angle relative to each other that allows system 400 to function as described. This may include positioning at specific relativedistances between elements, specific angles between elements, etc. In some embodiments, the various components are positioned relative to each other in system 400 via structural members, clips, clamps, screws, nuts, bolts, adhesive, and / or other mechanical devices. In some embodiments, various ones of the components are movable relative to each other. Movement may be configured to adjust locations of corresponding spots of radiation, for example. In some embodiments, movement comprises tilting, translating or otherwise changing a distance between components. Other examples of movement are contemplated.

[0088] In some embodiments, movement may be controlled electronically by a processor, such as processor 411. Processor 411 may be included in a computing system CS (Fig. 9) and may operate based on computer or machine readable instructions (e.g., as described below related to Fig. 9). Electronic communication may occur by transmitting electronic signals between separate components, transmitting data between separate components of system 400, transmitting values between separate components, and / or other communication. The components of system 400 may communicate via wires or wirelessly via a network, such as the Internet or the Internet in combination with various other networks, like local area networks, cellular networks, or personal area networks, internal organizational networks, and / or other networks.

[0089] In some embodiments, one or more actuators (not shown in Fig. 4) may be coupled to and configured to move one or more components of system 400. The actuators may be coupled to one or components of system 400 by adhesive, clips, clamps, screws, a collar, and / or other mechanisms. The actuators may be configured to be controlled electronically. Individual actuators may be configured to convert an electrical signal into mechanical displacement. The mechanical displacement is configured to move a component of system 400. As an example, one or more of the actuators may be piezoelectric. One or more processors 411 may be configured to control the actuators. One or more processors 411 may be configured to individually control each of the one or more actuators.

[0090] Fig. 8 illustrates a level sensing method 800. In some embodiments, one or more operations of method 800 may be implemented in or by a level sensing system such as system 400 illustrated in Fig. 4 (along with Fig. 5 and Fig. 6), a computer system (e.g., as illustrated in Fig. 9 and described below), and / or in or by other systems, for example. In some embodiments, the level sensing system forms a portion of and / or is configured for us in an exposure apparatus. In some embodiments, the level sensing system forms a portion of and / or is configured for use in a lithography apparatus. In some embodiments, the level sensing system may be used in an exposure apparatus, a lithography apparatus, and / or similar apparatuses as part of method 800. The exposure apparatus and / or the lithography apparatus may be used for semiconductor manufacturing, for example. In some embodiments, the level sensing system is configured to determine the level of the substrate surface as part of semiconductor manufacturing operations performed by the exposure apparatus, the lithography apparatus, and / or other apparatuses for method 800. In some embodiments, method 800 comprises generating (operation 802)radiation configured to be projected onto a substrate surface (the substrate may be a semiconductor wafer, for example, a carrier wafer - with semiconductor chips in a molding material for example, and / or other substrates); separately patterning (operation 804) different portions of the radiation; projecting (operation 806) the different portions onto the substrate surface; and determining (operation 808) a level of the substrate surface.

[0091] The operations of method 800 are intended to be illustrative. In some embodiments, method 800 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 800 may include an additional operation comprising determining an adjustment for a semiconductor device manufacturing process. Additionally, the order in which the operations of method 800 are illustrated in Fig. 8 and described herein is not intended to be limiting.

[0092] In some embodiments, one or more portions of method 800 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 800 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 800 (e.g., see discussion related to Fig. 9 below).

[0093] At operation 802, a radiation source generates radiation configured to be projected onto the substrate surface. In some embodiments, operation 802 is performed by a radiation source the same as or similar to radiation source 402 shown in Fig. 4, and / or other components described above.

[0094] At operation 804, different portions of the radiation are separately patterned with a projection grating comprising sub-fields. In some embodiments, the sub-fields comprise different physical areas of the projection grating. In some embodiments, the sub-fields comprise different separate individual projection gratings which together comprise the projection grating. In some embodiments, the projection grating comprises two, three, four, or more sub-fields configured to separately pattern two, three, four, or more different portions of the radiation (though just two sub-fields and two corresponding portions of radiation are discussed as examples here). In some embodiments, operation 804 is performed by a projection grating the same as or similar to projection grating 420 shown in Fig. 4, and / or other components described above.

[0095] At operation 806, the different portions of the radiation are projected onto the substrate surface with projection optics. The shape of each of the different portions of the radiation directed onto the substrate surface may be linear, arcuate, and / or have other shapes. The projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiationtoward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement. The field optics may be configured such that the different portions of the radiation directed onto the surface of the substrate are incident simultaneously across an entire width of the substrate surface. The field optics may comprise at least one mirror associated with each of the portions of radiation. In some embodiments, the at least one mirror comprises two field splitting mirrors per different portion of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement. In some embodiments, the at least one mirror comprises folding mirrors associated with each of the different portions of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the parallel arrangement.

[0096] In some embodiments, a footprint of the different portions of the radiation on a primary mirror of the mirror relay covers less than half of an area of the primary mirror. The footprint may be less than about 70mm x 150mm, for example.

[0097] The colinear arrangement comprises the different portions of the radiation arranged end to end adjacent to each other to form a continuous line of radiation. The parallel arrangement comprises the different portions of the radiation arranged side by side, with a target amount of separation space between them. Directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement enhances a field of view of the level sensing system on the substrate surface. In some embodiments, an enhanced field of view has a dimension of about 150-300mm . In some embodiments, directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement at least doubles a size of the field of view of the level sensing system on the substrate surface compared to prior level sensing systems. Enhancing the field of view of the level sensing system reduces a total required measurement time for the substrate surface compared to prior level sensing systems and / or has other advantages. In some embodiments, operation 806 is performed by projection optics the same as or similar to projection optics 450 shown in Fig. 4, and / or other components described above.

[0098] At operation 808, a detector determines a level of the substrate surface based on the different portions of the radiation that have been reflected form the substrate surface and received by the detector. Determining the level comprises constructing a height map for the substrate surface and / or other operations. The level may comprise height, topography, position, tilt, and / or other characteristics. In some embodiments, operation 808 is performed by a detector the same as or similar to detector 410 shown in Fig. 4, and / or other components described above.

[0099] Fig. 9 is a diagram of an example computer system CS that may be used for one or more of the operations described herein. Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors similar toand / or the same as processor 411 shown in Fig. 4) 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.

[0100] 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.

[0101] In some embodiments, all or some of one or more operations described herein may be performed and / or otherwise controlled or caused 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 is not limited to any specific combination of hardware circuitry and software.

[0102] The term “computer readable medium” or “machine-readable medium” refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-transitory, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD,any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non- transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the operations described herein. Transitory computer- readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[0103] 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. Computer system CS can receive and convert the data to a signal. A detector coupled to bus BS can receive the data carried in the 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.

[0104] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0105] 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.

[0106] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CI. 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 CI. One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other non-volatile storage forlater execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0107] 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 level sensing system, the system comprising: a radiation source configured to generate radiation configured to be projected onto a substrate surface; a projection grating comprising sub-fields configured to separately pattern different portions of the radiation; projection optics configured to project the different portions of the radiation onto the substrate surface, wherein the projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement; and a detector configured to determine a level of the substrate surface based on the different portions of the radiation that have been reflected from the substrate surface and received by the detector.2. The system of clause 1, wherein the field optics are configured such that the different portions of the radiation directed onto the surface of the substrate are incident simultaneously across an entire width of the substrate surface.3. The system of any of the previous clauses, wherein the field optics comprise at least one mirror associated with each of the portions of radiation.4. The system of any of the previous clauses, wherein the at least one mirror comprises two field splitting mirrors per different portion of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement.5. The system of clause 3, wherein the at least one mirror comprises folding mirrors associated with each of the different portions of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the parallel arrangement.6. The system of any of the previous clauses, wherein the sub-fields comprise different physical areas of the projection grating.7. The system of any of the previous clauses, wherein the sub-fields comprise different separate individual projection gratings which together comprise the projection grating.8. The system of any of the previous clauses, wherein the projection grating comprises two, three, four, or more sub-fields configured to separately pattern two, three, four, or more different portions of the radiation.9. The system of any of the previous clauses, wherein the colinear arrangement comprises the different portions of the radiation arranged end to end adjacent to each other to form a continuous line of radiation.10. The system of any of the previous clauses, wherein the parallel arrangement comprises the different portions of the radiation arranged side by side, with a target amount of separation space between them.11. The system of any of the previous clauses, wherein directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement enhances a field of view of the level sensing system on the substrate surface.12. The system of any of the previous clauses, wherein an enhanced field of view has a dimension of about 150-300mm.13. The system of any of the previous clauses, wherein directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement at least doubles a size of the field of view of the level sensing system on the substrate surface compared to prior level sensing systems.14. The system of any of the previous clauses, wherein enhancing the field of view of the level sensing system reduces a total required measurement time for the substrate surface compared to prior level sensing systems.15. The system of any of the previous clauses, wherein a shape of each of the different portions of the radiation directed onto the substrate surface is linear.16. The system of any of the previous clauses, wherein a footprint of the different portions of the radiation on a primary mirror of the mirror relay covers less than half of an area of the primary mirror.17. The system of any of the previous clauses, wherein the footprint is less than about 70mm x 150mm.18. The system of any of the previous clauses, wherein determining the level comprises constructing a height map for the substrate surface.19. The system of any of the previous clauses, wherein the level comprises height, topography, position, and / or tilt.20. The system of any of the previous clauses, wherein the level sensing system forms a portion of and / or is configured for use in an exposure apparatus.21. The system of any of the previous clauses, wherein the substrate is a carrier wafer.22. The system of any of the previous clauses, wherein the carrier wafer comprises one or more semiconductor chips in a molding material.23. The system of any of the previous clauses, wherein the level sensing system forms a portion of and / or is configured for use in a lithography apparatus.24. The system of any of the previous clauses, wherein the level sensing system is configured to determine the level of the substrate surface as part of semiconductor manufacturing operations performed by the lithography apparatus.25. The system of any of the previous clauses, wherein the substrate is a semiconductor wafer.26. A level sensing method, the method comprising: generating, with a radiation source, radiation configured to be projected onto a substrate surface; separately patterning different portions of the radiation with a projection grating comprising sub-fields; projecting, with projection optics, the different portions of the radiation onto the substrate surface, wherein the projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement; and determining, with a detector, a level of the substrate surface based on the different portions of the radiation that have been reflected from the substrate surface and received by the detector.27. The method of clause 26, wherein the field optics are configured such that the different portions of the radiation directed onto the surface of the substrate are incident simultaneously across an entire width of the substrate surface.28. The method of any of the previous clauses, wherein the field optics comprise at least one mirror associated with each of the portions of radiation.29. The method of any of the previous clauses, wherein the at least one mirror comprises two field splitting mirrors per different portion of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement.30. The method of any of the previous clauses, wherein the at least one mirror comprises folding mirrors associated with each of the different portions of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the parallel arrangement.31. The method of any of the previous clauses, wherein the sub-fields comprise different physical areas of the projection grating.32. The method of any of the previous clauses, wherein the sub-fields comprise different separate individual projection gratings which together comprise the projection grating.33. The method of any of the previous clauses, wherein the projection grating comprises two, three, four, or more sub-fields configured to separately pattern two, three, four, or more different portions of the radiation.34. The method of any of the previous clauses, wherein the colinear arrangement comprises the different portions of the radiation arranged end to end adjacent to each other to form a continuous line of radiation.35. The method of any of the previous clauses, wherein the parallel arrangement comprises the different portions of the radiation arranged side by side, with a target amount of separation space between them.36. The method of any of the previous clauses, wherein directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement enhances a field of view of a level sensing system on the substrate surface.37. The method of clause 31, wherein an enhanced field of view has a dimension of about 150- 300mm.38. The method of any of the previous clauses, wherein directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement at least doubles a size of the field of view of the level sensing system on the substrate surface compared to prior level sensing systems.39. The method of any of the previous clauses, wherein enhancing the field of view of the level sensing system reduces a total required measurement time for the substrate surface compared to prior level sensing systems.40. The method of any of the previous clauses, wherein a shape of each of the different portions of the radiation directed onto the substrate surface is linear.41. The method of any of the previous clauses, wherein a footprint of the different portions of the radiation on a primary mirror of the mirror relay covers less than half of an area of the primary mirror.42. The method of any of the previous clauses, wherein the footprint is less than about 70mm x 150mm.43. The method of any of the previous clauses, wherein determining the level comprises constructing a height map for the substrate surface.44. The method of any of the previous clauses, wherein the level comprises height, topography, position, and / or tilt.45. The method of any of the previous clauses, further comprising use of the level sensing method in an exposure apparatus.46. The method of any of the previous clauses, wherein the substrate is a carrier wafer.47. The method of any of the previous clauses, wherein the carrier wafer comprises one or more semiconductor chips in a molding material.48. The method of any of the previous clauses, further comprising use of the level sensing method in a lithography apparatus.49. The method of any of the previous clauses, wherein the level of the substrate surface is determined as part of semiconductor manufacturing operations performed by the lithography apparatus.50. The method of any of the previous clauses, wherein the substrate is a semiconductor wafer.51. Use of a level sensing system in an exposure apparatus, the system comprising: a radiation source configured to generate radiation configured to be projected onto a substrate surface; a projection grating comprising sub-fields configured to separately pattern different portions of the radiation; projection optics configured to project the different portions of the radiation onto the substrate surface, wherein the projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement; and a detector configured to determine a level of the substrate surface based on the different portions of the radiation that have been reflected from the substrate surface and received by the detector.52. Use of a level sensing method in an exposure apparatus, the method comprising: generating, with a radiation source, radiation configured to be projected onto a substrate surface; separately patterning different portions of the radiation with a projection grating comprising subfields; projecting, with projection optics, the different portions of the radiation onto the substrate surface, wherein the projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement; and determining, with a detector, a level of the substrate surface based on the different portions of the radiation that have been reflected from the substrate surface and received by the detector.53. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; determining a level of a surface of the substrate by: generating radiation configured to be projected onto the surface of the substrate; separately patterning different portions of the radiation with a projection grating comprising sub-fields; projecting the different portions of the radiation onto the surface of the substrate with projection optics, wherein the projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the surface of the substrate in a colinear arrangement or a parallel arrangement; and determining, with a detector, the level of the surface of the substrate based on the different portions of the radiation that have been reflected from the surface of the substrate and received by the detector; directing patterning radiation from a radiation source of a lithography apparatus to transfer a pattern from a mask onto the photoresist layer at least in part based on the level determination; and removing a portion the photoresist layer to form the pattern over the substrate.

[0108] The concepts disclosed herein may be associated with any generic imaging system for imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths. Emerging technologies already in use includeEUV (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.

[0109] While the concepts disclosed herein may be used for imaging on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of lithographic imaging systems, e.g., those used for imaging on substrates other than silicon wafers. In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments.

[0110] 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 level sensing system, the system comprising: a radiation source configured to generate radiation configured to be projected onto a substrate surface; a projection grating comprising sub-fields configured to separately pattern different portions of the radiation; projection optics configured to project the different portions of the radiation onto the substrate surface, wherein the projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement; and a detector configured to determine a level of the substrate surface based on the different portions of the radiation that have been reflected from the substrate surface and received by the detector.

2. The system of claim 1, wherein the field optics are configured such that the different portions of the radiation directed onto the surface of the substrate are incident simultaneously across an entire width of the substrate surface.

3. The system of claim 1 or 2, wherein the field optics comprise at least one mirror associated with each of the portions of radiation, and wherein the at least one mirror comprises; two field splitting mirrors per different portion of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement, or folding mirrors associated with each of the different portions of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the parallel arrangement.

4. The system of any of claims 1-3, wherein the projection grating comprises two, three, four, or more sub-fields configured to separately pattern two, three, four, or more different portions of the radiation.

5. The system of any of claims 1-4, wherein the colinear arrangement comprises the different portions of the radiation arranged end to end adjacent to each other to form a continuous line of radiation, wherein the parallel arrangement comprises the different portions of the radiation arranged side by side, with a target amount of separation space between them, wherein directing the different portionsof the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement enhances a field of view of the level sensing system on the substrate surface, and wherein an enhanced field of view has a dimension of about 150-300mm.

6. The system of any of claims 1-5, wherein determining the level comprises constructing a height map for the substrate surface.

7. The system of any of claims 1-6, wherein the level sensing system forms a portion of and / or is configured for use in a lithography apparatus.

8. The system of claim 7, wherein the level sensing system is configured to determine the level of the substrate surface as part of semiconductor manufacturing operations performed by the lithography apparatus.

9. The system of claims 7 or 8, wherein the substrate is a semiconductor wafer.

10. A level sensing method, the method comprising: generating, with a radiation source, radiation configured to be projected onto a substrate surface; separately patterning different portions of the radiation with a projection grating comprising sub-fields; projecting, with projection optics, the different portions of the radiation onto the substrate surface, wherein the projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement; and determining, with a detector, a level of the substrate surface based on the different portions of the radiation that have been reflected from the substrate surface and received by the detector.

11. The method of claim 10, wherein the field optics are configured such that the different portions of the radiation directed onto the surface of the substrate are incident simultaneously across an entire width of the substrate surface.

12. The method of claim 10 or 11, wherein the field optics comprise at least one mirror associated with each of the portions of radiation, and wherein the at least one mirror comprises;two field splitting mirrors per different portion of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement, or folding mirrors associated with each of the different portions of the radiation configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in the parallel arrangement.

13. The method of any of claims 10-12, wherein the projection grating comprises two, three, four, or more sub-fields configured to separately pattern two, three, four, or more different portions of the radiation.

14. The method of any of claims 10-12, wherein the colinear arrangement comprises the different portions of the radiation arranged end to end adjacent to each other to form a continuous line of radiation, wherein the parallel arrangement comprises the different portions of the radiation arranged side by side, with a target amount of separation space between them, wherein directing the different portions of the radiation from the mirror relay onto the substrate surface in the colinear arrangement or the parallel arrangement enhances a field of view of a level sensing system on the substrate surface, and wherein an enhanced field of view has a dimension of about 150-300mm.

15. Use of a level sensing system in an exposure apparatus, the system comprising: a radiation source configured to generate radiation configured to be projected onto a substrate surface; a projection grating comprising sub-fields configured to separately pattern different portions of the radiation; projection optics configured to project the different portions of the radiation onto the substrate surface, wherein the projection optics comprise a mirror relay, at least one folding mirror configured to direct the different portions of the radiation toward the mirror relay, and field optics configured to direct the different portions of the radiation from the mirror relay onto the substrate surface in a colinear arrangement or a parallel arrangement; and a detector configured to determine a level of the substrate surface based on the different portions of the radiation that have been reflected from the substrate surface and received by the detector.

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