Optical measurement system

Abstract

An optical measurement system for measuring a topology of a surface of a substrate is disclosed. The optical measurement system can include a light projector configured to project a light beam to the surface of the substrate. A light detector can be configured to receive the light beam from the light projector that has been reflected from the surface. There can be a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement. The first field of view and the second field of view can be offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

Description

OPTICAL MEASUREMENT SYSTEMCROSS-REFERENCE TO RELATED APPLICATION

[0001] The application claims priority of US provisional application number 63 / 699,437 which was filed on 26 September, 2024, and of US provisional application number 63 / 748,741 which was filed on 23 January, 2025, which are incorporated herein in their entirety by reference.TECHNICAL FIELD

[0002] The present disclosure relates to an optical design of an optical measurement system with improved field of view (FOV) such as when used in conjunction with measuring surface features of a semiconductor substrate.BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as "design layout" or "design") of a patterning device (e.g., a mask) onto a layer of radiation -sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually been reduced while the amount of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as 'Moore's law'. To keep up with Moore's law the semiconductor industry is chasing technologies that enable to create increasingly smaller features. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within a range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] Products that may be produced by the above methods (e.g., wafers used with the production of computer chip components) often require measurements of surface features to quantify the quality of production or to find unacceptable errors or deviations. Optical scanning of the surface of such wafers to determine height can then be a part of the production process. However, some scanning systems can have limited fields of view which can require multiple scans and thereby slow production throughput. Accordingly, there is a need for scanning systems with improved fields of view such that overall scanning time can be reduced and throughput increased.SUMMARY

[0006] An optical measurement system for measuring a topology of a surface of a substrate is disclosed. The optical measurement system can include a light projector configured to project a light beam to the surface of the substrate. A light detector can be configured to receive the light beam from the light projector that has been reflected from the surface. There can be a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement. The first field of view and the second field of view can be offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

[0007] In some embodiments, the first mirror relay can be adjacent the second mirror relay in the longitudinal direction. The first concave mirror arrangement and the second concave mirror arrangement can be abutting in the longitudinal direction. The first concave mirror arrangement can be a single mirror such as a rectangular mirror. The single mirror can be concave in both the longitudinal direction and a lateral direction. The first concave mirror arrangement can comprise two mirrors.

[0008] In some embodiments, the first field of view and the second field of view can be the same and also have a separation equal to the first field of view. The optical measurement system can be configured to scan the substrate by including a longitudinal step equal to the first field of view that fills in the separation. The first mirror relay and the second mirror relay can have a gap that contributes to the separation of the first field of view and the second field of view.

[0009] In some embodiments, the second mirror relay can have a lateral offset and a longitudinal offset from the first mirror relay. The first concave mirror arrangement can include first concave mirrors disposed in a lateral direction and the second concave mirror arrangement comprising second concave mirrors interleaved in the lateral direction with the plurality of first concave mirrors. The first mirror relays can be separated by one or more gaps in the longitudinal direction, and the second mirror relays can be separated by one or more gaps in the longitudinal direction. Longitudinal offsets of the one or more second mirror relays can cover the one or more gaps. The first mirror relays can have first fields of view with one or more gaps and the second mirror relay has a second field of view that fills at least one of the gaps. A fold mirror can be between the first mirror relay and the substrate, the fold mirror acting to reduce angles of reflection of light reflecting between the first convex mirror arrangement and the substrate.

[0010] In some embodiments, the first mirror relay can provide light to the substrate at a first angle of incidence and the second mirror relay provides light to the substrate at a second angle of incidence, the same as the first angle of incidence, the same angles of incidence causing the first field of view and the second field of view to be offset in a lateral direction. Also, the light projector can include a first light projector and a second light projector, and a path length for the first mirror relay from the first lightprojector to the first field of view is the same as for the second mirror relay from the second light projector to the second field of view.

[0011] In some embodiments, the first mirror relay can provide light to the substrate at a first angle of incidence and the second mirror relay provides light to the substrate a second angle of incidence, different than the first angle of incidence, the different angles of incidence causing the first field of view and the second field of view to align in a lateral direction.

[0012] In some embodiments, the first mirror relay can include a first tilted mirror to direct the light beam to the first field of view and the second mirror relay can include a second tilted mirror to direct the light beam to the second field of view. The first tilted mirror and the second tilted mirror can at least partially overlap in the horizontal direction and in a vertical direction to result in at least partially overlapping fields of view. In some cases, the first field of view and the second field of view can be aligned in the horizontal direction. Also, some embodiments can include a third mirror relay with a third tilted mirror to direct the light beam to the third field of view. The first tilted mirror and the third tilted mirror can at least partially overlap in the horizontal direction and in the vertical direction to result in at least partially overlapping fields of view. As such, in various embodiments, the first field of view, the second field of view, and the third field of view can be aligned in the horizontal direction.

[0013] In some embodiments, the optical measurement system can further include a processor configured to perform operations comprising: performing, on a calibration substrate, a first calibration of the optical measurement system for the first angle of incidence to the first field of view; performing, on the calibration substrate, a second calibration of the optical measurement system for the second angle of incidence to the second field of view; and determining a height map of the substrate utilizing the first calibration for the first field of view and the second calibration for the second field of view.

[0014] In some embodiments, the optical measurement system can include a processor configured to perform operations comprising: performing, on a calibration substrate, a first calibration of the optical measurement system for the first angle of incidence to the first field of view at a location on the substrate; generating a calibration map based on the first calibration; and determining a height map of the substrate by: applying the calibration map to measurements of the first field of view at the first angle of incidence; and applying the calibration map and a known difference between the first angle of incidence and the second angle of incidence to measurements of the second field of view at the second angle of incidence.

[0015] In some embodiments, the optical measurement system can include a processor configured to perform operations comprising: determining a height process dependence based on a static intrafield fingerprint measured by the first mirror relay and by the second mirror relay.

[0016] In some embodiments, the optical measurement system can include a processor configured to perform operations comprising: determining a height process dependence based on a varying intrafield fingerprint measured by the first mirror relay and by the second mirror relay, wherein the varyingintrafield fingerprint is measured at locations on the substrate that are equivalent to where the measurements from the first mirror relay were obtained.

[0017] In an interrelated aspect, a level sensor can include a projection unit arranged to direct a beam of radiation received from a light projector to a surface of a substrate, comprising a projection grating having a period, the projection grating configured to provide a patterned measurement beam having a periodically varying intensity distribution in a first direction having the period; a detection unit arranged to receive the beam of radiation reflected at the surface of the substrate, one or more detectors; a processing unit configured to determine a position of the surface of the substrate based on the beam of radiation received by the one or more detectors. The projection unit and / or detection unit can include a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

[0018] In an interrelated aspect, a method of determining a height level of a substrate can include projecting a patterned measurement beam having a periodically varying intensity distribution in a first direction having a period onto the substrate; receiving a reflected patterned measurement beam after reflection on the substrate on to a detector; determining the height level of the substrate based on one or more signals from the detector, where at least one of projecting the patterned measurement beam and receiving the reflected patterned measurement beam is by an optical measurement system for measuring a topology of a surface of the substrate. The optical measurement system can include a light projector configured to project a light beam to the surface of the substrate; a light detector configured to receive the light beam from the light projector that has been reflected from the surface; and a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

[0019] In some embodiments, the substrate and the patterned measurement beam can be moved relative to each other to make a scanning movement of the patterned measurement beam over the surface.

[0020] In an interrelated aspect, a semiconductor device manufacturing method can include receiving a substrate with a photoresist layer; directing radiation from radiation source to transfer a pattern from a mask onto the photoresist layer; removing a portion of the photoresist layer to form the pattern over the substrate; and performing metrology on the substrate with an optical measurement system. The optical measurement system can include a light projector configured to project a light beam to the surface of the substrate; a light detector configured to receive the light beam from the light projector that has been reflected from the surface; a first mirror relay having a first field of view and comprisinga first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, show certain aspects of the subject matter disclosed herein and, together with the description, help explain some of the principles associated with the disclosed implementations. In the drawings,

[0022] Figure 1 is a schematic diagram illustrating an exemplary lithographic apparatus, according to an embodiment of the present disclosure.

[0023] Figure 2 is a schematic diagram illustrating an exemplary level sensor, according to an embodiment of the present disclosure.

[0024] Figure 3A is a schematic diagram illustrating a side view of mirror relays in an exemplary optical measurement system, according to an embodiment of the present disclosure.

[0025] Figure 3B is a diagram depicting an improvement in measuring throughput utilizing offset mirror relays, according to an embodiment of the present disclosure.

[0026] Figure 4 is a schematic diagram illustrating offset mirror relays in an optical measurement system, according to an embodiment of the present disclosure.

[0027] Figure 5 is a schematic diagram illustrating an embodiment of offset mirrors with gaps between fields of view, according to an embodiment of the present disclosure.

[0028] Figure 6 is a schematic diagram illustrating an example optical measurement system with interlaced mirrors, according to an embodiment of the present disclosure.

[0029] Figures 7A-7F depict example configurations of optical measurement systems, according to embodiments of the present disclosure.

[0030] Figure 7G depicts a side view of optical measurement system showing tilted mirrors that can direct light to the substrate, according to embodiments of the present disclosure.

[0031] Figure 7H depicts a rear view of the optical measurement system shown in Figure 7G, according to embodiments of the present disclosure.

[0032] Figure 71 depicts an example of the resultant overlapping fields of view from the optical measurement system of Figures 7G and 7H, according to embodiments of the present disclosure.

[0033] Figure 8A is a schematic diagram illustrating an example optical measurement system with interlaced mirrors and same angles of incidence to the substrate, according to an embodiment of the present disclosure.

[0034] Figure 8B is a schematic diagram of mirror relays for a compact optical measurement system, according to an embodiment of the present disclosure.

[0035] Figure 8C is a schematic diagram of the mirror relays of Figure 8B combined to have the same angle of incidence to a wafer, according to an embodiment of the present disclosure.

[0036] Figure 9 is a process flow diagram illustrating an example method of determining a height map, according to an embodiment of the present disclosure.

[0037] Figure 10 is a process flow diagram illustrating an example method of determining a height map utilizing measurements at one angle of incidence, according to an embodiment of the present disclosure.

[0038] Figure 11 is a diagram illustrating an example height map of a substrate comprised of a global shape and an intrafield fingerprint, according to an embodiment of the present disclosure.

[0039] Figure 12 is a block diagram of an example computer system, according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0040] Figure 1 schematically depicts a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation or EUV radiation), a mask support (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 MA in accordance with certain parameters, a substrate support (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support in accordance with certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0041] In operation, the illumination system IL receives a radiation beam from a radiation source SO, e.g., via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, electromagnetic, and / or other types of optical components, or any combination thereof, for directing, shaping, and / or controlling radiation. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross section at a plane of the patterning device MA.

[0042] The term “projection system” PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, and / or electromagnetic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and / or for other factors such as the use of an immersion liquid or the use of a vacuum. Anyuse of the term “projection lens” herein may be considered as synonymous with the more general term “projection system” PS.

[0043] The lithographic apparatus LA may be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fdl a space between the projection system PS and the substrate W - which is also referred to as immersion lithography. More information on immersion techniques is given in U.S. 6,952,253, which is incorporated herein by reference.

[0044] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also named “dual stage”). In such “multiple stage” machine, the substrate supports WT may be used in parallel, and / or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate support WT while another substrate W on the other substrate support WT is being used for exposing a pattern on the other substrate W.

[0045] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measurement stage. The measurement stage is arranged to hold a sensor. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The measurement stage may move beneath the projection system PS when the substrate support WT is away from the projection system PS.

[0046] In operation, the radiation beam B may be incident on the patterning device, e.g., mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which may focus the beam onto a target portion C of the substrate W or onto a sensor arranged at a stage. With the aid of the second positioner PW and a position measurement system PMS, the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (which is not explicitly depicted in Figure 1) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B . Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks Pl, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions. Substrate alignment marks Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C. Substrate alignment marks Pl, P2 may also be arranged in the target portion C area as in-die marks. These in -die marks may also be used as metrology marks, for example, for overlay measurements.

[0047] To clarify the present disclosure, in some instances a Cartesian coordinate system may be used. The Cartesian coordinate system has three axis, i.e., an X-axis, a Y-axis and a Z-axis. Each of the three axis is orthogonal to the other two axis. A rotation around the x-axis is referred to as an Rx-rotation. A rotation around the Y-axis is referred to as an Ry-rotation. A rotation around the Z-axis is referred to asan Rz -rotation. The X-axis and the Y-axis define a horizontal plane, whereas the Z-axis is in a vertical direction. The Cartesian coordinate system is not limiting the disclosure and is used for clarification only. Instead, another coordinate system, such as a cylindrical or spherical coordinate system, may be used. The orientation of the Cartesian coordinate system may be different, for example, such that the Z-axis has a component along the horizontal plane.

[0048] A topography measurement system, level sensor or height sensor, and which may be integrated in the lithographic apparatus, is arranged to measure a topography of a top surface of a substrate (or wafer). 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 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.

[0049] Figure 2 illustrates an example of a level or height sensor LS. In this example, the level sensor LS comprises an optical measurement 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, which is imparted by a 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 W or from a layer at the substrate W.

[0050] The projection grating PGR is a grating comprising, for example, a periodic structure resulting in a beam of radiation BE1 having a periodically varying spatial intensity. The beam of radiation BE1 with the periodically varying spatial intensity is directed towards a measurement location MLO on a substrate W having an angle of incidence AOI 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.

[0051] In order to determine the height level at the measurement location MLO, the level sensor LS further comprises a detection unit LSD comprising a diffraction grating DGR, a detector DET and aprocessing unit (not shown) for processing an output signal of the detector DET. The diffraction 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.

[0052] 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, for example, a periodicity that depends, amongst others, on the design of the projection grating PGR and the (oblique) angle of incidence AOI.

[0053] 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 diffraction grating DGR.

[0054] In an embodiment, the diffraction grating DGR may be omitted, and the detector DET may be placed at the position where the diffraction grating DGR is located. Such a configuration provides a more direct detection of the image of the projection grating PGR.

[0055] 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 (e.g., measurements at several measurement locations) or spots covering a larger measurement range. As used herein, the term “field of view” can either be a two-dimensional area, or it can refer to the linear width of an area swept out by scanning the width in a direction orthogonal to the width (e.g., a scan direction of a wafer). In the context of measuring surface features, such as height, increasing the FOV can include increasing the number of measurement spots, so that an extended FOV can project the multiple measurement spots onto the wafer and the mirror relay can then also return the reflected light beams to a detector.

[0056] Various height sensors of a general type are disclosed for example in U.S. 7,265,364 and U.S. 7,646,471, both incorporated by reference. A height sensor using UV radiation instead of visible or infrared radiation is disclosed in U.S. 2010 / 233600 Al, incorporated by reference. In WO 2016 / 102127 A 1 , 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 diffraction grating. The combinations and sub-combinations of the elements disclosed herein constitute separate embodiments and are provided as examples only. Also, the descriptions are intended to be illustrative, not limiting.

[0057] Figure 3A is a schematic diagram illustrating a side view of mirror relays in an exemplary optical measurement system. Figure 3B is a diagram depicting an improvement in measuring throughput utilizing offset mirror relays.

[0058] To provide the desired field of view, optical measurement system 300 shown in Figure 3A can include multiple mirror relays, each having their own field of view (as shown in Figure 3B). By utilizingthe combined fields of view as disclosed in various embodiments herein, the total field of view of the optical measurement system 300 can be increased, which can improve the scanning throughput of the measurement system. The instant application builds on U.S. provisional patent application 63 / 699,437, filed September 26, 2024 entitled “OPTICAL MEASUREMENT SYSTEM” to clarify features of that previous disclosure and add additional embodiments (e.g., Figures 8B and 8C).

[0059] Figure 3A is a more detailed illustration of a system similar to that shown in Figure 2, in particular showing examples of concave and convex mirrors referred to in various embodiments of the present disclosure. Light can be emitted by radiation source LSO, and directed via light guide LG (e.g., fiber optics) to illumination optics IO that focuses the light to projection grating PGR, which acts as the object in the optical system. Light from the projection grating PGR can be directed to the surface S of substrate (e.g., wafer) W by the example level sensor assembly 310. Light reflecting from surface S can then be received at diffraction grating DGR, and provided to detector DET. In this example, detector DET can include optics to direct differing diffraction orders to detector modules that can include photodiodes or the like to convert the received light to a measurable electrical signal. In some embodiments, first mirror relay 320 can be protected by window 380 that can let light pass through but act to prevent pressure waves from the printing area (around wafer W) from affecting the mirrors in first mirror relay 320 or other components of the system.

[0060] As will be discussed in numerous embodiments herein, optical measurement system 300 can be used for measuring a topology of surface S of a substrate W, and can include a light projector (e.g., radiation source LSO) that can be configured to project a light beam (e.g., beam of radiation LSB) to surface S of substrate W. Light detector (e.g., detector DET) can be configured to receive the light beam from light projector LSO that has been reflected from surface S. For directing light to surface S and receiving light reflected from surface S, the example level sensor assembly 310 in Figure 3 A can include first mirror relay 320 having a first field of view 322 (shown in Fig. 3B). First mirror relay 320 can include first concave mirror arrangement 324 and first convex mirror arrangement 326. The term “mirror arrangement” can include a single mirror as depicted in Fig. 3A, but in other embodiments (e.g., as shown in Figs. 5, 6, and 8), some mirror arrangements can include multiple mirrors. Accordingly, the term “mirror arrangement” refers to one (or more) mirrors.

[0061] As there can be multiple mirror relays combining to improve the total field of view, there can be a second mirror relay (not visible in Figure 3A) having a second field of view 332 (depicted in Figure 3b). The second mirror relay can include a second concave mirror arrangement and a second convex mirror arrangement similar to first mirror relay 320.

[0062] As shown in Figure 3B, first field of view 322 and second field of view 332 can be offset in a longitudinal direction to form an expanded field of view in the longitudinal direction. Illustrating one improvement of such a design, when the total field of view is smaller, it may require raster scanning of surface S, as shown in the left diagram of Figure 3B. By having multiple mirror relays offset in thelongitudinal direction (here defined as perpendicular to the scan primary direction) the expanded field of view can be increased sufficiently to reduce the number of scans, including some embodiments only needing a single scan as shown by the right diagram in Figure 3B.

[0063] In various embodiments, there can also be one or more fold mirrors (e.g., first fold mirror 370 and second fold mirror 372). The disclosed fold mirrors are usually (though not necessarily) planar mirrors. Such fold mirrors can be utilized to direct light to the mirror relay and / or to substrate W. Fold mirrors can aid in allowing the mirror relays to be more compact such as by providing a small reflection angle between the concave and convex mirror arrangements. Some fold mirrors (e.g., fold mirror 372) can also be utilized to direct light at a desired angle of incidence (AOI) to the substrate W. As used herein and as shown in the example of Figure 3A, the AOI is from a line normal to the surface in question. While the example of Figure 3A shows two fold mirrors 370 and 372, in other embodiments there can be additional fold mirrors as needed to provide a desired AOI or to achieve a particular mirror configuration for the system (e.g., based on volume constraints, etc.). Figures 7A-F show examples of other arrangements that vary in part due to differing fold mirror configurations.

[0064] While the depicted examples show and describe the mirror arrangements usually being concave and / or convex (e.g., to provide a certain focusing geometry), it is not essential that in all embodiments the mirror arrangements have such curvatures. Instead, the present disclosure contemplates that the disclosed concave / convex mirrors can, in some embodiments, be planar mirrors. The desired focusing can then be provided via lenses, angling certain mirrors, or use of other optical elements outside of the mirror arrangements. Accordingly, mirror arrangements with planar instead of convex / concave mirrors are considered within the scope of the present disclosure and as such can be claimed as other examples of the inventive features provided herein. Similarly, in some embodiments, the mirrors can be aspheric or freeform in design (e.g., having varying curvatures rather than being on a planar or spherical surface). Such aspheric designs can have curvatures that may reduce aberrations.

[0065] Figure 4 is a schematic diagram illustrating offset mirror relays in an optical measurement system. Some embodiments of optical measurement system 400 can include mirror relays that are adjacent to each other in the longitudinal direction to provide a combined and expanded longitudinal field of view. For example, first mirror relay 420 can be adjacent the second mirror relay 430 in the longitudinal direction. In this context, the term “adjacent” can include touching / abutting but may also include being in close proximity with a small gap (e.g., 1-10 mm., 1-10 cm.). In some more particular embodiments, first concave mirror arrangement 424 and second concave mirror arrangement 434 can be abutting in the longitudinal direction. This is the configuration depicted in Figure 4. While Figure 4 also depicts a third mirror relay, there can be any number of mirror relays to extend the longitudinal field of view. Also, as with other embodiments, the corresponding mirrors on the other side (after reflecting off substrate W) can be similarly constructed.

[0066] In some cases, it can be easier to construct an optical measurement system using a reduced number of larger mirrors. Figure 4 depicts an embodiment where first concave mirror arrangement 424 can be a single mirror. This can be in contrast to other embodiments (e.g., Figure 5) where first concave mirror arrangement 424 can comprise two or more mirrors. Also, in some embodiments, the single mirror can be a rectangular mirror that can be square as illustrated or have different longitudinal and lateral dimensions. As also shown, in some embodiments first concave mirror arrangement 424 can have a single mirror concave in both the longitudinal direction and a lateral direction (e.g., focusing on first convex mirror arrangement 426). In other embodiments where first concave mirror arrangement 424 comprises multiple mirrors, two or more of the multiple mirrors can be concave mirrors. The embodiment of Figure 4 also shows a number of fold mirrors 470.

[0067] Figure 5 is a schematic diagram illustrating an embodiment of offset mirrors with gaps between fields of view. The present disclosure provides numerous embodiments that allow for an expanded field-of-view when measuring a surface. While the adjacent mirror relays can have fields -of-view adjacent each other (e.g., as in Figure 3B), some embodiments such as optical measurement system 500 can have first field of view 522 and second field of view 532 the same and also have a separation 542 equal to first field of view 522. Accordingly, some embodiments can have optical measurement system 500 be configured to scan substrate W by including a longitudinal step equal to first field of view 522 that fills in the separation. In operation then, with substrate W moved that longitudinal step in a raster scan, such a step could then fill in separation 542 in the fields-of-view between mirror relays in order to fully cover the expanded field-of-view. In the embodiment shown in Figure 5, first mirror relay 520 and second mirror relay 530 have a gap 552 that contributes to the separation of the first field of view and the second field of view. Other embodiments can have first mirror relay 520 and second mirror relay 530 be abutting similar to that shown in Figure 4, but still have separation 542 in the fields-of- view.

[0068] Figure 6 is a schematic diagram illustrating an example optical measurement system with interlaced mirrors. Optical measurement system 600 can also have an “interlaced” construction where, for example, second mirror relay 630 can have both a lateral offset and a longitudinal offset from first mirror relay 620. As shown, first concave mirror arrangement 624 can include a number of first concave mirrors disposed in a lateral direction and the second concave mirror arrangement 634 comprising a number of second concave mirrors interleaved in the lateral direction with the first concave mirrors. While the interleaved mirrors may be abutting in the lateral and / or longitudinal direction, in some embodiments such as in Figure 5, there can be multiple first mirror relays 620 separated by one or more gaps 652 in the longitudinal direction, and multiple second mirror relays 630 also separated by one or more gaps 654 in the longitudinal direction. In the depicted example, the longitudinal offsets of the second mirror relays 630 can cover the gaps between first mirror relays 620. Regarding gaps in the fields-of-view at substrate W, first mirror relays 620 can have first fields of view 622 with one or moregaps 642, second mirror relay 630 can provide a second field of view 632 that can fill at least one of the gaps. In the example of Figure 6, similar mirror relays (620, 630) are shown except that one or more of the mirrors can be adjusted to cause the first field of view 622 to be not offset in the lateral direction relative to second field of view 632. Thus, in some embodiments such as that of Figure 6, the AOI for mirror relay 620 can be different (e.g., smaller) than that for mirror relay 630.

[0069] As shown by the inset in Figure 6, there can be one or more fold mirrors to direct light from a mirror relay to the substrate given the optical measurement system being in a particular configuration, to achieve a particular AOI at the substrate, etc. In the example of Figure 6, there can be a first fold mirror (not shown) directing light to a mirror relay and a second fold mirror 672 between the mirror relay and the substrate. In this particular example, third fold mirror 674 and fourth fold mirror 676 are included for a particular technical effect. This three-fold mirror (672, 674, 676) embodiment reduces errors due to the height process dependence (HPD) performance of the system.

[0070] As discussed in U.S. 7,265,364, level sensors used for a lithographic projection apparatus may be subject to process dependency. Process dependency is a form of error in which level sensor measurements provide differing results depending on how a substrate being measured has previously been processed. For example, a level sensor may provide a particular height measurement for a wafer including a silicon substrate coated with a single layer of resist and may provide a different height measurement for a wafer including a silicon substrate coated with several layers of resist, even if both wafers are at the same actual height. One error caused by process dependency is referred to as processdependent apparent surface depression and is understood to be caused by an optical effect known as the Goos-Haenchen shift. The Goos-Haenchen shift is a lateral translation of light along a reflecting surface (in this case the resist) during reflection. The shift is dependent upon the material and layer structure of the substrate. As a result of process dependency, a substrate may not be correctly located in the focal plane of the projection lens. When this occurs, the resolution of a pattern imaged onto the substrate may be compromised.

[0071] To address such height process dependencies, various embodiments of the present disclosure can implement a large AOI at the substrate W (e.g., between 78 degrees to 84 degrees). Also, it can be desired to have a small AOI on the fold mirrors that are closer to substrate W to reduce the contribution of mirror coating retardance on the HPD. A larger AOI on fold mirror can result in a larger sensitivity of coating retardance gradient, leading to a higher HPD. Accordingly, in some embodiments, fold mirror(s) 672, 674, 676 between first mirror relay 620 and the substrate can act to reduce angles of reflection of light reflecting between the first convex mirror arrangement 626 and substrate W. In some embodiments, the AOI of those fold mirrors can be configured to be less than 40 degrees.

[0072] Figures 7A-7F depict example configurations of optical measurement systems. The depicted examples illustrate how depending on space constraints or other desired factors, mirror configurationsconsistent with the disclosed embodiments can be set up to position the mirror relays to be at different locations, have different orientations, and have different form factors (e.g., volume).

[0073] Figures 7G-I depict an example configuration of an optical measurement system having tilted mirrors that overlap vertically and horizontally to result in a stitched imaging region. Figure 7G depicts a side view of optical measurement system 700 showing tilted mirrors that are arranged at a non -zero angle with respect to the surface of the substrate W so as to direct light beam to substrate W. In this embodiment, first mirror relay (not shown except for first tilted mirror 710) can include first tilted mirror 710 to direct the light beam to first field of view 712. Similarly, second mirror relay can include second tilted mirror 720 to direct the light beam to second field of view 722. As shown, first tilted mirror 710 and second tilted mirror 720 can at least partially overlap in the horizontal direction (into the page) and in a vertical direction to result in at least partially overlapping fields of view. Also shown is third tilted mirror 730, described further below. Due the offsets between the tilted mirrors, light reaching substrate W can be at different angles of incidence. For example, light from first tilted mirror 710 can have AOI1, light from second tilted mirror 720 can have a steeper / smaller AOI2.

[0074] Figure 7H depicts a rear view of the optical measurement system shown in Figure 7G. This view better illustrates the horizontal overlapping between the tilted mirrors. Any number of additional tilted mirrors can be added to the optical measurement system. In the example shown, there can also be a third mirror relay with third tilted mirror 730 to direct the light beam to third field of view 732. As shown in Figure 7H, first tilted mirror 710 and third tilted mirror 730 can also at least partially overlap in the horizontal direction and in the vertical direction to result in at the least partially overlapping fields of view. Such overlapping can be used to reduce the space taken up by the mirrors, resulting in a more compact system.

[0075] Figure 71 depicts an example of the resultant overlapping fields of view from the optical measurement system of Figures 7G and 7H. This three-mirror configuration can have first field of view 712, second field of view 722, and third field of view 732, aligned in the horizontal direction, further extending the combined field of view. While the fields of view are shown as overlapping, the amount of overlap can vary with the implementation, including being only abutting.

[0076] Figure 8A is a schematic diagram illustrating an example optical measurement system with interlaced mirrors and same angles of incidence to the substrate. In various embodiments, the AOIs between mirror relays can be the same or can be different. In the example of Figure 8A and its inset showing a side view of the light between substrate W and a fold mirror, first mirror relay 820 provides light 824 to substrate W at a first angle of incidence AOI-1 and second mirror relay 830 provides light 834 to substrate W a second angle of incidence AOI-2, which is the same as the first angle of incidence. The two mirror relays are depicted as having positional differences in both a lateral direction and a longitudinal direction. The positional difference(s) (e.g., lateral and / or longitudinal) between first mirror relay 820 and second mirror relay 830 can cause first field of view 822 and second field of view832 to be offset in a lateral and / or longitudinal direction. This can also be seen by noting that in Figure 8A the path length from the first mirror relay 820 to substrate W is the same as the path length from second mirror relay 830 to substrate W, and so their positional difference translates to a similar corresponding lateral offset at substrate W. In contrast, in other embodiments such as the embodiment of Figure 6, first mirror relay 620 provides light to substrate W at a first angle of incidence and the second mirror relay 630 provides light to substrate W at a second angle of incidence, which is different than the first angle of incidence. There, the different angles of incidence can cause first field of view 622 and second field of view 632 to align in a lateral direction.

[0077] A third example embodiment can be where the mirror relays have both different angles of incidence and offset fields of view. For example, in a configuration where a 78 degree AOI and an 82 degree AOI result in non-offset fields of view, the same configuration with, for example, a 76 degree AOI and an 84 degree AOI would introduce an offset field of view. Such lateral offsets can be useful in some applications of determining a height map of substrate W.

[0078] Figure 8B is a schematic diagram of mirror relays for a compact optical measurement system. First mirror relay 850A and second mirror relay 850B can be combined to provide a compact optical measurement system design with light incident to wafer W having the same angle of incidence from both relays. Mirror relay 850A can include first concave mirror arrangement 850_MlA, second convex mirror arrangement 850_M2A, and second concave mirror arrangement 850_M3A. Mirror relay 850B is a mirrored version of mirror relay 850A, with first concave mirror arrangement 850_MlB, second convex mirror arrangement 850_M2B, and second concave mirror arrangement 850_M3B. Figure 8C also shows an example of the staggered pattern of fields of view that can be made on wafer W with numerous mirror relays.

[0079] Figure 8C is a schematic diagram of the mirror relays of Figure 8B combined to have the same angle of incidence to a wafer. In this embodiment, the light projector can include first light projector 850 PGA and second light projector 850 PGB. Also, the path length for first mirror relay 850A from first light projector 850_PGA to first field of view 870 A can be the same as for the second mirror relay 850B from second light projector 850 PGB to second field of view 870B. As shown in this example, there can be a single fold mirror 860 that directs light from first light projector 850_PGA and second light projector 850 PGB to the mirror. The placement and angle of fold mirror 860 and the positions of first light projector 850_PGA and second light projector 850_PGB can be selected to preserve the equal path lengths of the two mirror relays. Unlike the embodiment of Figure 8 A, here the respective first concave mirrors (850_MlA, 850_MlB) are not on approximately the same plane. The same is true for first convex mirrors (850_M2A, 850_M2B) and second concave mirrors (850_M3A, 850_M3B). This arrangement whereby the first concave mirrors (850_MlA, 850_MlB), second concave mirrors (850_M3A, 850_M3B) and first convex mirrors (850_M2A, 850_M2B) are not on approximately the same plane in combined relays advantageously provides a compact opticalmeasurement system. Furthermore, in the example of Figure 8C the mirror relays 850A and 850B are offset laterally, i.e. in the x-y plane. Figure 8C therefore shows an example of the staggered pattern of fields of view that can be made on wafer W with numerous mirror relays when arranged with a lateral offset. Similar to the examples of Figure 3A, the optical arrangement can be duplicated and mirrored to the other side of wafer W to allow the reflected light to be received at diffraction gratings.

[0080] In some embodiments, the mirror relays 850A and 850B may not be offset laterally. In such embodiments, the fields of view that can be made on wafer W with numerous mirror relays can be projected adjacently, i.e. without a staggered pattern. The mirror relays of Figure 8B can therefore be arranged such that the fields of view on the wafer present a continuous, enlarged field of view while still having the same angle of incidence to the wafer.

[0081] In some embodiments, the mirror relays 850A and 850B may be offset such that the fields of view on the wafer are staggered and at least partially overlapping. In some embodiments, the mirror relays 850A and 850B may be offset such that the fields of view on the wafer are staggered and have spaces (gaps) between the fields of view.

[0082] Figure 9 is a process flow diagram illustrating an example method of determining a height map. The present disclosure provides numerous embodiments of utilizing optical measurement systems to determine height maps of a substrate. In particular, while height maps can be determined with configurations having the same AOIs, other embodiments can leverage information resulting from different AOIs. In general, some embodiments for a method 900 of determining a height map can include a system with processor configured to perform operations of the method. For example, at 910, the method can include performing, on a calibration substrate, a first calibration of the optical measurement system for the first angle of incidence to the first field of view. At 920, the method can include performing, on the calibration substrate, a second calibration of the optical measurement system for the second angle of incidence to the second field of view. At 930, the method can include determining a height map of the substrate utilizing the first calibration for the first field of view and the second calibration for the second field of view.

[0083] Figure 10 is a process flow diagram illustrating an example method of determining a height map utilizing measurements at one angle of incidence. In some embodiments, a method of determining a height map can include, for a first substrate, measuring with two AOIs. The delta height information from both angles can be used as a calibration map to improve HPD. Then, for other substrates in a group, points can be measured with one angle of incidence. By assuming that the delta between the angle that is used and the corrected HPD is the same as the first substrate, then the calibration map can be applied to each substrate to improve HPD. As the manufacturing of the substrates improves in this way, the calibration can be changed from once per group to be less frequent (e.g., every two, three, etc. groups). As shown in Figure 10, an example process flow for such a method 1000 can include, at 1010 performing, on a calibration substrate, a first calibration of the optical measurement system for the firstangle of incidence to the first field of view at a location on the substrate. At 1020, the method can include generating a calibration map based on the first calibration. The method can include determining a height map of the substrate by, for example at 1030, applying the calibration map to measurements of the first field of view at the first angle of incidence. The method can include, at 1040, applying the calibration map and a known difference between the first angle of incidence and the second angle of incidence to measurements of the second field of view at the second angle of incidence.

[0084] Figure 11 is a diagram illustrating an example height map of a substrate comprised of a global shape and an intrafield fingerprint. A simplified substrate is represented by a raw height map 1100a (e.g., as measured with optical measurement systems consistent with the present disclosure) and a raw height map side view 1100b (e.g., taken along one line across the substrate). Raw height map 1100a can be decomposed into, for example, global shape 1110a (with corresponding global shape side view 1110b) and static intrafield fingerprint 1120a (with corresponding static intrafield fingerprint side view 1120b). The intrafield fingerprint 1120a can be considered to be a static intrafield fingerprint when the height variation from field to field is the same across all fields. In implementations of methods of improving determination of the HPD, a method can include determining the height process dependence based on static intrafield fingerprint 1120 measured by a first mirror relay and by a second mirror relay.

[0085] In some embodiments, the intrafield fingerprint can have variations (e.g., between measurement points obtained with the first mirror relay and the second mirror relay). In such embodiments, one method of improving determination of the HPD can include determining a height process dependence based on a varying intrafield fingerprint measured by the first mirror relay and by the second mirror relay. The varying intrafield fingerprint can be measured at locations on the substrate that are equivalent to where the measurements from the first mirror relay were obtained.

[0086] Figure 12 is a block diagram of an example computer system CS, according to an embodiment of the present disclosure.

[0087] Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processor) coupled with bus BS for processing information. Computer system CS also includes amain 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 to be executed 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.

[0088] Computer system CS may be coupled via bus BS to a display DS, such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user. An inputdevice 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.

[0089] According to one embodiment, portions of one or more methods described herein may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions contained in main memory MM causes processor PRO to perform the process steps 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 an alternative embodiment, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0090] The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-transitory, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non- transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the features described herein. Transitory computer- readable media can include a carrier wave or other propagating electromagnetic signal.

[0091] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and use an infrared transmitter to convertthe data to an infrared signal. An infrared detector coupled to bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[0092] 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.

[0093] 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) both 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.

[0094] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other non-volatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0095] The combinations and sub-combinations of the elements disclosed herein constitute separate embodiments and are provided as examples only. Also, 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.

[0096] Various embodiments of the present disclosure are presented in the subsequent list of numbered clauses:1. An optical measurement system for measuring a topology of a surface of a substrate, comprising: a light projector configured to project a light beam to the surface of the substrate; a light detector configured to receive the light beam from the light projector that has been reflected from the surface; a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.2. The optical measurement system of clause 1, wherein the first mirror relay is adjacent the second mirror relay in the longitudinal direction.3. The optical measurement system of clause 2, wherein the first concave mirror arrangement and the second concave mirror arrangement are abutting in the longitudinal direction.4. The optical measurement system of clause 1, wherein the first concave mirror arrangement is a single mirror.5. The optical measurement system of clause 4, wherein the single mirror is a rectangular mirror.6. The optical measurement system of clause 4, wherein the single mirror is concave in both the longitudinal direction and a lateral direction.7. The optical measurement system of clause 4, wherein the first concave mirror arrangement comprises two mirrors.8. The optical measurement system of clause 1, wherein the first field of view and the second field of view are the same and also have a separation equal to the first field of view.9. The optical measurement system of clause 8, wherein the optical measurement system is configured to scan the substrate by including a longitudinal step equal to the first field of view that fills in the separation.10. The optical measurement system of clause 8, wherein the first mirror relay and the second mirror relay have a gap that contributes to the separation of the first field of view and the second field of view.11. The optical measurement system of clause 1, wherein the second mirror relay has a lateral offset and a longitudinal offset from the first mirror relay.12. The optical measurement system of clause 11, the first concave mirror arrangement comprising a plurality of first concave mirrors disposed in a lateral direction and the second concave mirror arrangement comprising a plurality of second concave mirrors interleaved in the lateral direction with the plurality of first concave mirrors.13. The optical measurement system of clause 11, wherein a plurality of first mirror relays are separated by one or more gaps in the longitudinal direction, and a plurality of second mirror relays are separated by one or more gaps in the longitudinal direction.14. The optical measurement system of clause 13, wherein longitudinal offsets of one or more second mirror relays covers the one or more gaps.15. The optical measurement system of clause 11, wherein a plurality of first mirror relays have first fields of view with one or more gaps and the second mirror relay has a second field of view that fills at least one of the gaps.16. The optical measurement system of clause 1, further comprising a fold mirror between the first mirror relay and the substrate, the fold mirror acting to reduce angles of reflection of light reflecting between the first convex mirror arrangement and the substrate.17. The optical measurement system of clause 1, wherein the first mirror relay provides light to the substrate at a first angle of incidence and the second mirror relay provides light to the substrate a second angle of incidence, the same as the first angle of incidence, with a positional difference between the first mirror relay and the second mirror relay causing the first field of view and the second field of view to be offset in a lateral direction.18. The optical measurement system of clause 1, wherein the light projector comprises a first light projector and a second light projector, and a path length for the first mirror relay from the first light projector to the first field of view is the same as for the second mirror relay from the second light projector to the second field of view.19. The optical measurement system of clause 1, wherein the first mirror relay provides light to the substrate at a first angle of incidence and the second mirror relay provides light to the substrate a second angle of incidence, different than the first angle of incidence, the different angles of incidence causing the first field of view and the second field of view to align in a lateral direction.20. The optical measurement system of clause 1, wherein the first mirror relay includes a first tilted mirror to direct the light beam to the first field of view and the second mirror relayincludes a second tilted mirror to direct the light beam to the second field of view, the first tilted mirror and the second tilted mirror at least partially overlapping in the horizontal direction and in a vertical direction to result in at least partially overlapping fields of view.21. The optical measurement system of clause 20, wherein the first field of view and the second field of view are aligned in the horizontal direction.22. The optical measurement system of clause 20, further comprising a third mirror relay with a third tilted mirror to direct the light beam to the third field of view, the first tilted mirror and the third tilted mirror at least partially overlapping in the horizontal direction and in the vertical direction to result in at least partially overlapping fields of view.23. The optical measurement system of clause 22, wherein the first field of view, the second field of view, and the third field of view are aligned in the horizontal direction.24. The optical measurement system of clause 19, further including a processor configured to perform operations comprising: performing, on a calibration substrate, a first calibration of the optical measurement system for the first angle of incidence to the first field of view; performing, on the calibration substrate, a second calibration of the optical measurement system for the second angle of incidence to the second field of view; and determining a height map of the substrate utilizing the first calibration for the first field of view and the second calibration for the second field of view.25. The optical measurement system of clause 19, further including a processor configured to perform operations comprising: performing, on a calibration substrate, a first calibration of the optical measurement system for the first angle of incidence to the first field of view at a location on the substrate; generating a calibration map based on the first calibration; and determining a height map of the substrate by: applying the calibration map to measurements of the first field of view at the first angle of incidence; and applying the calibration map and a known difference between the first angle of incidence and the second angle of incidence to measurements of the second field of view at the second angle of incidence.26. The optical measurement system of clause 19, further including a processor configured to perform operations comprising:determining a height process dependence based on a static intrafield fingerprint measured by the first mirror relay and by the second mirror relay.27. The optical measurement system of clause 19, further including a processor configured to perform operations comprising: determining a height process dependence based on a varying intrafield fingerprint measured by the first mirror relay and by the second mirror relay, wherein the varying intrafield fingerprint is measured at locations on the substrate that are equivalent to where the measurements from the first mirror relay were obtained.28. A level sensor comprising: a projection unit arranged to direct a beam of radiation received from a light projector to a surface of a substrate, comprising a projection grating having a period, the projection grating configured to provide a patterned measurement beam having a periodically varying intensity distribution in a first direction having the period; a detection unit arranged to receive the beam of radiation reflected at the surface of the substrate, one or more detectors; a processing unit configured to determine a position of the surface of the substrate based on the beam of radiation received by the one or more detectors; and wherein the projection unit and / or detection unit comprise: a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.29. A method of determining a height level of a substrate, the method comprising: projecting a patterned measurement beam having a periodically varying intensity distribution in a first direction having a period onto the substrate; receiving a reflected patterned measurement beam after reflection on the substrate on to a detector; determining the height level of the substrate based on one or more signals from the detector, wherein at least one of projecting the patterned measurement beam and receiving the reflected patterned measurement beam is by an optical measurement system for measuring a topology of a surface of the substrate, the optical measurement system comprising:a light projector configured to project a light beam to the surface of the substrate; a light detector configured to receive the light beam from the light projector that has been reflected from the surface; and a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.30. The method according to clause 25, further comprising: moving the substrate and the patterned measurement beam relative to each other to make a scanning movement of the patterned measurement beam over the surface.31. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; directing radiation from radiation source to transfer a pattern from a mask onto the photoresist layer; removing a portion of the photoresist layer to form the pattern over the substrate; and performing metrology on the substrate with an optical measurement system comprising: a light projector configured to project a light beam to a surface of the substrate; a light detector configured to receive the light beam from the light projector that has been reflected from the surface; a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

Claims

CLAIMS1. An optical measurement system for measuring a topology of a surface of a substrate, comprising: a light projector configured to project a light beam to the surface of the substrate; a light detector configured to receive the light beam from the light projector that has been reflected from the surface; a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

2. The optical measurement system of claim 1, wherein the first mirror relay is adjacent the second mirror relay in the longitudinal direction.

3. The optical measurement system of claim 2, wherein the first concave mirror arrangement and the second concave mirror arrangement are abutting in the longitudinal direction.

4. The optical measurement system of claim 1, wherein the first field of view and the second field of view are the same and also have a separation equal to the first field of view, and wherein the optical measurement system is configured to scan the substrate by including a longitudinal step equal to the first field of view that fills in the separation.

5. The optical measurement system of claim 4, wherein the first mirror relay and the second mirror relay have a gap that contributes to the separation of the first field of view and the second field of view, and wherein the second mirror relay has a lateral offset and a longitudinal offset from the first mirror relay.

6. The optical measurement system of claim 5, the first concave mirror arrangement comprising a plurality of first concave mirrors disposed in a lateral direction and the second concave mirror arrangement comprising a plurality of second concave mirrors interleaved in the lateral direction with the plurality of first concave mirrors.

7. The optical measurement system of claim 5, wherein a plurality of first mirror relays are separated by one or more gaps in the longitudinal direction, and a plurality of second mirror relays areseparated by one or more gaps in the longitudinal direction, and wherein longitudinal offsets of one or more second mirror relays covers the one or more gaps.

8. The optical measurement system of claim 1, further comprising a fold mirror between the first mirror relay and the substrate, the fold mirror acting to reduce angles of reflection of light reflecting between the first convex mirror arrangement and the substrate.

9. The optical measurement system of claim 1, wherein the first mirror relay provides light to the substrate at a first angle of incidence and the second mirror relay provides light to the substrate a second angle of incidence, the same as the first angle of incidence, with a positional difference between the first mirror relay and the second mirror relay causing the first field of view and the second field of view to be offset in a lateral direction.

10. The optical measurement system of claim 1, wherein the first mirror relay provides light to the substrate at a first angle of incidence and the second mirror relay provides light to the substrate a second angle of incidence, different than the first angle of incidence, the different angles of incidence causing the first field of view and the second field of view to align in a lateral direction.

11. The optical measurement system of claim 1, wherein the first mirror relay includes a first tilted mirror to direct the light beam to the first field of view and the second mirror relay includes a second tilted mirror to direct the light beam to the second field of view, the first tilted mirror and the second tilted mirror at least partially overlapping in the horizontal direction and in a vertical direction to result in at least partially overlapping fields of view, and wherein the first field of view and the second field of view are aligned in the horizontal direction.

12. A level sensor comprising: a projection unit arranged to direct a beam of radiation received from a light projector to a surface of a substrate, comprising a projection grating having a period, the projection grating configured to provide a patterned measurement beam having a periodically varying intensity distribution in a first direction having the period; a detection unit arranged to receive the beam of radiation reflected at the surface of the substrate, one or more detectors; a processing unit configured to determine a position of the surface of the substrate based on the beam of radiation received by the one or more detectors; and wherein the projection unit and / or detection unit comprise:a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

13. A method of determining a height level of a substrate, the method comprising: projecting a patterned measurement beam having a periodically varying intensity distribution in a first direction having a period onto the substrate; receiving a reflected patterned measurement beam after reflection on the substrate on to a detector; determining the height level of the substrate based on one or more signals from the detector, wherein at least one of projecting the patterned measurement beam and receiving the reflected patterned measurement beam is by an optical measurement system for measuring a topology of a surface of the substrate, the optical measurement system comprising: a light projector configured to project a light beam to the surface of the substrate; a light detector configured to receive the light beam from the light projector that has been reflected from the surface; and a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

14. The method according to claim 13, further comprising: moving the substrate and the patterned measurement beam relative to each other to make a scanning movement of the patterned measurement beam over the surface.

15. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; directing radiation from radiation source to transfer a pattern from a mask onto the photoresist layer; removing a portion of the photoresist layer to form the pattern over the substrate; and performing metrology on the substrate with an optical measurement system comprising:a light projector configured to project a light beam to a surface of the substrate; a light detector configured to receive the light beam from the light projector that has been reflected from the surface; a first mirror relay having a first field of view and comprising a first concave mirror arrangement and a first convex mirror arrangement; and a second mirror relay having a second field of view and comprising a second concave mirror arrangement and a second convex mirror arrangement, the first field of view and the second field of view offset in a longitudinal direction to form an expanded field of view in the longitudinal direction.

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