Level sensing systems and methods

Abstract

A level sensor is an optical sensor that measures the height of a substrate surface. Current level sensors have a relatively limited range, which depends on the period or pitch of gratings used in these sensors. An enhanced level sensor with high resolution and enhanced range is described. In an embodiment, the enhanced level sensor incorporates an interferometric measurement scheme, and includes at least three detectors, each measuring a different part of the period of the imaged grating; dedicated dipole illumination, which ensures that an imaged grating (at a detection grating) comprises a pure sine wave for all wavelengths of radiation; and interferometry software, which determines phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, determines the height based on the phases, and uses phase unwrapping algorithms to accommodate phase jumps in reflected radiation received from the surface.

Description

LEVEL SENSING SYSTEMS AND METHODSCROSS-REFERENCE TO RELATED APPLICATION

[0001] The Application claims priority of US provisional application number 63 / 688,947 which was filed on 30 August, 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 projection 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 devices are then separated from one another by a technique such as dicing or sawing, such that the individualdevices can be mounted on a carrier, connected to pins, etc.

[0005] Accurate metrology, including level sensing and / or other metrology, is important for these operations.SUMMARY

[0006] A level sensor is an optical sensorthat measures the level (e.g., height) of a substrate surface. Current level sensors have a relatively limited range, which depends on the period or pitch (e.g., the distance between lines) of gratings used in these sensors. The grating pitch is the center-to-center distance between two adjacent lines in the grating. The grating period is the spatial interval over which the grating pattern repeats itself, or the distance between equivalent points (such as the centers) in adjacent lines of the grating. These definitions may overlap here because the pitch and period both refer to the repeating distance between lines in a grating. However, the term "pitch" is sometimes used more in the context of describing the spacing, while "period" can emphasize the repetitive nature of the pattern. An enhanced level sensor with high resolution and an enhanced range (potentially up to about 100X with respect to existing level sensors) is described. The enhanced level sensor incorporates an interferometric measurement scheme, and includes (1) at least three detectors, each measuring a different part of a period of the imaged grating; (2) dedicated dipole illumination, which ensures that an imaged grating (at a detection grating) comprises a pure sine wave for all wavelengths of radiation; and (3) interferometry software, which determines phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, determines the level based on the phases, and uses phase unwrapping algorithms to accommodate phase jumps in reflected radiation received from the substrate surface. In some embodiments, the enhanced level sensor is configured to perform a sequential sampling (of at least three samples) with different phases.

[0007] According to an embodiment, there is provided an interferometric level sensing system. The system comprises a radiation source configured to irradiate a substrate surface with radiation. The radiation source comprises a generator configured to generate radiation. The system comprises a shaper configured to shape the radiation to form dipole radiation. An object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface. The object grating, substrate surface, and detection grating are in conjugate planes. The system comprises at least three detectors. Each of the at least three detectors is configured to receive a portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating. The received portion corresponds to a part of a period of the detection grating. Each of the at least three detectors is configured to generate an output signal conveying an intensity of the received portion. The system comprises a processor configured to generate interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface.

[0008] In some embodiments, the shaper is configured such that an angular radiation distribution comprises two poles. In some embodiments, the dipole radiation comprises a leaf-shaped dipole. In some embodiments, the leaf-shaped dipole has an orientation aligned with the object grating. In some embodiments, the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation. In some embodiments, a spot size of the dipole radiation is sufficiently large to cover an area from where the portions of reflected radiation incident on the at least three detectors reflect from the substrate surface. In some embodiments, the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.

[0009] In some embodiments, the object grating is configured to diffract the dipole radiation into multiple diffraction orders, but the portions of reflected radiation from the substrate surface received by the at least three detectors each only comprise two diffraction orders for each illumination angle and wavelength.

[0010] In some embodiments, a numerical aperture of the system selects diffraction orders generated by the object grating. The numerical aperture may be about 0.01 to 0.03, for example.

[0011] In some embodiments, the object grating has a 1 : 1 duty cycle, such that second or higher even diffracted orders of radiation are removed. In some embodiments, the object grating comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system. In some embodiments, the object grating has a period or pitch of about 15um.

[0012] In some embodiments, generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals and caused by a shift of an image of the object grating at the detection grating. In some embodiments, generating the interferometric measurements comprises determining phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, and determining the level based on the phases. In some embodiments, determined phases comprise phase intervals. In some embodiments, the phase intervals are determined simultaneously. In some embodiments, the level comprises a height map. In some embodiments, determining the level comprises constructing a height map from a series of height measurements determined based on the phases.

[0013] In some embodiments, generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.

[0014] In some embodiments, the system comprises at least four detectors, such that redundancy within output signals enhances overall quality of output from the detectors.

[0015] In some embodiments, each period is divided into a number of segments that correspond to a number of the at least three detectors, and each segment comprises a wedge. Each wedge deflects radiation per field point to a detector.

[0016] In some embodiments, the dipole radiation, the at least three detectors, and the processor configured to determine the level of the substrate surface using interferometry decouples a range of the interferometric level sensing system from a period or pitch of gratings used in the system, such that the object grating has a relatively high resolution compared to gratings used in prior systems, without being limited by the range.

[0017] In some embodiments, the interferometric level sensing system forms a portion of a lithography apparatus used for semiconductor manufacturing. The substrate may be a semiconductor wafer, for example.

[0018] According to another embodiment, a second interferometric level sensing system is provided. This system comprises a radiation source configured to irradiate a substrate surface with radiation. The radiation source comprises a generator configured to generate radiation. This system comprises a shaper configured to shape the radiation to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes. This system comprises a detector configured to: receive at least three sequential portions of reflected radiation over time from the substrate surface as an image of the object grating is moved with respect to the detection grating; and generate an output signal conveying an intensity of the at least three sequential portions. This system comprises a processor configured to generate interferometric measurements based on the intensities in the output signal corresponding to the at least three sequential portions to determine a level of the substrate surface.

[0019] According to another embodiment, an object grating and a detection grating are configured to diffract the radiation, and provide field point diversity associated with diffracted radiation.

[0020] According to another embodiment, there are provided corresponding interferometric level sensing method(s) comprising one or more of the operations performed by the system(s) described above.

[0021] According to another embodiment, there is provided a non-transitory computer readable medium storing instructions that, when executed by a computer (e.g., comprising one or more processors), cause the computer to perform one or more of the operations performed by the system(s) described above.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] Fig. 1 illustrates a lithography apparatus, according to an embodiment.

[0024] Fig. 2A illustrates a base example level sensing system, according to an embodiment.

[0025] Fig. 2B illustrates another base example level sensing system, according to an embodiment.

[0026] Fig. 3 A illustrates in interferometric level sensing system, according to an embodiment.

[0027] Fig. 3B illustrates an example of a shaper shaping incoming radiation to form dipole radiation, according to an embodiment.

[0028] Fig. 4A illustrates examples of the functionality of the system shown in Fig. 3A and / or 3B, according to an embodiment.

[0029] Fig. 4B also illustrates examples of the functionality of the system shown in Fig. 3A and / or 3B, according to an embodiment.

[0030] Fig. 5 illustrates pupils of projection optics of the system shown in Fig. 3A and / or 3B, between an object grating and a substrate surface, and the substrate surface and a detection grating of the system, according to an embodiment.

[0031] Fig. 6 illustrates dipole radiation with an orientation aligned with the object grating, according to an embodiment.

[0032] Fig. 7 illustrates an image of the object grating at the detection grating, according to an embodiment.

[0033] Fig. 8 illustrates an interferometric level sensing method, according to an embodiment.

[0034] Fig. 9 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0035] 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 gratings, broadband (or multi-color) light, an object 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 object grating with respect to the detection grating. Current level sensors use two detectors, which each detect light from half a period of the detection grating (and are it out of phase with each other). This means the range of current level sensors is limited to less than one period of the grating (which is a very short distance). In addition, the levelling response is non-linear, and dependent on the size of the gratings imaged with respect to the resolution of the imaging optics used. If one attempts to increase the range of the level sensor by increasing the period of the detection grating, interference effects between the level sensor and a product patterned on the substrate are often observed (among other potential disadvantages).

[0036] Advantageously, an enhanced level sensor with high resolution and an enhanced range (potentially up to about 100X with respect to existing level sensors) is described below. The enhanced level sensor incorporates an interferometric measurement scheme, and includes (1) at least three detectors, each measuring a different part of the period of the imaged grating; (2) dedicated dipole illumination, which ensures that an imaged grating (at a detection grating) comprises a pure sine wavefor all wavelengths of radiation; and (3) interferometry software, which determines phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, determines the level based on the phases, and uses phase unwrapping algorithms to accommodate phase jumps in reflected radiation received from the substrate surface. This approach has several advantages, including (but not limited to) decoupling the range of the interferometric level sensing system from a period or pitch of gratings used in the system, such that the object grating has a relatively high resolution compared to gratings used in prior systems, without being limited by the range.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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. arefractive 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).

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.”

[0047] 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.

[0048] 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.

[0049] The term “projection system” should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system.”

[0050] 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.

[0051] 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 atable WTb below the projection system without a substrate that is dedicated to, for example, facilitating measurement, and / or cleaning, etc.). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be conducted on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using an alignment sensor AS and / or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0052] In operation of the lithographic apparatus, a radiation beam B is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a shortstroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0053] The depicted apparatus may be used in at least one of the following modes. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while a pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of theexposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

[0054] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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, forexample, a double paterning 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)).

[0059] The one or more measured parameters may include, for example, level (e.g., height), alignment, overlay between successive layers formed in or on the paterned substrate, critical dimension (CD) (e.g., critical linewidth) of, for example, features formed in or on the paterned 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.

[0060] There are various techniques for making measurements of the structures formed in the paterning 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 scatered (diffracted / reflected) beam are measured. By evaluating one or more properties of the radiation scatered 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).

[0061] 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 paterning 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)).

[0062] 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 thebatch 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.

[0063] A metrology system may be used to determine one or more properties of the substrate structure, and in particular, how one or more properties of different substrate structures vary, or different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithographic apparatus LA or the lithocell LC, or may be a stand-alone device. 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.

[0064] Fig. 2A 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), is arranged to measure a 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.

[0065] The example level or height sensor LS shown in Fig. 2A illustrates the 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 which 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 thelevel 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.

[0066] The object or projection grating PGR is a periodic grating comprising a periodic structure resulting in a beam of radiation BE1 having a periodically varying intensity. The beam of radiation 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.

[0067] 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.

[0068] 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.

[0069] 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).

[0070] 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.

[0071] 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.

[0072] Fig. 2B illustrates another base example level sensing system, or level sensor LS (also see LS in Fig. 1 and Fig. 2A). Fig. 2B illustrates additional potential aspects of the base example level sensing system shown in Fig. 2A.

[0073] As described above, the level sensor LS determines a surface height or surface height profile of substrate W (also see substrate W in Fig. 1 and Fig. 2A). Level sensor measurements are performedin many stages of substrate processing, including when substrate W already comprises a stack 204 of layers, such as oxide, poly-silicon, dielectric anti-reflective coating (DARC), metal layers (e.g. copper) and resist layers. A radiation source 206 (e.g., in the form of a light source similar to and or the same as LSO in Fig. 2A) emits radiation toward an object grating 207 (similar to and or the same as PGR in Fig. 2A) having a certain period or pitch p), and this radiation is projected onto substrate W (or a top surface of stack 204 of layers on substrate W) using projection optics 209 (e.g., in the form of a lens in this example), with a certain angle of incidence (e.g., as described above). The reflected radiation is again focused using additional optical components 210 on a detection (or reference) grating 208 (similar to and / or the same as DGR in Fig. 2A). A detector 205 (similar to and / or the same as DET in Fig. 2A) is then used to process the radiation transmitted by the detection grating 208, and the measurement signal is processed to obtain the level or height of stack 204 of layers. This level sensor arrangement is based on optical triangulation techniques. The detected height is directly related to the signal strength measured by detector 205, and has a periodicity dependent on the angle of incidence (p / 2 sinO - where 0 is the angle of incidence).

[0074] Fig. 3A illustrates an interferometric level sensing system 300. In some embodiments, interferometric level sensing system 300 forms a portion of a lithography apparatus (such as lithography apparatus LA shown in Fig. 1) used for semiconductor manufacturing. As described above, compared to prior systems, system 300 is an enhanced level sensing system with high resolution and an enhanced range (potentially up to about 100X with respect to existing level sensors). System 300 is configured to determine the level of a substrate 303 (e.g., a semiconductor wafer) surface 305 using interferometry, which decouples a range of interferometric level sensing system 300 from a period or pitch of gratings used in system 300, such that an object grating 320 can have a relatively high resolution (e.g., a period or pitch of about 15 pm) compared to gratings used in prior systems, with a much enhanced range (e.g., about a lOOx range enhancement). The level may comprise a height of substrate 303 surface 305, a height map of surface 305, and / or another level.

[0075] System 300 comprises a radiation source 302, object grating 320, a detection grating 322, at least three detectors 304, 306, 308, and 310 (there are four detectors in this example); one or more processors PRO, various optical components 312 (e.g., projection optics and / or other optical components including shaper 332, pupils 350, etc.), and / or other components. Each of these elements are described below.

[0076] Radiation source 302 is configured to irradiate substrate 303 surface 305 with radiation 324. Radiation source 302 comprises a generator 326, collection optics 328, a light guide 330, and / or other illumination optics, a reflector 334, and / or other components. In some embodiments, object grating 320 and / or a shaper 332 may be considered to be a part of radiation source 302, or they may form their own components.

[0077] Generator 326 is configured to generate radiation 324. Generator may be and / or include alamp, a laser, a light emitting diode (LED), 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. In some embodiments, radiation 324 comprises one or more wavelengths in a range of 225-450 nm, for example.

[0078] 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 a lens 333 and / or other components. Note that light guide 330 is an optional portion of the system. Other components may be used to guide radiation 324 toward object grating 320 and / or shaper 332, or radiation 324 could even proceed directly from generator 326 (toward object grating 320).

[0079] Shaper 332 is configured to shape radiation 324 to form dipole radiation, such that object grating 320 is imaged on detection grating 322 after diffracted radiation from object grating 320 reflects off of substrate 303 surface 305. The angular distribution of light is a dipole, and the spatial distribution of light is uniform (illuminating at least the complete mark uniformly). In some embodiments, shaper 332 is configured such that an angular radiation distribution comprises two poles. In some embodiments, dipole radiation 324 comprises a leaf-shaped dipole, for example. The exact components included in shaper 332 may depend on the other illumination components. One embodiment (e.g., for use with a lamp based system) may comprise a physical stop with two leaf shaped openings. This stop may be placed in between two imaging lenses, such that the spatial light selection is translated into an angular light selection. An alternative (e.g., for use with a laser) can be the use of diffractive optics, which generate an angular distribution of light. This might also be a micromirror device.

[0080] For example, Fig. 3B illustrates a more detailed example of shaper 332 (keeping in mind this is just one possible example) shaping radiation 324 to form dipole radiation 360. Fig. 3B illustrates a physical stop or filter 362 with two leaf shaped openings 364 and 366 that may be placed between two imaging lenses 368 and 370. Fig. 3B also illustrates (as another possible example), a diffractive element 380 placed in a field plane 382, which generates an angular distribution of light (e.g., dipole radiation 360). Field planes 382 may comprise the projection grating, the substrate surface, and / or the detection grating (as described herein), for example.

[0081] Returning to Fig. 3A, in system 300, object grating 320, substrate 303 surface 305, and detection grating 322 are in conjugate planes. In system 300, dipole radiation 324 is guided toward substrate 303 surface 305, and reflected radiation 324 is guided from substrate 303 surface 305 towarddetection grating 322 and detectors 304-310 by optical components 312 (e.g., which may include various lenses 333, reflectors 334 and 336 (e.g., flat or curved mirrors), wedges, etc.).

[0082] Object grating 320 is configured to diffract radiation 324 into multiple diffraction orders, but the portions of reflected radiation 324 from the substrate 303 surface 305 received by detectors 304- 310 each only comprise two diffraction orders for each illumination angle and wavelength. In some embodiments, a numerical aperture (NA) of system 300 selects diffraction orders generated by object grating 320. The numerical aperture may be about 0.01 to 0.03, for example.

[0083] In some embodiments, object grating 320 has a 1: 1 duty cycle, such that second or higher even diffracted orders of radiation 324 are removed. In some embodiments, object grating 320 comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in interferometric level sensing system 300. These features may provide several advantages, including but not limited to ensuring that an image of object grating 320 at detection grating 322 comprises a pure sine wave, and allowing the detection of phase jumps (thus increasing the range of system 300). By using a continuous grating, neighboring field points (both in x and y directions) can be used to detect phase jumps, and the recorded phase is continuous. Other advantages are contemplated.

[0084] For example, with respect to a wavelength range: Xmm and Xmax in relation to the NA of the optics of system 300 and the pole size s, system 300 is configured with an NA which projects object grating 320 to substrate 303 surface 305, and substrate 303 surface 305 to detection grating 322 (e.g., an NA = 0.022, or more generally, an NA between 0.01 and 0.03). Upon printing a grating, there is an order separation (distance between diffraction orders): sin 0 = A / pitch. This is referred to as Bragg’s law. Bragg's Law returns a relation between the angular separation of diffraction orders: sin 0 and the grating pitch (and wavelength A). By choosing an object grating with 1: 1 duty cycle, the second diffraction orders are suppressed. Thus system 300 is configured such that only two (0 and 1), and no other diffraction orders are present (excluding the third diffraction orders). System 300 is configured such that the third diffraction orders should not enter the NA of system 300. This defines a relation between the period or pitch of object grating 320, the minimum wavelength, and the NA:3 ■ ^min=2 ■ NA ■ pitch.A maximum allowed pole size s (in the grating direction) is defined by the maximum wavelength:The minimum pole size is 0. The optimum pole size also lies at this maximum. However, a slightly smaller value might be chosen to allow for some tolerance in the optical alignment of the system. Combining equations results in a maximum allowed pole size:In view of these relationships, system 300 is configured such that radiation 324 comprises one or more wavelengths in a range of 225-450 nm, for example. The minimum wavelength (and NA) defines the period or pitch (of object grating 320): 0.225*3 / 2 / 0.022 = 15 um (pitch / 2). The maximum wavelength defines the poles size (of the dipole radiation 324): 2*0.022(1 - 0.45 / 0.225 / 3) = 0.015 rad. This illustrates that due to limited spectrum usage, system 300 is configured to allow slightly larger poles than may be ordinarily expected. In case the spectral range is reduced, the light is more temporally coherent. In case the angular distribution is increased, the light is more spatially in-coherent. So by maximizing the pole size, one keeps the product of temporal coherence and spatial coherence also at its maximum. Spectrum ranges Amax / Amm may vary between 2.5 and 1.2, though variation may range from about 3 (no pole size) to about 1 (no spectrum), for example.

[0085] System 300 comprises at least three detectors, though four detectors 304-310 are shown in Fig. 3A. The intensity distribution of the image of the grating at the detector equals a pure sine. This is described by three variables: the average intensity, the modulation amplitude, and the phase. So in order to measure these variables, one needs at least three measurements. The orientation of the grating is aligned, so not a variable. In some embodiments, system 300 comprises at least four detectors (e.g., as shown in Fig. 3A), such that redundancy within output signals enhances overall quality of output from the detectors. Each of the detectors 304-310 is configured to receive a portion of reflected radiation 324 from substrate 303 surface 305 after the portion of reflected radiation is separated by detection grating 322. The received portion corresponds to a part of a period of detection grating 322. In some embodiments, each period is divided into a number of segments that correspond to a number of detectors, and each segment comprises a wedge. Each wedge deflects radiation per field point to a detector 304- 310, for example. Each of the at least three detectors (e.g., detectors 304-310 in Fig. 3A) is configured to generate an output signal conveying an intensity of the received portion. Processor PRO is configured to generate interferometric measurements based on the intensities in the output signals from detectors 304-310 to determine a level of substrate 303 surface 305.

[0086] In some embodiments, generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals and caused by a shift of an image of object grating 320 at detection grating 322. In some embodiments, generating the interferometric measurements comprises determining phases of the reflected radiation at each moment in time based on the output signals from the (at least three) detectors 304-310, and determining the level based on the phases. In some embodiments, determined phases comprise phase intervals. In some embodiments, the phase intervals are determined simultaneously, or (e.g., for temporally based embodiments described herein) radiation 324 within different phase intervals is detected sequentially via scanning of detection grating 322 with respect to a beam of dipole radiation 324.

[0087] Generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating. In some embodiments, the level comprises a height map. In some embodiments, determining the level comprises constructing a height map from a series of height measurements determined based on the phases.

[0088] Fig. 4A and 4B illustrate examples of the functionality of system 300 shown in Fig. 3A and / or 3B. Fig. 4A illustrates how one level sensor spot encompasses one extended grating imaged on a grating with corresponding detectors (e.g., detectors 304 - 310 shown in Fig. 3A) which measure the subsequent intensities. This facilitates measurement of level or height at one position. Fig. 4A illustrates a wafer or substrate level 401 (one spot), a detector level 403 (one spot), a grazing angle direction 405, a scan direction 407, and a static direction 409. Multiple field points 411 are measured in parallel (at the same time and at different x-positions - parallel measurement, multiple detection spots) and sequentially (at different times and different y-positions). Fig. 4A also illustrates an image 415 of a projection grating on a detection grating 417 (along with grazing angle direction 405), and how a stripe 421 is measured during a scan 423, with multiple stripes 421 covering the whole substrate topography.

[0089] In some embodiments, grazing angle direction 405 is in the scan direction 407. However, this does not need to be the case, but this returns some freedom in using different grating periods. As a result, the spots may be smaller in scan direction 407 at the projection and detection levels. Multiple field points 411 are present in static direction 409 (the x direction here, orthogonal to the grazing direction, thus the spots move in the y-direction if the wafer is defocused.). A detection spot may be overfilled in the grazing direction by the projection grating (and thus also illumination) - which is a reason the orthogonality between the grating angle direction the static direction is advantageous. In the static direction, it may be preferred to arrange the different detection spots against each other, such that each field point measures the average height of a certain interval. Keep in mind that underfilling is possible, and system 300 (Fig. 3A) will still function as described, but certain level or height information may be missing, making underfilling less accurate.

[0090] In order to measure the phase, thus the level or height, system 300 (Fig. 3A) needs to measure the interference (i.e., at least three measurements) between the object grating (e.g., 320 shown in Fig. 3A) and the detection grating (e.g., 322 shown in Fig. 3A). There are two embodiments: spatial and temporal. The description herein focuses primarily on the spatial embodiment, although the temporal embodiment is also important. For spatial phase measurement (or spatial phase stepping), at each moment in time, system 300 measures the intensity at different grating positions (in the phase direction) . This requires multiple parallel detectors (e.g., detectors 304 -310 shown in Fig. 3 and described herein). For temporal phase measurement (or temporal phase stepping), system 300 may be configured (e.g., using piezoelectric components as one possible example, though many other types of actuators may be used) to move the image of the object grating with respect to the detection grating. This requires onedetector and multiple measurements in time, plus a device to move the gratings with respect to each other (e.g., a translating or rotating piezoelectric element, a rotating polygon in a pupil (reflective) or field (transmissive) plane, etc.). With the temporal embodiment, there may be a sequential sampling (of at least three samples) with different phases by a single detector (e.g., one of detectors 304-310). Since the wafer is scanned underneath the sensors, temporal phase stepping requires a much shorter time scale compared to scan movement time scales.

[0091] Measurements are used to generate (e.g., using processor PRO shown in Fig. 3A) a two dimensional height map of the substrate (e.g., wafer) surface 413. Measured data points may be combined in a map like the one shown in image 420 in Fig. 4B. Fig. 4B also illustrates detected intensity 400 (denoted Ii, 2, 3, 4, 5) versus phase shift 402 (time) for different received portions 404 of radiation that correspond to parts of the period of detection grating 322 (Fig. 3A). Note that Fig. 4B shows five intensities (I1-5), where the fifth intensity (I5) measured is equal to the first one (but only shifted one period) - so this may be considered to be a second instance of ft. Fig. 4B shows the intensity signal independent of the sampling (a pure sine), where the measured intensities are 4 (or 5 in this case) discrete values - from the sinusoidal intensity distribution, four values are obtained. With phase stepping (e.g., as described herein) one can sequentially measure a sine as function of time (x-axis) and integrate over the various time intervals to get the intensity values. But in some embodiments (e.g., preferred embodiments), the x-axis equals the detection grating position, so the detectors measure the average intensities within a given (spatial) interval simultaneously. As described above, in some embodiments, generating the interferometric measurements comprises determining phases of the reflected radiation at each moment in time based on the output signals from the (at least three) detectors, and determining the level based on the phases. In some embodiments, determined phases comprise phase intervals.

[0092] A common algorithm for phase determinations is the four frame method (Wyant 1982). In this example (other examples are possible), four intensity measurements can be written:where ai = 0, TT / 2, TT, and 3TT / 2; y = y0for stepping the phase and 0.9 y0when the phase is integrated over A = TT / 2. There are three unknowns which need to be found (e.g., as described above): Io (the average intensity), y (the modulation amplitude) and 4> (the phase). The phase at each point is:and the detected fringe visibility is determined by:

[0093] As described above, generating the interferometric measurements (by processor PRO shown in Fig. 3 A) comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating. Fig. 4B also illustrates a module 2n phase determination 420, and an unwrapped phase 422. (See: “General methods for generating phase -shifting interferometry algorithms,” by D.W. Phillion, Applied optics 36 (31), p. 8098 - 8115 (1997); and “Interferogram Analysis; Digital Fringe Pattern Measurement Techniques,” edited by David. W. Robinson, Graeme T. Reid, IOP Publishing Ltd, 1993 (ISBN 0-7503- 0197-X)).

[0094] Fig. 5 illustrates pupils 500 of the projection optics of system 300 (see the left column labeled 312 in Fig. 3A) between object grating 320 and substrate 303 surface 305, and pupils 502 between substrate 303 surface 305 and detection grating 322 shown in Fig. 3A. Pupils 500 and 502 are similar to and / or the same as pupils 350 shown in Fig. 3A. Fig. 5 shows the shaded illumination mode (being a leaf shape dipole, having a first pole 550 and a second pole 552), the truncation NA 503 and 504 of the optics, the plus and minus diffraction orders 510, and arrows 512 and 514 indicating the separation between the diffraction orders. Fig. 5 also illustrates the relationship between radiation wavelength, the period or pitch of the object grating, and the NA of the system.

[0095] To cover a large wavelength range with similar contrast for all wavelengths, a leaf shape dipole illumination mode may be used (shaded). In this embodiment, the smallest usable wavelength (of radiation 324 shown in Fig. 3A) is given by:A >_ 2 ■ NA p 3

[0096] The left side of Fig. 5 shows the order separation for the largest wavelength. The illumination pole size (s) is related to the maximum wavelength by:Combining equations yields:As described herein, the wavelength ratio may vary between 1 (s = 4NA / 3, no bandwidth) and 3 (s = 0, no pupil fill.)

[0097] The right side of Fig. 5 shows the order separation for the smallest wavelength (with p indicating the period or pitch of object grating 320 shown in Fig. 3A). For an object grating with a 1 : 1, or equal, duty cycle (e.g., with as much of a bright area as a dark area), as described above, all even diffraction orders (except the zero order) are absent. This shows that for the whole wavelength range of radiation used in system 300 (Fig. 3 A), only the zero order radiation and one complete first diffraction order of radiation pass the NA. As a result, the image of object grating 320 (Fig. 3A) at detection grating 322 (Fig. 3A) has a pure sinusoidal intensity distribution. Phrased another way, the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation. Here the third diffraction order does not enter the NA. The second diffraction orders (e.g., represented by the dashed lines, in case of small wavelengths) are absent because of the 1: 1 duty cycle. This results in an intensity modulation which can be described by three constants, and thus be measured with at least three detectors. Note that this also increases contrast and averages the spectrum to enhance uniformity, among other advantages.

[0098] In some embodiments, the ratio between the largest and smallest wavelength (in radiation 324 shown in Fig. 3A) equals two (that is also what is shown in Fig. 5). In this example, the following relation for period or pitch (e.g., p as described above) holds:More generically, one may adapt the pole size (within the diffraction direction) such that the following holds (pole size is also indicated by the s in Fig. 5):such that the range can be larger or smaller than two. Maximum pupil filling (e.g., using a leaf shaped dipole) is desired to enhance photon efficiency. Radiation outside an optimal leaf shape (e.g., larger pupil filling), may reduce contrast of a projected grating projected, which may reduce the reproducibility of the system overall. Since any level (e.g., height) can be measured equally well, there is no need to adjust towards zero. The zero location is or corresponds to where a substrate (e.g., wafer)surface is in focus and the image of the object grating overlaps the detection grating. This could correspond to a phase of 0 degrees (I4 = I2), for example. Within a classic level sensor, one would like to work around 0, because there the level sensor is most "linear". Further away from zero, non-linearity errors are made.

[0099] In order to facilitate phase unwrapping (e.g., as described above) and / or avoiding jumps in a height map, the physical spot size of radiation 324 (Fig. 3 A) is configured to be larger than the from which the radiation that reflects off of the substrate surface then impinges on the detectors. The physical spot size corresponds to an area which is pointing to the (three or more) detectors. Phrased another way, the spot size of the dipole radiation is sufficiently large to cover an area from where the portions of reflected radiation incident on the at least three detectors reflect from the substrate surface. Note that spot size (at a detector, substrate surface, and object grating) is independent of the pupil light distribution. The spot size refers to the spatial distribution of light. The pupil refers to the angular distribution of light. (Within the optics, at the physical numerical aperture stop location, this is exactly the other way around: here the pupil equals the spatial distribution and the spot equals the angular distribution. )

[0100] A grating may provide field point diversity. In some embodiments, gratings with different periods or pitches may be used for even and odd field points. This facilitates phase unwrapping and increases the absolute accuracy / periodicity error by one over the delta frequency. This can be very powerful, useful, and practical. For example, when a grating period equals 15 pm, 33 periods fit within 0.5 mm, so a grating with a 16 pm period could be integrated at the other field points. The combined periodic phase error is now at 240 pm (= 1 / (1 / 15-1 / 16).), which is a 16x range increase, and still within the measurement capabilities of the detectors (e.g., detectors 304-310 shown in Fig. 3A). Note that this is an alternative to phase unwrapping (but which can also be used in combination). In some embodiments, system 300 (Fig. 3 A) may use phase offsets between different field points, such that a period jump occurs at different phases. In some embodiments, system 300 (Fig. 3A) may be configured to modulate the substrate height while scanning, and take its value as reference value, for example.

[0101] Fig. 6 illustrates dipole radiation 324 with an orientation 600 aligned with object grating 320. In this example, orientation 600 comprises a parallel alignment between an axis 602 of the dipole radiation, and an axis 604 of object grating 320. As described above, shaper 332 (Fig. 3A) may be configured such that dipole radiation 324 comprises a leaf-shaped dipole, for example. In some embodiments, the leaf-shaped dipole has orientation 600 aligned with object grating 320. Note that, while preferred, it is not a requirement that this orientation 600 is aligned to the grating 320 direction (although there needs to be at least some alignment).

[0102] Fig. 6 illustrates the period or pitch p of lines 650 (e.g., the center of one line 650 to the center of the next line 650). In this example, object grating 320 has a 1 : 1 duty cycle duty cycle (e.g., there are equal white and shaded areas), such that second or higher even diffracted orders of radiation 324 areremoved. Object grating 320 also comprises multiple lines 650, is continuous (e.g., no gaps between field points) in the x direction, is limited in size in a y dimension (see Fig. 4 A - the size in the grazing direction is defined by the detector, not by the projected grating (which is larger)) relative to an x direction (e.g., object grating is wider than it is tall in this example), and is oriented at an angle (with respect to other components of the system (e.g., with respect to the x and y direction of system 300 shown in Fig. 3A) which reduces the risk of interference with product patterns.

[0103] Fig. 7 illustrates an image 700 of object grating 320 at detection grating 322. Detection grating 322 has a similar size as object grating 320 (but may be smaller in a grazing direction). The sum of all detected intensities (by the three or more detectors 304-310 shown in Fig. 3A) is constant (in case of no intensity variations from the source). The lines of the detection grating 322 are aligned (same orientation) as the image of the object grating 320. As described above, the dipole radiation is configured such that image 700 of object grating 320 at detection grating 322 comprises a pure sine wave for all wavelengths of radiation. Generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals and caused by a shift of image 700 of object grating 320 at detection grating 322. The (three or more) detectors described above are each configured to receive a portion of reflected radiation from the substrate surface (see Fig. 3 A) after the portion of reflected radiation is separated by detection grating 322. The received portion corresponds to a part of a period of the detection grating. Each period is divided into a number of segments that correspond to a number of the at least three detectors (e.g., or four - as shown in Fig. 3A and at the bottom of Fig. 7, or more detectors).

[0104] Fig. 7 also illustrates an intensity 710 versus grazing angle direction 720 plot 750, and a spatial distribution 760 of (reflective in this example, but they could also be transmissive) wedges 762 that direct different portions of radiation 770 to different detectors 780 (e.g., the same as or similar to detectors 304 - 310 shown in Fig. 3A). The functionality shown here is twofold: selecting a specific region (the wedge area) and directing radiation 770 in a prescribed direction. The prescribed direction is in the direction of a target detector 780 (in this case one or another detector 780 out of the four shown). Plot 750 shows the image of the projection grating at the detector level. In dashed lines the alignment with respect to the wedges is shown (four wedges / period (box shapes in plot 750)). Thus, as shown in Fig. 7, each segment of a period comprises or is associated with a wedge 762. Each wedge 762 deflects radiation 770 per field point to a detector 780 (point). At substrate level the equivalent grating angle may be in the y-direction, such that a wafer height is translated into a y-movement (however as described above, the grating angle does not need to be aligned with the grazing angle). In some embodiments, a measurement grid may be defined by a number of points in an x and a y direction. This can be facilitated by interlacing a wedge assignment in the x direction and in the y-direction (as one potential option) via scanning and measuring in time denser than a marker size.

[0105] Returning to Fig. 3A, 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. The various components may be positioned in any location and / or at any angle relative to each other that allows system 300 to function as described herein. This may include positioning at specific relative distances between elements, specific angles between elements, etc. In some embodiments, the various components are positioned relative to each other in system 300 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.

[0106] In some embodiments, movement may be controlled electronically by a processor, such as processor PRO. Processor PRO 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 300, transmitting values between separate components, and / or other communication. The components of system 300 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.

[0107] In some embodiments, one or more actuators (not shown in Fig. 3 A) may be coupled to and configured to move one or more components of system 300. The actuators may be coupled to one or more components of system 300 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 300. As an example, one or more of the actuators may be piezoelectric. One or more processors PRO may be configured to control the actuators. One or more processors PRO may be configured to individually control each of the one or more actuators.

[0108] The quantity of the various optical components shown in Fig. 3 A is not intended to be limiting. The principles described herein may be extended such that, in some embodiments system 300 comprises additional or fewer lenses, reflectors, and / or other optical components.

[0109] Fig. 8 illustrates an interferometric level sensing method 800. In some embodiments, one or more operations of method 800 may be implemented in or by an interferometric level sensing system such as system 300 illustrated in Fig. 3 A, 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 interferometric level sensing system forms a portion of a lithography apparatus used for semiconductor manufacturing.Method 800 may be performed as part of semiconductor lithography operations in a semiconductor device manufacturing process, for example. In some embodiments, method 800 comprises irradiating (operation 802) a substrate surface with radiation (the substrate may be a semiconductor wafer, for example); receiving (operation 804) reflected radiation from the substrate surface; generating (operation 806) output signals conveying intensities of the reflected radiation; and generating (operation 808) interferometric measurements based on the intensities in the output signals to determine a level of the substrate surface.

[0110] 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.

[0111] 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).

[0112] At operation 802, a radiation source irradiates a substrate surface with radiation. The radiation source comprises a generator configured to generate radiation. A shaper is configured to shape the radiation to form dipole radiation, such that the object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface. The object grating, substrate surface, and detection grating are in conjugate planes.

[0113] The shaper is configured such that an angular radiation distribution comprises two poles. For example, the dipole radiation may comprise a leaf-shaped dipole. In some embodiments, the leafshaped dipole has an orientation aligned with the object grating. The dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation. A spot size of the dipole radiation is sufficiently large to cover an area from where the portions of reflected radiation incident on the at least three detectors reflect from the substrate surface. In some embodiments, the dipole radiation comprises one or more wavelengths in a range of 225-450 nm, for example.

[0114] In some embodiments, a numerical aperture of the system selects diffraction orders generatedby the object grating. The numerical aperture may be about 0.01 to 0.03, for example.

[0115] In some embodiments, the object grating has a 1 : 1 duty cycle, such that second or higher even diffracted orders of radiation are removed. In some embodiments, the object grating comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system. In some embodiments, the object grating has a period or pitch of about 15um. In some embodiments, operation 802 is performed by a radiation source the same as or similar to radiation source 302 shown in Fig. 3 A, and / or other components described above.

[0116] At operation 804, each of at least three detectors is configured to receive a portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating. The received portion corresponds to a part of a period of the detection grating. Each period is divided into a number of segments that correspond to a number of the at least three detectors, and each segment comprises a wedge. Each wedge deflects radiation per field point to a detector. The object grating is configured to diffract radiation into multiple diffraction orders, but the portions of reflected radiation from the substrate surface received by the at least three detectors each only comprise two diffraction orders for each illumination angle and wavelength. In some embodiments, the interferometric level sensing system comprises at least four detectors, such that redundancy within output signals enhances overall quality of output from the detectors. In some embodiments, operation 804 is performed by detectors the same as or similar to detectors 304-310 shown in Fig. 3A, and / or other components described above.

[0117] At operation 806, the at least three detectors each generate an output signal conveying an intensity of the received portion. In some embodiments, operation 806 may comprise detecting, with a detector, an intensity of the reflected radiation received from the substrate surface, and generating the output signal accordingly. In some embodiments, detecting the intensity of reflected radiation comprises detecting one or more intensity shifts in reflected radiation. An output signal comprises an electronic signal that represents and / or otherwise corresponds to the intensity of radiation reflected from the substrate surface. The output signal may indicate an intensity value, for example, and / or other information. Generating the output signal comprises sensing the reflected radiation and converting the sensed reflected radiation into an electronic signal. In some embodiments, generating an output signal comprises sensing different portions of the reflected radiation from different areas and / or different geometries of a grating (with the different detectors, as described above), and combining the different portions of the reflected radiation to form an output signal. In some embodiments, operation 806 is performed by detectors the same as or similar to detectors 304-310 shown in Fig. 3A, and / or other components described above.

[0118] At operation 808, a processor generates interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface. Insome embodiments, generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals and caused by a shift of an image of the object grating at the detection grating. Generating the interferometric measurements comprises determining phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, and determining the level based on the phases. In some embodiments, determined phases comprise phase intervals. The phase intervals may be determined simultaneously, or (e.g., for temporally based embodiments described herein) radiation within different phase intervals may be detected sequentially via scanning of the detection grating with respect to a beam of dipole radiation. In some embodiments, the level comprises a height map. In some embodiments, determining the level comprises constructing a height map from a series of height measurements determined based on the phases. In some embodiments, generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.

[0119] In some embodiments, the dipole radiation, the at least three detectors, and the processor configured to determine the level of the substrate surface using interferometry decouples a range of the interferometric level sensing system from a period or pitch of gratings used in the system, such that the object grating has a relatively high resolution compared to gratings used in prior systems, without being limited by the range.

[0120] Note as described above that spatial or temporal measurements may be made. Method 800 described above focuses primarily on the spatial embodiment. Hower one or more of the operations of method 800 may be adjusted to instead utilize temporal measurements. For temporal phase measurement (or temporal phase stepping), method 800 may include using piezoelectric components and / or other actuators to move the image of the object grating with respect to the detection grating. This requires one detector and multiple measurements in time, plus a device to move the gratings with respect to each other (e.g., a translating or rotating piezoelectric element, a rotating polygon in a pupil (reflective) or field (transmissive) plane, etc.). With the temporal embodiment, there may be a sequential sampling (of at least three samples) with different phases by a single detector that occurs as part of method 800.

[0121] In some embodiments, operation 808 includes determining a process adjustment based on the determined level, and / or other operations. For example, if a determined level is not within process tolerances, the out of tolerance measurement may be caused by one or more manufacturing processes whose process parameters have drifted and / or otherwise changed so that the process is no longer producing acceptable devices (e.g., measurements may breach a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the measurement determination. The new or adjusted process parameters may be configured to cause a manufacturing process to again produce acceptable devices.

[0122] For example, a new or adjusted process parameter may cause a previously unacceptable measurement value to be adjusted back into an acceptable range. The new or adjusted process parameters may be compared to existing parameters for a given process. If there is a difference, that difference may be used to determine an adjustment for an apparatus that is used to produce the devices (e.g., parameter “x” should be increased / decreased / changed so that it matches the new or adjusted version of parameter “x” determined as part of operation 808), for example. In some embodiments, operation 808 may include electronically adjusting an apparatus (e.g., based on the determined level). Electronically adjusting an apparatus may include sending an electronic signal, and / or other communications to the apparatus, for example, which causes a change in the apparatus. The electronic adjustment may include changing a setting on the apparatus, for example, and / or other adjustments. In some embodiments, operation 808 is performed by one or more processors the same as or similar to processor PRO shown in Fig. 3 A (along with processor PRO shown in Fig. 9 and described below).

[0123] 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) 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.

[0124] 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.

[0125] 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 asstorage 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.

[0126] 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.

[0127] 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.

[0128] 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 streamsrepresenting various types of information.

[0129] 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.

[0130] 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.

[0131] 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. An interferometric level sensing system, the system comprising: a radiation source configured to irradiate a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; a shaper configured to shape the radiation to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; at least three detectors, each of the at least three detectors configured to: receive a portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating, the received portion corresponding to a part of a period of the detection grating; and generate an output signal conveying an intensity of the received portion; and a processor configured to generate interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface.2. The system of clause 1, wherein the shaper is configured such that an angular radiation distribution comprises two poles.3. The system of any of the previous clauses, wherein the dipole radiation comprises a leaf-shaped dipole.4. The system of any of the previous clauses, wherein the leaf-shaped dipole has an orientation aligned with the object grating.5. The system of any of the previous clauses, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.6. The system of any of the previous clauses, wherein the object grating is configured to diffract the dipole radiation into multiple diffraction orders, but the portions of reflected radiation from the substrate surface received by the at least three detectors each only comprise two diffraction orders for each illumination angle and wavelength.7. The system of any of the previous clauses, wherein a numerical aperture of the system selects diffraction orders generated by the object grating.8. The system of any of the previous clauses, wherein the numerical aperture is about 0.01 to 0.03.9. The system of any of the previous clauses, wherein the object grating has a 1 : 1 duty cycle, such that second or higher even diffracted orders of radiation are removed.10. The system of any of the previous clauses, wherein the object grating comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system.11. The system of any of the previous clauses, wherein the object grating has a period of about 15um.12. The system of any of the previous clauses, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.13. The system of any of the previous clauses, wherein a spot size of the dipole radiation is sufficiently large to cover an area from where the portions of reflected radiation incident on the at least three detectors reflect from the substrate surface.14. The system of any of the previous clauses, wherein generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals and caused by a shift of an image of the object grating at the detection grating.15. The system of any of the previous clauses, wherein generating the interferometric measurements comprises determining phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, and determining the level based on the phases.16. The system of any of the previous clauses, wherein determined phases comprise phase intervals.17. The system of any of the previous clauses, wherein the phase intervals are determined simultaneously.18. The system of any of the previous clauses, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.19. The system of any of the previous clauses, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumpsin reflected radiation received from the substrate surface through the detection grating.20. The system of any of the previous clauses, wherein the level comprises a height map.21. The system of any of the previous clauses, further comprising at least four detectors, such that redundancy within output signals enhances overall quality of output from the detectors.22. The system of any of the previous clauses, wherein each period is divided into a number of segments that correspond to a number of the at least three detectors, and each segment comprises a wedge, wherein each wedge deflects radiation per field point to a detector.23. The system of any of the previous clauses, wherein the dipole radiation, the at least three detectors, and the processor configured to determine the level of the substrate surface using interferometry decouples a range of the interferometric level sensing system from a period of gratings used in the system, such that the object grating has a relatively high resolution compared to gratings used in prior systems, with an enhanced range.24. The system of any of the previous clauses, wherein the interferometric level sensing system forms a portion of a lithography apparatus used for semiconductor manufacturing.25. The system of any of the previous clauses, wherein the substrate is a semiconductor wafer.26. An interferometric level sensing method, the method comprising: irradiating, with a radiation source, a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; shaping the radiation with a shaper to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; receiving, with each of at least three detectors, a portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating, the received portion corresponding to a part of a period of the detection grating; generating, with each of the at least three detectors, an output signal conveying an intensity of the received portion; and generating, with a processor, interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface.27. The method of clause 26, wherein the shaper is configured such that an angular radiation distribution comprises two poles.28. The method of any of the previous clauses, wherein the dipole radiation comprises a leaf-shaped dipole.29. The method of any of the previous clauses, wherein the leaf-shaped dipole has an orientation aligned with the object grating.30. The method of any of the previous clauses, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.31. The method of any of the previous clauses, wherein the object grating is configured to diffract thedipole radiation into multiple diffraction orders, but the portions of reflected radiation from the substrate surface received by the at least three detectors each only comprise two diffraction orders for each illumination angle and wavelength.32. The method of any of the previous clauses, wherein a numerical aperture selects diffraction orders generated by the object grating.33. The method of any of the previous clauses, wherein the numerical aperture is about 0.01 to 0.03.34. The method of any of the previous clauses, wherein the object grating has a 1: 1 duty cycle, such that second or higher even diffracted orders of radiation are removed.35. The method of any of the previous clauses, wherein the object grating comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system.36. The method of any of the previous clauses, wherein the object grating has a period of about 15um.37. The method of any of the previous clauses, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.38. The method of any of the previous clauses, wherein a spot size of the dipole radiation is sufficiently large to cover an area from where the portions of reflected radiation incident on the at least three detectors reflect from the substrate surface.39. The method of any of the previous clauses, wherein generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals and caused by a shift of an image of the object grating at the detection grating.40. The method of any of the previous clauses, wherein generating the interferometric measurements comprises determining phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, and determining the level based on the phases.41. The method of any of the previous clauses, wherein determined phases comprise phase intervals.42. The method of any of the previous clauses, wherein the phase intervals are determined simultaneously.43. The method of any of the previous clauses, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.44. The method of any of the previous clauses, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.45. The method of any of the previous clauses, wherein the level comprises a height map.46. The method of any of the previous clauses, further comprising receiving a portion of reflected radiation and generating an output signal with at least four detectors, such that redundancy within output signals enhances overall quality of output from the detectors.47. The method of any of the previous clauses, wherein each period is divided into a number ofsegments that correspond to a number of the at least three detectors, and each segment comprises a wedge, wherein each wedge deflects radiation per field point to a detector.48. The method of any of the previous clauses, wherein the dipole radiation, the at least three detectors, and the processor configured to determine the level of the substrate surface using interferometry decouples a range of an interferometric level sensing system from a period of gratings used in the system, such that the object grating has a relatively high resolution compared to gratings used in prior systems, with an enhanced range.49. The method of any of the previous clauses, wherein the interferometric level sensing system forms a portion of a lithography apparatus used for semiconductor manufacturing.50. The method of any of the previous clauses, wherein the substrate is a semiconductor wafer.51. A non-transitory computer readable medium storing instructions that, when executed by a computer, cause the computer to perform operations comprising: controlling a radiation source to irradiate a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; causing a shaper, in combination with the generator, to shape the radiation to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; causing each of at least three detectors to generate an output signal conveying an intensity of a received portion of radiation, wherein each of the at least three detectors is configured to: receive the portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating, the received portion corresponding to a part of a period of the detection grating, and generate the output signal; and generating interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface.52. The medium of clause 51, wherein the shaper is configured such that an angular radiation distribution comprises two poles.53. The medium of any of the previous clauses, wherein the dipole radiation comprises a leaf-shaped dipole.54. The medium of any of the previous clauses, wherein the leaf-shaped dipole has an orientation aligned with the object grating.55. The medium of any of the previous clauses, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.56. The medium of any of the previous clauses, wherein the object grating is configured to diffract the dipole radiation into multiple diffraction orders, but the portions of reflected radiation from the substrate surface received by the at least three detectors each only comprise two diffraction orders for each illumination angle and wavelength.57. The medium of any of the previous clauses, wherein a numerical aperture selects diffraction orders generated by the object grating.58. The medium of any of the previous clauses, wherein the numerical aperture is about 0.01 to 0.03.59. The medium of any of the previous clauses, wherein the object grating has a 1: 1 duty cycle, such that second or higher even diffracted orders of radiation are removed.60. The medium of any of the previous clauses, wherein the object grating comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system.61. The medium of any of the previous clauses, wherein the object grating has a period of about 15um.62. The medium of any of the previous clauses, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.63. The medium of any of the previous clauses, wherein a spot size of the dipole radiation is sufficiently large to cover an area from where the portions of reflected radiation incident on the at least three detectors reflect from the substrate surface.64. The medium of any of the previous clauses, wherein generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals and caused by a shift of an image of the object grating at the detection grating.65. The medium of any of the previous clauses, wherein generating the interferometric measurements comprises determining phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, and determining the level based on the phases.66. The medium of any of the previous clauses, wherein determined phases comprise phase intervals.67. The medium of any of the previous clauses, wherein the phase intervals are determined simultaneously.68. The medium of any of the previous clauses, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.69. The medium of any of the previous clauses, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.70. The medium of any of the previous clauses, wherein the level comprises a height map.71. The medium of any of the previous clauses, wherein the at least three detectors comprise at least four detectors, such that redundancy within output signals enhances overall quality of output from the detectors.72. The medium of any of the previous clauses, wherein each period is divided into a number of segments that correspond to a number of the at least three detectors, and each segment comprises a wedge, wherein each wedge deflects radiation per field point to a detector.73. The medium of any of the previous clauses, wherein the dipole radiation, the at least three detectors, and a processor configured to determine the level of the substrate surface using interferometry decouples a range of an interferometric level sensing system from a period of gratings used in the system, such that the object grating has a relatively high resolution compared to gratings used in prior systems, with an enhanced range.74. The medium of any of the previous clauses, wherein the interferometric level sensing system forms a portion of a lithography apparatus used for semiconductor manufacturing.75. The medium of any of the previous clauses, wherein the substrate is a semiconductor wafer.76. An interferometric level sensing system, the system comprising: a radiation source configured to irradiate a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; a shaper configured to shape the radiation to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; a detector configured to: receive at least three sequential portions of reflected radiation over time from the substrate surface as an image of the object grating is moved with respect to the detection grating; and generate an output signal conveying an intensity of the at least three sequential portions; and a processor configured to generate interferometric measurements based on the intensities in the output signal corresponding to the at least three sequential portions to determine a level of the substrate surface.77. The system of any of the previous clauses, wherein the shaper is configured such that an angular radiation distribution comprises two poles.78. The system of any of the previous clauses, wherein the dipole radiation comprises a leaf-shaped dipole.79. The system of any of the previous clauses, wherein the leaf-shaped dipole has an orientation aligned with the object grating.80. The system of any of the previous clauses, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.81. The system of any of the previous clauses, wherein the object grating is configured to diffract the dipole radiation into multiple diffraction orders, but the reflected radiation from the substrate surface received by the detector only comprises two diffraction orders for each illumination angle and wavelength.82. The system of any of the previous clauses, wherein a numerical aperture of the system selects diffraction orders generated by the object grating.83. The system of any of the previous clauses, wherein the numerical aperture is about 0.01 to 0.03.84. The system of any of the previous clauses, wherein the object grating has a 1: 1 duty cycle, suchthat second or higher even diffracted orders of radiation are removed.85. The system of any of the previous clauses, wherein the object grating comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system.86. The system of any of the previous clauses, wherein the object grating has a period of about 15um.87. The system of any of the previous clauses, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.88. The system of any of the previous clauses, further comprising an actuator configured to cause the image of the object grating to move with respect to the detection grating.89. The system of any of the previous clauses, wherein generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals caused by a shift of the image of the object grating at the detection grating.90. The system of any of the previous clauses, wherein generating the interferometric measurements comprises determining phases of the reflected radiation at each sequential moment in time based on the output signal, and determining the level based on the phases.91. The system of any of the previous clauses, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.92. The system of any of the previous clauses, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.93. The system of any of the previous clauses, wherein the level comprises a height map.94. The system of any of the previous clauses, wherein the interferometric level sensing system forms a portion of a lithography apparatus used for semiconductor manufacturing.95. The system of any of the previous clauses, wherein the substrate is a semiconductor wafer.96. An interferometric level sensing method, the method comprising: irradiating a substrate surface with radiation from a radiation source, the radiation source comprising a generator configured to generate the radiation; shaping the radiation with a shaper to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; receiving, with a detector, at least three sequential portions of reflected radiation over time from the substrate surface as an image of the object grating is moved with respect to the detection grating; generating, with the detector, an output signal conveying an intensity of the at least three sequential portions; and generating, with a processor, interferometric measurements based on the intensities in the output signal corresponding to the at least three sequential portions to determine a level of the substrate surface.97. The method of any of the previous clauses, wherein the shaper is configured such that an angularradiation distribution comprises two poles.98. The method of any of the previous clauses, wherein the dipole radiation comprises a leaf-shaped dipole.99. The method of any of the previous clauses, wherein the leaf-shaped dipole has an orientation aligned with the object grating.100. The method of any of the previous clauses, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.101. The method of any of the previous clauses, wherein the object grating is configured to diffract the dipole radiation into multiple diffraction orders, but the reflected radiation from the substrate surface received by the detector only comprises two diffraction orders for each illumination angle and wavelength.102. The method of any of the previous clauses, wherein a numerical aperture selects diffraction orders generated by the object grating.103. The method of any of the previous clauses, wherein the numerical aperture is about 0.01 to 0.03.104. The method of any of the previous clauses, wherein the object grating has a 1: 1 duty cycle, such that second or higher even diffracted orders of radiation are removed.105. The method of any of the previous clauses, wherein the object grating comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system.106. The method of any of the previous clauses, wherein the object grating has a period of about 15um.107. The method of any of the previous clauses, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.108. The method of any of the previous clauses, further comprising causing, with an actuator, the image of the object grating to move with respect to the detection grating.109. The method of any of the previous clauses, wherein generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals caused by a shift of the image of the object grating at the detection grating.110. The method of any of the previous clauses, wherein generating the interferometric measurements comprises determining phases of the reflected radiation at each sequential moment in time based on the output signal, and determining the level based on the phases.111. The method of any of the previous clauses, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.112. The method of any of the previous clauses, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumpsin reflected radiation received from the substrate surface through the detection grating.113. The method of any of the previous clauses, wherein the level comprises a height map.114. The method of any of the previous clauses, wherein the method is performed by a portion of a lithography apparatus used for semiconductor manufacturing.115. The method of any of the previous clauses, wherein the substrate is a semiconductor wafer.116. A non-transitory computer readable medium storing instructions that, when executed by a computer, cause the computer to perform operations comprising: controlling a radiation source to irradiate a substrate surface with radiation, the radiation source comprising a generator configured to generate the radiation; causing a shaper to shape the radiation to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; controlling a detector to receive at least three sequential portions of reflected radiation overtime from the substrate surface as an image of the object grating is moved with respect to the detection grating; causing the detector to generate an output signal conveying an intensity of the at least three sequential portions; and controlling a processor to generate interferometric measurements based on the intensities in the output signal corresponding to the at least three sequential portions to determine a level of the substrate surface.117. The medium of any of the previous clauses, wherein the shaper is configured such that an angular radiation distribution comprises two poles.118. The medium of any of the previous clauses, wherein the dipole radiation comprises a leaf-shaped dipole.119. The medium of any of the previous clauses, wherein the leaf-shaped dipole has an orientation aligned with the object grating.120. The medium of any of the previous clauses, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.121. The medium of any of the previous clauses, wherein the object grating is configured to diffract the dipole radiation into multiple diffraction orders, but the reflected radiation from the substrate surface received by the detector only comprises two diffraction orders for each illumination angle and wavelength..122. The medium of any of the previous clauses, wherein a numerical aperture selects diffraction orders generated by the object grating.123. The medium of any of the previous clauses, wherein the numerical aperture is about 0.01 to 0.03.124. The medium of any of the previous clauses, wherein the object grating has a 1 : 1 duty cycle, such that second or higher even diffracted orders of radiation are removed.125. The medium of any of the previous clauses, wherein the object grating comprises multiple lines,is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system.126. The medium of any of the previous clauses, wherein the object grating has a period of about 15um.127. The medium of any of the previous clauses, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.128. The medium of any of the previous clauses, the operations further comprising causing, with an actuator, the image of the object grating to move with respect to the detection grating.129. The medium of any of the previous clauses, wherein generating the interferometric measurements comprises measuring intensity modulation indicated by the output signals caused by a shift of the image of the object grating at the detection grating.130. The medium of any of the previous clauses, wherein generating the interferometric measurements comprises determining phases of the reflected radiation at each sequential moment in time based on the output signal, and determining the level based on the phases.131. The medium of any of the previous clauses, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.132. The medium of any of the previous clauses, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.133. The medium of any of the previous clauses, wherein the level comprises a height map.134. The medium of any of the previous clauses, wherein the operations are performed by a portion of a lithography apparatus used for semiconductor manufacturing.135. The medium of any of the previous clauses, wherein the substrate is a semiconductor wafer.136. An interferometric level sensing system, the system comprising: a radiation source configured to irradiate a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; an object grating and a detection grating configured to diffract the radiation, wherein the object grating and / or the detection grating are configured to provide field point diversity associated with diffracted radiation; a shaper configured to shape the radiation to form dipole radiation, such that the object grating is imaged on the detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; at least one detector configured to receive reflected radiation from the substrate surface and generate an output signal conveying an intensity of the radiation; and a processor configured to generate interferometric measurements based on the intensity in the output signal and the associated field point diversity to determine a level of the substrate surface.137. The system of any of the previous clauses, wherein the object grating and / or the detection grating are configured such that field point diversity results from different periods and / or pitches in the objectgrating and / or the detection grating.138. The system of any of the previous clauses, wherein different periods and / or pitches are used for even and odd field points.139. The system of any of the previous clauses, wherein using the different periods and / or pitches for the even and odd field points facilitates phase unwrapping and / or increases an absolute accuracy / periodicity error by one over a delta frequency.140. The system of any of the previous clauses, wherein the field point diversity results from phase offsets between different field points, such that a period jump occurs at different phases.141. The system of any of the previous clauses, wherein the shaper is configured such that an angular radiation distribution comprises two poles forming a leaf-shaped dipole.142. The system of any of the previous clauses, wherein the leaf-shaped dipole has an orientation aligned with the object grating.143. The system of any of the previous clauses, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.144. The system of any of the previous clauses, wherein a numerical aperture of the system selects diffraction orders generated by the object grating.145. The system of any of the previous clauses, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.146. The system of any of the previous clauses, wherein generating the interferometric measurements comprises determining phases of the reflected radiation based on the output signal, and determining the level based on the phases.147. The system of any of the previous clauses, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.148. The system of any of the previous clauses, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.149. The system of any of the previous clauses, wherein the level comprises a height map.150. The system of any of the previous clauses, wherein the interferometric level sensing system forms a portion of a lithography apparatus used for semiconductor manufacturing, and the substrate is a semiconductor wafer.151. An interferometric level sensing method, the method comprising: irradiating a substrate surface with radiation from a radiation source, the radiation source comprising a generator configured to generate radiation; diffracting the radiation with an object grating and a detection grating, wherein the object grating and / or the detection grating are configured to provide field point diversity associated with diffracted radiation; shaping the radiation with a shaper to form dipole radiation, such that theobject grating is imaged on the detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; receiving, with a detector, reflected radiation from the substrate surface, and generating an output signal conveying an intensity of the radiation; and generating, with a processor, interferometric measurements based on the intensity in the output signal and the associated field point diversity to determine a level of the substrate surface.152. The method of any of the previous clauses, wherein the object grating and / or the detection grating are configured such that field point diversity results from different periods and / or pitches in the object grating and / or the detection grating.153. The method of any of the previous clauses, wherein different periods and / or pitches are used for even and odd field points.154. The method of any of the previous clauses, wherein using the different periods and / or pitches for the even and odd field points facilitates phase unwrapping and / or increases an absolute accuracy / periodicity error by one over a delta frequency.155. The method of any of the previous clauses, wherein the field point diversity results from phase offsets between different field points, such that a period jump occurs at different phases.156. The method of any of the previous clauses, wherein the shaper is configured such that an angular radiation distribution comprises two poles forming a leaf-shaped dipole.157. The method of any of the previous clauses, wherein the leaf-shaped dipole has an orientation aligned with the object grating.158. The method of any of the previous clauses, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.159. The method of any of the previous clauses, wherein a numerical aperture selects diffraction orders generated by the object grating.160. The method of any of the previous clauses, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.161. The method of any of the previous clauses, wherein generating the interferometric measurements comprises determining phases of the reflected radiation based on the output signal, and determining the level based on the phases.162. The method of any of the previous clauses, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.163. The method of any of the previous clauses, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.164. The method of any of the previous clauses, wherein the level comprises a height map.165. The method of any of the previous clauses, wherein the method is performed by a portion of a lithography apparatus used for semiconductor manufacturing, and the substrate is a semiconductor wafer.166. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; determining a level of a surface of the substrate by: irradiating, with a radiation source, a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; shaping the radiation with a shaper to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; receiving, with each of at least three detectors, a portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating, the received portion corresponding to a part of a period of the detection grating; generating, with each of the at least three detectors, an output signal conveying an intensity of the received portion; and generating, with a processor, interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface; 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.

[0132] The concepts disclosed herein may be associated with any generic imaging system for imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths. Emerging technologies already in use include EUV (extreme ultra violet), DUV lithography that is capable of producing a 193nm wavelength with the use of an ArF laser, and even a 157nm wavelength with the use of a Fluorine laser. Moreover, EUV lithography is capable of producing wavelengths within a range of 20-5nm by using a synchrotron or by hitting a material (either solid or a plasma) with high energy electrons in order to produce photons within this range.

[0133] 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.

[0134] 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

CLAIMS:

1. An interferometric level sensing system, the system comprising: a radiation source configured to irradiate a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; a shaper configured to shape the radiation to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; at least three detectors, each of the at least three detectors configured to: receive a portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating, the received portion corresponding to a part of a period of the detection grating; and generate an output signal conveying an intensity of the received portion; and a processor configured to generate interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface.

2. The system of claim 1, wherein the shaper is configured such that an angular radiation distribution comprises two poles.

3. The system of claims 1 or 2, wherein the dipole radiation comprises a leaf-shaped dipole having an orientation aligned with the object grating.

4. The system of any of claims 1-3, wherein the dipole radiation is configured such that an image of the object grating at the detection grating comprises a pure sine wave for all wavelengths of radiation.

5. The system of any of claims 1-4, wherein the object grating is configured to diffract the dipole radiation into multiple diffraction orders, but the portions of reflected radiation from the substrate surface received by the at least three detectors each only comprise two diffraction orders for each illumination angle and wavelength.

6. The system of any of claims 1-5, wherein a numerical aperture of the system selects diffraction orders generated by the object grating, and wherein the numerical aperture is about 0.01 to7. The system of any of claims 1-6, wherein the object grating has a 1 : 1 duty cycle, such that second or higher even diffracted orders of radiation are removed.

8. The system of any of claims 1-7, wherein the object grating comprises multiple lines, is continuous, is limited in size in a y dimension relative to an x direction, and / or is oriented at an angle with respect to other components in the interferometric level sensing system.

9. The system of any of claims 1-8, wherein the dipole radiation comprises one or more wavelengths in a range of 225-450 nm.

10. The system of any of claims 1-9, wherein generating the interferometric measurements comprises at least one of measuring intensity modulation indicated by the output signals and caused by a shift of an image of the object grating at the detection grating, or determining phases of the reflected radiation at each moment in time based on the output signals from the at least three detectors, and determining the level based on the phases comprising phase intervals, and wherein the phase intervals are determined simultaneously.

11. The system of claim 10, wherein determining the level comprises constructing a height map from a series of height measurements determined based on the phases.

12. The system of claim 11, wherein generating the interferometric measurements comprises using one or more phase unwrapping algorithms configured to accommodate phase jumps in reflected radiation received from the substrate surface through the detection grating.

13. An interferometric level sensing method, the method comprising: irradiating, with a radiation source, a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; shaping the radiation with a shaper to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; receiving, with each of at least three detectors, a portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating, the received portion corresponding to a part of a period of the detection grating; generating, with each of the at least three detectors, an output signal conveying an intensity of the received portion; andgenerating, with a processor, interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface.

14. The method of claim 13, by using the interferometric level sensing system of any of claims 1 to 12.

15. A semiconductor device manufacturing method comprising : receiving a substrate with a photoresist layer; determining a level of a surface of the substrate by: irradiating, with a radiation source, a substrate surface with radiation, the radiation source comprising a generator configured to generate radiation; shaping the radiation with a shaper to form dipole radiation, such that an object grating is imaged on a detection grating after diffracted radiation from the object grating reflects off of the substrate surface, with the object grating, substrate surface, and detection grating in conjugate planes; receiving, with each of at least three detectors, a portion of reflected radiation from the substrate surface after the portion of reflected radiation is separated by the detection grating, the received portion corresponding to a part of a period of the detection grating; generating, with each of the at least three detectors, an output signal conveying an intensity of the received portion; and generating, with a processor, interferometric measurements based on the intensities in the output signals from the at least three detectors to determine a level of the substrate surface; 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.

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