Lithographic apparatus, multi-wavelength phase modulation scanning metrology system and method

Abstract

A metrology system includes a radiation source, a first optical system, a second optical system and a third optical system, and a processor. The first optical system splits the radiation into first and second beams of radiation and imposes one or more phase differences between the first and second beams. The second optical system directs the first and second beams toward a target structure to produce first and second scattered beams of radiation. The third optical system causes the first and second scattered beams to interfere at an imaging detector. The imaging detector produces a detection signal based on the interfering first and second scattered beams. The metrology system modulates one or more phase differences of the first scattered beam and the second scattered beam based on the imposed one or more phase differences. The processor analyzes the detection signal to determine a property of the target structure based at least on the modulated one or more phase differences.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 029,984, filed May 26, 2020, and U.S. Provisional Patent Application No. 63 / 093,351, filed October 19, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to a measurement system, such as an alignment device for measuring the position of features on a substrate in a photolithography system. Background Technology

[0004] A photolithography apparatus is a machine that applies a desired pattern onto a substrate (typically a target portion of the substrate). For example, photolithography apparatus can be used in the fabrication of integrated circuits (ICs). In this case, a patterning apparatus, alternatively called a mask or photomask, can be used to generate a circuit pattern to be formed on a single layer of the IC. The pattern can be transferred onto a target portion (e.g., comprising a portion of a die, one or more dies) on a substrate (e.g., a silicon wafer). Typically, the pattern is transferred by imaging the pattern onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a grid of adjacent target portions patterned sequentially. Known photolithography apparatuses include so-called steppers and so-called scanners. In a stepper, each target portion is irradiated by exposing the entire pattern onto the target portion at once; in a scanner, each target portion is irradiated by scanning the pattern with a radiation beam in a given direction (“scanning” direction) while simultaneously scanning the target portion parallel or antiparallel to this scanning direction. A pattern can also be transferred from a patterning apparatus to a substrate by imprinting the pattern onto the substrate.

[0005] Another type of lithography system is the interferometric lithography system. In this system, there is no pattern forming device; instead, the light beam is split into two beams, and these two beams interfere at a target portion of the substrate using a reflection system. This interference causes a line to be formed at the target portion of the substrate.

[0006] During photolithography operations, different processing steps may need to be sequentially formed into different layers on the substrate. Therefore, it may be necessary to position the substrate with high accuracy relative to a previous pattern formed on it. Typically, alignment marks are placed on the substrate for alignment and positioning relative to a second object. The photolithography apparatus can use alignment devices to detect the position of the alignment marks and to align the substrate using these marks to ensure accurate exposure from the mask. Misalignment between alignment marks at two different layers is measured as overlap error.

[0007] To monitor the photolithography process, parameters of the patterned substrate are measured. These parameters may include, for example, overlap errors between successive layers formed in or on the patterned substrate, and the critical linewidth of the photoresist after development. Such measurements can be performed on the product substrate and / or on a dedicated measurement target. Various techniques exist for measuring the microstructures formed during the photolithography process, including the use of scanning electron microscopes and various specialized tools. A rapid and non-invasive form of specialized inspection tool is a scatterer in which a radiation beam is directed onto a target on the surface of the substrate, and the properties of the scattered or reflected beam are measured. The properties of the substrate can be determined by comparing the properties of the beam before and after it is reflected or scattered by the substrate. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements of known properties. A spectroscopic scatterer directs a broadband radiation beam onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered over a specific narrow angular range. In contrast, an angle-resolved scatterer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0008] Errors in wafer alignment in lithography equipment lead to reduced quality, unreliable performance, and lower yield of manufactured devices, which in turn increase the time and cost of device manufacturing. Summary of the Invention

[0009] Therefore, it is desirable to improve metrology techniques to allow for more accurate placement of lithographic structures on wafers.

[0010] In some embodiments, the measurement system includes a radiation source, a first optical system, a second optical system, a third optical system, and a processor. The first optical system is configured to split the radiation into a first beam and a second beam, and to apply one or more phase differences between the first and second beams. The second optical system is configured to guide the first and second beams toward a target structure to generate a first scattered beam and a second scattered beam. The third optical system is configured to cause the first and second scattered beams to interfere at an imaging detector. The imaging detector is configured to generate a detection signal based on the interfering first and second scattered beams. The measurement system is configured to modulate one or more phase differences between the first and second scattered beams based on the applied phase differences. The processor is configured to analyze the detection signal to determine the properties of the target structure based at least on the modulated phase differences.

[0011] In some embodiments, a photolithography apparatus system includes an illumination system, a projection system, and a measurement system. The measurement system includes a radiation source, a first optical system, a second optical system, and a third optical system, as well as a processor. The illumination system is configured to illuminate a pattern formed by a pattern forming apparatus. The projection system is configured to project an image of the pattern onto a substrate. The first optical system is configured to split the radiation into a first beam and a second beam, and to apply one or more phase differences between the first and second beams. The second optical system is configured to guide the first and second beams toward a target structure to generate a first scattered beam and a second scattered beam. The third optical system is configured to cause the first and second scattered beams to interfere at an imaging detector. The imaging detector is configured to generate a detection signal based on the interfering first and second scattered beams. The measurement system is configured to modulate one or more phase differences between the first and second scattered beams based on the applied phase differences. The processor is configured to analyze the detection signal to determine the properties of the target structure based at least on the modulated phase differences.

[0012] In some embodiments, a method includes generating radiation. The method further includes splitting the radiation into a first beam and a second beam using a first optical system. The method further includes applying one or more phase differences between the first beam and the second beam using the first optical system. The method further includes guiding the first and second beams toward a target to generate a first scattered beam and a second scattered beam of radiation. The method further includes causing the first and second scattered beams to interfere at an imaging detector. The method further includes modulating one or more phase differences between the first and second scattered beams. The method further includes using the imaging detector to generate a detection signal. The method further includes analyzing the detection signal to determine the properties of the target structure based at least on the modulated one or more phase differences.

[0013] Further features of this disclosure, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. It should be noted that this disclosure is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will become apparent to those skilled in the art based on the teachings contained herein. Attached Figure Description

[0014] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the disclosure and enable those skilled in the art to make and use the disclosure.

[0015] FIG. 1AA schematic diagram of a reflective lithography apparatus according to some embodiments is shown.

[0016] FIG. 1B A schematic diagram of a transmission lithography apparatus according to some embodiments is shown.

[0017] FIG. 2 A more detailed schematic diagram of the reflective lithography apparatus according to some embodiments is shown.

[0018] FIG. 3 A schematic diagram of a photolithography unit according to some embodiments is shown.

[0019] FIG. 4A and FIG. 4B An inspection device according to some embodiments is shown.

[0020] FIG. 5 The structure of the target is shown according to some embodiments.

[0021] FIG. 6 The images shown are detection images according to some embodiments.

[0022] FIG. 7 , FIG. 8 and FIG. 9 A measurement system according to some embodiments is shown.

[0023] FIG. 10 The following are method steps, according to some embodiments, for performing the functions of the embodiments described herein.

[0024] FIG. 11 An interference pattern formed on a detector according to some embodiments is shown.

[0025] FIG. 12 Various graphs illustrating the parameters and effects related to the phase difference of the modulated radiation beam, according to some embodiments, are shown.

[0026] FIG. 13 to FIG. 15 A phase modulation portion of an illumination system 1312 according to some embodiments is shown.

[0027] Features of this disclosure will become apparent from the specific embodiments described below, when taken in conjunction with the accompanying drawings, in which the same reference numerals consistently identify corresponding elements. In the drawings, similar reference numerals generally indicate the same, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost numeral of the reference numerals identifies the drawing in which such reference numeral first appears. Unless otherwise stated, the drawings provided throughout this disclosure should not be construed as tolerancing drawings. Detailed Implementation

[0028] This specification discloses one or more embodiments incorporating the features of this disclosure. The disclosed embodiments are provided as examples. The scope of the invention is not limited to the disclosed embodiments. The claimed features are defined by the appended claims.

[0029] The described embodiments, as well as the references to "an embodiment," "embodiment," "exemplary embodiment," etc., used in the specification, may include specific features, structures, or characteristics. However, each embodiment may not necessarily include the specific features, structures, or characteristics described. Furthermore, such phrases do not necessarily refer to the same embodiment. Additionally, when a specific feature, structure, or characteristic is described in connection with an embodiment, it should be understood that, whether explicitly described or not, implementing such a feature, structure, or characteristic in combination with other embodiments is within the knowledge of those skilled in the art.

[0030] For ease of description, spatial relative terms such as “below,” “under,” “lower,” “above,” “on,” “higher,” etc., are used herein to describe the relationship between one element or feature and another element or feature as illustrated in the accompanying drawings. These spatial relative terms are intended to cover different orientations of the device other than those depicted in the figures during use or operation. The device may be otherwise oriented (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein can be interpreted accordingly.

[0031] As used herein, the term "about" refers to a value relating to a given quantity that may vary based on a particular technique. Based on the particular technique, the term "about" may indicate the value of a given quantity that varies within, for example, 10-30% above or below the value (e.g., ±10%, ±20%, or ±30% of the value).

[0032] Embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of this disclosure may also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any means for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable magnetic storage medium may include read-only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash storage devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), etc. Additionally, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and these actions are actually generated by a computing device, processor, controller, or other means of executing firmware, software, routines, instructions, etc.

[0033] However, it is helpful to present example environments in which embodiments of this disclosure may be implemented before describing such embodiments in more detail.

[0034] Example lithography system

[0035] FIG. 1A and FIG. 1B These are schematic diagrams of lithography apparatus 100 and 100', respectively, which can implement embodiments of the present disclosure. Lithography apparatus 100 and 100' each include the following components: an irradiation system (irradiator) IL configured to modulate a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask stage) MT configured to support a pattern forming apparatus (e.g., a mask, stencil, or dynamic pattern forming apparatus) MA and connected to a first positioner PM configured to accurately position the pattern forming apparatus MA; and a substrate stage (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate W. Lithography apparatuses 100 and 100' also have a projection system PS configured to project a pattern imparted by the radiation beam B by the pattern forming apparatus MA onto a target portion (e.g., comprising one or more dies) C of the substrate W. In lithography apparatus 100, the pattern forming apparatus MA and the projection system PS are reflective. In the photolithography equipment 100', the pattern forming apparatus MA and the projection system PS are of the transmissive type.

[0036] The irradiation system IL may include various types of optical components, such as refractive, reflective, reflective-refractive, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for guiding, shaping, or controlling the radiation beam B.

[0037] The support structure MT holds the patterning apparatus MA in a manner dependent on the orientation of the patterning apparatus MA relative to a reference frame, the design of at least one of the lithography apparatuses 100 and 100', and other conditions such as whether the patterning apparatus MA is maintained in a vacuum environment. The support structure MT can employ mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning apparatus MA. The support structure MT can be a frame or a platform, and for example, it can be fixed or movable as needed. By using sensors, the support structure MT can ensure that the patterning apparatus MA is positioned, for example, relative to the projection system PS.

[0038] The term "patterning apparatus" MA is broadly interpreted to refer to any apparatus capable of imparting a pattern to a radiation beam B in the cross-section of the beam, thereby generating a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer of a device formed in the target portion C to form an integrated circuit.

[0039] The terms “inspection equipment”, “measuring equipment”, etc., may be used herein to refer to, for example, apparatus or systems used to measure the properties of a structure (e.g., overlap error, critical size parameters) or to inspect wafers (e.g., alignment equipment) in a lithography apparatus.

[0040] The pattern forming apparatus MA can be a transmissive type (e.g., FIG. 1B (like the lithography equipment 100') or reflective (such as...) FIG. 1A (As in the photolithography apparatus 100). Example MA of a pattern forming apparatus includes a photomask, a programmable mirror array, or a programmable LCD panel. Masks are well-known in photolithography and include mask types such as binary masks, alternating phase-shift masks, or attenuation phase-shift masks, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect the incident radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam B reflected by the matrix of small mirrors.

[0041] As used herein, the term "projection system" PS includes any type of projection system, including refractive, reflective, reflective-refractive, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as suitable for the exposure radiation used or for other factors such as the use of an immersion liquid on a substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation because other gases may absorb excessive radiation or electrons. A vacuum environment may therefore be provided throughout the beam path by means of vacuum walls and a vacuum pump.

[0042] The lithography apparatus 100 and / or lithography apparatus 100' can be of the type having two (dual-platform) or more substrate stages WT (and / or two or more mask stages). In such a "multi-platform substrate stage" machine, additional substrate stages WT can be used in parallel, or one or more other substrate stages WT can be used for exposure while preparatory steps are performed on one or more stages. In some cases, the additional stage may not be a substrate stage WT.

[0043] The photolithography apparatus can also be of the type in which at least a portion of the substrate can be covered by a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquid can also be applied to other spaces within the photolithography apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system. As used herein, the term "immersion" does not mean that a structure such as the substrate must be immersed in a liquid, but rather that "immersion" simply means that the liquid is located between the projection system and the substrate during exposure.

[0044] refer to FIG. 1A and 1B The irradiator IL receives a radiation beam from the radiation source SO. When the source SO is an excimer laser, the source SO and the lithography apparatus 100, 100' can be separate physical entities. In this case, the source SO is not considered part of the lithography apparatus 100 or 100', and the radiation beam is delivered by means of a beam delivery system BD (in which...) including, for example, suitable directional mirrors and / or beam expanders. FIG. 1B (In the middle) the beam is transferred from the source SO to the irradiator IL. In other cases, the source SO may be a component of the lithography apparatus 100, 100' – for example, when the source SO is a mercury lamp. The source SO, the irradiator IL, and the beam transfer system BD, which may be provided if necessary, can be collectively referred to as the radiation system.

[0045] The irradiator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam. FIG. 1B (In the middle). Typically, at least the outer radial range and / or inner radial range (typically referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the pupil plane of the irradiator can be adjusted. Furthermore, the irradiator IL may include various other components (in... FIG. 1B (In the middle), such as integrator IN and concentrator CO. Irradiator IL can be used to adjust the radiation beam B so as to have the desired uniformity and intensity distribution in its cross section.

[0046] refer to FIG. 1AThe radiation beam B is incident on and patterned by the patterning apparatus (e.g., mask) MA, which is held on the support structure (e.g., mask stage) MT. In the lithography apparatus 100, the radiation beam B is reflected from the patterning apparatus (e.g., mask) MA. After being reflected from the patterning apparatus (e.g., mask) MA, the radiation beam B is passed through a projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. The substrate stage WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B) by means of a second positioner PW and a position sensor IF2 (e.g., an interferometer device, a linear encoder, a 2D encoder, or a capacitive sensor). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning apparatus (e.g., mask) MA relative to the path of the radiation beam B. The pattern forming apparatus (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0047] refer to FIG. 1B The radiation beam B is incident on and patterned by the patterning apparatus (e.g., mask MA), which is held on the support structure (e.g., mask stage MT). Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto the target portion C of the substrate W. The projection system has a pupil PPU conjugate to the illumination system pupil IPU. A portion of the radiation originates from the intensity distribution at the illumination system pupil IPU and traverses the mask pattern unaffected by diffraction at the mask pattern, producing an image of the intensity distribution at the illumination system pupil IPU.

[0048] The projection system PS projects an image MP' of the mask pattern MP onto a photoresist layer coated on the substrate W, wherein the image is formed by a diffracted beam generated from the marked pattern MP by radiation passing through the intensity distribution. For example, the mask pattern MP may comprise an array of lines and spacings. Diffraction of radiation at the array that differs from zero-order diffraction produces a diffracted beam that has a directional change in a direction perpendicular to the lines. An undiffracted beam (i.e., the so-called zero-order diffracted beam) traverses the pattern without any change in propagation direction. The zero-order diffracted beam passes through the upper lens or upper lens group of the projection system PS (located upstream of the conjugate pupil PPU of the projection system PS) to reach the conjugate pupil PPU. A portion of the intensity distribution in the plane of the conjugate pupil PPU and associated with the zero-order diffracted beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. An aperture device PD is, for example, positioned at or approximately located in the plane including the conjugate pupil PPU of the projection system PS.

[0049] The projection system PS is arranged to capture not only the zero-order diffraction beam, but also first-order or higher-order diffraction beams (not shown) by means of a lens or lens group L. In some embodiments, dipole illumination for imaging a line pattern extending in a direction perpendicular to the line can be used to take advantage of the resolution enhancement effect of dipole illumination. For example, a first-order diffraction beam interferes with a corresponding zero-order diffraction beam at the level of the wafer W to produce an image of the line pattern MP with the highest possible resolution and process window (i.e., the available depth of focus combined with an acceptable exposure dose deviation). In some embodiments, astigmatism can be reduced by providing a radiating pole (not shown) in the phase limit of the pupil IPU of the illumination system. Furthermore, in some embodiments, astigmatism can be reduced by blocking the zero-order beam in the conjugate pupil PPU of the projection system that is associated with a radiating pole in the phase limit. Furthermore, some embodiments are described in more detail in US 7,511,799 B2, published March 31, 2009, the entire contents of which are incorporated herein by reference.

[0050] With the aid of a second positioner PW and a position sensor IF (e.g., an interferometer device, linear encoder, 2D encoder, or capacitive sensor), the substrate stage WT can be moved precisely (e.g., to position different target portions C in the path of the radiation beam B). Similarly, (e.g., after mechanical acquisition from a mask library or during scanning) the first positioner PM and another position sensor (not in use) can be moved. FIG. 1B (As shown in the figure) the mask MA is used to accurately position the path relative to the radiation beam B.

[0051] Typically, the mask stage MT can be moved using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) that form part of the first positioner PM. Similarly, the substrate stage WT can be moved using a long-stroke module and a short-stroke module that form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask stage MT may be connected only to the short-stroke actuator, or it may be fixed. The mask MA and substrate W can be aligned using mask alignment marks M1, M2, and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks occupy dedicated target portions, they can be located in the space between multiple target portions (these are called scribing alignment marks). Similarly, when more than one die is placed on the mask MA, patterning apparatus alignment marks can be located between these dies.

[0052] The mask stage MT and pattern forming apparatus MA can be located within a vacuum chamber, where an in-vacuum robot IVR can be used to move the pattern forming apparatus (such as a mask or template) into and out of the vacuum chamber. Alternatively, when the mask stage MT and pattern forming apparatus MA are outside the vacuum chamber, an out-of-vacuum robot can be used for various transport operations similar to an in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated to smoothly transfer any payload (e.g., a mask) to a fixed kinematic mount at the transport station.

[0053] Photolithography equipment 100 and 100 can be used in at least one of the following modes:

[0054] 1. In step mode, the support structure (e.g., mask stage) MT and substrate stage WT remain substantially stationary, while the entire pattern imparted to the radiation beam is projected onto the target portion C at once (i.e., single static exposure). The substrate stage WT then moves in the X and / or Y directions, allowing different target portions C to be exposed.

[0055] 2. In scanning mode, the support structure (e.g., mask stage) MT and the substrate stage WT are scanned simultaneously, while the pattern applied to the radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The velocity and orientation of the substrate stage WT relative to the support structure (e.g., mask stage) MT can be determined by the magnification (reduction) and image inversion characteristics of the projection system PS.

[0056] 3. In another mode, a pattern imparted by the radiation beam B is projected onto the target portion C while the support structure (e.g., mask stage) MT holding the programmable patterning apparatus (WT) is kept substantially fixed and the substrate stage WT is moved or scanned. A pulsed radiation source SO can be used, and the programmable patterning apparatus is updated as needed after each movement of the substrate stage WT or between successive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography utilizing programmable patterning apparatuses (such as programmable mirror arrays).

[0057] Alternatively, the described usage pattern or a combination and / or variation of completely different usage patterns may be adopted.

[0058] In another embodiment, the lithography apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Typically, the EUV source is configured in a radiation system, and a corresponding irradiation system is configured to adjust the EUV radiation beam from the EUV source.

[0059] FIG. 2 The lithography apparatus 100 is shown in more detail, including the source collector device SO, the irradiation system IL, and the projection system PS. The source collector device SO is constructed and arranged such that a vacuum environment is maintained within the enclosure structure 220 of the source collector device SO. The plasma 210 emitting EUV radiation can be formed by a discharge-generated plasma source. EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), in which a very hot plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. For example, the very hot plasma 210 is generated by a discharge that causes at least partial ionization of the plasma. For efficient radiation generation, it may be necessary to use, for example, Xe, Li, Sn vapor with a partial pressure of 10 Pa, or any other suitable gas or vapor. In some embodiments, a plasma of excited tin (Sn) is provided to generate EUV radiation.

[0060] Radiation emitted by the thermal plasma 210 is transferred from the source chamber 211 to the collector chamber 212 via a gas barrier or contaminant trap 230 (also referred to in some cases as a contaminant barrier or vane trap) optionally located in or behind an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier, or a combination of a gas barrier and a channel structure. The contaminant traps or contaminant barriers 230 further indicated herein include at least a channel structure.

[0061] The collector chamber 211 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected to be focused at a virtual source point IF. The virtual source point is generally referred to as the intermediate focus IF, and the source collector device is arranged such that the intermediate focus IF is located at or near the opening 219 in the enclosure structure 220. The virtual source point IF is an image of the radiative emission plasma 210. A grating spectral filter 240 is specifically used to suppress infrared (IR) radiation.

[0062] Subsequently, the radiation traverses the illumination system IL, which may include a faceted field mirror assembly 222 and a faceted pupil mirror assembly 224. The faceted field mirror assembly 222 and the faceted pupil mirror assembly 224 are arranged to provide a desired angular distribution of the radiation beam 221 at the patterning apparatus MA, and to provide desired radiation intensity uniformity at the patterning apparatus MA. When the radiation beam 221 is reflected at the patterning apparatus MA, it is held by the support structure MT to form a patterned beam 226, and the patterned beam 226 is imaged by the projection system PS via reflective elements 228 and 229 onto a substrate W held by a wafer stage or substrate stage WT.

[0063] In the illumination optics unit IL and projection system PS, there can typically be more components than shown. The grating spectral filter 240 may be optionally present, depending on the type of lithography equipment. Additionally, more components may be present than... FIG. 2 The mirror shown in the figure has more mirrors, for example, in the projection system PS, besides the mirrors that may exist. FIG. 2 In addition to the reflective element shown, there are one to six additional reflective elements.

[0064] Collector optics CO (e.g.) FIG. 2 The illustrated image is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, and is only one example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are arranged axially symmetrically about the optical axis O, and this type of collector optics CO is preferably used in conjunction with a plasma source generated by discharge (often referred to as a DPP source).

[0065] Exemplary photolithography unit

[0066] FIG. 3A lithography unit 300, sometimes referred to as a lithography cell or cluster, is shown according to some embodiments. A lithography apparatus 100 or 100' may form part of the lithography unit 300. The lithography unit 300 may also include one or more devices for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these devices include: a spin coater SC for depositing a resist layer, a developing apparatus DE for developing the exposed resist, a chill plate CH, and a baking plate BK. A substrate transport device or robot RO picks up a substrate from input / output ports I / O1, I / O2, moves the substrate between different process devices, and delivers the substrate to the feed stage LB of the lithography apparatus 100 or 100'. These devices are generally collectively referred to as a track or coating and developing system and are under the control of a track or coating and developing system control unit TCU, which is itself controlled by a management and control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Therefore, different devices can be operated to maximize throughput and processing efficiency.

[0067] Exemplary inspection device

[0068] To control the photolithography process and accurately place device features onto the substrate, alignment marks are typically set on the substrate, and the photolithography apparatus includes one or more alignment devices and / or systems by which the positions of the marks on the substrate must be accurately measured. These alignment devices are effective position measurement devices. Different types of marks and different types of alignment devices and / or systems are known from different times and different manufacturers. One type of system widely used in current photolithography apparatus is based on a self-reference interferometer as described in U.S. Patent No. 6,961,116 (denBoef et al.). Typically, the marks are measured separately to obtain the X and Y positions. However, combined X and Y measurements can be performed using the technique described in U.S. Publication No. 2009 / 195768A (Bijnen et al.). The entire contents of both disclosures are incorporated herein by reference.

[0069] FIG. 4AThe schematic diagram shows a cross-sectional view of an inspection apparatus 400 according to an embodiment, which may be implemented as part of a lithography apparatus 100 or 100'. In some embodiments, the inspection apparatus 400 may be configured to align a substrate (e.g., substrate W) relative to a patterning apparatus (e.g., patterning apparatus MA). The inspection apparatus 400 may also be configured to detect the position of alignment marks on the substrate and use the detected position of the alignment marks to align the substrate relative to the patterning apparatus or other components of the lithography apparatus 100 or 100'. Such alignment of the substrate ensures accurate exposure of one or more patterns on the substrate.

[0070] In some embodiments, the inspection device 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and an overlap calculation processor 432. The illumination system 412 may be configured to provide a narrow-band electromagnetic radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a wavelength spectrum between about 500 nm and about 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a wavelength spectrum between about 500 nm and about 900 nm. The illumination system 412 may also be configured to provide one or more passbands with a substantially constant center wavelength (CWL) value over a long period of time (e.g., over the lifetime of the illumination system 412). As discussed above, in current alignment systems, this configuration of the illumination system 412 can help prevent the actual CWL value from deviating from the desired CWL value. Therefore, using a constant CWL value can improve the long-term stability and accuracy or precision of the alignment system (e.g., inspection device 400) compared to the current alignment device.

[0071] In some embodiments, beam splitter 414 may be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 may be split into radiation sub-beams 415 and 417, such as... FIG. 4AAs shown in the diagram. The beam splitter 414 can also be configured to guide a sub-beam of radiation 415 onto a substrate 420 placed on a platform 422. In one example, the platform 422 can be moved along direction 424. The sub-beam of radiation 415 can be configured to illuminate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 can be coated with a radiation-sensitive film. In some embodiments, the alignment mark or target 418 can have 180° symmetry. That is, when the alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 can be substantially identical to the unrotated alignment mark or target 418. The target 418 on substrate 420 can be: (a) a resist layer grating comprising grating strips formed by solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlapping target structure, comprising resist gratings overlapping or interlaced on the product layer grating. The grating strips may alternatively be etched into the substrate. This pattern is sensitive to chromatic aberration and illumination symmetry in the photolithography projection apparatus (particularly the projection system PL), and the presence of such aberrations will indicate variations in themselves within the printed grating. An in-line method for measuring linewidth, spacing, and critical dimensions in device fabrication utilizes a technique known as "scattering measurement." The scattering measurement method is described in Raymond et al., “Multiparameter Grating Metrology Using SPIEScatterometry” (J. Vac. Sci. Tech. B, Vol. 15, No. 2, pp. 361-368 (1997)) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography” (SPIE, Vol. 3677 (1999)), both of which are incorporated herein by reference in their entirety. In scattering measurements, light is reflected by a periodic structure in the target, and the resulting reflection spectrum is detected at a given angle. The structure that produces the reflection spectrum is reconstructed, for example, using rigorous coupled-wave analysis (RCWA) or by comparison with a simulated library of patterns. Thus, scattering measurement data of the printed grating is used to reconstruct the grating. Parameters of the grating (such as linewidth and line shape) can be input into the reconstruction process, which is performed by a processing unit (PU) based on knowledge of the printing steps and / or other scattering measurement processes.

[0072] In some embodiments, according to the embodiments, the beam splitter 414 may also be configured to receive the diffracted radiation beam 419 and split the diffracted radiation beam 419 into at least two radiation sub-beams. The radiation beam 419 may be split into radiation sub-beams 429 and 439, such as... FIG. 4AAs shown in the image.

[0073] It should be noted that although beam splitter 414 is shown guiding radiant sub-beam 415 toward alignment mark or target 418 and diffracted radiant sub-beam 429 toward interferometer 426, this disclosure is not limited thereto. Those skilled in the art will appreciate that other optical arrangements can be used to obtain similar results in illuminating alignment mark or target 418 onto substrate 420 and detecting an image of alignment mark or target 418.

[0074] like FIG. 4A As illustrated, interferometer 426 can be configured to receive a radiating sub-beam 417 and a diffracted radiating sub-beam 429 via beam splitter 414. In an example embodiment, the diffracted radiating sub-beam 429 may be at least a portion of the radiating sub-beam 415 that can be reflected from the alignment mark or target 418. In this example embodiment, interferometer 426 includes any suitable set of optical elements, for example, it may be configured as a prism assembly that forms two images of the alignment mark or target 418 based on the received diffracted radiating sub-beam 429. It should be understood that it is not necessary to form images of good quality, but the features of the alignment mark 418 should be distinguishable. Interferometer 426 can also be configured to rotate one of the two images by 180° relative to the other image and to interferometrically recombine the rotated and unrotated images.

[0075] In some embodiments, detector 428 may be configured to receive a recombined image via interferometer signal 427 when the alignment axis 421 of inspection device 400 passes through the center of symmetry (not shown) of alignment mark or target 418, and to detect interference resulting from the recombined image. This interference may be due to the alignment mark or target 418 being 180° symmetrical, and according to an example embodiment, the recombined image interferes constructively or destructively. Based on the detected interference, detector 428 may also be configured to determine the position of the center of symmetry of alignment mark or target 418 and thus detect the position of substrate 420. According to an example, alignment axis 421 may be aligned with an optical beam perpendicular to substrate 420 and passing through the center of image rotation interferometer 426. Detector 428 may also be configured to estimate the position of alignment mark or target 418 by implementing sensor characteristics and interacting with changes in the wafer marking process.

[0076] In another embodiment, detector 428 determines the location of the center of symmetry of alignment mark or target 418 by performing one or more of the following measurements:

[0077] 1. Measure positional changes for each wavelength (positional shifts between different colors);

[0078] 2. Regarding the changes in measurement position at each order (positional shifts between diffraction orders); and

[0079] 3. For changes in the measurement position of each polarization (positional offset between each polarization).

[0080] For example, this data can be acquired using any type of alignment sensor, such as a SMASH (SMart alignment sensor hybrid) sensor, as described in U.S. Patent No. 6,961,116, which employs a self-reference interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software or ATHENA (an advanced technique using higher-order alignment enhancement), as described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector. Both patents are incorporated herein by reference in their entirety.

[0081] In some embodiments, the beam analyzer 430 may be configured to receive and determine the optical state of the diffracted sub-beams 439. The optical state may be a measure of beam wavelength, polarization, or beam profile. The beam analyzer 430 may also be configured to determine the position of the platform 422 and correlate the position of the platform 422 with the position of the center of symmetry of the alignment mark or target 418. This allows for accurate knowledge of the position of the alignment mark or target 418 relative to the alignment platform 422, and thus the position of the substrate 420 relative to the alignment platform 422. Alternatively, the beam analyzer 430 may be configured to determine the position of the inspection device 400 or any other reference element, such that the center of symmetry of the alignment mark or target 418 can be known relative to the inspection device 400 or any other reference element. The beam analyzer 430 may be a point or imaging polarimeter with some form of band selectivity. In some embodiments, according to other embodiments, the beam analyzer 430 may be directly integrated into the inspection device 400 or connected via several types of optical fiber: polarization-maintaining single-mode fiber, multimode fiber, or imaging fiber.

[0082] In some embodiments, the beam analyzer 430 may also be configured to determine overlap data between two patterns on the substrate 420. One of these patterns may be a reference pattern on a reference layer. The other pattern may be an exposure pattern on an exposure layer. The reference layer may be an etched layer already present on the substrate 420. The reference layer may be generated by exposing the reference pattern on the substrate using photolithography apparatus 100 and / or 100'. The exposure layer may be an exposed resist layer adjacent to the reference layer. The exposure layer may be generated by exposing an exposure pattern on the substrate 420 using photolithography apparatus 100 or 100'. The exposure pattern on the substrate 420 may correspond to movement of the substrate 420 due to platform 422. In some embodiments, the measured overlap data may also indicate the offset between the reference pattern and the exposure pattern. The measured overlap data may be used as calibration data to calibrate the exposure pattern exposed by photolithography apparatus 100 or 100' such that, after calibration, the offset between the exposure layer and the reference layer can be minimized.

[0083] In some embodiments, the beam analyzer 430 may also be configured to determine a model of the product stack profile of the substrate 420, and may be configured to measure the overlap, critical dimensions, and focal length of the target 418 in a single measurement. The product stack profile includes information about the stacked product, such as alignment marks, target 418, or substrate 420, and may include optical signature measurements caused by variations in the marking process, which are functions of illumination variations. The product stack profile may also include product grating profiles, mark stack profiles, and mark asymmetry information. An example of the beam analyzer 430 is the ieldstar manufactured by ASML in Veldhoven, Netherlands. TM As described in U.S. Patent No. 8,706,442, which is incorporated herein by reference in its entirety. The beam analyzer 430 may also be configured to process information relating to specific properties of the exposure pattern in the layer. For example, the beam analyzer 430 may process: overlap parameters (indicating the positioning accuracy or precision of the layer relative to a previous layer on the substrate, or the positioning accuracy or precision of the first layer relative to a mark on the substrate), focus parameters, and / or critical size parameters of the image depicted in the layer (e.g., linewidth and its variation). Other parameters are image parameters relating to the quality of the image of the depicted exposure pattern.

[0084] In some embodiments, a detector array (not shown) may be connected to the bundle analyzer 430, allowing for accurate stack-up profile detection, as discussed below. For example, detector 428 may be a detector array. Several options are possible for the detector array: multimode fiber bundles, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. For stability reasons, using multimode fiber bundles allows for remote positioning of any dissipative elements. Discrete pin detectors can provide a large dynamic range, but each requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays offer many elements that can be read at high speeds and are particularly valuable when using phase-stepped detection.

[0085] In some embodiments, the second beam analyzer 430' can be configured to receive and determine the optical state of the diffraction sub-beam 429, such as FIG. 4B As shown in the diagram. The optical state can be a measure of beam wavelength, polarization, or beam profile. The second beam analyzer 430' can be the same as beam analyzer 430. Alternatively, the second beam analyzer 430' can be configured to perform at least all the functions of beam analyzer 430, such as determining the position of platform 422 and associating the position of platform 422 with the position of the center of symmetry of alignment mark or target 418. In this way, the position of alignment mark or target 418 relative to alignment platform 422 can be accurately known, and therefore the position of substrate 420 relative to alignment platform 422 can be known. Alternatively, beam analyzer 430 can be configured to determine the position of inspection device 400 or any other reference element, such that the center of symmetry of alignment mark or target 418 can be known relative to inspection device 400 or any other reference element. The second beam analyzer 430' can also be configured to determine overlap data between two patterns and a model of the product stack profile of substrate 420. The second beam analyzer 430' can also be configured to measure the overlap, critical dimension, and focal length of target 418 in a single measurement.

[0086] In some embodiments, and according to other embodiments, the second beam analyzer 430' may be directly integrated into the inspection device 400, or it may be connected via several types of optical fibers: polarization-maintaining single-mode fiber, multimode fiber, or imaging fiber. Alternatively, the second beam analyzer 430' and the beam analyzer 430 may be combined to form a single analyzer (not shown) configured to receive and determine the optical state of the diffraction sub-beams 429 and 439.

[0087] In some embodiments, processor 432 receives information from detector 428 and beam analyzer 430. For example, processor 432 may be an overlap calculation processor. The information may include a model of the product stack profile constructed by beam analyzer 430. Alternatively, processor 432 may use received information about product markings to construct a model of the product marking profile. In either case, processor 432 uses or combines the model of the product marking profile to construct a model of the stacked product and overlap marking profiles. The stack model is then used to determine the overlap offset and to minimize the influence of the spectrum on the overlap offset measurement. Processor 432 may generate a basic correction algorithm based on information received from detector 428 and beam analyzer 430, including but not limited to the optical state of the illumination beam, alignment signal, associated position estimation, and optical state in the pupil, image, and other planes. The pupil plane is a plane in which the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth of the radiation. Processor 432 may use the basic correction algorithm to characterize the inspection device 400 with reference to wafer markings and / or alignment marks 418.

[0088] In some embodiments, processor 432 may also be configured to determine, for each mark, a printed pattern position offset error relative to the sensor-estimated error, based on information received from detector 428 and beam analyzer 430. This information includes, but is not limited to, the product stack profile, measurements of overlap, critical dimensions, and focal length for each alignment mark or target 418 on substrate 420. Processor 432 may utilize a clustering algorithm to group marks into sets of similar constant offset errors and generate an alignment error offset correction table based on this information. The clustering algorithm may be based on overlap measurements, position estimates, and additional optical stacking process information associated with each set of offset errors. Overlap is calculated for multiple different marks, such as overlapping targets with positive and negative deviations around a programmed overlap offset. The target with the smallest measured overlap is used as a reference (because it is measured with optimal accuracy, i.e., precision). The overlap error can be derived from this measured small overlap and the suppressed programmed overlap of its corresponding target. Table 1 illustrates how this is performed. In the example shown, the smallest measured overlap is -1 nm. However, this relates to a target with a programmed overlap of -30 nm. Therefore, the process must introduce an overlap error of 29 nm.

[0089]

[0090] The minimum value can be used as a reference point, relative to which the offset between the measured overlap and the expected overlap due to programmed overlap can be calculated. This offset determines the overlap error for each marker or a set of markers with similar offsets. Thus, in the example of Table 1, at the target location with a programmed overlap of 30 nm, the minimum measured overlap is -1 nm. The difference between the expected overlap and the measured overlap at other targets is compared with the reference. Tables such as Table 1 can also be obtained based on the markers and targets 418 under different irradiation settings, allowing the determination and selection of the irradiation settings that result in the minimum overlap error and their corresponding calibration factors. Subsequently, the processor 432 can group the markers into sets of similar overlap errors. The criteria used for marker grouping can be adjusted based on different process controls, such as different error tolerances for different processes.

[0091] In some embodiments, processor 432 may identify that all or most members of the group have similar offset errors and, based on their additional optical overlay measurements, apply individual offset corrections from the clustering algorithm to each mark. Processor 432 may determine the correction for each mark and feed the correction back to lithography apparatus 100 or 100' to correct errors in the overlap, for example, by feeding the correction to alignment apparatus 400.

[0092] FIG. 5 The structure of target 518 according to some embodiments is shown. In some embodiments, target 518 includes grating structures arranged in four quadrants. The grating structure in each quadrant is perpendicular to the grating structure in the adjacent quadrant. Circle 503 indicates the size of the illumination spot relative to the area of ​​target 518. The area of ​​the illumination spot is smaller than the area of ​​target 518 (e.g., underfilled). In some embodiments, the area of ​​the illumination spot is larger than the area of ​​target 518 (e.g., overfilled, not shown). The structure shown for target 518 can be used for, for example, target 418 ( FIG. 4A , FIG. 4B ), 718 FIG. 7 ) and 818 FIG. 8 ).

[0093] FIG. 6 A detection image 651 is shown according to some embodiments. In some embodiments, the detection image using a measurement system may include one or more moiré pattern 652, particularly if the measurement system is a system that performs image detection on, for example, a target 518. FIG. 5 In the case of ),

[0094] In some embodiments, the inspection apparatus and systems described herein may perform measurements at various locations on a target using multiple discrete steps or continuous scanning (or a combination of both). The embodiments described herein disclose the structure and functionality for improving the accuracy of inspections using scanning operations and modulation of the radiation phase.

[0095] FIG. 7 A measurement system 700 according to some embodiments is shown. In some embodiments, the measurement system 700 may also represent a more detailed view of the inspection device 400. FIG. 4A and FIG. 4B ).For example, FIG. 7 The figure shows a more detailed view of the irradiation system 412 and its function. Unless otherwise stated, FIG. 7 In and FIG. 4A and FIG. 4B Elements that share similar reference numerals (e.g., reference numerals that share the two rightmost numerals) can have similar structures and functions.

[0096] In some embodiments, the measurement system 700 includes an illumination system 712, an optical system 710, a detector 728, and a processor 732. The illumination system 712 may include a radiation source 702, an optical fiber 704 (e.g., a multimode fiber), an optical element 706 (e.g., a lens or lens system), and a diffraction element 708 (e.g., a grating, a tunable grating, etc.). The optical system 710 may include one or more of the optical element 706, a blocking element 736, a reflecting element 738 (e.g., a speckle mirror), and an optical element 740 (e.g., an objective lens). FIG. 7 A non-limiting depiction of a measurement system 700 for inspecting a target 718 (also referred to as a "target structure") located on a substrate 720 is shown. The substrate 720 is positioned on an adjustable platform 722 (e.g., a movable support structure). It should be understood that the structures drawn within the illumination system 712 and the optical system 710 are not limited to their depicted locations. For example, a diffraction element 708 may be located within the optical system 710. The location of the structures can be varied as needed, for example, as designed for modular components.

[0097] In some embodiments, radiation source 702 may generate radiation 716. Radiation 716 may be spatially incoherent. Since the output of radiation source 702 may not be directly directed to downstream optical structures, fiber optic cable 704 may guide radiation 716 to downstream optical structures. Optical element 706 may guide or modulate radiation 716 (e.g., focus, collimate, achieve parallelism, etc.). Diffraction element 708 may diffract radiation 716 to generate radiation beams 713 and 713' (i.e., a first radiation beam and a second radiation beam, or a first and a second radiated beam). Radiation beam 713 may include a first non-zero diffraction order (e.g., +1 order) from diffraction element 708. Radiation beam 713' may include a second non-zero diffraction order (e.g., -1 order) from diffraction element 708, different from the first non-zero diffraction order. Diffraction element 708 may also generate a zero-order beam (unlabeled). Blocking element 736 may block the zero-order beam to allow dark-field measurements. Spot mirrors guide radiation beams 713 and 713' toward target 718. Optical element 740 focuses radiation beams 713 and 713' onto target 718, such that the illumination spots of the two beams overlap. The illumination spots can underfill or overfill target 718.

[0098] In some embodiments, target 718 may include a diffraction structure (e.g., as shown in the figure). FIG. 5 (The grating shown is referenced in the diagram). Target 718 can reflect, refract, diffract, scatter, etc., radiation. For ease of discussion and without limitation, radiation interacting with the target will always be referred to as scattered radiation or scattered radiation. Target 718 can scatter incident radiation, which is represented by scattered radiation beams 719 and 719' (i.e., the first scattered radiation beam and the second scattered radiation beam, or the first and second scattered beams of radiation). Scattered radiation beam 719 can represent radiation from radiation beam 713 that has been scattered by target 718. Similarly, scattered radiation beam 719' can represent radiation from radiation beam 713 that has been scattered by target 718. Optical element 742 focuses scattered radiation beams 719 and 719' such that scattered radiation beams 719 and 719' interfere at detector 728. Optical element 740 guides radiation beams 713 and 713' such that they are incident on target 718 at a non-zero incident angle (e.g., off-axis). The terms "off-axis" and "wide-angle" can be used in this document to refer to the propagation direction tilted relative to the surface, and more particularly, the propagation direction tilted relative to the plane of the target. The image at detector 728 can be an interference pattern (e.g., as shown in the image). FIG. 6 (The moiré fringe pattern is shown in the diagram). Detector 728 can generate a detection signal based on the received scattered radiation beams 719 and 719'. Detector 728 can be an imaging detector (e.g., CCD, CMOS, etc.). In this scenario, the detection signal can include a digital or analog representation of an image (including the interference pattern), which is sent to processor 732.

[0099] In some embodiments, processor 732 may analyze the detection signal to determine the properties of target 718. It should be understood that the measurement process may vary depending on the specific properties of the target 718 being determined. For example, if the property of the target 718 being determined is alignment, the measurement is performed on target 718 alone. In another example, if the property of the target 718 being determined is overlap error, the measurement compares target 718 to a second target. Overlap error determination is the process of comparing a first target (located on a first manufacturing layer) with a second target (located on a second manufacturing layer different from the first layer) and determining whether the first and second layers correctly overlap each other. The first and second targets may, for example, be stacked on top of each other or manufactured side-by-side. It is conceivable that other properties of target 718 (e.g., linewidth, spacing, critical dimensions, etc.) may be determined based on target 718 alone, or target 718 in combination with another target. Furthermore, although radiation beams 713 and 713' are described above as both incident on target 718 (i.e., for alignment measurement), embodiments in which the radiation beams are directed to another target to allow, for example, overlap error measurement are conceivable. For example, radiation beams 713 and / or 713' can be duplicated (e.g., using a beam splitter) for transmission to another target.

[0100] In some embodiments, the analysis performed by processor 732 may be based on a target 718 that has been irradiated by radiation beams 713 and 713' with different diffraction orders (e.g., 1 and -1) (e.g., alignment measurement). The analysis includes, for example, performing a mathematical fitting on the moiré pattern (e.g., fitting a sine function along the direction of the spacing of the moiré pattern). Using information inferred from the mathematical fitting, the determined properties of target 718 can be improved and made more accurate. This technique reduces the impact of factors that reduce measurement accuracy, such as finite size effects, the presence of higher diffraction orders, defects in gratings and optics, etc. It should be understood that the mathematical fitting is performed on a still image. For example, regions of interest may be selected on target 718 and / or weights may be assigned to detected pixels to enhance the accuracy and robustness of the measurement. This is described in more detail in PCT / EP2019 / 072762, filed August 27, 2019, the entire contents of which are incorporated herein by reference.

[0101] In some embodiments, wavefront timing (e.g., phase) of radiation beams 719 and 719' can be used to enhance the accuracy of determining the properties of target 718. Adjusting the phase difference between the scattered radiation beams 719 and 719' can shift the detected moiré fringes (e.g., FIG. 6The analysis performed by processor 732 can be based on changes in the image over time (e.g., snapshots of two or more states of the detected image). To adjust the phase difference between the scattered radiation beams 719 and 719', diffraction element 708 can be adjusted (e.g., translated perpendicular to beam propagation). Diffraction element 708 can be actuated. Adjusting diffraction element 708 can effectively modulate the phase difference between radiation beams 713 and 713'. Therefore, the phase difference between scattered radiation beams 719 and 719' can also be modulated, as they are based on radiation beams 713 and 713', respectively.

[0102] In some embodiments, the diffractive element 708 may include an optical filter with periodic optical properties. Adjusting the diffractive element 708 may include adjusting the periodic optical properties. For example, the diffractive element 708 may include at least one of a piezoelectric device, an electro-optic device, a liquid crystal device, an acousto-optic device, etc., all of which may have an tunable diffractive optical structure. The modulation type of the phase difference may be, for example, sinusoidal, linear, sawtooth, triangular, etc.

[0103] To reiterate, in some embodiments, the measurement system 700 may be the phase difference between the scattered radiation beams 719 and 719' (i.e., the "first scattered beam and the second scattered beam"). Adjusting the phase difference between the scattered radiation beams 719 and 719' may include adjusting the diffraction element 708, adjusting the position of the target 718 (e.g., movement relative to the optical system 710), or adjusting the positions of the diffraction element 708 and the target 718.

[0104] In some embodiments, signals from one or more detector elements (e.g., pixels) of detector 728 are analyzed by processor 732. For simplicity, the following discussion will focus on one detector element, but it should be understood that other detector elements can be used in a similar manner. As the moiré stripes move across the entire detector 728, the detector elements can detect varying radiant intensities, which are characteristics of modulated phase differences (e.g., sinusoidal, linear, sawtooth, triangular, etc.). Similar to the mathematical fitting previously described for still images, here, a mathematical fitting is performed relative to time for the intensities detected at the detector elements. The fitting can be iterated over all relevant detector elements. Processor 732 can ignore one or more detector elements based on, for example, an algorithm that determines the absence of light energy or outlier behavior at the detector elements. For example, for periodic patterns (e.g., sine curves), the minimum number of required "snapshots" may be three. However, it should be understood that a larger number and density of data points (e.g., a higher sampling rate) can produce a more accurate mathematical fit. Whether to use more or fewer data points can be determined based on, for example, hardware processing constraints. Depending on the hardware, computing load, and cost, fewer or more data points can be used.

[0105] In some embodiments, processor 732 can determine the properties of target 718 by comparing information inferred from mathematical fitting with a reference (e.g., information from a benchmark on platform 722). For example, phase information from target 718 can be compared with phase information from a benchmark on platform 722. Phase information from a benchmark on platform 722 (not shown) can be acquired by performing a measurement similar to that on target 718 on the benchmark.

[0106] In some embodiments, the phase difference between the scattered radiation beams 719 and 719' can be modulated by moving the target 718 (e.g., by translating the platform 722). However, each detector element on the detector 728 will "see" a different portion of the target 718 when it is translated, which may render measurements unavailable. To address this issue, in some embodiments, the detector 728 can also be translated to match the movement of the target 718. In some embodiments, the processor 732 can be made aware of the translation of the target 718 and the associated detector elements (e.g., mapping pixels onto a spot on the target 718 for each snapshot as the target 718 moves). The image on the detector 728 can be associated with the movement of the target 718 based on the magnification of the detection optics.

[0107] In some embodiments, the movable component can be actuated either during continuous scanning or in multiple discrete steps. A combination of both types of movement can also be used. Multiple discrete steps for acquiring each data point can stabilize the captured image (e.g., a sharper image). However, the rapid acceleration and deceleration from said multiple discrete steps can put stress on the actuation hardware. If continuous motion is used, the hardware stress can be reduced, but the captured image may be somewhat blurry.

[0108] FIG. 8 A measurement system 800 according to some embodiments is illustrated. In some embodiments, the measurement system 800 may also represent a measurement system 700 (…). FIG. 7 A more detailed view of ( ). Unless otherwise stated, FIG. 8 In and FIG. 4A , FIG. 4B and FIG. 7 Elements that share similar reference numerals (e.g., reference numerals sharing the two rightmost numerals) may have similar structures and functions. For simplicity, such structures and their functions will not be reintroduced.

[0109] In some embodiments, the measurement system 800 may further include a waveform generator 844 and a frequency multiplier 846. The waveform generator 844 can generate a signal with a function (e.g., an oscillation signal) that can be used to adjust the diffraction element 808. Therefore, the adjustment of the diffraction element 808 can be based on the oscillation signal. The signal from the waveform generator 844 can be sent to the frequency multiplier 846. The frequency-multiplied signal from the frequency multiplier 846 can be sent as a reference signal to the detector 828. In some embodiments, the detector 828 may include a locking imaging detector (e.g., a locking camera).

[0110] In some embodiments, lock detection can utilize the principle of a lock-in amplifier to provide sensitive detection and selective filtering / filtering of weak or noisy signals, and can improve the signal-to-noise ratio (SNR). Lock-in amplifier technology can provide improved accuracy, faster detection time, and reduced noise in overlapping and / or alignment sensors. Furthermore, compact integrated systems, such as in a single "on-chip" detector, can provide miniaturized detectors for measuring specific characteristics (e.g., alignment) of alignment marks on a substrate.

[0111] In some embodiments, lock-in detection can use so-called phase-sensitive detection to pick out the components of a signal at a specific reference frequency and phase, and can extract the signal from a very noisy background (i.e., a cluttered background). Lock-in detection relies on the orthogonality of a sine function and can multiply the input signal by a reference signal and integrate the resulting signal over a specified time (e.g., low-pass filtering) to extract the desired components (e.g., phase and amplitude).

[0112] In some embodiments, lock-in detection can use either zero-difference detection or heterodyne detection. Zero-difference detection uses a single reference frequency (e.g., a first frequency f1) to extract the modulated signal. For example, zero-difference detection extracts coded information from the oscillating signal by comparing it (e.g., phase and / or frequency) with a standard reference oscillation (e.g., the same signal if it carries null information). Heterodyne detection uses two reference frequencies (e.g., a first frequency f1 and a second frequency f2) to extract the modulated signal. For example, heterodyne detection extracts coded information from the oscillating signal by comparing it (e.g., phase and / or frequency) with a standard reference oscillation (e.g., the same signal if it carries null information) and comparing it with a beat frequency (e.g., a difference) (e.g., f1-f2) between the first and second frequencies. Furthermore, by mixing the two frequencies (e.g., f1 and f2), frequencies higher than the detector response time (e.g., f1-f2) can be measured, and flicker noise (e.g., 1 / f power spectral density) can be reduced.

[0113] In some embodiments, adjusting the phase difference between radiation beams 813 and 813' may double the amount of change in the phase difference between scattered radiation beams 819 and 819'. Therefore, detector 828 may receive a reference signal (e.g., from frequency multiplier 846) having twice the frequency used on diffraction element 808. A portion of detector 828 (e.g., one or more detector elements) contributes to the detection signal the intensity modulation phase and / or frequency detected at one or more portions of detector 828. The detected intensity modulation phase will not be confused with the phase of the irradiated wavefront. Processor 832 may analyze the signals from said one or more portions of detector 828 to determine the intensity modulation phase and / or frequency at said one or more portions. Processor 832 may determine the nature of target 818 by comparing the modulation phase at each detector element with a reference (e.g., information from a reference on platform 822 or substrate 820). A portion (e.g., one or more detector elements) of detector 828 may be ignored by processor 832 based on algorithms, such as determining the absence of light energy, outlier behavior, and / or noise at the detector elements. Processor 832 may be a processor in a locked camera.

[0114] In some embodiments, detector 828 may include electronics for performing locking techniques for each detector element (e.g., C2heliCam from Heliotis AG in Lucerne, Switzerland).

[0115] In some embodiments, detector 828 may be positioned away from the location where optical element 842 focuses and scatters radiation beams 819 and 819'. In this case, an optical fiber array (not shown) may be positioned at the focal point of optical element 542. The optical fiber array can guide radiation representing the image to detector 828.

[0116] FIG. 9 A measurement system 900 according to some embodiments is illustrated. In some embodiments, the measurement system 900 may also represent a measurement system 700 (…). FIG. 7 A more detailed view of ( ). Unless otherwise stated, FIG. 9 In and FIG. 4A , FIG. 4B , FIG. 7 and FIG. 8 Elements that share similar reference numerals (e.g., reference numerals sharing the two rightmost numerals) may have similar structures and functions. For simplicity, these structures and their functions will not be reintroduced.

[0117] In some embodiments, the measurement system may include an optical system 908 (e.g., a beam-splitting element). For disambiguation relative to other optical systems disclosed herein, optical system 908 may be referred to as a “first optical system” and identified by its function (e.g., beam splitting). Similarly, second, third, and additional optical systems may be defined based on their function. For example, a “second” optical system 910 is used to guide the radiation beam. In another example, optical element 942 may be referred to as a “third” optical system for causing the scattered radiation beams 919 and 919' to interfere at detector 928. Optical system 908 may include diffraction elements (e.g., FIG. 8 The optical system 908 may include a beam splitter, a prism, a mirror, etc., in some embodiments. In some embodiments, the optical system 908 may be a combination of any of the beam splitter, prism, mirror, etc. The measurement system may also include one or more phase adjusters 948 and one or more phase adjusters 950. Each of the one or more phase adjusters 948 and / or 950 may be any of an acousto-optic modulator, an electro-optic modulator, a piezoelectric modulator, a thermo-optic modulator, a variable refractive index device, a variable path length device, etc. In some embodiments, each of the one or more phase adjusters 948 and / or 950 may be a combination of any of the acousto-optic modulator, electro-optic modulator, piezoelectric modulator, thermo-optic modulator, a variable refractive index device, a variable path length device, etc.

[0118] In some embodiments, the optical system 908 can generate radiation beams 913 and 913' (e.g., via diffraction or beam splitting of radiation 916). Either radiation beam 913 or 913' can be transmitted through one or more phase adjusters 948. One or more phase adjusters 948 can be adjusted to change the phase of radiation beams 913 and / or 913'. In this way, the phase difference between radiation beams 913 and 913' is adjusted. And, although in FIG. 9 Two phase adjusters 948 are shown, but it should be understood that the phase difference can be adjusted using only one phase adjuster 948. One or more phase adjusters 950 can be used to adjust the phase of the radiation beams 919 and 919' in a similar manner. It should be understood that one or more phase adjusters 950 can adjust the phase difference of the radiation after it has been scattered from the target 918, while one or more phase adjusters 948 can adjust the phase difference of the radiation before it has been scattered from the target 918.

[0119] In some embodiments, the optical system 908 can remain stationary by using one or more phase adjusters 948 and / or 950, which is consistent with... FIG. 7 andFIG. 8 On the contrary, FIG. 7 and FIG. 8 The diffraction element is adjustable to allow for adjustment of the phase difference. However, in some embodiments, the optical system 908 may be adjustable (e.g., allowing translation perpendicular to the beam direction) to adjust the phase difference between the radiation beams 913 and 913'.

[0120] FIG. 10 The following are method steps, according to some embodiments, for performing the functions described herein. FIG. 10 The method steps can be performed in any conceivable order, and it is not necessary to perform all steps. Furthermore, the steps described below... FIG. 10 The method steps described herein are merely examples of these steps and are not restrictive. That is, based on reference Figures 1 to 12, the steps described herein are merely examples of these steps and are not limiting. FIG. 9 Other method steps and functions can be envisioned based on the described embodiments.

[0121] In step 1002, radiation is generated.

[0122] In step 1004, the radiation is diffracted using an adjustable diffraction element to generate a first radiation beam and a second radiation beam. The first beam includes a first non-zero diffraction order. The second beam includes a second non-zero diffraction order, which is different from the first non-zero diffraction order.

[0123] In step 1006, the first and second beams are guided toward the target structure so that a first scattered radiation beam and a second scattered radiation beam are generated based on the first and second beams, respectively.

[0124] In step 1008, the phase difference between the first scattered beam and the second scattered beam is adjusted.

[0125] In step 1010, the first and second scattered beams are made to interfere at the imaging detector.

[0126] In step 1012, an imaging detector is used to generate a detection signal.

[0127] In step 1014, the detection signal is analyzed using a processor to determine the properties of the target structure based at least on the adjusted phase difference.

[0128] FIG. 10 The method steps can be performed in any conceivable order, and it is not necessary to perform all steps. Furthermore, the above-described... FIG. 10 The method steps described herein are merely examples of these steps and are not restrictive. That is, based on reference Figures 1 to 12, the steps described herein are merely examples of these steps and are not limiting. FIG. 9 as well as FIG. 11 to FIG. 15 Other method steps and functions can be envisioned based on the described embodiments.

[0129] FIG. 11 An interference pattern 1152 formed on detector 1128 is shown according to some embodiments. Brief reference is made in some embodiments. FIG. 9 Detector 1128 can be used as detector 928. An interference pattern 1152 can be formed because optical element 942 causes the scattered radiation beams 919 and 919' to interfere at the detector. Detector 1128 may include an imaging detector. Detector 1128 may include detector elements 1154 (e.g., pixels). As described above, the phase difference between the scattered radiation beams 919 and 919' can be modulated (e.g., sinusoidally modulated over time). Correspondingly, the interference pattern 1152 can be characterized by moving across the entire detector element 1154. When considering only a single detector element 1154, the illumination intensity detected at that single detector element 1154 can increase and / or decrease as the interference pattern 1152 moves.

[0130] In some embodiments, the interference pattern 1152 may be the result of superposition of multiple wavelengths. That is, the detector 1128 may simultaneously receive multiple wavelengths of radiation scattered by the target. Since the phase contribution of each wavelength at the detector 1128 depends on the wavelength, the intensity change at each detector element 1154 as the interference pattern moves may not have a direct correspondence with the modulation of the phase difference. There may be one or more phase difference values ​​corresponding to one or more wavelengths. However, the phase modulation scheme of the measurement device may be configured such that the modulation of the phase difference between two radiation beams (having multiple wavelengths) may, for example, be proportional to the wavelength.

[0131] FIG. 12 The description of modulated radiation beams (e.g., radiation beams 909 and 919') according to some embodiments is shown. FIG. 9 The various parameters and effects related to the phase difference are shown in plots 1256, 1258, and 1260. In plot 1256, the vertical axis represents the value of the modulated phase difference (also known as "phase shift") between the two radiation beams. The horizontal axis can represent progression parameters in arbitrary units, such as time, frame slices, optical system 908 ( FIG. 9 The amount of adjustment, the number of frames, etc. The phase shift modulation shown in graph 1256 is a sawtooth pattern modulation; however, it should be understood that the modulation can be any suitable pattern (e.g., a sine wave). As the phase shift is modulated, the detector (e.g., 1128) FIG. 11 The system can acquire image sequences represented by frame 1262. Frame 1262 may include multiple images. Each image may be divided into multiple parts, where each part corresponds to pixel 1254 of the detector.

[0132] In some embodiments, graph 1258 illustrates the detected intensity signal at a given pixel. The vertical axis of graph 1258 represents the detected intensity. The horizontal axis represents progression parameters (e.g., time, frame number, etc.). If the detected signal corresponds to a wavelength, the intensity data in graph 1258 will correspondingly display a phase-shifted signal similar to that in graph 1256 (e.g., sawtooth, sine, or other patterns with the same periodicity). However, when multiple wavelengths and the resulting phase deviations are superimposed on the detector, the evolution of the detected signal associated with a given pixel can be as shown in graph 1258.

[0133] In some embodiments, the processor can analyze the detected signal to determine the properties of the structure based on the phase difference applied to the detected radiation beam. For example, the processor can perform frequency analysis on the signal in Figure 1258 to extract wavelength information, such as the intensity of each wavelength contribution and the modulation phase value. Frequency analysis may include demodulating the information in the detected signal to the frequency domain. For example, demodulation may include a Fourier transform.

[0134] In some embodiments, graph 1260 illustrates an example of wavelength decomposition generated by frequency analysis of graph 1258. The horizontal axis represents wavelength. The vertical axis represents an index of the properties of the target (e.g., target 518) on which measurements are performed. For example, the index may be at least the modulation phase and / or intensity contributed by each wavelength, or a quantity determined therefrom. The modulation phase may be mapped to the corresponding wavelength. For example, as previously mentioned, the modulation of the phase difference may be proportional to the wavelength. The proportional mapping is provided as a non-limiting example, and therefore other suitable mapping schemes may be used. The properties of the target may be, for example, the alignment position of the target. The alignment position may be determined based on the index. The value of the index may be based on phase information determined for a given pixel using frequency analysis.

[0135] In some embodiments, multiple graphs 1256, 1258, and 1260 may be generated, for example, for each pixel 1254. The properties of the target can then be determined based on frequency analysis of all pixels 1254. Combining information from multiple pixels can enhance the accuracy of determining the properties of the target.

[0136] In some embodiments, manufacturing errors in the target cause changes in the scattering behavior at each wavelength. Therefore, due to manufacturing uncertainties, the data in graphs 1256, 1258, and 1260 may be difficult to reproduce from one manufacturing of the target to the next. Conversely, an ideal target without uncertainties will result in highly reproducible graphs 1256, 1258, and 1260. Therefore, compared to not using phase difference modulation, the effect of target uncertainty can be distinguished using a method that modulates the phase difference of the scattered radiation at multiple wavelengths, and the properties of the target can be determined with greater accuracy.

[0137] FIG. 13 A phase modulation portion of an illumination system 1312 according to some embodiments is shown. In some embodiments, illumination system 1312 may also represent illumination system 712 ( FIG. 7 ) and / or 912 ( FIG. 9 Alternative or more detailed views are provided. Unless otherwise stated, FIG. 13 In and FIG. 4A , FIG. 4B , FIG. 7 to FIG. 9 ,as well as FIG. 11 Elements that share similar reference numerals (e.g., reference numerals sharing the two rightmost numerals) may have similar structures and functions. For simplicity, such structures and their functions will not be reintroduced.

[0138] In some embodiments, the illumination system 1312 includes an optical system 1308. The optical system 1308 includes beam-splitting elements 1364 and 1364', optical elements 1366 and 1366' (e.g., reflectors), and a phase adjuster 1348. The phase adjuster 1348 (e.g., a piezoelectric device) may contact the optical element 1366'. If desired, a second phase adjuster (not shown) may be mechanically coupled to the optical element 1366. The beam-splitting elements 1364 and 1364' and the optical elements 1366 and 1366' may be arranged to split the input radiation beam 1316 into radiation beams 1313 and 1313'. Similarly, as... FIG. 13 The diagram shows an optical system 1310 for guiding radiation beams 1313 and 1313' onto a target 1318. The optical system 1310 may be located outside the illumination system 1312 or may be included within the illumination system.

[0139] In some embodiments, the radiation beam 1316 may interact with the beam-splitting element 1364' to generate a first beam and a second beam. The first beam is directed toward the optical element 1366' and subsequently reflected toward the optical system 1310 as the radiation beam 1313'. The second beam continues through the beam-splitting element 1364. The second beam is directed toward the optical system 1310 as the radiation beam 1313. It should be understood that the beam-splitting element 1364 may be omitted. In this context, the optical element 1366 may be used instead of the beam-splitting element 1364 to guide the radiation beam 1313. Using the beam-splitting element 1364 may help, for example, maintain structural symmetry and / or guide scattered radiation from the target 1318.

[0140] In some embodiments, the phase adjuster 1348 can be adjusted (e.g., actuated) along direction 1368 to adjust the path length of the radiation beam 1313'. Direction 1368 is parallel to the propagation direction of the first beam reflected from optical element 1366'. Therefore, the phase adjuster 1348 can be used to phase-shift the radiation beam 1313' relative to the radiation beam 1313, i.e., adjust the phase difference between the radiation beams 1313 and 1313'. The phase difference adjustment can be, for example, periodic (e.g., sawtooth or sinusoidal pattern).

[0141] FIG. 14 A phase modulation portion of an illumination system 1412 according to some embodiments is shown. In some embodiments, illumination system 1412 may also represent illumination system 712 ( FIG. 2 ) and 712 FIG. 7 ), 912 FIG. 9 ) and / or 1312 ( FIG. 13 Alternative or more detailed views are provided. Unless otherwise stated, FIG. 14 In and FIG. 4A , FIG. 4B , FIG. 7 to FIG. 9 , FIG. 11 ,as well as FIG. 13 Elements that share similar reference numerals (e.g., reference numerals sharing the two rightmost numerals) may have similar structures and functions. For simplicity, such structures and their functions will not be reintroduced.

[0142] In some embodiments, the illumination system 1412 includes an optical system 1408. The optical system 1408 includes a beam splitter 1464 and phase adjusters 1448 and 1448' (e.g., actuable retroreflectors / retroradiators). The beam splitter 1464 can split the input radiation beam 1416 into radiation beams 1413 and 1413'. Similarly, as... FIG. 14The diagram shows an optical system 1410 for guiding radiation beams 1413 and 1413' onto a target 1418. The optical system 1410 may be located outside the illumination system 1412 or contained within the illumination system.

[0143] In some embodiments, the radiation beam 1416 may interact with the beam splitter 1464 to generate a first beam and a second beam. The first beam is directed toward the optical element 1448 and then reflected toward the optical system 1410 as the radiation beam 1413. The second beam is directed toward the phase adjuster 1448' and then reflected toward the optical system 1410 as the radiation beam 1413'.

[0144] In some embodiments, the phase adjuster 1448 can be adjusted (e.g., actuated) along direction 1468 to adjust the path length of the radiation beam 1413. Direction 1468 is perpendicular to the propagation direction of the received first beam. By adjusting the phase adjuster 1448 along direction 1468, the path length 1470 of the first beam can be adjusted. Therefore, the phase adjuster 1448 can be used to phase-shift the radiation beam 1413' relative to the radiation beam 1413, i.e., adjust the phase difference between the radiation beams 1413 and 1413'. The phase difference adjustment can be, for example, periodic (e.g., sawtooth or sinusoidal pattern). Corresponding similar functions can be described with respect to the phase adjuster 1448', direction 1468', and radiation beam 1413'. It should be understood that a fixed reflector can be used instead of either the phase adjuster 1448 or 1448' while still achieving the goal of phase-shifting adjustment between the radiation beams 1413 and 1413'.

[0145] FIG. 15 A phase modulation portion of an illumination system 1512 according to some embodiments is shown. In some embodiments, illumination system 1512 may also represent illumination system 712 ( FIG. 7 ), 912 FIG. 9 ), 1312 FIG. 13 ), and / or 1512 ( FIG. 14 Alternative or more detailed views are provided. Unless otherwise stated, FIG. 15 In and FIG. 4A , FIG. 4B , FIG. 7 to FIG. 9 , FIG. 11 , FIG. 13 as well as FIG. 14 Elements that share similar reference numerals (e.g., reference numerals sharing the two rightmost numerals) may have similar structures and functions. For simplicity, such structures and their functions will not be reintroduced.

[0146] In some embodiments, the illumination system 1512 includes an optical system 1508. The optical system 1508 includes a beam splitter 1564 and a phase adjuster 1548. The phase adjuster 1548 may include a plurality of wedge prisms 1572. One or more of the wedge prisms 1572 may be adjusted (e.g., actuated). The beam splitter 1564 may split the input radiation beam 1516 into radiation beams 1513 and 1513'. Also as... FIG. 15 The image shows an optical system 1510 for guiding radiation beams 1513 and 1513' onto a target 1518. The optical system 1510 may be located outside the illumination system 1512 or may be included within the illumination system.

[0147] In some embodiments, the radiation beam 1513' may pass through the phase adjuster 1548. The phase adjuster 1548 can be adjusted to adjust the path length of the radiation beam 1513. For example, one or more of the actuable wedge prisms 1572 can be actuated along direction 1568. By adjusting the phase adjuster 1548 along direction 1568, the path length of the first beam can be adjusted by adjusting the amount of material (e.g., a material with a higher refractive index) that the radiation beam 1513' passes through. Thus, the phase adjuster 1548 can be used to phase-shift the radiation beam 1513' relative to the radiation beam 1513, i.e., adjust the phase difference between the radiation beams 1513 and 1513'. The phase difference adjustment can be, for example, periodic (e.g., sawtooth or sinusoidal pattern).

[0148] Although FIG. 13 to FIG. 15 The use of a discrete phase adjuster for modulating phase difference is described. It should be understood that the phase adjustment structures described in other figures can also be used for modulating phase difference (e.g., diffraction element 708). FIG. 7 )).

[0149] Further embodiments are disclosed in the following numbered aspects:

[0150] 1. A measurement system, comprising:

[0151] A radiation source, the radiation source being configured to generate radiation;

[0152] A tunable diffraction element configured to diffract the radiation to generate a first beam and a second beam of radiation, wherein the first beam includes a first non-zero diffraction order and the second beam includes a second non-zero diffraction order different from the first non-zero diffraction order.

[0153] An optical system configured to guide the first and second beams toward a target structure, such that a first scattered beam and a second scattered beam are generated based on the first and second beams, respectively, wherein a measurement system is configured to adjust the phase difference between the first and second scattered beams;

[0154] An optical element configured to cause the first scattered beam and the second scattered beam to interfere at an imaging detector, wherein the imaging detector is configured to generate a detection signal; and

[0155] A processor configured to receive and analyze the detection signal to determine the properties of the target structure based at least on an adjusted phase difference.

[0156] 2. The measurement system according to aspect 1, wherein adjusting the phase difference includes adjusting the tunable diffraction element, adjusting the position of the target structure relative to the optical system, and adjusting one of the position of the target structure and the tunable diffraction element.

[0157] 3. The measurement system according to aspect 2 further includes a support structure configured to support a substrate including the target structure and to perform position adjustment of the target structure.

[0158] 4. The measurement system according to aspect 2, wherein:

[0159] The tunable diffraction element includes a grating; and

[0160] Adjusting the adjustable diffraction element includes translating the grating.

[0161] 5. The measurement system according to aspect 1, wherein:

[0162] The tunable diffraction element includes an optical filter, which has periodic optical properties; and

[0163] Adjusting the tunable diffraction element includes adjusting the periodic optical properties.

[0164] 6. The measurement system according to aspect 5, wherein the optical filter includes at least one of an acousto-optic device, an electro-optic device, a piezoelectric device, and a liquid crystal device.

[0165] 7. The measurement system according to aspect 1, wherein the properties of the target structure include alignment position.

[0166] 8. The measurement system according to aspect 1 further includes a waveform generator for generating an oscillating signal, wherein the adjustment of the diffraction element is based on the oscillating signal.

[0167] 9. The measurement system according to aspect 8, wherein the imaging detector includes a locking camera.

[0168] 10. The measurement system according to aspect 9, wherein the detection signal includes an intensity-modulated phase at a portion of the locked camera.

[0169] 11. The measurement system according to aspect 10, wherein the property of the target structure is determined based on the intensity modulation phase at the portion of the locking camera.

[0170] 12. A photolithography apparatus, comprising:

[0171] An irradiation system configured to irradiate the pattern of a pattern forming device;

[0172] A projection system configured to project an image of the pattern onto a substrate; and

[0173] Measurement system, the measurement system comprising:

[0174] A radiation source, the radiation source being configured to generate radiation;

[0175] A tunable diffraction element configured to diffract the radiation to generate a first beam and a second beam of radiation, wherein the first beam includes a first non-zero diffraction order and the second beam includes a second non-zero diffraction order different from the first non-zero diffraction order.

[0176] An optical system configured to guide the first and second beams toward a target structure, such that a first scattered beam and a second scattered beam are generated based on the first and second beams, respectively, wherein a measurement system is configured to adjust the phase difference between the first and second scattered beams;

[0177] An optical element configured to focus and interfere with the first and second scattered beams at an imaging detector, wherein the imaging detector is configured to generate a detection signal; and

[0178] A processor configured to analyze the detection signal to determine the properties of the target structure based at least on an adjusted phase difference.

[0179] 13. The lithography apparatus according to aspect 12, wherein adjusting the phase difference includes adjusting the tunable diffraction element, adjusting the position of the target structure relative to the optical system, and adjusting one of the position of the target structure and the tunable diffraction element.

[0180] 14. The lithography apparatus according to aspect 13, wherein the measurement system further includes a support structure configured to support the substrate including the target structure and to perform position adjustment of the target structure.

[0181] 15. The photolithography apparatus according to aspect 13, wherein:

[0182] The tunable diffraction element includes a grating; and

[0183] Adjusting the adjustable diffraction element includes translating the grating.

[0184] 16. The photolithography apparatus according to aspect 13, wherein the tunable diffraction element comprises at least one of an acousto-optic device, an electro-optic device, a piezoelectric device, and a liquid crystal device.

[0185] 17. The lithography apparatus according to aspect 13, wherein the properties of the target structure include alignment position.

[0186] 18. The photolithography apparatus according to aspect 13, wherein:

[0187] The imaging detector includes a locked camera; and

[0188] The detection signal includes an intensity-modulated phase at a portion of the locked camera.

[0189] 19. The lithography apparatus according to aspect 18, wherein the property of the target structure is determined based on the intensity modulation phase at the portion of the locking camera.

[0190] 20. A method comprising:

[0191] It produces radiation;

[0192] The radiation is diffracted using an adjustable diffraction element to generate a first beam and a second beam of radiation, wherein the first beam includes a first non-zero diffraction order and the second beam includes a second non-zero diffraction order different from the first non-zero diffraction order.

[0193] The first and second beams are guided toward the target structure, such that a first and second scattered beams are generated based on the first and second beams, respectively;

[0194] Adjust the phase difference between the first and second scattered beams;

[0195] The first and second scattered beams interfere with each other at the imaging detector.

[0196] The imaging detector is used to generate a detection signal; and

[0197] The processor is used to analyze the detection signal to determine the properties of the target structure based at least on the adjusted phase difference.

[0198] 21. A measurement system, comprising:

[0199] A radiation source, the radiation source being configured to generate radiation;

[0200] A beam splitter is configured to split the radiation into a first beam and a second beam to generate radiation, and to adjust the phase difference between the first beam and the second beam.

[0201] An optical system configured to guide the first and second beams toward a target structure, such that a first scattering beam and a second scattering beam are generated based on the first and second beams, respectively, wherein the phase difference between the first and second scattering beams is based on the phase difference between the first and second beams.

[0202] An optical element configured to cause the first scattered beam and the second scattered beam to interfere at an imaging detector, wherein the imaging detector is configured to generate a detection signal; and

[0203] A processor configured to receive and analyze the detection signal to determine the properties of the target structure based at least on an adjusted phase difference.

[0204] 22. A measurement system, comprising:

[0205] A radiation source, the radiation source being configured to generate source radiation;

[0206] A beam splitter element is configured to split the source radiation to produce a first beam and a second beam of radiation.

[0207] An optical system configured to guide the first and second beams toward a target structure, such that a first scattering beam and a second scattering beam are generated based on the first beam and the second beam, respectively.

[0208] A phase adjuster configured to adjust the phase difference between the first scattered beam and the second scattered beam;

[0209] An optical element configured to cause the first scattered beam and the second scattered beam to interfere at an imaging detector, wherein the imaging detector is configured to generate a detection signal; and

[0210] A processor configured to receive and analyze the detection signal to determine the properties of the target structure based at least on an adjusted phase difference.

[0211] 23. The measurement system according to aspect 22, wherein the beam-splitting element includes any one of a beam splitter, a prism, and a mirror.

[0212] 24. The measurement system according to aspect 22, wherein:

[0213] The beam splitter includes a diffraction element configured to diffract the source radiation to generate the first and second beams; and

[0214] The first beam includes a first non-zero diffraction order, and the second beam includes a second non-zero diffraction order that is different from the first non-zero diffraction order.

[0215] 25. The measurement system according to aspect 22, wherein the phase adjuster is further configured to adjust the phase of the first of the first beam, the second beam, the first scattered beam, and the second scattered beam in order to adjust the phase difference.

[0216] 26. The measurement system according to aspect 25 further includes another phase adjuster configured to adjust the phase of the second of the first beam, the second beam, the first scattered beam, and the second scattered beam in order to adjust the phase difference.

[0217] 27. The measurement system according to aspect 22, wherein the properties of the target structure include alignment position.

[0218] 28. The measurement system according to aspect 22 further includes a waveform generator for generating an oscillation signal, wherein the adjustment is based on the oscillation signal.

[0219] 29. The measurement system according to aspect 28, wherein the imaging detector includes a locking camera.

[0220] 30. The measurement system according to aspect 29, wherein the detection signal includes an intensity-modulated phase at a portion of the locked camera.

[0221] 31. The measurement system according to aspect 30, wherein the property of the target structure is determined based on the intensity modulation phase at the portion of the locking camera.

[0222] 32. A measurement system, comprising:

[0223] A radiation source, the radiation source being configured to generate radiation;

[0224] A first optical system is configured to split the radiation into a first beam and a second beam, and to apply one or more phase differences between the first beam and the second beam.

[0225] A second optical system is configured to guide the first and second beams toward the target structure to generate a first and second scattered beam of radiation.

[0226] A third optical system is configured to cause the first and second scattered beams to interfere at an imaging detector, wherein the imaging detector is configured to generate a detection signal based on the interference of the first and second scattered beams, and wherein a measurement system is configured to modulate one or more phase differences between the first and second scattered beams based on applied phase differences; and

[0227] A processor configured to analyze the detection signal to determine the properties of the target structure based at least on one or more modulated phase differences.

[0228] 33. The measurement system according to aspect 32, wherein:

[0229] The radiation source is further configured to generate multiple wavelengths, such that each of the first and second scattered beams includes multiple wavelengths; and

[0230] The imaging detector is also configured to simultaneously receive the plurality of wavelengths of the first and second scattered beams of the interference.

[0231] 34. The measurement system according to aspect 33, wherein the processor is further configured to:

[0232] Perform frequency analysis of the detected signal to determine one or more modulation phases of the plurality of wavelengths received at one or more portions of the imaging detector; and

[0233] The properties of the target structure are determined based on the frequency analysis.

[0234] 35. The measurement system according to aspect 34, wherein:

[0235] The frequency analysis includes demodulating information from the detected signal to the frequency domain; and

[0236] Determining the one or more modulation phases includes mapping each of the one or more modulation phases to a corresponding wavelength among the plurality of wavelengths.

[0237] 36. The measurement system according to aspect 35, wherein the demodulation includes Fourier transform.

[0238] 37. The measurement system according to aspect 33, wherein the processor is further configured to:

[0239] Performing the frequency analysis of the detected signal to determine one or more modulation phases of the plurality of wavelengths received at two or more portions of the imaging detector; and

[0240] The properties of the target structure are determined based on the frequency analysis.

[0241] 38. The measurement system according to aspect 32, wherein the measurement system is further configured to modulate the one or more phase differences of the first and second scattered beams in proportion to the wavelength.

[0242] 39. The measurement system according to aspect 32, wherein modulating the one or more phase differences between the first and second scattered beams comprises: using the first optical system to adjust the one or more phase differences applied between the first and second beams, and / or adjusting the position of the target structure relative to the second optical system.

[0243] 40. The measurement system according to aspect 39, wherein the first optical system includes an adjustable periodic structure; and

[0244] Adjusting the one or more phase differences applied between the first and second beams includes adjusting the adjustable periodicity structure.

[0245] 41. The measurement system according to aspect 39, wherein the first optical system comprises:

[0246] Beam splitting element, the beam splitting element being configured to perform beam splitting;

[0247] A first optical element and a second optical element, configured to guide the first beam and the second beam, respectively; and

[0248] A phase adjuster, which is mechanically coupled to the first optical element and configured to adjust the first optical element to perform adjustment of the one or more phase differences applied between the first beam and the second beam.

[0249] 42. The measurement system according to aspect 39, wherein the first optical system comprises:

[0250] Beam splitting elements, the beam splitting elements being configured to perform beam splitting; and

[0251] A first retroreflector and a second retroreflector are configured to guide the first beam and the second beam, respectively, wherein at least one of the first retroreflector and the second retroreflector is further configured to be adjusted to perform adjustments to one or more phase differences applied between the first beam and the second beam.

[0252] 43. The measurement system according to aspect 39, wherein the first optical system comprises:

[0253] Beam splitting elements, the beam splitting elements being configured to perform beam splitting; and

[0254] A phase adjuster, the phase adjuster including wedges, wherein at least one of the wedges is configured to be adjusted to perform adjustment of the one or more phase differences applied between the first beam and the second beam.

[0255] 44. The measurement system according to aspect 32, wherein the properties of the target structure include alignment position.

[0256] 45. The measurement system according to aspect 32, wherein the imaging detector includes a locking camera.

[0257] 46. ​​The measurement system according to aspect 45, wherein the detection signal includes information about one or more modulated phase differences between the first scattered beam and the second scattered beam at one or more pixels of the locked camera.

[0258] 47. The measurement system according to aspect 46, wherein:

[0259] The processor is configured to analyze the information; and

[0260] The properties of the target structure are also determined based on the information.

[0261] 48. A photolithography apparatus, comprising:

[0262] An irradiation system configured to irradiate the pattern of a pattern forming device;

[0263] A projection system configured to project an image of the pattern onto a substrate; and

[0264] Measurement system, the measurement system comprising:

[0265] A radiation source, the radiation source being configured to generate radiation;

[0266] A first optical system is configured to split the radiation into a first beam and a second beam, and to apply one or more phase differences between the first beam and the second beam.

[0267] A second optical system is configured to guide the first and second beams toward the target structure to generate a first and second scattered beam of radiation.

[0268] A third optical system is configured to cause the first and second scattered beams to interfere at an imaging detector, wherein the imaging detector is configured to generate a detection signal based on the interference of the first and second scattered beams, and wherein a measurement system is configured to modulate one or more phase differences between the first and second scattered beams based on applied phase differences; and

[0269] A processor configured to analyze the detection signal to determine the properties of the target structure based at least on one or more modulated phase differences.

[0270] 49. The photolithography apparatus according to aspect 48, wherein:

[0271] The radiation source is further configured to generate multiple wavelengths, such that each of the first and second scattered beams includes multiple wavelengths; and

[0272] The imaging detector is also configured to simultaneously receive the plurality of wavelengths of the first and second scattered beams of the interference.

[0273] The processor is also configured to:

[0274] Perform frequency analysis of the detected signal to determine one or more modulation phases of the plurality of wavelengths received at one or more portions of the imaging detector; and

[0275] The properties of the target structure are determined based on the frequency analysis.

[0276] 50. The lithography apparatus according to aspect 48, wherein the properties of the target structure include alignment position.

[0277] 51. A method comprising:

[0278] It produces radiation;

[0279] The radiation is split into a first beam and a second beam using a first optical system;

[0280] The first optical system is used to apply one or more phase differences between the first beam and the second beam;

[0281] The first and second beams are guided toward the target to generate a first and second scattered beam of radiation.

[0282] The first and second scattered beams interfere with each other at the imaging detector.

[0283] Modulate one or more phase differences between the first and second scattered beams;

[0284] The imaging detector is used to generate the detection signal;

[0285] The detection signal is analyzed to determine the properties of the target structure based on at least one or more modulated phase differences.

[0286] While this document specifically refers to the use of lithography equipment in the manufacture of integrated circuits, it should be understood that the lithography equipment described herein can have other applications, such as the manufacture of integrated optical systems, the guiding and detection of patterns in magnetic domain memory, liquid crystal displays (LCDs), thin-film magnetic heads, etc. Those skilled in the art will understand that, in the context of such alternative applications, any terms “wafer” or “die” used herein can be considered synonymous with the more general terms “substrate” or “target portion,” respectively. Substrates mentioned herein can be processed before or after exposure, for example, in a track unit or coating and developing system unit (a tool typically used to apply a resist layer to a substrate and develop the exposed resist), a measurement unit, and / or an inspection unit. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Furthermore, substrates can be processed more than once, for example, to produce multilayer ICs, such that the term “substrate” used herein can also refer to a substrate that already contains multiple processed layers.

[0287] While specific reference has been made above to embodiments of this disclosure within the context of optical lithography, it will be understood that this disclosure can be used in other applications, such as imprint lithography, and is not limited to optical lithography where circumstances permit. In imprint lithography, the morphology in a patterning apparatus defines a pattern formed on a substrate. The morphology of the patterning apparatus can be imprinted into a resist layer supplied to the substrate, whereby the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has been cured, the patterning apparatus is removed from the resist, thereby leaving a pattern therein.

[0288] It should be understood that the wording or terminology used herein is for descriptive rather than restrictive purposes, and that the terminology or terminology used herein shall be interpreted by those skilled in the art in accordance with the teachings herein.

[0289] Additionally, the terms “radiation” and “beam,” “light,” “irradiation,” etc., used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., wavelengths λ of 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV or soft X-ray) radiation (e.g., wavelengths in the range of 5 nm to 20 nm, such as, for example, 13.5 nm), or hard X-rays operating at wavelengths less than 5 nm, as well as particle beams (such as ion beams or electron beams). Generally, radiation with wavelengths between approximately 00 nm and approximately 700 nm is considered visible light radiation; radiation with wavelengths between approximately 780 nm and 3000 nm (or greater) is considered IR radiation. UV refers to radiation with wavelengths between approximately 100 nm and 400 nm. In photolithography, the term “UV” also applies to wavelengths that can be produced by a mercury discharge lamp: G line 436 nm; H line 405 nm; and / or I line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by a gas) refers to radiation with wavelengths of approximately 100 nm to 200 nm. Deep UV (DUV) generally refers to radiation with wavelengths ranging from 126 nm to 428 nm, and in embodiments, excimer lasers can generate DUV radiation used within photolithography equipment. It should be understood that radiation with wavelengths in, for example, the range of 5 nm to 20 nm refers to radiation having a wavelength band at least partially within the 5 nm to 20 nm range.

[0290] As used herein, the term "substrate" describes the material on which the various material layers are added. In some embodiments, the substrate itself may be patterned, and the material added on top of it may also be patterned, or may remain unpatterned.

[0291] While specific reference may be made herein to the use of devices and / or systems according to this disclosure in the manufacture of ICs, it should be clearly understood that such devices and / or systems may have many other possible applications. For example, such devices and / or systems may be used in the manufacture of integrated optical systems, the guiding and detection of patterns for magnetic domain memories, LCD panels, thin-film magnetic heads, etc. Those skilled in the art will understand that in the context of such alternative applications, any use of the terms "mask," "wafer," or "die" should be considered to be replaced by the more general terms "mask," "substrate," and "target portion," respectively.

[0292] While specific embodiments of this disclosure have been described above, it should be understood that embodiments of this disclosure can be practiced in ways other than those described. These descriptions are intended to be exemplary and not restrictive. Therefore, those skilled in the art will understand that modifications can be made to the described disclosure without departing from the scope of the claims set forth below.

[0293] It will be understood that the Detailed Description section, but not the Summary of the Invention section and the Summary of the Specification section, is intended to be used to interpret the claims. As the inventors have considered, the Summary of the Invention section and the Summary of the Specification section may elucidate one or more, but not all, exemplary embodiments of this disclosure, and are therefore not intended to limit this disclosure and the appended claims in any way.

[0294] The present disclosure has been described above with the aid of functional building blocks that illustrate the implementation of the specified functions and their interrelationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined herein. Alternative boundaries can be defined as long as the specified functions and their relationships are properly performed.

[0295] The foregoing description of the specific embodiments so fully reveals the general nature of this disclosure that, without departing from the overall concept of this disclosure and without excessive experimentation, others can readily modify and / or adapt these specific embodiments to various applications by applying knowledge within the scope of the art. Therefore, based on the teachings and guidance set forth herein, such adaptations and modifications are intended to fall within the meaning and scope of equivalents of the disclosed embodiments.

[0296] The breadth and scope of the protected subject matter should not be limited by any of the exemplary embodiments described above, but should be defined only by the appended claims and their equivalents.

Claims

1. A measurement system, comprising: A radiation source, the radiation source being configured to generate radiation; A first optical system, comprising at least one beam splitter or diffraction element, the at least one beam splitter or diffraction element being configured to split the radiation into at least a first beam and a second beam, and to apply one or more phase differences between the first beam and the second beam; A second optical system, comprising at least an optical element configured to guide the first and second beams toward a target structure such that the first and second beams are incident on the target structure at a non-zero incident angle to produce a first and second scattered beam of radiation. A third optical system is configured to cause the first scattered beam and the second scattered beam to interfere at an imaging detector, wherein the imaging detector is configured to generate a detection signal based on the interference of the first scattered beam and the second scattered beam, and wherein the measurement system is configured to modulate one or more phase differences between the first scattered beam and the second scattered beam based on one or more applied phase differences. as well as A processor configured to analyze the detection signal to determine the properties of the target structure based at least on the modulated one or more phase differences.

2. The measurement system according to claim 1, wherein: The radiation source is further configured to generate multiple wavelengths, such that each of the first and second scattered beams includes multiple wavelengths; and The imaging detector is also configured to simultaneously receive the plurality of wavelengths of the first and second scattered beams of the interference.

3. The measurement system according to claim 2, wherein, The processor is also configured to: Perform frequency analysis of the detected signal to determine one or more modulation phases of the plurality of wavelengths received at one or more portions of the imaging detector; and The properties of the target structure are determined based on the frequency analysis.

4. The measurement system according to claim 3, wherein: The frequency analysis includes demodulating the information in the detected signal to the frequency domain; as well as Determining the one or more modulation phases includes mapping each of the one or more modulation phases to a corresponding wavelength among the plurality of wavelengths.

5. The measurement system according to claim 3, wherein, The processor is also configured to: Perform the frequency analysis of the detected signal to determine one or more modulation phases of the plurality of wavelengths received at two or more portions of the imaging detector; and The properties of the target structure are determined based on the frequency analysis.

6. The measurement system according to claim 1, wherein, The measurement system is also configured to modulate the one or more phase differences between the first and second scattered beams in proportion to the wavelength.

7. The measurement system according to claim 1, wherein, Modulating the one or more phase differences between the first and second scattered beams includes: using the first optical system to adjust the one or more phase differences applied between the first and second beams, and / or adjusting the position of the target structure relative to the second optical system.

8. The measurement system according to claim 7, wherein, The first optical system includes an adjustable periodic structure; and Adjusting the one or more phase differences applied between the first and second beams includes adjusting the adjustable periodicity structure.

9. The measurement system according to claim 7, wherein, The first optical system includes: Beam splitting element, the beam splitting element being configured to perform the beam splitting; A first optical element and a second optical element, configured to guide the first beam and the second beam, respectively; and A phase adjuster, which is mechanically coupled to the first optical element and configured to adjust the first optical element to perform adjustment of the one or more phase differences applied between the first beam and the second beam.

10. The measurement system according to claim 7, wherein, The first optical system includes: Beam splitting elements, the beam splitting elements being configured to perform beam splitting; and A first retroreflector and a second retroreflector are configured to guide the first beam and the second beam, respectively, wherein at least one of the first retroreflector and the second retroreflector is further configured to be adjusted to perform adjustments to one or more phase differences applied between the first beam and the second beam.

11. The measurement system according to claim 7, wherein, The first optical system includes: Beam splitting elements, the beam splitting elements being configured to perform the beam splitting; and A phase adjuster, the phase adjuster including wedges, wherein at least one of the wedges is configured to be adjusted to perform adjustment of the one or more phase differences applied between the first beam and the second beam.

12. A photolithography apparatus, comprising: An irradiation system configured to irradiate the pattern of a pattern forming device; A projection system configured to project an image of the pattern onto a substrate; as well as Measurement system, the measurement system comprising: A radiation source, the radiation source being configured to generate radiation; A first optical system, comprising at least one beam splitter or diffraction element, the at least one beam splitter or diffraction element being configured to split the radiation into at least a first beam and a second beam, and to apply one or more phase differences between the first beam and the second beam; A second optical system, comprising at least an optical element configured to guide the first and second beams toward a target structure such that the first and second beams are incident on the target structure at a non-zero incident angle to produce a first and second scattered beam of radiation. A third optical system is configured to cause the first and second scattered beams to interfere at an imaging detector, wherein the imaging detector is configured to generate a detection signal based on the interference of the first and second scattered beams, and wherein a measurement system is configured to modulate one or more phase differences between the first and second scattered beams based on applied phase differences; and A processor configured to analyze the detection signal to determine the properties of the target structure based at least on the modulated one or more phase differences.

13. The photolithography apparatus according to claim 12, wherein: The radiation source is further configured to generate multiple wavelengths, such that each of the first and second scattered beams includes multiple wavelengths; and The imaging detector is also configured to simultaneously receive the plurality of wavelengths of the first and second scattered beams of the interference. The processor is also configured to: Perform frequency analysis of the detected signal to determine one or more modulation phases of the plurality of wavelengths received at one or more portions of the imaging detector; and The properties of the target structure are determined based on the frequency analysis.

14. The photolithography apparatus according to claim 12, wherein, The properties of the target structure include alignment position.

15. A measurement method, comprising: It produces radiation; The radiation is split into at least a first beam and a second beam using a first optical system including at least one beam splitter or diffraction element; Using the first optical system, the diffraction element is used to apply one or more phase differences between the first beam and the second beam; The first and second beams are guided toward the target using at least optical elements such that the first and second beams are incident on the target at a non-zero incident angle to produce a first and second scattered beam of radiation. The first and second scattered beams interfere with each other at the imaging detector; Modulate one or more phase differences between the first and second scattered beams; The imaging detector is used to generate the detection signal; The detection signal is analyzed to determine the properties of the target structure based at least on the modulated one or more phase differences.

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