Measurement system and method

Abstract

The system includes an illumination system, a scanning system, an optical system, a detector system, and a processor. The illumination system directs a light beam to illuminate a target structure. The scanning system scans the light beam and controls the size of a focal spot of the light beam onto the target structure. The optical system maintains alignment with an optical axis of the system during scanning of the light beam. The detector system detects a signal beam generated from the target structure during the scanning of the light beam. The signal beam includes at least a scattered beam generated from the target structure. A processor analyzes the detected signal beam to determine an overlay characterization of the target structure.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 63 / 399,966, filed on August 22, 2022, and U.S. Application No. 63 / 512,677, filed on July 10, 2023, which are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates to a lithographic apparatus. For example, the present disclosure relates to a method and system for controlling aberrations in a lithographic apparatus and system. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (usually to a target portion of a substrate). A lithographic apparatus can be used, for example, in the manufacture of an integrated circuit (IC). In this case, a patterning device (alternatively referred to as a mask or reticle) can be used to generate a circuit pattern to be formed on a single layer of an IC. The pattern can be transferred to a target portion (e.g., including a die, several dies, or a portion of a die) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned continuously. Known lithographic apparatuses include so-called steppers and so-called scanners, wherein the steppers irradiate each target portion by exposing the entire pattern to the target portion at once; wherein the scanner irradiates each target portion by scanning the pattern through a radiation beam in a given direction (the "scanning" direction) while synchronously scanning the target portion parallel or antiparallel to the scanning direction. It is also possible to transfer a pattern from a patterning device to a substrate by imprinting the pattern onto the substrate.

[0005] During a lithography operation, different processing steps may require the formation of different layers in sequence on a substrate. Therefore, the substrate must be positioned with high accuracy relative to an existing pattern formed thereon. Typically, alignment marks are placed on the substrate to be aligned and positioned with reference to a second object. The lithography apparatus may use an alignment device to detect the position of the alignment marks and use the alignment marks to align the substrate to ensure accurate exposure from the mask. Misalignment between alignment marks at two different layers is measured as overlay error.

[0006] In order to monitor the lithography process, parameters of the patterned substrate are measured. The parameters may include, for example, the overlay error between successive layers formed in or on the patterned substrate; and the critical line width of the developed photoresist. The measurements may be performed on a product substrate and / or a dedicated metrology target. There are various techniques for measuring microstructures formed in the lithography process, including the use of scanning electron microscopes and various dedicated tools. A rapid non-invasive form of dedicated inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the surface of the substrate, and a characterization of the scattered or reflected beam is measured. By comparing the characterization of the beam before and after being reflected or scattered by the substrate, the characterization of the substrate can be determined. For example, this can be done by comparing the reflected beam with data stored in a library of known measurements associated with known substrate characterizations. A spectral scatterometer directs a broadband radiation beam onto a substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered into a specific narrow angular range. In contrast, an angle-resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0007] Such a light scatterer can be used to measure parameters such as the critical dimension of a developed photoresist or the overlay error (OV) between two layers formed in or on a patterned substrate. By comparing the characteristics of the illumination beam before and after the beam is reflected or scattered by the substrate, the characteristics of the substrate can be determined.

[0008] An overlay system may use four off-axis images to measure overlay errors between two layers formed in or on a patterned substrate. An overlay system may be affected by optical aberrations that affect the quality of the off-axis images. Summary of the invention

[0009] Therefore, there is a need to improve the quality of images in overlay systems. For example, it is desirable to control optical aberrations in overlay systems to achieve better image quality and focus.

[0010] In some embodiments, the system includes an illumination system, a scanning system, an optical system, a detector system, and a processor. The illumination system directs a light beam to illuminate a target structure. The scanning system scans the light beam and controls the size of a focal spot of the light beam onto the target structure. During scanning of the light beam, the optical system maintains alignment with an optical axis of the system. During scanning of the light beam, the detector system detects a signal beam generated from the target structure. The signal beam includes at least a scattered beam generated from the target structure. The processor analyzes the detected signal beam to determine an overlay characterization of the target structure.

[0011] In some embodiments, the method includes irradiating a target structure with a light beam and controlling a focal spot of the light beam on the target structure. The method also includes directing a signal beam from a scattered beam from the target structure toward a detector system. The signal beam includes at least a scattered beam generated from the target structure. The method also includes: analyzing the signal beam to determine an overlay characterization of the target structure.

[0012] In some embodiments, the lithography apparatus includes an irradiation device, a projection system, and a measurement system. The irradiation device irradiates a pattern of a patterning device. The projection system projects an image of the pattern onto a substrate. The measurement system includes an irradiation system, a scanning system, an optical system, a detector system, and a processor. The irradiation system guides a light beam to irradiate a target structure. The scanning system scans the light beam and controls the size of the focal spot of the light beam on the target structure. During scanning of the light beam, the optical system maintains alignment with the optical axis of the system. During scanning of the light beam, the detector system detects a signal beam generated from the target structure. The signal beam includes at least a scattered beam generated from the target structure. The processor analyzes the detected signal beam to determine an overlay characterization of the target structure.

[0013] Other features of the present disclosure and the structure and operation of various embodiments are described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific embodiments described herein. These embodiments proposed herein are for illustrative purposes only. Based on the teachings contained herein, other embodiments will be apparent to those skilled in the relevant art. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0018] Figure 3 A schematic diagram of a lithography cell is shown in accordance with some embodiments.

[0019] Figure 4A and Figure 4B A schematic diagram of an inspection device according to some embodiments is shown.

[0020] Figure 5A , Figure 5B and Figure 5C A schematic diagram of a lithography apparatus according to some embodiments is shown.

[0021] Figure 6 A schematic diagram of an exemplary field and pupil is shown in accordance with some embodiments.

[0022] Figure 7 A process for performing functions involving correcting aberrations is shown according to some embodiments.

[0023] Figure 8 A schematic diagram of an overlay system according to some embodiments is shown.

[0024] Fig. 9 A schematic diagram of an overlay system according to some embodiments is shown.

[0025] Fig.10 A process for performing functions related to determining an overlay characterization is shown in accordance with some embodiments.

[0026] Features of the present disclosure will become more apparent from the detailed description set forth below in conjunction with the accompanying drawings, in which the same reference numerals identify corresponding elements throughout. In the accompanying drawings, the same reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit of a reference numeral identifies the drawing in which the reference numeral first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be construed as drawings drawn to scale. DETAILED DESCRIPTION

[0027] This specification discloses one or more embodiments that include features of the present disclosure. The disclosed embodiments are provided as examples. The scope of the present disclosure is not limited to the disclosed embodiments. The attached claims define the features claimed for protection.

[0028] The described embodiments and references in the specification to "one embodiment," "an embodiment," "an example embodiment," etc. indicate that the described embodiments may include a particular feature, structure, or characterization, but every embodiment may not necessarily include the particular feature, structure, or characterization. In addition, such phrases do not necessarily refer to the same embodiment. Further, when particular features, structures, or characterizations are described in conjunction with an embodiment, it should be understood that it is within the knowledge of a person skilled in the art to implement these features, structures, or characterizations in conjunction with other embodiments, whether or not explicitly described.

[0029] Spatially relative terms, such as "below," "beneath," "lower," "on," "above," "upper," and the like, may be used herein to describe the relationship of one element or feature to another element or feature as illustrated in the figures. Spatially relative terms are also intended to encompass different orientations of the device in use or operation other than the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein should be interpreted accordingly.

[0030] As used herein, the term "about" indicates a value of a given amount that may vary based on a particular technology. Based on a particular technology, the term "about" may indicate a value of a given amount that varies within, for example, 10% to 30% of a value (e.g., ±10%, ±20%, or ±30% of a value).

[0031] Embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include a read-only memory (ROM); a random access memory (RAM); a disk storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be understood that such description is for convenience only, and such actions are in fact caused by a computing device, processor, controller, or other device that implements firmware, software, routines, instructions, etc.

[0032] Before describing these embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present disclosure may be implemented.

[0033] Example Lithography System

[0034] Figure 1A and Figure 1BSchematic diagrams of a lithographic apparatus 100 and a lithographic apparatus 100' are shown, respectively, in which embodiments of the present disclosure may be implemented. The lithographic apparatus 100 and the lithographic apparatus 100' each include the following items: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet radiation or extreme ultraviolet radiation); a support structure (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and a substrate stage (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with a resist) W and connected to a second positioner PW configured to accurately position the substrate W. The lithographic apparatus 100 and the lithographic apparatus 100' also have a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion (e.g., including one or more dies) C of the substrate W. In the lithographic apparatus 100, the patterning device MA and the projection system PS are of the reflective type. In the lithographic apparatus 100', the patterning device MA and the projection system PS are of the transmissive type.

[0035] The illumination system IL may include various types of optical components for directing, shaping or controlling the radiation beam B, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof.

[0036] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to the reference frame, the design of at least one of the lithographic apparatuses 100 and 100', and other conditions (such as whether the patterning device MA is held in a vacuum environment). The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be, for example, a frame or a stage, which may be fixed or movable as required. By using sensors, the support structure MT may ensure that the patterning device MA is, for example, in a desired position relative to the projection system PS.

[0037] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section so as to create 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 in the device created in the target portion C to form an integrated circuit.

[0038] The terms "inspection device", "measurement system", etc. may be used herein to refer to, for example, a device or system (e.g., an alignment device) used to measure characteristics of a structure (e.g., overlay error, critical dimension parameters) or used in a lithography device to check the alignment of a wafer.

[0039] The patterning device MA may be a transmissive device (e.g. Figure 1B lithography apparatus 100') or reflective (such as in Figure 1A 100). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, and programmable LCD panels. Masks are known in the art of lithography and include mask types such as binary masks, alternating phase-shift masks, and attenuated phase-shift masks, as well as various hybrid mask types. Examples of programmable mirror arrays employ a matrix arrangement of small mirrors, each of which can be independently tilted to reflect an incoming radiation beam in different directions. The tilted small mirrors impart a pattern in a radiation beam B reflected by the matrix of small mirrors.

[0040] The term "projection system" PS may cover any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems or any combination thereof, as appropriate to the exposure radiation used or to other factors such as the use of an immersion liquid or the use of a vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation, as other gases may absorb too much radiation or electrons. Therefore, with the aid of vacuum walls and a vacuum pump, a vacuum environment may be provided to the entire beam path.

[0041] The lithographic apparatus 100 and / or lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, additional substrate tables WT may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other substrate tables WT are being used for exposure. In some cases, the additional tables may not be substrate tables WT.

[0042] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g., water) to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are known in the art for increasing the numerical aperture of the projection system. The term "immersion" as used herein does not mean that the structure (such as the substrate) must be immersed in the liquid, but only means that the liquid is located between the projection system and the substrate during exposure.

[0043] refer to Figure 1A and Figure 1B, the illuminator IL receives a radiation beam from a radiation source SO. For example, when the source SO is an excimer laser, the source SO and the lithographic apparatus 100, 100' may be separate physical entities. In this case, the source SO is not considered to form part of the lithographic apparatus 100, 100', and the radiation beam B is delivered to the lithographic apparatus 100, 100' by means of a beam delivery system BD (in the case of a beam delivery system BD) comprising, for example, suitable directional mirrors and / or a beam expander. Figure 1B In other cases, for example, when the source SO is a mercury lamp, the source SO may be an integral part of the lithographic apparatus 100, 100'. The source SO and the illuminator IL together with the beam delivery system BD (if necessary) may be referred to as a radiation system.

[0044] The illuminator IL may comprise an adjuster AD (at Figure 1B In general, at least the outer radial extent and / or the inner radial extent (commonly referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components (in Figure 1B The illuminator IL may be used to condition the radiation beam B so as to have a desired uniformity and intensity distribution in its cross-section.

[0045] refer to Figure 1A , the radiation beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and is patterned by the patterning device MA. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., a mask) MA. After reflection from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometric measurement device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved (e.g., so as to position a different target portion C in the path of the radiation beam B). Similarly, a first positioner PM and a further position sensor IF1 can be used to accurately position the patterning device (e.g., a mask) MA relative to the path of the radiation beam B. The patterning device (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0046] refer to Figure 1B, the radiation beam B is incident on a patterning device (e.g., mask MA) held on a support structure (e.g., mask table MT) and is patterned by the patterning device. Having passed through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU with the illumination system pupil IPU. Part of the radiation, without being affected by diffraction at the mask pattern, emanates from the intensity distribution at the illumination system pupil IPU and passes through the mask pattern and creates an image of the intensity distribution at the illumination system pupil IPU.

[0047] The projection system PS projects an image of a mask pattern MP onto a photoresist layer coated on a substrate W, wherein the image is formed by a diffraction beam generated from the marking pattern MP by radiation from an intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. The diffraction of radiation located at the array and different from the zero-order diffraction generates a diffraction beam that is turned with a change of direction in a direction perpendicular to the lines. The undiffracted beam (i.e., the so-called zero-order diffraction beam) passes through the pattern without any change in the propagation direction. The zero-order diffraction beam passes through an upper lens or an upper lens group of the projection system PS upstream of the pupil conjugate PPU of the projection system PS to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zero-order diffraction beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD is, for example, positioned at or substantially positioned at a plane including the pupil conjugate PPU of the projection system PS.

[0048] The projection system PS is arranged to capture not only the zero-order diffraction beam, but also the first-order or first-order and higher-order diffraction beams (not shown) by means of a lens or a 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 exploit the resolution enhancement effect of dipole illumination. For example, the first-order diffraction beam interferes with the corresponding zero-order diffraction beam at the level of the wafer W to create an image of the line pattern MP at the highest possible resolution and in the process window (i.e., the available focal depth combined with the tolerable exposure dose deviation). In some embodiments, astigmatic aberrations can be reduced by providing radiation poles (not shown) in the opposite quadrants of the illumination system pupil IPU. In addition, in some embodiments, astigmatic aberrations can be reduced by blocking the zero-order beam in the pupil conjugate PPU of the projection system associated with the radiation poles in the opposite quadrant. This is described in more detail in US7,511,799B2 issued on March 31, 2009, which is incorporated herein by reference in its entirety.

[0049] With the help of a second positioner PW and a position sensor IFD (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. in order to position a different target portion C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor ( Figure 1B ) can be used to accurately position the mask MA relative to the path of the radiation beam B (eg, after mechanical retrieval from a mask library or during scanning).

[0050] In general, movement of the mask table MT can be achieved with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) forming part of the first positioner PM. Similarly, movement of the substrate table WT can be achieved using a long-stroke module and a short-stroke module forming part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected only to a short-stroke actuator or may be fixed. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 may be used to align the mask MA and the substrate W. Although the substrate alignment marks (as shown) occupy dedicated target portions, they may be located in the space between the target portions (referred to as scribe alignment marks). Similarly, in the case where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0051] The mask table MT and the patterning device MA may be in a vacuum chamber V, wherein an in-vacuum robot IVR may be used to move the patterning device (such as a mask) into and out of the vacuum chamber. Alternatively, when the mask table MT and the patterning device MA are outside the vacuum chamber, an out-of-vacuum robot may be used for various transport operations similar to the in-vacuum robot IVR. Both the in-vacuum robot and the out-of-vacuum robot need to be calibrated for smooth transfer of any payload (e.g., a mask) to the fixed kinematic support of the transfer station.

[0052] The lithographic apparatus 100 and the lithographic apparatus 100 ′ may be used in at least one of the following modes.

[0053] 1. In step mode, the support structure (e.g. mask table) MT and the substrate table WT are kept substantially stationary while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0054] 2. In scan mode, the support structure (e.g. mask table) MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e. a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g. mask table) MT can be determined by the (or less) magnification and image reversal characteristics of the projection system PS.

[0055] 3. In another mode, the support structure (e.g., mask table) MT is kept substantially stationary to hold the programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO may be employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography utilizing a programmable patterning device, such as a programmable mirror array.

[0056] Combinations and / or variations on the described modes of use or entirely different modes of use may also be employed.

[0057] In further embodiments, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Generally, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0058] Figure 2 The lithographic apparatus 100 is shown in more detail, and the lithographic apparatus 100 includes a source collector device SO, an illumination system IL, and a projection system PS. The source collector device SO is constructed and arranged so that a vacuum environment can be maintained in an enclosing structure 220 of the source collector device SO. An EUV radiation emitting plasma 210 can be formed by a discharge generated by a plasma source. EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein an extremely hot plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. For example, an extremely hot plasma 210 is generated by an electrical discharge resulting in at least partially ionized plasma. In order to efficiently generate radiation, a partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required. In some embodiments, an excited plasma of tin (Sn) is provided to generate EUV radiation.

[0059] The radiation emitted from the hot plasma 210 is passed from the source chamber 211 to the collector chamber 212 via an optional gas barrier or contaminant trap 230 (also referred to as a contaminant barrier or foil trap in some cases), which is positioned 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 trap or contaminant barrier 230 further indicated herein includes at least a channel structure.

[0060] The collector chamber 212 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 passing through the collector CO may be reflected from the grating spectral filter 240 to be focused in a virtual source point INTF. The virtual source point INTF is often referred to as an intermediate focal length, and the source collector arrangement is arranged so that the intermediate focal length INTF is located at or near an opening 219 in the enclosing structure 220. The virtual source point INTF is an image of the radiation emitting plasma 210. The grating spectral filter 240 is particularly used to suppress infrared (IR) radiation.

[0061] The radiation then passes through an illumination system IL which may include a faceted field mirror arrangement 222 and a faceted pupil mirror arrangement 224 which are arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA. When the radiation beam 221 is reflected at the patterning device MA held by the support structure MT, a patterned beam 226 is formed and is imaged by the projection system PS via reflective elements 228, 230 onto a substrate W held by a wafer stage or substrate table WT.

[0062] There may typically be more elements than those shown in the illumination optics unit IL and the projection system PS. Optionally, depending on the type of lithographic apparatus, a grating spectral filter 240 may be present. Further, there may be more than Figure 2 More reflectors than those shown, for example, may be present in the projection system PS than Figure 2 The reflective elements shown may range from 1 to 6 additional reflective elements.

[0063] like Figure 2As illustrated in FIG, the collector optics CO is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255, merely as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically around the optical axis O, and this type of collector optics CO is preferably used in combination with a discharge generated by a plasma source (often referred to as a DPP source).

[0064] Exemplary Lithography Cell

[0065] Figure 3 A lithography unit 300 (sometimes also referred to as a lithocell or cluster) according to some embodiments is shown. The lithography apparatus 100 or lithography apparatus 100' may form part of the lithography unit 300. The lithography unit 300 may also include one or more devices to perform pre-exposure processes and post-exposure processes on a substrate. In some examples, these devices include: a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH, and a baking plate BK. The substrate handler or robot RO picks up the substrate from the input / output ports I / O1, I / O2, moves the substrate between different processing devices, and delivers the substrate to the feed station LB of the lithography apparatus 100 or lithography apparatus 100'. These devices (often collectively referred to as tracks) are under the control of a track control unit TCU, which itself is controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Therefore, different devices can be operated to maximize production volume and processing efficiency.

[0066] Exemplary Inspection Devices

[0067] In order to control the lithography process to accurately place the device features on the substrate, alignment marks are usually provided on the substrate, and the lithography apparatus includes one or more inspection devices for accurately positioning the marks on the substrate. 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 lithography apparatus is based on the self-reference interferometer described in U.S. Patent No. 6,961,116 (den Boef et al.). Marks are usually measured separately to obtain X position and Y position. However, the technology described in U.S. Publication No. 2009 / 195768A (Bijnen et al.) can be used to perform combined X measurement and Y measurement. The entire contents of these disclosures are incorporated herein by reference.

[0068] Figure 4AA schematic cross-sectional view of an inspection apparatus 400 that may be implemented as part of the lithographic apparatus 100 or lithographic apparatus 100' according to some embodiments is shown. 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 positions of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate relative to a patterning apparatus or other components of the lithographic apparatus 100 or lithographic apparatus 100'. Such alignment of the substrate may ensure accurate exposure of one or more patterns on the substrate.

[0069] 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 overlay calculation processor 432. The illumination system 412 may be configured to provide an electromagnetic narrowband 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 having 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, such a configuration of the illumination system 412 may help prevent the actual CWL value from deviating from the desired CWL value. And therefore, using a constant CWL value may improve the long-term stability and accuracy of the alignment system (e.g., the inspection device 400) compared to current alignment devices.

[0070] In some embodiments, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 can be split into radiation sub-beam 415 and radiation sub-beam 417. Figure 4A. The beam splitter 414 may also be configured to direct the radiation sub-beam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 may be moved along a direction 424. The radiation sub-beam 415 may be configured to illuminate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 may be coated with a radiation sensitive film. In some embodiments, the alignment mark or target 418 may have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when the alignment mark or target 418 is rotated 180° around an axis of symmetry perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 may be substantially the same as the unrotated alignment mark or target 418. The target 418 on the substrate 420 may be (a) a resist layer grating including rods formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure including a resist grating overlaid or interlaced on a product layer grating. Alternatively, the rods may be etched into the substrate. The pattern is sensitive to chromatic aberrations in the lithographic projection apparatus (particularly the projection system PL), and the illumination symmetry and the presence of such aberrations will manifest themselves in variations in the printed grating. An inline method for measuring line width, spacing and critical dimensions in device manufacturing utilizes a technique known as "scatterometry". The method of scatterometry is described in Raymond et al., "Multiparameter Grating Metrology Using Optical Scatterometry", J. Vac. Sci. Tech. B, Vol. 15, No. 2, pp. 361 to 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 scatterometry, light is reflected by a periodic structure in the target, and the reflection spectrum obtained at a given angle is detected. The structure causing the reflection spectrum is reconstructed, for example, using rigorous coupled wave analysis (RCWA) or by comparison with a library of patterns derived from simulations. Thus, the scatterometry data of the printed grating are used to reconstruct the grating. The parameters of the grating, such as line width and shape, can be input to the reconstruction process performed by the processing unit PU from knowledge of the printing step and / or other scatterometry processes.

[0071] In some embodiments, according to one embodiment, 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 diffracted radiation beam 419 may be split into a diffracted radiation sub-beam 429 and a diffracted radiation sub-beam 439, as shown in FIG. Figure 4A as shown in .

[0072] It should be noted that although beam splitter 414 is shown as directing radiation sub-beam 415 toward alignment mark or target 418 and directing diffracted radiation sub-beam 429 toward interferometer 426, the present disclosure is not limited thereto. It will be apparent to one skilled in the relevant art that other optical arrangements may be used to obtain similar results of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0073] like Figure 4A , the interferometer 426 may be configured to receive the radiation sub-beam 417 and the diffracted radiation sub-beam 429 via the beam splitter 414. In an example embodiment, the diffracted radiation sub-beam 429 may be at least a portion of the radiation sub-beam 415 that may be reflected from the alignment mark or target 418. In an example of this embodiment, the interferometer 426 includes any suitable set of optical elements (e.g., a prism combination) that may be configured to form two images of the alignment mark or target 418 based on the received diffracted radiation sub-beams 429. It should be understood that high quality images need not be formed, but rather features of the alignment mark 418 should be resolved. The interferometer 426 may also be configured to rotate one of the two images by 180° relative to the other of the two images, and to interferometrically recombine the rotated image and the unrotated image.

[0074] In some embodiments, the detector 428 may be configured to receive the recombined image via the interferometer signal 427 and detect interference as a result of the recombined image when the alignment axis 421 of the inspection device 400 passes through the center of symmetry (not shown) of the alignment mark or target 418. According to an example embodiment, such interference may be caused by the alignment mark or target 418 being 180° symmetrical and the recombined image interfering constructively or destructively. Based on the detected interference, the detector 428 may also be configured to determine the position of the center of symmetry of the alignment mark or target 418 and thus detect the position of the substrate 420. According to an example, the alignment axis 421 may be aligned with a beam that is perpendicular to the substrate 420 and passes through the center of the image rotation interferometer 426. The detector 428 may also be configured to estimate the position of the alignment mark or target 418 by enabling sensor characterization and interacting with wafer marking process variations.

[0075] In further embodiments, the detector 428 determines the location of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements:

[0076] 1. Measure the position change of various wavelengths (position shift between colors);

[0077] 2. Measuring the positional changes of the various orders (positional shifts between diffraction orders); and

[0078] 3. Measure the positional changes of various polarizations (positional shifts between polarizations).

[0079] For example, any type of alignment sensor can be used to obtain this data, such as a SMASH (Smart Alignment Sensor Hybrid) sensor described in U.S. Pat. No. 6,961,116, which employs a self-referencing interferometer with a single detector and four different wavelengths, and extracts an alignment signal in software or Athena (Advanced Technology using High-Order Enhancements for Alignment), which directs each of the seven diffraction orders to a dedicated detector as described in U.S. Pat. No. 6,297,876, both of which are incorporated herein by reference in their entirety.

[0080] In some embodiments, the beam analyzer 430 may be configured to receive and determine the optical state of the diffracted radiation sub-beam 439. The optical state may be a measure of the wavelength, polarization, or beam profile of the beam. The beam analyzer 430 may also be configured to determine the position of the stage 422 and to relate the position of the stage 422 to the position of the center of symmetry of the alignment mark or target 418. In this way, the position of the alignment mark or target 418, and therefore the position of the substrate 420, may be accurately known with reference to the stage 422. Alternatively, the beam analyzer 430 may be configured to determine the position of the inspection device 400 or any other reference element so that the center of symmetry of the alignment mark or target 418 may be known with reference 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 wavelength band selectivity. In some embodiments, the beam analyzer 430 may be directly integrated into the inspection device 400, or connected via several types of optical fibers: polarization-maintaining single mode, multimode, or imaging, according to other embodiments.

[0081] In some embodiments, the beam analyzer 430 may also be configured to determine overlay data between two patterns on the substrate 420. One of the patterns may be a reference pattern on a reference layer. Another 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 a reference pattern exposed by the lithography apparatus 100 and / or the lithography apparatus 100' on the substrate. The exposure layer may be an exposed resist layer adjacent to the reference layer. The exposure layer may be generated by an exposure pattern exposed by the lithography apparatus 100 or the lithography apparatus 100' on the substrate 420. The exposure pattern on the substrate 420 may correspond to moving the substrate 420 by the stage 422. In some embodiments, the measured overlay data may also indicate a deviation between the reference pattern and the exposure pattern. The measured overlay data may be used as calibration data to calibrate the exposure pattern exposed by the lithography apparatus 100 or the lithography apparatus 100' so that after calibration, the deviation between the exposure layer and the reference layer may be minimized.

[0082] In some embodiments, the beam profiler 430 may also be configured to determine a model of a product stacking profile of the substrate 420 and may be configured to measure the overlay, critical dimensions, and focal length of the target 418 in a single measurement. The product stacking profile contains information about the stacked product (such as alignment marks, the target 418, or the substrate 420) and may include optical identification mark measurements caused by marking process variations as a function of illumination variations. The product stacking profile may also include product raster profiles, mark stacking profiles, and mark asymmetry information. An example of a beam profiler 430 is the Yieldstar manufactured by ASML of Veldhoven, The 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 related to a particular characterization of the exposure pattern in the layer. For example, the beam analyzer 430 may process overlay parameters (an indication of the accuracy of positioning of a layer relative to a previous layer on the substrate, or an indication of the accuracy of positioning of a first layer relative to a mark on the substrate), focus parameters, and / or critical dimension parameters (e.g., line width and its variation) of the image depicted in the layer. Other parameters are image parameters related to the quality of the depicted image of the exposure pattern.

[0083] In some embodiments, a detector array (not shown) can be connected to the beam analyzer 430 and allow the possibility of accurate stack profile detection to be performed accurately, as discussed below. For example, the detector 428 can be a detector array. For the detector array, there may be several options: a multimode optical fiber bundle, a discrete PIN detector for each channel, or a CCD or CMOS (linear) array. The use of a multimode optical fiber bundle enables any dissipative element to be remotely located for stability reasons. Discrete PIN detectors give a large dynamic range, but each detector requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays give many elements that can be read out at high speed, and are particularly interesting if phase-stepping detection is used.

[0084] In some embodiments, the second beam analyzer 430' may be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, such as Figure 4B . The optical state may be a measure of the wavelength, polarization or profile of the beam. The second beam analyzer 430' may be identical to the beam analyzer 430. Alternatively, the second beam analyzer 430' may be configured to perform at least all of the functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. In this way, the position of the alignment mark or target 418 and therefore the position of the substrate 420 may be accurately known with reference to the stage 422. The second beam analyzer 430' may also be configured to determine the position of the inspection device 400 or any other reference element, so that the center of symmetry of the alignment mark or target 418 may be known with reference to the inspection device 400 or any other reference element. The second beam analyzer 430' may also be configured to determine overlay data between two patterns and a model of the product stacking profile of the substrate 420. The second beam analyzer 430' may also be configured to measure the overlay, critical dimension and focal length of the target 418 in a single measurement.

[0085] In some 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, multimode or imaging, according to other embodiments. 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 both the diffracted radiation sub-beam 429 and the diffracted radiation sub-beam 439.

[0086] In some embodiments, the processor 432 receives information from the detector 428 and the beam analyzer 430. For example, the processor 432 can be an overlay calculation processor. The information may include a model of the product stacking profile constructed by the beam analyzer 430. Alternatively, the processor 432 may use the received information about the product markings to construct a model of the product marking profile. In either case, the processor 432 uses or combines the model of the product marking profile to construct a model of the stacked product and overlay marking profile. The stacking model is then used to determine the overlay offset and minimize the spectral impact on the overlay offset measurement. The processor 432 can create a basic correction algorithm based on the information received from the detector 428 and the beam analyzer 430, which includes but is not limited to the optical state of the illumination beam, the alignment signal, the associated position estimate, and the optical state in the pupil plane, the image plane, and the additional plane. 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 orientation angle of the radiation. The processor 432 can use the basic correction algorithm to characterize the inspection device 400 with reference to the wafer mark and / or alignment mark 418.

[0087] In some embodiments, the processor 432 may also be configured to determine the sensor-estimated printed pattern position offset error relative to each mark based on information received from the detector 428 and the beam analyzer 430. The information includes, but is not limited to, product stack profiles, measurements of overlay, critical dimensions, and focal lengths of each alignment mark or target 418 on the substrate 420. The processor 432 may group the marks into sets with similar constant offset errors using a clustering algorithm, and create an alignment error offset correction table based on the information. The clustering algorithm may be based on overlay measurements, position estimates, and additional optical stacking process information associated with each offset error set. Overlays of several different marks are calculated, for example, overlay targets with positive and negative offsets around programmed overlay offsets. The target for measuring the minimum overlay is considered a reference (because it is measured with the best accuracy). Based on the measured small overlay and the known programmed overlay of its corresponding target, an overlay error may be derived. Table 1 illustrates how this is performed. The minimum overlay measured in the example shown is -1nm. However, this is related to a programmed overlay target with -30nm. This process may introduce an overlay error of 29nm.

[0088]

[0089] The minimum value can be taken as a reference point, and relative to this reference point, the offset between the measured overlay and the expected overlay due to programmed overlay can be calculated. This offset determines the overlay error of each mark or a set of marks with similar offsets. Therefore, in the example of Table 1, the minimum overlay measured is -1nm at the target position, where the programmed overlay is 30nm. The difference between the expected overlay and the measured overlay at other targets is compared with this reference. A table (such as Table 1) can also be obtained from the marks and targets 418 under different illumination settings, and the illumination settings and their corresponding calibration factors that produce the minimum overlay error can be determined and selected. Thereafter, the processor 432 can group the marks into sets of similar overlay errors. The criteria for grouping the marks can be adjusted based on different process controls (e.g., different error tolerances for different processes).

[0090] In some embodiments, the processor 432 may confirm that all or most members of the group have similar offset errors and apply individual offset corrections from the clustering algorithm to each mark based on its additional optical stack measurement. The processor 432 may determine the correction for each mark and feed the correction back to the lithography apparatus 100 or lithography apparatus 100' for correcting errors in overlay, for example, by feeding the correction back into the inspection apparatus 400.

[0091] Example Overlay System

[0092] In some embodiments, in an overlay system (e.g., a wide field overlay system), four off-axis images are acquired by using four different positions of the pupil space of the overlay system. The four off-axis images can be created using positive first-order diffraction signals and negative first-order diffraction signals in two directions (i.e., both the x-direction and the y-direction).

[0093] In some embodiments, optical aberrations in the overlay system can reduce the quality of the four-axis image and can cause errors during overlay measurement. Exemplary aspects provide aberration correction in a partially coherent state. The overlay system described herein can use adaptive optics technology to control optical aberrations (e.g., wavelength- and polarization-related optical aberrations). In addition, the overlay system described herein can correct the optical aberrations of each quadrant of the pupil space (e.g., normal image and complementary image). Due to both iso- and non-iso-corona optical aberrations, each quadrant-based optical image can show different imaging qualities. For large targets, the measurement system may appear more non-iso-corona, and the overlay error may increase. The overlay system described herein corrects the non-iso-corona phenomenon and iso-corona phenomenon in the system, which in turn increases the imaging quality of all quadrant-based optical images, respectively.

[0094] Figure 5AA schematic diagram of an overlay system 500 is shown in accordance with some embodiments. In some embodiments, the system 500 may also represent a more detailed view of the beam analyzer 430. In some embodiments, the system 500 includes an illumination system 502, an optical system 504, a detector system 506, and a processor 508.

[0095] In some embodiments, the illumination system 502 may include a radiation source 510, optical elements (e.g., lenses or lens systems) 512, 514, 516, an optical element 518, a reflective element (e.g., a folding mirror) 520, an optical element 522 (e.g., a lens or lens system), a beam splitter 524, and an optical element 526 (e.g., a lens or lens system). The radiation source 510 is configured to generate a light beam to illuminate the target 532. The optical element 518 is configured to control (e.g., correct) optical aberrations in the system 500. In some embodiments, the optical element 518 may be an aberration correction device, such as a deformable mirror (DM), a spatial light modulator (SLM), or an aberration corrector plate (or mask). The optical element 518 may adjust the intensity and / or phase profile of the light beam.

[0096] In some embodiments, optical element 518 can be positioned in the optical path of the illumination beam before optical system 504. In some aspects, optical element 518 can be positioned at a location where the beam diameter of the light beam is suitable for aberration correction. For example, optical element 518 can be positioned at a pupil conjugate plane. The pupil conjugate plane can refer to an image plane in the image plane of the pupil plane of system 500. In some aspects, optical element 518 can be positioned slightly offset from the pupil conjugate plane, or positioned at a field plane location.

[0097] In some embodiments, the illumination system 502 may include a spot size selector (not shown). The spot size selector may be positioned after the radiation source 510. The spot size selector may be configured to select a spot size of the illumination beam. In addition, the illumination system 502 may include an illumination model selector (IMS) (not shown). The IMS may be positioned after the spot size selector. The IMS may be configured to select a pupil shape from a variety of pupil shapes. Thus, the illumination system 502 may illuminate the target 532 using a variety of spot sizes and a variety of pupil shapes.

[0098] In some embodiments, optical element 518 can control aberrations in the image created by two oppositely illuminated quadrants of the IMS (sometimes referred to as the BMW pupils).

[0099] In some aspects, the aberration correction performed by optical element 518 includes one or more of the following: (1) removal (or substantial reduction) of axial color throughout the illumination path (branch), (2) removal (or substantial reduction) of lateral color throughout the illumination path (branch), (3) removal (or substantial reduction) of spherical chromatic aberration throughout the illumination path, (4) removal (or substantial reduction) of on-axis coma throughout the illumination path, (5) removal (or substantial reduction) of on-axis astigmatism throughout the illumination path, (6) removal (or substantial reduction) of on-axis Petzval throughout the illumination path, and (7) removal (or substantial reduction) of on-axis distortion throughout the illumination path.

[0100] In some embodiments, optical system 504 can include reflective element 528 and optical element 530 (eg, an objective lens). Reflective element 528 can direct a portion of the light beam to optical element 530. Optical element 530 can direct a portion of the light beam to target 532.

[0101] Figure 5A A non-limiting depiction of system 500 inspecting a target 532 (also referred to as a "target structure") on a substrate 534 is shown. Substrate 534 is positioned on an adjustable stage 536 (e.g., a support structure that can be moved). It should be understood that the depicted structures within illumination system 502 and optical system 504 are not limited to their depicted locations. The locations of the structures can be varied as desired, for example, as designed for modular components.

[0102] In some embodiments, target 532 may include a diffraction structure (e.g., a grating). Target 532 may reflect, refract, diffract, scatter, etc. radiation. For ease of discussion, and without limitation, radiation that interacts with the target will always be referred to as scattered radiation. Scattered radiation is collected by optical element 530. Scattered radiation includes reflections of the illumination beam (zero order) as well as first diffraction order beams and second diffraction order beams (e.g., positive and negative first order diffraction beams, positive and negative second order diffraction beams). For example, scattered radiation may include ± first diffraction orders.

[0103] In some embodiments, detection system 506 may include optical element 538, reflective element (e.g., fold mirror) 540, optical element 542 (e.g., lens or lens system), reflective element (e.g., mirror) 544, reflective element (e.g., mirror) 546, reflective element (e.g., mirror) 548, optical element (e.g., lens or lens system) 550, reflective element (e.g., mirror) 552, reflective element (e.g., mirror) 554, optical element (e.g., lens or lens system) 556, beam splitter 558, optical element (e.g., lens or lens system) 560, and imaging device 562. Beam splitter 558 may direct a portion of the scattered radiation toward optical element 560. Optical element 560 may be configured to focus the scattered radiation into imaging device 562. Imaging device 562 may be coupled to processor 508. Imaging device 562 may form a two-dimensional image of target 532. Processor 508 may analyze the two-dimensional image to determine overlay error.

[0104] In some embodiments, the detection system 506 can measure the overlay error in both the x-direction and the y-direction simultaneously. For example, the imaging device 562 can capture the normal image and the complementary image in the x-direction and the y-direction, such as Figure 6 as shown in .

[0105] In some aspects, optical element 518 can introduce axial color correction due to color-dependent defocus correction such that the illumination path may not require additional axial correction by optical element 530 (i.e., by z-repositioning of optical element 530). Optical element 530 can be used to focus the beam onto substrate 534.

[0106] In some aspects, optical element 518 can introduce a wavefront tilt in the light beam. Thus, optical element 522 and optical element 524 can be used without x and / or y decentering compensators.

[0107] In some aspects, the system 500 can include a closed-loop or sensorless optical aberration control system. For example, the system 500 can include a wavefront sensor. The wavefront sensor (not shown) can be configured to provide feedback to the optical element 518. For example, the wavefront sensor can be configured to measure the aberrations of the optical wavefront of the light beam. The optical element 518 (such as a deformable mirror) can be controlled based on the measured aberrations. In some aspects, the processor 508 can receive input from the wavefront sensor. The processor 508 can determine the settings of the optical element 518 to correct the aberrations. For example, the processor 508 can determine the optimal shape of the surface of the deformable mirror.

[0108] In some aspects, optical elements used to correct optical aberrations in the overlay system can be positioned in the detection path, such as Figure 5B as shown in .

[0109] Figure 5B A schematic diagram of an overlay system 564 is shown in accordance with some embodiments. In some embodiments, the system 564 may also represent a more detailed view of the beam analyzer 430. In some embodiments, the system 564 includes an illumination system 502, an optical system 504, a detector system 506, and a processor 508.

[0110] In some embodiments, illumination system 502 may include radiation source 510, optical elements (e.g., lenses or lens systems) 512, 514, 516, reflective elements (e.g., mirrors) 566, reflective elements (e.g., folding mirrors) 520, optical elements 522 (e.g., lenses or lens systems), beam splitters 524, and optical elements 526 (e.g., lenses or lens systems). Radiation source 510 is configured to generate a beam to illuminate target 532.

[0111] In some embodiments, the illumination system 502 may include a spot size selector (not shown). The spot size selector may be positioned after the radiation source 510. The spot size selector may be configured to select a spot size of the illumination beam. In addition, the illumination system 502 may include an illumination model selector (IMS) (not shown). The IMS may be positioned after the spot size selector. The IMS may be configured to select a pupil shape from a variety of pupil shapes. Thus, the illumination system 502 may illuminate the target 532 using a variety of spot sizes and a variety of pupil shapes.

[0112] In some embodiments, optical system 504 can include reflective element 528 and optical element 530 (eg, an objective lens). Reflective element 528 can direct a portion of the light beam to optical element 530. Optical element 530 can direct a portion of the light beam to target 532.

[0113] Figure 5B A non-limiting depiction of a system 564 inspecting a target 532 (also referred to as a "target structure") on a substrate 534 is shown. The substrate 534 is positioned on an adjustable stage 536 (e.g., a support structure that can be moved). It should be understood that the structures depicted within the illumination system 502 and the optical system 504 are not limited to their illustrated locations. The locations of the structures can be varied as desired, for example, as designed for modular components.

[0114] In some embodiments, target 532 may include a diffraction structure (e.g., a grating). Target 532 may reflect, refract, diffract, scatter, etc. radiation. For ease of discussion, and without limitation, radiation that interacts with the target will always be referred to as scattered radiation. Scattered radiation is collected by optical element 530. Scattered radiation includes reflections of the illumination beam, first diffraction order beams, and second diffraction order beams. For example, scattered radiation may include ± first diffraction orders.

[0115] In some embodiments, detection system 506 may include optical element 538, reflective element (e.g., fold mirror) 540, optical element 542 (e.g., lens or lens system), reflective element (e.g., mirror) 544, optical element 568, reflective element (e.g., mirror) 548, optical element (e.g., lens or lens system) 550, reflective element (e.g., mirror) 552, reflective element (e.g., mirror) 554, optical element (e.g., lens or lens system) 556, beam splitter 558, optical element (e.g., lens or lens system) 560, and imaging device 562. Beam splitter 558 may direct a portion of the scattered radiation toward optical element 560. Optical element 560 may be configured to focus the scattered radiation into imaging device 562. Imaging device 562 may be coupled to processor 508. Imaging device 562 may form a two-dimensional image of target 532. Processor 508 may analyze the two-dimensional image to determine overlay error.

[0116] Optical element 568 is configured to control (e.g., correct) optical aberrations in system 564. In some embodiments, optical element 568 can be an aberration correction device (such as a deformable mirror (DM), a spatial light modulator (SLM), or an aberration corrector plate (or mask)). Optical element 568 can adjust the intensity and / or phase profile of the scattered radiation.

[0117] In some embodiments, optical element 568 can be positioned in the optical path of scattered radiation collected by optical element 530 after optical system 504. In some aspects, optical element 568 can be positioned at a position where the beam diameter of the light beam is suitable for aberration correction. For example, optical element 568 can be positioned at a pupil conjugate plane. The pupil conjugate plane can refer to an image plane in the image plane of the pupil plane of system 564. In some aspects, optical element 568 can be positioned slightly offset from the pupil conjugate plane, or positioned at a field plane position.

[0118] In some aspects, the aberration correction performed by optical element 568 includes one or more of the following: (1) removal (or substantial reduction) of axial color on the detection path (branch), (2) removal (or substantial reduction) of lateral color on the entire detection path (branch), (3) removal (or substantial reduction) of spherical chromatic aberration on the detection path, (4) removal (or substantial reduction) of on-axis coma on the detection path, (5) removal (or substantial reduction) of on-axis astigmatism on the detection path, (6) removal (or substantial reduction) of on-axis Petzval on the detection path, and (7) removal (or substantial reduction) of on-axis distortion on the detection path.

[0119] In some aspects, optical element 568 can introduce axial color correction due to color-dependent defocus correction such that the detection path may not require additional axial correction by optical element 530 (i.e., by z-repositioning of optical element 530). Optical element 530 can be used to focus the beam onto substrate 534.

[0120] In some embodiments, optical element 568 can control aberrations in the image created by each quadrant of the detection wedge pupil in the detection path.

[0121] In some aspects, the system 564 can include a wavefront sensor. The wavefront sensor (not shown) can be configured to provide feedback to the optical element 568. For example, the wavefront sensor can be configured to measure an aberration of an optical wavefront of scattered radiation (e.g., a first order diffracted beam). The optical element 568 (such as a deformable mirror) can be controlled based on the measured aberration. In some aspects, the processor 508 can receive input from the wavefront sensor. The processor 508 can determine a setting for the optical element 508 to correct for the aberration. For example, the processor 508 can determine an optimal shape for a surface of the deformable mirror.

[0122] In some embodiments, the overlay system can include two or more optical elements that are configured to correct for optical aberrations. For example, a first optical element configured to correct for optical aberrations can be positioned in the illumination path, and a second optical element configured to correct for optical aberrations can be positioned in the detection path, such as Figure 5C as shown in .

[0123] Figure 5C A schematic diagram of an overlay system 570 is shown in accordance with some embodiments. In the overlay system 570, optical element 518 can be positioned in the illumination path and optical element 568 can be positioned in the detection path. Figure 5C The components have Figure 5A and Figure 5B Components with similar numbers in the drawings have similar structures and functions. For the sake of brevity, the description of these components is omitted.

[0124] In some aspects, the system 570 can include a wavefront sensor (not shown). The wavefront sensor can be configured to provide feedback to the optical element 518 and the optical element 568. For example, the wavefront sensor can be configured to measure the aberration of the optical wavefront (in the detection path) of the scattered radiation (e.g., the first-order diffracted beam) and the aberration of the beam of the radiation source 510 (in the illumination path). The optical element 568 and the optical element 518 (e.g., a deformable mirror or a spatial light modulator) can be controlled based on the aberrations measured in the illumination path and / or the detection path. In some aspects, the processor 508 can receive input from the wavefront sensor. The processor 508 can determine the settings of the optical element 568 and the optical element 518 to correct the aberrations. For example, the processor 508 can determine the optimal shape of the surface of the deformable mirror.

[0125] Figure 6 A schematic diagram of an exemplary field and pupil is shown in accordance with some embodiments.

[0126] The normal image includes A-1X and B+1Y. A-1X corresponds to an image of the negative first diffraction order created in the x direction by the illumination pupil A at the IMS. B+1Y corresponds to an image of the positive first diffraction order created in the y direction by the illumination pupil B. The complementary image includes B+1X and A-1Y. B+1X corresponds to an image in the x direction by the illumination pupil B of the positive first diffraction order. A-1Y corresponds to an image in the y direction by the illumination pupil A of the negative first diffraction order.

[0127] In some embodiments, optical element 530 may be rotated to control the differential focus bias behavior between the normal image and the complementary image. This is described in more detail in U.S. Provisional Application 63 / 302,214, entitled "METHOD AND APPARATUS FOR ILLUMINATION ADJUSTMENT," the contents of which are incorporated herein by reference in their entirety. Rotation may not result in offset coma because the optical aberrations in both pupils are corrected simultaneously.

[0128] For example, when the optical element is positioned in the illumination path, the optical aberrations of the two illumination pupils (i.e., pupil A and pupil B) can be corrected (in Figure 6 When the optical element is positioned in the detection path, the aberrations of the two detection pupils (i.e., pupil A-1X / B+1Y and pupil B+1X / A-1Y) are corrected (in Figure 6 Thus, the optical aberrations of the eight images from the target 532 are individually controlled (ie, the x-image versus the y-image, and / or the positive first-order image versus the negative first-order image).

[0129] Figure 7 Method steps are shown (eg, using one or more processors) for performing method 700 including the functionality described herein, according to some embodiments. Figure 7 The method 700 may be performed in any desired order, and not all steps need to be performed. Figure 7 The method steps shown merely reflect examples of steps and are not limiting.

[0130] Method 700 illustrates a method for correcting aberrations. Method 700 includes adjusting a wavelength, polarization, and / or an illumination pupil shape of an illumination beam, as shown in step 702.

[0131] The method also includes correcting optical aberrations (such as wavelength-dependent, polarization-dependent optical aberrations) using optical elements positioned along the illumination path, as shown in step 704 .

[0132] The method further includes illuminating the target structure with the aberration-corrected illumination beam by loading the calibration information processed in step 704 , as shown in step 706 .

[0133] The method also includes directing the scattered beam from the target structure to an imaging detector, as shown in step 708. In some aspects, the scattered beam includes a first diffraction order beam and a second diffraction order beam (eg, a negative first diffraction order beam and a positive first diffraction order beam).

[0134] The method also includes forming, by an imaging detector, a two-dimensional image based on the scattered beam, as shown in step 710 .

[0135] The method also includes correcting additional aberrations in the two-dimensional image using additional optical elements positioned along the detection path, as shown in step 712. In some aspects, the optical elements are positioned at a conjugate plane of the pupil of the imaging detector. In some aspects, the additional aberrations may be caused by any interaction between the illumination beam and the target configuration, the detection optics alone, and / or the dynamic imaging environment (i.e., temperature, atmospheric pressure, turbulence).

[0136] The method also includes analyzing the corrected two-dimensional image to determine characteristics of the target structure, as shown in step 714 .

[0137] In some embodiments, in an overlay system, an IMS can be used to vary the size of the pupil. Changes in pupil size can result in changes in the spatial coherence of the system, which can reduce the quality of the overlay measurement. For example, the spatial coherence at the detector of the overlay system is a function of the wavelength and polarization of the illumination beam, the IMS aperture size, and the wavelength-to-spacing ratio. Spatial coherence can result in coherence effects in the overlay measurement, which can reduce the quality of the measurement. The overlay system described herein is not affected by the wavelength and polarization of the illumination beam.

[0138] In some embodiments, the target structure used in the overlay system may include four different grating pairs in close proximity to each other (e.g., a micro-diffraction based overlay measurement target). The proximity of the gratings may cause unavoidable intra-target intensity crosstalk. In addition, the proximity of adjacent diffraction structures around the target structure causes external intensity crosstalk, which depends on the specific situation. The crosstalk causes overlay measurement errors. The crosstalk in the overlay system described herein is reduced or eliminated. Therefore, the overlay measurement errors are reduced.

[0139] Figure 8 A schematic diagram of an overlay system 800 is shown in accordance with some embodiments. In some embodiments, the system 800 may also represent a more detailed view of the beam analyzer 430. In some embodiments, the system 800 includes an illumination system 802, an optical system 804, a detector system 806, and a processor 808.

[0140] In some embodiments, illumination system 802 may include radiation source 810, optical elements (e.g., lenses or lens systems) 812, 814, 816, optical element 818, reflective element (e.g., folding mirror) 820, optical element 822 (e.g., lens or lens system), beam splitter 824, and optical element 826 (e.g., lens or lens system). Radiation source 810 is configured to generate a beam to illuminate target 832.

[0141] In some embodiments, the radiation source 810 can be a spatially coherent light source. The radiation source 810 can have a low "optical extension". In some embodiments, the term "optical extension" can be used herein to refer to the characteristics of light of an optical system, which characterizes the expansion of the illumination intensity based on the propagation direction and spatial distribution (e.g., the solid angle relative to the origin). In some embodiments, the radiation source 810 is coupled to a single-mode optical fiber. The output from the single-mode optical fiber is imaged using an optical element 812. That is, a point source is imaged into a target 832. The point source is scanned on the target 832, and a confocal image of the target 832 can be obtained. Since the point source is used as the illumination source of the overlay system 800, the IMS pupil is fixed. Therefore, the aberration is uniform and can be controlled. The optical element 818 can control the field constant aberration related to wavelength and polarization.

[0142] In some embodiments, optical element 818 is configured to control (e.g., correct) optical aberrations in system 800. In some embodiments, optical element 818 can be an aberration correction device (such as a deformable mirror (DM), a spatial light modulator (SLM), or an aberration corrector plate (or mask)). Optical element 818 can adjust the intensity and / or phase profile of the light beam.

[0143] In some embodiments, optical element 818 can be positioned in the optical path of the illumination beam before optical system 804. In some aspects, optical element 818 can be positioned at a location where the beam diameter of the light beam is suitable for aberration correction. For example, optical element 818 can be positioned at a pupil conjugate plane. The pupil conjugate plane can refer to an image plane in an image plane of a pupil plane of system 800. In some aspects, optical element 818 can be positioned slightly offset from the pupil conjugate plane, or positioned at a field plane location.

[0144] In some aspects, the aberration correction performed by optical element 818 includes one or more of the following: (1) removal (or substantial reduction) of through-focus aberration along the entire illumination path (branch), (2) removal (or substantial reduction) of tilt aberration along the entire illumination path (branch), (3) removal (or substantial reduction) of spherical aberration along the entire illumination path, (4) removal (or substantial reduction) of offset coma along the entire illumination path, (5) removal (or substantial reduction) of offset astigmatism along the entire illumination path, (6) removal (or substantial reduction) of offset Petzval along the entire illumination path, and (7) removal (or substantial reduction) of offset distortion along the entire illumination path.

[0145] In some aspects, optical element 818 can control the beam (focal spot) to be focused or defocused into target 832. For example, target 832 may not move in the z-direction to focus or defocus the beam, but rather optical element 818 can control the focal spot of the illumination beam.

[0146] In some embodiments, optical element 818 may be a reflective element (eg, a mirror). In some embodiments, optical element 818 may not provide an optical aberration function.

[0147] In some embodiments, the optical system 804 can include a beam splitter system 828 (e.g., one or more beam splitters). The beam splitter 828 can direct a first portion of the light beam to a scanning system 868. The beam splitter 828 can direct a second portion of the light beam to a wavefront sensor 866. In some aspects, the beam splitter system 828 directs the entire light beam to the scanning system 868.

[0148] In some embodiments, the scanning system 868 is configured to scan the light beam in a first direction and a second direction. This is used to scan the target 832 in the first direction and the second direction. In some aspects, the scanning system 868 can be a MEMS mirror. In some aspects, the scanning system 868 can include one or more galvanometer mirrors. In some aspects, a two-dimensional MEMS mirror with a tilt angle of ±5mrad can be used. By controlling the angle of the MEMS mirror, the irradiation area on the target 832 can be changed. For example, the MEMS mirror can be controlled to move the light beam in a predefined scanning pattern on the target 832. The relay system can relay the light beam to the optical element 830. The optical element 830 can direct a portion of the light beam to the target 832. The relay system may include a first optical element 870 (e.g., a lens or a lens system) and a second optical element 872 (e.g., a lens or a lens system).

[0149] Figure 8 A non-limiting depiction of system 800 inspecting a target 832 (also referred to as a "target structure") on a substrate 834 is shown. Substrate 834 is positioned on an adjustable stage 836 (e.g., a support structure that can be moved). It should be understood that the depicted structures within illumination system 802 and optical system 804 are not limited to their depicted locations. The locations of the structures can be varied as desired, for example, as designed for modular components.

[0150] In some embodiments, the target 832 may include a diffraction structure (e.g., a grating). The target 832 may reflect, refract, diffract, scatter, etc. radiation. For ease of discussion, and without limitation, radiation that interacts with the target will always be referred to as scattered radiation. The scattered radiation is collected by the optical element 830. The scattered radiation includes a reflection of the illumination beam (zero order) and first diffraction order beams and second diffraction order beams (e.g., positive and negative first order diffraction beams, positive and negative second order diffraction beams). For example, the scattered radiation may include ± first diffraction orders.

[0151] In some embodiments, detection system 806 may include optical element 838, reflective element (e.g., fold mirror) 840, optical element (e.g., lens or lens system) 842, reflective element (e.g., mirror) 844, optical element 846, reflective element (e.g., mirror) 848, optical element (e.g., lens or lens system) 850, reflective element (e.g., mirror) 852, reflective element (e.g., mirror) 854, optical element (e.g., lens or lens system) 856, beam splitter 858, optical element 876 (e.g., wedge), optical element (e.g., lens or lens system) 860, and detector 862 (e.g., photodetector). Beam splitter 858 may direct a portion of the scattered radiation to optical element 860. Beam splitter 858 may direct another portion of the scattered radiation to wavefront sensor 864. Optical element 860 may be configured to focus the scattered radiation into detector 862. Detector 862 may be coupled to processor 808. Detector 862 may generate a signal beam as a function of the scattering direction. Processor 808 may form a two-dimensional image of target 832. Processor 808 may analyze the two-dimensional image to determine overlay error.

[0152] Optical element 846 is configured to control (e.g., correct) optical aberrations in system 800. In some embodiments, optical element 846 can be an aberration correction device (such as a deformable mirror (DM), a spatial light modulator (SLM), or an aberration corrector plate (or mask)). Optical element 846 can adjust the intensity and / or phase profile of the scattered radiation.

[0153] In some embodiments, optical element 846 can be positioned in the optical path of scattered radiation collected by optical element 830 after optical system 804. In some aspects, optical element 846 can be positioned at a position where the beam diameter of the light beam is suitable for aberration correction. For example, optical element 846 can be positioned at a pupil conjugate plane. The pupil conjugate plane can refer to an image plane in the image plane of the pupil plane of system 800. In some aspects, optical element 846 can be positioned slightly offset from the pupil conjugate plane, or positioned at a field plane position. In some aspects, optical element 846 can correct optical aberrations introduced by poor and inaccurate target alignment in the z direction.

[0154] In some aspects, the aberration correction performed by optical element 846 includes one or more of the following: (1) removal (or substantial reduction) of through-focus aberration along the entire illumination path (branch), (2) removal (or substantial reduction) of tilt aberration along the entire illumination path (branch), (3) removal (or substantial reduction) of spherical aberration along the entire illumination path, (4) removal (or substantial reduction) of offset coma along the entire illumination path, (5) removal (or substantial reduction) of offset astigmatism along the entire illumination path, (6) removal (or substantial reduction) of offset Petzval along the entire illumination path, and (7) removal (or substantial reduction) of offset distortion along the entire illumination path.

[0155] In some embodiments, optical element 846 may be a reflective element (eg, a mirror). In this case, optical element 846 may not be configured to control optical aberrations in system 800.

[0156] In some aspects, the system 800 can include a closed-loop or sensorless optical aberration control system. In some aspects, the system 800 can include a wavefront sensor 866 (e.g., a Shack Hartmann sensor) and a wavefront sensor 864 (e.g., a Shack Hartmann sensor). The wavefront sensor 866 can be configured to provide feedback to the optical element 818. For example, the wavefront sensor 866 can be configured to measure the aberrations of the optical wavefront of the light beam. The optical element 818 (such as a deformable mirror) can be controlled based on the measured aberrations (e.g., causing a control signal of the deformable mirror to vary). In some aspects, the processor 808 can receive input from the wavefront sensor 866. The processor 808 can determine a setting for the optical element 818 to correct for the aberrations. For example, the processor 808 can determine an optimal shape for a surface of the deformable mirror.

[0157] In some aspects, the wavefront sensor 864 can be configured to provide feedback to the optical element 846. For example, the wavefront sensor 864 can be configured to measure aberrations of the optical wavefront of the scattered beam. The optical element 846 (such as a deformable mirror) can be controlled based on the measured aberrations (e.g., causing a control signal of the deformable mirror to vary). In some aspects, the processor 808 can receive input from the wavefront sensor 864. The processor 808 can determine a setting for the optical element 846 to correct for the aberrations. For example, the processor 808 can determine an optimal shape for a surface of the deformable mirror.

[0158] In some embodiments, the field of view of system 800 is smaller than an overlay system with a different illumination source (ie, not a point source). At the location of the scanning system, only the region of interest of target 832 is illuminated. Thus, crosstalk from other features is minimized.

[0159] In some embodiments, the illumination size of the light beam can be controlled so that an overfill or underfill condition relative to the target 832 can be achieved. Overfill can refer to illuminating more than the desired target area. Underfill can refer to illuminating less than the desired target area. For example, if scattering from the background (i.e., an area adjacent to the desired target area) is detected by the detection system 806, the field of view can be reduced. In some aspects, if scattering from the background is not detected, the field of view can be increased during scanning.

[0160] Fig. 9 A schematic diagram of an overlay system 900 is shown in accordance with some embodiments. In some embodiments, the system 900 may also represent a more detailed view of the beam profiler 430. Fig. 9 The elements in Figure 8 Components with similar numbers (last two digits) in the same embodiment have similar structures and functions. For the sake of brevity, the description of these components is omitted.

[0161] In some embodiments, system 900 includes an illumination system 902 , an optical system 904 , a detector system 906 , and a processor 908 .

[0162] In some embodiments, illumination system 902 may include radiation source 910, optical elements (e.g., lenses or lens systems) 912, 914, 916, optical element 918, reflective element (e.g., folding mirror) 920, optical element 922 (e.g., lenses or lens systems), beam splitter 924, and optical element 926 (e.g., lenses or lens systems). Radiation source 910 is configured to generate a beam to illuminate target 932.

[0163] In some embodiments, radiation source 910, optical element 918, and optical element 946 may have similar structures and functions as radiation source 810, optical element 818, and optical element 846, respectively. For the sake of brevity, detailed descriptions of these elements are omitted.

[0164] In some embodiments, the optical system 904 can include a beam splitter system 928 (e.g., one or more beam splitters). The beam splitter 928 can direct a first portion of the light beam to a scanning system. The beam splitter 928 can direct a second portion of the light beam to a wavefront sensor (not shown). In some aspects, the beam splitter system 928 directs the entire light beam to the scanning system.

[0165] In some embodiments, the scanning system is configured to scan the light beam in a first direction and a second direction. In some aspects, the scanning system may include a first scanning device 968a and a second scanning device 968b. This is used to scan the target 932 in the first direction and the second direction. In some aspects, the first scanning device 968a may be a first MEMS mirror, and the second scanning device 968b may be a second MEMS device. By controlling the angle of the MEMS mirror, the irradiation area on the target 932 is changed. For example, the first scanning device 968a may be controlled to move the light beam in a first dimension (e.g., along the x direction) at a first speed on the target 932. The second scanning device 968b may be controlled to move the light beam in a second direction (e.g., along the y direction) at a second speed. In some aspects, the first speed may be greater than the second speed. Having two scanning devices may increase the detection speed of the system 900.

[0166] The relay system may relay the light beam to an optical element 930. The optical element 930 may direct part or all of the light beam to a target 932. The relay system may include a first optical element 970 (e.g., a lens or a lens system) and a second optical element 972 (e.g., a lens or a lens system). The second relay may be positioned after the scanning device 968b. The second relay may include a first optical element 978 (e.g., a lens or a lens system) and a second optical element 980 (e.g., a lens or a lens system).

[0167] Fig. 9 A non-limiting depiction of system 900 inspecting a target 932 (also referred to as a "target structure") on a substrate 934 is shown. Substrate 934 is positioned on an adjustable stage 936 (e.g., a support structure that can be moved). It should be understood that the structures depicted within illumination system 902 and optical system 904 are not limited to their illustrated locations. The locations of the structures can be varied as desired, for example, as designed for modular components.

[0168] In some embodiments, the target 932 may include a diffraction structure (e.g., a grating). The target 932 may reflect, refract, diffract, scatter, etc. radiation. For ease of discussion, and without limitation, radiation that interacts with the target will always be referred to as scattered radiation. The scattered radiation is collected by the optical element 830. The scattered radiation includes a reflection of the illumination beam (zero order) and first diffraction order beams and second diffraction order beams (e.g., positive and negative first order diffraction beams, positive and negative second order diffraction beams). For example, the scattered radiation may include ± first diffraction orders.

[0169] In some embodiments, detection system 906 may include optical element 938, reflective element (e.g., fold mirror) 940, optical element 942 (e.g., lens or lens system), reflective element (e.g., mirror) 944, optical element 946, reflective element (e.g., mirror) 948, optical element (e.g., lens or lens system) 950, reflective element (e.g., mirror) 952, reflective element (e.g., mirror) 954, optical element (e.g., lens or lens system) 956, beam splitter 958, optical element 976 (e.g., wedge), optical element (e.g., lens or lens system) 960, and detector 962 (e.g., photodetector). Beam splitter 958 may direct a portion of the scattered radiation to optical element 960. Beam splitter 958 may direct another portion of the scattered radiation to a wavefront sensor (not shown). Optical element 960 may be configured to focus the scattered radiation into detector 962. Detector 962 may be coupled to processor 908. Detector 962 may generate a signal beam as a function of the scattering direction. Processor 908 may form a two-dimensional image of target 932. Processor 908 may analyze the two-dimensional image to determine overlay error.

[0170] In some embodiments, the overlay systems described herein are not affected by coherence effects because there are time differences between different acquisitions of the signal beams.

[0171] Fig.10 Method steps are shown (eg, using one or more processors) for performing method 1000 including the functionality described herein, according to some embodiments. Fig.10 The method 1000 may be performed in any desired order, and not all steps need to be performed. Fig.10 The method steps shown reflect only examples of steps and are not limiting.

[0172] Method 1000 illustrates a method for determining an overlay characterization.

[0173] Method 1000 includes illuminating a target structure with a light beam, as shown in step 1002 .

[0174] The method also includes controlling a focal spot of the light beam on the target structure, as shown in step 1004 .

[0175] The method also includes directing a signal beam from the target structure to a detector system, as shown in step 1006. The signal beam includes at least a scattered beam generated from the target structure.

[0176] The method also includes analyzing the signal beam to determine an overlay characterization of the target structure, as shown in step 1008 .

[0177] The embodiments may also be described using the following terms:

[0178] 1. A system comprising:

[0179] an illumination system configured to: direct a light beam to illuminate a target structure;

[0180] a scanning system configured to: scan the light beam and control the size of a focal spot of the light beam on the target structure;

[0181] an optical system configured to: maintain alignment with an optical axis of the system during scanning of the light beam;

[0182] a detector system configured to: detect a signal beam generated from the target structure during scanning of the light beam, wherein the signal beam comprises at least a scattered beam generated from the target structure; and

[0183] A processor is configured to analyze the detected signal beam to determine an overlay characterization of the target structure.

[0184] 2. A system according to clause 1, wherein the irradiation system comprises:

[0185] Light source; and

[0186] A single mode optical fiber coupled to a light source, wherein the light source is a coherent light source.

[0187] 3. The system of clause 1, wherein the scanning system comprises a micro-electromechanical system (MEMS) scanning mirror.

[0188] 4. A system according to clause 1, wherein the scanning system comprises:

[0189] a first scanning mirror configured to scan the light beam in a first direction; and

[0190] The second scanning mirror is configured to scan the light beam in a second direction, wherein the first direction is orthogonal to the second direction.

[0191] 5. A system according to clause 4, wherein:

[0192] The first scanning mirror is configured to be actuated at a first speed;

[0193] The second scanning mirror is configured to be actuated at a second speed; and

[0194] The first speed is lower than the second speed.

[0195] 6. The system according to clause 1, further comprising:

[0196] An optical element is positioned within the illumination path and / or the detection path and is configured to correct aberrations in at least one image obtained by scanning the target structure using the scanning system.

[0197] 7. A system according to clause 6, wherein:

[0198] The illumination system includes a light source; and

[0199] An optical element is positioned in the illumination path between the light source and the target structure.

[0200] 8. A system according to clause 6, wherein the optical element is positioned in the detection path after the target structure.

[0201] 9. A system according to clause 8, further comprising:

[0202] another optical element configured to correct for aberrations; and

[0203] Another optical element is positioned in the illumination path.

[0204] 10. A system according to clause 6, wherein the optical element comprises a deformable mirror, a spatial light modulator or an aberration corrector plate.

[0205] 11. A system according to clause 6, further comprising:

[0206] Adaptive optics aberration control system,

[0207] The optical element is coupled to an adaptive optics aberration control system.

[0208] 12. The system according to clause 11, further comprising:

[0209] a sensor configured to: measure a wavefront of the scattered beam; and

[0210] The adaptive optics aberration control system is configured to control the optical element based on the measurement.

[0211] 13. The system according to clause 1, further comprising:

[0212] an objective lens; and

[0213] The optical system includes a pupil relay system, which is arranged between the scanning system and the objective lens.

[0214] 14. A method comprising:

[0215] irradiating a target structure with a light beam;

[0216] controlling the focal spot of the beam on the target structure;

[0217] directing a signal beam from the target structure toward a detector system, wherein the signal beam includes at least a scattered beam generated from the target structure; and

[0218] The signal beam is analyzed to determine the overlay characterization of the target structure.

[0219] 15. The method according to clause 14, further comprising:

[0220] A light source is coupled to a single mode optical fiber, wherein the light source is a coherent light source.

[0221] 16. The method according to clause 14, further comprising:

[0222] Scanning the light beam in a first direction at a first speed using a first scanning mirror; and

[0223] Scanning the light beam in a second direction at a second speed using a second scanning mirror,

[0224] wherein the first speed is lower than the second speed, and

[0225] The first direction is orthogonal to the second direction.

[0226] 17. The method according to clause 14, further comprising:

[0227] Using optical elements to correct optical aberrations; and

[0228] Position the optical element in the illumination path or the detection path.

[0229] 18. A method according to clause 17, wherein the optical element comprises a deformable mirror, a spatial light modulator or an aberration corrector plate.

[0230] 19. The method according to clause 17, further comprising:

[0231] coupling the optical element to an optical aberration control system;

[0232] measuring the wavefront of the scattered beam; and

[0233] Using an optical aberration control system, the optical elements are controlled based on the measurements.

[0234] 20. A lithographic apparatus comprising:

[0235] an irradiation device configured to irradiate the pattern of the patterning device;

[0236] a projection system configured to project an image of the pattern onto a substrate; and

[0237] Measuring system, including:

[0238] an illumination system configured to direct the light beam to illuminate the target structure,

[0239] a scanning system configured to scan the light beam and control the size of a focal spot of the light beam on the target structure;

[0240] an optical system configured to maintain alignment with an optical axis of the system during scanning of the light beam;

[0241] a detector system configured to detect a signal beam generated from a target structure during scanning of the light beam, wherein the signal beam includes at least a scattered beam generated from the target structure; and

[0242] A processor is configured to analyze the detected signal beam to determine an overlay characterization of the target structure.

[0243] Although specific reference may be made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film heads, etc. It should be understood by those skilled in the art that in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered as a specific example of the more general terms "substrate" or "target portion", respectively. Before or after exposure, the substrates referred to herein may be processed in, for example, a tracking unit (a tool that typically applies a resist layer to a substrate and develops the exposed resist) and / or a metrology unit. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, for example, in order to create a multi-layer IC, the substrate may be processed more than once, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0244] Although specific reference has been made above to the use of embodiments of the present disclosure in the context of optical lithography, it should be understood that the present disclosure may be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the topography in the patterning device defines the pattern created on the substrate. The topography of the patterning device can be pressed into a resist layer supplied to the substrate, thereby curing the resist by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern therein.

[0245] It is to be understood that the phraseology or terminology herein is for the purpose of description and not limitation, so that the phraseology or terminology of the present disclosure is to be interpreted by those skilled in the relevant art in view of the teachings herein.

[0246] As used herein, the terms "radiation", "radiation beam", etc. may encompass all types of electromagnetic radiation, for example, ultraviolet (UV) radiation (e.g., with a wavelength λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (e.g., with a wavelength in the range of 5 nm to 20 nm, such as 13.5 nm, for example), or hard X-rays operating at less than 5 nm, and material beams, such as ion beams or electron beams. The terms "light", "irradiation", etc. may refer to non-material radiation (e.g., photons, UV, X-rays, etc.). Typically, radiation with a wavelength between about 400 nm and about 700 nm is considered visible radiation; radiation with a wavelength between about 780 nm and 3000 nm (or greater) is considered IR radiation. UV refers to radiation with a wavelength of approximately 100 nm to 400 nm. Within lithography, the term "UV" also applies to wavelengths that can be produced by mercury discharge lamps: G-line 436 nm, H-line 405 nm, and / or I-line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by gases) refers to radiation having a wavelength of approximately 100 nm to 200 nm. Deep UV (DUV) generally refers to radiation having a wavelength range of from 126 nm to 428 nm, and in some embodiments, an excimer laser may generate DUV radiation for use within a lithographic apparatus. It should be understood that radiation having a wavelength in the range of, for example, 5 nm to 20 nm refers to radiation having a particular wavelength band, at least a portion of which is within the range of 5 nm to 20 nm.

[0247] It should be understood that the detailed description section, rather than the summary and abstract sections, is intended to be used to interpret the claims. The summary and abstract sections may set forth one or more exemplary embodiments of the present disclosure contemplated by one or more inventors, but not all exemplary embodiments, and therefore are not intended to limit the present disclosure and the appended claims in any way.

[0248] The present disclosure has been described above with the aid of functional building blocks that illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks are arbitrarily defined herein. Alternative boundaries may be defined as long as the specified functions and their relationships are appropriately performed.

[0249] Although specific embodiments of the present disclosure have been described above, it should be understood that the various embodiments of the present disclosure may be implemented in a manner different from that described. These descriptions are intended to be illustrative rather than limiting. Therefore, it is apparent to those skilled in the art that the disclosed content may be modified without departing from the scope of the claims set forth below.

[0250] The foregoing description of specific embodiments will reveal the general nature of the present disclosure so fully that others can easily modify and / or adapt such specific embodiments for various applications without undue experimentation by applying knowledge in the art without departing from the general concepts of the present disclosure. Therefore, based on the teaching and guidance given herein, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments.

[0251] The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A system comprising: an illumination system configured to direct the light beam to illuminate a target structure; a scanning system configured to scan the beam and control a size of a focal spot of the beam onto the target structure; an optical system configured to maintain alignment with an optical axis of the system during scanning of the light beam; a detector system configured to detect a signal beam generated from the target structure during scanning of the light beam, wherein the signal beam includes at least a scattered beam generated from the target structure; as well as A processor is configured to analyze the detected signal beam to determine an overlay characterization of the target structure.

2. The system of claim 1, wherein the illumination system comprises: light source; as well as A single mode optical fiber is coupled to the light source, wherein the light source is a coherent light source.

3. The system of claim 1, wherein the scanning system comprises a micro-electromechanical system (MEMS) scanning mirror.

4. The system of claim 1, wherein the scanning system comprises: a first scanning mirror configured to scan the light beam in a first direction; as well as A second scanning mirror is configured to scan the light beam in a second direction, wherein the first direction is orthogonal to the second direction.

5. The system of claim 4, wherein: The first scanning mirror is configured to be actuated at a first speed; The second scanning mirror is configured to be actuated at a second speed; and The first speed is lower than the second speed.

6. The system according to claim 1, further comprising: An optical element is positioned within the illumination path and / or the detection path and is configured to correct aberrations in at least one image obtained by scanning the target structure using the scanning system.

7. The system of claim 6, wherein: The illumination system comprises a light source; and The optical element is positioned in the illumination path between the light source and the target structure.

8. The system of claim 6, wherein the optical element is positioned in the detection path after the target structure.

9. The system according to claim 8, further comprising: another optical element configured to correct the aberration; and Wherein the further optical element is positioned in the illumination path.

10. The system of claim 6, wherein the optical element comprises a deformable mirror, a spatial light modulator, or an aberration corrector plate.

11. The system according to claim 6, further comprising: Adaptive optics aberration control system, Wherein the optical element is coupled to the adaptive optics aberration control system.

12. The system according to claim 11, further comprising: a sensor configured to measure a wavefront of the scattered beam; and Wherein the adaptive optics aberration control system is configured to control the optical element based on the measurement.

13. The system of claim 1, further comprising: Objective lens; and The optical system comprises a pupil relay system, wherein the pupil relay system is arranged between the scanning system and the objective lens.

14. A method comprising: irradiating a target structure with a light beam; controlling a focal spot of the light beam on the target structure; directing a signal beam from the target structure toward a detector system, wherein the signal beam includes at least a scattered beam generated from the target structure; as well as The signal beam is analyzed to determine an overlay characterization of the target structure.

15. The method according to claim 14, further comprising: A light source is coupled to the single mode optical fiber, wherein the light source is a coherent light source.

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