Measurement system using multiple radiation spots

Abstract

An inspection system includes a radiation source, first and second optical structures, and a detection system. The radiation source generates a radiation beam. An image formed by the beam includes a radiation spot corresponding to the beam. The diameter of the radiation spots is smaller than the size of the target, and the radiation spots are non-overlapping. The first optical structure travels the beam along a path toward the target so as to project a spot of radiation on the target and produce scattered radiation from the target. The second optical structure is configured to collect scattered radiation from the target. The detection system receives scattered radiation collected by the second optical structure and generates a measurement signal. Each of the measurement signals corresponds to each of the radiation spots.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 63 / 392,044, filed on July 25, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to inspection systems, such as metrology systems for measuring target marks used in lithography processes. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (usually to a target portion of the substrate). A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device (which can be a mask or a reticle) can be used to produce a circuit pattern to be formed on a separate layer of the IC. This pattern can be transferred to a target portion (e.g., a portion including a die, a die, or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually via imaging onto a layer of radiation-sensitive material (photoresist or simply "resist") disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned in succession. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at one time; and so-called scanners, in which each target portion is irradiated by scanning the radiation beam in a given direction (the "scanning" direction) while simultaneously scanning the target portion parallel or antiparallel to the scanning direction. The pattern may also be transferred from the patterning device to the substrate by printing the pattern onto the substrate.

[0005] During a lithography operation, different processing steps may require different layers to be sequentially formed on a substrate. Therefore, it may be necessary to position the substrate with high accuracy relative to an existing pattern formed on the substrate. Typically, alignment marks are placed on the substrate to be aligned and positioned with reference to a second object. The lithography equipment 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. The misalignment between alignment marks at two different layers is measured as overlay error.

[0006] In order to monitor the lithography process, the parameters of the patterned substrate are measured. For example, the parameters may include the overlay error between successive layers formed in or on the patterned substrate and the critical line width of the developed photoresist. The measurement may be performed on a product substrate and / or a dedicated metrology target. There are various techniques for measuring the microstructures formed during the lithography process, including the use of scanning electron microscopes and various dedicated tools. A fast and non-invasive dedicated inspection tool is a scatterometer, in which a radiation beam is directed to a target on the surface of the substrate and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after the beam is reflected or scattered by the substrate, the properties of the substrate can be determined. For example, this can be achieved by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. 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 angularly resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0007] Such optical scatterometers 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 properties of the illumination beam before and after the illumination beam is reflected or scattered by the substrate, the properties of the substrate can be determined.

[0008] Lithography systems can only output a limited number of manufactured devices in a given time frame. To reduce manufacturing time, lithography systems can increase measurement speed, but this strategy often reduces measurement accuracy. Summary of the invention

[0009] Therefore, it is desirable to increase manufacturing speed and throughput without sacrificing lithographic accuracy.For example, an optical inspection process can be performed faster by increasing the measurement radiation dose in a manner that circumvents certain limitations associated with higher radiation intensities based on aspects described herein.

[0010] In some aspects, the inspection system may include a radiation source configured to generate a radiation beam. An image formed by the beam may include radiation spots corresponding to the beam. Each of the diameters of the radiation spots may be smaller than the size of the target. The radiation spots may be non-overlapping. The inspection system may also include a first optical structure configured to cause the beam to travel along a route toward the target so as to project the radiation spots on the target and generate scattered radiation from the target. The inspection system may also include a second optical structure configured to collect scattered radiation from the target. The inspection system may also include a detection system configured to receive the scattered radiation collected by the second optical structure and generate measurement signals. Each of the measurement signals may correspond to each of the radiation spots.

[0011] In some aspects, a lithographic apparatus may include an illumination system configured to illuminate a pattern of a pattern forming device. The lithographic apparatus may also include a projection system configured to project an image of the pattern onto a substrate. The lithographic apparatus may also include an inspection system. The inspection system may include a radiation source configured to generate a radiation beam. The image formed by the beam may include a radiation spot corresponding to the beam. Each of the diameters of the radiation spots may be smaller than the size of a target. The radiation spots may be non-overlapping. The inspection system may also include a first optical structure configured to cause the beam to travel along a route toward the target so as to project the radiation spots on the target and generate scattered radiation from the target. The inspection system may also include a second optical structure configured to collect scattered radiation from the target. The inspection system may also include a detection system configured to receive the scattered radiation collected by the second optical structure and generate a measurement signal. Each of the measurement signals may correspond to each of the radiation spots.

[0012] Other features of various aspects of the present disclosure 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 aspects described herein. These aspects are presented herein for illustrative purposes only. Based on the teachings contained herein, (multiple) relevant technical personnel will understand additional aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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 one skilled in the relevant art(s) to make and use the aspects described herein.

[0014] Figure 1A A reflective lithographic apparatus according to some aspects is shown.

[0015] Figure 1B A transmissive lithographic apparatus according to some aspects is shown.

[0016] Figure 2 More details of a reflective lithography apparatus according to some aspects are shown.

[0017] Figure 3 A lithography cell according to some aspects is shown.

[0018] Figure 4A , Figure 4B , Figure 5 and Figure 6 An inspection system according to some aspects is shown.

[0019] Figure 7 and Figure 8 A scanning process using multiple radiation spots is shown in accordance with some aspects.

[0020] Figures 9 to 12 An inspection system according to some aspects is shown.

[0021] Features of the present disclosure will become more apparent from the following detailed description set forth in conjunction with the accompanying drawings, in which similar reference numerals identify corresponding elements throughout. In the accompanying drawings, similar reference numerals generally represent identical, functionally similar, and / or structurally similar elements. In addition, the leftmost digit(s) of a reference numeral generally 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

[0022] The various aspects described herein and references in the specification to "an aspect," "aspect," "exemplary aspect," "example aspect," etc. indicate that the various aspects described may include specific features, structures, or characteristics, but each aspect does not necessarily include the specific features, structures, or characteristics. Moreover, these words or phrases do not necessarily refer to the same aspect. In addition, when a specific feature, structure, or characteristic is described in conjunction with an aspect, it should be understood that it is within the knowledge of those skilled in the art to implement such features, structures, or characteristics in conjunction with other embodiments, regardless of whether the other aspects are explicitly described.

[0023] For ease of description, spatially relative terms such as "below," "beneath," "above," "over," and the like may be used herein to describe the relationship of one element or feature to other element(s) or feature(s) in the drawings. Spatially relative terms are intended to encompass different orientations of the apparatus or device in use or operation in addition to the orientation depicted in the drawings. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0024] The terms "about", "approximately", etc. may be used herein to indicate a value of a given quantity that may vary based on a particular technology. Based on a particular technology, the terms "about", "approximately", etc. may indicate a value of a given quantity that varies, for example, within 10% to 30% above or below the stated value (e.g., ±10%, ±20%, or ±30% of the stated value).

[0025] Aspects of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Aspects of the present disclosure may also be implemented as instructions stored on a computer-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 machine (e.g., a computing device) readable form. 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 propagation signal, an optical propagation signal, an acoustic propagation signal, or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.), etc. In addition, firmware, software, routines, and / or instructions may be described herein as performing specific actions. However, it should be understood that these descriptions are for convenience only, and that these actions are generated from a computing device, processor, controller, or other device that executes firmware, software, routines, instructions, etc. The term "machine-readable medium" may be interchangeable with similar terms such as "computer program product", "computer-readable medium", "non-transitory computer-readable medium", etc. The term "non-transitory" may be used herein to characterize one or more forms of computer-readable media other than transient propagation signals.

[0026] However, before describing these aspects in further detail, it is instructive to present an example environment in which aspects of the disclosure may be implemented.

[0027] Exemplary Lithography System

[0028] Figure 1A and Figure 1BA lithographic apparatus 100 and a lithographic apparatus 100' are respectively shown in which aspects of the present disclosure may be implemented. The lithographic apparatus 100 and the lithographic apparatus 100' respectively include the following: an illumination system (illuminator) IL, which is 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, which is configured to support a pattern forming device (e.g., a mask, a reticle, or a dynamic pattern forming device) MA and is connected to a first positioner PM configured to accurately position the pattern forming device MA; and a substrate stage (e.g., a wafer stage) WT, which is configured to hold a substrate (e.g., a wafer coated with a resist) W and is 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, which is configured to project a pattern imparted to the radiation beam B by the pattern forming device MA onto a target portion C (e.g., including one or more tube cores) of the substrate W. In lithographic apparatus 100, patterning device MA and projection system PS are reflective. In lithographic apparatus 100', patterning device MA and projection system PS are transmissive.

[0029] 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.

[0030] 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 table, which may be fixed or movable. By using sensors, the support structure MT may ensure that the patterning device MA is in a desired position, for example relative to the projection system PS.

[0031] 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 a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in a device created in the target portion C for forming an integrated circuit.

[0032] The pattern forming device MA can be a transmissive type (such as in Figure 1B lithographic apparatus 100') or a reflective type (as in Figure 1A100). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types. Examples of programmable mirror arrays use a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam B that is reflected by the matrix of small mirrors.

[0033] The term "projection system" PS may encompass any type of projection system suitable for the exposure radiation used or for other factors such as the use of an immersion liquid on the substrate W or the use of a vacuum, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof. A vacuum environment may be used for EUV or electron beam radiation, as other gases may absorb too much radiation or electrons. Thus, by means of vacuum walls and a vacuum pump, a vacuum environment may be set for the entire beam path.

[0034] The lithographic apparatus 100 and / or the 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, the additional substrate tables WT may be used in parallel, or one or more other substrate tables WT may be used for exposure while preparatory steps are being performed on one or more tables. In some cases, the additional tables may not be substrate tables WT.

[0035] 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) so as to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. Immersion techniques for increasing the numerical aperture of the projection system are well known in the art. The term "immersion" as used herein does not mean that structures such as the substrate must be immersed in the liquid. For example, the liquid may be located between the projection system and the substrate during exposure.

[0036] 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 such a case, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B is delivered to the lithographic apparatus 100 or 100' by means of a beam delivery system BD ( Figure 1BIn 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 radiation system may include the source SO, the illuminator IL and / or the beam delivery system BD.

[0037] The illuminator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam ( 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 ( Figure 1B ), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0038] 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 being reflected 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., a mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0039] 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. After 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 conjugate pupil PPU relative to the illumination system pupil IPU. Multiple portions of the radiation emanate from the intensity distribution at the illumination system pupil IPU and pass through the mask pattern without being affected by diffraction at the mask pattern and produce an image of the intensity distribution at the illumination system pupil IPU.

[0040] 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 by the mask pattern MP caused by radiation having an intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Diffraction of radiation at the array that is different from the zero-order diffraction produces a diffraction beam that is steered, and the diffraction beam that is steered has a change in direction in a direction perpendicular to the line. 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 that is located upstream of the conjugate pupil or conjugate pupil PPU of the projection system PS to reach the conjugate pupil PPU. The portion of the intensity distribution in the plane of the conjugate pupil 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, arranged at or approximately at a plane including the conjugate pupil PPU of the projection system PS.

[0041] The projection system PS is arranged to capture (e.g., by using a lens or lens group L) a zero-order diffraction beam, a first-order diffraction beam, and / or higher-order diffraction beams (not shown). In some aspects, 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, at the level of the wafer W, the first-order diffraction beam interferes with the corresponding zero-order diffraction beam to produce an image of the line pattern MP with the highest possible resolution and process window (i.e., available focal depth and tolerable exposure dose deviation). In some aspects, astigmatic aberrations can be reduced by providing a radiation pole (not shown) in the opposite quadrant of the illumination system pupil IPU. In addition, in some aspects, astigmatic aberrations can be reduced by blocking the zero-order beam in the conjugate pupil PPU of the projection system associated with the radiation pole in the opposite quadrant. This is described in more detail in US 7,511,799 B2, issued on March 31, 2009, the entire contents of which are incorporated herein by reference in their entirety.

[0042] 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 substrate table WT can be accurately moved using a first positioner PM and another position sensor ( Figure 1B ) 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).

[0043] Typically, 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) which form 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 which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected 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 with the substrate W. Although the substrate alignment marks (as shown) occupy dedicated target portions, these marks may be located in the spaces between 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.

[0044] The mask table MT and the patterning device MA may be in a vacuum chamber V, where 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 similar to the in-vacuum robot IVR may be used to perform various transport operations. Both the in-vacuum robot and the out-of-vacuum robot may be calibrated to smoothly transfer any payload (e.g., a mask) to the fixed kinematic support of the transfer station.

[0045] The lithographic apparatus 100 and 100' may be used in at least one of the following modes:

[0046] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept substantially stationary (i.e. a single static exposure) while the entire pattern imparted to the radiation beam B is projected at one time onto a target portion C. The substrate table WT is then shifted in the X-direction and / or Y-direction so that a different target portion C can be exposed.

[0047] 2. In scan mode, the support structure (e.g. mask table) MT and substrate table WT are scanned synchronously (i.e. single dynamic exposure) as a pattern imparted to the radiation beam B is projected onto a target portion C. The speed and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0048] 3. In another mode, the support structure (e.g. mask table) MT is kept substantially stationary, thereby holding 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 used, and the programmable patterning device updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation may be readily applicable to maskless lithography using a programmable patterning device, such as a programmable mirror array.

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

[0050] In other aspects, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Typically, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0051] 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 a closed structure 220 of the source collector device SO. The EUV radiation emitting plasma 210 can be formed by a discharge-generated plasma source. EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein the EUV radiation emitting plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. The EUV radiation emitting plasma 210 is generated by, for example, a discharge, which causes an at least partially ionized plasma. Radiation can be effectively generated using, for example, a partial pressure of 10Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor. In some aspects, an excited (e.g., via laser excitation) plasma of tin (Sn) is provided to generate EUV radiation.

[0052] The radiation emitted by the EUV radiation emitting plasma 210 enters the collector chamber 212 from the source chamber 11 via an optional gas barrier or contaminant trap 230 (also referred to as a contaminant barrier or fin trap in some cases) that 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. In this document, the contaminant trap or contaminant barrier 230 is additionally indicated as including at least a channel structure.

[0053] 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 by a grating spectral filter 240 to be focused at a virtual source point INTF. The virtual source point INTF is often referred to as an intermediate focus, and the source collector device is arranged so that the intermediate focus INTF is positioned at or near an opening 219 in the enclosed structure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. The grating spectral filter 240 is used in particular to suppress infrared (IR) radiation.

[0054] 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 arranged to provide a desired angular distribution of the radiation beam 21 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, 229 onto a substrate W held by a wafer stage or substrate table WT.

[0055] Typically more elements than shown may be present in the illumination optics unit IL and the projection system PS. A grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Furthermore, more than Figure 2 The reflectors shown in FIG. 5 are more reflectors, for example, compared to Figure 2 In addition to the reflective elements shown in FIG, there may be one to six additional reflective elements in projection system PS.

[0056] like Figure 2 The collector optics CO illustrated in FIG. 1 is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255, which is only an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged to be axially symmetric around the optical axis O, and this type of collector optics CO is preferably used in conjunction with a discharge produced plasma source, which is generally referred to as a DPP source.

[0057] Exemplary Lithography Cell

[0058] Figure 3A lithography unit 300 is shown according to some aspects, which is sometimes also referred to as a lithography cell or cluster. The lithography apparatus 100 or 100' may form a part of the lithography unit 300. The lithography unit 300 may also include one or more devices that perform pre-exposure processes and post-exposure processes on a substrate. Conventionally, 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. A substrate conveyor or robot RO picks up a substrate from an input / output port I / O1, I / O2, moves the substrate between different process devices, and transfers the substrate to a feed station LB of the lithography apparatus 100 or 100'. These devices, often collectively referred to as a track or coating and development control system, are under the control of a track or coating and development control system control unit TCU, which itself is controlled by a management 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.

[0059] Exemplary Inspection Equipment

[0060] 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 equipment includes one or more inspection devices for accurately locating the marks on the substrate. These alignment devices are actually 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 system widely used in current lithography equipment is based on a self-referencing interferometer described in U.S. Patent No. 6,961,116 (den Boef et al.). Typically, the marks are measured separately to obtain the X position and the Y position. However, combined X and Y measurements can be performed using the technology described in U.S. Publication No. 2009 / 195768 A (Bijnen et al.). The entire contents of these two disclosures are incorporated herein by reference.

[0061] Figure 4A A cross-sectional view of an inspection system 400 (or metrology system) that can be implemented as part of a lithographic apparatus 100 or 100' is shown according to some aspects. In some aspects, the inspection system 400 can be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). The inspection system 400 can also be configured to detect the position of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate relative to the patterning device or other components of the lithographic apparatus 100 or 100'. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0062] The terms "inspection equipment", "measurement system", etc. may be used herein to refer to, for example, a device for measuring properties of a structure (e.g., an overlay sensor, a critical dimension sensor, etc.), a device or system used in a lithography device to check the alignment of a wafer (e.g., an alignment sensor), etc.

[0063] In some aspects, the inspection system 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a 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 spectrum of wavelengths between about 500 nm and about 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a spectrum of wavelengths 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). This configuration of the illumination system 412 may help prevent a shift in actual CWL values ​​from a desired CWL value in current alignment systems, as described above. Thus, using a constant CWL value may improve the long-term stability and accuracy of an alignment system (e.g., the inspection system 400) compared to current alignment devices.

[0064] In some aspects, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. Figure 4AAs shown, the radiation beam 413 can be divided into radiation sub-beams 415 and 417. The beam splitter 414 can 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 can be moved along a direction 424. The radiation sub-beam 415 can be configured to illuminate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 can be coated with a radiation-sensitive film. In some aspects, the alignment mark or target 418 can have a one hundred and eighty degree (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 can be substantially the same as the unrotated alignment mark or target 418. The target 418 on the substrate 420 can be (a) a resist layer grating comprising strips formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack comprising a resist grating superimposed or interlaced on a product layer grating in an overlay target structure. Alternatively, the strips can be etched into the substrate. The pattern is sensitive to chromatic aberrations in the lithographic projection equipment (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 in-line method for measuring line width, pitch and critical dimensions in device manufacturing uses a technique known as "scatterometry". Methods of scatterometry are described in Raymond et al., "Multiparameter Grating Metrology Using Optical Scatterometry", J. Vac. Sci. Tech. B, Vol. 15, No. 2, pp. 361-368 (1997) and Niu et al., "Specular Spectroscopic Scatterometry in DUV Lithography", SPIE, Vol. 3677 (1999), both of which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by a periodic structure in a target and the resulting reflection spectrum at a given angle is detected. The structure that produces the reflection spectrum is reconstructed, for example, using rigorous coupled wave analysis (RCWA) or by comparison with a library of simulated patterns. Thus, the grating is reconstructed using scatterometry data of the printed grating. The parameters of the grating, such as line width and shape, can be input into the reconstruction process performed by the processing unit PU based on knowledge of the printing step and / or other scatterometry processes.

[0065] In some aspects, beam splitter 414 can also be configured to receive diffracted radiation beam 419 and, according to one aspect, can split diffracted radiation beam 419 into at least two radiation sub-beams. Diffracted radiation beam 419 can be split into diffracted radiation sub-beams 429 and 439, as shown in FIG. Figure 4A shown.

[0066] 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. 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.

[0067] like Figure 4A As shown, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414. In an example aspect, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In examples of this aspect, interferometer 426 includes any suitable set of optical elements, such as a prismatic combination that can be configured to form two images of alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be understood that high quality images need not be formed. It is sufficient to have resolved features of alignment mark 418. Interferometer 426 can also be configured to rotate one of the two images relative to the other of the two images. , and recombines the rotated and unrotated images in an interferometric manner.

[0068] In some aspects, the detector 428 can be configured to receive the recombined image via the interferometer signal 427 and detect interference caused by the recombined image when the alignment axis 421 of the inspection system 400 passes through the symmetry center (not shown) of the alignment mark or target 418. According to an example aspect, such interference can be caused by the alignment mark or target 418 being 180° symmetrical and the recombined images interfering constructively or destructively. Based on the detected interference, the detector 428 can also be configured to determine the position of the symmetry center of the alignment mark or target 418 and thereby detect the position of the substrate 420. According to an example, the alignment axis 421 can be aligned with a light beam that is perpendicular to the substrate 420 and passes through the center of the image rotation interferometer 426. The detector 428 can also be configured to estimate the position of the alignment mark or target 418 by implementing sensor characteristics and interacting with wafer marking process variations.

[0069] In other aspects, 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:

[0070] 1. Measure the position change of multiple wavelengths (position shift between colors);

[0071] 2. Measuring the positional changes of multiple orders (positional shifts between diffraction orders);

[0072] 3. Measuring the position change of multiple polarizations (position shift between polarizations).

[0073] This data can be obtained using any type of alignment sensor, such as a SMASH sensor (SMart Alignment Sensor Hybrid) as described in U.S. Patent No. 6,961,116, which uses a self-referencing interferometer with a single detector and four different wavelengths and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment) as described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector, both of which are incorporated herein by reference in their entirety.

[0074] In some aspects, the beam analyzer 430 can be configured to receive and determine the optical state of the diffracted radiation sub-beam 439. The optical state can be a measure of the beam wavelength, polarization, or beam profile. The beam analyzer 430 can also be configured to determine the position of the stage 422 and correlate the position of the stage 420 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418 can be accurately known with reference to the stage 422, and therefore the position of the substrate 420. Alternatively, the beam analyzer 430 can be configured to determine the position of the inspection system 400 or any other reference element, so that the center of symmetry of the alignment mark or target 418 can be known with reference to the inspection system 400 or any other reference element. The beam analyzer 430 can be a point or imaging polarimeter with some form of wavelength-band selectivity. In some aspects, beam analyzer 430 can be integrated directly into inspection system 400, or according to other aspects, beam analyzer 430 can be connected to inspection system 400 via several types of optical fibers: polarization-maintaining single-mode optical fiber, multimode optical fiber, or imaging optical fiber.

[0075] In some aspects, the beam analyzer 430 may also be configured to determine overlap 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 etching layer already present on the substrate 420. The reference layer may be generated by exposing the reference pattern on the substrate by the lithography apparatus 100 and / or 100'. The exposure layer may be a resist layer exposed adjacent to the reference layer. The exposure layer may be generated by exposing the exposure pattern on the substrate 420 by the lithography apparatus 100 or 100'. The exposure pattern on the substrate 420 may correspond to the movement of the stage 422 to the substrate 420. In some aspects, the measured overlap data may also indicate an offset between the reference pattern and the exposure pattern. The measured overlap data may be used as calibration data to calibrate the exposure pattern exposed by the lithography apparatus 100 or 100' so that after calibration, the offset between the exposure layer and the reference layer may be minimized.

[0076] In some aspects, the beam analyzer 430 may also be configured to determine a model of a product stack profile of the substrate 420, and may be configured to measure the overlay, critical dimension, and focal length of the target 418 in a single measurement. The product stack profile contains information about the stacked product (such as alignment marks, the target 418, or the substrate 420), and may include optical signal measurements caused by variations in the marking process as a function of variations in illumination. The product stack profile may also include product raster profiles, mark stack profiles, and mark asymmetry information. An example of a beam analyzer 430 is the Yieldstar manufactured by ASML of Wilhoven, 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 specific properties 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 the layer relative to the previous layer on the substrate or the accuracy of positioning of the first layer relative to a mark on the substrate), focus parameters, and / or critical dimension parameters (e.g., line width and variation in line width) of the depicted image in the layer. Other parameters are image parameters related to the quality of the depicted image of the exposure pattern.

[0077] In some aspects, a detector array (not shown) can be connected to the beam analyzer 430 and allow accurate stack profile detection to be performed, as described below. For example, the detector 428 can be a detector array. For the detector array, there are several options: a bundle of multimode optical fibers, discrete pin detectors per channel, or a CCD or CMOS (linear) array. For stability reasons, the use of a bundle of multimode optical fibers enables any dissipative elements to be positioned farther away. Discrete pin detectors provide a larger dynamic range, but each discrete pin detector requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays provide many elements that can be read out at high speed, and if phase-stepped detection is used, CCD linear arrays are particularly interesting.

[0078] In some aspects, the second beam analyzer 430' can be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, such as Figure 4B As shown. The optical state can be a measure of the beam wavelength, polarization, or beam profile. The second beam analyzer 430' can be the same as the beam analyzer 430. Alternatively, the second beam analyzer 430' can be configured to perform one or more functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 420 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418 can be accurately known with reference to the stage 422, and therefore the position of the substrate 420 can be accurately known. The second beam analyzer 430' can also be configured to determine the position of the inspection system 400 or any other reference element, so that the center of symmetry of the alignment mark or target 418 can be known with reference to the inspection system 400 or any other reference element. The second beam analyzer 430' can also be configured to determine the overlap data between the two patterns and a model of the product stack profile of the substrate 420. The second beam analyzer 430' can also be configured to measure the overlap, critical dimension, and focal length of the target 418 in a single measurement.

[0079] In some aspects, the second beam analyzer 430' can be directly integrated into the inspection system 400, or according to other aspects, the second beam analyzer 430' can be connected to the inspection system 400 via several types of optical fibers: polarization-maintaining single-mode optical fibers, multimode optical fibers, or imaging optical fibers. Alternatively, the second beam analyzer 430' and the beam analyzer 430 can be combined to form a single analyzer (not shown) configured to receive and determine the optical state of both the diffracted radiation sub-beams 429 and 439.

[0080] In some aspects, the processor 432 receives information from the detector 428 and the beam analyzer 430. For example, the processor 432 can be an overlap calculation processor. The information may include a model of the product stack profile constructed by the beam analyzer 430. Alternatively, the processor 432 may use the received information about the product marking to construct a model of the product marking profile. In either case, the processor 432 may use or combine the model of the product marking profile to construct a model of the stacked product and the overlapped marking profile. The stack model is then used to determine the overlap offset and minimize the effect of the spectrum on the overlap offset measurement. The processor 432 may create a basic correction algorithm based on the information received from the detector 428 and the beam analyzer 430, including but not limited to the optical state of the illumination beam, the alignment signal, the associated position estimate, and the optical state in the pupil, image, and additional planes. The pupil plane is a plane in which the radial position of the radiation defines the angle of incidence and the angular position of the radiation defines the azimuth angle of the radiation. The processor 432 may characterize the inspection system 400 using the basic correction algorithm with reference to the wafer mark and / or alignment mark 418.

[0081] In some aspects, the processor 432 may also be configured to determine the offset error of the printed pattern position relative to the sensor estimate of each mark based on information received from the detector 428 and the beam analyzer 430. The information includes, but is not limited to, the product stack profile, the measurement of the overlap, the critical dimension, and the focus or focal length for each alignment mark or target 418 on the substrate 420. The processor 432 may utilize a clustering algorithm to group the marks into sets with similar constant offset errors and create an alignment error offset correction table based on this information. The clustering algorithm may be based on the overlap measurement results, the position estimation results, and the additional optical stack process information associated with each offset error set. Overlap is calculated for a plurality of different marks, such as overlap targets with positive and negative deviations offset near the planned overlap. The target measuring the minimum overlap is considered as a reference (because the target measuring the minimum overlap is measured with the best accuracy). Based on this measured smaller overlap, and the known planned overlap of its corresponding target, the overlap error can be inferred. Table 1 illustrates how this is performed. The measured minimum overlap in the example shown is -1 nm. However, this was associated with a target of having a planned overlay of -30 nm. The process may have introduced an overlay error of 29 nm.

[0082]

[0083] The minimum value can be taken as a reference point, and relative to this reference point, the offset between the measured overlap and the expected overlap due to the planned overlap can be calculated. This offset determines the overlap error of each mark or a set of marks with similar offsets. Therefore, in the example of Table 1, the minimum measured overlap is -1 nm, with a planned overlap of 30 nm at the target position. The difference between the expected overlap and the measured overlap 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 that produce the minimum overlap error and the corresponding calibration factors of the illumination settings can be determined and selected. After this, the processor 432 can group the marks into sets with similar overlap errors. The criteria for grouping the marks can be adjusted based on different process controls (e.g., different error tolerances for different processes).

[0084] In some aspects, the processor 432 can confirm that all or most members of the group have similar offset errors based on its additional optical stack measurements and apply a single offset correction to each mark according to the clustering algorithm. The processor 432 can determine the correction for each mark and feed the correction back to the lithographic apparatus 100 or 100' to correct the error in overlay, for example, by feeding the correction back into the inspection system 400 to correct the error in overlay.

[0085] Exemplary High Dose Inspection System

[0086] In some aspects, the term "yield" can be used to characterize the rate of photolithography manufacturing. For example, yield can refer to the rate at which photolithography manufacturing is completed on a wafer, the rate at which a specific manufacturing step is completed on a wafer and moved to the next step, etc. Yield can be a performance indicator of a lithography device. It is expected that the lithography system outputs as many products as possible in the shortest possible time. Photolithography manufacturing can include several complex processes. Each part of the process may involve technical choices that balance quality and disadvantages (e.g., sub-nanometer accuracy, high yield and slower manufacturing, cost, etc.). For example, in order to improve pattern transfer accuracy, lithography can include checking printed marks on a substrate. This inspection can be used to determine the consistency of the printed pattern on the substrate, or to align the substrate so as to correctly receive a new pattern. However, the increased time of the inspection process can greatly affect the yield.

[0087] In some aspects, sub-nanometer manufacturing accuracy can be achieved by using the inspection system 400 to perform alignment of the substrate or check critical dimensions and overlap. The accuracy of such inspection tools may be inherently limited (e.g., equipment noise, shot noise, Rayleigh criterion, etc.). In particular, improving the signal-to-noise ratio (SNR) of any given measurement is of great value. The SNR can be improved by increasing the exposure dose to the target. In one example, the dose can be increased by allowing the target to be irradiated for a longer period of time. However, the additional time may reduce the yield. In another example, the dose can be increased by increasing the radiation intensity (e.g., more photons per unit time, higher flux, higher irradiance, etc.). However, the limitation is that increasing the intensity only at the location of the target may damage or ablate the target. If the intensity is high enough to deform the target so that the inspection accuracy is significantly affected (e.g., resulting in a higher pattern transfer inconsistency rate), the target can be considered to be damaged by high-intensity radiation.

[0088] In some aspects, small spots of high intensity radiation can be dispersed across the target surface. In particular, the radiation power per unit surface area can be reduced by dispersing the radiation to compensate for the overall higher radiation dose. However, the optical operating principles for small spots may make it insufficient to inspect using dispersed radiation. Aspects of the inspection apparatus described herein can implement high power radiation to increase inspection accuracy and speed while mitigating the disadvantages associated with high power radiation.

[0089] Figure 5 Inspection system 500 is shown according to some aspects. In some aspects, inspection system 500 can include radiation source 502, optical structures 504 and 506, and detection system 508. Inspection system 500 can also include lens systems 510 and 512. Although lens systems 510 and 512 are illustrated as a single lens, each of lens systems 510 and / or 512 can include a system of lenses.

[0090] In some aspects, inspection system 500 can be used to perform various inspection operations described with respect to inspection system 400 ( FIG. 4 ) (e.g., wafer alignment, critical dimension inspection, overlay inspection, etc.). However, the difference is that inspection system 500 implements a structure for sourcing and detecting multiple beams of radiation in a single inspection system. Compared to arranging multiple inspection systems 400 side by side to implement the multi-beam functionality, the arrangement of inspection system 500 can occupy less space and can be more cost-effective.

[0091] In some aspects, the radiation source 502 may generate a plurality of radiation beams 514 corresponding to an image of the radiation spot 516 rather than corresponding to a single spot. The radiation beam 514 may include coherent or incoherent radiation. The radiation source 502 may include an optical device 518 for generating the radiation spot 516. To list a few non-limiting examples, the optical device 518 may include a diffractive structure, a porous structure, a spatial light modulator (SLM) (e.g., a digital micromirror device, a liquid crystal device, etc.), a holographic structure, an optical fiber array, etc. In some aspects, the diameter of each radiation spot 516 may be smaller than the size of the target 520. Smaller spots allow for resolution of smaller features of the target. The size of the target 520 may be defined as the width or length of the entire structure. For example, if the target 520 has a grating structure, the size may be the width of the pitch along the grating, the width starting at one end of the grating line and ending at the opposite end of the grating line. In some aspects, the radiation spots 516 may be non-overlapping to prevent crosstalk between signals corresponding to each of the radiation spots 516.

[0092] In some aspects, optical structure 504 (e.g., "first optical structure") can include a beam splitter, a reflective structure, a refractive structure, a waveguide, etc., or a combination of beam splitters, reflective structures, refractive structures, waveguides, etc. Optical structure 504 can cause radiation beam 514 to travel along a route toward the surface of target 520 so as to project radiation spot 516 onto target 520 and produce scattered radiation from target 520. Optical structure 506 (e.g., "second optical structure") can include a lens objective, a reflective structure, a refractive structure, etc., or a combination of lens objective, a reflective structure, a refractive structure, etc. Optical structure 506 can focus an image of radiation spot 516 and / or collect scattered radiation from target 520.

[0093] In some aspects, enumerated adjectives (e.g., "first," "second," "third," etc.) can be used to distinguish similar elements without establishing an order, hierarchy, or numerical correspondence (unless otherwise specified). For example, the terms "first optical structure" and "second optical structure" can distinguish two optical structures without specifying a particular order or hierarchy. Moreover, the elements in the figures are not limited to any particular enumerated adjectives. For example, optical structure 504 can be referred to as a first optical structure or a second optical structure, in which case the other optical structure can be given a different enumerated adjective.

[0094] In some aspects, radiation source 502 can output radiation beam 514 having a total power density sufficient to damage target 520. However, radiation source 502 can spread the total power density among the beams such that the average power density of each of the beams is insufficient to damage target 520. In cases where multiple radiation spots 516 produce scattered radiation from target 520, analysis of this scattered radiation can include additional considerations compared to the simpler analysis in single spot metrology.

[0095] In some aspects, the detection system 508 can receive scattered radiation collected by the optical structure 506. The detection system 508 can generate a measurement signal corresponding to each radiation spot 516 in the radiation spots 516. The inspection system 500 can include an analyzer to analyze each measurement signal corresponding to each radiation spot 516 in the radiation spots 516 in the measurement signal to determine a value of a property of the target 520. Some non-limiting examples of the property of the target 520 can include alignment position, critical dimension, overlay offset, etc. For example, the analyzer can be the processor 432 (FIG. 4). In the context of a diffraction target 520 (e.g., a grating), when analyzing specular reflection scattering, each radiation spot 516 in the radiation spots 516 can correspond to a zero order. Each of the zero orders can be received at a corresponding detection element in the detection elements 508a to 508n (n is an arbitrary number) of the detection system 508. The detection elements 508a to 508n can be pixels of a detector array (e.g., a 1D or 2D array), an image capture device (e.g., a camera), etc. If a camera is used, the analyzer 432 (FIG. 4) can be programmed to assign a corresponding pixel to each of the zeroth orders. The function can be extended to higher diffraction orders, such as the + (positive) and - (negative) orders used in dark field metrology. Two or more detector elements can correspond to one of the radiation spots 516. The radiation spots 516 can be non-overlapping to avoid crosstalk between the measurement signals.

[0096] In some aspects, images of the spots corresponding to the diffraction orders can be formed at image plane 522 (or field plane). Figure 5A non-limiting example of a zero diffraction order ray trace is illustrated, but it should be understood that higher diffraction orders may propagate according to their corresponding diffraction interactions with the target 520. The inspection system 500 may include a lens array 524. Due to the collimating effect of the lens array 524, a pupil plane 526 may be disposed downstream of the lens array 524. The pupil plane 526 may be a Fourier conjugate plane of the image plane 522. The detection system 508 may be disposed at the pupil plane 526. That is, the lens array 524 may be disposed between the image plane 522 and the detection system 508. Each lens element of the lens array 524 may correspond to each of the detection elements 508a to 508n. The arrangement of the lens array 524 and the detection system 508 may allow for analysis of the pupil contribution of each of the radiation spots 516.

[0097] Figure 6 An inspection system 600 is shown according to some aspects. In some aspects, the inspection system 600 may include a system similar to that of reference Figure 5 Therefore, unless otherwise stated, the structure and function of the inspection system 500 are described. Figure 5 The description of the elements can also be applied to Figure 6 Corresponding elements (e.g., reference numerals sharing the two rightmost digits) are not strictly reintroduced. Figure 6 The elements in FIG. 6 may include a radiation source 606, optical structures 604 and 606, a detection system 608 having detection elements 608a to 608n, lens systems 610 and 612, a radiation beam 614, a radiation spot 616, an optical device 618, a target 620, and an image plane 622—which may be obtained from Figure 5 The structure and function of the above items can be inferred from the description of the corresponding elements in .

[0098] In some aspects, Figure 5 In contrast to the arrangement or arrangement in , the detection system 608 may be arranged at the image plane 622. An image of the spot corresponding to the diffraction order may be focused at the detection system 608. The optical arrangement may allow analysis of the re-projected scatter of each of the radiation spots 616.

[0099] In some aspects, radiation spot 516 ( Figure 5 ) or radiation spot 616 ( Figure 6 ) can cross target 520 ( Figure 5 ) or target 620 ( Figure 6 ) to determine how the measured signal changes due to being in multiple different positions relative to the target.

[0100] In some aspects, the optical structure 604 can be a polarizing beam splitter. In this case, the scattered radiation received at the detection elements 608a to 608n can have a polarization that is orthogonal to the polarization of the incident radiation illuminating the target 620.

[0101] Figure 7 716 according to some aspects. In some aspects, the radiation spots 716 may include radiation spots 716a to 716n. Here, n may be 3, but it should be understood that n may be 2 or greater. The radiation spots 716 may be provided by the inspection system 500 or 600 ( Figure 5 or Figure 6 ). Unless otherwise stated, Figure 5 and Figure 6 The description of the elements can also be applied to Figure 7 corresponding elements (eg, reference numerals that share the two rightmost digits). Figure 5 or Figure 6 716. Although not shown, it is understood that the inspection system 500 and / or 600 may include an actuator for moving the radiation spot 716 relative to the target 720. Moving the target 720 relative to the radiation spot 716 may also be considered as moving the radiation spot 716 relative to the target 720, based on a stationary reference frame of the target 720. The scan may be performed using a continuous motion or discrete steps.

[0102] In some aspects, target 720 may include area 728. Radiation spot 716 may be scanned over the entire area 728 such that each of radiation spots 716a to 716n may detect area 728. In other words, the same area of ​​target 720 may be scanned three times. This is more convenient than using only a single radiation spot at the same scanning speed. Figure 7 The method shown can effectively increase the radiation dose by a factor of n (e.g., 3 in this non-limiting example). In this way, the inspection system 500 and 600 can be improved compared to a single spot inspection system ( Figure 5 and Figure 6 ). The analyzer may then analyze each measurement signal corresponding to each of the radiation spots 716 to determine a value of the property of the target 720. The analysis may include summing the measurement signals (e.g., averaging, integrating, etc.). In one non-limiting example, the SNR may increase in proportion to the square root of the dose. With a higher SNR, the accuracy of determining the value of the property of the target 720 may be increased (due to the dispersion of the radiation power without damaging the target 720).

[0103] Figure 8816 according to some aspects. In some aspects, the radiation spots 816 may include radiation spots 816a to 816n. Here, n may be 3, but it should be understood that n may be 2 or greater. The radiation spots 816 may be provided by the inspection system 500 or 600 ( Figure 5 or Figure 6 ). Unless otherwise stated, Figure 5 and Figure 6 The description of the elements can also be applied to Figure 8 corresponding elements (eg, reference numerals that share the two rightmost digits). Figure 5 or Figure 6 816. Although not shown, it is understood that the inspection system 500 and / or 600 may include an actuator for moving the radiation spot 816 relative to the target 820. Moving the target 820 relative to the radiation spot 816 may also be considered as moving the radiation spot 816 relative to the target 820, based on a stationary reference frame of the target 820. The scan may be performed using a continuous motion or discrete steps.

[0104] In some aspects, the target 820 may include regions 828a to 828n. Here, n may be the same as the number of radiation spots used. The radiation spots 816 may be scanned across the regions 828a to 828n so that each of the radiation spots 828a to 828n may detect a corresponding region in the regions 828a to 828n. In other words, different targets 820 may be scanned once (although the regions are not the same, there may be partial overlap of the regions). Compared to Figure 7 The method shown in the figure can perform the scan at a slower speed. For example, Figure 8 The scan in can be performed so that the amount of time required to scan across all regions 828a to 828n with a single radiation spot 816 incident on the target 820 continues. In this way, Figure 8 The method shown can effectively increase the radiation dose by a factor of n (e.g., 3 in this non-limiting example). Accordingly, the inspection systems 500 and 600 can be improved compared to a single spot inspection system ( Figure 5 and Figure 6 ) of the signal-to-noise ratio.

[0105] and Figure 7Similarly, the analyzer can then analyze each measurement signal corresponding to each of the radiation spots 816 to determine the value of the property of the target 820. The analysis can include summing the measurement signals (e.g., averaging, integrating, etc.). In one non-limiting example, the SNR can increase in proportion to the square root of the dose. With a higher SNR, the accuracy of determining the value of the property of the target 820 can be increased (due to the dispersion of the radiation power without damaging the target 720).

[0106] Although Figure 7 and Figure 8 An exemplary one-dimensional linear arrangement of radiation spots is shown, but the present disclosure is not limited thereto. It is also contemplated to have an arrangement of radiation spots in two dimensions (eg, a square pattern, a honeycomb pattern, etc.).

[0107] The inspection systems and methods disclosed herein may be enhanced by additional features. Fig. 9 An inspection system 900 is shown according to some aspects. In some aspects, the inspection system 900 may include a system similar to that of reference Figures 5 to 8 Therefore, unless otherwise stated, Figures 5 to 8 The description of the elements can also be applied to Fig. 9 Corresponding elements (eg, reference numerals sharing the two rightmost digits) are not strictly reintroduced. Fig. 9 The elements in FIG. 9 may include a radiation source 902, optical structures 904 and 906, a detection system 908 having detection elements 908a to 908n, lens systems 910 and 912, a radiation beam 914, a radiation spot 916, an optical device 918, a target 920, an image plane 922, a lens array 924, and a pupil plane 926—which may be obtained from Figures 5 to 8 The structure and function of the above items can be inferred from the description of the corresponding elements in .

[0108] In some aspects, each of the detection elements 908a-908n can include a quadrant unit photodetector 908', respectively (non-limiting example). Other examples can include other types of photodetectors, such as balanced photodiodes. Such photodetectors can measure very small changes in the position of the light beam and can be used for centering, zeroing, detecting, and measuring displacement of position, etc.

[0109] Fig.10 An inspection system 1000 is shown according to some aspects. In some aspects, the inspection system 1000 may include a system similar to that of reference Figures 5 to 9 Therefore, unless otherwise stated, Figures 5 to 9 The description of the elements can also be applied to Fig.10Corresponding elements (eg, reference numerals sharing the two rightmost digits) are not strictly reintroduced. Fig.10 The elements in the embodiment may include a radiation source 1002, optical structures 1004 and 1006, a detection system 1008 having detection elements 1008a to 1008n, lens systems 1010 and 1012, a radiation beam 1014, a radiation spot 1016, an optical device 1018, a target 1020, an image plane 1022, a lens array 1024, and a pupil plane 1026—which may be obtained from Figures 5 to 9 The structure and function of the above items can be inferred from the description of the corresponding elements in .

[0110] In some aspects, each of the detection elements 1008a-1008n can include a birefringence-based detector 1008', respectively (non-limiting example). The birefringence-based detector 1008' can include a Wollaston prism 1030 and detection elements 1032 and 1034 (e.g., one element for each of polarizations H and V).

[0111] Fig.11 An inspection system 1100 is shown according to some aspects. In some aspects, the inspection system 1100 may include a system similar to that of reference Figures 5 to 10 Therefore, unless otherwise stated, Figures 5 to 10 The description of the elements can also be applied to Fig.11 Corresponding elements (eg, reference numerals sharing the two rightmost digits) are not strictly reintroduced. Fig.11 The elements in may include radiation source 1102, optical structures 1104 and 1106, lens systems 1110 and 1112, radiation beam 1114, radiation spot 1116, optical device 1118, target 1120, image plane 1122—which may be obtained from Figures 5 to 10 The structure and function of the above items can be inferred from the description of the corresponding elements in .

[0112] In some aspects, the detection system of the inspection system 1100 is not shown (e.g., off-page). The inspection system 1100 can include an optical fiber array 1136 to direct scattered radiation from the target 1120 to the detection system. The input end of the optical fiber array 1136 can be disposed at the image plane 1122 (or at the pupil plane; not shown).

[0113] According to some aspects, other fiber-based concepts are envisioned, e.g. Fig.12 An inspection system 1200 is shown. The inspection system 1200 may include a system similar to that of reference Figures 5 to 11Therefore, unless otherwise stated, Figures 5 to 11 The description of the elements can also be applied to Fig.12 Corresponding elements (eg, reference numerals sharing the two rightmost digits) are not strictly reintroduced. Fig.12 The elements in the image may include a radiation source 1202, optical structures 1204 and 1206, a detection system 1208, lens systems 1210 and 1212, a radiation beam 1214, an optical device 1218 (e.g., an optical fiber array), a target 1220, an image plane 1222, and an optical fiber array 1236—which may be obtained from Figures 5 to 10 The structure and function of each of the above items can be inferred from the description of the corresponding elements in FIG. The optical fibers in the optical fiber array may include multimode optical fibers. The input end of the optical fiber array 1236 may be arranged at the image plane 1222 (or at the pupil plane; not shown).

[0114] In some aspects, inspection system 1200 may also include blocking device 1238 and splitter 1240. Blocking device 1238 may be a zero-order aperture for dark field measurement. Splitter 1240 may be used to use multiple bands (e.g., radiation spots with different wavelengths) in the measurement. At least one of the radiation spots generated by optical device 1218 may have multiple bands. Therefore, the scattered radiation from target 1220 may also have multiple bands. Splitter 1240 may be used to separate the bands of scattered radiation.

[0115] In some aspects, each optical fiber in optical device 1218 can be actuated using an actuator. Actuation can allow each of the radiation spots to be placed at a desired focal depth and in different arrangements (e.g., a linear (or column) array or a two-dimensional array). To account for this movement, each optical fiber in optical device 1236 can be actuated in a similar manner to accommodate the shift in focal length.

[0116] In some aspects, the reference may be analyzed in different ways. Figures 5 to 12 Here are some examples of radiation spots described.

[0117] In some aspects, reference may be made to Figures 5 to 12 The radiation spots described are "incoherent" with other radiation spots. For example, a different wavelength is used for each of the radiation spots. This is useful for mitigating crosstalk interference between signals corresponding to different radiation spots.

[0118] In some aspects, the reference can be divided by assigning different wavelengths to the radiation spots. Figures 5 to 12 The inspection system described is used as a hyperspectral sensor. Fig.12The splitter 1240 is described, but it should be understood that the splitter 1240 may also be described in reference Figures 5 to 11 These features are implemented in the described systems and methods.

[0119] In some aspects, reference Figures 5 to 12 The inspection system described can be used as a 3D confocal microscope capable of acquiring 3D image data in a single scan. For example, the radiation source may include an optical device configured to split the source radiation to form a radiation beam so that the radiation spot has different focal planes, and the detection system may include detection elements arranged to correspond to the different focal planes.

[0120] In some aspects, reference Figures 5 to 12 The described inspection system can be used for tomographic reconstruction of an object. For example, each radiation spot can have a different diameter.

[0121] In some aspects, reference Figures 5 to 12 The inspection system described can be implemented with spots having different polarization states. The polarization state can be tailored for the expected response from a given design of grating target.

[0122] The embodiments may be further described using the following aspects:

[0123] 1. An inspection system, comprising:

[0124] a radiation source configured to generate a radiation beam, wherein an image formed by the beam includes radiation spots corresponding to the beam, wherein a diameter of the radiation spots is smaller than a size of the target and the radiation spots are non-overlapping;

[0125] a first optical structure configured to cause the beam to follow a path toward the target so as to project the radiation spot onto the target and produce scattered radiation from the target;

[0126] a second optical structure configured to collect scattered radiation from the target; and

[0127] A detection system is configured to receive scattered radiation collected by the second optical structure and to generate measurement signals, wherein each of the measurement signals corresponds to each of the radiation spots.

[0128] 2. An inspection system according to aspect 1, wherein the radiation source outputs a beam having a total power density sufficient to damage the target, and disperses the total power density among the beams so that the average power density of each of the beams is insufficient to damage the target.

[0129] 3. The inspection system according to aspect 1, further comprising an analyzer configured to analyze each of the measurement signals corresponding to each of the radiation spots to determine a value of the property of the target.

[0130] 4. The inspection system according to aspect 3, wherein:

[0131] The scattered radiation comprises diffraction orders; and

[0132] The analyzer is configured to determine the value of the property based on analyzing interference of the diffraction orders.

[0133] 5. The inspection system according to aspect 1, wherein:

[0134] The scattered radiation includes diffraction orders;

[0135] The inspection system further includes a blocking element configured to block a zeroth diffraction order of the scattered radiation.

[0136] 6. The inspection system according to aspect 1, further comprising: an actuator for moving the radiation spot relative to the target.

[0137] 7. The inspection system according to aspect 6, wherein:

[0138] The target includes an area; and

[0139] The actuator is further configured to move the radiation spots such that each of the radiation spots irradiates the area.

[0140] 8. The inspection system according to aspect 6, wherein:

[0141] The target includes a plurality of areas; and

[0142] The actuator is further configured to move the radiation spots such that each of the radiation spots irradiates a corresponding one of the plurality of regions.

[0143] 9. The inspection system according to aspect 1, wherein the detection system is arranged at an image plane so that the image of the radiation spot is focused at the detection system.

[0144] 10. The inspection system of clause 1, wherein the detection system is arranged at a pupil plane, wherein the pupil plane is a conjugate plane of an image plane, and the image of the radiation spot is focused at the image plane.

[0145] 11. The inspection system according to aspect 1, wherein:

[0146] The detection system includes a plurality of detection elements, and

[0147] Each detection element of the plurality of detection elements corresponds to each radiation spot of the radiation spots.

[0148] 12. The inspection system according to aspect 1, wherein:

[0149] The detection system includes a camera;

[0150] The inspection system further comprises an analyzer configured to analyze each of the measurement signals corresponding to each of the radiation spots to determine a value of a property of the target; and

[0151] Different pixel areas of the camera correspond to different ones of the radiation spots.

[0152] 13. The inspection system of aspect 1, wherein the radiation source comprises an optical device configured to split source radiation to form the beam.

[0153] 14. The inspection system of aspect 13, wherein the optical device comprises at least one of the following:

[0154] Diffraction structure;

[0155] Porous structure;

[0156] Spatial light modulator;

[0157] holographic structures; or

[0158] Fiber Optic Array.

[0159] 15. The inspection system of aspect 1, wherein:

[0160] The radiation source comprises an optical arrangement configured to split the source radiation to form the beam so that the radiation spots have different focal planes; and

[0161] The detection system includes detection elements corresponding to the different focal planes.

[0162] 16. The inspection system of aspect 1, wherein:

[0163] at least one of the radiation spots has a wavelength different from the wavelength of another of the radiation spots; and

[0164] The inspection system also includes a splitter configured to separate wavelengths of the scattered radiation.

[0165] 17. The inspection system of aspect 1, wherein:

[0166] At least one of the radiation spots has a plurality of wavelength bands; and

[0167] The inspection system also includes a splitter configured to separate wavelength bands of the scattered radiation.

[0168] 18. The inspection system according to aspect 1, wherein at least some of the radiation spots have different diameters.

[0169] 19. The inspection system of aspect 1, wherein at least a portion of the radiation spots have different polarization states.

[0170] 20. The inspection system according to aspect 1, wherein at least a portion of the radiation spots are distributed on the target in a linear arrangement or a two-dimensional arrangement.

[0171] 21. The inspection system of aspect 1, at least one of the radiation spots having a beam profile different from a beam profile of another of the radiation spots.

[0172] 22. The inspection system of aspect 1, wherein the first optical structure is a polarization beam splitter.

[0173] 23. A lithographic apparatus comprising:

[0174] an illumination system configured to illuminate a pattern forming device;

[0175] a projection system configured to project an image of the pattern onto a substrate; and

[0176] An inspection system, the inspection system comprising:

[0177] a radiation source configured to generate a radiation beam, wherein an image formed by the beam includes radiation spots corresponding to the beam, wherein a diameter of the radiation spots is smaller than a size of the target and the radiation spots are non-overlapping;

[0178] a first optical structure configured to cause the beam to follow a path toward the target so as to project the radiation spot onto the target and produce scattered radiation from the target;

[0179] a second optical structure configured to collect scattered radiation from the target; and

[0180] A detection system is configured to receive scattered radiation collected by the second optical structure and to generate measurement signals, wherein each of the measurement signals corresponds to each of the radiation spots.

[0181] 24. A lithographic apparatus according to aspect 23, wherein the radiation source outputs beams having a total power density sufficient to damage the target, and disperses the total power density among the beams so that the average power density of each of the beams is insufficient to damage the target.

[0182] The terms "radiation," "beam," "light," "irradiation," and the like may be used herein to refer to one or more types of electromagnetic radiation, such as ultraviolet (UV) radiation (e.g., having 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., having a wavelength in the range of 5 nm to 100 nm, such as, for example, 13.5 nm), or hard X-rays operating at less than 5 nm, and particle beams (such as ion beams or electron beams). Generally, radiation having a wavelength between about 400 nm and about 700 nm is considered visible radiation; radiation having a wavelength between about 780 nm and 3000 nm (or greater) is considered IR radiation. UV refers to radiation having a wavelength of about 100 nm to 400 nm. In photolithography, 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 about 100 nm to 200 nm. Deep DU (DUV) generally refers to radiation having a wavelength in the range of 126 nm to 428 nm, and in some aspects, an excimer laser can produce DUV radiation used 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 specific wavelength band, at least a portion of which is in the range of 5 nm to 20 nm.

[0183] Although some aspects of the present disclosure are described in the context of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as manufacturing integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film heads, etc. Those skilled in the art will understand that in the context of such alternative applications, any use of the term "wafer" or "die" herein may be considered to be a specific example of the more general term "substrate" or "target portion", respectively. The substrate may be processed before or after exposure, for example in a track or coating and developing control system unit (a tool that applies a resist layer to a substrate and develops the exposed resist in a typical manner) and / or a measurement unit. Where applicable, the aspects disclosed herein may be applied to such and other substrate processing tools. In addition, the substrate may be processed more than once, for example to produce a multi-layer IC, so that the term "substrate" used herein may also refer to a substrate that already contains multiple processing layers.

[0184] In addition, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, the topography in the patterning device defines the pattern formed on the substrate. The topography of the patterning device can be pressed into a resist layer supplied to the substrate, and then the resist is cured 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 in the resist.

[0185] It will 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 application document is to be interpreted by those skilled in the relevant art(s) based on the teachings herein.

[0186] The present disclosure has been described above with the aid of functional building blocks, which illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined in this article. As long as specific functions and their relationships are properly performed, alternative boundaries can be defined. The above description of specific aspects will fully reveal the general nature of the present disclosure, so that others can easily modify and / or adjust the various applications of these specific aspects by applying knowledge in the art without excessive experimentation and without departing from the general concept of the present disclosure. Therefore, based on the teachings and guidance presented herein, such modifications and adjustments are intended to fall within the meaning and scope of equivalents of the disclosed aspects.

[0187] It should be understood that the "Detailed Description" section, rather than the "Summary" section and the "Abstract" section, is intended to be used to interpret the claims. The "Summary" section and the "Abstract" section may set forth one or more aspects of the disclosure contemplated by the inventor(s), but not necessarily all aspects, and are therefore not intended to limit the disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

1. An inspection system, comprising: a radiation source configured to generate a radiation beam, wherein an image formed by the beam includes radiation spots corresponding to the beam, wherein a diameter of the radiation spots is smaller than a size of the target and the radiation spots are non-overlapping; a first optical structure configured to cause the beam to follow a path toward the target so as to project the radiation spot onto the target and produce scattered radiation from the target; a second optical structure configured to collect scattered radiation from the target; and A detection system is configured to receive scattered radiation collected by the second optical structure and to generate measurement signals, wherein each of the measurement signals corresponds to each of the radiation spots.

2. The inspection system according to claim 1, wherein: The radiation source outputs beams having a total power density sufficient to damage the target and disperses the total power density among the beams such that an average power density of each of the beams is insufficient to damage the target. 3 . The inspection system of claim 1 , further comprising an analyzer configured to analyze each of the measurement signals corresponding to each of the radiation spots to determine a value of the property of the target.

4. The inspection system according to claim 3, wherein: The scattered radiation comprises diffraction orders; and The analyzer is configured to determine the value of the property based on analyzing interference of the diffraction orders.

5. The inspection system according to claim 1, wherein: The scattered radiation includes diffraction orders; The inspection system further includes a blocking element configured to block a zeroth diffraction order of the scattered radiation.

6. The inspection system according to claim 1, further comprising: An actuator for moving the radiation spot relative to the target.

7. The inspection system according to claim 6, wherein: The target includes an area; and The actuator is further configured to move the radiation spots such that each of the radiation spots irradiates the area.

8. The inspection system according to claim 6, wherein: The target includes a plurality of areas; and The actuator is further configured to move the radiation spots such that each of the radiation spots irradiates a corresponding one of the plurality of regions.

9. The inspection system according to claim 1, wherein: The detection system is arranged at an image plane such that an image of the radiation spot is focused at the detection system.

10. The inspection system according to claim 1, wherein: The detection system is arranged at a pupil plane, wherein the pupil plane is a conjugate plane of an image plane, at which the image of the radiation spot is focused.

11. The inspection system of claim 1, wherein: The detection system includes a plurality of detection elements, and Each detection element of the plurality of detection elements corresponds to each radiation spot of the radiation spots.

12. The inspection system of claim 1, wherein: The detection system includes a camera; The inspection system further comprises an analyzer configured to analyze each of the measurement signals corresponding to each of the radiation spots to determine a value of a property of the target; and Different pixel areas of the camera correspond to different ones of the radiation spots.

13. The inspection system according to claim 1, wherein: The radiation source comprises an optical arrangement configured to split the source radiation to form the beam.

14. The inspection system according to claim 13, wherein: The optical device comprises at least one of the following: Diffraction structure; Porous structure; Spatial light modulator; holographic structures; or Fiber Optic Array.

15. The inspection system of claim 1, wherein: The radiation source comprises an optical arrangement configured to split the source radiation to form the beam so that the radiation spots have different focal planes; and The detection system includes detection elements corresponding to the different focal planes.

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