Lithographic apparatus, measurement system and measurement of intensity imbalance for error correction

Abstract

The measurement system includes a beam splitter and first and second sensors. The beam splitter splits scattered radiation scattered by the target into first and second portions of radiation. The first sensor receives the first portion. The second sensor receives the second portion after the second portion propagates along a path that includes a wedge system including a first wedge configured to diverge the second portion.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 070,553, filed on August 26, 2020, which is hereby incorporated by reference in its entirety.

[0002]

[0002] The present disclosure relates to a measurement system, for example, for improving the accurate positioning of wafers within a lithographic apparatus and system.

Background Art

[0003]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually 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, alternatively referred to as a mask or reticle, can be used to generate the circuit patterns formed on the individual layers of the IC. This pattern can be transferred onto a target portion (e.g., part of a die, one die, or a plurality of dies) of a substrate (e.g., a silicon wafer). The transfer of the pattern is typically done via imaging onto a layer of radiation - sensitive material (resist) provided on the substrate. Generally, a single substrate includes a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so - called steppers and so - called scanners. In a stepper, each target portion is irradiated by exposing the entire pattern onto the target portion at once, and in a scanner, each target portion is irradiated by scanning the pattern with a radiation beam in a given direction (the "scanning" direction) while simultaneously scanning the target portion in a direction parallel or anti - parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004]

[0004] During the lithography operation, different processing steps may require different layers to be sequentially formed on the substrate. Therefore, it may be necessary to position the substrate with high precision relative to the previously formed pattern thereon. Generally, alignment marks are arranged on the substrate to be aligned and positioned with respect to a second object. The lithography apparatus may use an alignment apparatus that detects the position of the alignment marks and uses the alignment marks to align the substrate to ensure accurate exposure from the mask. The misalignment between alignment marks in two different layers is measured as an overlay error.

[0005]

[0005] To monitor the lithography process, parameters of the patterned substrate are measured. The parameters can include, for example, the overlay error between successive layers formed in or on the patterned substrate and the critical line width of the developed photosensitive resist. This measurement can be performed on product substrates and / or dedicated measurement targets. There are various techniques for measuring microscopic structures formed in the lithography process, including the use of scanning electron microscopes and various dedicated tools. A fast and non-invasive form of dedicated inspection tool is a scatterometer in which a radiation beam is guided onto a target on the surface of the substrate and the characteristics of the scattered or reflected beam are measured. The characteristics of the substrate can be determined by comparing the characteristics of the beam before and after reflection or scattering by the substrate. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate characteristics. A spectroscopic scatterometer guides a broadband radiation beam onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered within a specific narrow angular range. In contrast, an angle-resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0006]

[0006] Such an optical scatterometer can be used to measure parameters such as the critical dimension of a developed photosensitive resist or the overlay error (OV) between two layers formed within or on a patterned substrate. By comparing the characteristics of the illumination beam before and after the beam is reflected or scattered by the substrate, the characteristics of the substrate can be determined.

[0007]

[0007] An alignment measurement system can be used in a lithography tool to properly align a wafer so that it undergoes pattern transfer in a way that reduces OV. The measurement system is typically programmed using specific assumptions regarding the alignment marks being measured. For example, the measurement system can be programmed to predict the diffracted radiation scattered by the grating pattern of the alignment marks. However, non-ideal gratings can diffract radiation in a different way than ideal gratings, causing the measurement system to generate errors in its measurement results.

Summary of the Invention

[0008]

[0008] Therefore, it is desirable to improve the accuracy and reduce errors in measurement tools used in conjunction with lithography apparatuses.

[0009]

[0009] In some embodiments, the measurement system includes a beam splitter and first and second sensors. The beam splitter is configured to split the radiation scattered by the target into first and second portions of the radiation. The first sensor is configured to receive the first portion. The second sensor is configured to receive the second portion after the second portion has propagated along a path that includes a wedge system that includes a first wedge configured to diverge the second portion.

[0010]

[0010] In some embodiments, a lithographic apparatus includes an illumination system, a projection system, and a measurement system. The measurement system includes a beam splitter and first and second sensors. The illumination system illuminates a pattern of a patterning device. The projection system projects an image of the pattern onto a substrate. The beam splitter is configured to split radiation scattered by a target into first and second portions of the radiation. The first sensor is configured to receive the first portion. The second sensor is configured to receive the second portion after the second portion has propagated along a path including a wedge system including a first wedge configured to diverge the second portion.

[0011]

[0011] In some embodiments, a method includes splitting scattered radiation scattered by a target into first and second portions of the radiation. The method further includes receiving the first portion at a first sensor. The method further includes receiving the second portion at a second sensor after the second portion has propagated along a path including a wedge system including a first wedge. The method further includes using the first wedge to diverge the second portion.

[0012]

[0012] Further features of the present disclosure and the structure and operation of various embodiments will be described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Based on the teachings contained herein, further embodiments will be apparent to those skilled in the art.

[0013]

[0013] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate the present disclosure and, together with the description, explain the principles of the present disclosure and further function to enable one skilled in the art to practice and use the embodiments described herein.

Brief Description of the Drawings

[0014]

Figure 1A

[0014] Shows a schematic diagram of a reflective lithography apparatus according to some embodiments.

Figure 1B

[0015] Shows a schematic diagram of a transmissive lithography apparatus according to some embodiments.

Figure 2

[0016] Shows a more detailed schematic diagram of a reflective lithography apparatus according to some embodiments.

Figure 3

[0017] Shows a schematic diagram of a lithographic cell according to some embodiments.

Figure 4A

[0018] Shows a schematic diagram of an inspection apparatus according to some embodiments.

Figure 4B

[0018] Shows a schematic diagram of an inspection apparatus according to some embodiments.

Figure 5

[0019] Shows the pupil in a measurement system according to some embodiments.

Figure 6

[0020] Shows a prism system for splitting the pupil according to some embodiments.

Figure 7

[0021] Shows a wedge system for splitting the pupil according to some embodiments.

Figure 8

[0022] Shows a wedge that can be used within the wedge system according to some embodiments.

Figure 9

[0023] Shows a sensor according to some embodiments.

Figure 10

[0024] Shows a diverging pupil image according to some embodiments.

Figure 11A

[0025] Shows a portion of a detector system that can be used within the sensor shown in FIG. 9 according to some embodiments.

Figure 11B

[0025] Shows a portion of a detector system that can be used within the sensor shown in FIG. 9 according to some embodiments.

Figure 12

[0026] Shows a flowchart showing a method according to some embodiments.

Best Mode for Carrying Out the Invention

[0015]

[0027] The features of the present disclosure will become more apparent from the detailed description set forth below in conjunction with the drawings. In the drawings, like reference numerals identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Further, generally, the leftmost digit of a reference number identifies the drawing in which that reference number first appears. Unless otherwise specified, the drawings provided throughout the present disclosure should not be construed as being to scale.

[0016]

[0028] This specification discloses one or more embodiments incorporating the features of the present disclosure. The disclosed embodiments are provided by way of example. The scope of the present disclosure is not limited to the disclosed embodiments. The claimed features are defined by the claims appended hereto.

[0017]

[0029] References in this specification to an “embodiment,” “one embodiment,” “an embodiment,” “exemplary embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes that particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood within the knowledge of one of ordinary skill in the art that such feature, structure, or characteristic may be brought about in connection with other embodiments, whether or not explicitly described.

[0018]

[0030] Spatially relative terms such as "directly below," "below," "lower," "directly above," "above," "upper," etc. may be used herein for ease of explanation to describe the relationship of one element or feature to another element or feature as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation shown in the figures. The device may be in a different orientation (rotated 90 degrees or otherwise), and the spatially relative descriptors used herein may be interpreted accordingly as well.

[0019]

[0031] The term "about," as used herein, indicates a value of a given quantity that may vary based on a particular technology. Based on a particular technology, the term "about" may indicate a value of a given quantity that varies within, for example, 10 to 30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0020]

[0032] Embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer device). For example, a machine-readable medium may include read-only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Further, firmware, software, routines, and / or instructions may be described herein as performing particular operations. However, such descriptions are for convenience only, and such operations actually result from execution of the firmware, software, routines, instructions, etc. by a computer device, processor, controller, or other device.

[0021]

[0033] However, before describing such embodiments in more detail, it is beneficial to present an exemplary environment in which embodiments of the present disclosure can be implemented.

[0022]

[0034] Example of a lithography system

[0023]

[0035] FIGS. 1A and 1B respectively show schematic views of a lithography apparatus 100 and a lithography apparatus 100' in which embodiments of the present disclosure can be implemented. In some embodiments, the lithography apparatus 100 and the lithography apparatus 100' each include: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask, reticle or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. The lithography apparatuses 100 and 100' also have a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W. In the lithography apparatus 100, the patterning device MA and the projection system PS are reflective. In the lithography apparatus 100', the patterning device MA and the projection system PS are transmissive.

[0024]

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

[0025]

[0037] The support structure MT holds the patterning device MA in a manner that depends on, for example, the orientation of the patterning device MA relative to a reference coordinate system, 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 can hold the patterning device MA using mechanical, vacuum, electrostatic or other clamping techniques. The support structure MT can be, for example, a frame or table which can be fixed or movable as required. By using sensors, the support structure MT can ensure that the patterning device MA is in the desired position relative to, for example, the projection system PS.

[0026]

[0038] The term "patterning device" MA should be broadly interpreted as referring to any device that can be used to impart a pattern to a cross-section of the radiation beam B so as to generate a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer of a device that is to be generated in the target portion C to form an integrated circuit.

[0027]

[0039] Terms such as "inspection device", "measurement device", etc. can be used in this specification to refer to a device or system that is used, for example, to measure characteristics of a structure (such as overlay error, critical dimension parameters) or that is used within a lithographic apparatus to inspect the alignment of a wafer (such as an alignment device).

[0028]

[0040] The patterning device MA can be transmissive (such as the lithographic apparatus 100' of Figure 1B) or reflective (such as the lithographic apparatus 100 of Figure 1A). 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. In one example of a programmable mirror array, a matrix arrangement of small mirrors is used, and each small mirror can be individually tilted so as to reflect an incident radiation beam in a different direction. The tilted mirrors impart a pattern to the radiation beam B reflected by the matrix of small mirrors.

[0029]

[0041] The term "projection system" PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems suitable for the exposure radiation used or for other factors such as the use of immersion liquid or vacuum on the substrate W, or any combination thereof. A vacuum environment can be used for EUV or electron beam radiation, because other gases can absorb too much of the radiation or electrons. Thus, a vacuum wall and vacuum pump can be used to provide a vacuum environment throughout the beam path.

[0030]

[0042] The lithographic apparatus 100 and / or the lithographic apparatus 100' can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, additional substrate tables WT can be used in parallel, or while one or more tables are performing a preparation step, one or more other substrate tables WT can be used for exposure. Optionally, the additional table may not be a substrate table WT.

[0031]

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

[0032]

[0044] Referring to FIGS. 1A and 1B, an illuminator IL receives a radiation beam from a radiation source SO. For example, if the radiation source SO is an excimer laser, the radiation source SO and the lithographic apparatuses 100, 100' can be separate physical elements. In such a case, the radiation source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B passes from the radiation source SO to the illuminator IL using a beam delivery system BD (FIG. 1B) that includes, for example, suitable guiding mirrors and / or beam expanders. In other cases, for example if the radiation source SO is a mercury lamp, the radiation source SO can be an integrated part of the lithographic apparatuses 100, 100'. The radiation source SO and the illuminator IL can, if desired, be grouped together with the beam delivery system BD and referred to as a radiation system.

[0033]

[0045] The illuminator IL can include an adjuster AD (FIG. 1B) for adjusting the angular intensity distribution of the radiation beam. In general, at least the outer and / or inner radial ranges of the intensity distribution within the pupil plane of the illuminator (commonly referred to as "σ - outer" and "σ - inner" respectively) can be adjusted. Further, the illuminator IL can include various other components (FIG. 1B) such as an integrator IN and a condenser CO. The illuminator IL can be used to adjust the radiation beam B such that it has a desired uniformity and intensity distribution across the cross-section of the radiation beam B.

[0034]

[0046] Referring 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 the projection system PS, and the projection system PS focuses the radiation beam B onto the target portion C of the substrate W. The second positioner PW and the position sensor IF2 (e.g., an interference device, a linear encoder or a capacitance sensor) can be used to accurately move the substrate table WT (e.g., to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., a mask) MA with respect 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.

[0035]

[0047] Referring to Figure 1B, 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. After passing through the mask MA, the radiation beam B passes through the projection system PS, and the projection system PS focuses the beam onto the target portion C of the substrate W. The projection system has a pupil conjugate PPU to the pupil IPU of the illumination system. The radiation portion is emitted from the intensity distribution at the pupil IPU of the illumination system, passes through the mask pattern without being affected by diffraction at the mask pattern, and generates an image of the intensity distribution at the pupil IPU of the illumination system.

[0036]

[0048] The projection system PS projects an image of the mask pattern MP onto a photoresist layer coated on a substrate W, where the image is formed by diffracted beams generated from the mask pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Diffraction of radiation different from the 0th order diffraction in the array generates a deflected diffracted beam with a change in direction in a direction perpendicular to the lines. The non-diffracted beam (i.e., the so-called 0th order diffracted beam) traverses the pattern without any change in the propagation direction. The 0th order diffracted beam traverses the upper lens or upper lens group of the projection system PS upstream of the pupil conjugate PPU of the projection system PS and reaches the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the 0th order diffracted beam is an image of the intensity distribution in the pupil IPU of the illumination system IL of the illumination system. The aperture device PD is disposed, for example, in or substantially in a plane including the pupil conjugate PPU of the projection system PS.

[0037]

[0049] The projection system PS is configured to capture not only the 0th order diffracted beam but also the 1st order or higher order diffracted beams (not shown) using the lens or lens group L. In some embodiments, dipole illumination for imaging a line pattern extending in a direction perpendicular to the lines can be used to utilize the resolution enhancement effect of dipole illumination. For example, the 1st order diffracted beam interferes with the corresponding 0th order diffracted beam at the level of the wafer W to create an image of the line pattern MP with the highest possible resolution and process window (i.e., the usable depth of focus combined with the allowable exposure dose deviation). In some embodiments, astigmatism can be reduced by providing radiation poles (not shown) in the quadrants opposite to the pupil IPU of the illumination system. Further, in some embodiments, astigmatism can be reduced by blocking the 0th order beam in the pupil conjugate PPU of the projection system associated with the radiation poles in the opposite quadrants. This is described in more detail in U.S. Patent No. 7,511,799B2, issued on March 31, 2009, which is hereby incorporated by reference in its entirety.

[0038]

[0050] Using a second positioner PW and a position sensor IF (e.g., an interference device, a linear encoder, or a capacitance sensor), the substrate table WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B). Similarly, using a first positioner PM and another position sensor (not shown in FIG. 1B), the mask MA can be accurately positioned with respect to the path of the radiation beam B (e.g., after a mechanical search of the mask library or during scanning).

[0039]

[0051] Generally, the movement of the mask table MT can be realized using a long stroke module (coarse positioning) and a short stroke module (fine positioning) that form part of the first positioner PM. Similarly, the movement of the substrate table WT can be realized using a long stroke module and a short stroke module that form part of the second positioner PW. In the case of a stepper (in contrast to a scanner), the mask table MT can be connected to or fixed to only the short stroke actuator. The mask MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks occupy a dedicated target portion (as shown), but these marks can also be arranged in the space between the target portions (known as scribe lane alignment marks). Similarly, when two or more dies are provided on the mask MA, the mask alignment marks can be arranged between the dies.

[0040]

[0052] The mask table MT and the patterning device MA can be within the vacuum chamber V, where an in-vacuum robot IVR can be used to move patterning devices such as masks in and out of the vacuum chamber. Alternatively, if the mask table MT and the patterning device MA are outside the vacuum chamber, an out-of-vacuum robot can be used for various transport operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated to smoothly transfer any payload (e.g., a mask) to a fixed kinematic mount of the transfer station.

[0041]

[0053] The lithographic apparatuses 100 and 100’ can be used in at least one of the following modes.

[0042]

[0054] 1. In step mode, while keeping the support structure (e.g., mask table) MT and the substrate table WT essentially stationary, the overall pattern imparted to the radiation beam B is projected onto the target portion C at once (i.e., single static exposure). Then, the substrate table WT is shifted in the X and / or Y direction so that different target portions C can be exposed.

[0043]

[0055] 2. In scan mode, while scanning the support structure (e.g., mask table) MT and the substrate table WT synchronously, the pattern imparted to the radiation beam B is projected onto the target portion C (i.e., single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g., mask table) MT can be determined by the (reduction) magnification and image inversion characteristics of the projection system PS.

[0044]

[0056] 3. In another mode, the support structure (e.g., mask table) MT is kept substantially stationary while holding the programmable patterning device, and the pattern imparted to the radiation beam B is projected onto the target portion C while moving or scanning the substrate table WT. A pulsed radiation source SO can be used, and the programmable patterning device is updated as necessary in between successive radiation pulses after each movement or during scanning of the substrate table WT. This mode of operation can be readily applied to maskless lithography using a programmable patterning device such as a programmable mirror array.

[0045]

[0057] Combinations and / or variants of the described usage modes or entirely different usage modes can also be used.

[0046]

[0058] In a further embodiment, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) radiation source configured to generate a beam of EUV radiation for EUV lithography. Generally, the EUV radiation source is configured within a radiation system, and the corresponding illumination system is configured to condition the EUV radiation beam of the EUV radiation source.

[0047]

[0059] Figure 2 shows lithographic apparatus 100 in more detail, including source collector apparatus SO, illumination system IL, and projection system PS. The source collector apparatus SO is configured and arranged to maintain a vacuum environment within the encapsulation structure 220 of the source collector apparatus SO. EUV radiation emitting plasma 210 can be formed by a discharge generating plasma source. EUV radiation can be generated by a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, that generates a very hot plasma 210 and emits radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is generated, for example, by a discharge that causes at least a partially ionized plasma. For efficient generation of radiation, a partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor, or other suitable gas or vapor may be required. In some embodiments, an excited tin (Sn) plasma is supplied to generate EUV radiation.

[0048]

[0060] Radiation emitted by the hot plasma 210 is sent from the source chamber 211 to the collector chamber 212 via an optional gas barrier or contaminant trap 230 (also sometimes called a contaminant barrier or foil trap) located in or behind the opening of the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further shown herein includes at least a channel structure.

[0049]

[0061] 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 can be reflected from the grating spectral filter 240 and focused on a virtual light source point IF. The virtual light source point IF is generally referred to as an intermediate focus, and the source collector device is configured such that this intermediate focus IF is located at or near the opening 219 of the sealing structure 220. The virtual light source point IF is an image of the radiation-emitting plasma 210. The grating spectral filter 240 is used in particular to suppress infrared (IR) radiation.

[0050]

[0062] Subsequently, the radiation passes through the illumination system IL, which may include a faceted field mirror device 222 and a faceted pupil mirror device 224 configured to provide a desired angular distribution of the radiation beam 221 and a desired uniformity of radiation intensity in the patterning device MA. When the radiation beam 221 is reflected in the patterning device MA held by the support structure MT, a patterned beam 226 is formed, and the patterned beam 226 is imaged onto a substrate W held by a wafer stage or a substrate table WT by a projection system PS via reflection elements 229, 230.

[0051]

[0063] Generally, more elements may be present within the illumination optical unit IL and the projection system PS than shown in FIG. 2. The grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Furthermore, more mirrors may be present than the mirrors shown in the figure, for example, one to six additional reflective elements may be present in the projection system PS than shown in FIG. 2.

[0052]

[0064] As shown in FIG. 2, the condenser optical system CO is shown as a nested collector having diagonally incident reflectors 253, 254, and 255, as just one example of a collector (or condenser mirror). The diagonally incident reflectors 253, 254, and 255 are arranged axially symmetrically around the optical axis O, and this type of condenser optical system CO is preferably used in combination with a discharge generating plasma source, often called a DPP source, in many cases.

[0053]

[0065] Exemplary lithographic cell

[0054]

[0066] FIG. 3 shows a lithographic cell 300 according to several embodiments, which is sometimes also called a litho cell or a cluster. The lithographic apparatuses 100 and 100' may form part of the lithographic cell 300. The lithographic cell 300 may also include one or more apparatuses for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these apparatuses include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH, and a bake plate BK. A substrate handler or robot RO picks up the substrate from the input / output ports I / O1, I / O2, moves the substrate between different processing apparatuses, and delivers them to the loading bay LB of the lithographic apparatus 100 or 100'. These devices are often collectively referred to as a track and are under the control of a track control unit TCU, which itself is controlled by a monitoring control system SCS, which also controls the lithographic apparatus via a lithography control unit LACU. Thus, different apparatuses can be operated to maximize throughput and processing efficiency.

[0055]

[0067] Exemplary inspection apparatus

[0056]

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

[0057]

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

[0058]

[0070] In some embodiments, inspection apparatus 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a superposition calculation processor 432. The illumination system 412 may be configured to provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a spectrum of wavelengths from about 500 nm to about 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a spectrum of wavelengths from about 500 nm to about 900 nm. The illumination system 412 may be further configured to supply one or more passbands having a substantially constant center wavelength (CWL) value over a long period (e.g., over the lifetime of the illumination system 412). Such a configuration of the illumination system 412 may, as described above, help prevent a shift of the actual CWL value from the desired CWL value in current alignment systems. Further, as a result, the use of a constant CWL value may improve the long-term stability and accuracy of the alignment system (e.g., inspection apparatus 400) compared to current alignment devices.

[0059]

[0071] In some embodiments, the beam splitter 414 may be configured to receive the radiation beam 413 and split the radiation beam 413 into at least two radiation sub - beams. For example, the radiation beam 413 may be split into radiation sub - beams 415 and 417 as shown in FIG. 4A. The beam splitter 414 may be further configured to direct the radiation sub - beam 415 onto a substrate 420 disposed on the stage 422. In one example, the stage 422 is movable along the direction 424. The radiation sub - beam 415 may be configured to illuminate an alignment mark or target 418 disposed on the substrate 420. The alignment mark or target 418 may be coated with a radiation - sensitive film. In some embodiments, the alignment mark or target 418 may have 180 - degree (i.e., 180°) symmetry. That is, when the alignment mark or target 418 is rotated 180° about a symmetry axis perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 may be substantially identical to the non - rotated alignment mark or target 418. The target 418 on the substrate 420 may be a composite grating stack within an overlay target structure that includes (a) a resist layer grating including bars formed of solid - line resist lines, or (b) a product layer grating, or (c) a resist grating overlaid or alternately arranged on the product layer grating. The bars may alternatively be etched into the substrate. This pattern is sensitive to chromatic aberration and illumination symmetry in a lithographic projection apparatus, particularly in the projection system PL, and the presence of such aberrations will, in themselves, appear in the form of variations in the printed grating. One in - line method used in the manufacture of devices for the measurement of line width, pitch, and critical dimensions utilizes a technique known as "scatterometry".The method of scatterometry is described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry”, J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography”, SPIE, Vol. 3677 (1999), both of which are hereby incorporated by reference in their entirety. In scatterometry, light is reflected by a periodic structure within a target and the resulting reflection spectrum at a given angle is detected. The structure that gives rise to the reflection spectrum is reconstructed, for example, using rigorous coupled-wave analysis (RCWA) or by comparison with a library of patterns derived by simulation. Thus, scatterometry data of a printed grating is used to reconstruct the grating. Parameters of the grating, such as line width and shape, can be input into a reconstruction process executed by a processing unit PU from knowledge of the printing step and / or other scatterometry processes.

[0060]

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

[0061]

[0073] The beam splitter 414 is shown as guiding the radiation sub-beam 415 towards the alignment mark or target 418 and guiding the diffracted radiation sub-beam 429 towards the interferometer 426, but it should be noted that the present disclosure is not so limited. It will be apparent to those skilled in the art that other optical arrangements may be used to illuminate the alignment mark or target 418 on the substrate 420 and obtain a similar result of detecting an image of the alignment mark or target 418.

[0062]

[0074] As shown in FIG. 4A, the interferometer 426 may be configured to receive the radiation sub-beam 417 and the diffracted radiation sub-beam 429 through the beam splitter 414. In an exemplary embodiment, the diffracted radiation sub-beam 429 may be at least a portion of the radiation sub-beam 415 that can be reflected from the alignment mark or target 418. In an example of this embodiment, the interferometer 426 may include any suitable set of optical elements, such as a combination of prisms configured to form two images of the alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be understood that it is not necessary to form an image with good image quality, and the features of the alignment mark 418 should be resolved. The interferometer 426 may be further configured to rotate one of the two images 180° with respect to the other of the two images and recombine the rotated image and the non-rotated image by interference.

[0063]

[0075] In some embodiments, detector 428 may be configured to receive the recombined image via the interferometer signal 427 and detect the interference resulting from the recombined image when the alignment axis 421 of inspection apparatus 400 passes through the center of symmetry (not shown) of the alignment mark or target 418. Such interference may, according to an exemplary embodiment, be due to the alignment mark or target 418 being 180° symmetric and interfering such that the recombined images either reinforce or cancel each other out. Based on the detected interference, detector 428 may be further configured to determine the position of the center of symmetry of the alignment mark or target 418 and, as a result, detect the position of substrate 420. According to one example, alignment axis 421 may be perpendicular to substrate 420 and may be aligned with an optical beam passing through the center of image rotation of interferometer 426. Detector 428 may be further configured to perform sensor characteristics and interact with process variations of the wafer mark to estimate the position of the alignment mark or target 418.

[0064]

[0076] In a further embodiment, detector 428 determines the position of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements. 1. Measuring the position variation (position shift between colors) for various wavelengths, 2. Measuring the position variation (position shift between diffraction orders) for various orders, and 3. Measuring the position variation (position shift between polarizations) for various polarizations.

[0065]

[0077] This data can be obtained, for example, using a SMASH (Smart Alignment Sensor Hybrid) sensor as described in U.S. Patent No. 6,961,116, which employs, for example, any kind of alignment sensor, such as a single detector and a self-referencing interferometer using four different wavelengths, and extracts the alignment signal in software, or Athena (Advanced Technology using Higher-Order Expansion of Alignment) as described in U.S. Patent No. 6,297,876, which guides each of seven diffraction orders to dedicated detectors, both of which are hereby incorporated by reference in their entirety.

[0066]

[0078] In some embodiments, the beam analyzer 430 can be configured to receive the diffracted radiation sub-beam 439 and determine its optical state. The optical state can be a measure of the beam wavelength, polarization, or beam profile. The beam analyzer 430 can be further configured to determine the position of the stage 422 and correlate the position of the stage 422 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, and thus the position of the substrate 420, can be accurately known with respect to the stage 422. Alternatively, the beam analyzer 430 can be configured to determine the position of the inspection device 400 or any other reference element, whereby the center of symmetry of the alignment mark or target 418 can be known with respect to the inspection device 400 or any other reference element. The beam analyzer 430 can be a point or imaging polarimeter having some form of wavelength band selectivity. In some embodiments, the beam analyzer 430 can be directly integrated within the inspection device 400, or according to other embodiments, can be connected via some type of polarization-preserving single-mode, multi-mode, or imaging optical fiber.

[0067]

[0079] In some embodiments, the beam analyzer 430 may be further configured to determine overlay data between two patterns on the substrate 420. One of these patterns may be a reference pattern on a reference layer. The other pattern may be an exposure pattern on an exposure layer. The reference layer may be an etching layer already present on the substrate 420. The reference layer may be generated by a reference pattern exposed 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 an exposure pattern exposed on the substrate 420 by the lithography apparatus 100 or 100'. The patterns exposed on the substrate 420 may correspond to the movement of the substrate 420 by the stage 422. In some embodiments, the measured overlay data may also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data may be used as calibration data for calibrating the exposure pattern exposed by the lithography apparatus 100 or 100', whereby the offset between the exposure layer and the reference layer can be minimized after calibration.

[0068]

[0080] In some embodiments, the beam analyzer 430 may be further configured to determine a model of the product stack profile of the substrate 420 and may be configured to measure the overlay, critical dimensions, and focus of the target 418 in a single measurement. The product stack profile includes information about the stacked product such as alignment marks, the target 418, or the substrate 420, and may include mark process variation induced optical signature measurements that are a function of illumination variation. The product stack profile may also include product grid profiles, mark stack profiles, and mark asymmetry information. An example of the beam analyzer 430 is the Yieldstar™ manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, which is hereby incorporated by reference in its entirety. The beam analyzer 430 may be further configured to process information related to specific characteristics within the exposure pattern in that layer. For example, the beam analyzer 430 may process overlay parameters (indications of the layer's positioning accuracy relative to a previous layer on the substrate or the first layer's positioning accuracy relative to a mark on the substrate), focus parameters, and / or critical dimension parameters (e.g., line width and its variation) of the drawn image within the layer. Other parameters are image parameters related to the quality of the drawn image of the exposure pattern.

[0069]

[0081] In some embodiments, an array of detectors (not shown) may be connected to the beam analyzer 430, providing the possibility of accurate stack profile detection as described hereinafter. For example, the detector 428 may be an array of detectors. For the detector array, a number of options are possible, such as a bundle of multimode fibers, discrete pin detectors per channel, or a CCD or CMOS (linear) array. The use of a bundle of multimode fibers allows any dissipative elements to be placed remotely for stability reasons. Discrete pin detectors provide a large dynamic range but each requires a separate preamplifier. Thus, the number of elements is limited. A CCD linear array provides many elements that can be read out quickly and is particularly significant when phase stepping detection is used.

[0070]

[0082] In some embodiments, as shown in FIG. 4B, the second beam analyzer 430 may be configured to receive the diffracted radiation sub-beam 429 and determine its optical state. The optical state may be a measure of the beam wavelength, polarization, or beam profile. The second beam analyzer 430' may be identical to the beam analyzer 430. Alternatively, the second beam analyzer 430' may be configured to perform at least all the functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418, and thus the position of the substrate 420, can be accurately known with respect to the stage 422. The second beam analyzer 430' may also be configured to determine the position of the inspection apparatus 400 or any other reference element, whereby the center of symmetry of the alignment mark or target 418 can be known with respect to the inspection apparatus 400 or any other reference element. The second beam analyzer 430' may be further configured to determine the overlay data between two patterns and the model of the product stack profile of the substrate 420. The second beam analyzer 430' may also be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement.

[0071]

[0083] In some embodiments, the second beam analyzer 430' can be directly integrated within the inspection apparatus 400, or according to other embodiments, it can be connected via several types of polarization-preserving single-mode, multimode, 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 both diffracted radiation sub-beams 429 and 439 and determine their optical states.

[0072]

[0084] In some embodiments, the processor 432 receives information from the detector 428 and the beam analyzer 430. For example, the processor 432 can be a superposition calculation processor. The information can include a model of the product stack profile constructed by the beam analyzer 430. Alternatively, the processor 432 can construct a model of the product mark profile using the received information regarding the product mark. In either case, the processor 432 uses or incorporates the model of the product mark profile to construct a model of the stacked product and the superposition mark profile. The stack model is then used to determine the superposition offset and minimize the spectral effects on the superposition offset measurement. The processor 432 can create a basic correction algorithm based on the information received from the detector 428 and the beam analyzer 430, including but not limited to the optical state of the illumination beam, alignment signals, associated position estimates, and the optical states in the pupil, image, and additional planes. The pupil plane is the plane where the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. The processor 432 can utilize the basic correction algorithm to characterize the inspection apparatus 400 with reference to the wafer mark and / or the alignment mark 418.

[0073]

[0085] In some embodiments, the processor 432 may be further configured to determine a print pattern position offset error for per - mark sensor estimation based on information received from the detector 428 and the beam analyzer 430. The information may include, but is not limited to, the product stack profile, overlay measurements, critical dimensions, and the focus of each alignment mark or target 418 on the substrate 420. The processor 432 may utilize a clustering algorithm to group the marks into sets of similar constant offset errors and create an alignment error offset correction table based on the information. The clustering algorithm may be based on additional optical stack process information associated with each set of overlay measurements, position estimations, and offset errors. Overlays are calculated for a number of different marks, for example, overlay targets having positive and negative biases around a programmed overlay offset. The target with the smallest measured overlay is selected as a reference (since it is measured with the best accuracy). From this measured small overlay and the known programmed overlay of its corresponding target, an overlay error can be inferred. Table 1 shows how this can be done. The smallest measured overlay in the illustrated example is - 1nm. However, this is for a target having a programmed overlay of - 30nm. Therefore, the process results in an overlay error of 29nm.

[0074]

Table 1

[0075] The minimum value can be selected to be a reference point, and based on this comparison, an offset between the measured overlay and what is expected for the programmed overlay can be calculated. This offset determines the overlay error for each mark or set of marks having a similar offset. Thus, in the example of Table 1, the minimum measured overlay was -1 nm at the target position of the programmed overlay of 30 nm. The difference between the expected and measured overlays at other targets is compared to this reference. Tables such as Table 1 can also be obtained from marks and targets 418 under different illumination settings, and the illumination setting that results in the minimum overlay error and its corresponding calibration factor can be determined and selected. Subsequently, the processor 432 can group the marks into sets of similar overlay errors. The criteria for grouping the marks can be adjusted based on different process controls, such as different error tolerances for different processes.

[0076]

[0086] In some embodiments, the processor 432 can confirm that all or most of the elements of the group have a similar offset error and, based on its further optical stack measurements, apply individual offset corrections from a clustering algorithm to each mark. The processor 432 can determine the correction for each mark and send the correction back to the lithography apparatus 100 or 100' to correct the error in the overlay, for example, by feeding the correction into the inspection apparatus 400.

[0077]

[0087] Exemplary Characterization of Intensity Imbalances in a Measurement System

[0078]

[0088] A measurement system (e.g., inspection apparatus 400) is typically programmed using specific assumptions about the target it is to measure. For example, the measurement system can be programmed to predict diffracted radiation scattered by a grating used as an alignment mark. An ideal grating can generate diffraction orders in a predictable manner. The characteristics of the diffracted radiation (e.g., the intensity at each diffraction order) can be analyzed by the measurement system to generate, for example, the alignment position of the grating. However, an actual grating on a wafer can deviate from the ideal. For example, a wafer can have one or more gratings fabricated thereon when it undergoes multiple lithography processes to form different layers of lithographically fabricated devices. The process can require polishing and / or etching that distort, contaminate, or otherwise damage an already existing grating on the wafer from a previous lithography process. A damaged grating can then diffract the measurement radiation in a different manner than an ideal grating, causing the measurement system to generate an error in its measurement results. For example, a damaged grating can cause an intensity imbalance between different diffraction orders, while the measurement system can predict perfectly balanced intensities based on the assumption that an ideal or nearly perfect grating was measured.

[0079]

[0089] The present disclosure provides the structure and function of a measurement system for reducing or eliminating errors associated with measurements performed on a damaged target. However, before describing such embodiments in more detail, it is first beneficial to describe the optical elements within the measurement system upon which embodiments of the present disclosure can depend.

[0080]

[0090] Referring again briefly to FIG. 4A, the measurement system 400 may include a beam splitter 434 and a sensor 436. The sensor 436 may be referred to as a second sensor, and the detector 428 serves as the first sensor. The beam splitter 434 may receive the diffracted radiation 419. The target 418 may interact with the incident radiation via reflection, refraction, diffraction, scattering, etc., and generate scattered radiation (e.g., diffracted radiation 419). For ease of explanation and not by way of limitation, such radiation may be referred to as scattered radiation throughout. The beam splitter 434 may split the radiation scattered by the target 418 into a first portion 441 of the radiation and a second portion 443 of the radiation. The first portion 441 of the radiation may continue to proceed for the subsequent receiving detector 428 (e.g., sub-beam 429, and then as an interferometer signal). The subsequent determination of the characteristics of the target 418 (e.g., alignment position) may be performed as described above. The sensor 436 may be used to determine a correction for the characteristics determined via the detector 428. The sensor 436 may operate in conjunction with the processor 432 to determine the correction. Although not shown in FIG. 4B, it should be understood that the structure and function of the beam splitter 434 and the sensor 436 may be implemented in the embodiment with reference to FIG. 4B.

[0081]

[0091] Figure 5 shows the pupil 550 within a measurement system (not shown) according to some embodiments. In some embodiments, the measurement system can be, for example, the inspection apparatus 400 (Figs. 4A and 4B). The pupil 550 can be, for example, the plane through which diffracted radiation from the target passes within the path of diffracted radiation 419 from the target 418 (Figs. 4A and 4B). The target can have a combination of vertical and horizontal gratings that can generate a plurality of radiation beams within the pupil 550. The beams can have different diffraction orders. For example, there can be diffraction orders 552 (e.g., -n, ..., -2, -1, 0, +1, +2, ..., +n) arranged along the horizontal direction (labeled "X") within the pupil 550. Similarly, there can be diffraction orders 554 arranged along the vertical direction (labeled "Y") within the pupil 550. The measurement system can be a dark-field measurement system, in which case the zero order can be blocked using a blocking element, an aperture stop, etc.

[0082]

[0092] In some embodiments, additional optical elements (not shown) within the measurement system can cause the spatial distribution of the diffraction orders within the pupil 550 to change (e.g., to be rotated). For example, the diffraction orders can be aligned with rotated axes X' and Y' shown as dashed lines. The labels X, Y, X', and Y' are provided as an example of relative directionality and are not limiting.

[0083]

[0093] In some embodiments, diffraction orders 552 and / or 554 may be arranged close to each other due to the spatial constraints of inspection apparatus 400 (Figs. 4A and 4B). For example, an optical component such as an objective system may limit the pupil diameter to less than 20 mm. Such constraints can cause problems in characterizing individual diffraction orders when using discrete detectors for each diffraction order (e.g., when using photodiodes). Any number or type of detector may be used (e.g., a camera, a 2D array sensor), but a single-cell photodiode may be more cost-effective and have reduced complexity in its electronic circuitry. However, diffraction orders 552 and / or 554 may be too close to each other to allow individual photodiodes to be placed for each diffraction order (e.g., the photodiodes may be too large). To effectively use a single-cell detector, it may be preferable to spatially separate the diffraction orders (e.g., divide the pupil). However, it should be understood that spatially separating the diffraction orders can be implemented using any type of detector.

[0084]

[0094] FIG. 6 shows an optical system 656, e.g., a prism system, for dividing the pupil according to some embodiments. In some embodiments, prism system 656 includes diagonal surfaces 658 and 660. The diagonal surfaces include coatings that are sensitive to the characteristics of diffraction orders 652 and 654. For example, a coating on diagonal surface 658 may reflect one of diffraction orders 652 while allowing another diffraction order 654 to pass based on their respective polarizations.

[0085]

[0095] In some embodiments, when using the prism system 656, some undesirable errors in measurement may occur. For example, the diffraction order 652 may only encounter the coating provided on the diagonal plane 658, while the diffraction order 654 may interact with the coatings on both diagonal planes 658 and 660. Such differences in interaction may add undesirable errors to the intensity measurements of the diffraction orders 652 and 654. In addition, when the diffraction orders 652 and 654 are generated by a target lattice having a small pitch (e.g., 1.6 - 2.1 μm), the prism system 656 may become difficult to implement. In some aspects, as the pitch size becomes smaller, the separation of the diffraction orders 652 and 654 increases. For reasons of the optical arrangement, in some aspects, the radiation beams of the diffraction orders 652 and 654 initially remain close to each other, and then an optical system such as the prism system 656 can separate the diffraction orders 652 and 654 further downstream.

[0086]

[0096] In one example, if the diffraction orders 652 and 654 are overly separated due to a target lattice having a small pitch, the prism system 656 may not be large enough to be in the paths of both diffraction orders 652 and 654 (e.g., due to volume constraints of the measurement system). Further, in some embodiments, the manufacturing process of the prism system 656 may have complexities that can introduce additional errors. For example, the coating processes for the diagonal planes 658 and 660 can become complex, and the assembly of the prism system 656 may require tight tolerances.

[0087]

[0097] FIG. 7 shows an optical system 762, e.g., a wedge system, for splitting a pupil, according to some embodiments. The description with reference to FIG. 7 is intended to provide a basic overview of the optical phenomena relied upon by the embodiments with reference to FIGS. 8 and 9. Some aspects of how the wedge system 762 can be used to overcome the above-described problems related to the prism system 656 are described in more detail with reference to FIGS. 8 and 9.

[0088]

[0098] In some embodiments, the wedge system 762 includes an optical element 764, such as a wedge, and an optical element 766, such as a wedge (also referred to as the "first wedge" and the "second wedge"). The wedge system 762 can be arranged to intersect the path of the radiation beam 768. The wedge 764 can include a surface 770 and a surface 772 (also a "facet") that is inclined with respect to the surface 770. The surface 770 can be the input surface of the wedge system 762 for receiving the radiation beam 768 (e.g., received at normal incidence). The wedge 764 can diverge the radiation beam 768 away from the optical axis 774.

[0089]

[0099] In some embodiments, the wedge 766 can include a surface 776 and a surface 778 (also a "facet") that is inclined with respect to the surface 776. The wedge 766 can diverge the radiation beam 768 in a direction opposite to the divergence created by the wedge 764. That is, the wedge 766 can refract the radiation beam 768, thereby reducing or reversing the divergence created by the wedge 764. The surface 776 can be the output surface of the wedge system 762 for transmitting the radiation beam 768 (e.g., the beam exits perpendicular to the surface 776). Thus, the radiation beam 768 can exit the wedge system 762 along a direction parallel to the optical axis 774. Accordingly, the wedge system 762 can separate or displace the exit path of the radiation beam 768 from the initial path (e.g., the input path) of the radiation beam 768 by a separation distance 780.

[0090]

[0100] FIG. 8 shows first and second optical elements 864 and 866, such as first and second wedges, that can be used within an optical system, such as a wedge system, according to some embodiments. For clarity, the figures in FIG. 8 are of two independent wedges 864 and 866 that are not yet arranged within an optical mechanism, while FIG. 9 shows an embodiment of a mechanism that can include the wedges 864 and 866.

[0091]

[0101] In some embodiments, the wedge 864 can be a segmented or multifaceted wedge. The wedge 864 can be a disk or cylinder having facets 806 disposed within the quadrants of the disk. FIG. 8 shows the wedge 864 as having four facets 872, but it should be understood that fewer or more facets can be employed. The wedge 864 can also have a flat bottom surface 870 (blocked from view for perspective) that extends across the circular area of the disk. The facets 872 on the wedge 864 can be designed such that the wedge 864 has a concave geometry - i.e., inset or recessed. Accordingly, the facets 872 can be inclined with respect to the flat bottom surface 870. The flat bottom surface 870 can receive a plurality of radiation beams, such as those of diffraction orders 552 and 554 (FIG. 5). Each facet is arranged to diverge the radiation beam received in its respective quadrant.

[0092]

[0102] In some embodiments, the wedge 866 is a segmented or multifaceted wedge that is similar to the wedge 864, but different in that the wedge 866 can have a convex geometry. The number of facets of the wedge 866 desirably matches that of the wedge 864. The wedge 866 can have a flat top surface 876 and facets 878. The facets 878 can be inclined with respect to the flat top surface 876 (e.g., match the relative angle between the facet 872 and the flat bottom surface 870). Each of the facets 878 can match the corresponding one of the facets 872 such that any two corresponding facets have a cross-sectional arrangement similar to that of surfaces 770 and 778, as shown in FIG. 7.

[0093]

[0103] In some embodiments, the facets 878 can receive the radiation beam diverged by the wedge 864. The wedge 866 can collimate the received radiation beam. In other words, the wedge 866 can make the received radiation beam parallel.

[0094]

[0104] Figure 9 shows mechanism 900 according to some embodiments. In some embodiments, mechanism 900 represents a mechanism (Figure 4A) that includes a part of a measurement system, such as sensor 436 of inspection device 400. In some embodiments, mechanism 900 includes an optical system 962 and a detection system 982. In some aspects, optical system 962 is disposed between pupil 950 and detection system 982. In some embodiments, radiation exiting an object (e.g., target 418 (Figures 4A and 4B)) forms beams 968-1 to 968-n, where n is 4. Beams 968 pass through pupil 950 with little separation. In such an example, optical system 962 can expand the spacing between beams 968 before they are received at detection system 982. It should be understood that beams 968 can correspond to a second portion 443 of the radiation generated via beam splitter 434 (Figure 4A).

[0095]

[0105] In some embodiments, optical system 962, such as a wedge system, includes first and second optical elements 964 and 966, such as first and second wedges. In some aspects, each of wedges 964 and 966 includes, for example, four sectors (e.g., the facets shown in Figure 8). In some aspects, each of beams 968-1 to 968-4 passes through corresponding facets 972-1 to 972-n on wedge 964 and then through corresponding facets (blocked from view for the sake of perspective) on wedge 966.

[0096]

[0106] In some embodiments, the wedge 964 is configured to expand or diverge the beam 968 to provide more space between the beams. For example, the wedge 964 can have a concave exit surface that diverges the beam 968 at an angle greater than about 0.5 degrees with respect to the central axis 974. The central axis 974 can also be referred to as the optical axis of the beam 968. In some embodiments, the angular divergence provided by the wedge 964 can be greater than about 1 degree. In some embodiments, the angular divergence provided by the wedge 964 can be greater than about 2 degrees. In some embodiments, the angular divergence provided by the wedge 964 can be greater than about 5 degrees. In some embodiments, the angular divergence provided by the wedge 964 can be greater than about 10 degrees. In some embodiments, the angular divergence provided by the wedge 964 can be greater than about 20 degrees. In some embodiments, the angular divergence provided by the wedge 964 can be greater than about 30 degrees. In some embodiments, the angular divergence provided by the wedge 964 can be from about 0.5 degrees to 45 degrees. In some embodiments, the angular divergence provided by the wedge 964 can be from about 2 degrees to 30 degrees. In some embodiments, the angular divergence provided by the wedge 964 can be from about 5 degrees to 20 degrees.

[0097]

[0107] In some aspects, the optical element 966 is configured to collimate or refract the beam 968 to guide the now-separated beams onto corresponding portions of the detection system 982. In some aspects, the detection system 982 includes one or more detection portions 982-1 through 982-n, where n is 4 (also "first detector", "second detector", etc.). Continuing with the previous description, each beam 968-1 through 968-n is received by the corresponding detection portion 982-1 through 982-n.

[0098]

[0108] In some embodiments, the detection portions 982-1 to 982-n may each include a single self-photodiode. However, in some aspects, it may be desirable to receive the beams 968-1 to 968-n at a remote location (e.g., away from the mechanism 900). Accordingly, the detection portions 982-1 to 982-n may each include an optical coupler connected to corresponding optical fibers 984-1 to 984-n that guide the received beams 968-1 to 968-n to respective photodiodes disposed at the remote location.

[0099]

[0109] The wedges 964 and 966 may have a structure and function as described with reference to the wedges 864 and 866 (FIG. 8). The mechanism 900 may receive a beam 968 separated from scattered radiation (also “the second portion of the radiation”, e.g., the second portion of the radiation 443 (FIG. 4A)) scattered by the target. Specifically, the mechanism 900 may receive the beam 968 after the beam 968 has propagated along a path including the wedge system 962 including the wedges 964 and 966. Before reaching the wedge system 962, the beam 968 may pass through the pupil 950. An example of an image in the pupil 950 may be the one shown in the pupil 550 (FIG. 5). FIG. 9 may show four beams 968-1 to 968-4 (e.g., diffraction orders of +1X, -1X, +1Y, and -1Y), but it should be understood that a greater or fewer number of diffraction orders may be received by the mechanism 980. The mechanism 900 may diverge the beam 968 and create a diverging pupil image.

[0100]

[0110] In some embodiments, the beam 968-1, e.g., the first beam, may include a first diffraction order. The beam 968-2, e.g., the second beam, may include a diffraction order different from the first diffraction order. The wedge 964 may diverge the beam 968 with respect to the central axis 974. The central axis 974 may be oriented parallel to the overall propagation direction of the beam 968. The first sensor may be used to determine the characteristics of the target based on the first portion of the received radiation (e.g., the detector 428 (FIG. 4A) that receives the first portion 441 of the radiation), while the second sensor (e.g., the sensor 436 (FIG. 4A) using the mechanism 900) may be used to determine a correction value for the characteristics of the target based on the beam 968 received in the detection system 982. The determined correction value may be based on a comparison (e.g., intensity imbalance) of the intensities of the diverged beams 968-1 to 968-n (e.g., the diverged diffraction orders). Next, the measurement system may use the correction value to adjust the value of the determined characteristics. For example, if the measured characteristic of the target is the alignment position, the measurement system may use the correction value to adjust the alignment position.

[0101]

[0111] In some embodiments, the wedge 966 may apply a divergence opposite to the divergence generated by the wedge 964, thereby making the beam 968 parallel after the beam crosses the wedge system 962. In other words, the wedge 966 may collimate the beam 968.

[0102]

[0112] In some embodiments, the detection portions 982-1 to 982-n may each receive the beams 968-1 to 968-n after the beams 968-1 to 968-n are separated or spread by the wedge system 962. The detection system 982 may be disposed in the plane 986. The spatial distribution of the radiation intensity in the plane 986 may be described as a diverging pupil image (or a separated or divided pupil image).

[0103]

[0113] In some embodiments, the wedge 966 is optional. For example, when the wedge 966 is omitted, the detection portions 982-1 to 982-n can be disposed more upstream so that the beams 968-1 to 968-n can enter the detection portions 982-1 to 982-n before the separation distance between the beams becomes too large even if they are inclined.

[0104]

[0114] FIG. 10 shows a diverging pupil image 1088 according to some embodiments. In some embodiments, the diverging pupil image 1088 includes sections 1088-1 to 1088-n. Here, as an example, n is 4. Section 1088-1 can be the first section, section 1088-2 can be the second section, and so on. The number of sections within the diverging pupil image can be based on the number of facets on the wedge used to diverge the initial pupil image. An example of an initial non-diverging pupil image is shown within the pupil 550 (FIG. 5). The diverging pupil image can occur in the plane 986 (FIG. 9).

[0105]

[0115] In some embodiments, different diffraction orders can be present within sections 1088-1 to 1088-n. The diffraction orders can be those that were initially closer to each other within the initial pupil image. FIG. 10 is intended to show that not only are the diffraction orders separated, but also that as a result of using the wedge system shown in FIGS. 8 and 9, the entire sections (e.g., quadrants) of the initial pupil image can be separated from each other. For example, in a scenario where the entire initial pupil is filled with radiation, the hatched quadrants of sections 1088-1 to 1088-n can each be filled with radiation, while the regions outside the quadrants can have little or no radiation present.

[0106]

[0116] In some embodiments, at least the wedge 964 can be used such that a separation 1080 can be formed between sections 1088-1 and 1088-2. It should be understood that the separation 1080 is not limited to only sections 1088-1 and 1088-2, and that similar separations can be defined between any of sections 1088-1 through 1088-n. The separation 1080 can be, for example, about 1 mm. In some embodiments, the separation 1080 can be about 2 mm. In some embodiments, the separation 1080 can be about 5 mm. In some embodiments, the separation 1080 can be about 10 mm. In some embodiments, the separation 1080 can be from about 1 mm to 1 m. In some embodiments, the separation 1080 can be greater than about 1 mm. In some embodiments, the separation 1080 can be greater than about 1 m. A large separation can be desirable if the detector placement is at different ends of the measurement system due to optical and / or volume constraints.

[0107]

[0117] FIG. 11A shows a portion of a detection system 1182 that can be used, for example, within the mechanism 900, according to some embodiments. The description of the embodiments with reference to FIG. 11A can also refer to the structures and functions previously described with reference to FIGS. 9 and 10.

[0108]

[0118] In some embodiments, the detection system 1182 includes optical couplers 1182-1 to 1182-n, where n is 4 (n can be different from 4). The optical couplers 1182-1 to 1182-n can include lenses (e.g., one or more lenses per coupler). The optical couplers 1182-1 to 1182-n can couple the received beams 968-1 to 968-n to respective optical fibers 984-1 to 984-n. The optical fibers 984-1 to 984-n can guide the received radiation to respective photodiodes. The photodiodes can generate measurement signals. A processor can receive and analyze the measurement signals and determine a corrected value of the measured target characteristic. In embodiments where fibers are not used, the optical couplers 1182-1 to 1182-n can include lenses for focusing the received beams 968-1 to 968-n onto respective detectors (first photodiode, second photodiode, and so on).

[0109]

[0119] In some embodiments, the optical couplers 1182-1 to 1182-n can be disposed downstream at or near the plane 986. The diverging and converging image 1088 can occur at the plane 986. The diverging and converging image 1088 can include sections 1088-1 to 1088-n. The optical couplers 1182-1 to 1182-n can each receive radiation from the sections 1088-1 to 1088-n of the diverging and converging image.

[0110]

[0120] In some embodiments, the optical coupler 1182-1 can have an optical cross-sectional area smaller than that of the section 1088-1. This can be desirable when multiple diffraction orders are present within the section 1088-1 but only one diffraction order, excluding others, is to be detected. The optical coupler 1182-1 can be driven to move from one diffraction order to the next within the section 1088-1. It should be understood that the optical couplers 1182-2 to 1182-n can also have the same features as those described for the optical coupler 1182-1.

[0111]

[0121] In some embodiments, the optical coupler 1182-1 may have an optical cross-sectional area larger than that of section 1088-1. This may be desirable for simplifying the detector mechanism (e.g., no actuators and complex machinery are present) and for optical alignment.

[0112]

[0122] FIG. 11B shows a detection system 1182 with additional optical structures according to some embodiments. The description of the embodiments with reference to FIG. 11B may also refer to the structures and functions previously described with reference to FIGS. 9, 10, and 11A. In some embodiments, a radiation adjustment structure may be disposed at the input of the detection system 1182. For example, FIG. 11B shows a slit structure 1190 that may be disposed at one input of the optical couplers 1082-1 to 1082-n. In another example, an aperture 1192 may be disposed at the input of another one of the optical couplers 1082-1 to 1082-n. It should be understood that the radiation adjustment structure is not limited to only slits and apertures, and other radiation adjustment structures may also be used. FIG. 11B shows different radiation adjustment structures disposed at different inputs, but it should also be understood that any combination of radiation adjustment structures (e.g., all the same, one of each type, pairs of each type, etc.) may be disposed at the input of the detection system 1182. The radiation adjustment structure may, for example, enable measurement of the detailed structure of the diffraction order.

[0113]

[0123] In some embodiments, the mechanism 900 may be a rigid assembly. That is, the wedges 964 and 966, and the detection system 982 may be assembled and fixed such that their relative positions are held constant. It was mentioned with reference to FIG. 5 that the diffraction order may be rotated within the pupil plane. Thus, the mechanism 900 as a rigid assembly may be driven to align the mechanism 900 with the displacement of the radiation within the pupil.

[0114]

[0124] It should be understood that in some embodiments, mechanism 900 may be different from detector 428 (Figs. 4A and 4B). While the functions disclosed with reference to detector 428 describe determining target characteristics (e.g., alignment position), mechanism 900 may be applicable to a separate measurement to obtain a correction value for the characteristics determined by detector 428. Detector 428 has been described with reference to an interferometry method that may include scanning a target to obtain an intensity signal that varies over time (e.g., the intensity varies sinusoidally over time). Mechanism 900 is not limited by the interferometry method and may perform the determination of correction values based on an instantaneous measurement.

[0115]

[0125] FIG. 12 shows method steps for performing the functions as described with reference to FIGS. 1 - 10, 11A, and 11B according to some embodiments. In step 1202, scattered radiation scattered by a target may be split into first and second portions of the radiation. In step 1204, the first portion of the radiation may be received at a first sensor. In step 1206, after the second portion of the radiation propagates along a path including a wedge system including a first wedge, the second portion of the radiation may be received at a second sensor. In step 1208, the first wedge may be used to diverge the second portion of the radiation.

[0116]

[0126] The method steps of FIG. 12 may be performed in any conceivable order, and not all steps need to be performed. Further, the method steps of FIG. 12 described above merely reflect an example of steps and are not limiting. That is, based on the embodiments described with reference to FIGS. 1 - 10, 11A, and 11B, additional method steps and functions may be contemplated.

[0117]

[0127] Embodiments may be further described using the following clauses. 1. A measurement system, a beam splitter configured to split scattered radiation scattered by a target into first and second portions of the radiation, a first sensor configured to receive the first portion, After the second portion propagates along a path including a wedge system including a first wedge configured to diverge the second portion, a second sensor configured to receive the second portion and a measurement system. 2. The second portion includes first and second radiation beams, and The first wedge is further configured to diverge the first and second beams at an angle greater than 0.5 degrees with respect to the optical axis of the second portion, the measurement system according to clause 1. 3. The second portion includes first and second radiation beams, and The first wedge is further configured to diverge the first and second beams such that the lateral distance between the first and second beams is increased by more than about 1 mm, the measurement system according to clause 1. 4. The wedge system includes a second wedge configured to collimate the second portion, the measurement system according to clause 1. 5. The wedge system includes a second wedge configured to receive the diverged second portion from the first wedge and collimate the second portion before it is transmitted through the second sensor, the measurement system according to clause 1. 6. The first sensor is configured to determine the characteristics of the target based on the received first portion, the measurement system according to clause 1. 7. The second sensor is further configured to determine a correction value for the characteristics based on the received second portion, the measurement system according to clause 6. 8. Determining the correction value is further based on a comparison of the intensity imbalance between the divergent emissions of the second portion, the measurement system according to clause 7. 9. The characteristic is the alignment position of the target, and The measurement system is further configured to adjust the alignment position using the correction value, the measurement system according to clause 7. 10. The second portion forms a pupil image in front of the wedge system, the measurement system according to clause 1. 11. The first wedge is further configured to divide the pupil image into at least first and second sections and to diverge at least the first and second sections, the measurement system according to clause 10. 12. The target includes a grid structure, The first section includes a first diffraction order from the target, and The second section includes a second diffraction order from the target, different from the first diffraction order, the measurement system according to clause 11. 13. The second sensor is a first detector configured to receive the first section, and a second detection system configured to receive the second section and includes the measurement system according to clause 11. 14. The second sensor includes an actuator configured to adjust the position of the second sensor such that the first and second detectors are aligned with any two of the first section, the second section, and other sections of the pupil image divided by the first wedge system, the measurement system according to clause 13. 15. The second sensor is a first aperture structure configured to adjust the radiation within the first section before being received by the first detector, and a second aperture structure configured to adjust the radiation within the second section before being received by the second detector and further includes the measurement system according to clause 13. 16. The second sensor is a first lens configured to focus the first section onto the first detector, and a second lens configured to focus the second section onto the second detector and includes the measurement system according to clause 13. 17. The detector system is a first lens configured to select a diffraction order to be focused onto the first detector from among the diffraction orders within the first section, a second lens configured to select a diffraction order from among the diffraction orders within the second section to be focused onto the second detector The measurement system according to claim 13, comprising: 18. A lithographic apparatus, an illumination system configured to illuminate a pattern of a patterning device, a projection system configured to project an image of the pattern onto a substrate, a measurement system comprising, wherein the measurement system a beam splitter configured to split scattered radiation scattered by a target into first and second portions of the radiation, a first sensor configured to receive the first portion, a second sensor configured to receive the second portion after the second portion has propagated along a path including a wedge system including a first wedge configured to diverge the second portion, The lithographic apparatus comprising: 19. The second portion forms a pupil image before the wedge system, and The lithographic apparatus according to claim 18, wherein the first wedge is further configured to split the pupil image into at least first and second sections and to diverge at least the first and second sections. 20. Splitting scattered radiation scattered by a target into first and second portions of the radiation, receiving the first portion at a first sensor, receiving the second portion at a second sensor after the second portion has propagated along a path including a wedge system including a first wedge, diverging the second portion using the first wedge A method comprising:

[0118]

[0128] Although the present specification may specifically refer to the use of a lithographic apparatus in the manufacture of an IC, it should be understood that the lithographic apparatus described in this specification may have other applications, such as for guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, etc., and for the manufacture of integrated optical systems. Those skilled in the art will understand that, in relation to such alternative applications, the use of the terms "wafer" or "die" in this specification can be regarded as synonyms for the more general terms "substrate" or "target portion" respectively. The substrate referred to in this specification can be processed, before or after exposure, by, for example, a track unit (usually a tool for applying a layer of resist to the substrate and developing the exposed resist), a metrology unit and / or an inspection unit. Where applicable, the disclosure of this specification can be applied to such other substrate processing tools. Further, the substrate can be processed more than once, for example, to produce a multilayer IC, and as a result, the term "substrate" as used in this specification can also refer to a substrate that already includes a plurality of processed layers.

[0119]

[0129] Although the use of embodiments of the present disclosure in relation to optical lithography has been specifically referred to above, it should be understood that the present disclosure can also be used in other applications, such as imprint lithography, and is not limited to optical lithography if the circumstances permit. In imprint lithography, the topography in the patterning device defines the pattern that is created on the substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate, and on the substrate, the resist is hardened by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved away from the resist, leaving a pattern in the resist after the resist has been hardened.

[0120]

[0130] It should be understood that the phrases or terms in this specification are for the purpose of explanation and not limitation, and the terms or phrases of the present disclosure should be interpreted by those skilled in the relevant technical field in light of the teachings of this specification.

[0121]

[0131] As used herein, terms such as "radiation", "beam", "light" and "illumination" can include all kinds of electromagnetic radiation, such as ultraviolet (UV) radiation (e.g., having a wavelength λ of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength in the range of 5 - 20 nm such as 13.5 nm) or hard X-rays operating below 5 nm, as well as particle beams such as ion beams or electron beams. Generally, radiation having a wavelength of about 400 - about 700 nm is considered visible radiation, and radiation having a wavelength of about 780 - 3000 nm (or more) is considered infrared radiation. UV refers to radiation having a wavelength of about 100 - 400 nm. In lithography, the term "UV" also applies to wavelengths that can be generated by a mercury discharge lamp, namely G-line 436 nm, H-line 405 nm and / or I-line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by gas) refers to radiation having a wavelength of about 100 - 200 nm. Deep ultraviolet (DUV) generally refers to radiation having a wavelength in the range from 126 nm to 428 nm, and in some embodiments, an excimer laser can generate DUV radiation used inside a lithographic apparatus. For example, it should be understood that radiation having a wavelength in the range of 5 - 20 nm relates to radiation having a specific wavelength band at least partially within the range of 5 - 20 nm.

[0122]

[0132] As used herein, the term "substrate" represents the material on which a material layer is added. In some embodiments, the substrate itself can be patterned, or the material added on top of the substrate can be patterned, or it can remain unpatterned.

[0123]

[0133] Although specific references may be made herein to the use of the apparatus and / or system according to the present disclosure in the manufacture of integrated circuits, it should be clearly understood that such apparatus and / or system has many other possible applications. For example, this can be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, LCD panels, thin film magnetic heads, etc. Those skilled in the art will understand that, in connection with such alternative applications, the use of the terms "reticle", "wafer" or "die" should be regarded as being replaced herein by the more general terms "mask", "substrate" and "target portion", respectively.

[0124]

[0134] Although specific embodiments of the present disclosure have been described above, it will be understood that the embodiments of the present disclosure may be implemented in ways other than those described. The description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that modifications may be made to the present disclosure without departing from the scope of the claims presented below.

[0125]

[0135] It should be understood that the detailed description section, rather than the summary and abstract sections, is intended to be used to interpret the claims. The summary and abstract sections may describe one or more, but not all, of the exemplary embodiments of the present disclosure contemplated by the inventors, and thus are in no way intended to limit the present disclosure and the scope of the appended claims.

[0126]

[0136] The present disclosure has been described above using functional building blocks that show specific function implementations and their relationships. The boundaries of these functional building blocks are arbitrarily defined herein for convenience of explanation. Alternative boundaries can be defined as long as the specific functions and their relationships are properly executed.

[0127]

[0137] The foregoing description of specific embodiments has been presented to fully disclose the general nature of the present disclosure so that others, by applying knowledge within the scope of the technology in the art, can readily modify such specific embodiments and / or adapt them to various uses without departing from the general concepts of the present disclosure and without undue experimentation. Accordingly, such adaptations and modifications are intended to be within the spirit and scope of the equivalents of the disclosed embodiments based on the teachings and guidance presented herein.

[0128]

[0138] The breadth and scope of the protected subject matter should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A measurement system, comprising: a beam splitter that splits scattered radiation scattered by a target into first and second portions of the radiation; a first sensor that receives the first portion; a second sensor that receives the second portion after the second portion has propagated along a path including a wedge system that includes a first wedge that diverges the second portion; A measurement system comprising.

2. The second portion includes first and second radiation beams, The measurement system according to claim 1, wherein the first wedge further diverges the first and second radiation beams at an angle greater than 0.5 degrees with respect to the optical axis of the second portion.

3. The second portion includes first and second radiation beams, The measurement system according to claim 1, wherein the first wedge further diverges the first and second radiation beams such that a lateral distance between the first and second radiation beams is increased by more than about 1 mm.

4. The measurement system according to claim 1, wherein the wedge system includes a second wedge that collimates the second portion.

5. The measurement system according to claim 1, wherein the wedge system includes a second wedge that receives the diverged second portion from the first wedge and collimates the second portion before it passes through the second sensor.

6. The measurement system according to claim 1, wherein the first sensor determines characteristics of the target based on the received first portion.

7. The measurement system according to claim 6, wherein the second sensor further determines a correction value for the characteristics based on the received second portion.

8. The measurement system according to claim 7, wherein determining the correction value is further based on a comparison of intensity imbalances between the divergent radiations of the second portion.

9. The characteristic is an alignment position of the target, The measurement system according to claim 7, wherein the measurement system further adjusts the alignment position using the correction value.

10. The measurement system according to claim 1, wherein the second portion forms a pupil image in front of the wedge system.

11. The measurement system according to claim 10, wherein the first wedge further divides the pupil image into at least first and second sections and diverges the at least first and second sections.

12. The target includes a grating structure, The first section includes a first diffraction order from the target, The second section includes a second diffraction order from the target, different from the first diffraction order, of the measurement system according to claim 11. **Claim 13** The second sensor includes a detector system including a first detector receiving the first section and a second detector receiving the second section of the measurement system according to claim 11. **Claim 14** The second sensor includes an actuator for adjusting the position of the second sensor such that the first and second detectors are aligned with any two of the first section, the second section, and other sections of the pupil image divided by the wedge system. of the measurement system according to claim 13. **Claim 15** The second sensor further includes a first aperture structure for adjusting radiation within the first section before being received by the first detector, and a second aperture structure for adjusting radiation within the second section before being received by the second detector of the measurement system according to claim 13. **Claim 16** The second sensor includes a first lens for focusing the first section onto the first detector, and a second lens for focusing the second section onto the second detector of the measurement system according to claim 13. **Claim 17** The detector system includes a first lens for selecting a diffraction order to be focused onto the first detector from among the diffraction orders within the first section, and a second lens for selecting a diffraction order to be focused onto the second detector from among the diffraction orders within the second section of the measurement system according to claim 13. **Claim 18** A lithographic apparatus comprising an illumination system for illuminating a pattern of a patterning device, a projection system for projecting an image of the pattern onto a substrate, and a measurement system wherein the measurement system includes a beam splitter for splitting scattered radiation scattered by a target into first and second portions of radiation, a first sensor for receiving the first portion, and a second sensor for receiving the second portion after the second portion has propagated along a path including a wedge system including a first wedge for diverging the second portion of the lithographic apparatus. **Claim 19** The second portion forms a pupil image before the wedge system, The lithographic apparatus according to claim 18, wherein the first wedge further divides the pupil image into at least first and second sections and diverges the at least first and second sections. **Claim 20** Dividing scattered radiation scattered by a target into first and second portions of the radiation; Receiving the first portion at a first sensor; After the second portion has propagated along a path including a wedge system including a first wedge, receiving the second portion at a second sensor; Diverging the second portion using the first wedge; A method comprising.

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