Inspection apparatus, motorized aperture, and background method

Abstract

The system includes an imaging system, a spatial filter, and a detector. The system is configured to receive a plurality of diffraction orders. The spatial filter is configured to block one or more undesired diffraction orders of the plurality of diffraction orders and pass one or more desired diffraction orders of the plurality of diffraction orders. The spatial filter includes one or more obscurations having an angle-dependent radius that varies with azimuth angle. The detector is configured to receive and measure intensities of the one or more desired diffraction orders. The spatial filter is motorized.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Patent Application No. 63 / 307,439, filed February 7, 2022, which is incorporated by reference in its entirety.

[0002] FIELD OF THEINVENTION The present disclosure relates to filtering of diffraction orders, such as motorized apertures to block high order diffracted beams in inspection and lithography tools. [Background technology]

[0003] A lithographic apparatus is a machine that transfers a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus are used, for example, in the manufacture of integrated circuits (ICs). A patterning device, also called a mask or reticle, can then be used to create a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of one or several dies) on the substrate (e.g. a silicon wafer). The pattern is usually imaged onto a layer of radiation-sensitive material (resist) provided on the substrate. Generally, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include the so-called steppers and scanners. In a stepper, each target portion is irradiated by exposing the entire pattern onto the target portion at once. In a scanner, each target portion is irradiated by scanning the radiation beam in a given direction (scan direction) and scanning the target portion parallel or anti-parallel to this scan direction. The pattern can also be transferred from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During lithography operations, different processing steps may require different layers to be successively formed on a substrate. Therefore, the substrate may need to be positioned with high accuracy with respect to previous patterns formed thereon. Generally, alignment marks are placed on the substrate to be aligned and positioned with reference to a second object. The lithography apparatus may use an alignment device to detect the position of the alignment marks and align the substrate using the alignment marks to ensure accurate exposure from the mask. The deviation between the alignment marks in two different layers is measured as the overlay error.

[0005] To monitor the lithography process, parameters of the patterned substrate are measured. The parameters may include, for example, the overlay error between successive layers formed in or on the patterned substrate, and the critical line width of the developed photosensitive resist. The measurements may be performed on the product substrate and / or on dedicated metrology targets. There are various techniques for measuring the microstructures formed in the lithography process, including the use of scanning electron microscopes and various dedicated tools. A form of fast, non-invasive specialized inspection tool is the scatterometer, which directs a beam of radiation onto a target on the substrate surface and measures properties of the scattered or reflected beam. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This may be done, for example, by comparing the reflected beam to data stored in a library of known measurements associated with known substrate properties.

[0006] Such optical scatterometers can be used to measure parameters such as the critical dimensions of a developed photosensitive resist or the overlay error (OV) between two layers formed in or on a patterned substrate. The properties of the substrate can be determined by comparing the properties of the illumination beam before and after the beam has been reflected or scattered by the substrate. Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore desirable to improve the measurement of target mark asymmetry in metrology tools in order to increase capture speed at multiple wavelengths. [Means for solving the problem]

[0008] In some embodiments, the system includes an imaging system, a spatial filter, and a detector. The system is configured to receive a plurality of diffraction orders. The spatial filter is configured to block one or more undesired diffraction orders of the plurality of diffraction orders and pass one or more desired diffraction orders of the plurality of diffraction orders. The spatial filter includes one or more obscurations having an angle-dependent radius that varies with azimuth angle. The detector is configured to receive and measure the intensity of the one or more desired diffraction orders.

[0009] In some embodiments, the spatial filter includes an aperture, the aperture including one or more obscurations having an angle-dependent radius that varies with azimuth from a first radial distance to a second radial distance, and one or more ridges located on inner edges of the one or more obscurations, the aperture configured to rotate about its center.

[0010] In some embodiments, a method includes receiving a plurality of diffraction orders, using a spatial filter to block one or more undesired diffraction orders of the plurality of diffraction orders and pass one or more desired diffraction orders of the plurality of diffraction orders, and measuring an intensity of the one or more desired diffraction orders, wherein the spatial filter includes one or more obscurations having an angle-dependent radius that varies with azimuth angle.

[0011] Further features and advantages of the present disclosure, as well as the structure and operation of various embodiments of the present disclosure, are described in detail below with reference to the accompanying drawings. It is 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 relevant art. [Brief description of the drawings]

[0012] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate the present disclosure and, together with the detailed description, serve to explain the principles of the present disclosure and to enable a person skilled in the relevant art to make and use the embodiments described herein.

[0013] [Figure 1A] 1 is a schematic diagram of a reflective lithographic apparatus according to some embodiments;

[0014] [Figure 1B] 1 is a schematic diagram of a transmissive lithographic apparatus according to some embodiments;

[0015] [Diagram 2] 2 is a more detailed schematic diagram of a reflective lithographic apparatus according to some embodiments;

[0016] [Diagram 3] 1 is a schematic diagram of a lithographic cell according to some embodiments.

[0017] [Figure 4A-4B] 1 is a schematic diagram of an inspection apparatus according to some embodiments.

[0018] [Figure 5A-5C] 1A-1D are schematic diagrams of pupil planes for different target types in accordance with some embodiments.

[0019] [Figure 6A] 1 is a schematic diagram of a spatial filter according to some embodiments.

[0020] [Figure 6B] FIG. 1 is a schematic diagram of a blocker according to some embodiments.

[0021] [Figure 7A-7B] FIG. 1 is a schematic diagram of an optical system according to some embodiments.

[0022] [Figure 8A] 1 is a schematic diagram of a pupil plane according to some embodiments.

[0023] [Fig. 8B-8H] 1 is a schematic diagram of a hybrid spatial filter according to some embodiments.

[0024] [Figure 9] FIG. 1 is a schematic diagram of an optical system according to some embodiments.

[0025] [Figure 10] 4 is a schematic diagram of diffraction orders in a pupil plane according to some embodiments.

[0026] [Figure 11A-11B] 1 is a schematic diagram of a hybrid spatial filter according to some embodiments.

[0027] [Figure 12] FIG. 1 is a schematic diagram of an axicon optical system according to some embodiments.

[0028] [Figure 13] 1 is a schematic diagram of an optical system according to some embodiments.

[0029] [Figure 14] FIG. 1 illustrates a flowchart of a method according to some embodiments.

[0030] Features of the present disclosure will become more apparent from the detailed description set forth below in conjunction with the drawings, in which like reference numbers identify corresponding elements throughout. Generally, like reference numbers in the drawings represent identical, functionally similar, and / or structurally similar elements. Moreover, the leftmost digit(s) of a reference number generally identifies the drawing in which the reference number first appears. Unless otherwise specified, the drawings provided throughout this disclosure should not be construed as drawings to scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] This specification discloses one or more embodiments that incorporate 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 appended claims.

[0032] References in the specification to an embodiment being described, and to "one embodiment," "embodiment," "exemplary embodiment," and the like, indicate that the embodiment being described may include a particular feature, structure, or characteristic, but not every embodiment necessarily needs to include that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one of ordinary skill in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether or not expressly described.

[0033] Spatially relative terms such as "beneath," "below," "lower," "above," "on," "upper," and the like, may be used herein to describe the relationship of one element or feature illustrated in the figures to another element or feature for ease of description. The spatially relative terms are intended to encompass various orientations of the device in use or operation in addition to the orientation shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly as well.

[0034] As used herein, the term "about" refers to a given quantity value that may vary based on the particular technique. Based on the particular technique, the term "about" can refer to a given quantity value that varies, for example, within 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0035] The embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. The embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium that may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include 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.), and others. Furthermore, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be understood that such description is merely for convenience and that such actions actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc.

[0036] 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.

[0037] Lithography system embodiment

[0038] 1A and 1B are schematic diagrams of lithographic apparatus 100 and lithographic apparatus 100', respectively, in which embodiments of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100' each comprise: an illumination system (illuminator) IL that conditions a radiation beam B (e.g. deep ultraviolet radiation or extreme ultraviolet (EUV) radiation), a support structure (e.g. mask table) MT configured to support a patterning device (e.g. mask, reticle, or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device, and a substrate table (e.g. wafer table) WT configured to hold a substrate (e.g. resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate. Lithographic apparatus 100 and lithographic apparatus 100' also comprise 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. comprising one or more dies) of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100', the patterning device MA and the projection system PS are transmissive.

[0039] The illumination system IL may include various optical elements, or combinations thereof, such as refractive optical elements, reflective optical elements, catadioptric optical elements, magnetic optical elements, electromagnetic optical elements, electrostatic optical elements, or other types of optical elements, to direct, shape, or otherwise steer the radiation beam B.

[0040] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to a reference frame, the design of at least one of lithographic apparatuses 100 and 100', and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be for example a frame or a table, which may be fixed or movable as required. By using sensors the support structure MT may ensure that the patterning device MA is positioned at a desired position, for example with respect to the projection system PS.

[0041] The term "patterning device" MA may be broadly interpreted to refer to any device that can be used to impart a radiation beam B with a pattern in its cross-section to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B corresponds to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0042] In this specification, terms such as "inspection apparatus", "metrology system" and the like may be used to refer to, for example, an apparatus or system used to measure characteristics of structures (e.g., overlay error, critical dimension parameters) or an apparatus or system used within a lithographic apparatus to inspect the alignment of a wafer (e.g., an alignment apparatus).

[0043] The patterning device MA may be of a transmissive type (such as lithographic apparatus 100' in FIG. 1B) or a reflective type (such as lithographic apparatus 100 in FIG. 1A). Patterning device MA may include, for example, a mask, a programmable mirror array, or a programmable LCD panel. Masks are well known in lithography and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid masks. A programmable mirror array may, for example, comprise a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The radiation beam is reflected by the matrix of small mirrors and is patterned by the tilted mirrors.

[0044] The term "projection system" PS can encompass any projection system including refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic optics, or a combination thereof, appropriate for the exposure radiation being used, or other factors such as the use of an immersion liquid or a vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation, as other gases will absorb the excess radiation or electrons. Therefore, a vacuum environment may be provided throughout the beam path with the aid of a vacuum wall and vacuum pumps.

[0045] Lithographic apparatus 100 and / or lithographic apparatus 100' may comprise two or more (in which case it is called dual stage) substrate tables WT (and / or two or more mask tables). In such a multi-stage apparatus, the additional substrate tables WT may be used in parallel, or exposure may be taking place on one or more tables whilst preparation steps are being carried out on one or more other substrate tables WT. In some circumstances the additional tables need not be substrate tables WT.

[0046] The lithographic apparatus may be of a type in which at least a part of the substrate is covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. Immersion liquids may also be applied to other spaces in the lithographic apparatus, for example between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not imply that a structure such as the substrate has to be immersed in liquid, but simply that a liquid is between the projection system and the substrate during exposure.

[0047] 1A and 1B, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be separate physical entities, for example if the source SO is an excimer laser. In this case, the source SO is not considered to be part of the lithographic apparatus 100, 100' and the radiation beam B reaches the illuminator IL from the source SO via a beam delivery system BD (FIG. 1B), which may for example include suitable redirecting mirrors and / or beam expanders. Alternatively, the source SO may be an integral part of the lithographic apparatus 100, 100', for example if the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, may be referred to as a radiation system.

[0048] The illuminator IL may comprise an adjuster AD (Figure 1B) for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial values ​​(commonly referred to as "σouter" and "σinner", respectively) of the irradiance distribution in a pupil plane of the illuminator are adjusted. In addition, the illuminator IL may comprise other elements, such as an integrator IN and a condenser CO (Figure 1B). The illuminator IL is used to adjust the radiation beam B to obtain a desired uniformity and intensity distribution in its cross-section.

[0049] Referring to FIG. 1A, a radiation beam B is incident on a patterning device (e.g. mask) MA, which is held on a support structure (e.g. mask table) MT, and is patterned by the patterning device. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g. mask) MA. After reflecting from the patterning device (e.g. mask) MA, the radiation beam B passes through a projection system PS. The projection system PS focuses the beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g. an interferometer, a linear encoder, a capacitive sensor, etc.), the substrate table WT is accurately moved (e.g. to position each of the different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 may be used to align the patterning device (eg mask) MA and substrate W.

[0050] Referring to Figure 1B, a beam of radiation B is incident on a patterning device (e.g. mask MA), which is held on a support structure (e.g. mask table MT), and is patterned by the patterning device. After passing the mask MA, the beam of radiation B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. A portion of the radiation originates from the intensity distribution in the illumination system pupil IPU and traverses the mask pattern without being subjected to diffraction at the mask pattern, creating an image of the intensity distribution at the illumination system pupil IPU.

[0051] The projection system PS projects an image of the mask pattern MP onto a photoresist layer applied on the substrate W. The image is formed by diffracted beams generated from the mark pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Non-zero order diffraction of radiation at the array generates redirected diffracted beams that are redirected perpendicular to the lines. The non-diffracted beams (i.e. the so-called zero order diffracted beams) traverse the pattern without changing their propagation direction. The zero order diffracted beams traverse an upper lens or an upper lens group of the projection system PS, which is upstream of the pupil conjugate PPU of the projection system PS, and reach the pupil conjugate PPU. The part of the intensity distribution in the plane of the pupil conjugate PPU that is associated with the zero order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD is for example arranged in a plane or substantially in a plane that includes the pupil conjugate PPU of the projection system PS.

[0052] The projection system PS is arranged to capture not only the zeroth order diffracted beam but also the first or higher order diffracted beams (not shown) by means of a lens or lens group L. In some embodiments, the resolution enhancing effect of dipole illumination may be exploited by using a dipole illumination for imaging a line pattern extending in a direction perpendicular to the line. For example, a first order diffracted beam interferes with a corresponding zeroth order diffracted beam at the level of the wafer W to create an image of the line pattern MP at the highest possible resolution and process window (i.e., usable depth of focus combined with an acceptable exposure dose deviation). In some embodiments, astigmatism may be reduced by providing opposing quadrant poles (not shown) of the illumination system pupil IPU. Furthermore, in some embodiments, astigmatism may be reduced by blocking the zeroth order beam at the pupil conjugate PPU of the projection system associated with the opposing quadrant pole. This is described in more detail in U.S. Pat. No. 7,511,799 B2, issued Mar. 31, 2009, which is incorporated herein by reference in its entirety.

[0053] With the aid of the second positioner PW and a position sensor IFD (e.g. an interferometer, linear encoder, capacitive sensor, etc.), the substrate table WT can be accurately moved (e.g. to position a different target portion C in the path of the radiation beam B). Similarly, the mask MA can be accurately positioned with respect to the path of the radiation beam B by the first positioner PM and another position sensor (not shown in FIG. 1B ) (e.g. after a mask change from a mask library or during a scan).

[0054] In general, movement of the mask table MT is realized by means of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT is realized by means of a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to the short-stroke module only, or may be fixed. The mask MA and substrate W are aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks (as shown) occupy dedicated target portions, the substrate alignment marks may be located in the areas between the target portions (known as scribe-lane alignment marks). Similarly, in case of more than one die on the mask MA, the mask alignment marks may be located between the dies.

[0055] The mask table MT and patterning device MA can be located inside the vacuum chamber. An in-vacuum robot IVR can be used to move the patterning device, such as a mask, in and out of the vacuum chamber. Alternatively, the mask table MT and patterning device MA can be outside the vacuum chamber and an ex-vacuum robot can be used for various transport tasks similar to the in-vacuum robot IVR. The in-vacuum and ex-vacuum robots need to be calibrated for smooth transport of any payload (e.g. a mask) to the fixed kinematic mount of the transfer station.

[0056] Lithographic apparatus 100, 100' can be used in at least one of the following modes.

[0057] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept substantially stationary while the entire pattern imparted to the radiation beam B is projected onto one target portion C in one go (i.e. a single static exposure), and the substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed.

[0058] 2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously (i.e. a single dynamic exposure) while a pattern imparted to the radiation beam is projected onto a target portion C. The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT is determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0059] 3. In another mode, the support structure (e.g. mask table) MT holds a programmable patterning device and is held substantially stationary, while the substrate table WT is moved or scanned, while a pattern imparted to the radiation beam is projected onto a target portion C. A pulsed radiation source SO is used, and the programmable patterning device is updated each time the substrate table WT is moved during a scan, or as required between successive pulses. This mode of operation is applicable to maskless lithography using a programmable patterning device such as a programmable mirror array.

[0060] The above modes may be combined, modified, or even used in a completely different mode.

[0061] 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. Typically, the EUV radiation source is configured in a radiation system and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV radiation source.

[0062] Figure 2 shows the lithographic apparatus 100 in more detail. The EUV lithographic apparatus 100 comprises a radiation collector apparatus SO, an illumination system IL, and a projection system PS. The radiation collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained within an enclosure 220 of the radiation collector apparatus SO. An EUV radiation emitting plasma 210 is formed by a discharge plasma source. The EUV radiation is generated by a gas or vapor, such as for example Xe gas, Li vapor, or Sn vapor. A high temperature plasma 210 is formed in the gas or vapor, emitting radiation in the EUV region of the electromagnetic radiation spectrum. The high temperature plasma 210 is formed by for example generating an at least partially ionized plasma by an electric discharge. To efficiently generate radiation, a partial pressure of for example 10 Pa of Xe, Li, Sn vapor or other suitable gas or vapor is required. In some embodiments, an excited tin (Sn) plasma is provided to generate the EUV radiation.

[0063] Radiation emitted by the high temperature plasma 210 passes from the source chamber 211 through an optional gas barrier or contaminant trap 230 (sometimes referred to as a contaminant barrier or foil trap) to the collector chamber 212. The gas barrier or contaminant trap 230 is located at or behind the opening of the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 shown herein includes at least a channel structure.

[0064] The collector chamber 212 comprises a radiation collector CO. The radiation collector CO 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 radiation collector CO is reflected by a grating spectral filter 240 and focused into a virtual point source INTF located at an opening of the collector chamber 48. The virtual point source INTF is commonly referred to as an intermediate focus, and the source collector arrangement is arranged such that the intermediate focus INTF is located at or near the opening 219 of the enclosure structure 220. The virtual point source INTF is an image of the radiation emitting plasma 210. The grating spectral filter 240 is used in particular to suppress infrared (IR) radiation.

[0065] The radiation then traverses the illumination system IL, which includes a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA with a desired radiation intensity uniformity at the patterning device MA. Reflection of the radiation beam 221 off the patterning device MA, which is held by the support structure MT, forms a patterned beam 226 which is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by a wafer stage or substrate table WT.

[0066] Typically, more elements than shown may be present in the illumination optics unit IL and projection system PS. A grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Furthermore, more mirrors may be present than shown in Figure 2. For example, one to six additional reflective elements may be present in the projection system PS than shown in Figure 2.

[0067] 2, the collector optical system CO is shown as a nested collector with grazing incidence reflectors 253, 254 and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically about the optical axis O, and this type of collector optical system CO is suitable for use in combination with a discharge plasma source, referred to as a DPP source.

[0068] Exemplary Lithography Cell

[0069] FIG. 3 shows a lithography cell 300, sometimes also referred to as a lithocell or cluster, according to some embodiments. The lithography apparatus 100 or 100′ may form part of the lithography cell 300. The lithography cell 300 may also include one or more apparatuses for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill 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 the different process apparatus, and delivers the substrate to a loading bay LB of the lithography apparatus 100 or 100′. These apparatuses (often collectively referred to as a track) are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, different equipment can be operated to maximize throughput and process efficiency.

[0070] Exemplary Inspection Equipment

[0071] To control the lithographic process and accurately place device features on the substrate, alignment marks are usually provided on the substrate and the lithographic apparatus includes one or more inspection apparatus for accurately placing the marks on the substrate. These alignment apparatus are essentially position measurement apparatus. Different types of marks and different types of alignment apparatus and / or systems are known from different times and different manufacturers. A type of system that is widely used in current lithographic apparatus is based on a self-referencing interferometer as described in U.S. Pat. No. 6,961,116 (den Boef et al.). Typically, the marks are measured separately to obtain X and Y positions. However, combined X and Y measurements can be performed using techniques described in U.S. Publication No. 2009 / 195768 A (Bijnen et al.), the entire disclosures of both of which are incorporated herein by reference.

[0072] 4A shows a schematic cross-sectional view of an inspection apparatus 400 that may be implemented as part of lithographic apparatus 100 or 100' according to some embodiments. In some embodiments, inspection apparatus 400 may be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). Inspection apparatus 400 may further be configured to detect positions of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate relative to a patterning device or other components of lithographic apparatus 100 or 100'. Such alignment of the substrate may ensure accurate exposure of one or more patterns on the substrate.

[0073] In some embodiments, the inspection apparatus 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and an overlay calculation processor 432. The illumination system 412 may be configured to provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more passbands may be in a wavelength spectrum between about 500 nm and about 900 nm. In another example, the one or more passbands may be discrete narrow passbands in a wavelength spectrum between about 500 nm and about 900 nm. The illumination system 412 may further be configured to provide one or more passbands having a substantially constant central wavelength (CWL) value over an extended period of time (e.g., over the lifetime of the illumination system 412). Such a configuration of the illumination system 412 may help prevent shifts in the actual CWL value from the desired CWL value in current alignment systems as discussed above. Also as a result, the use of a constant CWL value can improve the long-term stability and accuracy of an alignment system (eg, inspection tool 400) compared to current alignment tools.

[0074] 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, as shown in FIG. 4A, the radiation beam 413 may be split into radiation sub-beams 415 and 417. The beam splitter 414 may be further configured to direct the radiation sub-beam 415 onto a substrate 420 disposed on a stage 422. In one example, the stage 422 is movable along a direction 424. The radiation sub-beam 415 may be configured to illuminate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 may be coated with a radiation sensitive film. In some embodiments, the alignment mark or target 418 may have 180 degree (i.e., 180°) symmetry. That is, if the alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 may be substantially identical to the non-rotated alignment mark or target 418. The target 418 on the substrate 420 may be (a) a resist layer grating including bars formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on the product layer. Alternatively, the bars may be etched into the substrate. This pattern is subject to chromatic aberrations in the lithographic projection apparatus, in particular the projection system PL, and the illumination symmetry and the presence of such aberrations will manifest themselves in variations in the printed grating. One in-line method used in device manufacturing for the measurement of line widths, pitches, and critical dimensions utilizes a technique known as "scatterometry."Methods of scatterometry are described in Raymond et al., "Multiparameter Grating Metrology Using Optical Scatterometry," J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997), and Niu et al., "Specular Spectroscopic Scatterometry in DUV Lithography," SPIE, Vol. 3677 (1999), both of which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by periodic structures in the target and the resulting reflection spectrum at a given angle is detected. The structures giving rise to the reflection spectrum are reconstructed, for example, using rigorous coupled wave analysis (RCWA) or by comparison with a library of patterns derived by simulation. Thus, the scatterometry data of the printed grating is used to reconstruct the grating. Parameters of the grating, such as line width and shape, may be input to the reconstruction process performed by the processing unit PU from knowledge of the printing step and / or other scatterometry processes.

[0075] In some embodiments, the beam splitter 414 may be further configured to receive the diffracted radiation beam 419 according to an embodiment and split the diffracted radiation beam 419 into at least two radiation sub-beams. As shown in Figure 4A, the diffracted radiation beam 419 may be split into diffracted radiation sub-beams 429 and 439.

[0076] It should be noted that although beam splitter 414 is shown directing radiation sub-beam 415 towards alignment mark or target 418 and diffracted radiation sub-beam 429 towards interferometer 426, the disclosure is not so limited. It will be apparent to one skilled in the art that other optical configurations can be used to achieve similar results in illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0077] As shown in Figure 4A, the interferometer 426 may be configured to receive the radiation sub-beam 417 and the diffracted radiation sub-beam 429 via the beam splitter 414. In an exemplary embodiment, the diffracted radiation sub-beam 429 may be at least a portion of the radiation sub-beam 415 that may be reflected from the alignment mark or target 418. In one example of this embodiment, the interferometer 426 comprises any suitable set of optical elements, for example a combination of prisms, which may be configured to form two images of the alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It will be appreciated that it is not necessary to form a good quality image, but features of the alignment mark 418 should be resolved. The interferometer 426 may further be configured to rotate one of the two images by 180 degrees relative to the other and interferometrically recombine the rotated and unrotated images.

[0078] In some embodiments, the detector 428 may be configured to receive the recombined image via the interferometer signal 427 and detect the resulting interference of the recombined image when the alignment axis 421 of the inspection apparatus 400 passes through a center of symmetry (not shown) of the alignment mark or target 418. According to an exemplary embodiment, such interference may be due to the alignment mark or target 418 being 180° symmetrical and the recombined image constructively or destructively interfering. Based on the detected interference, the detector 428 may be further configured to determine the position of the center of symmetry of the alignment mark or target 418 and, consequently, detect the position of the substrate 420. According to an example, the alignment axis 421 may be aligned with a light beam perpendicular to the substrate 420 and passing through the center of the image rotation interferometer 426. The detector 428 may be further configured to estimate the position of the alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

[0079] In a further embodiment, the detector 428 determines the location of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements: 1. Measuring the position variation (position shift between colors) for various wavelengths; 2. Measuring the positional variation for the various orders (positional shift between the diffraction orders); and 3. Measuring the position variation for different polarizations (position shift between polarizations).

[0080] This data may be obtained, for example, using any type of alignment sensor, such as a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Pat. No. 6,961,116, which employs a self-referencing interferometer with a single detector and four different wavelengths and extracts the alignment signal in software, or an Athena (Advanced Technology using High order ENhancement of Alignment), as described in U.S. Pat. No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector, both of which are incorporated by reference in their entireties herein.

[0081] In some embodiments, the beam analyzer 430 may be configured to receive the diffracted radiation sub-beam 439 and determine its optical state. The optical state may be a measure of the beam wavelength, polarization, or beam profile. The beam analyzer 430 may further be 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 therefore the position of the substrate 420, may be precisely known relative to the stage 422. Alternatively, the beam analyzer 430 may be configured to determine the position of the inspection apparatus 400 or any other reference element such that the center of symmetry of the alignment mark or target 418 may be known relative to the inspection apparatus 400 or any other reference element. The beam analyzer 430 may be a point or imaging polarimeter with some form of wavelength band selectivity. In some embodiments, the beam analyzer 430 may be directly integrated into the inspection apparatus 400 or, according to other embodiments, may be connected via some type of optical fiber, such as polarization-preserving single mode, multimode, or imaging.

[0082] In some embodiments, the beam analyzer 430 may be further configured to measure overlay data between two patterns on the substrate 420. One of these patterns may be a reference pattern on the reference layer. The other pattern may be an exposure pattern on the exposure layer. The reference layer may be an etched layer already present on the substrate 420. The reference layer may be generated by a reference pattern exposed on the substrate by the lithographic 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 lithographic apparatus 100 or 100'. The exposure pattern 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 to calibrate the exposure pattern exposed by the lithographic apparatus 100 or 100', so that after calibration, the offset between the exposure layer and the reference layer may be minimized.

[0083] 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 products, such as the alignment marks, the target 418, or the substrate 420, and may also include optical signature measurements induced by mark processing variations that are a function of illumination variations. The product stack profile may also include product grating profiles, mark stack profiles, and mark asymmetry information. One example of the beam analyzer 430 is the Yieldstar™ manufactured by ASML, Veldhoven, The Netherlands, described in U.S. Pat. No. 8,706,442, which is incorporated herein by reference in its entirety. The beam analyzer 430 may be further configured to process information related to specific characteristics of the exposure pattern in the layer. For example, the beam analyzer 430 may process overlay parameters of the rendered image in that layer (a measure of the accuracy of positioning of that layer relative to the previous layer on the substrate, or the accuracy of positioning of the first layer relative to a mark on the substrate), focus parameters, and / or critical dimension parameters (e.g. line width and its variation). Other parameters include image parameters related to the quality of the rendered image of the exposure pattern.

[0084] In some embodiments, an array of detectors (not shown) may be connected to the beam analyzer 430, allowing the possibility of accurate stack profile detection as discussed below. For example, the detector 428 may be an array of detectors. For the detector array, several options are possible: multimode fiber bundles, individual pin detectors per channel, or CCD or CMOS (linear) arrays. Using multimode fiber bundles allows the dissipating elements to be placed far apart for stability reasons. Individual PIN detectors offer a large dynamic range, but each may require a separate preamplifier. Therefore, the number of elements is limited. A CCD linear array offers a large number of elements that can be read out at high speed, and is particularly useful when phase stepping detection is used.

[0085] In some embodiments, as shown in FIG. 4B, a 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 of the functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418, and therefore the position of the substrate 420, may be precisely 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, such that the center of symmetry of the alignment mark or target 418 may 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 overlay data between the two patterns and a model of the product stack profile of the substrate 420. The second beam analyzer 430' may also be configured to measure the overlay, critical dimensions, and focus of the target 418 in a single measurement.

[0086] In some embodiments, the second beam analyzer 430' may be directly integrated into the inspection apparatus 400, or according to other embodiments, may be connected via some type of optical fiber, such as polarization-preserving single mode, multimode, or imaging. Alternatively, the second beam analyzer 430' and the beam analyzer 430 may 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.

[0087] In some embodiments, the processor 432 receives information from the detector 428 and the beam analyzer 430. For example, the processor 432 may be an overlay calculation processor. The information may include a model of the product stack profile constructed by the beam analyzer 430. Alternatively, the processor 432 may utilize the received information about the product mark to construct a model of the product mark profile. 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 overlay mark profile. The stack model is then used to determine the overlay offset and minimize the spectral effects on the overlay offset measurement. The processor 432 may generate 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 conditions of the illumination beam, the alignment signal, the associated position estimates, the optical conditions at the pupil plane, the image plane, 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 may utilize the basic correction algorithms to characterize the inspection system 400 with respect to the wafer marks and / or alignment marks 418 .

[0088] In some embodiments, the processor 432 may be further configured to determine the printed pattern position offset error relative to the sensor estimate for each mark based on information received from the detector 428 and the beam analyzer 430. This information may include, but is not limited to, the product stack profile, the overlay, critical dimension, and focus measurements of each alignment mark or target 418 on the substrate 420, and the like. The processor 432 may utilize a clustering algorithm to group the marks into sets of similar constant offset errors and generate an alignment error offset correction table based on that information. The clustering algorithm may be based on additional optical stack processing information associated with each set of overlay measurements, position estimates, and offset errors. The overlay is calculated for a number of different marks, for example, overlay targets with positive and negative biases around the programmed overlay offset. The target that measures the smallest overlay is taken as the reference (because it is measured with the highest accuracy). From this measured small overlay and the known programmed overlay of its corresponding target, the overlay error can be estimated. By way of example and not limitation, Table 1 shows how this may be done. The minimum overlay measured in the example shown is -1 nm. However, this relates to a target with a programmed overlay of -30 nm. As a result, the process should have resulted in an overlay error of 29 nm.

[0089] [Table 1] The minimum value may be considered as a reference point, against which an offset between the measured overlay and the expected overlay due to the programmed overlay can be calculated. This offset determines the overlay error for each mark or a set of marks with similar offsets. Thus, in the example of Table 1, the minimum measured overlay was −1 nm at the target location where the programmed overlay was 30 nm. The difference between the expected and measured overlays at other targets is compared to this reference. A table such as Table 1 may also be obtained from the marks and targets 418 under various illumination settings, and the illumination setting that results in the minimum overlay error, and its corresponding calibration factor, may be determined and selected. Following this, the processor 432 may group the marks into sets of similar overlay errors. The criteria for grouping the marks may be adjusted based on different process controls, e.g., different error tolerances for different processes.

[0090] In some embodiments, processor 432 can determine that all or most elements of a group have similar offset errors and can apply an individual offset correction from a clustering algorithm to each mark based on its additive optical stack metrology. Processor 432 can determine a correction value for each mark and feed the correction value back to lithographic apparatus 100 or 100' to correct for overlay errors, for example by providing the correction value to inspection apparatus 400.

[0091] Exemplary Motorized Aperture for Multi-Wavelength Signals

[0092] Alignment is increasingly becoming the major contribution to overlay. There are limits to how much better the optics and hardware can be without increasing cost. There are also physical limitations to how much algorithmic effectiveness can be improved. Mark asymmetries are inherently present on the wafer. In previous generations of mark designs, mark asymmetries were ignored because they are a contribution coming from the mark and not the sensor.

[0093] The intensity signal captured using the intensity channel allows for decoupling of mark asymmetry from actual wafer deformation. Without using the intensity channel, which is defined in detail below, the mark asymmetry can be determined by evaluating and training an alignment recipe (e.g., selecting different wavelengths and colors from the phase measurements) from the overlay data.

[0094] In the phase channel, different diffraction orders can be measured. The signal associated with each diffraction order can change at a different frequency during the scan. Thus, signals of different diffraction orders may be detected simultaneously at the detector. Due to the asymmetry of the marks, the diffraction orders may experience different uncorrelated (depending on the stack, asymmetric mode, and mark design) errors. However, for the intensity channel, each diffraction order is measured independently. In some embodiments, the + / - diffraction orders are the desired diffraction orders (e.g., for 1.6-3.5 μm marks). All other orders (e.g., higher orders) are undesired orders and can be blocked in the intensity channel.

[0095] According to some embodiments, the interferometer 426 and the detector 428 can include (or be part of) one or more phase channels of the metrology system 400 of Figures 4A and 4B, which can be configured to determine the alignment and / or the position of the alignment mark or target 418. In some embodiments, the beam analyzer 430 and / or the beam analyzer 430' can include (or be part of) one or more intensity channels of the metrology system 400 of Figures 4A and 4B.

[0096] 4A and 4B can be designed such that different diffraction orders diffracted from the alignment mark or target 418 are separated, for example, in the beam analyzer 430 and / or the beam analyzer 430′. In other words, the total intensity (e.g., I +total =I +1 +I +2 +I +3 Instead of (or in addition to) measuring the intensity of the different diffraction orders, the intensity channel can measure the intensities of the different diffraction orders separately (e.g., I +1 and I -1 , I +2 and I -2 etc.), where I is the measured intensity. According to some embodiments, by blocking undesired diffraction orders and separately detecting the desired diffraction orders, metrology system 400 can be configured to measure and determine, for example, the intensity imbalance (e.g., intensity difference) of the different diffraction orders. In some aspects, the output of the intensity channel is a parameter Q. Parameter Q can correspond to a measure of the difference in power between the + and - diffraction orders for each wavelength of the multiple wavelengths.

[0097] According to some embodiments, the intensity imbalance of the diffraction orders may be due to asymmetries in the alignment mark or target 418. Additionally or alternatively, the background of the alignment mark or target 418 may also contribute to the intensity imbalance of the diffraction orders.

[0098] In some embodiments, by determining and measuring the intensity imbalance of the diffraction orders, as described in more detail below, the metrology system 400 can determine correction factors that can be used to correct characteristics of the alignment mark or target 418 determined by the metrology system 400 (e.g., alignment, position, overlay errors, etc.).

[0099] In some embodiments, higher diffraction orders may contaminate the algorithm and introduce errors into the mark asymmetry correction (e.g., correction coefficients). For different mark pitches, the spots of higher diffraction orders (order m>1) are located at different locations in the pupil plane. Thus, the desired diffraction orders may move toward or away from the pupil center as a function of grating pitch and wavelength.

[0100] In some embodiments, a single aperture mask can block higher diffraction orders from passing through the optical system for all pitch ranges supported by inspection apparatus 400. For example, the same area of ​​the pupil may allow a first diffraction order spot for 1.6 μm pitch alignment marks, but block higher diffraction orders for 3.2 μm pitch marks.

[0101] FIG. 5A is a schematic diagram of a pupil plane (i.e., pupil image) 500 of a first alignment mark, according to some embodiments. The pupil plane 500 includes a positive first diffraction order 502a and a negative first diffraction order 502b. The pupil plane 500 also includes a positive second diffraction order 504a and a negative second diffraction order 504b. The pitch of the first alignment mark may be, for example, 1.6 μm. In some embodiments, the pitch of the alignment mark may be between 1.6 μm and 3.5 μm. These orders are located at different radial positions in the pupil plane 500. Furthermore, each order may include multiple wavelengths. The multiple wavelengths are indicated by different line types in the pupil plane 500.

[0102] 5B is a schematic diagram of a pupil plane 512 of the second alignment mark according to some embodiments. The pupil plane 512 can include a positive first diffraction order (+1) 506a, a negative first diffraction order (-1) 506b, a positive second diffraction order (+2) 508a, a negative second diffraction order (-2) 508b, a positive third diffraction order (+3) 510a, and a negative third diffraction order (-3) 510b. The pitch of the second alignment mark is 3.2 μm. As shown in FIG. 5B, the second and third diffraction orders pass through the pupil plane 512 in the same area as the first diffraction order of the first alignment mark.

[0103] 5C is a schematic diagram of a pupil plane 514 of a third alignment mark, according to some embodiments. The pupil plane 514 shows diffraction orders in both two lateral directions (e.g., x-direction and y-direction). For example, a diffraction order along the x-direction can exist simultaneously with a diffraction order along the y-direction. The pupil plane 514 can include a positive first diffraction order 516a, a negative first diffraction order 516b, a positive higher diffraction order 518a, and a negative higher diffraction order 518b in the x-direction. The pupil plane 514 can also include a first diffraction order 516d, a negative first diffraction order 516c, a positive higher diffraction order 518d, and a negative higher diffraction order 518c in the y-direction.

[0104] In some embodiments, during scanning of the third alignment mark, the diffraction orders along the x direction and the diffraction orders along the y direction are blocked separately. For example, the diffraction spots arranged along the x direction and the diffraction spots arranged along the y direction are blocked sequentially. In some embodiments, the second alignment mark may be a combined bidirectional (CB) mark or a two-dimensional mark.

[0105] FIG. 6A is a schematic diagram of a spatial filter 600 according to some embodiments. The spatial filter 600 can be configured to block one or more undesired diffraction orders (e.g., higher orders). The spatial filter 600 can include one or more obscurations. For example, the spatial filter 600 (having a central opening) can include obscurations 604a, 604b, 604c, and 604d. In some aspects, the obscurations 604a, 604b, 604c, and 604d can have angle-dependent radii that vary with azimuth angles. The respective radii of each obscuration 604a, 604b, 604c, and 604d can vary from a first radial distance to a second radial distance. In some aspects, the obscurations 604a, 604b, 604c, and 604d can be the same shape. The illustrated shapes of each obscuration 604a, 604b, 604c and 604d are shown by way of example and not by way of limitation.

[0106] In some embodiments, the spatial filter 600 may be a motorized spatial filter. The spatial filter 600 may, for example, rotate about its center in a direction A. Thus, by rotating the spatial filter 600, the radius of the aperture may be changed.

[0107] Spatial filter 600 can be used to block undesired diffraction orders from multiple marks with diffraction spots in the x direction, y direction, and / or ±45°.

[0108] FIG. 6B shows a schematic diagram of a blocker 602 according to some embodiments. The blocker 602 can include an obscuration 606. The obscuration 606 can have a rectangular shape capable of blocking positive and negative diffraction orders along a first direction. The blocker 602 can be a motorized blocker configured to rotate in a direction A about a center. Thus, by rotating the blocker 602, the positive and negative diffraction orders along the first direction can be blocked. For example, if the positive and negative diffraction orders along the y direction are not desired, the blocker 602 can be rotated such that the obscuration 606 is in the y direction. The blocker 602 can then be continuously rotated such that the obscuration 606 is in the x direction to collect measurements associated with the desired diffraction orders in the y direction.

[0109] The spatial filter 600 and the blocker 602 can be independently controlled by motors coupled to a processor or controller.

[0110] Exemplary Apparatus for Target Asymmetry Measurement

[0111] FIG. 7A shows a schematic diagram of an optical system 700 according to some embodiments. In some embodiments, the system 700 may represent a more detailed view of the inspection apparatus 400 (FIGS. 4A and 4B). In some embodiments, the system 700 includes an illumination system 702, an optical system 704, a detection system 706, and a processor 708. The optical system 704 may include a reflective element 710 (such as a spot mirror) and an optical element 712 (such as an objective lens). The reflective element 710 serves as a field stop for the zeroth order diffraction radiation. It should be understood that the depicted structures in the illumination system 702 and the optical system 704 are not limited to the positions shown. The positions of the structures may be changed as needed, for example, to be designed for modular assembly.

[0112] 7A shows a non-limiting depiction of a system 700 for inspecting a target 714 (also referred to as a "target structure") on a substrate 716. The substrate 716 is disposed on an adjustable stage 718 (e.g., a moveable support structure).

[0113] In some embodiments, the target 714 may include a diffractive structure. The target 714 may reflect, refract, diffract, scatter, etc., radiation incident thereon. The target 714 may be an alignment mark or target 418 of Figures 4A and 4B. For ease of explanation, and without limitation, radiation that interacts with the target is referred to throughout as scattered radiation. The scattered radiation may be collected by the optical element 712.

[0114] The illumination system 702 can be configured to generate a radiation beam 736 that illuminates the target 714. The optical system 704 can be configured to collect diffraction orders diffracted from the target 714 and direct the diffraction orders to a detection system 706.

[0115] In some embodiments, the detection system 706 can include a beam splitter 720 (one or more beam splitters) and one or more detectors. The scattered radiation passes through the optical element 712 to the beam splitter 720. The beam splitter 720 can split a portion of the optical signal into two paths. In some embodiments, each path can correspond to a polarization channel. In some aspects, a portion of the optical path passes through the beam splitter 720 to a phase channel (not shown) of the system 700.

[0116] In one embodiment, the optical element 722 (e.g., a split mirror) can split the optical signal into two paths A and B. One path can include one or more positive orders (e.g., +1, +2) and the other path can include one or more negative orders (e.g., -1, -2). Similarly, the optical element 724 can split the optical signal into two paths C and D. The radiation of each path A, B, C, and D can be collected by a respective lens assembly (not shown) that can focus the radiation field onto a respective detector 726A, 726B, 726C, and 726D, respectively. The detectors 726A, 726B, 726C, and 726D can be used as (or as part of) the beam analyzer 430 and / or 430' of Figures 4A and 4B. Each detector can provide a time-varying signal (such as a waveform) synchronized with the physical scanning motion between the system 700 and the target 714. The signal from the detector may be processed by a processor 708 .

[0117] In some embodiments, the detection system 706 can further include a first spatial filter 730A, a second spatial filter 730B, a first blocker 728A, and a second blocker 728B. Each of the first spatial filter 730A, the second spatial filter 730B, the first blocker 728A, and the second blocker 728B can be coupled to a respective motor that is individually controlled. In some aspects, the first spatial filter 730A and the second spatial filter 730B can be controlled to block undesired diffraction orders (e.g., diffraction orders higher than ±1 order).

[0118] In some embodiments, the first blocker 728A and the second blocker 728B can be controlled to block diffraction orders in the x-direction and / or the y-direction. In some aspects, the first blocker 728A and the first spatial filter 730A can be disposed in the optical path between the beam splitter 720 and the optical element 722. In some aspects, the second blocker 728B and the second spatial filter 730B can be disposed in the optical path between the beam splitter 720 and the optical element 724.

[0119] In some embodiments, the first blocker 728A and the second blocker 728B may be similar to the blocker 602 of Figure 6B. In some embodiments, the first spatial filter 730A and the spatial filter 730B may be similar to the spatial filter 600 of Figure 6A.

[0120] In some embodiments, the target 714 is a one-dimensional target. For example, the target 714 may include a grating with segments in the x-direction (e.g., but not limited to grating lines) or a grating with segments in the y-direction. In some embodiments, the target 714 may include segments at diagonal lines or other angles. The target 714 may include dual pitch marks. The target 714 may include segments with different pitches in the x-direction and the y-direction, for example.

[0121] The examples described herein focus on ±1st order diffraction signals as the desired diffraction orders, however it will be understood that the disclosure extends to the capture and analysis of higher orders (e.g., ±2nd orders, ±3rd orders, etc.).

[0122] In some embodiments, the diffraction orders in the first and second directions may be blocked separately for positive and negative orders, as shown in FIG. 7B. The first blocker 728A may be disposed in the positive order path after the optical element 722. The second blocker 728B may be disposed in the negative order path after the optical element 722. In some embodiments, the third blocker 728C and the fourth blocker 728D may be disposed in the positive order path and the negative order path, respectively, after the optical element 724. Each of the first blocker 728A, the second blocker 728B, the third blocker 728C, and the fourth blocker 728D may be coupled to a respective motor (not shown). The motors may be configured to control the first blocker 728A, the second blocker 728B, the third blocker 728C, and the fourth blocker 728D. For example, a motor can be configured to rotate the first blocker 728A to block the positive first diffraction order in the x-direction during a first measurement and to block the positive first diffraction order in the y-direction during a second measurement.

[0123] First blocker 728A, second blocker 728B, third blocker 728C, and fourth blocker 728D may be similar to blocker 602 of Figure 6B. In some embodiments, having four blockers as shown in Figure 7B instead of two blockers has the advantage of minimizing the space requirements between beam splitter 720 and each of optical elements 722 and 724.

[0124] 8A is a schematic diagram of a pupil plane 802 according to some embodiments. The pupil plane 802 can include a spot mirror shadow 804, a first diffraction order 806 at multiple wavelengths, and higher diffraction orders 808 at multiple wavelengths. The first diffraction order 806 can include positive and negative first diffraction orders.

[0125] 8B is a schematic diagram of a hybrid spatial filter 800. In some embodiments, the hybrid spatial filter 800 can be rotated between different positions based on the target type (e.g., CB mark). The hybrid spatial filter 800 can be rotated about its center in direction A. Thus, the hybrid spatial filter 800 rotates such that the desired diffraction orders pass and the undesired diffraction orders are blocked despite the change in the position of the desired diffraction orders due to the target type (e.g., different pitch).

[0126] The hybrid spatial filter 800 (e.g., an aperture mask) is configured to block undesired diffraction orders (e.g., higher diffraction orders) and diffraction orders along undesired directions (e.g., x-direction, y-direction) using a single motor. Thus, the hybrid spatial filter 800 can be used as an alternative to the separate spatial filters 600 and blockers 602 of FIG. 6. Thus, one hybrid spatial filter can be used in each polarization path, as further described below in connection with FIG. 9.

[0127] In some embodiments, the hybrid spatial filter 800 can include a rotatable aperture that includes one or more obscurations 812 with angle-dependent radii. The radius of the obscuration in each section varies from a first radial distance to a second radial distance. In some embodiments, the hybrid spatial filter 800 can include one or more ridges (or discontinuities) 810 located at the inner edge of the one or more obscurations. In some embodiments, the ridges 810 can pass all diffraction orders in the first dimension and block all diffraction orders in the second dimension.

[0128] Embodiments of the present disclosure are not limited to this exemplary design and hybrid spatial filter 800 can include other designs (e.g., different numbers of opaque obscurations / openings, different shapes of obscurations / openings, etc.).

[0129] 8C-8H show schematic diagrams of a hybrid spatial filter 800 in different positions, according to some embodiments. As can be seen in FIG. 8B, only the first diffraction order 806 (positive and negative diffraction orders) along the x-direction passes through. Other diffraction orders are outside the aperture and are blocked by an obscuration 812. For example, diffraction order 808 is blocked.

[0130] The hybrid spatial filter 800 can be rotated as shown in Figures 8C-8H when the position of the desired diffraction order (e.g., 1st diffraction order 806) changes. The diffraction orders shown in Figure 8B correspond to an alignment mark with a pitch of 1.6 μm in the x-direction. Figure 8C shows the diffraction orders for an alignment mark with a pitch of 2 μm in the x-direction. The positions of the 1st diffraction order 806 and the higher diffraction orders 808 have shifted towards the center of the hybrid spatial filter. Thus, the hybrid spatial filter 800 is rotated such that the radius of the aperture is smaller to block the higher diffraction orders 808. For an alignment mark with a pitch of 3.2 μm in the x-direction, the positions of the 1st diffraction order 802 and the higher diffraction orders 808 are shifted further towards the center of the pupil plane as shown in Figure 8D. Thus, the hybrid spatial filter can be rotated further to narrow the aperture and block the higher diffraction orders 808.

[0131] The diffraction orders shown in FIG. 8E correspond to an alignment mark with a pitch of 1.6 μm in the y-direction. FIG. 8F shows the diffraction orders for an alignment mark with a pitch of 2 μm in the y-direction. The positions of the first diffraction order 806 and the higher diffraction orders 808 have shifted toward the center of the hybrid spatial filter. Thus, the hybrid spatial filter 800 can be rotated to have a smaller aperture radius to block the higher diffraction orders 808. For an alignment mark with a pitch of 3.2 μm in the x-direction, the positions of the first diffraction order 802 and the higher diffraction orders 808 have shifted further toward the center of the pupil plane, as shown in FIG. 8G. Thus, the hybrid spatial filter 800 can be rotated to have a narrower aperture to block the higher diffraction orders 808.

[0132] The diffraction orders shown in FIG. 8H correspond to a two-dimensional alignment mark with a pitch of 2 μm in the y and x directions. The diffraction orders appear in the x and y directions. The hybrid spatial filter 800 is rotated such that one or more ridges (or discontinuities) 810 block the diffraction orders along the y direction. Additionally, higher diffraction orders 808 along the x direction are blocked. The pitches shown in these figures are provided by way of example and not limitation.

[0133] FIG. 9 is a schematic diagram of an optical system 900 according to some embodiments. In some embodiments, the system 900 may represent a more detailed view of the inspection apparatus 400 (FIGS. 4A and 4B). In some embodiments, the system 900 includes an illumination system 902, an optical system 904, a detection system 906, and a processor 908. The optical system 904 may include a reflective element 910 (such as a spot mirror) and an optical element 912 (such as an objective lens). The reflective element 910 may function as a field stop for zero-order diffraction radiation. It should be understood that the structures depicted in the illumination system 902 and the optical system 904 are not limited to the depicted positions. The positions of the structures may be changed as needed, for example, as designed for module assembly.

[0134] 9 shows a non-limiting depiction of a system 900 inspecting a target 914 (also referred to as a "target structure") on a substrate 916. The substrate 916 is positioned on an adjustable stage 918 (e.g., a moveable support structure).

[0135] In some embodiments, the target 914 may include a diffractive structure. The target 914 may reflect, refract, diffract, scatter, etc. radiation. For ease of explanation, and without limitation, radiation that interacts with the target is referred to throughout as scattered radiation. The scattered radiation may be collected by the optical element 912.

[0136] The detection system 906 may include a beam splitter 920 (one or more beam splitters) and one or more detectors. The scattered radiation passes through the optical element 912 to the beam splitter 920. The beam splitter 920 may split a portion of the optical signal into two paths. In some embodiments, each path may correspond to a polarization channel.

[0137] In some embodiments, the optical element 922 (e.g., a split mirror) can split the optical signal into two paths A and B. One path can include one or more positive orders (e.g., +1, +2) and the other path can include one or more negative orders (e.g., -1, -2). Similarly, the optical element 924 can split the optical signal into two paths C and D. The radiation of each path A, B, C, and D can be collected by a respective lens assembly (not shown) that can focus the radiation field onto each detector 926A, 926B, 926C, and 926D, respectively. Each detector can provide a time-varying signal (e.g., a waveform) synchronized with the physical scanning motion between the system 900 and the target structure 914. The signals from the detectors can be processed by the processor 908. The detection system 906 can further include one or more phase channels (not shown).

[0138] In some embodiments, the detection system 906 may further include a first hybrid spatial filter 932A and a second hybrid spatial filter 932B. Each of the first hybrid spatial filter 932A and the second hybrid spatial filter 932B may be coupled to a respective motor that is individually controlled. In some aspects, the first hybrid spatial filter 932A and the second hybrid spatial filter 932B may be controlled to block undesired diffraction orders in one lateral direction. For example, the first hybrid spatial filter 932A and the second hybrid spatial filter 932B may block all diffraction orders in one direction and one or more undesired diffraction orders (e.g., diffraction orders higher than 1) in the other direction.

[0139] A first hybrid spatial filter 932A can be disposed between the optical element 922 and the beam splitter 920 (e.g., the x-polarization path). A second hybrid spatial filter 932B can be disposed between the beam splitter 920 and the optical element 924 (e.g., the y-polarization path).

[0140] 10 illustrates a graph 1000 of diffraction orders at a pupil plane, according to some embodiments. In some embodiments, each diffraction order can include multiple wavelengths. For example, the target 418 in FIGS. 4A and 4B can be illuminated using multiple wavelengths.

[0141] In some embodiments, the first diffraction order 1002 may include a cluster of wavelengths from 508 nm to 885 nm at increasing pupil diameter positions, for example. The diffraction orders at multiple wavelengths are shown with different line types. The second diffraction orders 1004 may include a cluster of wavelengths from 508 nm to 885 nm at increasing pupil diameter positions. As shown in graph 1000, the second diffraction orders 1004 (as a group) are located radially further away than the first diffraction orders 1002. As shown in graph 1000, the third diffraction order 1006 is located radially further away than the second diffraction orders 1004.

[0142] In some embodiments, the second order at 508 nm overlaps with the first order at 885 nm, as indicated by arrow 1008, so the spatial filter (e.g., hybrid spatial filter, spatial filter, etc.) may not be able to completely separate the orders. In some aspects, the first diffraction order at the longest wavelength of the multiple wavelengths may overlap with the second diffraction order at the shortest wavelength of the multiple wavelengths. Thus, not all of the second order light is blocked, which may corrupt the intensity measurement of the shortest wavelength and impair the performance of the intensity channel correction.

[0143] 11A is a schematic diagram of a hybrid spatial filter 1102 according to some embodiments. A first diffraction order 1108 at a first wavelength and a second diffraction order 1110 at a second wavelength may overlap. As mentioned above, a spatial filter (e.g., hybrid spatial filter 800 of FIG. 8, spatial filter 600 of FIG. 6) may pass both the first diffraction order 1108 at a first wavelength and the second diffraction order 1110 at a second wavelength, which may adversely affect the measurement of the intensity channel.

[0144] In some embodiments, a variable color filter 1106 can be used to block the second order of the second wavelength, as shown in Figure 1 IB. In some aspects, the variable color filter 1106 comprises a coated glass surface placed behind a spatial filter (e.g., hybrid spatial filter 800 of Figure 8, spatial filter 600 of Figure 6). In some embodiments, the variable color filter and spatial filter are bonded together.

[0145] In some embodiments, the hybrid spatial filter 1104 can include a coating that can pass one or more of the wavelengths and block one or more of the wavelengths. For example, the coating can pass wavelengths at the upper end of the band (e.g., 500 nm to 900 nm) and block wavelengths at the lower end of the band. In some embodiments, the coating is disposed on the glass only in a narrow region around the edge of the opening of the hybrid spatial filter 1104, as shown in FIG. 11B. Thus, the hybrid spatial filter 1104 can pass a first diffraction order 1108 at a first wavelength (e.g., the longest wavelength of the multiple wavelengths) and block a second diffraction order 1110 at a second wavelength (e.g., the shortest wavelength of the multiple wavelengths). In some aspects, errors in the measurement of Q are reduced.

[0146] FIG. 12 shows a schematic diagram of an axicon system 1200 according to some embodiments.

[0147] The axicon system 1200 may include a first axicon including a first optical element 1202 and a second optical element 1204. The first axicon expands the beam in the pupil. A spatial filter 1210 (e.g., hybrid spatial filter 800 in FIG. 8B, spatial filter 600 in FIG. 6) is placed in the expanded profile. A second axicon including a third optical element 1206 and a fourth optical element 1208 may return the beam to its original diameter. In some embodiments, the first diffraction order 1212 at the first wavelength is separated from the second diffraction order 1214 at the second wavelength. The spatial filter 1210 may block the second diffraction order 1214 at the second wavelength. The second axicon has a mirrored design with respect to the first axicon to restore the wavefront of the first diffraction order 1212 at the first wavelength. In some embodiments, the apex angles of each of the first optical element 1202, the second optical element 1204, the third optical element 1206, and the fourth optical element 1208 may be equal to one another. In some aspects, the apex angles may be equal to 120°. In some aspects, the first axicon and the second axicon may be 7 mm apart, and the total length of the axicon optics may be equal to 48 mm.

[0148] FIG. 13 is a schematic diagram of an optical system 1300 according to some embodiments. In some embodiments, the system 1300 may represent a more detailed view of the inspection apparatus 400 (FIGS. 4A and 4B). In some embodiments, the system 1300 includes an illumination system 1302, an optical system 1304, a detection system 1306, and a processor 1308. The optical system 1304 may include a reflective element 1310 (e.g., a spot mirror) and an optical element 1312 (e.g., an objective lens). The reflective element 1310 may function as a field stop for zero-order diffraction radiation. It should be understood that the structures depicted in the illumination system 1302 and the optical system 1304 are not limited to the depicted positions. The positions of the structures may be changed as needed, for example, as designed for module assembly.

[0149] 13 shows a non-limiting depiction of a system 1300 for inspecting a target 1314 (also referred to as a "target structure") on a substrate 1316. The substrate 1316 is positioned on an adjustable stage 1318 (e.g., a moveable support structure).

[0150] In some embodiments, the target 1314 may include a diffractive structure. The target 1314 may reflect, refract, diffract, scatter, etc. radiation. The target 1314 may be the alignment mark or target 418 of Figures 4A and 4B. For ease of explanation, and without limitation, radiation that interacts with the target is referred to throughout as scattered radiation. The scattered radiation may be collected by the optical element 1312.

[0151] The illumination system 1302 can be configured to generate a radiation beam 1336 that illuminates the target 1314. The optical system 1304 can be configured to collect diffraction orders diffracted from the target 1314 and direct the diffraction orders to a detection system 1306.

[0152] In some embodiments, the detection system 1306 can include a beam splitter 1320 (one or more beam splitters) and one or more detectors. The scattered radiation passes through the optical element 1312 to the beam splitter 1320. The beam splitter 1320 can split a portion of the optical signal into two paths. In some embodiments, each path can correspond to a polarization channel. In some aspects, a portion of the optical path passes through the beam splitter 1320 to a phase channel (not shown) of the system 1300.

[0153] In one embodiment, the optical element 1322 (e.g., a split mirror) can split the optical signal into two paths A and B. One path can include one or more positive orders (e.g., +1, +2) and the other path can include one or more negative orders (e.g., -1, -2). Similarly, the optical element 1324 can split the optical signal into two paths C and D. The radiation of each path A, B, C, and D can be collected by a respective lens assembly (not shown) that can focus the radiation field onto each detector 1326A, 1326B, 1326C, and 1326D, respectively. The detectors 1326A, 1326B, 1326C, and 1326D can be used as (or as part of) the beam analyzer 430 and / or 430' of Figures 4A and 4B. Each detector may provide a time-varying signal (such as a waveform) synchronized with the physical scanning motion between the system 1300 and the target structure 1314. The signals from the detectors may be processed by a processor 1308.

[0154] In some embodiments, the detection system 1306 may further include a first axicon optic 1334A and a second axicon optic 1334B. The first axicon optic 1334A and the second axicon optic 1334B may be similar to the axicon optic 1200 of FIG.

[0155] In some embodiments, the target 1314 can be a one-dimensional target. For example, the target 1314 can include a grating with segments in the x-direction (e.g., but not limited to grating lines) or a grating with segments in the y-direction. In some embodiments, the target 1314 can include diagonal segments or segments of any other angle. The target 1314 can include dual pitch marks. The target 1314 can include, for example, segments in the x-direction and y-direction with different pitches.

[0156] FIG. 14 illustrates a flowchart 1400 of method steps for performing at least the functions described with reference to FIGS. 4A, 4B, 7A, 7B, 9, and / or 13, according to some embodiments.

[0157] In step 1402, multiple diffraction orders are received (e.g., with an objective lens of an optical system). In step 1404, a spatial filter is used to block one or more undesired diffraction orders and pass one or more desired diffraction orders. In some aspects, the spatial filter may include one or more obscurations with an angle-dependent radius that varies with azimuth angle. In some aspects, the spatial filter may be rotated (e.g., using a motor) based on the type of target. The multiple diffraction orders may be a beam of radiation scattered from the target at multiple wavelengths.

[0158] The intensities of one or more desired diffraction orders are measured, step 1406. In some embodiments, a characteristic of the target is determined based on a difference in the measured intensities of the positive and negative diffraction orders for the at least one desired diffraction order.

[0159] The method steps of Figure 14 may be performed in any conceivable order, and not all steps need to be performed. Furthermore, the method steps of Figure 14 described above merely reflect example steps and are not limiting. That is, further method steps and functions may be envisioned based on the embodiments described with reference to Figures 1-13.

[0160] The embodiments can be further described using the following clauses. 1. An imaging system configured to receive a plurality of diffraction orders; a spatial filter configured to block one or more undesired diffraction orders of the plurality of diffraction orders and pass one or more desired diffraction orders of the plurality of diffraction orders, the spatial filter comprising one or more obscurations having an angle-dependent radius that varies with azimuth angle; and a detector configured to receive and measure the intensities of the one or more desired diffraction orders; A system comprising: 2. The system of claim 1, wherein the spatial filter includes two or more sections, the radius of obscuration of each section varying from a first radial distance to a second radial distance. 3. The system of claim 1, wherein the spatial filter is a motorized spatial filter, the spatial filter being configured to rotate about its center to adjust for changing positions of the one or more desired diffraction orders. 4. The system of claim 3, wherein the spatial filter is further configured to block the one or more desired diffraction orders in a first lateral direction and pass the one or more desired diffraction orders in a second lateral direction, the first lateral direction being different from the second lateral direction. 5. The system of claim 4, wherein the spatial filter is motorized and rotatable about a first axis, the first axis extending perpendicular to a plane defined by the first lateral direction and the second lateral direction. 6. Further comprising a blocker configured to block the one or more desired diffraction orders in a first lateral direction and pass the one or more desired diffraction orders in a second lateral direction; the first lateral direction is different from the second lateral direction; The blocker is actuated by a motor; The motion of the blocker is rotation around its center. Item 3. The system according to item 3. 7. The system of claim 1, wherein the multiple diffraction orders are beams of scattered radiation at multiple wavelengths. 8. The system of claim 7, wherein the one or more desired diffraction orders are ±1st diffraction orders. 9. A first axicon system configured to spatially separate a first diffraction order at a first wavelength from a second diffraction order at a second wavelength; a second axicon system configured to realign a wavefront of the first diffraction order at the first wavelength; the spatial filter is disposed in an optical path between the first axicon system and the second axicon system; 8. The system of claim 7, wherein a position of the first diffraction order at the first wavelength coincides with a position of the second diffraction order at the second wavelength. 10. Further comprising a filter configured to block one or more wavelengths of the plurality of wavelengths; Item 8. The system of item 7, wherein the filter is positioned in an optical path of the beam of scattered radiation at the multiple wavelengths before the spatial filter. 11. The spatial filter further comprises a coating; the coating is configured to block one or more wavelengths of the plurality of wavelengths; 8. The system of claim 7, wherein the coating is deposited on an inner edge of the one or more obscurations. 12. The spatial filter is a motorized spatial filter; a radiation source configured to generate a beam of radiation; an optical system configured to receive the beam along an optical axis and direct it toward a target to generate scattered radiation from the target; Item 1, the system further comprising: a processor configured to control movement of the motor-driven spatial filter based on the type of the target. 13. The system of claim 12, wherein the processor is further configured to determine a characteristic of the target based on a difference in measured intensity between a positive diffraction order and a negative diffraction order for at least one desired diffraction order of the one or more desired diffraction orders of the plurality of diffraction orders. 14. One or more obscurations having an angle-dependent radius that varies with azimuth angle from a first radial distance to a second radial distance; one or more ridges located on an inner edge of the one or more obscurations; an aperture comprising: The aperture is configured to rotate about its center. 15. The spatial filter of claim 14, wherein the spatial filter comprises two or more sections, the angular dependent radius of obscuration in each section varying from the first radial distance to the second radial distance. 16. The aperture further comprises a coating configured to block one or more wavelengths; Item 15. The spatial filter of item 14, wherein the coating is deposited on an inner edge of the one or more obscurations. 17. The spatial filter of claim 14, wherein the one or more ridges are configured to block radiation in a first direction and pass radiation in a second direction, the first direction being orthogonal to the second direction. 18. Receiving a plurality of diffraction orders; using a spatial filter to block one or more undesired diffraction orders of the plurality of diffraction orders and pass one or more desired diffraction orders of the plurality of diffraction orders; measuring the intensities of the one or more desired diffraction orders, the spatial filter comprising one or more obscurations having an angle-dependent radius that varies with azimuth angle; The method includes: 19. The method of claim 18, wherein the multiple diffraction orders are a beam of radiation scattered from a target at multiple wavelengths, and further comprising rotating the spatial filter based on a characteristic of the target. 20. The method of claim 19, further comprising determining a characteristic of the target based on a difference in measured intensity between a positive diffraction order and a negative diffraction order for at least one desired diffraction order of the one or more desired diffraction orders of the plurality of diffraction orders.

[0161] Although the use of lithography apparatus in the manufacture of ICs is described as an example herein, it should be understood that lithography apparatus can be applied to other applications, such as integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, etc. In these other applications, a person skilled in the art will understand that the terms "wafer" and "die" herein are considered specific examples of the more general terms "substrate" and "target portion", respectively. The substrate may be processed by a track unit (typically a tool that applies a layer of resist to the substrate and develops the exposed resist) and / or a metrology unit before or after exposure. Where applicable, the disclosure herein may also be applied to these or other substrate processing apparatus. The substrate may also be processed multiple times, for example to manufacture multi-layer ICs, in which case the term substrate herein refers to a substrate including multiple processing layers that have already been processed.

[0162] Although particular reference has been made above to the use of embodiments of the present disclosure in the context of optical lithography, it will be understood that the present disclosure may also be used in other applications, such as imprint lithography, and is not limited to optical lithography, where the context permits. In imprint lithography, a topography of a patterning device defines the pattern created on a substrate. The topography of the patterning device is pressed into a layer of resist supplied to the substrate and the resist is subsequently cured by electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is then moved away from the resist, leaving a pattern behind after the resist has been cured.

[0163] It is to be understood that the phraseology or terminology used herein is for the purpose of description and not of limitation, and that the terminology or terminology used herein is to be interpreted by one of ordinary skill in the art in light of the teachings of the present disclosure.

[0164] As used herein, the terms "radiation", "beam of radiation", and the like include any electromagnetic radiation, such as ultraviolet (UV) radiation (e.g., having a wavelength λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft x-ray) radiation (e.g., having a wavelength in the range of 5-20 nm (e.g., 13.5 nm) or hard x-ray operating below 5 nm), and matter beams, such as ion beams or electron beams. The terms "light", "illumination", and the like can refer to non-material radiation (e.g., photons, UV, x-rays, and the like). Generally, radiation having a wavelength between about 400 and about 700 nm is considered visible radiation, and radiation having a wavelength between about 780 and 3000 nm (or greater) is considered infrared radiation. UV refers to radiation having a wavelength of approximately 100 to 400 nm. In lithography, the term "UV" is also used for the wavelengths produced by mercury discharge lamps. These are G-line at 436 nm, H-line at 405 nm, and I-line at 365 nm. Vacuum UV (VUV, i.e. UV absorbed by gases) refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having a wavelength of 126 nm to 428 nm. In some embodiments, an excimer laser can generate DUV radiation for use in lithography equipment. It should be understood that radiation having a wavelength of, for example, 5-20 nm, refers to radiation having a certain wavelength range, at least a portion of the range of 5-20 nm.

[0165] It should be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections describe one or more embodiments of the disclosure contemplated by the inventors, but do not describe all exemplary embodiments. As such, they are not intended to limit the scope of the disclosure and the appended claims in any manner.

[0166] The present disclosure has been described above with the aid of functional components illustrating the implementation of specific functions and relationships. The boundaries of these functional components have been arbitrarily defined for the convenience of description. Other boundaries may also be defined as long as the specific functions and relationships are appropriately performed.

[0167] Although specific embodiments of the present disclosure have been described above, it will be understood that the embodiments of the present disclosure can be practiced otherwise than as described. The description is given by way of illustration and not by way of limitation. Thus, it will be apparent to one skilled in the art that modifications can be made to the present disclosure as described without departing from the scope of the claims set forth below.

[0168] The above description of the specific embodiments fully discloses the general nature of the present disclosure, and thus, by applying knowledge within the skill of the art, such specific embodiments can be readily modified and / or adapted for various applications without undue experimentation and without departing from the general concept of the present disclosure. Accordingly, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0169] The breadth and scope of protection 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. an imaging system configured to receive a plurality of diffraction orders; a spatial filter configured to block one or more undesired diffraction orders of the plurality of diffraction orders and to pass one or more desired diffraction orders of the plurality of diffraction orders, the spatial filter comprising one or more obscurations having an angle-dependent radius that varies with azimuth angle; and a detector configured to receive and measure the intensities of the one or more desired diffraction orders; A system comprising:

2. The system of claim 1 , wherein the spatial filter includes two or more sections, the radius of obscuration of each section varying from a first radial distance to a second radial distance.

3. 10. The system of claim 1, wherein the spatial filter is a motorized spatial filter, the spatial filter configured to rotate about its center to adjust for changing positions of the one or more desired diffraction orders.

4. 4. The system of claim 3, wherein the spatial filter is further configured to block the one or more desired diffraction orders in a first lateral direction and pass the one or more desired diffraction orders in a second lateral direction, the first lateral direction being different from the second lateral direction.

5. 5. The system of claim 4, wherein the spatial filter is motorized and rotatable about a first axis, the first axis extending perpendicular to a plane defined by the first lateral direction and the second lateral direction.

6. a blocker configured to block the one or more desired diffraction orders in a first lateral direction and pass the one or more desired diffraction orders in a second lateral direction; the first lateral direction is different from the second lateral direction; The blocker is actuated by a motor; The motion of the blocker is rotation around its center. The system of claim 3.

7. The system of claim 1 , wherein the multiple diffraction orders are beams of scattered radiation at multiple wavelengths.

8. The system of claim 7 , wherein the one or more desired diffraction orders are ±1 st diffraction orders.

9. a first axicon system configured to spatially separate a first diffraction order at a first wavelength from a second diffraction order at a second wavelength; a second axicon system configured to realign a wavefront of the first diffraction order at the first wavelength, the spatial filter is disposed in an optical path between the first axicon system and the second axicon system; The system of claim 7 , wherein a position of the first diffraction order at the first wavelength coincides with a position of the second diffraction order at the second wavelength.

10. a filter configured to block one or more wavelengths of the plurality of wavelengths; The system of claim 7 , wherein the filter is positioned in an optical path of the beam of scattered radiation at the multiple wavelengths before the spatial filter.

11. the spatial filter further comprising a coating; the coating is configured to block one or more wavelengths of the plurality of wavelengths; The system of claim 7 , wherein the coating is deposited on an inner edge of the one or more obscurations.

12. the spatial filter is a motorized spatial filter; a radiation source configured to generate a beam of radiation; an optical system configured to receive the beam along an optical axis and direct it toward a target to generate scattered radiation from the target; The system of claim 1 , further comprising: a processor configured to control movement of a motorized spatial filter based on the type of target.

13. 13. The system of claim 12, wherein the processor is further configured to determine a characteristic of the target based on a difference in measured intensities between positive and negative diffraction orders for at least one desired diffraction order of the one or more desired diffraction orders of the plurality of diffraction orders.

14. one or more obscurations having an angle-dependent radius that varies with azimuth angle from a first radial distance to a second radial distance; one or more ridges located on an inner edge of the one or more obscurations; an aperture comprising: The aperture is configured to rotate about its center.

15. 15. The spatial filter of claim 14, wherein the spatial filter comprises two or more sections, the angular dependent radius of obscuration in each section varying from the first radial distance to the second radial distance.

16. the aperture further comprises a coating configured to block one or more wavelengths; The spatial filter of claim 14 , wherein the coating is deposited on an inner edge of the one or more obscurations.

17. 15. The spatial filter of claim 14, wherein the one or more ridges are configured to block radiation in a first direction and pass radiation in a second direction, the first direction being orthogonal to the second direction.

18. receiving a plurality of diffraction orders; using a spatial filter to block one or more undesired diffraction orders of the plurality of diffraction orders and pass one or more desired diffraction orders of the plurality of diffraction orders; measuring the intensities of the one or more desired diffraction orders, the spatial filter comprising one or more obscurations having an angle-dependent radius that varies with azimuth angle; The method includes:

19. 20. The method of claim 18, wherein the multiple diffraction orders are a beam of radiation scattered from a target at multiple wavelengths, and further comprising rotating the spatial filter based on a characteristic of the target.

20. 20. The method of claim 19, further comprising determining a characteristic of the target based on a difference in measured intensities of positive and negative diffraction orders for at least one desired diffraction order of the one or more desired diffraction orders of the plurality of diffraction orders.

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