Alignment system, lithography apparatus and method for resist tilt

Abstract

An alignment system includes a radiation source, a self-reference interferometer, a spatial filter assembly, a measurement device, and a detection system. The radiation source generates one or more illumination beams that direct the one or more illumination beams toward an alignment target on the wafer. The self-reference interferometer receives one or more diffracted beams and generates an alignment signal comprising diffracted sub-beams, where the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about an alignment axis, and spatially overlapping. The spatial filter component restores the modulation depth of the alignment signal. The measuring device measures a light intensity measurement of the alignment signal. The detection system determines a position of the alignment target based on a light intensity measurement of the alignment signal.

Description

Cross-reference to related applications

[0001] This application claims priority to U.S. Application No. 63 / 518598, filed August 10, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] This disclosure relates to measurement systems, such as alignment systems for measuring the position of alignment marks in lithography apparatuses and systems. Background Technology

[0003] A photolithography apparatus is a machine that applies a desired pattern onto a substrate (typically onto a target portion of the substrate). Photolithography apparatuses can be used, for example, in the fabrication of integrated circuits (ICs). In this case, a patterning apparatus (which may be a mask or a stencil) can be used to generate a circuit pattern to be formed on a single layer of the IC. This pattern can be transferred onto a target portion of a substrate (e.g., a silicon wafer) that includes, for example, a portion of one or more dies. Typically, the transfer of the pattern is performed by imaging onto a radiation-sensitive material layer (photoresist, or simply "resist") provided on the substrate. Generally, a single substrate will contain a network of adjacent target portions that are patterned sequentially. Known photolithography apparatuses include so-called steppers and so-called scanners. In a stepper, each target portion is irradiated by exposing the entire pattern onto the target portion at once. In a scanner, each target portion is irradiated by scanning the pattern via a radiation beam in a given direction ("scanning" direction) while simultaneously scanning the target portion parallel or antiparallel to that scanning direction. The pattern can also be transferred from the patterning apparatus to the substrate by imprinting the pattern onto the substrate.

[0004] During photolithography operations, different processing steps may require the sequential formation of different layers on a substrate. Accordingly, it may be necessary to position the substrate with high precision relative to a pre-formed pattern. Generally, alignment marks are placed on the substrate to be aligned and positioned with reference to a second object. The photolithography apparatus can use alignment devices to detect the position of the alignment marks and use them to align the substrate, thereby ensuring accurate exposure from the mask. Misalignment between alignment marks at two different layers is measured as overlap error.

[0005] To monitor the photolithography process, parameters of the patterned substrate are measured. These parameters may include, for example, overlap errors between adjacent layers formed in or on the patterned substrate, and the critical linewidth of the developed photoresist. Such measurements can be performed on the product substrate and / or on a dedicated measurement target. Various techniques exist for measuring the microstructures formed during photolithography, including the use of scanning electron microscopy and various specialized tools. One rapid, non-invasive form of specialized inspection tool is a scattering instrument, in which a beam of radiation is directed onto a target on the substrate surface, and the properties of the scattered or reflected beam are measured. The properties of the substrate can be determined by comparing the properties of the beam before and after it is reflected or scattered by the substrate. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. A spectroscopic scattering instrument directs a broadband beam of radiation onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered over a specific narrow angular range. In contrast, an angle-resolved scattering instrument uses a monochromatic beam of radiation and measures the intensity of the scattered radiation as a function of angle.

[0006] This type of optical scattering instrument can be used to measure parameters such as the critical size of a developed photoresist, or the overlap 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 is reflected or scattered by the substrate.

[0007] Current alignment sensors use a self-referenced interferometer to interfere with the positive and negative orders of diffracted light from a substrate to form an alignment signal. The detection system can measure the peak position of the alignment signal and compare it with an expected peak position to determine the location of the alignment mark on the substrate. As the resist thickness on the substrate increases, material inconsistencies can cause resist tilting over the alignment mark. Resist tilting can cause alignment signal degradation (e.g., loss of modulation depth), which can lead to alignment errors in the detection system. Summary of the Invention

[0008] Accordingly, it is desirable to recover the degraded alignment signal caused by resist tilting. For example, based on the aspects described herein, the recovered alignment signal can be used to perform optical inspection procedures.

[0009] In some aspects, an alignment system may include a radiation source, a self-reference interferometer, a spatial filter assembly, a measuring device, and a detection system. The radiation source may generate one or more illumination beams and direct them toward an alignment target on a wafer. One or more diffracted beams may be reflected from the alignment target, wherein the one or more diffracted beams may include at least one positive diffraction order and one negative diffraction order. The self-reference interferometer may receive one or more diffracted beams and generate an alignment signal comprising diffracted sub-beams, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about an alignment axis, and are spatially overlapping. The spatial filter assembly may recover the modulation depth of the alignment signal. The measuring device may measure the optical intensity of the alignment signal. The detection system may determine the position of the alignment target based on the optical intensity measurement of the alignment signal.

[0010] In some aspects, a photolithography apparatus may include an illumination system, a projection system, and an alignment system. The illumination system illuminates the patterning apparatus. The projection system projects an image from the patterning apparatus onto a wafer. The alignment system may include a radiation source, a self-reference interferometer, a spatial filter assembly, a measurement device, and a detection system. The radiation source generates one or more illumination beams and directs them toward an alignment target on the wafer. One or more diffracted beams may be reflected from the alignment target, wherein the one or more diffracted beams may include at least one positive diffraction order and one negative diffraction order. The self-reference interferometer receives one or more diffracted beams and generates an alignment signal comprising diffracted sub-beams, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about an alignment axis, and are spatially overlapping. The spatial filter assembly recovers the modulation depth of the alignment signal. The measurement device measures the light intensity of the alignment signal. The detection system determines the position of the alignment target based on the light intensity measurements of the alignment signal.

[0011] In some aspects, a method may include generating one or more illumination beams using a radiation source. The method may also include guiding one or more illumination beams toward an alignment target on a wafer using the radiation source. The method may further include receiving one or more diffracted beams reflected from the alignment target using a self-reference interferometer, wherein the one or more diffracted beams include at least one positive diffraction order and one negative diffraction order. The method may further include generating an alignment signal comprising diffracted sub-beams using the self-reference interferometer, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about an alignment axis, and are spatially overlapping. The method may further include recovering the modulation depth of the alignment signal using a spatial filter assembly. The method may further include measuring the light intensity of the alignment signal using a measuring device. The method may further include determining the position of the alignment target using a detection system based on the light intensity measurements of the alignment signal.

[0012] Further features of various aspects of this disclosure are described in detail below with reference to the accompanying drawings. Note that this disclosure is not limited to the specific aspects described herein. These aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the art based on the teachings contained herein. Attached Figure Description

[0013] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, serve to explain the principles of the disclosure and to enable those skilled in the art to make and use the aspects described herein.

[0014] Figure 1A A reflective lithography apparatus based on some aspects is shown.

[0015] Figure 1B A transmission lithography apparatus based on some aspects is shown.

[0016] Figure 2 More details of the reflective lithography apparatus are shown, based on some aspects.

[0017] Figure 3 The photolithography unit is shown according to some aspects.

[0018] Figure 4A and Figure 4B The inspection device is shown according to some aspects.

[0019] Figure 5 A photolithography apparatus with a spatial filter assembly is shown according to some aspects.

[0020] Figure 6 A spatial filter assembly with a reference grating is shown according to some aspects.

[0021] Figures 7A to 7C A reference grating is shown according to some aspects.

[0022] Figures 8A to 8B The modulation depth of the alignment signal is shown according to some aspects.

[0023] Figure 9 A photolithography apparatus with a pupil filter is shown according to some aspects.

[0024] Figures 10A to 10B The pupil filter is shown according to some aspects.

[0025] Figure 11 A method for recovering the modulation depth of an alignment signal is shown, based on several aspects.

[0026] The features of this disclosure will become more apparent from the following detailed description of the "Specific Embodiments" when taken in conjunction with the accompanying drawings, in which the same reference numerals identify corresponding elements throughout. In the drawings, the same reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost numeral(s) of the reference numeral(s) identifies the first drawing in which that reference numeral appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as being drawn to scale. Detailed Implementation

[0027] The aspects described herein, as well as references to "an aspect," "one aspect," "exemplary aspect," "example aspect," etc., in the specification indicate that the described aspects may include a particular feature, structure, or characteristic, but each aspect may not necessarily include that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same aspect. Moreover, when a particular feature, structure, or characteristic is described in conjunction with an aspect, it should be understood that achieving such a feature, structure, or characteristic in conjunction with other aspects is within the knowledge of those skilled in the art, whether explicitly described or not.

[0028] For ease of description, spatial relative terms (such as “below,” “under,” “lower,” “above,” “upper,” “upper,” etc.) are used herein to describe the relationship of one element or feature to another (or more) elements or features shown in the figures. In addition to the orientations depicted in the figures, spatial relative terms are intended to cover different orientations of the device in use or operation. The device may be oriented in other ways (rotated 90 degrees or otherwise), and the spatial relative descriptive terms used herein shall be interpreted accordingly.

[0029] The terms “approximately”, “approximately”, etc., may be used herein to indicate the value of a given quantity that may vary based on a particular technique. Based on a particular technique, the terms “approximately”, “approximately”, etc., may indicate the value of a given quantity that varies within, for example, 10% to 30% of the value (e.g., 10%, 20%, or 30% of the value).

[0030] Various aspects of this disclosure can be implemented in hardware, firmware, software, or any combination thereof. Various aspects of this disclosure can also be implemented as instructions stored on a computer-readable medium that can be read and executed by one or more processors. A machine-readable medium can include any mechanism for storing or transmitting information in a machine-readable form (e.g., a computing device). For example, a machine-readable medium can include: read-only memory (ROM); random access memory (RAM); disk storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.); and so on. Furthermore, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be understood that this description is merely for convenience, and such actions are generated by a computing device, processor, controller, or other device that executes the firmware, software, routines, instructions, etc. The term "machine-readable medium" may be used interchangeably with similar terms, such as "computer program product," "computer-readable medium," "non-transitory computer-readable medium," etc. The term "non-transitory" may be used herein to characterize one or more forms of computer-readable medium other than transient propagation signals.

[0031] However, it is instructive to present example environments in which various aspects of this disclosure may be implemented before describing these aspects in more detail.

[0032] Example lithography system

[0033] Figure 1A and Figure 1B Lithography apparatus 100 and 100', in which aspects of the present disclosure may be implemented, are shown respectively. Lithography apparatus 100 and 100' each include: an illumination system (illuminator) IL configured to modulate a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask stage) MT configured to support a pattern forming apparatus (e.g., a mask, stencil, or dynamic pattern forming apparatus) MA and connected to a first positioner PM configured to accurately position the pattern forming apparatus MA; and a substrate stage (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate W. Lithography apparatuses 100 and 100' also have a projection system PS configured to project a pattern imparted by the radiation beam B by the pattern forming apparatus MA onto a target portion (e.g., comprising one or more dies) C of the substrate W. In the photolithography apparatus 100, the pattern forming apparatus MA and the projection system PS are reflective. In the photolithography apparatus 100', the pattern forming apparatus MA and the projection system PS are transmissive.

[0034] The lighting system IL may include various types of optical components for guiding, shaping, or controlling the radiated beam B, such as refractive, reflective, anti-refractive, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

[0035] The support structure MT holds the patterning apparatus MA in a manner dependent on the orientation of the patterning apparatus MA relative to the reference frame, the design of at least one of the lithography apparatuses 100 and 100', and other conditions such as whether the patterning apparatus MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning apparatus MA. For example, the support structure MT can be a frame or a stage, and it can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning apparatus MA is in the desired position, for example, relative to the projection system PS.

[0036] The term "patterning apparatus" MA should be interpreted broadly as any device that can be used to pattern a radiation beam B in its cross-section (such as creating a pattern in a target portion C of a substrate W). The pattern applied to the radiation beam B can correspond to a specific functional layer created in the target portion C within the apparatus to form an integrated circuit.

[0037] The pattern forming apparatus MA can be transmissive (e.g., in...) Figure 1B In the photolithography apparatus 100') or reflective (such as in Figure 1A (In the photolithography apparatus 100). Examples of pattern forming apparatus may include a photomask, a mask, a programmable mirror array, or a programmable LCD panel. Masks are well known in photolithography and include mask types such as binary, alternating phase-shift, or attenuation phase-shift masks, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect incoming radiation beams in different directions. The tilted mirrors impart a pattern to the radiation beam B reflected by the matrix of small mirrors.

[0038] The term "projection system" PS can encompass any type of projection system, including refractive, reflective, antirefractive, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, provided that it is suitable for the exposure radiation used, or for other factors such as immersion on a substrate W or the use of a vacuum. A vacuum environment can be used for EUV (extreme ultraviolet) or electron beam radiation because other gases may absorb too much radiation or electrons. Therefore, a vacuum environment can be provided throughout the optical path by means of vacuum walls and a vacuum pump.

[0039] The lithography apparatus 100 and / or lithography apparatus 100' can be of the type having two substrate stages WT (dual platforms) or more substrate stages WT (and / or two or more mask stages). In such a "multi-platform" machine, additional substrate stages WT can be used in parallel, or fabrication steps can be performed on one or more stages while one or more other substrate stages WT are used for exposure. In some cases, the additional stages may not be substrate stages WT.

[0040] Photolithography apparatuses can also be of this type, in which at least a portion of the substrate can be covered by a liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquid can also be applied to other spaces within the photolithography apparatus, such as between the mask and the projection system. Immersion techniques for increasing the numerical aperture of a projection system are well known in the art. The term "immersion" as used herein does not imply that structures such as the substrate must be submerged in a liquid. For example, during exposure, the liquid may be positioned between the projection system and the substrate.

[0041] refer to Figure 1A and Figure 1B The illuminator IL receives the radiated beam from the radiation source SO. The source SO and the lithography apparatus 100, 100' can be separate physical entities, for example, when the source SO is an excimer laser. In this case, the source SO is not considered to be part of the lithography apparatus 100 or 100', and the radiated beam B is delivered by means of the beam delivery system BD (in...). Figure 1B (In the middle) From the source SO to the illuminator IL, the beam delivery system BD includes, for example, suitable directional mirrors and / or beam expanders. In other cases, the source SO may be a component of the lithography apparatus 100, 100', for example, when the source SO is a mercury lamp. The radiation system may include the source SO, the illuminator IL, and / or the beam delivery system BD.

[0042] The illuminator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiated beam (in Figure 1B (In the middle). Generally, the intensity distribution can be adjusted at least in the outer radial range and / or inner radial range (often referred to as "σ-outer" and "σ-inner" respectively) within the pupil plane of the illuminator. Furthermore, the illuminator IL can include various other components (in... Figure 1B (In the middle), such as integrator IN and condenser CO. Illuminator IL can be used to adjust the radiant beam B to have the desired uniformity and intensity distribution in its cross-section.

[0043] refer to Figure 1AA radiation beam B is incident on a patterning apparatus (e.g., a mask) MA held on a support structure (e.g., a mask stage) MT, and patterning is performed by the patterning apparatus MA. In the lithography apparatus 100, the radiation beam B is reflected from the patterning apparatus (e.g., the mask) MA. After reflection from the patterning apparatus (e.g., the mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. The substrate stage WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B) by means of a second positioner PW and a position sensor IF2 (e.g., an interferometric device, a linear encoder, or a capacitive sensor). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning apparatus (e.g., the mask) MA relative to the path of the radiation beam B. The patterning apparatus (e.g., the mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0044] refer to Figure 1B A radiation beam B is incident on a patterning apparatus (e.g., a mask MA) held on a support structure (e.g., a mask stage MT), and patterning is performed by the patterning apparatus. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU of an illumination system pupil IPU. Part of the radiation emanates from the intensity distribution at the illumination system pupil IPU, passes through the mask pattern unaffected by diffraction at the mask pattern, and creates an image of the intensity distribution at the illumination system pupil IPU.

[0045] The projection system PS projects an image of a mask pattern MP onto a photoresist layer coated on a substrate W, where the image is formed by diffracted beams generated from radiation of an intensity distribution from the marked pattern MP. For example, the mask pattern MP may comprise an array of lines and spacings. Diffraction at this array, distinct from zero-order diffraction, generates a diffracted beam whose direction changes perpendicular to the lines. An undiffracted beam (i.e., the so-called zero-order diffracted beam) traverses the pattern without any change in its propagation direction. The zero-order diffracted beam passes through an upper lens or upper lens group of the projection system PS, located upstream of the pupil conjugate PPU, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU associated with the zero-order diffracted beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. For example, an aperture device PD is positioned or substantially positioned at the plane comprising the pupil conjugate PPU of the projection system PS.

[0046] The projection system PS is arranged to capture (e.g., using a lens or lens group L) a zero-order diffracted beam, a first-order diffracted beam, and / or higher-order diffracted beams (not shown). In some aspects, bipolar illumination for imaging a line pattern extending in a direction perpendicular to the line can be used to utilize the resolution-enhancing effect of bipolar illumination. For example, the first-order diffracted beam interferes with the corresponding zero-order diffracted beam at the horizontal plane of the wafer W, thereby creating an image of the line pattern MP with the highest possible resolution and processing window (i.e., the available depth of focus combined with tolerable exposure dose deviations). In some aspects, astigmatic aberration can be reduced by providing a radiating pole (not shown) in the opposite confinement of the illumination system pupil IPU. Furthermore, in some aspects, astigmatic aberration can be reduced by blocking the zero-order beam in the projection system pupil conjugate PPU associated with the radiating pole in the opposite confinement. This is described in more detail in US 7511799B2, authorized March 31, 2009, which is incorporated herein by reference in its entirety.

[0047] With the aid of a second positioner PW and a position sensor IFD (e.g., an interferometric apparatus, a linear encoder, or a capacitive sensor), the substrate stage WT can be moved precisely (to position different target portions C, for example, along the path of the radiation beam B). Similarly, the first positioner PM and another position sensor ( Figure 1B (Not shown) can be used to accurately position the mask MA relative to the path of the radiation beam B (e.g., after a mechanical retrieval from a mask library or during scanning).

[0048] Generally, the movement of the mask stage MT can be achieved using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) that form part of the first positioner PM. Similarly, the movement of the substrate stage WT can be achieved using a long-stroke module and a short-stroke module that form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask stage MT can be connected to a short-stroke actuator, or it can be fixed. The mask MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks (as shown) occupy dedicated target portions, they can also be located in the space between the target portions (called scribing alignment marks). Similarly, in cases where more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0049] The mask stage MT and pattern forming apparatus MA can be located within a vacuum chamber V, where an in-vacuum robot IVR can be used to move the pattern forming apparatus (such as a mask) into and out of the vacuum chamber. Alternatively, when the mask stage MT and pattern forming apparatus MA are outside the vacuum chamber, an out-of-vacuum robot can be used similarly to the in-vacuum robot IVR for various transport operations. Both the in-vacuum and out-of-vacuum robots can be calibrated to smoothly transfer any payload (e.g., a mask) onto a fixed kinematic support at the transfer station.

[0050] The photolithography apparatuses 100 and 100' can be used in at least one of the following modes:

[0051] 1. In stepping mode, the support structure (e.g., mask stage) MT and substrate stage WT are kept substantially stationary, while the entire pattern imparting the radiation beam B is projected onto the target portion C in a single exposure (i.e., a single static exposure). The substrate stage WT is then moved in the X and / or Y directions, allowing different target portions C to be exposed.

[0052] 2. In the scanning mode, the support structure (e.g., mask stage) MT and the substrate stage WT are scanned synchronously while a pattern imparting a radiation beam B is projected onto the target portion C (i.e., single dynamic exposure). The velocity and direction of the substrate stage WT relative to the support structure (e.g., mask stage) MT can be determined by the magnification (reduction ratio) and image inversion characteristics of the projection system PS.

[0053] 3. In another mode, the support structure (e.g., a mask stage) MT is kept substantially stationary, thereby holding the programmable patterning apparatus in place, while the substrate stage WT is moved or scanned, simultaneously projecting a pattern imparted to the radiation beam B onto the target portion C. A pulsed radiation source SO can be employed, and the programmable patterning apparatus can be updated as needed after each movement of the substrate stage WT or between successive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography utilizing programmable patterning apparatuses such as programmable mirror arrays.

[0054] Alternatively, combinations and / or variations of the described usage patterns, or entirely different usage patterns, may be adopted.

[0055] In some aspects, the lithography apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Generally, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to modulate the EUV radiation beam from the EUV source.

[0056] In some aspects, the lithography apparatus 100' includes a deep ultraviolet (DUV) source configured to generate a DUV radiation beam for DUV lithography. Generally, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to modulate the DUV radiation beam from the DUV source.

[0057] Figure 2 A lithography apparatus 100 is shown in more detail, comprising a source-collector device SO, an illumination system IL, and a projection system PS. The source-collector device SO is constructed and arranged such that a vacuum environment can be maintained within a closed structure 220 of the source-collector device SO. EUV radiation-emitting plasma 210 can be formed by a plasma source generated by a discharge. EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein EUV radiation-emitting plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. EUV radiation-emitting plasma 210 is created by, for example, an electrical discharge that causes at least partial ionization of the plasma. For example, a partial pressure of 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor can be used for efficient radiation generation. In some aspects, a plasma of stimulated tin (Sn) (e.g., stimulated via a laser) is provided to generate EUV radiation.

[0058] Radiation emitted by EUV radiation-emitting plasma 210 is transferred from source cavity 211 to collector cavity 212 via an optional gas barrier or contaminant trap 230 (also referred to in some cases as a contaminant barrier or foil trap), which is located in or behind an opening in source cavity 211. Contaminant trap 230 may include a channel structure. Contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 also indicated herein includes at least a channel structure.

[0059] Collector cavity 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation passing through the collector CO may be reflected by a grating spectral filter 240 to be focused into a virtual source point INTF. The virtual source point INTF is often referred to as the intermediate focus, and the source collector arrangement is such that the intermediate focus INTF is located at or near the opening 219 in the enclosed structure 220. The virtual source point INTF is an image of the EUV radiation-emitting plasma 210. The grating spectral filter 240 is used in particular to suppress infrared (IR) radiation.

[0060] Subsequently, radiation passes through an illumination system IL, which may include a faceted field mirror device 222 and a faceted pupil mirror device 224. The faceted field mirror device 222 and the faceted pupil mirror device 224 are arranged to provide a desired angular distribution of the radiation beam 221 at the patterning apparatus MA, and to provide a desired uniformity of radiation intensity at the patterning apparatus MA. When the radiation beam 221 is reflected at the patterning apparatus MA, which is held by a support structure MT, a patterning beam 226 is formed, and the patterning beam 226 is imaged by a projection system PS onto a substrate W held by a wafer platform or substrate stage WT via reflective elements 228 and 229.

[0061] In general, more components than are shown can be present in the illumination optics unit IL and the projection system PS. Depending on the type of photolithography apparatus, a grating spectral filter 240 may optionally be present. Furthermore, more than... Figure 2 As shown, more mirrors, for example, can exist in a projection system PS. Figure 2 The diagram shows one to six additional reflective elements.

[0062] like Figure 2 As shown, the collector optics CO is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, merely as one example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are arranged symmetrically about the optical axis O, and this type of collector optics CO is preferably used in conjunction with a plasma source generated by discharge (often referred to as a DPP source).

[0063] Example lithography unit

[0064] Figure 3 A lithography unit 300 (sometimes also called a photocell or cluster) is shown according to some aspects. A lithography apparatus 100 or 100' may form part of the lithography unit 300. The lithography unit 300 may also include one or more devices for performing pre-exposure and post-exposure processing 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 baking plate BK. A substrate processor or robot RO picks up substrates from input / output ports I / O1, I / O2, moves them between different processing devices, and delivers them to the feed stage LB of the lithography apparatus 100 or 100'. These devices, often collectively referred to as tracks, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which in turn controls the lithography apparatus via a lithography control unit LACU. Therefore, different devices can be operated to maximize throughput and processing efficiency.

[0065] Example inspection device

[0066] To control the photolithography process and accurately place device features onto a substrate, alignment marks are typically provided on the substrate, and the photolithography apparatus includes one or more inspection devices for accurately positioning these marks on the substrate. These alignment devices are effective position measurement devices. Different types of marks and different types of alignment devices and / or systems are known from different times and different manufacturers. One system widely used in current photolithography apparatuses is based on a self-reference interferometer described in U.S. Patent No. 6,961,116 (den Boef et al.). Generally, the marks are measured separately to obtain the X and Y positions. However, combined X and Y measurements can be performed using the technique described in U.S. Publication No. 2009 / 195768A (Bijnen et al.). The full contents of both disclosures are incorporated herein by reference.

[0067] Figure 4A A cross-sectional view of an inspection apparatus 400, which may be implemented as part of a lithography apparatus 100 or 100', is shown according to some aspects. In some aspects, the inspection apparatus 400 may be configured to align a substrate (e.g., substrate W) relative to a patterning apparatus (e.g., patterning apparatus MA). The inspection apparatus 400 may also be configured to detect the position of alignment marks on the substrate and use the detected position of the alignment marks, relative to the patterning apparatus or other components of the lithography apparatus 100 or 100', to align the substrate. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0068] The terms “inspection apparatus” and “measuring system” may be used in this document to refer to, for example, devices used to measure structural properties (e.g., overlap sensors, critical size sensors, etc.), devices or systems used in a lithography apparatus to inspect wafer alignment (e.g., alignment sensors), etc.

[0069] In some aspects, 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 a processor 432. The illumination system 412 may be configured to provide a narrow-band electromagnetic radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a spectrum with wavelengths between approximately 500 nm and approximately 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a spectrum with wavelengths between approximately 500 nm and approximately 900 nm. The illumination system 412 may also be configured to provide one or more passbands with a substantially constant center wavelength (CWL) value over a long period of time (e.g., throughout the lifetime of the illumination system 412). As described above, in current alignment systems, this configuration of the illumination system 412 can help prevent the actual CWL value from deviating from the desired CWL value. And, as a result, the use of a constant CWL value can improve the long-term stability and accuracy of the alignment system (e.g., the inspection apparatus 400) compared to current alignment apparatuses.

[0070] In some respects, beam splitter 414 can be configured to receive radiated beam 413 and split radiated beam 413 into at least two radiated sub-beams. For example, radiated beam 413 can be split into radiated sub-beams 415 and 417, as... Figure 4AAs shown. Beam splitter 414 can also be configured to guide radiant sub-beam 415 onto substrate 420 placed on platform 422. In one example, platform 422 may be movable along direction 424. Radiant sub-beam 415 may be configured to illuminate alignment marks or targets 418 located on substrate 420. Alignment marks or targets 418 may be coated with a radiation-sensitive film. In some respects, alignment marks or targets 418 may have 180° symmetry. That is, when alignment marks or targets 418 are rotated 180° about an axis of symmetry perpendicular to the plane of alignment marks or targets 418, the rotated alignment marks or targets 418 may be substantially identical to the unrotated alignment marks or targets 418. Target 418 on substrate 420 may be (a) a resist layer grating comprising strips formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack comprising resist gratings overlapping or interlaced on the product layer grating in an overlapping target structure. Alternatively, the stripes can be etched into the substrate. This pattern is sensitive to chromatic aberration in photolithography projection equipment (particularly projection systems, PL), and the presence of illumination symmetry and this aberration will cause them to appear in variations of the printed grating. An in-line method for measuring linewidth, pitch, and critical dimensions in device fabrication utilizes a technique called “scattering measurement.” The method of scattering measurement is described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry” (J. Vac. Sci. Tech. B, Vol. 15, No. 2, pp. 361-368 (1997)) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography” (SPIE, Vol. 3677 (1999)), both of which are incorporated herein by reference in their entirety. In scattering measurement, light is reflected by a periodic structure in the target, and the resulting reflection spectrum is detected at a given angle. The structure generating the reflection spectrum is reconstructed, for example, using rigorous coupled-wave analysis (RCWA) or by comparing it with a library of patterns derived from simulation. Accordingly, the grating is reconstructed using scattering measurement data of the printed grating. The parameters of the grating (such as linewidth and shape) can be input into the reconstruction process performed by the processing unit PU based on knowledge of the printing steps and / or other scattering measurement processes.

[0071] In some aspects, according to one aspect, beam splitter 414 can also be configured to receive the diffracted radiation beam 419 and split the diffracted radiation beam 419 into at least two radiation sub-beams. The diffracted radiation beam 419 can be split into diffracted radiation sub-beams 429 and 439, as... Figure 4A As shown.

[0072] It should be noted that this disclosure is not limited to the fact that the beam splitter 414 is shown guiding the radiant sub-beam 415 toward the alignment mark or target 418 and the diffracted radiant sub-beam 429 toward the interferometer 426. Other optical arrangements can be used to obtain similar results in illuminating and detecting the alignment mark or target 418 on the substrate 420.

[0073] like Figure 4A As shown, interferometer 426 can be configured to receive a radiating sub-beam 417 and a diffracted radiating sub-beam 429 via beam splitter 414. In one example aspect, the diffracted radiating sub-beam 429 may be at least a portion of a radiating sub-beam 415 that can be reflected from the alignment mark or target 418. In one example of this aspect, interferometer 426 includes any suitable set of optical elements, such as a prism assembly, which can be configured to form two images of the alignment mark or target 418 based on the received diffracted radiating sub-beam 429. It should be understood that it is not necessary to form images of good quality. It is sufficient to be able to resolve the features of the alignment mark 418. Interferometer 426 can also be configured to rotate one of the two images by 180° relative to another image, and to reconstruct the rotated image and the unrotated image using the interferometer.

[0074] In some aspects, detector 428 can be configured to receive the reconstructed image via interferometer signal 427 and detect interference as a result of the reconstructed image when the alignment axis 421 of inspection device 400 passes through the center of symmetry (not shown) of alignment mark or target 418. According to one example aspect, this interference may be due to the alignment mark or target 418 being 180° symmetrical, and the reconstructed image interfering constructively or destructively. Based on the detected interference, detector 428 can also be configured to determine the position of the center of symmetry of alignment mark or target 418, and thus detect the position of substrate 420. According to one example, alignment axis 421 can be aligned with a beam perpendicular to substrate 420 and passing through the center of image rotation interferometer 426. Detector 428 can also be configured to estimate the position of alignment mark or target 418 by implementing sensor characteristics and interacting with changes in the wafer marking process.

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

[0076] 1. Measure the positional changes at various wavelengths (positional shifts between colors);

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

[0078] 3. Measure the positional changes of various polarizations (positional offsets between polarizations); and

[0079] 4. Measure the intensity difference between relative orders in a diffraction order pair (to characterize and correct for asymmetry, for example).

[0080] This data can be obtained using any type of alignment sensor, such as the SMASH (Smart Alignment Sensor Hybrid) sensor described in U.S. Patent No. 6,961,116, or the Athena (Advanced Techniques Using Higher-Order Alignment Enhancement) sensor described in U.S. Patent No. 6,297,876, both of which are incorporated herein by reference in their entirety. The SMASH sensor employs a self-reference interferometer with a single detector and four different wavelengths and extracts the alignment signal in software. The Athena directs each of the seven diffraction orders to a dedicated detector.

[0081] In some aspects, the beam analyzer 430 can be configured to receive and determine the optical state of the diffracted radiant sub-beam 439. The optical state can be a measure of beam wavelength, polarization, or beam profile. The beam analyzer 430 can also be configured to determine the position of the platform 422 and correlate the position of the platform 422 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418 can be accurately determined with reference to the platform 422, and therefore the position of the substrate 420. Alternatively, the beam analyzer 430 can be configured to determine the position of the inspection device 400 or any other reference element, such that the center of symmetry of the alignment mark or target 418 can be determined relative to the inspection device 400 or any other reference element. The beam analyzer 430 can be a point polarimeter or imaging polarimeter with some form of band selectivity. In some aspects, the beam analyzer 430 can be directly integrated into the inspection device 400, or, depending on other aspects, connected via several types of optical fibers: polarization-maintaining single-mode, multimode, or imaging.

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

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

[0084] In some respects, a detector array (not shown) can be connected to beam analyzer 430, allowing for accurate stack-up profile detection, as described below. For example, detector 428 can be a detector array. Several options are possible for the detector array: multimode fiber bundles, discrete PIN detectors per channel, CCD or CMOS (linear) arrays. The use of multimode fiber bundles allows any dissipative elements to be located at a distance for stability reasons. Discrete PIN detectors offer a large dynamic range, but each discrete PIN detector requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays offer many elements that can be read out at high speeds, which are particularly interesting if phase-stepped detection is used.

[0085] In some respects, the second beam analyzer 430' can be configured to receive and determine the optical state of the diffracted sub-beam 429, such as Figure 4B As shown. Optical state can be a measure of beam wavelength, polarization, or beam profile. The second beam analyzer 430' can be identical to beam analyzer 430. Alternatively, the second beam analyzer 430' can be configured to perform one or more functions of beam analyzer 430, such as determining the position of platform 422 and relating the position of platform 422 to the position of the center of symmetry of alignment mark or target 418. Thus, the position of alignment mark or target 418 can be accurately determined with reference to platform 422, and therefore the position of substrate 420. The second beam analyzer 430' can also be configured to determine the position of inspection device 400 or any other reference element, such that the center of symmetry of alignment mark or target 418 can be determined relative to inspection device 400 or any other reference element.

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

[0087] In some aspects, processor 432 receives information from detector 428 and beam analyzer 430. Processor 432 can create a basic correction algorithm based on the information received from detector 428 and beam analyzer 430, including but not limited to the optical state of the illumination beam, alignment signal, associated position estimation, and optical state in the pupil, image, and additional plane. The pupil plane is a plane in which the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor 432 can characterize inspection apparatus 400 using the basic correction algorithm, reference wafer markings, and / or alignment marks 418.

[0088] Example photolithography apparatus with spatial filter assembly

[0089] Figure 5 A lithography apparatus 500 with a spatial filter assembly is shown according to some aspects. The lithography apparatus 500 can be configured to measure the position of an aligned target. In some aspects, the lithography apparatus 500 can represent an inspection apparatus 400 ( Figure 4A and Figure 4B A detailed view of the lithography apparatus 500. The lithography apparatus 500 may be constructed as part of the lithography apparatus 100 or 100', or it may be constructed as a separate unit within the lithography unit 300 and work in conjunction with other apparatuses during operation. In some aspects, the lithography apparatus 500 may include an illumination system 502, a projection system 512, a self-referenced interferometer (SRI) 532, a beam analyzer 536, and a detection system 548.

[0090] In some aspects, the illumination system 502 may include a radiation source 504, an objective lens 508, and a reflector 510. In some aspects, the radiation source 504 may be configured to emit a spatially coherent illumination beam 506. The illumination beam 506 may have a narrow electromagnetic band with one or more passbands. In some aspects, the illumination beam 506 may be visible or infrared light with wavelengths in the ranges of approximately 500 nm to approximately 700 nm and approximately 700 nm to approximately 2 μm, respectively. In some aspects, the radiation source 504 may include one or more radiation sources, each source generating one or more passbands within a spectrum with wavelengths between approximately 500 nm and approximately 2 μm. For example, the illumination beam 506 may be a combination of one or more passbands from one or more radiation sources and may have a substantially continuous wavelength. In some aspects, the wavelength range of the illumination beam 506 may also include ultraviolet light.

[0091] In some aspects, objective lens 508 focuses illumination beam 506 onto mirror 510. In some aspects, mirror 510 can be positioned at any angle to redirect illumination beam 506 toward projection system 512. Those skilled in the art will recognize that other focusing optics within the illumination system can also be used to provide similar functionality.

[0092] In some aspects, the projection system 512 of the lithography apparatus 500 may include a beam splitter 514 and an objective lens 516, and may be configured to direct an illumination beam 506 toward an alignment target 518, and to direct diffracted beams 530a, 530b diffracted from the alignment target 518 toward a self-reference interferometer (SRI) 532. For example, the illumination beam 506 may be directed toward the alignment target 518 at any incident angle.

[0093] In some respects, beam splitter 514 may be a point mirror formed of a transmission cube, wherein a reflective metal layer is disposed at the center of the cube. It should be noted that this disclosure is not limited to the fact that beam splitter 514 is shown reflecting illumination beam 506 toward alignment target 518 and transmitting diffracted beams 530a, 530b toward SRI 532. It will be apparent to those skilled in the art that similar results can be obtained using other optical arrangements.

[0094] In some respects, objective lens 516 focuses illumination beam 506 onto alignment target 518 and collects diffracted beams 530a, 530b reflected from alignment target 518. Those skilled in the art will know that other focusing optical systems can also be used to provide similar functionality.

[0095] It should be understood that the structures drawn within the lighting system 502 and projection system 512 are not limited to the locations they depict. The location of the structures can vary as needed (e.g., depending on the design for modular components).

[0096] In some aspects, substrate 520 (e.g., a semiconductor wafer) may be positioned on an adjustable platform 522 (e.g., a movable support structure). In some aspects, alignment target 518 may be a structure formed on substrate 520 by pattern transfer using a preceding photomask (not shown). The materials and thin film stacks used to form alignment target 518 may depend on the layout of alignment target 518 on the preceding photomask and the processes performed on substrate 520. The design requirements (e.g., shape and size) of alignment target 518 may depend on the alignment system and alignment method used. In some aspects, alignment target 518 may include a diffractive structure (e.g., multiple gratings). Alignment target 518 may reflect, refract, diffract, scatter, etc., radiation (e.g., illumination beam 506). For ease of discussion, without limitation, radiation interacting with alignment target will be referred to throughout as scattered radiation. In some aspects, scattered radiation may be collected by objective lens 516.

[0097] In some aspects, the alignment target 518 may be made of or coated with a radiation-sensitive film, such as a photoresist (“resist”). Uneven increases in the thickness of the resist layer 524 may cause height differences across the substrate 520. The top surface 528 of the resist layer 524 may not be parallel to the alignment target 518, but may be tilted. Accordingly, the resist layer 524 disposed on the surface of the substrate 520 may be considered a “tilted resist” or a “wedge resist.” Resist tilting may occur in the scribe lines of the substrate 520 where the alignment target (e.g., alignment target 518) is located. In some aspects, the scribe lines may form trenches on the surface of the substrate 520. When the substrate 520 is covered with resist, the resist does not uniformly fill the trenches. As a result, the alignment target 518 may be located below the area with the tilted resist surface, such as… Figure 5 As shown.

[0098] In some aspects, the thickness of the resist layer 524 can be from about 10 μm to about 20 μm. For example, the thickness of the resist layer 524 can be about 10 μm. In some aspects, the top surface 528 of the resist layer 524 can have a tilt angle 526 of about 0 degrees to about 5 degrees. For example, the resist layer 524 can have a tilt angle 526 of about 1 degree.

[0099] In some aspects, the diffracted beams 530a and 530b from the aligned target 518 comprise symmetrically distributed higher-order diffracted beams, for example, +1 and -1, +2 and -2, ..., +n and -n, respectively (where n is an integer greater than 2). Depending on the diffraction angle, the different orders of the diffracted beams are spatially separated. In some aspects, the diffracted beams 530a and 530b include at least one positive diffraction order or one negative diffraction order.

[0100] However, in some respects, the illumination beam 506 can be refracted by the resist layer 524 before it can properly illuminate the alignment target 518. As a result, the diffracted beams 530a, 530b may be reflected from the alignment target 518 and subsequently refracted by the resist layer 524 in an undesirable manner. Therefore, due to the refraction of the illumination beam 506 and the reflection and refraction of the diffracted beams 530a, 530b, the diffraction angles of higher-order diffracted beams 530a, 530b (e.g., +1 / -1, ..., +m / -m, where m is any integer greater than 1) relative to the optical axis of the lithography apparatus 500 may not be equal. Accordingly, when resist tilting is present, the position measurement of the alignment target may be inaccurate. For example, the lithography apparatus 500 may lose its alignment signal as the modulation depth of the alignment signal decreases, as further described below.

[0101] In some respects, the inhomogeneity of the top surface 528 may be detrimental to the accurate operation of the photolithography apparatus. In some respects, due to Snell's law, the tilt angle 526 of the top surface 528 and the varying amounts of material across the resist layer 524 may cause angular deviations in the diffraction beams 530a, 530b. In some respects, due to unequal diffraction angles or different optical path lengths between each pair of higher-order diffraction beams 530a, 530b (e.g., +1 / -1, ..., +m / -m), phase increments may be introduced between the higher-order diffraction beams 530a, 530b (e.g., +1 / -1, ..., +m / -m). These phase increments may introduce alignment errors proportional to their magnitude.

[0102] In some respects, SRI 532 is configured to receive diffracted beams 530a and 530b and generate diffracted sub-beams 534a-534d. SRI 532 can project two overlapping images of a target 518 rotated 180° relative to each other. At SRI 532, a pair of positive and negative diffracting orders of diffracted beams 530a and 530b can generate two pairs of diffracted sub-beams 534a-534d, wherein each pair of diffracted sub-beams 534a-534d includes a spatial overlap component of both the positive and negative diffracting orders from diffracted beams 530a and 530b.

[0103] To enable the detection system 548 to accurately align the substrate 520, the SRI 532 needs to generate a symmetrical overlap of positive and negative diffraction beams 530a and 530b. The amount of symmetrical overlap between the diffraction beams 530a and 530b may directly relate to the amount of modulation present in the light intensity of the alignment signal. In some respects, the depth of modulation (DoM) can indicate the intensity of a sinusoidal signal. Therefore, analyzing the DoM allows the lithography apparatus 500 to pinpoint the alignment position of the alignment target 518 to a fraction of a nanometer. In some respects, the DoM can be calculated by finding the difference between the 99th percentile alignment signal and the 1st percentile alignment signal, and then dividing that difference by the 99th percentile alignment signal.

[0104] In some aspects, the resist layer 524 can shift the interpeak distance of the sinusoidal signal of the diffracted beam 530a relative to the interpeak distance of the sinusoidal signal of the diffracted beam 530b in the pupil plane. In some aspects, the diffracted beams 530a and 530b may be asymmetrical with respect to the optical axis of the lithography apparatus 500. After replicating the diffracted beams 530a and 530b in the SRI 532, the two copies of the diffracted beams 530a and 530b may not overlap symmetrically and may not undergo symmetrical interference, thereby weakening the self-reference process and reducing the DoM of the alignment signal. In some aspects, the SRI 532 can generate a standing wave pattern created by the diffracted beams 530a and 530b in the field of the alignment sensor. In some aspects, the detection system 548 can interpret the asymmetrical overlap between the diffracted beams 530a and 530b as a positional offset deviation from the center of the optical axis of the lithography apparatus 500, resulting in alignment errors. Therefore, in some respects, the detection system 548 may receive a reduced alignment signal, which makes the position of the alignment target more uncertain (e.g., in nanometers). In some respects, the alignment signal may be lost completely. In some respects, a tilt angle of approximately one degree 526 in the resist layer 524 may cause the lithography apparatus 500 to lose the alignment signal.

[0105] In some aspects, beam analyzer 536 (e.g., beam analyzer 430) may be configured to allow diffracted sub-beams 534a, 534b to pass through mirror 538 and reflect diffracted sub-beams 534c, 534d towards objective lens 540b. In some aspects, mirror 538 may reflect diffracted sub-beams 534a, 534b towards objective lens 540a. In some aspects, diffracted sub-beams 534a-534d pass through objective lenses 540a, 540b, respectively, and objective lenses 540a, 540b are configured to focus diffracted sub-beams 534a-534d towards spatial filter assemblies 542a, 542b, respectively.

[0106] In some aspects, spatial filter assemblies 542a and 542b can be disposed before field stops 544a and 544b, respectively. In some aspects, an image of the alignment target 518 can be radiated at the output plane through spatial filter assemblies 542a and 542b to generate an intensity signal as a function of the position of the alignment target 518 on the substrate 520. In some aspects, spatial filter assemblies 542a and 542b can be configured to recover the modulation depth of the alignment signal and can generate recovered alignment signals 546a and 546b, as described below. Figure 6 The subject of discussion.

[0107] In some respects, field stops 544a and 544b can be located at the output plane of the alignment system.

[0108] In some respects, the detection system 548 of the lithography apparatus 500 can measure the light intensity of the recovered alignment signals 546a, 546b, and thus measure the modulation depth of the alignment signals. The detection system 548 can be configured to determine the position of the alignment target 518 based on the light intensity measurement of the recovered alignment signals 546a, 546b, wherein the light intensity is modulated to extract alignment information from other parameters of the lithography apparatus 500.

[0109] Figure 6 A spatial filter assembly 600 with a reference grating 602 is shown according to some aspects. In some aspects, the spatial filter assembly 600 can represent Figure 5 A detailed view of the spatial filter assembly 542a is shown. The following discussion applies to the spatial filter assembly 542b and its corresponding input and output signals. In some aspects, the spatial filter assembly 600 may include a reference grating 602, a substrate 604, a movable platform 608, and a multimode fiber 614.

[0110] In some aspects, the spatial filter assembly 600 may include a field stop (e.g., disposed in the output plane of the alignment system) Figure 5 The reference grating 602 is shown at field stops 544a and 544b. In some aspects, when the reference grating 602 generates a recovered alignment signal 612 (e.g., Figure 5 When the restored alignment signals 546a, 546b are shown, the reference grating 602 can recover the DoM from approximately 0% to approximately 80%. In some aspects, for resist layers (e.g., Figure 5 Any tilt angle of the resist layer 524 shown (e.g., Figure 5 (As shown at a tilt angle of 526), ​​the reference grating 602 can generate a DoM-improved restored alignment signal 612. In some aspects, the reference grating can simultaneously generate restored alignment signals 612 for all colors (e.g., a 4C system or a 12 system) because the reference grating 602 is located in the field plane of the lithography apparatus 500.

[0111] In some aspects, the reference grating 602 may include at least one or a combination of a 1D X-direction filter, a 1D Y-direction filter, a 2D XY-direction filter, a binary filter, a gray filter, and a spectral filter. In some aspects, the reference grating 602 may be configured to have an alignment with an alignment target (e.g., Figure 5The reference grating pitch corresponds to the target pitch of the alignment target 518 shown. In some aspects, the reference grating 602 can be optimized for higher-order target pitches of the alignment target without compromising the self-reference process. In some aspects, the reference grating 602 can generate a recovered alignment signal 612 without compromising the detection of the alignment target under a flat resist layer (e.g., tilt angle 526 equals 0). For example, when the tilt angle 526 of the resist layer 524 is equal to 0, the reference grating 602 can generate a recovered alignment signal 612 with a DoM of 100%.

[0112] In some aspects, the reference grating 602 can be formed by etching the reference grating 602 into the substrate 604. In some aspects, the substrate 604 can be a photomask or a glass plate. In some aspects, the reference grating 602 can be formed by a MEMS mirror configured to change the period or profile of the reference grating 602, thereby tuning the reference grating 602 for a target wavelength. In some aspects, the reference grating 602 can be formed by using an acousto-optic tunable filter (AOTF) or a liquid crystal tunable filter (LCTF) to transmit the target wavelength while excluding other wavelengths.

[0113] In the presence of resist tilt, a self-referenced interferometer (e.g., Figure 5 The SRI 532 shown can be obtained from a diffraction beam (e.g., Figure 5 Standing wave patterns are generated in the diffracted beams 530a and 530b shown. For example, the signal generated by the self-reference interferometer can have separate modulation regions that are out of phase with each other. Therefore, separating the modulation regions can restore the DoM of the alignment signal by blocking out-of-phase signals to allow the sinusoidal modulation signal to pass through and reach the detection system 548.

[0114] Accordingly, in some aspects, the reference grating 602 can filter out portions of the diffracting sub-beams 606a and 606b that do not contribute to the alignment signal for the alignment target 518. In some aspects, the reference grating 602 can recover the DoM of the alignment signal by separating two signals residing in spatially different regions, thereby blocking the standing wave effect of the interference pattern and allowing the modulation signal to pass through the reference grating 602. For example, the reference grating 602 can be configured to block the first diffracting sub-beam 606a (e.g., Figure 5 The diffractor beam 534a shown is shown, and a second diffractor beam 606b is allowed (e.g., Figure 5 The diffracted sub-beam 534b) shown passes through the reference grating 602 to transmit the recovered (e.g., modulated) alignment signal 612 to the detection system 548. As a result, the reference grating 602 can increase the DoM of the lithography apparatus 500, thereby allowing the alignment signal to be detected at a lower signal-to-noise ratio level.

[0115] In the presence of resist tilt, a self-referenced interferometer (e.g., Figure 5 The SRI 532 shown can produce diffractive beams (e.g., Figure 5 The asymmetric overlap of the diffraction beams 530a and 530b shown. In some aspects, in photolithography apparatus (e.g., Figure 5 The photolithography apparatus 500 shown creates an alignment target (e.g., at the output plane of the photolithography apparatus 500) to align the target. Figure 5 The image of the aligned target (518) shown may be more efficient without relying on the self-reference process.

[0116] In some aspects, the reference grating 602 can be configured to form diffracting sub-beams 606a, 606b (e.g., Figure 5 The interference pattern of the diffracting sub-beams 534a and 534b shown is independent of any spatial overlap in the pupil plane of the alignment system. For example, the positive and negative diffraction orders of the diffracting sub-beams 606a and 606b can interfere with the reference grating 602 at the output plane, independent of any offset of the diffracting sub-beams 606a and 606b in the pupil plane. In some aspects, the reference grating 602 can be coupled with a self-reference interferometer (e.g., Figure 5 It operates in conjunction with the SRI 532 shown. In some respects, the reference grating 602 can still generate the recovered alignment signal 612 without the need for a self-reference interferometer in the alignment system.

[0117] In some aspects, a reference grating 602 within the substrate 604 may be mounted on a movable platform 608. In some aspects, the movable platform may be a filter wheel or an electromechanical assembly. In some aspects, the movable platform 608 may be configured to tune the reference grating pitch to a target pitch by adjusting the reference grating 602 using at least one of translational or rotational motion. In some aspects, the translational motion may be in the XY plane. In some aspects, the rotational motion may be in the XY plane about the Z-axis.

[0118] In some aspects, the movable platform 608 can be controlled by a processor (e.g., processor 432) or a controller. In some aspects, the movable platform 608 can be controlled based on measurement data from the beam position sensor 610. In some aspects, the beam position sensor 610 can be configured to depend on the tilted resist layer (e.g., Figure 5 The resist layer 524 shown) and the alignment target (e.g., Figure 5The positions of the diffracting sub-beams 606a and 606b are measured by the pitch of the alignment target 518 shown. The beam position sensor can output position-indicating data to a processor or controller. As a result, the processor or controller can actuate the movable platform 608 based on the output data to adjust the position of the diffracting sub-beams generated by the pitch of the tilted resist layer and the alignment target.

[0119] In some respects, the operation of the movable platform 608 can be preset based on a predetermined value of the tilt angle 526 of the resist layer 524. In this case, the beam position sensor 610 can be omitted.

[0120] In some aspects, the spatial filter assembly 600 may use a multimode fiber 614 to transmit the recovered alignment signal 614 to the detection system 548. In some aspects, the reference grating 602 may integrate energy from diffracting sub-beams 606a, 606b to create a single interference signal (e.g., the recovered alignment signal 612), which illuminates the multimode fiber 614 to propagate the recovered alignment signal 612 to the detection system 548. In some aspects, the multimode fiber 614 may be spaced tens or hundreds of micrometers from the substrate 604 such that when actuated by the movable platform 608, only the reference grating 602 moves, while the multimode fiber 614 remains stationary.

[0121] Figures 7A to 7C Reference gratings 602a-602c are shown according to some aspects. Figure 7A A reference grating 602a is shown as a 1D Y-direction filter according to some aspects. Figure 7B A reference grating 602b is shown as a 1D X-direction filter according to some aspects. Figure 7C A reference grating 602c is shown as a 2D XY direction checkerboard filter according to some aspects. In some aspects, the reference gratings 602a-602c can be Figure 6 Alternative aspect of the reference grating 602 shown.

[0122] In some aspects, spatial filter assembly 542a may use reference grating 602a, while spatial filter assembly 542b may use reference grating 602b. In some aspects, spatial filter assembly 542a may use reference grating 602b, while spatial filter assembly 542b may use reference grating 602a. In any exemplary configuration, the alignment system can read the X-direction alignment target and the Y-direction alignment target by applying a 1D reference grating to different channels. In some aspects, both spatial filter assemblies 542a and 542b may use reference grating 602c to enable the alignment system to read the X-direction alignment target and the Y-direction alignment target by applying a 2D reference grating to both channels. In some aspects, any of reference gratings 602a-602c may be positioned on a movable platform (e.g., Figure 6 On the movable platform 608 shown, the movable platform is configured to tune the pitch of any of the reference gratings 602a-602c to the target pitch by adjusting any of the reference gratings 602a-602c using at least one of translational or rotational motion.

[0123] Figures 8A to 8B The modulation depth of the alignment signal is shown according to some aspects. Figures 8A to 8B The modulation depth is plotted on the graph, where the light intensity amplitude is 802 on the Y-axis and the position is 804 on the X-axis.

[0124] Figure 8A The weak modulation depth 800 of the alignment signal based on the presence of resist tilt is shown according to some aspects. In some aspects, the detection system (e.g., Figure 5 The detection system 548 shown can read the power of the integrated output as a function of the alignment target position. In some aspects, the presence of resist tilt may introduce small modulations in the alignment signal, increasing the difficulty for the detection system to extract position information from the alignment signal. In some aspects, the peak-to-valley distance between data point 806 and data point 808 may be low when a poor DoM is present. For example, when the tilt angle (e.g., ...) is low... Figure 5 The tilt angle shown (526) is 1 degree, and the tilted resist layer (e.g., Figure 5 The resist layer 524 shown has a thickness of 10 μm and is aligned with the target (e.g., Figure 5 The aligned target 518 shown is 16 μm, and the diffracted beam (e.g., Figure 5 When the diffraction beams 530a and 530b shown are +1st order diffraction beams and -1st order diffraction beams, the modulation depth 800 can be approximately 8%.

[0125] Figure 8BA spatial filter assembly based on the presence of a counteracting resist tilt is shown, according to some aspects (e.g., Figure 5 The spatial filter assemblies 542a and 542b shown use a modulation depth 800' for the recovered alignment signal. In some aspects, the spatial filter assemblies can increase the peak-to-valley distance between data points 806' and 808', thereby improving DoM relative to the modulation depth 800. In some aspects, the DoM improvement can vary based on the thickness of the resist layer, the tilt angle of the resist layer, and the size of the alignment target. In some aspects, the DoM improvement may be maximized when the pitch of the reference grating matches the pitch of the alignment target. For example, when the tilt angle (e.g., ...) is... Figure 5 The tilt angle shown (526) is 1 degree, and the tilted resist layer (e.g., Figure 5 The resist layer 524 shown has a thickness of 10 μm and is aligned with the target (e.g., Figure 5 The aligned target 518 shown is 16 μm, and the diffracted beam (e.g., Figure 5 When the diffraction beams 530a and 530b shown are +1st order diffraction beams and -1st order diffraction beams, a reference grating optimized for a 16μm alignment mark (e.g., Figure 7A The reference grating 602a shown can produce a modulation depth of approximately 76%. For this exemplary aspect, the reference grating 602a can recover the DoM from approximately 8% to approximately 76%.

[0126] Example alignment system with pupil filter

[0127] Figure 9 A photolithography apparatus with a pupil filter is shown according to some aspects. Figure 5 The above discussion of the photolithography apparatus 500 shown applies to Figure 9 The photolithography apparatus 500' shown is an example. Figure 5 The photolithography apparatus 500 shown in various aspects and Figure 9 The aspects of the photolithography apparatus 500' shown may be similar. Similar reference numerals are used to indicate... Figure 5 Features of the photolithography apparatus 500 shown Figure 9 Similar features to the photolithography apparatus 500' shown.

[0128] In some aspects, spatial filter assemblies 542a', 542b' may include pupil filters configured to collect one or more overlapping diffracted sub-beams 534a-534d of predetermined wavelengths. In some aspects, the pupil filters may be positioned in the collimation space of the pupil in front of the objectives 540a, 540b in the alignment system. In some aspects, the pupil filters may include multiple openings to filter higher-order diffracted sub-beams 534a-534d before they reach the detection system 548. Offset diffraction orders in the pupil plane may be blocked by the pupil filters because the diffracted beams are no longer aligned with the openings in the pupil filters and are therefore not detected by the detection system 548. In some aspects, the pupil filters of spatial filter assemblies 542a', 542b' may be compatible with any tilt angle 526 of the resist layer 524.

[0129] Accordingly, in some aspects, spatial filter assemblies 542a' and 542b' can filter out portions of the diffracted sub-beams 534a-534d that do not contribute to the alignment signal for the alignment target 518. In some aspects, spatial filter assemblies 542a' and 542b' can recover the DoM of the alignment signal by separating two signals residing in different spatial regions, thereby blocking the standing wave effect of the interference pattern and allowing the modulated signal to pass through the spatial filter assemblies 542a' and 542b'. For example, spatial filter assembly 542a' can be configured to block the first diffracted sub-beam 534a and allow the second diffracted sub-beam 534b to pass through the spatial filter assemblies 542a' and 542b' to send the recovered (e.g., modulated) alignment signal 546a to the detection system 548. As a result, spatial filter assemblies 542a' and 542b' can increase the DoM of the lithography apparatus 500', thereby allowing the alignment signal to be detected at a lower signal-to-noise ratio level. For example, the pupil filters of spatial filter assemblies 542a' and 542b' can restore DoM from approximately 8% to approximately 71%.

[0130] In some aspects, the pupil filter of the spatial filter assemblies 542a', 542b' can be a rotating disk with an opening optimized for a specific pitch. In some aspects, the pupil filter can be configured to be tuned to a target pitch aligned with the target 518 by means of at least one translational or rotational motion.

[0131] Figures 10A to 10B Pupil filters 1000a and 1000b are shown according to some aspects. In some aspects, pupil filters 1000a and 1000b can be incorporated into... Figure 9The spatial filter assemblies 542a' and 542b' are shown. In some aspects, the pupil filters 1000a and 1000b may include four or more openings configured to collect overlapping diffracted sub-beams of one or more predetermined wavelengths. In some aspects, the four or more openings may have a spectral coating to allow only specific wavelengths or wavelength ranges at a specific pupil location. In some aspects, the wavelength range may be visible light wavelengths from approximately 380 nm to approximately 750 nm.

[0132] In some respects, Figure 10A The spectral coating 1002 on the illustrated pupil filter 1000a can be a monochromatic filter. In some aspects, the spectral coating 1002 can transmit a single wavelength. For example, the spectral coating 1002 can transmit a single wavelength of 550 nm.

[0133] In some respects, Figure 10B The spectral coating on the illustrated pupil filter 1000b can be a multicolor filter, wherein each coating transmits only a single wavelength. In some aspects, the spectral coating 1004 can transmit a first wavelength. For example, the spectral coating 1004 can transmit a first wavelength of 550 nm. In some aspects, the spectral coating 1006 can transmit a second wavelength. For example, the spectral coating 1006 can transmit a second wavelength of 700 nm. In some aspects, the spectral coating overlap 1008 can transmit both the first and second wavelengths. For example, the spectral coating overlap 1008 can transmit both a first wavelength of 550 nm and a second wavelength of 700 nm.

[0134] Example Method

[0135] Figure 11 A method 1100 for recovering the modulation depth of an alignment signal is shown, according to some aspects. In some aspects, in step 1102, the radiation source (e.g., Figure 5 The radiation source 504 shown can produce one or more illumination beams (e.g., Figure 5 The illumination beam shown is 506.

[0136] In some respects, in step 1104, the radiation source can be directed toward the wafer (e.g., Figure 5 Alignment target (e.g., on substrate 520) shown Figure 5 The target 518 shown guides one or more illumination beams.

[0137] In some respects, in step 1106, the self-reference interferometer (e.g., Figure 5The SRI 532 shown can receive one or more diffracted beams (e.g., diffracted beams 530a, 530b) reflected from the aligned target, wherein the one or more diffracted beams include at least one positive diffraction order and one negative diffraction order.

[0138] In some respects, in step 1108, the self-reference interferometer can generate a beam including diffracted sub-beams (e.g., Figure 5 Alignment signals for diffracted sub-beams 534a-534d shown, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about the alignment axis, and are spatially overlapping.

[0139] In some respects, in step 1110, the spatial filter assembly (e.g., Figure 5 The spatial filter assemblies 542a and 542b shown can recover the modulation depth of the alignment signal. In some aspects, the spatial filter assembly may include a field stop (e.g., ...) disposed in the output plane of the alignment system. Figure 5 The reference grating at the field stops 544a and 544b shown is, for example, Figure 6 The reference grating 602 shown is illustrated. In some aspects, the reference grating can be configured to block the first diffractor beam (e.g., Figure 6 The diffractor beam 606a shown is shown, and a second diffractor beam (e.g., Figure 6 The diffracting sub-beam 606b shown passes through a reference grating to modulate the alignment signal (e.g., Figure 6 The restored alignment signal 612 shown is sent to the detection system (e.g., Figure 5 and Figure 6 The detection system shown is 548. In some aspects, the reference grating can be configured to form an interference pattern of the diffracted sub-beams, independent of any spatial overlap with the pupil plane of the alignment system.

[0140] In some respects, in step 1112, the measuring device can measure the light intensity of the alignment signal.

[0141] In some respects, in step 1114, the detection system can determine the position of the alignment target based on the light intensity measurement of the alignment signal.

[0142] Figure 11 The method steps can be performed in any conceivable order, and it is not necessary to perform all the steps. In addition, the above... Figure 11 The method steps described are merely examples, not limitations. That is, based on the reference... Figures 1A to 10B The described aspects envision further methodological steps and functionalities.

[0143] The following terms may also be used to describe the embodiments: 1. An alignment system, comprising: A radiation source configured to generate one or more illumination beams and direct one or more illumination beams toward an alignment target on a wafer, wherein one or more diffracted beams are reflected from the alignment target and the one or more diffracted beams include at least one positive diffraction order and one negative diffraction order; A self-reference interferometer is configured to receive one or more diffracted beams and generate an alignment signal comprising diffracted sub-beams, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about an alignment axis, and are spatially overlapping. A spatial filter assembly configured to recover the modulation depth of the alignment signal; A measuring device configured to measure the light intensity of an alignment signal; and A detection system configured to determine the position of the alignment target based on light intensity measurements of the alignment signal. 2. The alignment system according to Clause 1, wherein the spatial filter assembly includes a reference grating disposed at a field stop in the output plane of the alignment system. 3. The alignment system according to Clause 2, wherein the reference grating includes at least one of a 1D X-direction filter, a 1D Y-direction filter, a 2D XY-direction filter, a binary filter, a gray filter, or a spectral filter. 4. The alignment system according to Clause 3, wherein the reference grating includes a reference grating pitch corresponding to the target pitch of the alignment target. 5. The alignment system according to Clause 4, wherein the spatial filter assembly further includes a movable platform configured to tune the reference grating pitch to the target pitch by adjusting the reference grating using at least one of translational or rotational movements. 6. The alignment system according to Clause 5, wherein a reference grating is configured to block a first diffractor beam and allow a second diffractor beam to pass through the reference grating to send a modulated alignment signal to a detection system. 7. The alignment system according to Clause 5, wherein the reference grating is configured to form an interference pattern of the diffracting sub-beams, independent of any spatial overlap with the pupil plane of the alignment system. 8. The alignment system according to Clause 1, wherein the spatial filter assembly includes a pupil filter having four or more openings configured to collect one or more overlapping diffracted sub-beams of predetermined wavelengths, the pupil filter being disposed in front of an output lens in the alignment system and configured to be tuned to a target pitch of the alignment target by means of at least one of translational or rotational motion. 9. A photolithography apparatus, comprising: A lighting system configured to illuminate the pattern forming apparatus; A projection system configured to project an image from a pattern forming apparatus onto a wafer; and; Alignment system, the alignment system comprising: A radiation source configured to generate one or more illumination beams and direct one or more illumination beams toward an alignment target on a wafer, wherein one or more diffracted beams are reflected from the alignment target and the one or more diffracted beams include at least one positive diffraction order and one negative diffraction order; A self-reference interferometer is configured to receive one or more diffracted beams and generate an alignment signal comprising diffracted sub-beams, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about an alignment axis, and are spatially overlapping. A spatial filter assembly configured to recover the modulation depth of the alignment signal; A measuring device configured to measure the light intensity of an alignment signal; and A detection system configured to determine the position of the alignment target based on light intensity measurements of the alignment signal. 10. A lithography apparatus according to Clause 9, wherein the spatial filter assembly includes a reference grating disposed at a field stop in the output plane of the alignment system. 11. The photolithography apparatus according to Clause 10, wherein the reference grating includes at least one of a 1D X-direction filter, a 1D Y-direction filter, a 2D XY-direction filter, a binary filter, a gray filter, or a spectral filter. 12. A lithography apparatus according to Clause 11, wherein the reference grating includes a reference grating pitch corresponding to the target pitch of the aligned target. 13. The lithography apparatus according to Clause 12, wherein the spatial filter assembly further includes a movable platform configured to tune the reference grating pitch to a target pitch by adjusting the reference grating using at least one of translational or rotational motion. 14. A lithography apparatus according to Clause 13, wherein a reference grating is configured to block a first diffractor beam and allow a second diffractor beam to pass through the reference grating to transmit a modulation alignment signal to a detection system. 15. A photolithography apparatus according to Clause 13, wherein a reference grating is configured to form an interference pattern of diffracted sub-beams, independent of any spatial overlap with the pupil plane of the alignment system. 16. A lithography apparatus according to Clause 9, wherein the spatial filter assembly includes a pupil filter having four or more openings configured to collect one or more overlapping diffracted sub-beams of predetermined wavelengths, the pupil filter being disposed in front of an output lens in an alignment system and configured to be tuned to a target pitch for alignment using at least one of translational or rotational motion. 17. A method comprising: Guide one or more illumination beams toward the alignment target on the chip; One or more diffracted beams reflected from an aligned target are received using a self-reference interferometer, wherein the one or more diffracted beams include at least one positive diffraction order and one negative diffraction order; Alignment signals including diffracted sub-beams are generated using a self-reference interferometer, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about the alignment axis, and are spatially overlapping. The modulation depth of the alignment signal is recovered using a spatial filter assembly; The light intensity of the alignment signal was measured using measuring equipment; and The position of the target to be aligned is determined by using a detection system based on the light intensity measurement of the alignment signal. 18. The method according to Clause 17, wherein the spatial filter assembly includes a reference grating disposed at a field stop in the output plane of the alignment system. 19. The method according to Clause 18, wherein a reference grating is configured to block a first diffractor beam and allow a second diffractor beam to pass through the reference grating to send a modulation alignment signal to a detection system. 20. The method according to Clause 18, wherein the reference grating is configured to form an interference pattern of the diffracting sub-beams, independent of any spatial overlap with the pupil plane of the alignment system.

[0144] The terms “radiation,” “beam,” “light,” “illumination,” etc., used herein may refer to one or more types of electromagnetic radiation, such as ultraviolet (UV) radiation (e.g., wavelengths λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (e.g., wavelengths in the range of 5 nm–100 nm, such as 13.5 nm), or hard X-rays operating at less than 5 nm, and particle beams such as ion beams or electron beams. Generally, radiation with wavelengths between approximately 400 nm and approximately 700 nm is considered visible radiation; radiation with wavelengths between approximately 780 nm and 3000 nm (or greater) is considered IR radiation. UV refers to radiation with wavelengths approximately 100 nm–400 nm. In photolithography, the term “UV” also applies to wavelengths that can be produced by a mercury discharge lamp: G line 436 nm; H line 405 nm; and / or I line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by a gas) refers to radiation with wavelengths approximately 100 nm to 200 nm. Deep UV (DUV) generally refers to radiation with wavelengths ranging from 126 nm to 428 nm. In some applications, excimer lasers can generate DUV radiation for use within photolithography apparatuses. It should be understood that radiation with wavelengths in, for example, the range of 5 nm to 20 nm refers to radiation having a specific wavelength band, at least a portion of which falls within the 5 nm to 20 nm range.

[0145] Although some aspects of this disclosure are described in the context of a lithography apparatus in IC manufacturing, it should be understood that the lithography apparatus described herein can also be used for other applications, such as the fabrication of integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, LCDs, thin-film magnetic heads, etc. Those skilled in the art will understand that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion,” respectively. The substrate can be processed before or after exposure in, for example, a tracking unit (typically a tool for applying a resist layer to the substrate and developing the exposed resist) and / or a measurement unit. Where applicable, aspects of the disclosure herein can be applied to such substrate processing tools and other substrate processing tools. Furthermore, the substrate can be processed more than once to, for example, create multilayer ICs, such that the term “substrate” as used herein can also refer to a substrate that already contains multiple processed layers.

[0146] Furthermore, although some aspects of this disclosure have been described in the context of optical lithography, it should be understood that aspects of this disclosure are not limited to optical lithography. For example, in imprint lithography, the morphology in the patterning apparatus defines a pattern created on a substrate. The morphology of the patterning apparatus can be pressed into a resist layer provided to the substrate, whereby the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning apparatus is removed from the resist, thereby leaving a pattern therein after the resist has cured.

[0147] It should be understood that the wording or terminology used herein is for descriptive purposes and not for limiting purposes, and that the terminology or terminology used herein shall be interpreted by those skilled in the art based on the teachings herein.

[0148] The present disclosure has been described above by way of functional building blocks illustrating the implementation of specified functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined herein. Alternative boundaries can be defined as long as the specified functions and their relationships are properly performed. The foregoing description of specific aspects will fully reveal the general nature of the present disclosure, enabling others to readily modify and / or adapt various applications of these specific aspects by applying knowledge within the art, without excessive experimentation and without departing from the general concepts of the present disclosure. Therefore, based on the teachings and guidance presented herein, such adaptations and modifications are intended to fall within the meaning and scope of equivalents of the disclosed aspects.

[0149] It should be understood that the “Detailed Description” section (rather than the “Summary” and “Abstract” sections) is intended to interpret the claims. The “Summary” and “Abstract” sections may set forth one or more, but not necessarily all, aspects of this disclosure as conceived by (multiple) inventors, and are therefore not intended to limit this disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the foregoing aspects, but should be defined by the claims and their equivalents.

Claims

1. An alignment system, the alignment system comprising: A radiation source configured to generate one or more illumination beams and direct the one or more illumination beams toward an alignment target on a wafer, wherein one or more diffracted beams are reflected from the alignment target and the one or more diffracted beams include at least one positive diffraction order and one negative diffraction order; A self-reference interferometer is configured to receive the one or more diffracted beams and generate an alignment signal including diffracted sub-beams, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about an alignment axis, and are spatially overlapping. A spatial filter assembly configured to recover the modulation depth of the alignment signal; A measuring device configured to measure the light intensity of the alignment signal; as well as A detection system configured to determine the position of the alignment target based on the light intensity measurement of the alignment signal.

2. The alignment system of claim 1, wherein the spatial filter assembly includes a reference grating disposed at a field stop in the output plane of the alignment system.

3. The alignment system of claim 2, wherein the reference grating comprises at least one of a 1D X-direction filter, a 1D Y-direction filter, a 2D XY-direction filter, a binary filter, a gray filter, or a spectral filter.

4. The alignment system of claim 3, wherein the reference grating includes a reference grating pitch corresponding to the target pitch of the alignment target.

5. The alignment system of claim 4, wherein the spatial filter assembly further comprises a movable platform configured to tune the reference grating pitch to the target pitch by adjusting the reference grating using at least one of translational or rotational motion.

6. The alignment system of claim 5, wherein the reference grating is configured to block the first diffracting beam and allow the second diffracting beam to pass through the reference grating to transmit a modulated alignment signal to the detection system.

7. The alignment system of claim 5, wherein the reference grating is configured to form an interference pattern of the diffracted sub-beams, independent of any spatial overlap with the pupil plane of the alignment system.

8. The alignment system of claim 1, wherein the spatial filter assembly includes a pupil filter having four or more openings configured to collect one or more overlapping diffracted sub-beams of predetermined wavelengths, the pupil filter being disposed in front of an output lens in the alignment system and configured to be tuned to the target pitch of the alignment target by at least one of translational or rotational motion.

9. A photolithography apparatus, the photolithography apparatus comprising: A lighting system configured to illuminate the pattern forming apparatus; A projection system configured to project an image from the pattern forming apparatus onto a wafer; as well as ； Alignment system, the alignment system comprising: A radiation source configured to generate one or more illumination beams and direct the one or more illumination beams toward an alignment target on the wafer, wherein one or more diffracted beams are reflected from the alignment target and the one or more diffracted beams include at least one positive diffraction order and one negative diffraction order; A self-reference interferometer is configured to receive the one or more diffracted beams and generate an alignment signal including diffracted sub-beams, wherein the diffracted sub-beams are orthogonally polarized, rotated 180 degrees relative to each other about an alignment axis, and are spatially overlapping. A spatial filter assembly configured to recover the modulation depth of the alignment signal; A measuring device configured to measure the light intensity of the alignment signal; and A detection system configured to determine the position of the alignment target based on light intensity measurements of the alignment signal.

10. The lithography apparatus of claim 9, wherein the spatial filter assembly includes a reference grating disposed at a field stop in the output plane of the alignment system.

11. The photolithography apparatus of claim 10, wherein the reference grating comprises at least one of a 1D X-direction filter, a 1D Y-direction filter, a 2D XY-direction filter, a binary filter, a gray filter, or a spectral filter.

12. The lithography apparatus of claim 11, wherein the reference grating includes a reference grating pitch corresponding to the target pitch of the aligned target.

13. The lithography apparatus of claim 12, wherein the spatial filter assembly further comprises a movable platform configured to tune the reference grating pitch to the target pitch by adjusting the reference grating using at least one of translational or rotational motion.

14. The lithography apparatus of claim 13, wherein the reference grating is configured to block the first diffracting beam and allow the second diffracting beam to pass through the reference grating to transmit a modulation alignment signal to the detection system.

15. The lithography apparatus of claim 13, wherein the reference grating is configured to form an interference pattern of the diffracting sub-beams, independent of any spatial overlap with the pupil plane of the alignment system.

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