Alignment system and lithography device

Abstract

The alignment system comprises a radiation source, a self-reference interferometer, a spatial filter assembly, a measuring device, and a detection system. The radiation source generates one or more illumination beams and directs one or more illumination beams to an alignment target on a wafer. The self-reference interferometer receives one or more diffracted beams and generates an alignment signal comprising diffracted subbeams, which are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlap. The spatial filter assembly restores the modulation degree of the alignment signal. The measuring device measures the optical intensity measurement of the alignment signal. The detection system determines the position of the alignment target based on the optical intensity measurement of the alignment signal.

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the priority of U.S. Application No. 63 / 518,598, filed on August 10, 2023, which is hereby incorporated by reference in its entirety.

[0002] [Technical Field] The present disclosure relates to measurement systems, for example, alignment systems for measuring the position of alignment marks in lithography apparatuses and systems.

Background Art

[0003] A lithography apparatus is a machine that typically applies a desired pattern to a target portion of a substrate. Lithography apparatuses are used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device, such as a mask or reticle, can be used to generate the circuit patterns formed on the individual layers of the IC. This pattern is transferred to a target portion (e.g., a part of a die, or a portion comprising one or more dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is typically by imaging onto a layer of radiation - sensitive material (photoresist, or simply "resist") provided on the substrate. Generally, a single substrate includes a network of adjacent target portions that are successively patterned. Known lithography apparatuses include so - called steppers that expose the entire pattern to each target portion at once, and so - called scanners that scan the pattern in a predetermined direction ("scan" direction) through a radiation beam and irradiate each target portion by synchronously scanning the target portion parallel or antiparallel to this scan direction. Also, the pattern can be transferred from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During the lithography process, different processing steps may inevitably involve the sequential formation of different layers on a substrate. Therefore, it may be necessary to position the substrate with high precision relative to previously formed patterns on it. Generally, alignment marks are placed on the substrate to be aligned, and are positioned relative to a second object. A lithography apparatus can use an alignment device to detect the position of the alignment marks, align the substrate using the alignment marks, and ensure accurate exposure from the mask. A misalignment between alignment marks on two different layers is measured as an overlay error.

[0005] To monitor the lithography process, parameters of the patterned substrate are measured. These parameters include, for example, overlay errors between continuous layers formed within or on the patterned substrate, and the critical linewidth of the developed photosensitive resist. This measurement can be performed on the product substrate and / or on a dedicated measurement target. Various techniques exist for measuring the microstructure formed during the lithography process, including the use of scanning electron microscopes and various specialized tools. A fast and non-invasive specialized inspection tool is a scattermeter, which irradiates a beam of radiation onto a target on the substrate surface and measures the characteristics of the scattered or reflected beam. By comparing the characteristics of the beam before and after reflection or scattering by the substrate, the characteristics of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurement values ​​associated with known substrate characteristics. A spectroscattermeter irradiates a substrate with a broadband beam of radiation and measures the spectrum (intensity as a function of wavelength) of the radiation scattered over a specific narrow angular range. In contrast, angle-resolved scattermeters use a monochromatic radiation beam to measure the intensity of scattered radiation as a function of angle.

[0006] Such light scattering meters can be used to measure parameters such as the critical dimensions of a developed photosensitive resist or the overlay error (OV) between two layers formed in or on a patterned substrate. The characteristics of the substrate can be determined by comparing its characteristics before and after the illumination beam is reflected or scattered by the substrate.

[0007] Current alignment sensors can generate an alignment signal by interfering the positive and negative orders of diffracted light from the substrate using a self-reference interferometer. The detection system can determine the position of the alignment marks on the substrate by measuring the position of the peak in the alignment signal and comparing it to the predicted peak position. As the thickness of the resist on the substrate increases, the resist covering the alignment marks may tilt due to material non-uniformity. The tilted resist can cause degradation of the alignment signal (e.g., a decrease in modulation), potentially leading to alignment errors in the detection system. [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, it is desirable to restore the degraded alignment signal caused by the tilted resist. For example, an optical inspection process can be performed using the restored alignment signal based on the embodiments described herein. [Means for solving the problem]

[0009] In some embodiments, the 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 can generate one or more illumination beams and guide one or more illumination beams to an alignment target on a wafer. One or more diffracted beams may be reflected from the alignment target, and one or more diffracted beams may include at least one positive diffraction order and one negative diffraction order. The self-reference interferometer can receive one or more diffracted beams and generate an alignment signal including diffracted subbeams, which are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlap. The spatial filter assembly can restore the modulation degree of the alignment signal. The measuring device can measure the optical intensity measurement of the alignment signal. The detection system can determine the position of the alignment target based on the optical intensity measurement of the alignment signal.

[0010] In some embodiments, a lithography apparatus may include an illumination system, a projection system, and an alignment system. The illumination system can illuminate a patterning device. The projection system can project an image of the patterning device onto a wafer. The 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 can generate one or more illumination beams and guide one or more illumination beams to an alignment target on the wafer. One or more diffracted beams may be reflected from the alignment target, and one or more diffracted beams may include at least one positive diffraction order and one negative diffraction order. The self-reference interferometer can receive one or more diffracted beams and generate an alignment signal including diffracted subbeams, which are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlap. The spatial filter assembly can restore the modulation degree of the alignment signal. The measuring device can measure the optical intensity measurement of the alignment signal. The detection system can determine the position of the alignment target based on the optical intensity measurement of the alignment signal.

[0011] In some embodiments, the method may include generating one or more illumination beams using a radiation source. The method may further include guiding one or more illumination beams to an alignment target on a wafer using a 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 have at least one positive diffraction order and one negative diffraction order. The method may further include generating an alignment signal comprising diffracted subbeams using a self-reference interferometer, wherein the diffracted subbeams are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlap. The method may further include restoring the modulation degree of the alignment signal using a spatial filter assembly. The method may further include measuring the optical intensity measurement of the alignment signal using a measuring device. The method may further include determining the position of the alignment target based on the optical intensity measurement of the alignment signal using a detection system.

[0012] Further features of various aspects of this disclosure are described below in detail with reference to the accompanying drawings. It should be noted that this disclosure is not limited to the specific aspects described herein. Such 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. [Brief explanation of the drawing]

[0013] The accompanying drawings incorporated herein and constituting part of this specification are illustrative of the disclosure and, together with the description herein, further illustrate the principles of the disclosure and enable those skilled in the art to carry out and use the embodiments described herein.

[0014] [Figure 1A]A diagram showing a reflective lithography apparatus according to some embodiments.

[0015] [Figure 1B] A diagram showing a transmissive lithography apparatus according to some embodiments.

[0016] [Figure 2] A diagram showing more details of a reflective lithography apparatus according to some embodiments.

[0017] [Figure 3] A diagram showing a lithography cell according to some embodiments.

[0018] [Figure 4A] A diagram showing an inspection apparatus according to some embodiments. [Figure 4B] A diagram showing an inspection apparatus according to some embodiments.

[0019] [Figure 5] A diagram showing a lithography apparatus having a spatial filter assembly according to some embodiments.

[0020] [Figure 6] A diagram showing a spatial filter assembly having a reference grating according to some embodiments.

[0021] [Figure 7A] A diagram showing a reference grating according to some embodiments. [Figure 7B] A diagram showing a reference grating according to some embodiments. [Figure 7C] A diagram showing a reference grating according to some embodiments.

[0022] [Figure 8A] A diagram showing the modulation degree of an alignment signal according to some embodiments. <000​​​

[0023] [Figure 9] This figure shows a lithography apparatus having a pupil filter according to several embodiments.

[0024] [Figure 10A] This figure shows pupil filters in several embodiments. [Figure 10B] This figure shows pupil filters in several embodiments.

[0025] [Figure 11] This figure shows a method for restoring the modulation degree of an alignment signal according to several embodiments.

[0026] The features of this disclosure will become clearer when the following detailed description is read in conjunction with the drawings. In the drawings, the same reference numeral indicates a corresponding element throughout. In the drawings, the same reference numeral generally indicates the same, functionally similar, and / or structurally similar element. Also, generally, the leftmost number of a reference numeral indicates the drawing in which that reference numeral first appears. Unless otherwise specified, the drawings provided throughout this disclosure should not be interpreted as to scale drawings. [Modes for carrying out the invention]

[0027] The embodiments described herein, and references thereto such as “one embodiment,” “a certain embodiment,” “a certain exemplary embodiment,” and “an example embodiment,” indicate that the described embodiments may include certain features, structures, or characteristics, but not all embodiments necessarily include certain features, structures, or characteristics. Furthermore, these expressions do not necessarily refer to the same embodiment. Moreover, if certain features, structures, or characteristics are described in relation to an embodiment, it is understood that realizing such features, structures, or characteristics in relation to other embodiments, whether or not they are explicitly stated, is within the scope of the knowledge of those skilled in the art.

[0028] Spatially relative terms such as "down," "below," "underside," "up," "above," and "upper side" may be used for explanatory convenience to describe the relationship between one element or feature and another, as shown in the drawings. These spatially relative terms are intended to encompass various orientations of the device during use or operation, in addition to the orientation shown in the drawings. The device may be oriented in other directions (90-degree rotation or other directions), and therefore, spatially relative descriptions used herein can be interpreted accordingly.

[0029] In this specification, terms such as “approximately” and “about” can be used to indicate a value of a given quantity that may vary based on a particular technology. Based on a particular technology, terms such as “approximately” and “about” may indicate a value that varies within a range of 10 to 30% (e.g., ±10%, ±20%, or ±30% of the given value) of the given quantity.

[0030] Aspects of this disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of this disclosure can also be implemented as instructions stored in a computer-readable medium that is readable and executable by one or more processors. The machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, the machine-readable medium may include read-only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, and propagating signals in electrical, optical, acoustic, or other forms (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, routines, and / or instructions may be described herein as performing certain operations. However, such descriptions are for convenience only, and it should be understood that such operations are produced by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc. The term “machine-readable medium” can be used interchangeably with similar terms such as “computer program product,” “computer-readable medium,” and “non-temporary computer-readable medium.” The term “non-transient” may be used herein to characterize one or more forms of computer-readable media, excluding transient propagating signals.

[0031] However, before describing such embodiments in more detail, it is useful to present exemplary environments in which embodiments of this disclosure can be implemented.

[0032] Examples of lithography systems

[0033] Figures 1A and 1B show lithography apparatus 100 and 100', respectively, that can implement embodiments of the present disclosure. Each of lithography apparatus 100 and 100' includes the following components: an illumination system (illuminator) IL configured to adjust a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask, reticle, or dynamic patterning device) MA and connected to a first positioning device PM configured to precisely position the patterning device MA; and a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioning device PW configured to precisely position the substrate W. Lithography apparatuses 100 and 100' also include a projection system PS configured to project the pattern applied to the radiation beam B by the patterning device MA onto a target portion (e.g., comprising one or more dies) C of the substrate W. In lithography apparatus 100, the patterning device MA and projection system PS are reflective. In lithography apparatus 100', the patterning device MA and projection system PS are transmissive.

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

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

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

[0037] The patterning device MA can be transmissive (as in lithography apparatus 100' in Figure 1B) or reflective (as in lithography apparatus 100 in Figure 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography and include various hybrid mask types, as well as mask types such as binary masks, Levenson phase-shift masks, and halftone phase-shift masks. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be tilted individually to reflect the incident radiation beam 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, reflector-refracting, magnetic, electromagnetic, electrostatic, or any combination thereof, depending on the exposure radiation used or other factors such as the use of immersion liquid in the substrate W and the use of vacuum. A vacuum environment can be used for EUV or electron beam radiation because other gases may excessively absorb radiation or electrons. Therefore, a vacuum environment can be provided throughout the beam path using vacuum walls and vacuum pumps.

[0039] Lithography apparatus 100 and / or lithography apparatus 100' may be of a type that includes two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a “multistage” machine, additional substrate tables WT may be used in parallel, or preparation steps may be performed on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional tables do not have to be substrate tables WT.

[0040] A lithography apparatus can be of a type in which at least a portion of the substrate is coated with a liquid having a relatively high refractive index (e.g., water) to fill the space between the projection system and the substrate. The immersion liquid can also be applied to other spaces within the lithography apparatus, such as between the mask and the projection system. Immersion techniques are well known in the art as a technique for increasing the numerical aperture of the projection system. As used herein, the term “immersion” does not mean that structures such as the substrate must be immersed in the liquid. For example, the liquid can be located between the projection system and the substrate during exposure.

[0041] Referring to Figures 1A and 1B, the illuminator IL receives the radiation beam from the radiation source SO. The radiation source SO and the lithography apparatus 100, 100' can be separate physical entities, for example, if the radiation source SO is an excimer laser. In such a case, the radiation source SO is not considered part of the lithography apparatus 100 or 100', and the radiation beam B passes from the radiation source SO to the illuminator IL with the help of a beam delivery system BD (see Figure 1B), which includes, for example, a suitable guide mirror and / or beam expander. In other cases, for example, if the radiation source SO is a mercury lamp, the radiation source SO can be an integrated part of the lithography apparatus 100, 100'. The radiation system can comprise the radiation source SO, the illuminator IL, and / or the beam delivery system BD.

[0042] The illuminator IL may be equipped with an adjuster AD (see Figure 1B) for adjusting the angular intensity distribution of the radiated beam. Generally, at least the outer diameter range and / or inner diameter range (commonly referred to as "σ outer" and "σ inner," respectively) of the intensity distribution at the pupil plane of the illuminator can be adjusted. Furthermore, the illuminator IL may be equipped with various other components (see Figure 1B), such as an integrator IN and a capacitor CO. The illuminator IL is used to adjust the radiated beam B so that a desired uniformity and intensity distribution is obtained in the cross-section of the radiated beam B.

[0043] Referring to Figure 1A, the radiant beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and patterned by the patterning device MA. In the lithography apparatus 100, the radiant beam B is reflected from the patterning device (e.g., a mask) MA. After being reflected from the patterning device (e.g., a mask) MA, the radiant beam B passes through a projection system PS, which focuses the radiant beam B onto a target portion C of the substrate W. With the help of a second positioning device PW and a position sensor IF2 (e.g., an interferometer, a linear encoder, or a capacitive sensor), the substrate table WT can be precisely moved (e.g., so that different target portions C are located within the path of the radiant beam B). Similarly, a first positioning device PM and another position sensor IF1 can be used to precisely position the patterning device (e.g., a mask) MA relative to the path of the radiant beam B. The patterning device (e.g., a mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0044] Referring to Figure 1B, the radiant beam B is incident on a patterning device (e.g., mask MA) held on a support structure (e.g., mask table MT) and patterned by the patterning device. After passing through the mask MA, the radiant beam B passes through a projection system PS and is focused by the projection system PS onto a target portion C of the substrate W. The projection system has a pupil PPU conjugate to the illumination system pupil IPU. A portion of the radiant beam originates from the intensity distribution in the illumination system pupil IPU, passes through the mask pattern without being affected by diffraction in the mask pattern, and forms an image of the intensity distribution in 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, and this image is formed by a diffracted beam generated from the mask pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may include a line-and-space array. The diffraction of radiation in the array, unlike zero-order diffraction, produces a deflected diffracted beam whose direction changes in the direction perpendicular to the lines. The undiffracted beam (the so-called zero-order diffracted beam) passes through the pattern without changing its propagation direction. The zero-order diffracted beam passes through the upper lens or upper lens group of the projection system PS, which is upstream of the pupil-conjugate PPU of the projection system PS, and reaches the pupil-conjugate PPU. The portion of the in-plane intensity distribution of the pupil-conjugate PPU that is related to 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, the aperture device PD is positioned in the plane containing the pupil-conjugate PPU of the projection system PS, or substantially in that plane.

[0046] The projection system PS is configured (e.g., using lenses or lens group L) to capture a zero-order diffraction beam, a primary diffraction beam, and / or a higher-order diffraction beam (not shown). In some embodiments, dipole illumination for imaging a line pattern extending in a direction perpendicular to the line can be used to take advantage of the resolution-enhancing effect of dipole illumination. For example, a primary diffraction beam interferes with the corresponding zero-order diffraction beam at the wafer W level to produce an image of the line pattern MP with the highest possible resolution and process window (i.e., usable depth of field in combination with an acceptable exposure dose deviation). In some embodiments, astigmatism can be reduced by providing radiating poles (not shown) in the opposing quadrants of the illumination system pupil IPU. Furthermore, in some embodiments, astigmatism can be reduced by blocking the zero-order beam in the projection system pupil conjugate PPU related to the radiating pole in the opposing quadrant. This is described in more detail in US7,511,799B2, issued March 31, 2009, which is incorporated herein by reference in its entirety.

[0047] With the help of a second positioning device PW and a position sensor IFD (e.g., an interferometer, linear encoder, or capacitive sensor), the substrate table WT can be precisely moved (e.g., so that different target portions C are positioned within the path of the radiation beam B). Similarly, a first positioning device PM and another position sensor (not shown in Figure 1B) can be used to precisely position the mask MA relative to the path of the radiation beam B (e.g., after a machine search from the mask library or during scanning).

[0048] Generally, the movement of the mask table MT can be achieved using long-stroke modules (coarse positioning) and short-stroke modules (fine positioning) that form part of the first positioning device PM. Similarly, the movement of the substrate table WT can be achieved using long-stroke modules and short-stroke modules that form part of the second positioning device PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to or fixed to a short-stroke actuator. The mask MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks occupy dedicated target areas (as shown in the figure), but can also be placed in the space between the target areas (called scribe line alignment marks). Similarly, if two or more dies are provided on the mask MA, the mask alignment marks can be placed between the dies.

[0049] The mask table MT and patterning device MA can be located inside the vacuum chamber V, and an in-vacuum robot IVR can be used to move the patterning device, such as a mask, in and out of the vacuum chamber. Alternatively, if the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot can be used for various transport operations, similar to an in-vacuum robot IVR. Both in-vacuum and out-of-vacuum robots can be calibrated to smoothly transport any payload (e.g., a mask) to a fixed kinematic mount on a transport station.

[0050] Lithography devices 100 and 100' can be used in at least one of the following modes:

[0051] 1. In step mode, while the support structure (e.g., mask table) MT and substrate table WT are kept essentially stationary, the entire pattern applied to the radiation beam B is projected onto the target portion C at once (i.e., single static exposure). Subsequently, the substrate table WT is shifted in the X and / or Y directions to expose another target portion C.

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

[0053] 3. In another mode, the support structure (e.g., mask table) MT is kept substantially stationary while holding the programmable patterning device, and the pattern applied to the radiated beam B is projected onto the target portion C while the substrate table WT is moved or scanned. A pulsed radiation source SO can be employed, and the programmable patterning device is updated as needed after each movement of the substrate table WT or between consecutive radiated pulses during scanning. This operating mode can be readily applied to maskless lithography utilizing programmable patterning devices such as programmable mirror arrays.

[0054] Combinations and variations of the modes described, or even the use of entirely different modes, can be employed.

[0055] In some embodiments, 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 within a radiation system, and the corresponding illumination system is configured to adjust the EUV radiation beam of the EUV source.

[0056] In some embodiments, the lithography apparatus 100' includes a deep ultraviolet (DUV) source configured to produce a DUV radiation beam for DUV lithography. Generally, the DUV source is configured within a radiation system, and the corresponding illumination system is configured to adjust the DUV radiation beam of the DUV source.

[0057] Figure 2 shows a lithography apparatus 100 in more detail, including a source collector apparatus SO, an illumination system IL, and a projection system PS. The source collector apparatus SO is constructed and configured to maintain a vacuum environment within the surrounding structure 220 of the source collector apparatus SO. The EUV radiative emission plasma 210 can be formed by a discharge-generating plasma source. EUV radiation can be generated by a gas or vapor such as, for example, Xe gas, Li vapor, or Sn vapor, in which the EUV radiative emission plasma 210 is generated and radiation of the electromagnetic spectrum in the EUV region is emitted. The EUV radiative emission plasma 210 is generated, for example, by a discharge that produces at least a partially ionized plasma. For example, partial pressures of Xe, Li, Sn vapor, or other suitable gas or vapor at 10 Pa can be used to efficiently generate radiation. In some embodiments, a plasma of excited tin (Sn) (e.g., excited by a laser) is provided to generate EUV radiation.

[0058] The radiation emitted by the EUV radiative emission plasma 210 passes from the source chamber 211 to the collector chamber 212 through an optional gas barrier or contaminant trap 230 (also referred to as a contaminant barrier or foil trap, in some cases), the contaminant trap 230 being located within or behind the opening of the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier, or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 includes at least a channel structure, as further described herein.

[0059] The collector chamber 212 may include a radiation collector CO, which can be a so-called oblique incidence (grazing incidence) collector. The radiation collector CO has an upstream radiation collector surface 251 and a downstream radiation collector surface 252. Radiation passing through collector CO can be reflected by a grating spectral filter 240 and focused to a virtual source point INTF. The virtual source point INTF is commonly called an intermediate focus, and the source collector apparatus is positioned such that the intermediate focus INTF is located at or near the opening 219 of the surrounding 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] The radiation then passes through the illumination system IL. The illumination system IL comprises a faceted field mirror device 222 and a faceted pupil mirror device 224, configured to provide a desired angular distribution of the radiation beam 221 at the patterning device MA, and to provide a desired uniformity of radiation intensity at the patterning device MA. When the radiation beam 221 is reflected by the patterning device MA, which is held by the support structure MT, a pattern beam 226 is formed, and the pattern beam 226 is imaged by the projection system PS onto a substrate W held by a wafer stage or substrate table WT via reflective elements 228, 229.

[0061] The illumination optical system unit IL and the projection optical system PS typically contain more elements than those shown. The grating spectral filter 240 can be optionally present depending on the type of lithography apparatus. Furthermore, more mirrors than those shown in Figure 2 may be provided; for example, the projection optical system PS may have one to six additional reflective elements than those shown in Figure 2.

[0062] As shown in Figure 2, the collector optical system CO is depicted as a nested collector with oblique incidence reflectors 253, 254, and 255, as just one example of a collector (or collector mirror). The oblique incidence reflectors 253, 254, and 255 are arranged axially around the optical axis O, and this type of collector optical system CO is often preferred to be used in combination with a discharge-generating plasma source, often called a DPP source.

[0063] Examples of lithography cells

[0064] Figure 3 shows a lithography cell 300, sometimes also called a lithocell or cluster. A lithography apparatus 100 or 100' can form part of the lithography cell 300. The lithography cell 300 may also include one or more apparatuses for performing pre-exposure and post-exposure processes on the substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH, and a bake plate BK. A substrate handler or robot RO picks up the substrate from input / output ports I / O1 and I / O2, moves it between different process apparatuses, and transports it to the loading bay LB of the lithography apparatus 100 or 100'. These apparatuses are often collectively referred to as a track and are under the control of a track control unit TCU, which in turn is controlled by a monitoring and control system SCS that controls the lithography apparatus via a lithography control unit LACU. Thus, various apparatuses can operate to maximize throughput and processing efficiency.

[0065] Examples of inspection equipment

[0066] To control the lithography process and accurately position device features on the substrate, alignment marks are typically provided on the substrate, and the lithography apparatus includes one or more inspection devices for accurately positioning the marks on the substrate. These alignment devices are, in effect, position measuring devices. Various types of marks, various types of alignment devices and / or systems are known from various eras and various manufacturers. A type of system widely used in current lithography apparatus is based on a self-referencing interferometer described in U.S. Patent No. 6,961,116 (den Boef et al.). Typically, marks are measured individually to obtain the X and Y positions. However, combined measurements of the X and Y positions can be performed using the technique described in U.S. Patent Publication No. 2009 / 195768A (Bijnen et al.). The entire contents of both of these disclosures are incorporated herein by reference.

[0067] Figure 4A shows a cross-sectional view of an inspection device 400 that can be implemented as part of a lithography apparatus 100 or 100' according to several embodiments. In some embodiments, the inspection device 400 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). The inspection device 400 can be further configured to detect the position of alignment marks on the substrate and to use the detected position of the alignment marks to align the substrate with respect to the patterning device or other components of the lithography apparatus 100 or 100'. Such alignment of the substrate can ensure that one or more patterns are accurately exposed on the substrate.

[0068] In this specification, terms such as “inspection apparatus” and “measurement system” may be used to refer to, for example, devices used to measure structural properties (e.g., overlay sensors, critical dimension sensors, etc.), devices or systems used to inspect wafer alignment in lithography apparatus (e.g., alignment sensors), etc.

[0069] In some embodiments, the inspection apparatus 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a processor 432. The illumination system 412 may be configured to provide a narrowband electromagnetic radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a wavelength spectrum from about 500 nm to about 900 nm. In another example, the one or more passbands may be discrete narrowbands within a wavelength spectrum from about 500 nm to about 900 nm. The illumination system 412 may be further configured to provide one or more passbands having a substantially constant center wavelength (CWL) value over a long period of time (e.g., over the lifetime of the illumination system 412). Such a configuration of the illumination system 412 can help prevent the actual CWL value from shifting from the desired CWL value in the current alignment system, as described above. As a result, the use of a constant CWL value can improve the long-term stability and accuracy of the alignment system (e.g., inspection device 400) compared to current alignment devices.

[0070] In some embodiments, the beam splitter 414 can be configured to receive the radiating beam 413 and split the radiating beam 413 into at least two radiating subbeams. For example, as shown in Figure 4A, the radiating beam 413 can be split into radiating subbeams 415 and 417. The beam splitter 414 can be further configured to irradiate the radiating subbeam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 is movable along a direction 424. The radiating subbeam 415 can be configured to irradiate an alignment mark or target 418 placed on the substrate 420. The alignment mark or target 418 can be coated with a photosensitive film. In some embodiments, the alignment mark or target 418 can have 180-degree (i.e., 180°) symmetry. In other words, if the alignment mark or target 418 is rotated 180° around an axis of symmetry perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 can be substantially identical to the unrotated alignment mark or target 418. The target 418 on the substrate 420 can be a composite grating stack in an overlay target structure comprising (a) a resist layer grating with bars formed of solid resist lines, (b) a product layer grating, or (c) resist gratings superimposed on or alternately arranged on the product layer grating. Alternatively, the bars can also be etched into the substrate. This pattern is susceptible to chromatic aberration in lithography projection equipment, particularly in projection systems PL, and the symmetry of illumination and the presence of such aberrations will manifest as variations in the printed grating. One inline method used for measuring line width, pitch, and critical dimensions in device manufacturing utilizes a technique known as "scatter measurement."The scattering measurement method is described in "Multiparameter Grating Metrology Using Optical Scatterometry" by Raymond et al., J. Vac. Sci. Tech. B, Vol.15, no.2, pp.361-368 (1997), and in "Specular Spectroscopic Scatterometry in DUV Lithography" by Niu et al., SPIE, Vol.3677 (1999), both of which are incorporated herein by reference in their entirety. In scattering measurement, light is reflected by periodic structures within the target, and the reflection spectrum at a given angle is detected. The structures that produce the reflection spectrum are reconstructed, for example, using exact coupled-wave analysis (RCWA) or by comparison with a library of patterns obtained by simulation. Thus, scattering measurement data of printed gratings are used to reconstruct the gratings. Grating parameters such as linewidth and shape can be input into the reconstruction process performed by the processing unit (PU) from insights gained from the printing process and / or other scattering measurement processes.

[0071] In some embodiments, the beam splitter 414 can be further configured to receive the diffractive radiation beam 419 and split the diffractive radiation beam 419 into at least two radiation subbeams. The diffractive radiation beam 419 can be split into diffractive radiation subbeams 429 and 439, as shown in Figure 4A.

[0072] While the beam splitter 414 is shown to guide the radiating subbeam 415 to the alignment mark or target 418 and the diffracting radiating subbeam 429 to the interferometer 426, it should be noted that the disclosure is not limited thereto. Other optical configurations may also be used to obtain similar results, such as illuminating the alignment mark or target 418 on the substrate 420 and detecting an image of the alignment mark or target 418.

[0073] As shown in Figure 4A, the interferometer 426 can be configured to receive a radiating subbeam 417 and a diffracting radiating subbeam 429 through a beam splitter 414. In one exemplary embodiment, the diffracting radiating subbeam 429 may be at least a portion of the radiating subbeam 415 that can be reflected from the alignment mark or target 418. In one example of this embodiment, the interferometer 426 comprises any suitable set of optical elements, such as a combination of prisms that can be configured to form two images of the alignment mark or target 418 based on the received diffracting radiating subbeam 429. It should be understood that it is not necessary to form images of good quality; it is sufficient that the features of the alignment mark 418 are resolved. The interferometer 426 can be further configured to rotate one of the two images 180° relative to the other and to interferometrically recombine the rotated image with the unrotated image.

[0074] In some embodiments, the detector 428 may be further configured to receive the recombined image via the interferometer signal 427 when the alignment axis 421 of the inspection apparatus 400 passes through the center of symmetry (not shown) of the alignment mark or target 418, and to detect interference as a result of the recombined image. Such interference may, according to one exemplary embodiment, result from the alignment mark or target 418 being 180° symmetric and the recombined image interfering constructively or destructively. Based on the detected interference, the detector 428 may be further configured to determine the position of the center of symmetry of the alignment mark or target 418, and as a result detect the position of the substrate 420. According to one example, the alignment axis 421 can be aligned with a light beam orthogonal to the substrate 420 and passing through the center of the image rotation interferometer 426. The detector 428 may be further configured to estimate the position of the alignment mark or target 418 by implementing sensor characteristics and interacting with variations in the wafer marking process.

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

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

[0077] 2. Measure the change in position at various orders (position shift between diffraction orders).

[0078] 3. Measure the change in position (position shift between polarizations) under various polarizations.

[0079] 4. Measure the intensity difference between opposing orders of diffraction order pairs (e.g., to characterize and correct for asymmetry).

[0080] This data can be acquired using any type of alignment sensor, for example, the SMASH (Smart Alignment Sensor Hybrid) sensor described in U.S. Patent No. 6,961,116, which uses a single detector and a self-reference interferometer with four different wavelengths to extract the alignment signal in software, or Athena (Advanced Technology using High-order ENhancement of Alignment) described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector. Both of these are incorporated herein by reference in their entirety.

[0081] In some embodiments, the beam analyzer 430 can be configured to receive and determine the optical state of the diffracted radiation subbeam 439. The optical state can be a measure of beam wavelength, polarization, or beam profile. The beam analyzer 430 can be further configured to determine the position of the stage 422 and correlate the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. In this way, the position of the alignment mark or target 418, and consequently the position of the substrate 420, can be precisely determined with respect to the stage 422. Alternatively, the beam analyzer 430 can be configured to determine the position of the inspection device 400 or any other reference element, thereby determining the center of symmetry of the alignment mark or target 418 with respect to the inspection device 400 or any other reference element. The beam analyzer 430 can be a point polarimeter or imaging polarimeter using some form of wavelength band selectivity. In some embodiments, the beam analyzer 430 can be directly integrated into the inspection device 400, or, according to other embodiments, it can be connected via multiple types of optical fibers, such as polarization-preserving single-mode, multi-mode, or imaging optical fibers.

[0082] In some embodiments, the beam analyzer 430 can be further configured to determine overlay data between two patterns on the substrate 420. One of these patterns may be a reference pattern on a reference layer. The other pattern may be an exposure pattern on an exposure layer. The reference layer may be an etching layer already present on the substrate 420. The reference layer can 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 can 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 the movement of the substrate 420 by the stage 422. In some embodiments, the measured overlay data may also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by the lithography apparatus 100 or 100', thereby minimizing the offset between the exposure layer and the reference layer after calibration.

[0083] In some embodiments, the beam analyzer 430 can be further configured to determine a model of the product stack profile of the substrate 420 and can be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement. The product stack profile includes information about the stacked product, such as alignment marks, target 418, or substrate 420, and may include mark process variation-induced optical signature measurements, which are 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 in Veldehoven, Netherlands, and is described in U.S. Patent No. 8,706,442, which is incorporated herein by reference in its entirety. The beam analyzer 430 can be further configured to process information about specific characteristics of the exposure pattern within its layer. For example, the beam analyzer 430 can process overlay parameters (an indicator of the positioning accuracy of the first layer relative to previous layers on the substrate, or the positioning accuracy of the first layer relative to marks on the substrate), focus parameters, and / or critical dimension parameters of the image drawn in that layer (e.g., line width and its variation). Other parameters are image parameters related to the quality of the image drawn of the exposure pattern.

[0084] In some embodiments, a detector array (not shown) can be connected to a beam analyzer 430, enabling accurate stack profile detection, as described later. For example, detector 428 can be a detector array. Many options are available for the detector array, including multimode fiber bundles, per-channel discrete PIN detectors, and CCD or CMOS (linear) arrays. The use of multimode fiber bundles allows for the remote placement of energy-consuming elements for stability reasons. Discrete PIN detectors offer a wide dynamic range, but each requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays have a large number of elements with high-speed readout and are particularly useful when using phase-step detection.

[0085] In some embodiments, the second beam analyzer 430' can be further configured to receive the diffracted radiation subbeam 429 and determine its optical state, as shown in Figure 4B. The optical state can be a measure of beam wavelength, polarization, or beam profile. The second beam analyzer 430' can be identical to the beam analyzer 430. Alternatively, the second beam analyzer 430' can be configured to perform one or more functions of the beam analyzer 430, for example, determining the position of the stage 422 and correlating the position of the stage 422 with the position of the alignment mark or target 418's center of symmetry. In this way, the position of the alignment mark or target 418, and consequently the position of the substrate 420, can be accurately determined with respect to the stage 422. The second beam analyzer 430' can also be configured to determine the position of the inspection device 400 or any other reference element, thereby determining the center of symmetry of the alignment mark or target 418 with respect to the inspection device 400 or any other reference element.

[0086] In some embodiments, the second beam analyzer 430' can be directly integrated into the inspection device 400, or, according to other embodiments, it can be connected via multiple types of optical fibers, such as polarization-preserving single-mode, multi-mode, or imaging optical fibers. Alternatively, the second beam analyzer 430' and the beam analyzer 430 can be combined to form a single analyzer (not shown) configured to receive both diffracted radiation subbeams 429 and 439 and determine their optical states.

[0087] In some embodiments, the processor 432 receives information from the detector 428 and the beam analyzer 430. Based on the information received from the detector 428 and the beam analyzer 430, the processor 432 can create a basic correction algorithm, which includes, but is not limited to, the optical state of the illumination beam, alignment signals, associated position estimates, the optical state in the pupil plane, the image plane, and additional planes. The pupil plane is a plane in which the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Using the basic correction algorithm, the processor 432 can evaluate the characteristics of the inspection apparatus 400 relative to the wafer mark and / or alignment mark 418.

[0088] Example of a lithography apparatus with a spatial filter assembly

[0089] Figure 5 shows a lithography apparatus 500 having a spatial filter assembly according to several embodiments. The lithography apparatus 500 can be configured to measure the position of an alignment target. In some embodiments, the lithography apparatus 500 can represent a detailed view of the inspection apparatus 400 (Figures 4A and 4B). The lithography apparatus 500 can be built as part of the lithography apparatus 100 or 100', or as a standalone unit within the lithography cell 300 to work in conjunction with other devices during operation. In some embodiments, the lithography apparatus 500 may include an illumination system 502, a projection system 512, a self-referencing interferometer (SRI) 532, a beam analyzer 536, and a detection system 548.

[0090] In some embodiments, the illumination system 502 may include a radiation source 504, an objective lens 508, and a mirror 510. In some embodiments, the radiation source 504 may be configured to emit a spatially coherent illumination beam 506. The illumination beam 506 may have an electromagnetic narrowband with one or more passbands. In some embodiments, the illumination beam 506 may be visible light with wavelengths ranging from about 500 nm to about 700 nm, or infrared light with wavelengths ranging from about 700 nm to about 2 μm. In some embodiments, the radiation source 504 may include one or more radiation sources, each capable of generating one or more passbands in the wavelength spectrum from about 500 nm to about 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 substantially continuous wavelengths. In some embodiments, the wavelength range of the illumination beam 506 may also include ultraviolet light.

[0091] In some embodiments, the objective lens 508 focuses the illumination beam 506 onto the mirror 510. In some embodiments, the mirror 510 can be positioned at any angle to guide the illumination beam 506 toward the projection system 512. It is well known to those skilled in the art that other focusing optical elements in the illumination system can be used to provide a similar function.

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

[0093] In some embodiments, the beam splitter 514 can be a spot mirror formed by a cube with a reflective metal layer at the center of a transmissive cube. The beam splitter 514 is shown to reflect the illumination beam 506 toward the alignment target 518 and transmit the diffracted beams 530a, 530b toward the SRI 532, but it should be noted that the disclosure is not limited thereto. It will be obvious to those skilled in the art that other optical configurations may be used to obtain similar results.

[0094] In some embodiments, the objective lens 516 focuses the illumination beam 506 onto the alignment target 518 and collects the diffracted beams 530a and 530b reflected from the 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 noted that the structures depicted within the lighting system 502 and the projection system 512 are not limited to their illustrated positions. The positions of the structures can be changed as needed, for example, depending on the design of the modular assembly.

[0096] In some embodiments, the substrate 520 (e.g., a semiconductor wafer) can be placed on an adjustable stage 522 (e.g., a movable support structure). In some embodiments, the alignment target 518 can be a structure formed on the substrate 520 by pattern transfer using a lithography mask (not shown) of a previous layer. The materials and film stacks used to form the alignment target 518 may depend on the layout of the alignment target 518 on the lithography mask of the previous layer and the process the substrate 520 has undergone. The design requirements of the alignment target 518 (e.g., shape and size) may depend on the alignment system and alignment method used. In some embodiments, the alignment target 518 may comprise a diffracting structure (e.g., a grating). The alignment target 518 can reflect, refract, diffract, or scatter radiation (e.g., an illumination beam 506). For the sake of ease of discussion and not for limitation, radiation interacting with the alignment target will be referred to as scattered radiation as herein. In some embodiments, scattered radiation can be collected by an objective lens 516.

[0097] In some embodiments, the alignment target 518 may be fabricated or coated with a photosensitive film, such as a photoresist ("resist"). If the thickness of the resist layer 524 increases unevenly, a difference in height may occur across the substrate 520. The top surface 528 of the resist layer 524 may not be parallel to the alignment target 518 and may be tilted. Thus, the resist layer 524 placed on the surface of the substrate 520 may be considered a "tilted resist" or "wedge resist". The tilt of the resist may occur in the scribe lines of the substrate 520 where the alignment target (e.g., alignment target 518) is placed. In some embodiments, the scribe lines may form trenches on the surface of the substrate 520. If the substrate 520 is coated with resist, the resist will not uniformly fill the trenches. As a result, the alignment target 518 may be located below a region having a tilted resist surface, as shown in Figure 5.

[0098] In some embodiments, the thickness of the resist layer 524 can be about 10 μm to about 20 μm. For example, the thickness of the resist layer 524 can be about 10 μm. In some embodiments, the upper 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 embodiments, the diffracted beams 530a and 530b from the alignment target 518 include symmetrically distributed higher-order diffracted beams, e.g., +1 and -1, +2 and -2, ..., +n and -n (where n is an integer greater than 2). The diffracted beams of different orders are spatially separated according to the diffraction angle. In some embodiments, the diffracted beams 530a and 530b include at least one positive order of diffraction or one negative order of diffraction.

[0100] However, in some embodiments, the illumination beam 506 may be refracted by the resist layer 524 before it can properly illuminate the alignment target 518. As a result, the diffracted beams 530a and 530b may be reflected by the alignment target 518 and then refracted in undesirable ways by the resist layer 524. Therefore, the refraction of the illumination beam 506 and the reflection and refraction of the diffracted beams 530a and 530b may result in the diffraction angles of the higher-order diffracted beams 530a and 530b relative to the optical axis of the lithography apparatus 500 (e.g., +1 / -1, ..., +m / -m, where m is any integer greater than 1) not being equal. Consequently, in the presence of a tilted resist, the measurement of the alignment target's position may be inaccurate. For example, the lithography apparatus 500 may lose the alignment signal as the modulation degree of the alignment signal decreases, as will be discussed separately.

[0101] In some embodiments, non-uniformity of the top surface 528 may adversely affect the accurate operation of the lithography apparatus. In some embodiments, differences in the tilt angle 526 of the top surface 528 and the amount of material across the resist layer 524 may cause angular deviations of the diffracted beams 530a and 530b due to Snell's Law. In some embodiments, a phase difference between the higher-order diffracted beams 530a and 530b (e.g., +1 / -1, ..., +m / -m) may be introduced due to mismatches in the diffraction angles or differences in the optical path lengths of each pair of higher-order diffracted beams 530a and 530b (e.g., +1 / -1, ..., +m / -m). The phase difference may introduce alignment position errors proportional to the magnitude of the phase difference.

[0102] In some embodiments, the SRI 532 is configured to receive diffracted beams 530a and 530b and generate diffracted subbeams 534a to 534d. The SRI 532 can project two overlapping images of the alignment target 518 that are rotated 180° relative to each other. In the SRI 532, pairs of positive and negative diffraction orders of diffracted beams 530a and 530b can generate two pairs of diffracted subbeams 534a to 534d, each pair of diffracted subbeams 534a to 534d containing spatially overlapping components resulting from both the positive and negative diffraction orders of diffracted beams 530a and 530b.

[0103] For the detection system 548 to obtain the precise alignment position of the substrate 520, the SRI 532 needs to generate a symmetrical overlap of the positive and negative diffraction beams 530a and 530b. The amount of symmetrical overlap between the diffraction beams 530a and 530b can be directly related to the degree of modulation present in the optical intensity of the alignment signal. In some embodiments, the degree of modulation (DoM) can indicate the strength of the sinusoidal signal. Therefore, by analyzing the DoM, the lithography apparatus 500 can pinpoint the alignment position of the alignment target 518 with precision (pinpoint accuracy) to a fraction of a nanometer. In some embodiments, the DoM can be calculated by finding the difference between the 99th percentile and the 1st percentile of the alignment signal and dividing that difference by the 99th percentile of the alignment signal.

[0104] In some embodiments, the resist layer 524 can shift the peak-to-peak distance of the sinusoidal signal of the diffracted beam 530a at the pupil plane relative to the peak-to-peak distance of the sinusoidal signal of the diffracted beam 530b. In some embodiments, the diffracted beams 530a and 530b may not be symmetrical with respect to the optical axis of the lithography apparatus 500. After the diffracted beams 530a and 530b are replicated in the SRI 532, the two replicates of the diffracted beams 530a and 530b may not overlap symmetrically, preventing symmetrical interference, thus impairing the self-referencing process and reducing the DoM of the alignment signal. In some embodiments, the SRI 532 can generate standing wave patterns from the diffracted beams 530a and 530b within the field of view of the alignment sensor. In some embodiments, the detection system 548 may interpret the asymmetrical overlap between the diffracted beams 530a and 530b as a displacement from the optical axis center of the lithography apparatus 500, potentially causing an alignment error. Therefore, in some embodiments, the detection system 548 may receive a reduced alignment signal, which increases the uncertainty of the alignment target's position (e.g., in nanometer units). In some embodiments, the alignment signal may be lost completely. In some embodiments, a tilt angle 526 of about 1 degree in the resist layer 524 may cause the lithography apparatus 500 to lose the alignment signal.

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

[0106] In some embodiments, the spatial filter assemblies 542a and 542b can be positioned in front of the field diaphragms 544a and 544b, respectively. In some embodiments, the image of the alignment target 518 can be projected onto the spatial filter assemblies 542a and 542b at the output surface, generating an intensity signal as a function of the position of the alignment target 518 on the substrate 520. In some embodiments, the spatial filter assemblies 542a and 542b can be configured to restore the modulation degree of the alignment signal, generating the restored alignment signals 546a and 546b, as will be discussed later with respect to Figure 6.

[0107] In some embodiments, the field diaphragms 544a and 544b can be positioned on the output surface within the alignment system.

[0108] In some embodiments, the detection system 548 of the lithography apparatus 500 can measure the light intensity of the restored alignment signals 546a and 546b, and therefore the modulation degree of the alignment signals. The detection system 548 can be configured to determine the position of the alignment target 518 based on the measured light intensity of the restored alignment signals 546a and 546b, and the light intensity is modulated to extract alignment information from other parameters of the lithography apparatus 500.

[0109] Figure 6 shows a spatial filter assembly 600 having a reference grid 602 according to several embodiments. In some embodiments, the spatial filter assembly 600 can represent a detailed view of the spatial filter assembly 542a shown in Figure 5. The following description can be applied to the spatial filter assembly 542b and its respective input and output signals. In some embodiments, the spatial filter assembly 600 may include a reference grid 602, a substrate 604, a movable stage 608, and a multimode fiber 614.

[0110] In some embodiments, the spatial filter assembly 600 may include a reference grid 602 positioned at the field diaphragm (e.g., field diaphragms 544a, 544b shown in Figure 5) on the output surface of the alignment system. In some embodiments, the reference grid 602 can restore the DoM from about 0% to about 80% when generating the restored alignment signal 612 (e.g., the restored alignment signals 546a, 546b shown in Figure 5). In some embodiments, the reference grid 602 can generate the restored alignment signal 612 with an improved DoM for any tilt angle (e.g., tilt angle 526 shown in Figure 5) of the resist layer (e.g., resist layer 524 shown in Figure 5). In some embodiments, since the reference grid 602 is positioned on the field surface of the lithography apparatus 500, the reference grid can generate the restored alignment signal 612 simultaneously for all colors (e.g., a 4C system or a 12 system).

[0111] In some embodiments, the reference grid 602 may include at least one of a one-dimensional X-direction filter, a one-dimensional Y-direction filter, a two-dimensional X-direction and Y-direction filter, a binary filter, a Gray filter, a spectral filter, or a combination thereof. In some embodiments, the reference grid 602 may be configured with a reference grid pitch corresponding to the target pitch of the alignment target (e.g., the alignment target 518 shown in Figure 5). In some embodiments, the reference grid 602 may be optimized to match the higher-order target pitch of the alignment target without compromising the self-referencing process. In some embodiments, the reference grid 602 may generate a restored alignment signal 612 without compromising the detection of the alignment target when the resist layer is flat (e.g., when the tilt angle 526 is equal to 0). For example, the reference grid 602 may generate a restored alignment signal 612 with 100% DoM when the tilt angle 526 of the resist layer 524 is equal to 0.

[0112] In some embodiments, the reference grid 602 can be formed by etching the reference grid 602 onto a substrate 604. In some embodiments, the substrate 604 can be a reticle or a glass plate. In some embodiments, the reference grid 602 can be formed by a MEMS mirror configured to change the period or profile of the reference grid 602, thereby tuning the reference grid 602 to a target wavelength. In some embodiments, the reference grid 602 can be formed using an acousto-optic tunable filter (AOTF) or a liquid crystal tunable filter (LCTF), thereby transmitting the target wavelength while blocking other wavelengths.

[0113] In the presence of a tilted resist, a self-reference interferometer (e.g., SRI 532 shown in Figure 5) can generate standing wave patterns from the diffracted beams (e.g., diffracted beams 530a and 530b shown in Figure 5). For example, the signals generated by the self-reference interferometer may have separate modulation regions that are out of phase with each other. By separating the modulation regions, the out-of-phase signals can be blocked, allowing the sinusoidal modulation signal to pass towards the detection system 548, and the DoM of the alignment signal can be restored.

[0114] Therefore, in some embodiments, the reference grid 602 can filter out portions of the diffracted subbeams 606a and 606b that do not contribute to the alignment signal of the alignment target 518. In some embodiments, the reference grid 602 can restore the DoM of the alignment signal by separating two signals located in spatially different regions, thereby blocking the standing wave effect of the interference pattern and allowing the modulated signal to pass through the reference grid 602. For example, the reference grid 602 can be configured to block the first diffracted subbeam 606a (e.g., the diffracted subbeam 534a shown in Figure 5) while allowing the second diffracted subbeam 606b (e.g., the diffracted subbeam 534b shown in Figure 5) to pass through the reference grid 602, thereby allowing the restored (e.g., modulated) alignment signal 612 to be transmitted to the detection system 548. As a result, the reference grid 602 can increase the DoM of the lithography apparatus 500, thereby enabling detection of the alignment signal at a low signal-to-noise level.

[0115] In the presence of a tilted resist, a self-reference interferometer (e.g., SRI532 shown in Figure 5) can generate an asymmetrical overlap of diffracted beams (e.g., diffracted beams 530a and 530b shown in Figure 5). In some embodiments, it may be effective to create an image of an alignment target (e.g., alignment target 518 shown in Figure 5) on the output surface of a lithography apparatus (e.g., lithography apparatus 500 shown in Figure 5) without relying on a self-reference process.

[0116] In some embodiments, the reference grid 602 can be configured to form interference patterns of diffracting subbeams 606a and 606b (e.g., diffracting subbeams 534a and 534b shown in Figure 5) regardless of the spatial overlap of the diffracting subbeams 606a and 606b at the pupil plane. For example, the positive and negative diffraction orders of the diffracting subbeams 606a and 606b can interfere on the reference grid 602 at the output plane regardless of the shift of the diffracting subbeams 606a and 606b at the pupil plane. In some embodiments, the reference grid 602 can operate with a self-reference interferometer (e.g., SRI 532 shown in Figure 5). In some embodiments, the reference grid 602 can generate the reconstructed alignment signal 612 even without a self-reference interferometer in the alignment system.

[0117] In some embodiments, the reference grid 602 in the substrate 604 can be mounted on a movable stage 608. In some embodiments, the movable stage can be a filter wheel or a mechatronic component. In some embodiments, the movable stage 608 can be configured to adjust the reference grid pitch to a target pitch by adjusting the reference grid 602 using at least one of translational or rotational motion. In some embodiments, the translational motion can be performed in the XY plane. In some embodiments, the rotational motion can be performed around the Z axis in the XY plane.

[0118] In some embodiments, the movable stage 608 can be controlled by a processor (e.g., processor 432) or a controller. In some embodiments, the movable stage 608 can be controlled based on measurement data from a beam position sensor 610. In some embodiments, the beam position sensor 610 can be configured to measure the positions of the diffracting subbeams 606a, 606b according to the pitch of the tilted resist layer (e.g., resist layer 524 shown in Figure 5) and the alignment target (e.g., alignment target 518 shown in Figure 5). The beam position sensor can output position data to the processor or controller. As a result, the processor or controller can drive the movable stage 608 based on the output data and adjust it to the position of the diffracting subbeams generated by the tilted resist layer and the pitch of the alignment target.

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

[0120] In some embodiments, the spatial filter assembly 600 can transmit the restored alignment signal 614 to the detection system 548 using a multimode fiber 614. In some embodiments, the reference grating 602 can integrate the energies from the diffracted subbeams 606a and 606b to create a single interference signal (e.g., the restored alignment signal 612). This interference signal illuminates the multimode fiber 614 and carries the restored alignment signal 612 to the detection system 548. In some embodiments, the multimode fiber 614 can be positioned tens or hundreds of microns away from the substrate 604, so that the multimode fiber 614 remains fixed while only the reference grating 602 is moved when driven by the movable stage 608.

[0121] Figures 7A to 7C show reference grids 602a to 602c in several embodiments. Figure 7A shows reference grid 602a as a one-dimensional Y-direction filter in several embodiments. Figure 7B shows reference grid 602b as a one-dimensional X-direction filter in several embodiments. Figure 7C shows reference grid 602c as a two-dimensional X-direction and Y-direction checkerboard filter in several embodiments. In some embodiments, reference grids 602a to 602c can be alternative embodiments of reference grid 602 shown in Figure 6.

[0122] In some embodiments, spatial filter assembly 542a can use reference grid 602a, while spatial filter assembly 542b can use reference grid 602b. In some embodiments, spatial filter assembly 542a can use reference grid 602b, while spatial filter assembly 542b can use reference grid 602a. In any exemplary configuration, the alignment system can read the alignment targets in the X and Y directions by applying a one-dimensional reference grid to different channels. In some embodiments, both spatial filter assemblies 542a and 542b can use reference grid 602c, and the alignment system can read the alignment targets in the X and Y directions by applying a two-dimensional reference grid to both channels. In some embodiments, any of the reference grids 602a to 602c can be placed on a movable stage (for example, the movable stage 608 shown in Figure 6) configured to adjust any of the reference grids 602a to 602c to match the pitch of any of the reference grids 602a to 602c to the pitch of a target by adjusting any of the reference grids 602a to 602c using at least one of translational motion or rotational motion.

[0123] Figures 8A and 8B show the modulation degree of alignment signals in several embodiments. Figures 8A and 8B plot the modulation degree on a graph where the Y-axis represents the light intensity amplitude 802 and the X-axis represents the position 804.

[0124] Figure 8A shows the weak modulation degree 800 of the alignment signal based on the presence of a tilted resist according to several embodiments. In some embodiments, a detection system (e.g., detection system 548 shown in Figure 5) can read the integrated output intensity as a function of the alignment target position. In some embodiments, the presence of a tilted resist causes small modulation in the alignment signal, which may make it difficult for the detection system to extract positional information from the alignment signal. In some embodiments, if the DoM is poor, the peak-to-trough distance between data point 806 and data point 808 may be low. For example, if the tilt angle (e.g., tilt angle 526 shown in Figure 5) is 1 degree, the thickness of the tilted resist layer (e.g., resist layer 524 shown in Figure 5) is 10 μm, the alignment target (e.g., alignment target 518 shown in Figure 5) is 16 μm, and the diffraction beams (e.g., diffraction beams 530a, 530b shown in Figure 5) are +1st order diffraction beams and -1st order diffraction beams, the modulation degree 800 may be approximately 8%.

[0125] Figure 8B shows the restored modulation degree 800' of the alignment signal based on the use of spatial filter assemblies (e.g., spatial filter assemblies 542a, 542b shown in Figure 5) that compensate for the presence (effect) of the tilted resist, according to several embodiments. In some embodiments, the peak-to-trough distance between data point 806' and data point 808' can be increased by the spatial filter assembly, thereby improving the DoM for modulation degree 800. In some embodiments, the improvement in DoM may 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 embodiments, the improvement in DoM can be maximized when the pitch of the reference grid matches the pitch of the alignment target. For example, a reference grating optimized for a 16 μm alignment mark (e.g., reference grating 602a shown in Figure 7A) can generate a modulation degree of 800' of approximately 76% when the tilt angle (e.g., tilt angle 526 shown in Figure 5) is 1 degree, the thickness of the tilted resist layer (e.g., resist layer 524 shown in Figure 5) is 10 μm, the alignment target (e.g., alignment target 518 shown in Figure 5) is 16 μm, and the diffracted beams (e.g., diffracted beams 530a, 530b shown in Figure 5) are +1st and -1st order diffracted beams. In this exemplary embodiment, the reference grating 602a can restore DoM from approximately 8% to approximately 76%.

[0126] Example of an alignment system using pupil filters

[0127] Figure 9 shows a lithography apparatus having a pupil filter according to several embodiments. The above description of the lithography apparatus 500 shown in Figure 5 also applies to the lithography apparatus 500' shown in Figure 9. For example, the embodiment of the lithography apparatus 500 shown in Figure 5 and the embodiment of the lithography apparatus 500' shown in Figure 9 may be similar. Similar reference numerals are used to indicate the features of the embodiment of the lithography apparatus 500 shown in Figure 5 and the features of the embodiment of the lithography apparatus 500' shown in Figure 9.

[0128] In some embodiments, the spatial filter assemblies 542a', 542b' may include pupil filters configured to collect diffracted subbeams 534a-534d that overlap at one or more predetermined wavelengths. In some embodiments, the pupil filters may be positioned in collimated space within the pupil plane prior to the objective lenses 540a, 540b in the alignment system. In some embodiments, the pupil filters may include multiple apertures for filtering higher-order diffracted beam subbeams 534a-534d before they reach the detection system 548. Diffraction orders shifted within the pupil plane can be blocked by the pupil filters because the diffracted beams no longer coincide with the holes in the pupil filters and are therefore not detected by the detection system 548. In some embodiments, the pupil filters of the spatial filter assemblies 542a', 542b' may conform to any tilt angle 526 of the resist layer 524.

[0129] Therefore, in some embodiments, the spatial filter assemblies 542a', 542b' can filter out portions of the diffracted subbeams 534a to 534d that do not contribute to the alignment signal of the alignment target 518. In some embodiments, the spatial filter assemblies 542a', 542b' can restore the DoM of the alignment signal by separating two signals that are in spatially different regions, thereby blocking the standing wave effect of the interference pattern and allowing the modulated signal to pass through the spatial filter assemblies 542a', 542b'. For example, the spatial filter assembly 542a' can be configured to block the first diffracted subbeam 534a and allow the second diffracted subbeam 534b to pass through the spatial filter assemblies 542a', 542b', so that the restored (e.g., modulated) alignment signal 546a can be transmitted to the detection system 548. As a result, the spatial filter assemblies 542a' and 542b' can increase the DoM of the lithography apparatus 500', thereby enabling the detection of alignment signals at low signal-to-noise levels. For example, the pupil filters of the spatial filter assemblies 542a' and 542b' can restore the DoM from approximately 8% to approximately 71%.

[0130] In some embodiments, the pupil filters of the spatial filter assemblies 542a', 542b' may be rotating disks having apertures optimized for a specific pitch. In some embodiments, the pupil filters may be configured to adjust to the target pitch of the alignment target 518 using at least one of translational or rotational motion.

[0131] Figures 10A and 10B show pupil filters 1000a and 1000b according to several embodiments. In some embodiments, pupil filters 1000a and 1000b can be incorporated into spatial filter assemblies 542a' and 542b' shown in Figure 9. In some embodiments, pupil filters 1000a and 1000b may include four or more apertures configured to collect diffracted subbeams that overlap at one or more predetermined wavelengths. In some embodiments, the four or more apertures may have a spectral coating that allows only specific wavelengths or wavelength ranges at a particular pupil position. In some embodiments, the wavelength range may be visible light wavelengths from about 380 nm to about 750 nm. In some embodiments, the wavelength range may be visible light wavelengths from about 380 nm to about 750 nm. In some embodiments, the wavelength range may be visible light wavelengths from about 380 nm to about 750 nm.

[0132] In some embodiments, the spectral coating 1002 on the pupil filter 1000a shown in Figure 10A can be a single-color filter. In some embodiments, 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 embodiments, the spectral coating on the pupil filter 1000b shown in Figure 10B can be a multicolor filter, where each coating transmits only a specific wavelength. In some embodiments, spectral coating 1004 can transmit a first wavelength. For example, spectral coating 1004 can transmit a first wavelength of 550 nm. In some embodiments, spectral coating 1006 can transmit a second wavelength. For example, spectral coating 1006 can transmit a second wavelength of 700 nm. In some embodiments, the spectral coating overlap 1008 can transmit both the first and second wavelengths. For example, the spectral coating overlap 1008 can transmit a first wavelength of 550 nm and a second wavelength of 700 nm.

[0134] Example of a method

[0135] Figure 11 shows a method 1100 for restoring the modulation degree of an alignment signal according to several embodiments. In some embodiments, in step 1102, a radiation source (e.g., radiation source 504 shown in Figure 5) can generate one or more illumination beams (e.g., illumination beam 506 shown in Figure 5).

[0136] In some embodiments, in step 1104, the radiation source can direct one or more illumination beams toward alignment targets (e.g., alignment target 518 shown in Figure 5) on a wafer (e.g., substrate 520 shown in Figure 5).

[0137] In some embodiments, in step 1106, a self-reference interferometer (e.g., SRI532 shown in Figure 5) can receive one or more diffracted beams (e.g., diffracted beams 530a, 530b) reflected from an alignment target, the one or more diffracted beams comprising at least one positive diffraction order and one negative diffraction order.

[0138] In some embodiments, in step 1108, the self-reference interferometer can generate an alignment signal comprising diffracted subbeams (e.g., diffracted subbeams 534a-534d shown in Figure 5), where the diffracted subbeams are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlap.

[0139] In some embodiments, in step 1110, a spatial filter assembly (e.g., spatial filter assemblies 542a, 542b shown in Figure 5) can restore the modulation degree of the alignment signal. In some embodiments, the spatial filter assembly may include a reference grid (e.g., reference grid 602 shown in Figure 6) positioned at a field aperture (e.g., field apertures 544a, 544b shown in Figure 5) on the output surface of the alignment system. In some embodiments, the reference grid may be configured to block a first diffracted subbeam (e.g., diffracted subbeam 606a shown in Figure 6) and allow a second diffracted subbeam (e.g., diffracted subbeam 606b shown in Figure 6) to pass through the reference grid, thereby transmitting the modulated alignment signal (e.g., restored alignment signal 612 shown in Figure 6) to a detection system (e.g., detection system 548 shown in Figures 5 and 6). In some embodiments, the reference grid may be configured to form an interference pattern of diffracted subbeams regardless of spatial overlap at the pupil plane of the alignment system.

[0140] In some embodiments, in step 1112, the measuring device can measure the optical intensity measurement of the alignment signal.

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

[0142] The method steps in Figure 11 can be performed in any possible order, and it is not necessary to perform all steps. Furthermore, the method steps in Figure 11 described above only reflect one example of the steps and are not limiting. That is, other method steps and functions can be envisioned based on the embodiments described with reference to Figures 1A to 10B.

[0143] Embodiments may be further described using the following clauses. (Item 1) A radiation source configured to generate one or more illumination beams and to guide the one or more illumination beams to an alignment target on a wafer, wherein the one or more diffracted beams are reflected from the alignment target, and the one or more diffracted beams have at least one positive diffraction order and one negative diffraction order, A self-reference interferometer configured to receive one or more diffracted beams and generate an alignment signal comprising diffracted subbeams, wherein the diffracted subbeams are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlapping. A spatial filter assembly configured to restore the modulation degree of the alignment signal, A measuring device configured to measure the optical intensity measurement value of the alignment signal, The system comprises a detection system configured to determine the position of the alignment target based on the measured light intensity of the alignment signal, Alignment system. (Item 2) The spatial filter assembly comprises a reference grid positioned in the field aperture within the output plane of the alignment system. The alignment system described in item 1. (Item 3) The reference grid comprises at least one of the following: a one-dimensional X-direction filter, a one-dimensional Y-direction filter, a two-dimensional X-direction and Y-direction filter, a binary filter, a Gray filter, or a spectral filter. The alignment system described in item 2. (Item 4) The reference grid has a reference grid pitch corresponding to the target pitch of the alignment target. The alignment system described in item 3. (Item 5) The spatial filter assembly further comprises a movable stage configured to adjust the reference grid pitch to the target pitch by adjusting the reference grid using at least one of translational or rotational motion, The alignment system described in item 4. (Item 6) The reference grid is configured to block the first diffracted subbeam and allow the second diffracted subbeam to pass through the reference grid, and to transmit the modulated alignment signal to the detection system. The alignment system described in item 5. (Item 7) The reference grating is configured to form the interference pattern of the diffracted subbeams regardless of the spatial overlap at the pupil plane of the alignment system. The alignment system described in item 5. (Item 8) The spatial filter assembly comprises a pupil filter having four or more apertures configured to collect diffracted subbeams that overlap at one or more predetermined wavelengths, wherein the pupil filter is positioned prior to the output lens in the alignment system and is configured to be adjusted to match the target pitch of the alignment target using at least one of translational or rotational motion. The alignment system described in item 1. (Item 9) A lighting system configured to illuminate a patterning device, A projection system configured to project an image of the patterning device onto a wafer, Equipped with an alignment system, The alignment system is A radiation source configured to generate one or more illumination beams and guide the one or more illumination beams to an alignment target on the wafer, wherein the one or more diffracted beams are reflected from the alignment target, and the one or more diffracted beams have at least one positive diffraction order and one negative diffraction order. A self-reference interferometer configured to receive one or more diffracted beams and generate an alignment signal comprising diffracted subbeams, wherein the diffracted subbeams are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlapping. A spatial filter assembly configured to restore the modulation degree of the alignment signal, A measuring device configured to measure the optical intensity measurement value of the alignment signal, The system comprises a detection system configured to determine the position of an alignment target based on the measured light intensity of the alignment signal, Lithography equipment. (Item 10) The spatial filter assembly comprises a reference grid positioned in the field aperture within the output plane of the alignment system. Lithography apparatus as described in item 9. (Clause 11) The reference grid comprises at least one of a one-dimensional X-direction filter, a one-dimensional Y-direction filter, a two-dimensional X-direction and Y-direction filter, a binary filter, a Gray filter, or a spectral filter. Lithography apparatus as described in item 10. (Item 12) The reference grid comprises a reference grid pitch corresponding to the target pitch of the alignment target. Lithography apparatus as described in item 11. (Clause 13) The spatial filter assembly further comprises a movable stage configured to adjust the reference grid pitch to the target pitch by adjusting the reference grid using at least one of translational or rotational motion, Lithography apparatus as described in item 12. (Item 14) The reference grid is configured to block the first diffracted subbeam and allow the second diffracted subbeam to pass through the reference grid, and to transmit the modulated alignment signal to the detection system. Lithography apparatus as described in item 13. (Clause 15) The reference grating is configured to form the interference pattern of the diffracted subbeams regardless of the spatial overlap at the pupil plane of the alignment system. Lithography apparatus as described in item 13. (Item 16) The spatial filter assembly comprises a pupil filter having four or more apertures configured to collect diffracted subbeams that overlap at one or more predetermined wavelengths, wherein the pupil filter is positioned prior to the output lens in the alignment system and is configured to be adjusted to match the target pitch of the alignment target using at least one of translational or rotational motion. Lithography apparatus as described in item 9. (Item 17) Guiding one or more illumination beams to an alignment target on a wafer, Receiving one or more diffracted beams reflected from the alignment target using a self-reference interferometer, wherein the one or more diffracted beams have at least one positive diffraction order and one negative diffraction order. The method involves generating an alignment signal comprising diffracted subbeams using the self-reference interferometer, wherein the diffracted subbeams are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlap. Using a spatial filter assembly, the modulation depth of the alignment signal is restored, Using a measuring device, the optical intensity measurement value of the alignment signal is measured, The system includes determining the position of the alignment target based on the measured light intensity of the alignment signal using a detection system. method. (Item 18) The spatial filter assembly comprises a reference grid positioned in the field aperture within the output plane of the alignment system, The method described in item 17. (Item 19) The reference grid is configured to block the first diffracted subbeam and allow the second diffracted subbeam to pass through the reference grid, and transmits the modulated alignment signal to the detection system. The method described in item 18. (Clause 20) The reference grating is configured to form the interference pattern of the diffracted subbeams regardless of the spatial overlap at the pupil plane of the alignment system. The method described in item 18.

[0144] In this specification, terms such as “radiation,” “beam,” “light,” and “illumination” can be used to refer to one or more types of electromagnetic radiation, such as ultraviolet (UV) radiation (e.g., having wavelengths of 365, 248, 193, 157, or 126 nm), extreme ultraviolet (EUV) radiation (e.g., in the range of 5–100 nm, having a wavelength of 13.5 nm), or hard X-rays acting at less than 5 nm, as well as particle beams such as ion beams and electron beams. Generally, radiation with wavelengths of about 400–700 nm is considered visible radiation, and radiation with wavelengths of about 780–3000 nm (or above) is considered infrared radiation. UV refers to radiation with wavelengths of about 100–400 nm. In lithography, the term “UV” also applies to wavelengths that can be produced by mercury discharge lamps: G-line 436 nm, H-line 405 nm, and / or I-line 365 nm. Vacuum ultraviolet (VUV), or VUV (i.e., UV absorbed by gas), refers to radiation with wavelengths of approximately 100–200 nm. Deep ultraviolet (DUV) generally refers to radiation with wavelengths of 126–428 nm, and in some embodiments, excimer lasers can generate DUV radiation used in lithography equipment. For example, radiation with wavelengths in the 5–20 nm range should be understood as radiation having a specific wavelength band that is at least partially in the 5–20 nm range.

[0145] While some aspects of this disclosure are described in the context of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein can also be used for other applications, such as the manufacture of integrated optical systems, induction and detection patterns for magnetic domain memory, flat panel displays, LCDs, thin-film magnetic heads, etc. Those skilled in the art will understand that in the context of such alternative applications, where the terms “wafer” or “die” are used herein, they can be considered as specific examples of the more general terms “substrate” or “target portion,” respectively. Substrates can be processed, for example, in a track unit (typically a tool for coating a resist layer onto a substrate and developing the exposed resist) and / or a measurement unit, either before or after exposure. Where applicable, the aspects disclosed herein can be applied to such substrate processing tools and other substrate processing tools. Furthermore, substrates can be processed multiple times, for example, to produce a multilayer IC, and therefore, the term “substrate” as used herein can also refer to a substrate that already contains multiple processed layers.

[0146] Furthermore, while some aspects of this disclosure are described in the context of optical lithography, it should be understood that the aspects of this disclosure are not limited to optical lithography. For example, in imprint lithography, the topography of a patterning device defines the pattern formed on the substrate. The topography of the patterning device can be pressed onto a resist layer supplied to the substrate, and the resist is then cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has cured, the patterning device is removed from the resist, leaving the pattern in the resist.

[0147] It should be understood that the expressions and terms used herein are for illustrative purposes only and not for limitation. Therefore, the terms and expressions used herein should be interpreted by those skilled in the art in light of the teachings provided herein.

[0148] This disclosure is described above using functional components that illustrate how specific functions are implemented and their relationships. The boundaries of these functional components are arbitrarily defined herein for the sake of clarity. Alternative boundaries may also be defined, as long as the specific functions and their relationships are adequately performed. The above descriptions of specific embodiments are intended to fully illustrate the general nature of this disclosure, and a person skilled in the art can easily modify and / or adapt these specific embodiments to various uses by applying their knowledge without excessive experimentation and without departing from the general concepts of this disclosure. Accordingly, such adaptations and modifications are intended to be within the meaning and scope of equivalents of the disclosed embodiments, based on the teachings and guidance presented herein.

[0149] It should be understood that the interpretation of the claims is intended to be based on the detailed description section, not the summary and abstract. The summary and abstract section may describe one or more aspects of the disclosure as envisioned by the inventors, but not necessarily all, and therefore does not limit the disclosure and the attached claims in any way. The scope of the subject matter to be protected should not be limited by any of the above aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

1. A radiation source configured to generate one or more illumination beams and guide the one or more illumination beams to an alignment target on a wafer, wherein the one or more diffracted beams are reflected from the alignment target, and the one or more diffracted beams have at least one positive diffraction order and one negative diffraction order. A self-reference interferometer configured to receive one or more diffracted beams and generate an alignment signal comprising diffracted subbeams, wherein the diffracted subbeams are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlapping. A spatial filter assembly configured to restore the modulation degree of the alignment signal, A measuring device configured to measure the optical intensity measurement value of the alignment signal, The system comprises a detection system configured to determine the position of the alignment target based on the measured light intensity of the alignment signal, Alignment system.

2. The spatial filter assembly comprises a reference grid positioned in the field aperture within the output plane of the alignment system. The alignment system according to claim 1.

3. The reference grid comprises at least one of the following: a one-dimensional X-direction filter, a one-dimensional Y-direction filter, a two-dimensional X-direction and Y-direction filter, a binary filter, a Gray filter, or a spectral filter. The alignment system according to claim 2.

4. The reference grid has a reference grid pitch corresponding to the target pitch of the alignment target. The alignment system according to claim 3.

5. The spatial filter assembly further comprises a movable stage configured to adjust the reference grid pitch to the target pitch by adjusting the reference grid using at least one of translational or rotational motion. The alignment system according to claim 4.

6. The reference grid is configured to block the first diffracted subbeam and allow the second diffracted subbeam to pass through the reference grid, and transmits the modulated alignment signal to the detection system. The alignment system according to claim 5.

7. The reference grating is configured to form the interference pattern of the diffracted subbeams regardless of the spatial overlap at the pupil plane of the alignment system. The alignment system according to claim 5.

8. The spatial filter assembly comprises a pupil filter having four or more apertures configured to collect diffracted subbeams that overlap at one or more predetermined wavelengths, the pupil filter being positioned prior to the output lens in the alignment system and configured to be adjusted to match the target pitch of the alignment target using at least one of translational or rotational motion. The alignment system according to claim 1.

9. A lighting system configured to illuminate a patterning device, A projection system configured to project an image of the patterning device onto a wafer, Equipped with an alignment system, The alignment system is A radiation source configured to generate one or more illumination beams and guide the one or more illumination beams to an alignment target on the wafer, wherein the one or more diffracted beams are reflected from the alignment target, and the one or more diffracted beams have at least one positive diffraction order and one negative diffraction order. A self-reference interferometer configured to receive one or more diffracted beams and generate an alignment signal comprising diffracted subbeams, wherein the diffracted subbeams are orthogonally polarized, rotated 180 degrees relative to each other around the alignment axis, and spatially overlapping. A spatial filter assembly configured to restore the modulation degree of the alignment signal, A measuring device configured to measure the optical intensity measurement value of the alignment signal, The system comprises a detection system configured to determine the position of an alignment target based on the measured light intensity of the alignment signal, Lithography equipment.

10. The spatial filter assembly comprises a reference grid positioned in the field aperture within the output plane of the alignment system. The lithography apparatus according to claim 9.

11. The reference grid comprises at least one of the following: a one-dimensional X-direction filter, a one-dimensional Y-direction filter, a two-dimensional X-direction and Y-direction filter, a binary filter, a Gray filter, or a spectral filter. The lithography apparatus according to claim 10.

12. The reference grid has a reference grid pitch corresponding to the target pitch of the alignment target. The lithography apparatus according to claim 11.

13. The spatial filter assembly further comprises a movable stage configured to adjust the reference grid pitch to the target pitch by adjusting the reference grid using at least one of translational or rotational motion. The lithography apparatus according to claim 12.

14. The reference grid is configured to block the first diffracted subbeam and allow the second diffracted subbeam to pass through the reference grid, and transmits the modulated alignment signal to the detection system. The lithography apparatus according to claim 13.

15. The reference grating is configured to form the interference pattern of the diffracted subbeams regardless of the spatial overlap at the pupil plane of the alignment system. The lithography apparatus according to claim 13.

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