Topologically optimized alignment mark

Abstract

The invention discloses an inverse design method of alignment marks for topological optimization. A first alignment mark is generated for use on a substrate such that the first alignment mark has a topology of at least two pixels having different characteristics. One or more characteristics of each of the at least two pixels are determined. A topology of the first alignment mark is optimized based on one or more characteristics of the at least two pixels. A second alignment mark is formed on the substrate based on optimization of the first alignment mark.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application 63 / 483,711, filed February 7, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to alignment marks, for example, a general framework for designing topology-optimized alignment marks using inverse design methods to find highly complex alignment marks with optimal performance in lithographic apparatus and systems. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate, typically onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device, which can be a mask or reticle, can be used to produce the circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., a portion comprising one or more dies) on a substrate (e.g., a silicon wafer). The pattern is typically transferred by imaging onto a layer of radiation-sensitive material (photoresist, or simply "resist") provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned sequentially. Known lithographic apparatus include so-called steppers, in which each target portion is illuminated by exposing the entire pattern onto the target portion at once, and so-called scanners, in which each target portion is illuminated by scanning the pattern with a radiation beam in a given direction (the "scanning" direction) while simultaneously scanning the target portion parallel or antiparallel to the scan direction. A pattern can also be transferred from a patterning device to a substrate by imprinting the pattern onto the substrate.

[0005] During a photolithography operation, different processing steps may require sequential formation of different layers on a substrate. Therefore, it is necessary to accurately position the substrate relative to the existing pattern formed thereon. Typically, alignment marks are placed on the substrate to be aligned and positioned relative to a second object. The photolithography system may use an alignment device to detect the position of the alignment marks and use them to align the substrate to ensure accurate exposure from the mask. Misalignment between alignment marks at two different layers is measured as overlay error.

[0006] To monitor the lithography process, parameters of the patterned substrate are measured. Parameters may include, for example, the overlay error between successive layers formed in or on the patterned substrate and the critical linewidth of the developed photoresist. The measurements can be performed on production substrates and / or dedicated metrology targets. Various techniques are used to measure the microstructures formed in the lithography process, including the use of scanning electron microscopes and various specialized tools. A rapid and non-invasive form of specialized inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the substrate surface and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it is reflected or scattered by the substrate, the properties of the substrate can be determined. For example, this can be achieved by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Spectral scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function of wavelength) of the radiation scattered into a specific narrow angular range. In contrast, angle-resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0007] Such light scatterometers can be used to measure parameters such as the critical dimension of a developed photoresist or the overlay error (OV) between two layers formed in or on a patterned substrate. The characteristics of the substrate can be determined by comparing the characteristics of the illumination beam before and after it is reflected or scattered by the substrate.

[0008] Conventional alignment mark design techniques, for example, focus on using known materials and optimizing the electromagnetic response of alignment marks based on Maxwell's equations. However, increasingly complex manufacturing requirements require more complex alignment marks to more accurately align with the substrate. Conversely, the desire to implement faster scanning algorithms (e.g., diagonal scanning, etc.) to increase processing throughput requires faster scanning of more and smaller alignment marks. Those skilled in the art will understand that these criteria create tradeoffs that impact the overall performance of the alignment mark. These competing factors make conventional alignment mark design techniques difficult, if not impossible, to address. Summary of the Invention

[0009] Given the constraints described above, the exemplary lithography systems described herein can be configured using an inverse design methodology framework to optimize the topology of alignment marks, thereby discovering highly complex alignment marks that still provide optimal performance in the lithography system.

[0010] According to one aspect, the complexity of the alignment mark can be characterized by alignment mark definition parameters, which may include but are not limited to mark size, grating pitch, scanning speed, pupil diagram, etc. Similarly, the alignment mark scanning performance can be characterized by alignment mark performance parameters, which may include but are not limited to alignment accuracy, process accuracy, product crosstalk, lateral scan offset, etc. A set of key performance indicators (KPIs) can be used to characterize the final overall performance of the alignment mark. Such KPIs may include but are not limited to alignment measurement reproducibility, scan offset that may cause alignment errors due to wafer deformation and coarse wafer alignment (COWA) accuracy, six degrees of freedom accuracy (6DOF) to measure alignment position deviation (APD) caused by defocus and / or local tilt of the wafer or mark, and layer thickness of the APD that can be measured due to layer thickness variation.

[0011] In some embodiments, a method may include generating a first alignment mark to be used on a substrate. The first alignment mark may include a topology of at least two pixels having different characteristics. The method may include determining one or more characteristics of each of the at least two pixels. The method may also include optimizing the topology of the first alignment mark based on the one or more characteristics of the at least two pixels. The method may also include forming a second alignment mark on the substrate based on optimizing the first alignment mark.

[0012] In some embodiments, the metrology system may include an illumination system, a projection system, and a detector. The illumination system may be configured to generate a radiation beam. The projection system may be configured to project the radiation beam onto an alignment mark on the substrate. The detector may be configured to measure the position of the alignment mark by measuring radiation diffracted by the alignment mark, thereby detecting the position of the substrate. The alignment mark may include an optimized topology defined by at least two pixels having different characteristics.

[0013] In some embodiments, alignment marks may be formed on a substrate according to embodiments disclosed herein. In some embodiments, a lithography system may include a metrology system according to embodiments disclosed herein.

[0014] In some embodiments, a method may include receiving a first alignment mark to be used on a substrate. The first alignment mark may include a topology of at least two pixels having different characteristics. The method may include determining one or more characteristics of each of the at least two pixels. The method may include optimizing the topology of the first alignment mark based on the one or more characteristics of the at least two pixels. The method may include storing or displaying a set of values ​​used to form a second alignment mark having the optimized topology.

[0015] In some embodiments, a non-transitory computer-readable medium may include an instruction set that, when executed by a processor, causes the processor to perform operations. The operations may include receiving a first alignment mark to be used on a substrate, the first alignment mark including a topology of at least two pixels having different characteristics. The operations may include determining one or more characteristics of each of the at least two pixels. The operations may include optimizing the topology of the first alignment mark based on the one or more characteristics of the at least two pixels. The operations may include storing or displaying a set of values ​​used to form a second alignment mark having an optimized topology.

[0016] In some embodiments, the processor may be configured to receive a proposed alignment mark to be used on the substrate, the proposed alignment mark comprising a topology of at least two pixels having different characteristics. The processor may be configured to determine one or more characteristics of each of the at least two pixels. The processor may be configured to optimize the topology of the proposed alignment mark based on the one or more characteristics of the at least two pixels. The processor may be configured to store or display a set of values ​​for forming an alignment mark having an optimized topology.

[0017] Other features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Based on the teachings contained herein, those skilled in the relevant art will understand other aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the invention and to enable one skilled in the relevant art to make and use the aspects described herein.

[0019] Figure 1A A reflective lithographic apparatus according to some aspects is shown.

[0020] Figure 1B A transmissive lithographic apparatus according to some aspects is shown.

[0021] Figure 2 More details of a reflective lithography apparatus according to some aspects are shown.

[0022] Figure 3 A lithographic cell according to some aspects is shown.

[0023] Figure 4A and Figure 4B An inspection apparatus according to some aspects is shown.

[0024] Figure 5 A schematic diagram illustrating an alignment mark generated using an inverse design method and an enlarged portion of the alignment mark according to some embodiments is shown.

[0025] Figure 6A and Figure 6B Two different schematic configurations of alignment marks generated using an inverse design approach according to some embodiments are shown.

[0026] Figure 7 An example computer system is shown that can be used to implement various embodiments in accordance with some embodiments.

[0027] Features of the present disclosure will become more apparent from the detailed description set forth below in conjunction with the accompanying drawings, in which like reference numerals identify corresponding elements throughout. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, the leftmost digit of a reference numeral generally identifies the drawing in which the reference numeral first appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as being drawn to scale. DETAILED DESCRIPTION

[0028] The aspects described herein and references in the specification to "one aspect," "an aspect," "exemplary aspect," "example aspect," etc. indicate that the aspects described may include a particular feature, structure, or characteristic, but each aspect may not necessarily include the particular feature, structure, or characteristic. Furthermore, these phrases are not necessarily referring to the same aspect. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an aspect, it should be understood that it is within the knowledge of those skilled in the art to implement the feature, structure, or characteristic in conjunction with other aspects (whether or not explicitly described).

[0029] Spatially relative terms, such as "below," "beneath," "lower," "above," "upper," and the like, may be used herein to describe the relationship of one element or feature to another element or feature as illustrated in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly.

[0030] The terms "about," "approximately," and the like may be used herein to indicate that a value of a given quantity may vary based on a particular technology. Depending on the particular technology, the terms "about," "approximately," and the like may indicate that a value of a given quantity varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0031] Aspects of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Aspects of the present disclosure may also be implemented as instructions stored on a computer-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), etc. In addition, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only and that such actions are generated by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc. The term "machine-readable medium" may be interchangeable with similar terms, such as "computer program product," "computer-readable medium," "non-transitory computer-readable medium," etc. The term "non-transitory" may be used herein to characterize one or more forms of computer-readable media other than transient propagated signals.

[0032] However, before describing these aspects in greater detail, it is instructive to present an example environment in which aspects of the present disclosure may be implemented.

[0033] Example lithography system

[0034] Figure 1A and Figure 1B A lithographic apparatus 100 and a lithographic apparatus 100' are shown, respectively, in which aspects of the present disclosure may be implemented. The lithographic apparatus 100 and the lithographic apparatus 100' each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to precisely position the patterning device MA; and a substrate table (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to precisely position the substrate W. The lithographic apparatus 100 and 100' further have a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion (e.g., comprising one or more dies) C of the substrate W. In the lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In the lithographic apparatus 100', the patterning device MA and the projection system PS are transmissive.

[0035] The illumination system IL may include various types of optical components for directing, shaping, or controlling the radiation beam B, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

[0036] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to the reference frame, the design of at least one of the lithographic apparatuses 100 and 100', and other conditions, such as whether the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be, for example, a frame or a table, which can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is located at a desired position, for example, relative to the projection system PS.

[0037] The term "patterning device" MA should be broadly interpreted as referring to any device that can be used to impart a pattern in the cross-section of a radiation beam B, such as to produce a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in a device produced in the target portion C to form an integrated circuit.

[0038] The patterning device MA may be transmissive (e.g. Figure 1B lithographic apparatus 100') or reflected (as in Figure 1A lithographic apparatus 100). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase-shift, or attenuated phase-shift, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by the matrix of small mirrors.

[0039] The term "projection system" PS may include any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, depending on the exposure radiation used, or other factors such as the use of an immersion liquid or a vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation, as other gases may absorb excess radiation or electrons. Therefore, a vacuum environment may be provided for the entire beam path with the aid of vacuum walls and a vacuum pump.

[0040] The lithographic apparatus 100 and / or the lithographic apparatus 100' may be of a type having two (dual-stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, the additional substrate tables WT may be used in parallel, or preparatory steps may be performed on one or more stages while exposure is being performed using one or more other substrate tables WT. In some cases, the additional stages may not be substrate tables WT.

[0041] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g., water) so as to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art and are used to increase the numerical aperture of the projection system. The term "immersion" as used herein does not mean that structures such as the substrate must be immersed in the liquid. For example, during exposure, the liquid may be located between the projection system and the substrate.

[0042] refer to Figure 1A and Figure 1B , the illuminator IL receives a radiation beam from a radiation source SO. For example, when the source SO is an excimer laser, the source SO and the lithographic apparatus 100, 100' may be separate physical entities. In this case, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B is delivered to the lithographic apparatus 100 or 100' by means of a beam delivery system BD (in the embodiment of FIG. 1 ) comprising, for example, suitable directing mirrors and / or a beam expander. Figure 1B In other cases, for example when the source SO is a mercury lamp, the source SO may be an integral part of the lithographic apparatus 100, 100'. The radiation system may include the source SO, the illuminator IL and / or the beam delivery system BD.

[0043] The illuminator IL may comprise an adjuster AD (at Figure 1B In general, at least the outer and / or inner radial extent (commonly referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components (in Figure 1B ), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0044] Reference Figure 1A, a radiation beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and is patterned by the patterning device MA. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., a mask) MA. After reflecting from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be precisely moved (e.g., in order to position a different target portion C in the path of the radiation beam B). Similarly, a first positioner PM and a further position sensor IF1 can be used to precisely position the patterning device (e.g., a mask) MA relative to the path of the radiation beam B. The patterning device (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0045] Reference Figure 1B , radiation 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 mask MA, radiation beam B passes through a projection system PS, which focuses the radiation beam onto a target portion C of a substrate W. The projection system has a pupil PPU that is conjugate to an illumination system pupil IPU. Part of the radiation emerges from the intensity distribution at illumination system pupil IPU and passes through the mask pattern without being affected by diffraction at the mask pattern, producing an image of the intensity distribution at illumination system pupil IPU.

[0046] The projection system PS projects an image of a mask pattern MP onto a photoresist layer coated on a substrate W, wherein the image is formed by a diffracted beam generated from the mask pattern MP by radiation from an intensity distribution. For example, the mask pattern MP may comprise an array of lines and spaces. The diffraction of the radiation at the array is different from the zeroth order diffraction, resulting in a steered diffraction beam with a change of direction in a direction perpendicular to the lines. The undiffracted beam, the so-called zeroth order diffraction beam, passes through the pattern without any change in the propagation direction. The zeroth order diffraction beam passes through the upper lens or upper lens group of the projection system PS upstream of the pupil conjugate PPU of the projection system PS and reaches the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zeroth order diffraction 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 arranged or substantially arranged at a plane including the pupil conjugate PPU of the projection system PS.

[0047] The projection system PS is arranged to capture (e.g., using a lens or lens group L) a zeroth-order diffracted beam, a first-order diffracted beam, and / or higher-order diffracted beams (not shown). In some aspects, dipole illumination for imaging a line pattern extending in a direction perpendicular to the line can be used to exploit the resolution enhancement effect of dipole illumination. For example, a first-order diffracted beam interferes with a corresponding zeroth-order diffracted beam at the level of the wafer W, thereby producing an image of the line pattern MP with the highest possible resolution and process window (i.e., usable depth of focus combined with tolerable exposure dose deviation). In some aspects, astigmatic aberrations can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Furthermore, in some aspects, astigmatic aberrations can be reduced by blocking the zeroth-order beam in the projection system's pupil conjugate PPU associated with the radiation pole in the opposite quadrant. This is described in more detail in US Pat. No. 7,511,799 B2, published on Mar. 31, 2009, which is incorporated herein by reference in its entirety.

[0048] With the help of a second positioner PW and a position sensor IFD (e.g. an interferometer device, a linear encoder or a capacitive sensor), the substrate table WT can be precisely moved (e.g. to position a different target portion C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor ( Figure 1B ) can be used to accurately position the mask MA relative to the path of the radiation beam B (eg after mechanical retrieval from a mask library or during scanning).

[0049] Typically, movement of the mask table MT may be achieved with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be achieved using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected to a short-stroke actuator or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks (as shown) occupy dedicated target portions, they may be located in the space between target portions (called scribe line alignment marks). Similarly, where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0050] The mask table MT and patterning device MA can be within the vacuum chamber V, where an in-vacuum robot (IVR) can be used to move the patterning device, such as a mask, into and out of the vacuum chamber. Alternatively, when the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot can be used to perform various transport operations, similar to the in-vacuum robot (IVR). Both in-vacuum and out-of-vacuum robots can be calibrated to smoothly transfer any payload (e.g., a mask) to the fixed kinematic support of the transfer station.

[0051] The lithographic apparatuses 100 and 100 ′ may be used in at least one of the following modes:

[0052] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept essentially stationary, and an entire pattern imparted to the radiation beam B is simultaneously projected onto a target portion C (i.e. a single static exposure). The substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed.

[0053] 2. In scan mode, the support structure (e.g. mask table) MT and substrate table WT are scanned synchronously (i.e. single dynamic exposure) while projecting a pattern imparted to the radiation beam B onto a target portion C. The speed and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0054] 3. In another mode, the support structure (e.g., mask table) MT is held essentially stationary, thereby holding the programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO may be employed, and the programmable patterning device updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation is readily applicable to maskless lithography utilizing a programmable patterning device, such as a programmable mirror array.

[0055] Combinations and / or variations of the described modes of use or entirely different modes of use may also be employed.

[0056] In some aspects, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Typically, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0057] In some aspects, the lithographic apparatus 100' includes a deep ultraviolet (DUV) source configured to generate a DUV radiation beam for DUV lithography. Typically, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source.

[0058] Figure 2 The lithographic apparatus 100 is shown in greater detail, including a source collector arrangement SO, an illumination system IL, and a projection system PS. The source collector arrangement SO is constructed and arranged so that a vacuum environment can be maintained within an enclosure 220 of the source collector arrangement SO. An EUV radiation emitting plasma 210 can be formed by a plasma source generated by a discharge. In some aspects, a plasma that excites tin (Sn) (e.g., via laser excitation) is provided to generate EUV radiation.

[0059] Radiation emitted by EUV radiation emitting plasma 210 passes from source chamber 211 into collector chamber 212 via an optional gas barrier or contamination trap 230 (also referred to in some cases as a contamination barrier or fin trap), which is positioned in or behind an opening in source chamber 211. Contamination trap 230 may include a channel structure. Contamination trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. Further herein, contamination trap or contamination barrier 230 includes at least a channel structure.

[0060] The collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation passing through the collector CO may be reflected from the grating spectral filter 240 to be focused into a virtual source point INTF. The virtual source point INTF is often referred to as an intermediate focus, and the source collector arrangement is arranged such that the intermediate focus INTF is located at or near the opening 219 in the enclosure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. The grating spectral filter 240 is particularly useful for suppressing infrared (IR) radiation.

[0061] The radiation then passes through the illumination system IL, which may include a faceted field mirror arrangement 222 and a faceted pupil mirror arrangement 224 arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA. When the radiation beam 221 reflects at the patterning device MA, which is held by the support structure MT, a patterned beam 226 is formed, and the patterned beam 226 is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by a wafer stage or substrate table WT.

[0062] There may typically be more elements than shown in the illumination optics unit IL and projection system PS. Depending on the type of lithographic apparatus, a grating spectral filter 240 may optionally be present. Additionally, there may be more than Figure 2 More reflectors than the ones shown, for example, may be present in the projection system PS. Figure 2 From 1 to 6 additional reflective elements are shown.

[0063] like Figure 2 As shown, the collector optics CO is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axisymmetrically around the optical axis O, and this type of collector optics CO is preferably used in conjunction with a discharge produced plasma source (commonly referred to as a DPP source).

[0064] Example Lithography Cell

[0065] Figure 3 A lithography unit 300, sometimes also referred to as a lithography cell or cluster, is shown according to some aspects. The lithography apparatus 100 or 100' may form part of the lithography unit 300. The lithography unit 300 may also include one or more devices for performing pre-exposure and post-exposure 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 cooling plate CH, and a bake plate BK. A substrate handler or robot RO picks up substrates from input / output ports I / O1, I / O2, moves them between the different processing devices, and delivers them to the loading bay LB of the lithography apparatus 100 or 100'. These devices, often collectively referred to as a track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, the different devices can be operated to maximize throughput and processing efficiency.

[0066] Example inspection device

[0067] In order to control the lithographic process so that device features are accurately placed on the substrate, alignment marks are usually provided on the substrate, and the lithographic equipment includes one or more inspection devices for accurately locating the marks on the substrate. These alignment devices are effective position measuring devices. Different types of marks and different types of alignment devices and / or systems are known from different times and different manufacturers. A type of system widely used in current lithographic equipment is based on the self-referencing interferometer described in U.S. Patent number 6,961,116 (den Boef et al.). Usually, the marks are measured separately to obtain X-position and Y-position. However, the combined X-position and Y-measurement can be carried out using the technology described in U.S. Publication No. 2009 / 195768A (Bijnen et al.). The entire contents of these two disclosures are hereby incorporated by reference.

[0068] Figure 4A A cross-sectional view of an inspection apparatus 400 that can be implemented as part of a lithographic apparatus 100 or 100' is shown, according to some aspects. In some aspects, the inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). The inspection apparatus 400 can also be configured to detect positions of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate relative to the patterning device or other components of the lithographic apparatus 100 or 100'. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0069] The terms "inspection device", "measurement system", etc. may be used in this document to refer to, for example, a device for measuring the characteristics of a structure (e.g., an overlay sensor, a critical dimension sensor, etc.), a device or system used in a lithography device to check the alignment of a chip (e.g., an alignment sensor), etc.

[0070] In some aspects, inspection apparatus 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam profiler 430, and an overlay calculation processor 432. Illumination system 412 may be configured to provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a wavelength spectrum between approximately 500 nm and approximately 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a wavelength spectrum between approximately 500 nm and approximately 900 nm. Illumination system 412 may further be configured to provide one or more passbands having a substantially constant center wavelength (CWL) value over a long period of time (e.g., over the lifetime of illumination system 412). As described above, in current alignment systems, this configuration of illumination system 412 may help prevent actual CWL values ​​from drifting from desired CWL values. As a result, using a constant CWL value may improve the long-term stability and accuracy of an alignment system (e.g., inspection apparatus 400) compared to current alignment apparatuses.

[0071] In some aspects, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 can be split into radiation sub-beams 415 and 417, as shown in FIG. Figure 4AAs shown. Beam splitter 414 can also be configured to direct radiation sub-beam 415 onto substrate 420 placed on platform 422. In one example, platform 422 can be moved along direction 424. Radiation sub-beam 415 can be configured to illuminate alignment mark or target 418 located on substrate 420. Alignment mark or target 418 can be coated with a radiation-sensitive film. In some aspects, alignment mark or target 418 can have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to the plane of 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) a resist layer grating comprising stripes formed from solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlying or interleaved on the product layer grating. Alternatively, the stripes can be etched into the substrate. The pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and the illumination symmetry and the presence of such aberrations will manifest themselves in variations in the printed grating. One in-line method for measuring line width, pitch, and critical dimensions in device manufacturing utilizes a technique known as "scatterometry." The method of scatterometry is described in Raymond et al., "Multiparameter Grating Metrology Using Optical Scatterometry", J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997) and Niu et al., "Specular Spectroscopic Scatterometry in DUV Lithography", SPIE, Vol. 3677 (1999), both of which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by a periodic structure in the target and the resulting reflection spectrum at a given angle is detected. The structure that produces the reflection spectrum is reconstructed, for example, using rigorous coupled wave analysis (RCWA) or by comparison with a library of patterns derived from simulations. Therefore, the scatterometry data of the printed grating are used to reconstruct the grating. The parameters of the grating, such as line width and shape, can be input into the reconstruction process performed by the processing unit PU from knowledge of the printing step and / or other scatterometry processes.

[0072] In some aspects, according to one aspect, beam splitter 414 can also be configured to receive diffracted radiation beam 419 and split diffracted radiation beam 419 into at least two radiation sub-beams. Diffracted radiation beam 419 can be split into diffracted radiation sub-beams 429 and 439, as shown in FIG. Figure 4A shown.

[0073] It should be noted that although beam splitter 414 is shown as directing radiation sub-beam 415 toward alignment mark or target 418 and directing diffracted radiation sub-beam 429 toward interferometer 426, the present disclosure is not limited thereto. Other optical arrangements may be used to achieve similar results of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0074] like Figure 4A As shown, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 via beam splitter 414. In one exemplary aspect, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In one example of this aspect, interferometer 426 includes any suitable set of optical elements, such as a combination of prisms, that can be configured to form two images of alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be understood that high quality images need not be formed. It may be sufficient to resolve features of alignment mark 418. Interferometer 426 can also be configured to rotate one of the two images by 180° relative to the other of the two images and interferometrically recombine the rotated and unrotated images.

[0075] In some aspects, detector 428 can be configured to receive the recombined image via interferometer signal 427 and detect interference resulting from the recombined image when alignment axis 421 of inspection apparatus 400 passes through the center of symmetry of alignment mark or target 418 (not shown). According to one example aspect, this interference can be due to alignment mark or target 418 being 180° symmetrical and the recombined image interfering constructively or destructively. Based on the detected interference, detector 428 can be further configured to determine the position of the center of symmetry of alignment mark or target 418 and, therefore, detect the position of substrate 420. According to one example, alignment axis 421 can be aligned with a beam perpendicular to substrate 420 and passing through the center of image rotation interferometer 426. Detector 428 can also be configured to estimate the position of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer marking process variations.

[0076] In another aspect, the detector 428 determines the location of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements:

[0077] 1. Measure the positional shift of various wavelengths (positional shift between colors);

[0078] 2. Measure the positional variation of the various orders (positional shifts between diffraction orders); and

[0079] 3. Measure the positional changes of the various polarizations (positional shifts between polarizations).

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

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

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

[0083] In some aspects, the beam profiler 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 dimensions, and focus of the target 418 in a single measurement. The product stack profile contains information about the stacked product, such as alignment marks, the target 418, or the substrate 420, and can include optical feature measurements caused by variations in the marking process as a function of illumination variations. The product stack profile can also include product raster profiles, mark stack profiles, and mark asymmetry information. An example of a beam profiler 430 is the Yieldstar TM , manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, the entire contents of which are incorporated herein by reference. The beam profiler 430 may be further configured to process information related to specific properties of the exposed pattern in the layer. For example, the beam profiler 430 may process overlay parameters (an indication of the accuracy of positioning of a layer relative to a previous layer on the substrate or an indication of the accuracy of positioning of a first layer relative to a mark on the substrate), focus parameters, and / or critical dimension parameters (e.g., line width and its variation) of the depicted image in the layer. Other parameters are image parameters related to the quality of the depicted image of the exposed pattern.

[0084] In some aspects, a detector array (not shown) may be connected to the beam profiler 430 and allow the possibility of accurate stack profile detection as discussed below. For example, the detector 428 may be a detector array. For the detector array, multiple options are possible: a multimode fiber bundle, a discrete pin detector for each channel, or a CCD or CMOS (linear) array. The use of a multimode fiber bundle enables any dissipative elements to be remotely located for stability reasons. Discrete PIN detectors provide a large dynamic range, but require a separate preamplifier for each detector. Therefore the number of elements is limited. A CCD linear array provides many elements that can be read out at high speed and is of particular interest if phase stepped detection is used.

[0085] In some aspects, the second beam profiler 430' can be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, such as Figure 4B. The optical state can be a measure of the beam amplitude and phase, the beam wavelength, the polarization, or the beam profile. The second beam profiler 430' can be identical to the beam profiler 430. Alternatively, the second beam profiler 430' can be configured to perform one or more functions of the beam profiler 430, such as determining the position of the platform 422 and correlating the position of the platform 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 therefore the position of the substrate 420 can be precisely known with reference to the platform 422. The second beam profiler 430' can also be configured to determine the position of the inspection device 400 or any other reference element so that the center of symmetry of the alignment mark or target 418 can be known with reference to the inspection device 400 or any other reference element. The second beam profiler 430' can further be configured to determine overlay data between the two patterns and a model of the product stack profile of the substrate 420. The second beam profiler 430' can also be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement.

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

[0087] In some aspects, processor 432 receives information from detector 428 and beam profiler 430. For example, processor 432 may be an overlay calculation processor. This information may include a model of the product stack profile constructed by beam profiler 430. Alternatively, processor 432 may use information received about product markings to construct a model of the product marking profile. In either case, processor 432 uses or combines the model of the product marking profile to construct a model of the stacked product and the overlay marking profile. The stack model is then used to determine overlay offset and minimize spectral effects on the overlay offset measurement. Processor 432 may create a basic correction algorithm based on the information received from detector 428 and beam profiler 430, including but not limited to the optical state of the illumination beam, alignment signals, associated position estimates, and optical states in pupil, image, and additional planes. The pupil plane is a plane where the radial position of the radiation defines the angle of incidence, and the angular position defines the azimuth angle of the radiation. Processor 432 may utilize the basic correction algorithm to characterize inspection apparatus 400 with reference to wafer marks and / or alignment marks 418.

[0088] In some aspects, processor 432 may be further configured to determine, for each mark, a printed pattern position offset error relative to the sensor estimate based on information received from detector 428 and beam profiler 430. This information includes, but is not limited to, the product stack profile, overlay measurements, critical dimensions, and the focal point of each alignment mark or target 418 on substrate 420. Processor 432 may utilize a clustering algorithm to group marks into sets of similar constant offset errors and, based on this information, create an alignment error offset correction table. The clustering algorithm may be based on the overlay measurements, position estimates, and additional optical stack process information associated with each set of offset errors. Overlay is calculated for multiple different marks, for example, overlay targets with positive and negative offsets around a programmed overlay offset. The target with the smallest measured overlay is used as a reference (because it is measured with the best accuracy). From this measured small overlay, and the known programmed overlay of its corresponding target, the overlay error can be derived. Table 1 illustrates how this is performed. In the example shown, the smallest measured overlay is -1 nm. However, this is relative to a target with a programmed overlay of -30 nm. This process may introduce an overlay error of 29nm.

[0089]

[0090] A minimum value can be taken as a reference point, and relative to this, the offset between the measured overlay and the expected overlay due to programmed overlay can be calculated. This offset determines the overlay error for each mark or group of marks with similar offsets. Thus, in the example of Table 1, the minimum measured overlay is -1 nm, at a target position with a programmed overlay of 30 nm. The differences between the expected and measured overlay at other targets are compared with this reference. A table such as Table 1 can also be obtained from the marks and targets 418 under different illumination settings, and the illumination settings and their corresponding calibration factors that result in the minimum overlay error can be determined and selected. Thereafter, the processor 432 can group the marks into sets of similar overlay errors. The criteria for grouping marks can be adjusted based on different process controls, for example, different error tolerances for different processes.

[0091] In some aspects, the processor 432 can confirm that all or most members of the group have similar offset errors and apply individual offset corrections from the clustering algorithm to each mark based on their additional optical stack measurements. The processor 432 can determine the correction for each mark and feed the correction back to the lithographic apparatus 100 or 100' to correct errors in overlay, for example, by feeding the correction to the inspection device 400.

[0092] Example topology optimized alignment mark

[0093] Figure 5Schematically illustrates a topology optimized alignment mark that can be designed using an inverse design method according to some embodiments. Figure 5 As shown, the alignment mark 500 according to some embodiments may include a plurality of unit cells 502 (in Figure 5 (shown enlarged on the right). Figure 5 A unit cell 502 of an alignment mark 500 is shown divided into white individual pixels 504 and black individual pixels 506. Different pixels 504, 506 can be formed of materials having different properties (e.g., refractive index, material, etch depth, etc.), and thus the pixels 504, 506 will constitute the topology of the alignment mark 500. In some embodiments, the pixels 504, 506 can be divided into two groups, the first group being formed of a first material having a first property (e.g., a first refractive index) and the second group being formed of a second material having a second property (e.g., a second refractive index). However, the present invention is not limited to using only two materials with different properties, but includes using three or more materials with different properties. In some aspects, the choice of material can be arbitrary, as long as the material has appropriately different properties. On the other hand, a material with optimized properties can be selected based on one or more properties of the material forming the pixel, the wafer being processed, the radiation used by the alignment system, or any other aspect of the lithography system.

[0094] In some embodiments, the alignment mark 500 can be processed by scanning the alignment mark along a given direction using a metrology system. In some aspects, scanning the alignment mark 500 can be represented by a translation along the x-direction and / or the y-direction, such as Figure 5 is shown by the scanning function (x0, y0).

[0095] The following description of an inverse design method for topology-optimized alignment marks is provided for alignment marks comprising two materials with different refractive indices. However, it should be noted that this description can be generalized to alignment marks having n different materials, or alignment marks composed of materials comprising n different refractive indices, where n is any integer, or multiple materials with varying etch depths such that the materials form any portion of a pixel between 0 and 1.

[0096] According to some embodiments, the alignment mark 500 can be divided into at least two pixels 504, 506 (e.g., a bright pixel 504 and a dark pixel 506) made of different materials. In some aspects, the diffraction efficiency of such an alignment mark can be modeled. In practice, the specific choice of material may have some impact on the diffraction efficiency of the alignment mark 500. In some aspects, by using a shallow grating approximation, the far-field radiation pattern of the alignment mark 500 will be independent of the choice of material (or the etch depth of the material), and thus the diffraction efficiency can be approximated by considering only the far-field radiation pattern of the alignment mark 500. In other aspects, if a full wave vector simulation is performed, the mark material, the substrate, and the layers above and below the mark also contribute to the far-field radiation pattern.

[0097] In some aspects, a shallow grating approximation of the far-field radiation pattern of an alignment mark 500 comprising materials having two different refractive indices can be expressed as follows:

[0098]

[0099] where φ(θ x ,θ y ) is the radiation angle θ x and θ y The far field diagram, E in is the electric field incident on the alignment mark, (x0, y0) represents the center of the incident radiation beam, G(x m ,y n ) is a function specific to the design of the alignment mark, and is the Fourier transform. Since E in G(x) is a function of (x0, y0, x, y), so the electric field distribution in the x and y directions changes along the scanning direction of the alignment mark. m ,y n ) adds phase to the electric field in each pixel and can depend on the refractive index of the pixel material, the etch depth of the alignment mark, etc.

[0100] In some aspects, while the characteristics of alignment mark 500 may affect the strength of the electric field and the pattern of zeroth order diffraction from alignment mark 500, using two materials with different refractive indices allows first order diffraction from the alignment mark to remain independent of material selection.

[0101] Using the above general expression for the far-field radiation pattern of an alignment mark, an optimization framework can be developed for any proposed alignment mark. In some aspects, such an optimization framework can be developed by defining a cost function. According to some embodiments, the cost function based on the above general expression for the far-field pattern can be defined as:

[0102] F(φ(θ x ,θy ),ε(x m ,y n ), [x0, y0 = αx0 + β]),

[0103] where F is the cost function, ε is the dielectric constant of either material, and y0=αx0+β is Figure 5 The scanning function shown. Other functions can also be included in the cost function. For example, for some sensors, a self-referenced interferometer (SRI) transfer function can be included, while for image-based sensors, a different transfer function can be used.

[0104] In some aspects, the cost function can define the sensitivity of the radiation pattern to the scan function, to one or more of the KPIs discussed above (e.g., 6DOF), to alignment mark asymmetry, etc. In some aspects, it may be desirable for the cost function to be insensitive to polarization, alignment mark symmetry, tilt, defocus, etc.

[0105] In some embodiments, the optimal topology of the alignment marks can be identified by minimizing the cost function according to the above description. Therefore, the optimization objective can be defined as one or more of the following conditions:

[0106]

[0107] Those skilled in the art will appreciate that the optimization goal(s) may vary depending on the specific characteristics of the alignment mark or the application for which the alignment mark is to be used.

[0108] In some embodiments, an inverse design method for an alignment mark can be performed by determining the far-field radiation pattern of a proposed alignment mark. Based on the far-field radiation pattern, a cost function can be developed for the proposed alignment mark. The specific topology of the alignment mark can then be adjusted by minimizing the cost function to achieve one or more of the aforementioned optimization objectives. This optimization will produce a set of values ​​that can be used to form an alignment mark with an optimized topology. In other embodiments, as described above, alignment marks with optimized topologies can be automatically identified by optimizing the cost function along one or more parameters.

[0109] The above method can be generalized to any alignment mark and thus constitutes a general framework for topology optimized alignment marks.

[0110] In some aspects, the pattern of alignment marks includes repeating unit cells of pixels (such as, for example, Figure 5), and the pixels 504 and 506 of each unit cell form a pixel sub-pattern. In some embodiments, the pixel sub-pattern may repeat periodically or semi-periodically, or may not repeat within the unit cell, making the sub-pattern aperiodic. As described above, the sub-pattern of the unit cell can be determined based on one or more optimization objectives of the cost function. That is, once a sub-pattern for a unit cell is determined, the sub-pattern can be adjusted by determining the corresponding cost function for the far-field diffraction pattern and the sub-pattern, and then optimizing the cost function as described above.

[0111] In addition to determining the sub-pattern of the unit cell, the symmetry of the repeating unit cell can also be determined. Figure 6A As schematically shown in , the unit cells of the alignment marks may be repeated periodically, in which case the unit cells are translated across the alignment marks. As another example, Figure 6B An example is schematically shown in which the unit cells of the alignment mark are arranged to form a centrally symmetric pattern, such that the unit cells are symmetric about the center of the alignment mark. Those skilled in the art will appreciate that such unit cell symmetry is merely an example, and that other types of unit cell symmetry can be readily implemented, such as inversion or rotational symmetry about a non-central point of the alignment mark, mirror symmetry, or a combination of two or more such symmetries. Here, too, as described above, the symmetry of the unit cell can be determined based on one or more optimization objectives of the cost function.

[0112] Once the pattern of the alignment marks, including the sub-patterns of the pixels and the symmetry of the unit cells, has been determined and optimized, the alignment marks can be formed on the device. For example, the alignment marks can be formed by depositing a first material and a second material. Alternatively, the alignment marks can be formed by removing the first material (e.g., by etching) to expose the second material. Other methods of forming alignment marks will be apparent to those of ordinary skill in the art, such as a combination of etching and deposition, additive manufacturing, nanolithography, and the like. The first and second materials can be similar but different materials, such as, for example, different metallic materials or different dielectric materials, or can be different materials, such as, for example, a metal and a dielectric material.

[0113] When more than two materials or materials having more than two effective refractive indices are used, any suitable method may be used to form the desired number of materials into the alignment mark pattern.

[0114] According to some embodiments, minimization of a cost function allows for optimization of one or more KPIs of the optimized alignment mark. By comparing the results of different minimizations of the cost function, the optimal solution and fundamental limits of the cost function can be found. Furthermore, the costs and benefits can be compared between alignment mark designs to determine the optimal pattern of alignment marks.

[0115] Computer Implementation of Design Process

[0116] For example, one or more well-known computer systems (such as Figure 7 Various embodiments may be implemented using the computer system 700 shown in FIG. 7 . For example, a combination or subcombination of computer systems 700 may be used to implement a media device. Similarly or alternatively, one or more computer systems 700 may be used, for example, to implement any of the embodiments discussed herein, and combinations and subcombinations thereof.

[0117] Computer system 700 may include one or more processors (also called central processing units or CPUs), such as processor 704. Processor 704 may be connected to a communication infrastructure or bus 706.

[0118] The computer system 700 may also include user input / output device(s) 703 , such as a monitor, keyboard, pointing device, etc., which may communicate with the communication infrastructure 706 through the user input / output interface(s) 702 .

[0119] One or more processors 704 may be a graphics processing unit (GPU). In one embodiment, a GPU may be a processor that is a specialized electronic circuit designed to handle mathematically intensive applications. A GPU may have a parallel architecture that is efficient for parallel processing of large blocks of data, such as mathematically intensive data common to computer graphics applications, images, videos, etc.

[0120] The computer system 700 may also include a main or primary memory 708, such as random access memory (RAM). The main memory 708 may include one or more levels of cache. The main memory 708 may have control logic (i.e., computer software) and / or data stored therein.

[0121] The computer system 700 may also include one or more secondary storage devices or memories 710. The secondary storage 710 may include, for example, a hard disk drive 712 and / or a removable storage device or drive 714. The removable storage drive 714 may be a floppy disk drive, a tape drive, an optical disk drive, an optical storage device, a tape backup device, and / or any other storage device / drive.

[0122] Removable storage drive 714 can interact with removable storage unit 718. Removable storage unit 718 may include a computer-usable or readable storage device having computer software (control logic) and / or data stored thereon. Removable storage unit 718 may be a floppy disk, magnetic tape, optical disk, DVD, optical storage disk, and / or any other computer data storage device. Removable storage drive 714 can read from and / or write to removable storage unit 718.

[0123] Secondary memory 710 may include other means, devices, components, tools, or other methods for allowing computer system 700 to access computer programs and / or other instructions and / or data. Such means, devices, components, tools, or other methods may include, for example, a removable storage unit 722 and an interface 720. Examples of removable storage unit 722 and interface 720 may include a program cartridge and a cartridge interface (such as found in video game devices), a removable memory chip (such as an EPROM or PROM) and an associated socket, a memory stick and a USB or other port, a memory card and an associated memory card slot, and / or any other removable storage unit and associated interface.

[0124] The computer system 700 may also include a communication or network interface 724. The communication interface 724 may enable the computer system 700 to communicate and interact with any combination of external devices, external networks, external entities, and the like (individually and collectively represented by reference numeral 728). For example, the communication interface 724 may allow the computer system 700 to communicate with an external or remote device 728 via a communication path 726, which may be wired and / or wireless (or a combination thereof) and may include any combination of a LAN, a WAN, the Internet, and the like. Control logic and / or data may be sent to and from the computer system 700 via the communication path 726.

[0125] The computer system 700 may also be any of the following: a personal digital assistant (PDA), a desktop workstation, a laptop or notebook computer, a notebook computer, a tablet computer, a smart phone, a smart watch or other wearable device, an appliance, part of the Internet and / or an embedded system, to name a few non-limiting examples, or any combination thereof.

[0126] The computer system 700 can be a client or server that accesses or hosts any applications and / or data through any delivery paradigm, including but not limited to remote or distributed cloud computing solutions; local or on-premises software (cloud-based on-premises solutions); "as a service" models (e.g., Content as a Service (CAAS), Digital Content as a Service (DCaaS), Software as a Service (SAAS), Management Software as a Service (MSaaS), Platform as a Service (PAAS), Desktop as a Service (DAAS), Framework as a Service (FAAS), Backend as a Service (BAAS), Mobile Backend as a Service (MBaaS), Infrastructure as a Service (IAAS), etc.); and / or hybrid models including any combination of the foregoing examples or other services or delivery paradigms.

[0127] Any applicable data structures, file formats, and schemas in the computer system 700 may be derived from standards including, but not limited to, JavaScript Object Notation (JSON), Extensible Markup Language (XML), Yet Another Markup Language (YAML), Extensible Hypertext Markup Language (XHTML), Wireless Markup Language (WML), message packages, XML User Interface Language (XUL), or any other functionally similar representations, alone or in combination. Alternatively, proprietary data structures, formats, or schemas may be used exclusively or in combination with known or open standards.

[0128] In some embodiments, a tangible, non-transitory device or article of manufacture comprising a tangible, non-transitory computer-usable or readable medium having control logic (software) stored thereon may also be referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 700, primary memory 708, secondary memory 710, and removable storage units 718 and 722, as well as tangible articles of manufacture embodying any combination of the foregoing. When executed by one or more data processing devices (such as computer system 700 or processor(s) 704), such control logic may cause such data processing devices to operate as described herein.

[0129] These embodiments can be further described using the following terms:

[0130] 1. A method comprising:

[0131] generating a first alignment mark to be used on a substrate, the first alignment mark comprising a topology of at least two pixels having different characteristics;

[0132] determining one or more characteristics of each of the at least two pixels;

[0133] optimizing the topology of the first alignment mark based on the one or more characteristics of the at least two pixels; and

[0134] Based on optimizing the first alignment mark, a second alignment mark is formed on the substrate.

[0135] 2. The method of clause 1, wherein optimizing the topology of the first alignment mark comprises determining a far-field pattern of radiation diffracted by the first alignment mark.

[0136] 3. The method of clause 2, wherein optimizing the topology of the first alignment mark comprises defining a cost function based on the far-field pattern.

[0137] 4. The method of clause 3, wherein optimizing the topology of the first alignment mark comprises minimizing the cost function based on one or more optimization objectives.

[0138] 5. The method of clause 4, wherein the optimized topology is automatically identified by optimizing the cost function along one or more parameters.

[0139] 6. The method of clause 1, wherein:

[0140] The at least two pixels include at least a first pixel and a second pixel, and

[0141] The one or more characteristics include a refractive index, a material forming each pixel, and / or an etch depth of each pixel.

[0142] 7. The method according to clause 6, wherein:

[0143] The first pixel has a first refractive index, and

[0144] The second pixel has a second refractive index different from the first refractive index.

[0145] 8. The method of clause 7, wherein the far-field pattern of radiation diffracted by the first alignment mark is calculated using Fourier optics or full-wave simulation.

[0146] 9. The method according to clause 8, wherein:

[0147] The cost function based on the far-field pattern is defined as

[0148] F(φ(θ x ,θ y ),ε(x m ,y n ), [x0, y0 = αx0 + β])

[0149] where F is the cost function, ε is the dielectric constant of either material, and y0=αx0+β is the scanning function.

[0150] 10. The method according to clause 9, wherein:

[0151] The topology of the first alignment mark is optimized by minimizing the cost function of variations in incident field, mark topology, and scan function.

[0152] 11. The method of clause 1, wherein optimizing the topology of the first alignment mark comprises determining a sub-pattern of a plurality of pixels in a unit cell of the first alignment mark.

[0153] 12. The method of clause 1, wherein:

[0154] The first alignment mark includes a plurality of unit cells, and

[0155] The optimizing of the topology of the first alignment mark includes determining a symmetry of the unit cell.

[0156] 13. The method of clause 12, wherein the symmetry of each unit cell is periodic, semi-periodic or aperiodic.

[0157] 14. The method of clause 12, wherein the plurality of unit cells are arranged to have centrosymmetric symmetry about the center of the alignment mark, inversion or rotational symmetry about a non-central point of the alignment mark, mirror symmetry, or a combination thereof, or no symmetry.

[0158] 15. The method of clause 1, wherein forming the second alignment mark comprises depositing the at least two pixels by depositing at least a first material and a second material on the substrate.

[0159] 16. The method of clause 15, wherein the first material and the second material are dielectrics or metals.

[0160] 17. A measurement system comprising:

[0161] an illumination system configured to generate a radiation beam;

[0162] a projection system configured to project the radiation beam onto an alignment mark on a substrate; and

[0163] a detector configured to detect the position of the substrate by measuring the position of the alignment mark by measuring radiation diffracted by the alignment mark, wherein

[0164] The alignment mark includes an optimized topology defined by at least two pixels having different characteristics.

[0165] 18. The metrology system of clause 17, wherein:

[0166] The at least two pixels include at least a first pixel and a second pixel.

[0167] 19. The metrology system of clause 18, wherein the first pixel has a first refractive index and the second pixel has a second refractive index different from the first refractive index.

[0168] 20. The metrology system of clause 17, wherein the alignment mark comprises a plurality of unit cells.

[0169] 21. The metrology system of clause 20, wherein the symmetry of each unit cell of the alignment mark is periodic, semi-periodic, or aperiodic.

[0170] 22. The metrology system of clause 20, wherein the plurality of unit cells are arranged to have centrosymmetric symmetry about a center of the alignment mark, inversion or rotational symmetry about a non-central point of the alignment mark, mirror symmetry, or a combination thereof.

[0171] 23. The metrology system of clause 19, wherein the first pixel is formed of a first material and the second pixel is formed of a second material different from the first material.

[0172] 24. The metrology system of clause 23, wherein the first material and the second material are dielectrics or metals.

[0173] 25. An alignment mark formed on a substrate by the method according to clause 1.

[0174] 26. A lithography system comprising the metrology system according to clause 17.

[0175] 27. A method comprising:

[0176] receiving a first alignment mark to be used on a substrate, the first alignment mark comprising a topology of at least two pixels having different characteristics;

[0177] determining one or more characteristics of each of the at least two pixels;

[0178] optimizing the topology of the first alignment mark based on the one or more characteristics of the at least two pixels; and

[0179] A set of values ​​for forming a second alignment mark having the optimized topology is stored or displayed.

[0180] 28. A non-transitory computer-readable medium comprising a set of instructions that, when executed by a processor, cause the processor to:

[0181] receiving a first alignment mark to be used on a substrate, the first alignment mark comprising a topology of at least two pixels having different characteristics;

[0182] determining one or more characteristics of each of the at least two pixels;

[0183] optimizing the topology of the first alignment mark based on the one or more characteristics of the at least two pixels; and

[0184] A set of values ​​for forming a second alignment mark having the optimized topology is stored or displayed.

[0185] 29. A processor configured to perform the following process, the process comprising:

[0186] receiving a proposed alignment mark to be used on a substrate, the proposed alignment mark comprising a topology of at least two pixels having different characteristics;

[0187] determining one or more characteristics of each of the at least two pixels;

[0188] optimizing the topology of the proposed alignment mark based on the one or more characteristics of the at least two pixels; and

[0189] A set of values ​​for forming an alignment mark having the optimized topology is stored or displayed.

[0190] Based on the teachings contained in this disclosure, it will be readily apparent to those skilled in the relevant art how to use different Figure 7 It will be apparent that the data processing devices, computer systems, and / or computer architectures shown are used to make and use the embodiments of the present disclosure. In particular, the embodiments can be implemented with software, hardware, and / or operating systems other than those described herein.

[0191] Although specific reference may be made herein to the use of lithographic apparatus in the manufacture of ICs, it will be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film heads, and the like. It will be understood by those skilled in the art that any use of the terms "wafer" or "die" herein in the context of such alternative applications may be considered as a specific example of the more general terms "substrate" or "target portion", respectively. Before or after exposure, the substrates referred to herein may be processed in, for example, a tracking unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a metrology unit. Where applicable, the disclosure herein may be applicable to such and other substrate processing tools. Furthermore, a substrate may be processed more than once, for example to produce a multi-layer IC, so that the term substrate as used herein may also refer to a substrate that already contains multiple processed layers.

[0192] Although specific reference has been made above to the use of embodiments of the present disclosure in the context of optical lithography, it should be understood that the present disclosure can be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the topography in the patterning device defines the pattern produced on the substrate. The topography of the patterning device can be pressed into a resist layer provided to the substrate, whereupon the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist after the resist has cured, leaving a pattern therein.

[0193] It is to be understood that the phraseology or terminology herein is for the purpose of description and not limitation, so that the phraseology or terminology of the present disclosure will be interpreted by those skilled in the relevant art based on the teachings herein.

[0194] The terms "radiation," "beam," "light," "irradiation," and the like may be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (e.g., having a wavelength λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength in the range of 5-100 nm, such as 13.5 nm), or hard X-rays operating at less than 5 nm, and particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 400 nm and about 700 nm is considered visible radiation; radiation having wavelengths between about 780 nm and 3000 nm (or greater) is considered IR radiation. UV refers to radiation having a wavelength of about 100-400 nm. In photolithography, the term "UV" also applies to wavelengths that can be produced by mercury discharge lamps: G-line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by gases) refers to radiation having a wavelength of about 100-200 nm. Deep UV (DUV) generally refers to radiation having a wavelength ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can produce DUV radiation for use within a lithographic apparatus. In some embodiments, inspection, alignment, and / or measurement can be performed using, for example, radiation having a wavelength ranging from 400 nm to 900 nm. It should be understood that radiation having a wavelength in the range of, for example, 5-20 nm refers to radiation having a specific wavelength band, at least a portion of which is within the range of 5-20 nm.

[0195] Although some aspects of the present disclosure are described in the context of lithographic equipment in IC manufacturing, it will be understood that the lithographic systems and alignment and measurement systems described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film heads. Those skilled in the art will understand that in the context of such alternative applications, any use of the terms "wafer" or "die" herein can be considered as specific examples of the more general terms "substrate" or "target portion", respectively. The substrate can be processed before or after exposure in, for example, a tracking unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a measurement unit. Where applicable, the aspects disclosed herein can be applied to such and other substrate processing tools. In addition, for example to produce a multi-layer IC, a substrate can be processed more than once, so that the term substrate used herein can also refer to a substrate that already includes multiple processing layers.

[0196] Furthermore, while some aspects of the present disclosure have been described above in the context of photolithography, it should be understood that aspects of the present disclosure are not limited to photolithography. For example, in imprint lithography, the topography in a patterning device defines the pattern produced on a substrate. The topography of the patterning device can be pressed into a resist layer provided to the substrate, whereupon the resist is 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 a pattern therein.

[0197] It will be understood that the phraseology or terminology herein is for the purpose of description rather than limitation, so that the phraseology or terminology of this specification should be interpreted by those skilled in the relevant art based on the teachings herein.

[0198] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined herein. As long as the specified functions and their relationships are properly performed, alternative boundaries may be defined. The above description of specific aspects will fully reveal the general nature of the present disclosure so that others can easily modify and / or adjust these specific aspects for various applications by applying the knowledge of those skilled in the art without excessive experimentation and without departing from the general concept of the present disclosure. Therefore, based on the teachings and guidance presented herein, such adjustments and modifications are intended to be within the meaning and scope of the equivalents of the disclosed aspects.

[0199] It should be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventors, and thus, are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the claimed subject matter should not be limited by any of the above-described aspects, but should be defined only in accordance with the appended claims and their equivalents.

Claims

1. A method comprising: generating a first alignment mark to be used on a substrate, the first alignment mark comprising a topology of at least two pixels having different characteristics; determining one or more characteristics of each of the at least two pixels; optimizing the topology of the first alignment mark based on the one or more characteristics of the at least two pixels; as well as Based on optimizing the first alignment mark, a second alignment mark is formed on the substrate. 2 . The method of claim 1 , wherein optimizing the topology of the first alignment mark comprises determining a far-field pattern of radiation diffracted by the first alignment mark. 3 . The method of claim 2 , wherein optimizing the topology of the first alignment mark comprises defining a cost function based on the far-field pattern. The method of claim 3 , wherein optimizing the topology of the first alignment mark comprises minimizing the cost function based on one or more optimization objectives. The method of claim 4 , wherein an optimized topology is automatically identified by optimizing the cost function along one or more parameters.

6. The method according to claim 1, wherein: The at least two pixels include at least a first pixel and a second pixel, and The one or more characteristics include a refractive index, a material forming each pixel, and / or an etch depth of each pixel.

7. The method according to claim 6, wherein: The first pixel has a first refractive index, and The second pixel has a second refractive index different from the first refractive index.

8. The method of claim 7, wherein the far-field pattern of radiation diffracted by the first alignment mark is calculated using Fourier optics or full-wave simulation.

9. The method according to claim 8, wherein: The cost function based on the far-field pattern is defined as F(φ(θ x ,θ y ),ε(x m ,y n ), [x0, y0 = αx0 + β]) where F is the cost function, ε is the dielectric constant of either material, and y0 = αx0 + β is the scanning function.

10. The method according to claim 9, wherein: The topology of the first alignment mark is optimized by minimizing the cost function of variations in incident field, mark topology, and scan function. The method of claim 1 , wherein optimizing the topology of the first alignment mark comprises determining a sub-pattern of a plurality of pixels in a unit cell of the first alignment mark.

12. The method of claim 1, wherein: The first alignment mark includes a plurality of unit cells, and The optimizing of the topology of the first alignment mark includes determining a symmetry of the unit cell.

13. The method of claim 12, wherein the symmetry of each unit cell is periodic, semi-periodic, or aperiodic.

14. The method of claim 12, wherein the plurality of unit cells are arranged to have centrosymmetric symmetry about the center of the alignment mark, inversion or rotational symmetry about a non-central point of the alignment mark, mirror symmetry, or a combination thereof, or no symmetry. 15 . The method of claim 1 , wherein forming the second alignment mark comprises depositing the at least two pixels by depositing at least a first material and a second material on the substrate.

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