Lithographic apparatus and method with fast alignment measurements using deformation prediction models

Abstract

A lithographic apparatus includes an illumination system, a substrate support structure including a sensor, and a computing system. The illumination system generates a beam of radiation to illuminate a pattern of a patterning device. The patterning device includes reference marks. The substrate support structure performs alignment operations of substrates during fabrication cycles. Each of the fabrication cycles comprises an exposure operation on a substrate and a substrate alignment operation. The sensor performs measurements of the reference marks for the substrate alignment operation of each of the fabrication cycles. The computing system forecasts a distortion of the patterning device using a distortion prediction model and one or more parameters of the beam. The computing system also prompts the sensor to waive one or more of the measurements. The computing system also adjusts the alignment operations using the forecasted distortion to offset the waived one or more of the measurements.

Description

LITHOGRAPHIC APPARATUS AND METHOD WITH FAST ALIGNMENT MEASUREMENTS USING DEFORMATION PREDICTION MODELSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 552,256 which was filed on February 12, 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to metrology systems, for example, a method to reduce measurement time and increase fabrication speed in lithographic systems.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which can be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiationsensitive material (photoresist or simply “resist”) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During lithographic operation, different processing steps can entail different layers to be sequentially formed on the substrate. Accordingly, it can be necessary to position the substrate relative to prior patterns formed thereon with a high degree of accuracy. Generally, alignment marks are placed on the substrate to be aligned and are located with reference to a second object. A lithographic apparatus can use an alignment apparatus for detecting positions of the alignment marks and for aligning the substrate using the alignment marks to ensure accurate exposure from a mask. Misalignment between the alignment marks at two different layers is measured as overlay error.

[0005] In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters can include, for example, the overlay error between successive layers formed in or on the patterned substrate and critical linewidth of developed photosensitive resist. This measurement can be performed on a product substrate and / or on a dedicated metrology target. There are various techniquesfor making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes and various specialized tools. A fast and non-invasive form of a specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Spectroscopic 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 particular narrow angular range. By contrast, angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

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

[0007] For accurate pattern transfers, measurement tools and techniques are used to measure relative alignment between a wafer and a reticle. In the absence of such tools and techniques, a new pattern layer overlaid on a prior pattern layer on the wafer may be positioned incorrectly, rendering the wafer a total loss.

[0008] The alignment techniques described above consume valuable time that could otherwise be spent on fabrication operations. Increased measurement times result in slower chip fabrication.SUMMARY

[0009] Accordingly, it is desirable to improve wafer alignment operations in order to increase fabrication speed and throughput. Aspects described herein can be implemented for faster wafer alignment.

[0010] In some aspects, a lithographic apparatus can comprise an illumination system, a substrate support structure comprising a sensor, and a computing system. The illumination system can generate a beam of radiation to illuminate a pattern of a patterning device for projecting an image of the pattern onto substrates. The patterning device can comprise reference marks. The substrate support structure can support the substrates and perform alignment operations during fabrication cycles. Each of the fabrication cycles can comprise an exposure operation on a substrate and a substrate alignment operation. The sensor can perform measurements of the reference marks for the substrate alignment operation of each of the fabrication cycles. The computing system can forecast a distortion of the patterning device using a distortion prediction model and one or more parameters of the beam. The computing system can also prompt the sensor to waive one or more of the measurements, thereby increasing fabrication speed of the lithographic apparatus. The computing system can also adjust thealignment operations using the forecasted distortion to offset the waived one or more of the measurements.

[0011] In some aspects, a method can comprise performing lithographic fabrication cycles of substrates using a patterning device comprising reference marks and a beam of radiation. Each of the lithographic fabrication cycles can comprise an exposure operation on a substrate and a substrate alignment operation. The substrate alignment operation can comprise use of a sensor configured to perform measurements of the reference marks at each of the fabrication cycles. The method can also comprise forecasting a distortion of the patterning device using a distortion prediction model and one or more parameters of the beam. The method can also comprise prompting the sensor to waive one or more of the measurements, thereby increasing fabrication speed of the lithographic apparatus. The method can also comprise adjusting one or more substrate alignment operations using the forecasted distortion to offset the waived one or more of the measurements.

[0012] In some aspects, a non-transitory computer readable medium having instructions stored thereon, that, when executed on a computing system cause the computing system to perform operations. The operations can comprise forecasting a distortion of a patterning device comprising reference marks using a distortion prediction model and one or more parameters of a beam of radiation. The patterning device and the beam of radiation are associated with lithographic fabrication cycles comprising an exposure operation on a substrate and a substrate alignment operation. The substrate alignment operation can comprise use of a sensor configured to perform measurements of the reference marks at each of the fabrication cycles. The operations can also comprise prompting the sensor to waive one or more of the measurements, thereby increasing speed of the lithographic fabrication cycles. The operations can also comprise adjusting one or more alignment operations using the forecasted distortion to offset the waived one or more of the measurements.

[0013] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0014] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0015] FIG. 1 A shows a reflective lithographic apparatus, according to some aspects.

[0016] FIG. IB shows a transmissive lithographic apparatus, according to some aspects.

[0017] FIG. 2 shows more details of a reflective lithographic apparatus, according to some aspects.

[0018] FIG. 3 shows a lithographic cell, according to some aspects.

[0019] FIGS. 4 A and 4B show inspection apparatuses, according to some aspects.

[0020] FIG. 5 shows a substrate stage, according to some aspects.

[0021] FIG. 6 shows a graph of thermally induced deformations with respect to operation time in a lithographic apparatus, according to some aspects.

[0022] FIG. 7 shows a flowchart of a method 700 for reducing the time of alignment operations in a lithographic process, according to some aspects.

[0023] FIG. 8 shows a computer system for implementing various aspects for faster metrology.

[0024] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0025] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0026] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The 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 apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0027] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0028] Enumerative adjectives (e.g., “first,” “second,” “third,” or the like) can be used as labels to distinguish like elements without establishing an order, hierarchy, quantity, or permanent numeric assignment (unless otherwise noted). For example, a given element can be referred to as a “secondreference mark” in one labeling scheme while the same element can be referred to as a “first reference mark” in another labeling scheme.

[0029] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium can include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine -readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like. The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0030] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0031] Example Lithographic Systems

[0032] FIGS. 1A and IB show a lithographic apparatus 100 and a lithographic apparatus 100’, respectively, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100’ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100’ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0033] The illumination system IL can include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0034] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus 100 and 100’, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0035] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0036] The patterning device MA can be transmissive (as in lithographic apparatus 100’ of FIG. IB) or reflective (as in lithographic apparatus 100 of FIG. 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by a matrix of small mirrors.

[0037] The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0038] Lithographic apparatus 100 and / or lithographic apparatus 100’ can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.

[0039] The lithographic apparatus can also be of a type wherein at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniquesare well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be located between the projection system and the substrate during exposure.

[0040] Referring to FIGS. 1A and IB, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100’ can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100’, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (in FIG. IB) including, for example, suitable directing mirrors and / or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100’, for example, when the source SO is a mercury lamp. A radiation system can comprise the source SO, the illuminator IL, and / or the beam delivery system BD.

[0041] The illuminator IL can include an adjuster AD (in FIG. IB) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “o-outer” and “o-inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (in FIG. IB), 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.

[0042] Referring to FIG. 1A, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.

[0043] Referring to FIG. IB, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern withoutbeing affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0044] The projection system PS projects an image of the mask pattern MP, where the image is formed by diffracted beams produced from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP can include an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction generates diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) traverse the pattern without any change in propagation direction. The zeroth order diffracted beams traverse an upper lens or upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD, for example, is disposed at or substantially at a plane that includes the pupil conjugate PPU of the projection system PS.

[0045] The projection system PS is arranged to capture (e.g., using a lens or lens group L) the zeroth order diffracted beams, first order diffracted beams, and / or higher order diffracted beams (not shown). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first- order diffracted beams interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some aspects, astigmatism aberration can be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in US 7,511,799 B2, issued Mar. 31 , 2009, which is incorporated by reference herein in its entirety.

[0046] With the aid of the second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in FIG. IB) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

[0047] In general, movement of the mask table MT can be realized 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 can be realized 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 opposedto a scanner), the mask table MT can be connected to a short-stroke actuator or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe -lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0048] Mask table MT and patterning device MA can be in a vacuum chamber V, where an in-vacuum robot IVR can be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot can be used for various transportation operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0049] The lithographic apparatus 100 and 100’ can be used in at least one of the following modes:

[0050] 1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0051] 2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de- ) magnification and image reversal characteristics of the projection system PS.

[0052] 3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a 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 can be employed and the programmable patterning device is updated as needed after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0053] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0054] In some aspects, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, 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.

[0055] In some aspects, lithographic apparatus 100’ includes a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography. In general, the DUV sourceis configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source.

[0056] FIG. 2 shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. EUV radiation can be produced by a gas or vapor, for example Xe gas, Li vapor, or Sn vapor in which EUV radiation emitting plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The EUV radiation emitting plasma 210 is created by, for example, an electrical discharge causing at least a partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor can be used for efficient generation of the radiation. In some aspects, a plasma of excited tin (Sn) (e.g., excited via a laser) is provided to produce EUV radiation.

[0057] The radiation emitted by the EUV radiation emitting plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap), which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 can include a channel structure. Contamination trap 230 can also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure.

[0058] The collector chamber 212 can include a radiation collector CO, which can be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point INTF. The virtual source point INTF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus INTF is located at or near an opening 219 in the enclosing structure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infra-red (IR) radiation.

[0059] Subsequently the radiation traverses the illumination system IL, which can include a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 221 at the patterning device MA, 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 the wafer stage or substrate table WT.

[0060] More elements than shown can generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 can optionally be present, depending upon the type oflithographic apparatus. Further, there can be more mirrors present than those shown in the FIG. 2, for example there can be one to six additional reflective elements present in the projection system PS than shown in FIG. 2.

[0061] Collector optic CO, as illustrated in FIG. 2, 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 disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[0062] Example Lithographic Cell

[0063] FIG. 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some aspects. Lithographic apparatus 100 or 100’ canformpart of lithographic cell 300. Lithographic cell 300 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input / output ports I / Ol, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100 or 100’ . These devices, which are often collectively referred to as the 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 lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0064] Example Inspection Apparatus

[0065] In order to control the lithographic process to place device features accurately on the substrate, alignment marks are generally provided on the substrate, and the lithographic apparatus includes one or more inspection apparatuses for accurate positioning of marks on a substrate. These alignment apparatuses are effectively position measuring apparatuses. Different types of marks and different types of alignment apparatuses and / or systems are known from different times and different manufacturers. A type of system widely used in current lithographic apparatus is based on a self-referencing interferometer as described in U.S. Patent No. 6,961,116 (den Boef et al.). Generally marks are measured separately to obtain X- and Y-positions. A combined X- and Y-measurement can be performed using the techniques described in U.S. Publication No. 2009 / 195768 A (Bijnen et al.), however. The full contents of both of these disclosures are incorporated herein by reference.

[0066] FIG. 4A shows a cross-sectional view of an inspection apparatus 400 that can be implemented as a part of lithographic apparatus 100 or 100’, according to some aspects. In some aspects, inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Inspection apparatus 400 can be further configured to detect positions of alignment marks on the substrate and to align the substrate with respect to the patterning device or other components of lithographic apparatus 100 or 100’ using the detected positions of thealignment marks. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0067] The terms “inspection apparatus,” “metrology system,” or the like can be used herein to refer to, e.g., a device used for measuring a property of a structure (e.g., overlay sensor, critical dimension sensor, or the like), a device or system used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment sensor), or the like.

[0068] In some aspects, inspection apparatus 400 can include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a processor 432. Illumination system 412 can be configured to provide an electromagnetic narrow band radiation beam 413 having one or more passbands. In an example, the one or more passbands can be within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the one or more passbands can be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. Illumination system 412 can be further configured to provide one or more passbands having substantially constant center wavelength (CWL) values over a long period of time (e.g., over a lifetime of illumination system 412). Such configuration of illumination system 412 can help to prevent the shift of the actual CWL values from the desired CWL values, as discussed above, in current alignment systems. And, as a result, the use of constant CWL values can improve long-term stability and accuracy of alignment systems (e.g., inspection apparatus 400) compared to the current alignment apparatuses.

[0069] 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. 4A. Beam splitter 414 can be further configured to direct radiation sub-beam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 is movable along direction 424. Radiation sub-beam 415 can be configured to illuminate an alignment mark or a 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 a plane of alignment mark or target 418, rotated alignment mark or target 418 can be substantially identical to an unrotated alignment mark or target 418. The target 418 on substrate 420 can be (a) a resist layer grating comprising bars that are formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on a product layer grating. The bars can alternatively be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberrations will manifest themselves in a variation in the printed grating. One in-line method used in device manufacturing for measurements of line width, pitch, and critical dimension makes use of a technique known as “scatterometry”. Methods of scatterometry are described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry”, J. Vac. Sci. Tech. B, Vol. 15, no. 2,pp. 361-368 (1997) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography”, SPIE, Vol. 3677 (1999), which are both incorporated by reference herein in their entireties. In scatterometry, light is reflected by periodic structures in the target, and the resulting reflection spectrum at a given angle is detected. The structure giving rise to the reflection spectrum is reconstructed, e.g. using Rigorous Coupled- Wave Analysis (RCWA) or by comparison to a library of patterns derived by simulation. Accordingly, the scatterometry data of the printed gratings is used to reconstruct the gratings. The parameters of the grating, such as line widths and shapes, can be input to the reconstruction process, performed by processing unit PU, from knowledge of the printing step and / or other scatterometry processes.

[0070] In some aspects, beam splitter 414 can be further configured to receive diffraction radiation beam 419 and split diffraction radiation beam 419 into at least two radiation sub-beams, according to an aspect. Diffraction radiation beam 419 can be split into diffraction radiation sub-beams 429 and 439, as shown in FIG. 4A.

[0071] It should be noted that even though beam splitter 414 is shown to direct radiation sub-beam 415 towards alignment mark or target 418 and to direct diffracted radiation sub-beam 429 towards interferometer 426, the disclosure is not so limiting. Other optical arrangements can be used to obtain the similar result of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0072] As illustrated in FIG. 4A, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414. In an example 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 an example of this aspect, interferometer 426 comprises any appropriate set of optical-elements, for example, 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 appreciated that a good quality image need not be formed. It can be enough to have the features of alignment mark 418 resolved. Interferometer 426 can be further configured to rotate one of the two images with respect to the other of the two images 180° and recombine the rotated and unrotated images interferometrically.

[0073] In some aspects, detector 428 can be configured to receive the recombined image via interferometer signal 427 and detect interference as a result of the recombined image when alignment axis 421 of inspection apparatus 400 passes through a center of symmetry (not shown) of alignment mark or target 418. Such interference can be due to alignment mark or target 418 being 180° symmetrical, and the recombined image interfering constructively or destructively, according to an example aspect. Based on the detected interference, detector 428 can be further configured to determine a position of the center of symmetry of alignment mark or target 418 and consequently, detect a position of substrate 420. According to an example, alignment axis 421 can be aligned with an optical beam perpendicular to substrate 420 and passing through a center of image rotation interferometer 426.Detector 428 can be further configured to estimate the positions of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

[0074] In a further aspect, detector 428 determines the position of the center of symmetry of alignment mark or target 418 by performing one or more of the following measurements:

[0075] 1. measuring position variations for various wavelengths (position shift between colors);

[0076] 2. measuring position variations for various orders (position shift between diffraction orders);

[0077] 3. measuring position variations for various polarizations (position shift between polarizations) ; and

[0078] 4. measuring intensity difference between opposite orders of a diffraction order pair (e.g., to characterize and correct for asymmetry).

[0079] 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 that employs a selfreferencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment), as described in U.S. Patent No. 6,297,876, which directs each of seven diffraction orders to a dedicated detector, which are both incorporated by reference herein in their entireties.

[0080] In some aspects, beam analyzer 430 can be configured to receive and determine an optical state of diffracted radiation sub-beam 439. The optical state can be a measure of beam wavelength, polarization, or beam profile. Beam analyzer 430 can be further configured to determine a position of stage 422 and correlate the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420 can be accurately known with reference to stage 422. Alternatively, beam analyzer 430 can be configured to determine a position of inspection apparatus 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 apparatus 400 or any other reference element. Beam analyzer 430 can be a point or an imaging polarimeter with some form of wavelength-band selectivity. In some aspects, beam analyzer 430 can be directly integrated into inspection apparatus 400, or connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other aspects.

[0081] In some aspects, beam analyzer 430 can be further configured to determine the overlay data between two patterns on substrate 420. One of these patterns can be a reference pattern on a reference layer. The other pattern can be an exposed pattern on an exposed layer. The reference layer can be an etched layer already present on substrate 420. The reference layer can be generated by a reference pattern exposed on the substrate by lithographic apparatus 100 and / or 100’. The exposed layer can be a resist layer exposed adjacent to the reference layer. The exposed layer can be generated by an exposure pattern exposed on substrate 420 by lithographic apparatus 100 or 100’. The exposed pattern on substrate 420 can correspond to a movement of substrate 420 by stage 422. In some aspects, the measured overlay data can also indicate an offset between the reference pattern and the exposurepattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus 100 or 100’, such that after the calibration, the offset between the exposed layer and the reference layer can be minimized.

[0082] In some aspects, beam analyzer 430 can be further configured to determine a model of the product stack profile of substrate 420, and can be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement. The product stack profile contains information on the stacked product such as alignment mark, target 418, or substrate 420, and can include mark process variation-induced optical signature metrology that is a function of illumination variation. The product stack profile can also include product grating profile, mark stack profile, and mark asymmetry information. An example of beam analyzer 430 is Yieldstar™, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, which is incorporated by reference herein in its entirety. Beam analyzer 430 can be further configured to process information related to a particular property of an exposed pattern in that layer. For example, beam analyzer 430 can process an overlay parameter (an indication of the positioning accuracy of the layer with respect to a previous layer on the substrate or the positioning accuracy of the first layer with respective to marks on the substrate), a focus parameter, and / or a critical dimension parameter (e.g., line width and its variations) of the depicted image in the layer. Other parameters are image parameters relating to the quality of the depicted image of the exposed pattern.

[0083] In some aspects, an array of detectors (not shown) can be connected to beam analyzer 430, and allows the possibility of accurate stack profile detection as discussed below. For example, detector 428 can be an array of detectors. For the detector array, a number of options are possible: a bundle of multimode fibers, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of a bundle of multimode fibers enables any dissipating elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range but each need separate pre-amps. The number of elements is therefore limited. CCD linear arrays offer many elements that can be read-out at high speed and are especially of interest if phase-stepping detection is used.

[0084] In some aspects, a second beam analyzer 430’ can be configured to receive and determine an optical state of diffracted radiation sub-beam 429, as shown in FIG. 4B. The optical state can be a measure of beam wavelength, polarization, or beam profile. Second beam analyzer 430’ can be identical to beam analyzer 430. Alternatively, second beam analyzer 430’ can be configured to perform one or more of the functions of beam analyzer 430, such as determining a position of stage 422 and correlating the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420, can be accurately known with reference to stage 422. Second beam analyzer 430’ can also be configured to determine a position of inspection apparatus 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 apparatus 400, or any other reference element. Second beam analyzer 430’ can be further configured to determine theoverlay data between two patterns and a model of the product stack profile of substrate 420. Second beam analyzer 430’ can also be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement.

[0085] In some aspects, second beam analyzer 430’ can be directly integrated into inspection apparatus 400, or it can be connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other aspects. Alternatively, second beam analyzer 430’ and beam analyzer 430 can be combined to form a single analyzer (not shown) configured to receive and determine the optical states of both diffracted radiation sub-beams 429 and 439.

[0086] In some aspects, processor 432 receives information from detector 428 and beam analyzer 430. For example, processor 432 can be an overlay calculation processor. The information can comprise a model of the product stack profile constructed by beam analyzer 430. Alternatively, processor 432 can construct a model of the product mark profile using the received information about the product mark. In either case, processor 432 constructs a model of the stacked product and overlay mark profile using or incorporating a model of the product mark profile. The stack model is then used to determine the overlay offset and minimizes the spectral effect on the overlay offset measurement. Processor 432 can create a basic correction algorithm based on the information received from detector 428 and beam analyzer 430, including but not limited to the optical state of the illumination beam, the alignment signals, associated position estimates, and the optical state in the pupil, image, and additional planes. The pupil plane is the plane in which the radial position of radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor 432 can utilize the basic correction algorithm to characterize the inspection apparatus 400 with reference to wafer marks and / or alignment marks 418.

[0087] In some aspects, processor 432 can be further configured to determine printed pattern position offset error with respect to the sensor estimate for each mark based on the information received from detector 428 and beam analyzer 430. The information includes but is not limited to the product stack profile, measurements of overlay, critical dimension, and focus of each alignment marks or target 418 on substrate 420. Processor 432 can utilize a clustering algorithm to group the marks into sets of similar constant offset error, and create an alignment error offset correction table based on the information. The clustering algorithm can be based on overlay measurement, the position estimates, and additional optical stack process information associated with each set of offset errors. The overlay is calculated for a number of different marks, for example, overlay targets having a positive and a negative bias around a programmed overlay offset. The target that measures the smallest overlay is taken as reference (as 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 deduced. Table 1 illustrates how this can be performed. The smallest measured overlay in the example shown is -1 nm. However this is in relation to a target with a programmed overlay of -30 nm. The process may have introduced an overlay error of 29 nm.

[0088] The smallest value can be taken to be the reference point and, relative to this, the offset can be calculated between measured overlay and that expected due to the programmed overlay. This offset determines the overlay error for each mark or the sets of marks with similar offsets. Therefore, in the Table 1 example, the smallest measured overlay was -1 nm, at the target position with programmed overlay of 30 nm. The difference between the expected and measured overlay at the other targets is compared to this reference. A table such as Table 1 can also be obtained from marks and target 418 under different illumination settings, the illumination setting, which results in the smallest overlay error, and its corresponding calibration factor, can be determined and selected. Following this, processor 432 can group marks into sets of similar overlay error. The criteria for grouping marks can be adjusted based on different process controls, for example, different error tolerances for different processes.

[0089] In some aspects, processor 432 can confirm that all or most members of the group have similar offset errors, and apply an individual offset correction from the clustering algorithm to each mark, based on its additional optical stack metrology. Processor 432 can determine corrections for each mark and feed the corrections back to lithographic apparatus 100 or 100’ for correcting errors in the overlay, for example, by feeding corrections into the inspection apparatus 400.

[0090] Example Substrate Table

[0091] FIG. 5 shows a substrate stage 500, according to some aspects. In some aspects, substrate stage 500 can comprise a substrate table 502, a support structure 504, and one or more sensors 506. Support structure 504 can be a frame of an actuated translation stage. Substrate table 502 and one or more sensors 506 are disposed on support structure 504. Substrate table 502 can comprise a clamp to hold a substrate 508 (e.g., an electrostatic clamp). Substrate stage 500 can be implemented in a lithographic apparatus. FIG. 5 illustrates components of a lithographic apparatus, such as projection system 510, a patterning device 512, and a computing system 514. Patterning device 512 can comprise one or more reference marks 516-z. The index i is used to distinguish reference marks. For example purposes, FIG. 5 shows reference marks 516-1, 516-2, 516-3, and 516-4 (e.g., first through fourth reference marks). Projection system 510, patterning device 512, and one or more reference marks 516- / can be implemented inlithographic apparatus 100 / 100' as projection system PS, mask MA, and alignment marks M1 / M2 respectively (FIGS. 1A and IB).

[0092] In some aspects, one or more sensors 506 can be used to accurately position substrate table 502 and substrate 508 relative to projection system 510 and mask 512. Radiation scattered by one or more target 516 can be received at one or more sensors 506. Computing system 514 can analyze measurement signals from one or more sensors 506 to determine an alignment position of substrate table 502 and / or substrate 508 relative to patterning device 512. Positions of elements on substrate 508 can be determined using inspection apparatus 400 (FIGS. 4A and 4B).

[0093] Example Mitigation of Errors Caused by Thermally Induced Distortions

[0094] Furthermore, when exposing a substrate with illumination during a lithographic fabrication process, the illumination is incident on a patterning device (e.g., mask). Such exposures occur in repeated on / off cycles using a predetermined illumination dose and exposure time, layer after layer, substrate after substrate. The patterning device can absorb a portion of the illumination energy as heat during each exposure. The absorbed heat energy can increase the temperature of the patterning device, causing distortion of the patterning device in terms of structure and optical properties (e.g., thermal expansion and refractive index shifting). A substrate receiving the radiation can also be similarly heated and deformed.

[0095] Thermal distortion can cause a prior alignment measurement to become unreliable. Furthermore, the one or more sensors 506 may be partially or entirely insensitive to thermal distortions. For example, one or more sensors 506 are purposed for interacting with one or more reference marks 516. Therefore, deformations at other regions of patterning device 512 can go undetected.

[0096] In some aspects, errors caused by thermal distortion can be compensated for. For example, distortion prediction models can be implemented. Distortion prediction models can provide an estimate of the amount of misalignment by taking into account the material of the heated object (e.g., a glass / quartz patterning device), dose of illumination, exposure time, amount of illumination energy transmitted through and / or reflected from the object, expected shift of refractive index of the patterning device and / or the gas proximal to the patterning device, or the like.

[0097] Further examples of models for determining thermally induced deformation are disclosed in U.S. Patent No. 10,281,825 B2, issued on May 7, 2019, and International Application Publication No. WO 2022 / 258251 Al, published on December 15, 2022. The full contents of both of these disclosures are incorporated herein by reference.

[0098] In some aspects, mass fabrication of electronic devices can involve repeated applications of illumination exposure of substrates and of the various optical components of the lithographic apparatus, such as the patterning device and components of the projection system (e.g., lenses). While frequent alignment measurements help to mitigate errors in pattern transfer (e.g., overlay errors), frequent measurements can be time consuming and can slow down mass fabrication of devices, which can resultin quantifiable economic impact to device manufacturers and dependent markets (e.g., global chip shortage).

[0099] The term “throughput” can be used herein to refer to a speed at which an amount of material or items pass through a system or process. For example, throughput can characterize a speed of overall lithographic fabrication, a rate at which a wafer passes through a lithographic apparatus, a rate at which a wafer clears a particular fabrication step and moves on to the next step, or the like. Hence, throughput can be a performance marker of a lithographic apparatus.

[0100] It is desirable for lithographic systems to output as many products as possible in as little time as possible. Lithographic fabrication can comprise several layered and complex processes. In some aspects, lithographic fabrication of nano-devices can involve tradeoffs that balance desired qualities and drawbacks (e.g., sub-nanometer accuracy, high yield / throughput, slower fabrication, increased cost). To improve accuracy of lithographic patterning, lithographic processes can implement high precision alignment measurements of a substrate relative to a patterning device. One or more sensors 506 are examples of inspection apparatuses used for this purpose. A drawback is that the added time of the inspection operation reduces throughput.

[0101] Systems and operations of aspects disclosed herein can reduce the time of measurements, thereby increasing throughput in lithographic apparatuses.

[0102] FIG. 6 shows a graph 602, according to some embodiments. For example, graph 602 can show thermally induced deformations with respect to operation time in a lithographic apparatus. FIG. 6 shall be described with reference to FIG. 5. However, the features of FIG. 6 are not limited to the example embodiment of FIG. 5. While the data in graph 602 is described in the context of patterning device 512 and one or more sensors 506, the functions described in relation to FIG. 6 are also applicable to other patterning devices, sensors, and lithographic apparatuses and functions.

[0103] The vertical axis of graph 602 represents a thermally induced distortion of patterning device 512, a component of projection system 510 (e.g., lens(es)), or a gas in the vicinity thereof (e.g., distorted refractive index). In an example, a higher value of distortion can represent thermal expansion due to absorbed heat while a lower value of deformation can represent structural contraction due to cooling. The horizontal axis of graph 602 represents a timeline of lithographic operations relating to the use of patterning device 512. The labels of the time axis represent times at which substrates on substrate stage 500 are swapped.

[0104] In one aspect, inset 604 represents a magnified view of some of the data in graph 602.

[0105] In some aspects, lithographic operations can include a series of exposure periods and nonexposure periods. A fabrication cycle 606 can comprise an exposure period 608 and a substrate swap period 610. Though one instance of fabrication cycle 606 is expressly labeled, it is to be appreciated fabrication cycle 606 repeats from substrate to substrate. For example purposes, substrates are labeled si through s6. At the beginning of inset 604, exposure period 608 corresponds to a time period in which a substrate si (e.g., a first wafer) is exposed to illumination for achieving a pattern transfer frompatterning device 512 onto substrate si. While exposure period 608 may be further subdivided into multiple exposures, for simplicity of description, the complete exposure of a substrate will be referred to as a single exposure operation. With exposure of substrate si completed, the lithographic apparatus then performs a substrate swap operation to unload the finished substrate and load a new substrate s2 to begin a new fabrication cycle. In mass production, a lithographic apparatus can cycle through thousands of substrates in a day. The term “fabrication cycle” can be used herein to characterize the lithographic processing from substrate to substrate. A fabrication cycle can comprise exposure of a substrate and a substrate swap operation. The substrate swap operation is responsible for loading a new substrate on substrate stage 500 for the next fabrication cycle.

[0106] In some aspects, an exposure period is characterized by a rise 612 of distortion. When objects are exposed to illumination, a portion of the illumination can be absorbed by the materials. Exposed objects can include patterning device 512 and / or projection system 510 (e.g., glass or quartz materials of transparent optical elements or chrome or reflective metal on patterning device 512). When exposure is finished, the non-exposure period (e.g., substrate swap period 610) can cause the distortion to decrease (indicated as decrease 614) as heat energy dissipates from patterning device 512 and / or projection system 510.

[0107] In some aspects, a substrate swap operation includes an alignment measurement so that a newly loaded substrate is properly aligned with respect to patterning device 512 and / or projection system 510. Some instances of alignment measurements in FIG. 6 are indicated by nominal measurement operations 616 (circle symbol), which occur during substrate swap periods 608 after new substrates are loaded. The qualifier “nominal” is directed to a nominal set of measurements using one or more sensors 506. The nominal set of measurements is purposed for determining, within a nominal or prescribed tolerance, a position of substrate 508 with respect to patterning device 512 and / or projection system 510. For example, a nominal set of measurements can comprise measuring a position of reference mark 516-1 (e.g., a first reference mark) and also aposition of reference mark 516-2 (e.g., a second reference mark). Skipping a measurement of either reference mark 516-1 or reference mark 516-2 (or skipping both) is not a nominal alignment measurement and there is a risk of introducing errors in an alignment operation, resulting in overlay error.

[0108] However, by supplementing alignment operations with distortion forecasts from prediction models, aspects described herein can implement omission of one or more measurements and still achieve prescribed tolerances while reducing measurement time, thereby increasing throughput of wafers processed in a lithographic apparatus.

[0109] In some aspects, the data in graph 602 can be generated using a distortion prediction model as described above. The data can be stored and / or generated by computing system 514. Alignment measurements can be distributed across fabrication cycles such that the nominal set of measurements are (optionally) performed after every substrate swap operation. Performing the nominal set of measurements after every substrate swap operation can result in high alignment accuracy but lowerthroughput. Therefore, one or more of substrate swap periods 610 can be shortened by waiving measurements and still achieve alignment tolerances by leveraging deformation forecast data. Instances where a measurement is omitted are indicated as shortened measurement operations 618 (x symbol).

[0110] In contrast to nominal measurement operations 616, shortened measurement operations 618 can waive measurements of one or more reference marks 516- / . For example, in inset 604, the substrate swap period associated with the loading of substrate s2 includes performing nominal measurement operations 616. In the next substrate swap period, when substrate s2 is unloaded and substrate s3 is loaded, shortened measurement operations can be performed.

[0111] In some aspects, alignment operations can be adjusted such that one or more sensors 506 (configured to measure all reference marks 516- / ) have instructions to waive measurements of one or more reference marks. In the example provided above in which a set of nominal measurements comprises measuring a position of reference mark 516-1 and also a position of reference mark 516-2, the shortened measurement operations can comprise measuring only reference mark 516-1 but not reference mark 516-2, measuring reference mark 516-2 but not measuring reference mark 516-1, or not measuring either of reference mark 516-1 or reference mark 516-2. Since a distortion prediction model is capable of forecasting a positional offset of a reference mark, an alignment operation can be adjusted so as to waive one or more measurements of reference marks 516- / .

[0112] When a measurement is skipped, the position of reference marks 516- / can be inferred by computing system 514 using data generated by a deformation prediction model (e.g., the data in graph 602) in order to offset the waived measurement. For example, one or more vacant parameters can be associated with one or more waived measurements. Instead of populating the vacant parameters using a time consuming measurement, the one or more vacant parameters can be populated based on the forecasted distortion. Alignment position can also be inferred based on a measurement performed in a prior fabrication cycle. For example, since alignment operations for substrate s3 use the less accurate shortened measurement operations 618, any skipped measurements can be supplemented by looking to prior results of nominal measurement operations 616 that were performed when substrate s2 was loaded in a prior fabrication cycle.

[0113] In some aspects, though inset 604 indicates periods of heating and cooling of patterning device 512 and / or projection system 510 (rise 612 and decrease 614), patterning device 512 and / or projection system 510 can accumulate heat over many fabrication cycles. The steady accumulation of heat is reflected in unstable period 616 in graph 602. At a certain heat level, the dissipation of heat begins to come into balance with the absorption of heat. The balance is reflected in steady-state period 618 in graph 602. During steady-state period 618, the behavior of the distortion is less volatile. As distortion fluctuations are less volatile, forecasts from distortion prediction models during steady-state period 618 can be relied upon with greater confidence than forecasts associated with unstable period 616.

[0114] In some aspects, shortened measurement operations 618 need not be identical from cycle to cycle. For example, in a first instance of a shortened measurement operation, measurement of referencemark 516-2 can be waived. In a later fabrication cycle, a shortened measurement operation can include waiving a measurement of reference mark 516-1 instead. Then the next shortened measurement operation can go back to waiving measurement of reference mark 516-2, and so on.

[0115] In some aspects, measurements can be waived based on user-preferences. A user of the lithographic apparatus may provide user-input to select specific measurements to waive. Computing system 514 can prompt one or more sensors 506 to waive one or more measurements based on the userinput. Additionally, or alternatively, computing system 514 can be programmed to determine which measurements to waive based on a favorable feature present in forecasted distortion by prediction models. For example, distortion forecasts are more reliable when thermal behavior is in a steady-state regime (e.g., as in steady-state period 618). Computing system 514 can be programmed to prompt one or more sensors 506 to waive one or more measurements when patterning device 512 and / or projection system 510 reach a steady-state regime regarding thermal fluctuations.

[0116] In some aspects, one or more sensors 506 can be prompted to waive by any suitable method. For example, computing system 514 can send a command to stage 500 to skip a measurement, a value in memory can be adjusted (e.g., flipping a bit) and the relevant devices can refer to the value in the memory to determine whether a measurement should be performed or skipped, or the like.

[0117] FIG. 7 shows a flowchart of a method 700, according to some aspects. For example, method 700 can be for reducing the time of alignment operations in a lithographic process. In some aspects, at operation 702, lithographic fabrication cycles are performed on substrates. The lithographic fabrication cycles are performed in a lithographic apparatus using a patterning device comprising reference marks and a beam of radiation. Each of the lithographic fabrication cycles comprises an exposure operation on a substrate and a substrate alignment operation. The substrate alignment operation comprises use of a sensor configured to perform measurements of the reference marks for the alignment operation of each of the fabrication cycles.

[0118] In one aspect, at operation 704 a distortion of the patterning device can be forecasted using a distortion prediction model and one or more parameters of the beam.

[0119] In one aspect, at operation 706 the sensor can be prompted to waive one or more of the measurements, thereby increasing fabrication speed of the lithographic apparatus.

[0120] In one aspect, at operation 708 one or more substrate alignment operations can be adjusted using the forecasted distortion to offset the waived one or more of the measurements.

[0121] The method steps of FIG. 7 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 7 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based aspects described in reference to FIGS. 1-6.

[0122] FIG. 8 shows a computer system 800, according to some aspects. Various aspects and components therein can be implemented, for example, using computer system 800 or any other well-known computer systems. For example, the computing system 514 of FIG. 5 and the method steps of FIG. 7 can be implemented via computer system 700.

[0123] In some aspects, computer system 800 can comprise one or more processors (also called central processing units, or CPUs), such as a processor 804. Processor 804 can be connected to a communication infrastructure or bus 806.

[0124] In some aspects, one or more processors 804 can each be a graphics processing unit (GPU). In some aspects, a GPU is a processor that is a specialized electronic circuit designed to process mathematically intensive applications. The GPU can have a parallel structure that is efficient for parallel processing of large blocks of data, such as mathematically intensive data common to computer graphics applications, images, videos, etc.

[0125] In some aspects, computer system 800 can further comprise user input / output device(s) 803, such as monitors, keyboards, pointing devices, etc., that communicate with communication infrastructure 806 through user input / output interface(s) 802. Computer system 800 can further comprise a main or primary memory 808, such as random access memory (RAM). Main memory 808 can comprise one or more levels of cache. Main memory 808 has stored therein control logic ( / '.<?.. computer software) and / or data.

[0126] In some aspects, computer system 800 can further comprise one or more secondary storage devices or memory 810. Secondary memory 810 can comprise, for example, a hard disk drive 812 and / or a removable storage device or drive 814. Removable storage drive 814 can be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, tape backup device, and / or any other storage device / drive. Removable storage drive 814 can interact with a removable storage unit 818. Removable storage unit 818 can comprise a computer usable or readable storage device having stored thereon computer software (control logic) and / or data. Removable storage unit 818 can be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and / any other computer data storage device. Removable storage drive 814 reads from and / or writes to removable storage unit 818 in a well-known manner.

[0127] In some aspects, secondary memory 810 can comprise other means, instrumentalities or other approaches for allowing computer programs and / or other instructions and / or data to be accessed by computer system 800. Such means, instrumentalities or other approaches can comprise, for example, a removable storage unit 822 and an interface 820. Examples of the removable storage unit 822 and the interface 820 can comprise a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and / or any other removable storage unit and associated interface.

[0128] In some aspects, computer system 800 can further comprise a communication or network interface 824. Communication interface 824 enables computer system 800 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually andcollectively referenced by reference number 828). For example, communication interface 824 can allow computer system 800 to communicate with remote devices 828 over communications path 826, which can be wired and / or wireless, and which can comprise any combination of LANs, WANs, the Internet, etc. Control logic and / or data can be transmitted to and from computer system 800 via communications path 826.

[0129] In some aspects, a non-transitory, tangible apparatus or article of manufacture comprising a non-transitory, tangible computer useable or readable medium having control logic (software) stored thereon is also referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 800, main memory 808, secondary memory 810, and removable storage units 818 and 822, as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system 800), causes such data processing devices to operate as described herein.

[0130] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:1. A lithographic apparatus comprising: an illumination system configured to generate a beam of radiation to illuminate a pattern of a patterning device for projecting an image of the pattern onto substrates, wherein the patterning device comprises reference marks; a substrate support structure configured to support the substrates and perform alignment operations during fabrication cycles, wherein each of the fabrication cycles comprises an exposure operation on a substrate and a substrate alignment operation, and wherein the substrate support structure comprises: a sensor configured to perform measurements of the reference marks for the substrate alignment operation of each of the fabrication cycles; and a computing system configured to: forecast a distortion of the patterning device using a distortion prediction model and one or more parameters of the beam; prompt the sensor to waive one or more of the measurements, thereby increasing fabrication speed of the lithographic apparatus; and adjust the alignment operations using the forecasted distortion to offset the waived one or more of the measurements.2. The lithographic apparatus of clause 1, wherein: the alignment operations comprise a first substrate alignment operation for a first one of the fabrication cycles and a second substrate alignment operation for a second one of the fabrication cycles; the computing system is further configured to adjust the second substrate alignment operation based on at least one of the measurements performed in the first one of the fabrication cycles.3. The lithographic apparatus of clause 1, wherein the computing system is further configured to: store one or more vacant parameters associated with the waived one or more measurements; and populate the one or more vacant parameters based on the forecasted distortion.4. The lithographic apparatus of clause 1, wherein the computing system is further configured to: receive user-input; prompt the sensor to waive one or more of the measurements based on the user-input.5. The lithographic apparatus of clause 1, wherein: the sensor is further configured to perform a first measurement of a first one of the reference marks and a second one of the reference marks; the computing system is further configured to: prompt the sensor to waive the first measurement during a first one of the fabrication cycles; and prompt the sensor to waive the second measurement during a second one of the fabrication cycles.6. The lithographic apparatus of clause 1 , wherein the computing system is further configured to prompt the sensor to waive one or more of the measurements based on a feature of the forecasted distortion.7. The lithographic apparatus of clause 6, wherein the feature comprises a steady-state regime of the forecasted distortion.8. A method comprising: performing lithographic fabrication cycles of substrates using a patterning device comprising reference marks and a beam of radiation, wherein each of the lithographic fabrication cycles comprises an exposure operation on a substrate and a substrate alignment operation, and wherein the substrate alignment operation comprises use of a sensor configured to perform measurements of the reference marks at each of the fabrication cycles; forecasting a distortion of the patterning device using a distortion prediction model and one or more parameters of the beam; prompting the sensor to waive one or more of the measurements, thereby increasing fabrication speed of the lithographic apparatus; and adjusting one or more substrate alignment operations using the forecasted distortion to offset the waived one or more of the measurements.9. The method of clause 8, wherein: a first substrate alignment operation is associated with a first one of the fabrication cycles and a second substrate alignment operation is associated with a second one of the fabrication cycles; the method further comprises adjusting the second substrate alignment operation based on at least one of the measurements performed in the first one of the fabrication cycles.10. The method of clause 8, further comprising: storing one or more vacant parameters associated with the waived one or more measurements; and populating the one or more vacant parameters based on the forecasted distortion.11. The method of clause 8, the prompting comprises prompting the sensor to waive the one or more of the measurements based on user-input.12. The method of clause 8, wherein: the sensor is further configured to perform a first measurement of a first one of the reference marks and a second one of the reference marks; the method further comprises: prompting the sensor to waive the first measurement during a first one of the fabrication cycles; and prompting the sensor to waive the second measurement during a second one of the fabrication cycles.13. The method of clause 8, wherein the prompting comprises prompting the sensor to waive one or more of the measurements based on a feature of the forecasted distortion.14. The method of clause 3, wherein the feature comprises a steady-state regime of the forecasted distortion.15. A non-transitory computer readable medium having instructions stored thereon, that, when executed on a computing system cause the computing system to perform operations, the operations comprising: forecasting a distortion of a patterning device comprising reference marks using a distortion prediction model and one or more parameters of a beam of radiation, wherein the patterning device and the beam of radiation are associated with lithographic fabrication cycles comprising an exposure operation on a substrate and a substrate alignment operation, and wherein the substrate alignment operation comprises use of a sensor configured to perform measurements of the reference marks at each of the fabrication cycles; prompting the sensor to waive one or more of the measurements, thereby increasing speed of the lithographic fabrication cycles; and adjusting one or more substrate alignment operations using the forecasted distortion to offset the waived one or more of the measurements.16. The non-transitory computer-readable medium of clause 15, wherein: a first substrate alignment operation is associated with a first one of the fabrication cycles and a second substrate alignment operation is associated with a second one of the fabrication cycles; the adjusting comprises adjusting the second alignment operation based on at least one of the measurements performed in the first one of the fabrication cycles.17. The non-transitory computer-readable medium of clause 15, wherein the operations further comprise: one or more vacant parameters are associated with the waived one or more measurements; and populating the one or more vacant parameters based on the forecasted distortion.18. The non-transitory computer-readable medium of clause 15, the prompting comprises prompting the sensor to waive the one or more of the measurements based on user-input.19. The non-transitory computer-readable medium of clause 15, wherein: the sensor is further configured to perform a first measurement of a first one of the reference marks and a second one of the reference marks; the operations further comprise: prompting the sensor to waive the first measurement during a first one of the fabrication cycles; and prompting the sensor to waive the second measurement during a second one of the fabrication cycles.20. The non-transitory computer-readable medium of clause 15, wherein the prompting comprises prompting the sensor to waive one or more of the measurements based on a steady-state regime of the forecasted distortion.

[0131] Based on the teachings contained in this disclosure, it will be apparent to those skilled in the relevant art(s) how to make and use aspects of this disclosure using data processing devices, computer systems and / or computer architectures other than that shown in FIG. 8. In particular, aspects described herein can operate with software, hardware, and / or operating system implementations other than those described herein.

[0132] The terms “radiation,” “beam,” “light,” “illumination,” or the like can be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength k of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-100 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G- line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

[0133] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses 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 magnetic heads, etc. Those skilled in the art will appreciate 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. A substrate can be processed before or after exposure in, for example, a track 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, aspects disclosed herein can be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0134] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0135] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. The foregoing description of specific aspects will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0136] It is to 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 can set forth one or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above-described aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A lithographic apparatus comprising: an illumination system configured to generate a beam of radiation to illuminate a pattern of a patterning device for projecting an image of the pattern onto substrates, wherein the patterning device comprises reference marks; a substrate support structure configured to support the substrates and perform alignment operations during fabrication cycles, wherein each of the fabrication cycles comprises an exposure operation on a substrate and a substrate alignment operation, and wherein the substrate support structure comprises: a sensor configured to perform measurements of the reference marks for the substrate alignment operation of each of the fabrication cycles; and a computing system configured to: forecast a distortion of the patterning device using a distortion prediction model and one or more parameters of the beam; prompt the sensor to waive one or more of the measurements, thereby increasing fabrication speed of the lithographic apparatus; and adjust the alignment operations using the forecasted distortion to offset the waived one or more of the measurements.

2. The lithographic apparatus of claim 1, wherein: the alignment operations comprise a first substrate alignment operation for a first one of the fabrication cycles and a second substrate alignment operation for a second one of the fabrication cycles; the computing system is further configured to adjust the second substrate alignment operation based on at least one of the measurements performed in the first one of the fabrication cycles.

3. The lithographic apparatus of claim 1, wherein the computing system is further configured to: store one or more vacant parameters associated with the waived one or more measurements; and populate the one or more vacant parameters based on the forecasted distortion.

4. The lithographic apparatus of claim 1, wherein the computing system is further configured to: receive user-input; prompt the sensor to waive one or more of the measurements based on the user-input.

5. The lithographic apparatus of claim 1, wherein:the sensor is further configured to perform a first measurement of a first one of the reference marks and a second one of the reference marks; the computing system is further configured to: prompt the sensor to waive the first measurement during a first one of the fabrication cycles; and prompt the sensor to waive the second measurement during a second one of the fabrication cycles.

6. The lithographic apparatus of claim 1 , wherein the computing system is further configured to prompt the sensor to waive one or more of the measurements based on a feature of the forecasted distortion.

7. The lithographic apparatus of claim 6, wherein the feature comprises a steady-state regime of the forecasted distortion.

8. A method comprising: performing lithographic fabrication cycles of substrates using a patterning device comprising reference marks and a beam of radiation, wherein each of the lithographic fabrication cycles comprises an exposure operation on a substrate and a substrate alignment operation, and wherein the substrate alignment operation comprises use of a sensor configured to perform measurements of the reference marks at each of the fabrication cycles; forecasting a distortion of the patterning device using a distortion prediction model and one or more parameters of the beam; prompting the sensor to waive one or more of the measurements, thereby increasing fabrication speed of the lithographic apparatus; and adjusting one or more substrate alignment operations using the forecasted distortion to offset the waived one or more of the measurements.

9. The method of claim 8, wherein: a first substrate alignment operation is associated with a first one of the fabrication cycles and a second substrate alignment operation is associated with a second one of the fabrication cycles; the method further comprises adjusting the second substrate alignment operation based on at least one of the measurements performed in the first one of the fabrication cycles.

10. The method of claim 8, further comprising: storing one or more vacant parameters associated with the waived one or more measurements; andpopulating the one or more vacant parameters based on the forecasted distortion.

11. The method of claim 8, the prompting comprises prompting the sensor to waive the one or more of the measurements based on user-input.

12. The method of claim 8, wherein: the sensor is further configured to perform a first measurement of a first one of the reference marks and a second one of the reference marks; the method further comprises: prompting the sensor to waive the first measurement during a first one of the fabrication cycles; and prompting the sensor to waive the second measurement during a second one of the fabrication cycles.

13. The method of claim 8, wherein the prompting comprises prompting the sensor to waive one or more of the measurements based on a feature of the forecasted distortion.

14. The method of claim 3, wherein the feature comprises a steady-state regime of the forecasted distortion.

15. A non-transitory computer readable medium having instructions stored thereon, that, when executed on a computing system cause the computing system to perform operations, the operations comprising: forecasting a distortion of a patterning device comprising reference marks using a distortion prediction model and one or more parameters of a beam of radiation, wherein the patterning device and the beam of radiation are associated with lithographic fabrication cycles comprising an exposure operation on a substrate and a substrate alignment operation, and wherein the substrate alignment operation comprises use of a sensor configured to perform measurements of the reference marks at each of the fabrication cycles; prompting the sensor to waive one or more of the measurements, thereby increasing speed of the lithographic fabrication cycles; and adjusting one or more substrate alignment operations using the forecasted distortion to offset the waived one or more of the measurements.

Images