System and method for generating multiple illumination spots from a single illumination source - Patents.com

Abstract

An illumination spot directed at a target is described. The illumination spot is generated from a single illumination source. Ghost reflections common to wafer alignment sensors are reduced or eliminated. First, second, and third spot mirrors are described. The first spot mirror receives illumination along a first axis, reflects a first portion of the illumination away from the first axis, and transmits a second portion of the illumination along the first axis. The second spot mirror receives the reflected first portion of the illumination and at least partially reflects a third portion of the illumination along the second axis. The third spot mirror receives and fully reflects a fourth portion of the illumination along a third axis. The second, third, and fourth portions of the illumination are directed at the target at different angles relative to one another to generate three distinct illumination spots.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 293,260, filed December 23, 2021, and is incorporated by reference in its entirety into this specification.

[0002] This description relates generally to generating multiple illumination spots from a single illumination source. [Background technology]

[0003] Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A patterning device (e.g. a mask) may contain or provide a pattern ("design layout") corresponding to an individual layer of the IC, which can be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g. a silicon wafer) that is coated with a layer of radiation-sensitive material ("resist"), such as by irradiating the target portion through the pattern on the patterning device. Typically, a single substrate will contain several adjacent target portions onto which the lithographic projection apparatus transfers the pattern, one at a time. In one type of lithographic projection apparatus, the pattern of the entire patterning device is transferred onto one target portion in one step. Such an apparatus is commonly referred to as a stepper. In another apparatus, commonly referred to as a step-and-scan apparatus, the projection beam scans the patterning device in a predetermined reference direction (the "scan" direction), while the substrate is moved synchronously parallel or anti-parallel to this reference direction. Different portions of the pattern on the patterning device are transferred progressively onto one target portion. Generally, a lithographic projection apparatus will have a demagnification ratio M (e.g. 4), so the speed F at which the substrate moves will be 1 / M times the speed at which the projection beam scans the patterning device. More information on lithographic devices as described herein can be gleaned, for example, from U.S. Patent No. 6,046,792, which is incorporated herein by reference.

[0004]

[0004] Before transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures such as priming, resist coating, and a soft bake. After exposure, the substrate may be subjected to other procedures ("post-exposure procedures") such as a post-exposure bake (PEB), development, a hard bake, and metrology / inspection of the transferred pattern. This sequence of procedures is used as a basis for manufacturing an individual layer of a device, e.g. an IC. The substrate may then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, deposition, chemical-mechanical polishing, all of which are aimed at completing an individual layer of the device. If the device requires several layers, the entire procedure, or a variant thereof, is repeated for each layer. Eventually, a device will be present on each target portion on the substrate. These devices are then separated from one another by techniques such as dicing or sawing, so that the individual devices can be attached to a carrier or connected to pins.

[0005]

[0005] Thus, the manufacture of devices such as semiconductor devices typically involves processing a substrate (e.g., a semiconductor wafer) using multiple manufacturing processes to form various features and multiple layers of the device. Such layers and features are usually manufactured and processed using, for example, deposition, lithography, etch, deposition, chemical mechanical polishing, and ion implantation. Multiple devices may be manufactured into multiple dies on a substrate and then separated into individual devices. This device manufacturing process may be considered as a patterning process. A patterning process includes a patterning step, such as optical lithography and / or nanoimprint lithography, in which a patterning device is used in a lithography apparatus to transfer a pattern on the patterning device to a substrate, typically optionally accompanied by one or more associated pattern processing steps, such as developing a resist in a developer, baking the substrate using a bake tool, etching with the pattern using an etcher, deposition, etc.

[0006]

[0006] Lithography is a central process in the manufacture of devices such as ICs, where patterns formed on a substrate define the functional elements of devices such as microprocessors, memory chips, etc. Similar lithographic techniques are used in the formation of flat panel displays, micro-electromechanical systems (MEMS), and other devices.

[0007]

[0007] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements are continually shrinking, while the number of functional elements, such as transistors, per device has been steadily increasing for decades, following a trend commonly referred to as "Moore's Law". In current technology, layers of devices are fabricated using lithographic projection apparatus that projects a design layout onto a substrate using illumination from a deep ultraviolet illumination source, producing individual functional elements with dimensions well below 100 nm, i.e., less than half the wavelength of radiation from the illumination source (e.g., a 193 nm illumination source).

[0008]

[0008] This process of printing features with dimensions smaller than the conventional resolution limit of the lithographic projection apparatus is commonly known as low k1 lithography, according to the resolution equation CD=k1×λ / NA, where λ is the wavelength of the radiation used (currently mostly 248 nm or 193 nm), NA is the numerical aperture of the projection optics in the lithographic projection apparatus, CD is the "critical dimension", i.e., the minimum feature size that is typically printed, and k1 is an empirical resolution factor. In general, the smaller k1 is, the more difficult it is to reproduce a pattern on a substrate that resembles the shape and dimensions planned by the designer to achieve a particular electrical functionality and performance. To overcome such difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, the use of phase-shifting patterning devices, optical proximity correction (OPC, sometimes called "optical and process correction") in the design layout, or other methods commonly defined as "resolution enhancement techniques" (RET). Summary of the Invention

[0009]

[0009] The optical element array generates multiple illumination spots. The multiple illumination spots may be used to simultaneously illuminate multiple metrology marks and / or other targets and / or for other purposes. The optical element array is relatively low cost compared to other methods of generating multiple illumination spots and is compatible with existing metrology systems. Advantageously, the present system and method provide off-axis illumination spots that facilitate separation of ghost reflections from intensity channel measurements in such systems. Additional optical paths are generated in collimated space at different angles relative to each other, resulting in separate illumination spots on the target. The illumination spots may be arranged along one axis on the target or in a two-dimensional pattern, for example.

[0010] According to an embodiment, a system for generating an illumination spot configured to be directed toward a target is provided. The system includes a first optical element configured to receive illumination from an illumination source along a first axis, reflect a first portion of the illumination away from the first axis, and transmit a second portion of the illumination along the first axis. The system includes a second optical element configured to receive the reflected first portion of the illumination and at least partially reflect a third portion of the illumination along a second axis that is at a different angle from the first axis. The second and third portions of the illumination are directed toward the target at an angle relative to each other in a pupil plane to generate two distinct illumination spots on the target.

[0011] In some embodiments, the system includes a third optical element configured to receive and fully reflect a fourth portion of the illumination along a third axis that is angularly distinct from the first and second axes. The fourth portion of the illumination is transmitted by the second optical element. The second, third, and fourth portions of the illumination are directed toward the target at different angles relative to each other in the pupil plane to generate three distinct illumination spots on the target.

[0012] In some embodiments, the illumination spots corresponding to illumination from the first axis include on-axis spots, and the illumination spots corresponding to illumination from the second axis and the third axis include off-axis spots, hi some embodiments, the off-axis spots are configured to reduce or eliminate ghost reflections.

[0013] In some embodiments, the first optical element, the second optical element, and the third optical element are movable relative to each other. In some embodiments, the movement of the first optical element, the second optical element, and / or the third optical element is configured to adjust the position of the corresponding illumination spot on the target. In some embodiments, the movement includes tilting the first optical element, the second optical element, and / or the third optical element, and / or changing the distance between one or more of the first optical element, the second optical element, and the third optical element.

[0014] In some embodiments, the first optical element, the second optical element, and the third optical element each comprise a spot mirror. In some embodiments, the first optical element is partially reflective, the second optical element is at least partially reflective, and the third optical element is fully reflective.

[0015] In some embodiments, the system comprises a fourth optical element configured to reflect illumination received along the first axis in a column direction substantially perpendicular to the first axis, in some embodiments, the fourth optical element comprises a spot mirror cube.

[0016] In some embodiments, the illumination spots corresponding to illumination from the first axis include on-axis spots, and the illumination spots corresponding to illumination from the second and third axes include off-axis spots, and the on-axis and off-axis spots are movable relative to one another. In some embodiments, the illumination spots directed at the target are configured to be moved relative to one another based on movement of the first, second, third, and / or fourth optical elements.

[0017] In some embodiments, the illumination spots are aligned in a line. In some embodiments, the illumination spots are arranged in a two-dimensional pattern.

[0018] In some embodiments, the system comprises an illumination source including a single radiation source configured to generate illumination along a first axis.

[0019]

[0019] In some embodiments, the system includes a lens configured to receive the illumination beam formed by the optical element and focus the illumination spot on the target.

[0020] In some embodiments, the first, second, third and fourth optical elements form part of an alignment sensor, the alignment sensor being a wafer alignment sensor used in a semiconductor manufacturing process.

[0021]

[0021] In some embodiments, the system includes an additional optical element configured to receive reflected illumination transmitted by the previous optical element and configured to at least partially reflect the received illumination along an additional axis to generate an additional illumination spot directed toward the target.

[0022]

[0022] According to another embodiment, a method is provided for generating an illumination spot configured to be directed toward a target. The method includes receiving illumination from an illumination source along a first axis with a first optical element, reflecting a first portion of the illumination away from the first axis and transmitting a second portion of the illumination along the first axis, and receiving the reflected first portion of the illumination with a second optical element and at least partially reflecting a third portion of the illumination along a second axis that is at a different angle from the first axis. The second and third portions of the illumination are directed toward the target at an angle relative to each other in a pupil plane to generate two distinct illumination spots on the target.

[0023]

[0023] According to another embodiment, a non-transitory computer readable medium having instructions that, when executed by a computer, cause operations including receiving, with a first optical element, illumination from an illumination source along a first axis, reflecting a first portion of the illumination away from the first axis, and transmitting a second portion of the illumination along the first axis, and receiving, with a second optical element, the reflected first portion of the illumination and at least partially reflecting a third portion of the illumination along a second axis that is at a different angle from the first axis. The second and third portions of the illumination are directed toward a target at an angle relative to each other in a pupil plane to generate two distinct illumination spots on the target.

[0024]

[0024] According to another embodiment, a system for generating illumination spots configured to be directed toward a target for a wafer alignment sensor used in a semiconductor manufacturing process is provided. The system is configured to generate multiple illumination spots from a single illumination source. The system is configured to reduce or eliminate ghost reflections common to other wafer alignment sensors. The system includes a single illumination source. The system includes a first spot mirror included in a first glass plate. The first spot mirror is configured to receive illumination from the single illumination source along a first axis, reflect a first portion of the illumination away from the first axis, and transmit a second portion of the illumination along the first axis. The system includes a second spot mirror included in a second glass plate. The second spot mirror is configured to receive a first portion of the reflected illumination and at least partially reflect a third portion of the illumination along a second axis different from the first axis. The system includes a third spot mirror included in a third glass plate. The third spot mirror is configured to receive and fully reflect a fourth portion of the illumination along a third axis that is angled differently from the first axis and the second axis. The fourth portion of the illumination is transmitted by the second spot mirror. The second portion, the third portion, and the fourth portion of the illumination are directed toward the target at different angles relative to one another in the pupil plane to generate three distinct illumination spots on the target corresponding to the illumination on the first axis, the second axis, and the third axis. [Brief description of the drawings]

[0025]

[0025] The above aspects and other aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

[0026] [Figure 1] 1 illustrates a lithographic apparatus according to an embodiment; [Diagram 2]

[0027] 1 illustrates a schematic representation of an embodiment of a lithographic cell or cluster according to an embodiment. [Diagram 3]

[0028] 1 illustrates a schematic diagram of an exemplary inspection system according to an embodiment. [Figure 4]

[0029] 1 illustrates a schematic diagram of an exemplary metrology technique in accordance with an embodiment; [Diagram 5]

[0030] 1 illustrates a relationship between a radiation illumination spot and a metrology target of an inspection system in accordance with an embodiment. [Figure 6]

[0031] 1 illustrates a system for generating an illumination spot configured to be directed toward a target, according to an embodiment. [Figure 7]

[0032] 1 illustrates various different illumination spot arrangements according to embodiments. [Figure 8]

[0033] 1 illustrates a method for generating an illumination spot configured to be directed toward a target, according to an embodiment. [Figure 9]

[0034] FIG. 1 is a block diagram of an exemplary computer system, according to an embodiment. [Figure 10]

[0035] FIG. 2 is a schematic diagram of a lithographic projection apparatus similar to FIG. 1, according to an embodiment. [Figure 11]

[0036] FIG. 11 is a more detailed diagram of the device of FIG. 10, according to an embodiment. [Figure 12]

[0037] 12 is a more detailed diagram of a source collector module of the apparatus of FIGS. 10 and 11 according to one embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027]

[0038] In semiconductor device manufacturing, determining alignment typically involves determining the location of an alignment mark (or marks) and / or other targets in a layer of a semiconductor device structure. Alignment is typically determined by illuminating the alignment mark with radiation and comparing the characteristics of different diffraction orders of radiation reflected from the alignment mark. Similar techniques are used to measure overlay and / or other parameters. Current alignment sensors have a single measurement illumination spot that is projected onto a substrate (e.g., a wafer). The single illumination spot is used to measure multiple alignment parameters, phase, and intensity detection. Current sensors measure metrology marks sequentially. Thus, the number of measurement marks on a given substrate is limited by throughput considerations. Also, the accuracy of mark detection is affected by ghost reflections in the sensor. The effect of ghost reflections is particularly pronounced in the case of intensity detection of current sensors, limiting the ability of the sensor to accurately measure intensity.

[0028]

[0039] For example, there is a need to more accurately and efficiently measure a larger number of metrology marks to enable a higher order grid fit and / or for other reasons. A higher order grid fit allows for a more accurate determination of wafer distortion by fitting a higher order polynomial, which requires a larger number of measurement points. Previously proposed solutions required a significant redesign of the sensor hardware, which was costly and risky, and generally not backward compatible with existing sensors.

[0029]

[0040] Advantageously, the present system and method generates multiple illumination spots by an arrangement of optical elements. The multiple illumination spots may be used to simultaneously illuminate one or more portions of a single metrology mark, multiple metrology marks, and / or other targets, and / or may be used for other purposes. The arrangement of optical elements is relatively low cost compared to other methods of generating multiple illumination spots and is compatible with existing metrology systems. The present system and method provides off-axis illumination spots that facilitate separation of ghost reflections from intensity channel measurements in such systems. Additional optical paths are made in collimated space at different angles to each other, resulting in the formation of separate illumination spots on the target. The illumination spots may be arranged along one axis on the target, or in a two-dimensional pattern, for example.

[0030]

[0041] Briefly, the description herein generally relates to semiconductor device manufacturing and patterning processes. More specifically, the following paragraphs describe several components of systems and / or methods for semiconductor device manufacturing. These systems and methods may be used, for example, for alignment measurements or other operations in the semiconductor device manufacturing process.

[0031]

[0042] Although specific reference may be made herein to measuring the alignment of semiconductor devices and the manufacture of integrated circuits (ICs), it should be understood that the description herein has many other possible applications. For example, it may be used in the manufacture of magnetic domain memories, liquid crystal display panels, integrated optical systems such as thin film magnetic heads, guidance and detection patterns. Those skilled in the art will appreciate that in the context of such alternative applications, the terms "reticle," "wafer," or "die" as used herein should be considered interchangeable with the more general terms "mask," "substrate," and "target portion," respectively.

[0032]

[0043] The term "projection optics" as used herein should be broadly interpreted to encompass various types of optical systems including, for example, refractive optics, reflective optics, apertures, and catadioptric optics. The term "projection optics" may also include components that collectively or alone operate according to any of these design types to direct, shape or control a projection beam of radiation. The term "projection optics" may include any optical component in a lithographic projection apparatus, regardless of where it is located on the optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, conditioning and / or projecting radiation from a radiation source before it passes through a patterning device, and / or optical components for shaping, conditioning and / or projecting radiation after it has passed through a patterning device. Generally, projection optics does not include a radiation source and a patterning device.

[0033]

[0044] Fig. 1 shows a schematic representation of an embodiment of a lithographic apparatus LA. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV, DUV or EUV radiation), a support structure (e.g. mask table) MT constructed to support a patterning device (e.g. mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters, a substrate table (e.g. wafer table) WT (e.g. WTa, WTb or both) configured to hold a substrate (e.g. resist coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate according to certain parameters, and a projection system (e.g. refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies, often referred to as a field) of the substrate W. The projection system is supported on a reference frame RF. As shown, the apparatus is of a transmissive type (e.g. using a transmissive mask). Alternatively, the apparatus may be of a reflective type (eg employing a programmable mirror array, or employing a reflective mask).

[0034]

[0045] The illuminator IL receives the radiation beam from the radiation source SO. The source and the lithographic apparatus may be separate, for example when the source is an excimer laser. In such cases the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL using a beam delivery system BD, for example comprising suitable directing mirrors and / or beam expanders. In other cases the source may be an integral part of the apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0035]

[0046] The illuminator IL may vary the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution is non-zero in an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the distribution of the beam in the pupil plane such that the intensity distribution is non-zero in a number of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in the pupil plane of the illuminator IL may be referred to as the illumination mode.

[0036]

[0047] The illuminator IL may comprise an adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Typically, at least the outer and / or inner radial extent (typically referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to vary the number and angular extent of sectors in the pupil plane where the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, various illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multipole distribution, such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, for example, by inserting an optical component providing that illumination mode into the illuminator IL or by using a spatial light modulator.

[0037]

[0048] The illuminator IL may be operable to change the polarization of the beam and may be operable to adjust the polarization using the adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as the polarization mode. Using different polarization modes may result in greater contrast in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across the pupil plane of the illuminator IL. The polarization direction of the radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen depending on the illumination mode. In the case of a multipole illumination mode, the polarization of each pole of the radiation beam may be approximately perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, in the case of a dipole illumination mode, the radiation may be linearly polarized in a direction substantially perpendicular to a line that bisects two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as the X and Y polarization states. In a quadrupole illumination mode, the radiation in each pole sector may be linearly polarized in a direction substantially perpendicular to a line that bisects the sector. This polarization mode may be referred to as XY polarization. Similarly, in a hexapole illumination mode, the radiation in each pole sector may be linearly polarized in a direction substantially perpendicular to a line that bisects the sector. This polarization mode may be referred to as TE polarization.

[0038]

[0049] The illuminator IL will generally also comprise various other components, such as an integrator IN and a condenser CO. An illumination system may comprise various optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling radiation.

[0039]

[0050] The illuminator thus provides a conditioned beam of radiation B having a desired uniformity and intensity distribution in its cross-section.

[0040]

[0051] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be for example a frame or a table, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms "reticle" or "mask" herein may be considered as synonymous with the more general term "patterning device".

[0041]

[0052] The term "patterning device" as used herein should be interpreted broadly to refer to any device that can be used to impart a pattern to a target portion of a substrate. In an embodiment, a patterning device is any device that can be used to impart a radiation beam with a pattern in its cross-section to generate a pattern in the target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the pattern desired in the target portion of the substrate, for example if the pattern includes phase-shifting features or so-called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion of the device, such as an integrated circuit.

[0042]

[0053] A patterning device may be of a transmissive or reflective type. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid masks. 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 tilting mirrors impart a pattern to the radiation beam which is reflected from the mirror matrix.

[0043]

[0054] The term "projection system" as used herein includes refractive optics, catadioptric, catadioptric, magnetic, electromagnetic and electrostatic optics, or any combination thereof, and should be interpreted broadly to encompass any type of projection system that is suitable with respect to the exposure radiation used or with respect to other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system".

[0044]

[0055] The projection system PS may comprise a number of optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of the optical elements to correct aberrations (phase changes across the pupil plane across the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements in the projection system PS in one or more different ways. The projection system may have a coordinate system whose optical axis extends in the z-direction. The adjustment mechanism may be operable to displace one or more optical elements, tilt one or more optical elements, and / or deform one or more optical elements in any combination. The displacement of the optical elements may be in any direction (x, y, z, or combinations thereof). The tilt of the optical elements is typically out of plane perpendicular to the optical axis by rotation about an axis in the x and / or y directions, although rotation about the z-axis may be used for non-rotationally symmetric aspheric optical elements. The deformation of the optical element may include a low frequency shape (e.g. astigmatism) and / or a high frequency shape (e.g. free form asphericity). The deformation of the optical element may be performed, for example, by exerting a force on one or more sides of the optical element using one or more actuators and / or by heating one or more selected regions of the optical element using one or more heating elements. In general, it may not be possible to adjust the projection system PS to correct the apodization (change in transmission at the pupil plane). A transmission map of the projection system PS may be used in designing a patterning device (e.g. mask) MA for the lithographic apparatus LA. Computational lithography techniques may be used to design the patterning device MA to at least partially correct the apodization.

[0045]

[0056] The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g. two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system that does not contain the substrate, e.g. dedicated to facilitating measurement and / or cleaning, etc.). In such a "multi-stage" machine, the additional tables may be used in parallel, or preparatory steps may be performed on one or more tables whilst the other one or more tables are used for exposure. For example, alignment measurements may be made using alignment sensors AS and / or level (height, tilt, etc.) measurements using level sensors LS.

[0046]

[0057] The lithographic apparatus may also be of a type in which at least a portion of the substrate is covered by a liquid having a relatively high refractive index, e.g. water, filling a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example between the patterning device and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not imply that a structure such as the substrate has to be immersed in liquid, but simply that a liquid is located between the projection system and the substrate during exposure.

[0047]

[0058] In operation of a lithographic apparatus, a radiation beam is conditioned and provided by an illumination system IL. The radiation beam B is incident on a patterning device (e.g. mask) MA, which is held on a support structure (e.g. mask table) MT, and is patterned by the patterning device. After traversing the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. Using a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder, a 2D encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (not explicitly shown in FIG. 1 ) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during a scan. In general, movement of the support structure MT may be realized using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be 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 opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. The patterning device MA and the substrate W may be aligned using the patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between the target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0048]

[0059] The depicted apparatus may be used in at least one of the following modes: In step mode, the support structure MT and the substrate table WT are kept substantially stationary while a pattern imparted to the radiation beam is projected onto the target portion C in one go (i.e. a single static exposure), and the substrate table WT is moved in the X and / or Y direction so that a different target portion C can be exposed. In step mode, a maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto the target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in non-scan direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in scan direction) of the target portion. In another mode, the support structure MT is kept substantially stationary holding the programmable patterning device and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto the target portion C. In this mode, a pulsed radiation source is generally used and the programmable patterning device is updated as required after each movement of the substrate table WT, or between successive radiation pulses during a scan. This mode of operation can readily be applied to maskless lithography employing a programmable patterning device such as a programmable mirror array of the type mentioned above.

[0049]

[0060] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0050]

[0061] Substrates referred to herein may be processed, before or after exposure, for example in a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology tool or an inspection tool. Where applicable, the disclosure herein may apply to these and other substrate processing tools. Furthermore, a substrate may be processed more than once, for example to produce a multi-layer IC, and thus the term substrate as used herein may also refer to a substrate that already includes multiple processed layers.

[0051]

[0062] The terms "radiation" and "beam" as used herein with respect to lithography encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 to 20 nm), as well as particle beams such as ion beams and electron beams.

[0052]

[0063] Various patterns on or provided by a patterning device may have different process windows, i.e., a space of process variables within which the patterns are to be produced. Examples of pattern specifications related to potential systematic defects include checking necking, line pullback, thinning, CD, edge placement, overlap, resist top loss, resist undercut and / or bridging. The process window of a pattern on a patterning device or an area thereof may be obtained by merging (e.g., overlapping) the process windows of each of the individual patterns. The boundary of the process window of a group of patterns includes the boundaries of the process windows of several individual patterns. In other words, these individual patterns limit the process window of the group of patterns.

[0053]

[0064] As shown in FIG. 2, the lithographic apparatus LA may form part of a lithographic cell LC, sometimes called a lithocell or cluster, which also includes apparatus for performing pre-exposure and post-exposure processes on the substrate. Conventionally, these include one or more spin coaters SC for depositing one or more resist layers, one or more developers for developing the exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler or robot RO picks up one or more substrates from input / output ports I / O1, I / O2, moves them between the different process apparatus and delivers them to a loading bay LB of the lithographic apparatus. These apparatuses are often collectively referred to as a track, and 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 a lithography control unit LACU. The various apparatuses can thus be operated to maximize throughput and processing efficiency.

[0054]

[0065] To ensure that a substrate exposed by a lithographic apparatus is accurately and consistently exposed and / or to monitor a part of a patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., a photolithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties, such as alignment, overlay (e.g., between structures of overlapping layers, or between structures in the same layer, e.g., provided separately in that layer by a double patterning process), linewidth, critical dimension (CD), focus offset, material properties, etc. Thus, a manufacturing facility in which the lithocell LC is located typically also includes a metrology system that measures some or all of the substrates W (FIG. 1) processed in the lithocell, or other objects in the lithocell. The metrology system may be part of the lithocell LC, or may be part of the lithographic apparatus LA (e.g., alignment sensor AS (FIG. 1)).

[0055]

[0066] The one or more parameters measured may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, critical dimension (CD) (e.g., critical line width) of features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. The measurements are often made on dedicated metrology targets provided on the substrate. The measurements may be made after resist development and before etching, after etching, after deposition, and / or at other times.

[0056]

[0067] There are various techniques, including the use of scanning electron microscopes, image-based metrology tools, and / or various specialized tools, for making measurements of structures formed in the patterning process. A fast and non-invasive form of specialized metrology tool is to direct a beam of radiation onto a target on the substrate surface and measure the properties of the scattered (diffracted / reflected) beam. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this is sometimes called diffraction-based metrology. One application of this diffraction-based metrology is the measurement of alignment. For example, alignment can be measured by comparing portions of a diffraction spectrum (e.g., comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0057]

[0068] Thus, in a device manufacturing process (e.g., a patterning process or a lithography process), a substrate or other object may be subjected to various types of measurements during or after the process. The measurements may determine whether a particular substrate is defective, may establish adjustments of the process and the equipment used in the process (e.g., aligning two layers on a substrate or aligning a patterning device to a substrate), may measure the performance of the process and the equipment, or may be for other purposes. Examples of measurements include optical imaging (e.g., optical microscopes), non-imaging optical measurements (e.g., diffraction-based measurements such as ASML's YieldStar metrology tools, ASML's SMASH metrology systems), mechanical measurements (e.g., profiling with a stylus, atomic force microscope (AFM)), and / or non-optical imaging (e.g., scanning electron microscope (SEM)). The SMASH (SMart Alignment Sensor Hybrid) system, described in U.S. Pat. No. 6,961,116, the entirety of which is incorporated herein by reference, employs a self-referencing interferometer that produces two overlapping, relatively rotated images of an alignment marker, detects the intensity in the pupil plane where the Fourier transforms of the images are interfered, and extracts position information from the phase difference between the diffraction orders of the two images, which appears as an intensity change in the interfered orders.

[0058]

[0069] The metrology results may be provided directly or indirectly to a supervisory control system SCS. If errors are detected, adjustments may be made to the exposure of subsequent substrates (especially if inspection can be done soon enough and quickly enough to allow further exposure of one or more other substrates in the batch) and / or to subsequent exposures of the exposed substrate. Also, already exposed substrates may be stripped and reworked to improve yield, or may be discarded, thereby avoiding further processing of substrates known to be defective. If only some target portions of a substrate are defective, further exposures may be made only to those target portions that meet specifications. Other manufacturing process adjustments are also possible.

[0059]

[0070] A metrology system may be used to determine one or more properties of a substrate structure, in particular how one or more properties vary for different substrate structures or how different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithographic apparatus LA or lithocell LC, or may be a stand-alone device.

[0060]

[0071] To enable metrology, one or more targets are often specially provided on the substrate. The targets may include, for example, alignment marks and / or other targets. Typically, the targets are specially designed and may include periodic structures. For example, the target on the substrate may include one or more 1D periodic structures (e.g., geometric features such as gratings) that are printed such that, after development, the periodic structural features are formed with solid resist lines. As another example, the target may include one or more 2D periodic structures (e.g., gratings) that are printed such that, after development, the periodic structures are formed with solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., one or more layers on the substrate).

[0061]

[0072] FIG. 3 shows an exemplary inspection system 10 that may be used to detect alignment and / or perform other metrology operations. The inspection system 10 includes an illumination source 2 that projects or otherwise illuminates radiation onto a substrate W (e.g., which may typically include alignment marks). The redirected radiation is passed to a sensor such as a spectrometer detector 4 and / or other sensors that measure the spectrum (intensity as a function of wavelength) of the specularly reflected and / or diffracted radiation, for example as shown in the graph on the left of FIG. 4. The sensor may generate an alignment signal that conveys alignment data characteristic of the reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in FIG. 4, or by other operations.

[0062]

[0073] Similar to the lithographic apparatus LA of FIG. 1, one or more substrate tables (not shown in FIG. 4) may be provided to hold the substrate W during measurement operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of FIG. 1. In an example where the inspection system 10 is integrated with a lithographic apparatus, it may be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate with respect to the measurement optical system. For example, various sensors and actuators are provided to acquire the position of the target portion of the structure (e.g., alignment mark) of interest and to bring the target portion into position under the objective lens. Typically, many measurements will be made on the target portion of the structure at different locations on the substrate W. The substrate support can be moved in the X and Y directions to acquire the various targets and in the Z direction to obtain the desired location of the target portion relative to the focus of the optical system. For example, when in fact the optical system remains substantially stationary (typically in X and Y directions, but possibly also in Z direction) but the substrate moves, it is convenient to think about and describe operation as if the objective lens were brought to different locations relative to the substrate. Provided the relative positions of the substrate and optical system are correct, in principle it does not matter which of them, or both, or some combination of the optical system are moving (e.g. in Z and / or tilt directions), while the rest of the optical system remains stationary and the substrate is moving (e.g. in X and Y directions, but optionally also in Z and / or tilt directions).

[0063]

[0074] In a typical alignment measurement, the target (portion) 30 on the substrate W may be a 1D grating that is printed such that after development, the bars are formed of solid resist lines (which may be covered by a deposition layer, for example) and / or other material. Alternatively, the target 30 may be a 2D grating that is printed such that after development, the grating is formed of solid resist pillars and / or other features in the resist.

[0064]

[0075] The bars, pillars, vias, and / or other features may be etched into or on the substrate (e.g., in one or more layers on the substrate), deposited on the substrate, covered with a deposition layer, and / or have other properties. The target (portion) 30 (e.g., the bars, pillars, vias, etc.) is sensitive to processing variations in the patterning process (e.g., optical aberrations, focus changes, dose changes, etc., in the lithographic projection apparatus, e.g., in the projection system), such that process variations manifest themselves as variations in the target 30. Measurement data from the target 30 may therefore be used to determine adjustments to one or more of the manufacturing processes and / or used as a basis for making actual adjustments.

[0065]

[0076] For example, the measurement data from the target 30 may indicate an alignment for a layer of a semiconductor device. The measurement data from the target 30 may be used (e.g., by the one or more processors PRO and / or other processors) to determine one or more semiconductor device manufacturing process parameters based on the alignment, and to determine adjustments to the semiconductor device manufacturing apparatus based on the determined one or more semiconductor device manufacturing process parameters. In some embodiments, this may include, for example, stage position adjustments, or may include determining adjustments to the mask design, the metrology target (e.g., alignment mark) design, the semiconductor device design, the intensity of radiation, the angle of incidence of radiation, the wavelength of radiation, the pupil size and / or shape, the resist material, and / or other process parameters.

[0066]

[0077] Angle resolved scatterometry is useful in measuring the asymmetry of product features and / or resist patterns. A particular application of asymmetry measurement is for alignment measurements. The basic concept of asymmetry measurement using the system 10 of FIG. 3 is described, for example, in U.S. Patent Application Publication No. 2006-066855, which is incorporated herein in its entirety. Briefly, in alignment measurements, the positions of the diffraction orders in the diffraction spectrum of a target are determined by the periodicity of the target (e.g., alignment marks). The asymmetry of the diffraction spectrum indicates the asymmetry of the individual features that make up the target.

[0067]

[0078] FIG. 5 shows a plan view of a typical target (e.g., alignment mark) 30 and the extent of a typical emitted illumination spot S in the system of FIG. 4. Typically, to obtain a diffraction spectrum without interference from surrounding structures, in one embodiment, the target 30 is a periodic structure (e.g., grating) that is larger than the width (e.g., diameter) of the illumination spot S. The width of the spot S may be smaller than the width and length of the target. The target is in other words "underfilled" by the illumination, and the diffraction signal essentially does not include any signal from product features outside the target itself, etc. The illuminator may be configured to provide a uniform intensity illumination across, for example, the back focal plane of the objective lens. Alternatively, the illumination may be limited in the on-axis or off-axis direction, for example, by including an aperture in the illumination path.

[0068]

[0079] FIG. 6 illustrates a system 600 configured to generate an illumination spot configured to be directed toward a target. The illumination may include light and / or other radiation. The target may include, for example, one or more metrology marks. The system 600 may form part of the system 10 described above with respect to FIG. 3. The system 600 may be, for example, a subsystem of the system 10. In some embodiments, one or more components of the system 600 may be similar and / or the same as one or more components of the system 10. In some embodiments, one or more components of the system 600 may replace, be used in conjunction with, and / or augment one or more components of the system 10. The system 600 is configured to generate multiple illumination spots from a single illumination source (e.g., radiation source 2 shown in FIG. 3). The system 600 is also configured to reduce or eliminate ghost reflections common in other wafer alignment sensors, and / or has other advantages.

[0069]

[0080] FIG. 6 shows a system 600 for generating multiple measurement spots (e.g., as discussed below). The multiple spots are created by arranging parallel optical elements (in this example) with partially reflective and fully reflective spot mirrors in combination with a cube spot mirror. Additional optical paths are created at different angles in the collimated space, resulting in separate illumination spots on the substrate. The implementation shown in FIG. 6 generates two off-axis illumination spots in addition to the main on-axis spot. The additional illumination spots can be positioned along the axis of the substrate or in a two-dimensional pattern (also discussed below). The number of additional illumination spots is not limited to the three shown in the figure. Multiple optical elements can be used to generate the additional spots. These and other features of system 600 are described in more detail below.

[0070]

[0081] System 600 includes a first optical element 602, a second optical element 604, a third optical element 606, a fourth optical element 608, a lens 610, and / or other components. In some embodiments, the first, second, third, and fourth optical elements 602-608, the lens 610, and / or other components of system 600 form part of an alignment sensor used in a semiconductor manufacturing process. The alignment sensor may be, for example, a wafer alignment sensor used as described above. In some embodiments, system 600 may have other applications including, for example, any metrology system that requires multiple illumination spots on a target generated from a single illumination beam.

[0071]

[0082] In some embodiments, the first optical element 602, the second optical element 604, the third optical element 606, and / or the fourth optical element 608 each comprise a local reflective and / or transmissive surface. For example, the optical elements 602-608 may comprise a corresponding spot mirror 603, 605, 607, and / or 609, respectively. The spot mirrors comprise relatively small reflective and / or transmissive surfaces. For example, the spot mirrors may have a diameter slightly larger than or corresponding to the size of the illumination beam from the illumination source. The spot mirrors 603-609 may be formed by coated parts of the optical elements 602-608, devices inserted and / or coupled to the optical elements 602-608, other local reflective and / or transmissive surfaces, and / or other components. For example, the reflective spot mirrors may also be formed by local TIR (total internal reflection) areas. In some embodiments, the optical elements 602-608 comprise filters configured to control the wavelengths and / or other characteristics of the illumination reflected and / or transmitted by each optical element 602-608. The filters may comprise specific coatings and / or other components coupled to or included in one or more of the optical elements 602-608.

[0072]

[0083] In some embodiments, optical elements 602, 604, and / or 606 each include a corresponding optically transparent plate 620, 622, 624 coupled to and / or comprising a corresponding spot mirror 603, 605, or 607. Plates 620, 622, and / or 624 include an optically transparent material. Plates 620, 622, and / or 624 may be formed from any transparent material, such as glass, quartz, and / or other optically transparent materials. Plates 620, 622, and / or 624 may have a circular cross-sectional shape, a square cross-sectional shape, a rectangular cross-sectional shape, and / or other cross-sectional shapes. Plates 620, 622, and / or 624 may have a constant thickness and / or other characteristics. The shape and / or dimensions of plates 620, 622, and / or 624 may be determined by a user based on, for example, the material used for plates 620, 622, and / or 624, the application for which plates 620, 622, and / or 624 are used (e.g., alignment measurements), the optical behavior requirements of plates 620, 622, and / or 624, the handling and / or movement requirements of plates 620, 622, and / or 624, and / or other factors. It should be noted, however, that in some embodiments, plates 620-624 are optional and only spot mirrors 603-607 are included in system 600.

[0073]

[0084] In some embodiments, the first optical element 602 is or has a partially reflective portion (e.g., spot mirror 603), the second optical element 604 is or has an at least partially reflective portion (e.g., spot mirror 605), and the third optical element 606 is or has a fully reflective portion (e.g., spot mirror 607). A partially reflective portion may comprise a surface that reflects at least a portion of radiation incident on the surface and transmits another portion through the surface.

[0074]

[0085] For example, a first optical element 602 with a spot mirror 603 is configured to receive illumination 650 (e.g., directional radiation) from an illumination source (e.g., radiation source 2 shown in FIG. 3) along a first axis 651 at the spot mirror 603, reflect a first portion 652 of the illumination away from the first axis 651, and transmit a second portion 654 of the illumination 650 along the first axis 651. A second optical element 604 with a spot mirror 605 is configured to receive the reflected first portion 652 of the illumination and at least partially reflect a third portion 660 of the illumination along a second axis 662 that is at an angle different from the first axis 651. A third optical element 606 with a spot mirror 607 is configured to receive and fully reflect a fourth portion 670 of the illumination along a third axis 672 that is at an angle different from the first axis 651 and the second axis 662. A fourth portion 670 of the illumination is transmitted by the spot mirror 605 of the second optical element 604, as shown in FIG.

[0075]

[0086] The second portion 654, third portion 660, and fourth portion 670 of the illumination are directed (680) at different angles relative to one another in the pupil plane towards the target 30 to generate three different spots 690, 692, 694 of illumination 650 on the target 30. The target 30 may be, for example, one or more metrology marks on a semiconductor wafer as described herein.

[0076]

[0087] The fourth optical element 608 may comprise a spot mirror 609 and / or other reflective or at least partially reflective surface. In some embodiments, the fourth optical element 608 comprises a transmissive optical element. In some embodiments, the fourth optical element 608 comprises, for example, a spot mirror cube. A spot mirror cube may comprise two prisms joined by optical contact or adhesive (or other bonding mechanism) to form a cube or rhombus with a localized reflective area at the joined surface. The reflective area may be formed by a reflective coating or TIR, which is a portion of a surface that has an air pocket (or other optical material with a lower refractive index) behind it, causing light to reflect in an optical material with a higher refractive index. The spot mirror cube is configured to reflect light that is incident on the spot mirror (in the cube) to change its direction and transmit other light. The objective here is to change the direction of one selected beam to a different direction than the other beams passing through the optical element. A fourth optical element 608 having a spot mirror 609 is configured to reflect illumination received along the first axis 651, the second axis 662, and the third axis 672 in a column direction 680 substantially perpendicular to the first axis 651.

[0077]

[0088] As shown in FIG. 6, lens 610 is configured to receive illumination beam 685 formed by optical elements 602-608 and focus (687) spots 690, 692, and 694 of illumination 650 onto target 30. Lens 610 may include any type of lens configured to function as described. For example, lens 610 may be an objective lens. Lens 610 may be formed from any transparent material and may have a curved surface configured to focus or converge beam 685. In some embodiments, spot 690 of illumination 650 corresponding to illumination from first axis 651 comprises an on-axis spot, and spots 692 and 694 of illumination 650 corresponding to illumination from second and third axes 662 and 672 comprise off-axis spots. The off-axis spots (e.g., 692 and / or 694) are configured to reduce or eliminate ghost reflections and / or provide other benefits. Ghost reflections include unwanted reflections from one or more optical surfaces that are perpendicular to the illumination axis or direction in collimated space. Because the illumination that forms these spots is not perpendicularly incident on one or more surfaces of optical element 608 (e.g., cube surfaces) and / or other surfaces of optical elements in system 600, ghost reflections are reduced and / or eliminated.

[0078]

[0089] The optical elements 602-608 may be positioned at any position and / or angle relative to one another that enables the system 600 to function as described herein. This may include positioning at a particular relative distance between the elements, at a particular angle between the elements, etc. In some embodiments, two or more of the optical elements 602-608 are positioned parallel to one another in the system 600 (e.g., as shown in FIG. 6). In some embodiments, one or more of the optical elements 602-608 are positioned at an angle relative to one or more of the other optical elements in the system 600.

[0079]

[0090] In some embodiments, the optical elements 602-608 are positioned relative to one another in the system 600 via structural members, clips, clamps, screws, nuts, bolts, adhesives, and / or other mechanical devices. In some embodiments, the first optical element 602, the second optical element 604, the third optical element 606, and / or the fourth optical element 608 can move relative to one another. Movement of the first optical element 602, the second optical element 604, and / or the third optical element 606 is configured to adjust the position of the corresponding illumination spots 690-694 on the target 30. In some embodiments, the movement includes, for example, tilting the first optical element 602, the second optical element 604, and / or the third optical element 606. In some embodiments, the movement includes translating or changing the distance between one or more of the first optical element 602, the second optical element 604, the third optical element 606, and / or the fourth optical element 608. Other examples of movement are also contemplated.

[0080]

[0091] In other words, spot 690 of illumination 650 corresponding to illumination from first axis 651 comprises an on-axis spot, and spots 692 and 694 of illumination 650 corresponding to illumination from second axis 662 and third axis 672, respectively, comprise off-axis spots. On-axis spot 690 and off-axis spots 692 and / or 694 are movable relative to one another. Spots 690-694 of illumination 650 directed at target 30 are configured to be moved relative to one another based on movement of the first, second, third, and / or fourth optical elements (e.g., elements 602-608).

[0081]

[0092] In some embodiments, the movement of the optical elements 602-608 may be electronically controlled by a processor such as the processor PRO shown in FIG. 3 (and also shown in FIG. 9 discussed below). The processor PRO may be included in a computing system CS (FIG. 9) and may operate based on computer or machine-readable instructions MRI (e.g., as described below in connection with FIG. 9). Electronic communication may be by conveying electronic signals between individual components, transmitting data between individual components of the system 600, conveying values ​​between individual components, and / or other communication. The components of the system 600 may communicate by wire or wirelessly over a network such as the Internet or the Internet in combination with various other networks such as a local area network, a cellular network, or a personal area network, an internal organizational network, and / or other networks.

[0082]

[0093] In some embodiments, one or more actuators (not shown in FIG. 6) may be coupled to one or more of the optical elements 602-608 and configured to move one or more of the optical elements 602-608. The actuators may be coupled to one or more edges of the one or more optical elements 602-608 by adhesives, clips, clamps, screws, collars, and / or other mechanisms. The actuators may be configured to be electronically controlled. An individual actuator may be configured to convert an electrical signal into a mechanical displacement. The mechanical displacement is configured to move the optical elements 602-608. As an example, one or more of the actuators may be piezoelectric. One or more processors PRO may be configured to control the actuators. The one or more processors PRO may be configured to individually control each of the one or more actuators.

[0083]

[0094] FIG. 7 illustrates various different illumination spot arrays 702, 704, 706, and 708. In some embodiments, for example in arrays 702 and 704, illumination spots 710, 712, and 714 are aligned in a line. In some embodiments, for example in arrays 706 and 708, illumination spots 710, 712, and 714 are arranged in a two-dimensional pattern. In FIG. 7, spot 710 comprises an on-axis spot, and spots 712 and 714 comprise off-axis spots. Array 702 illustrates how spots 712 and 714 can both be located in a line on one side of spot 710. Array 704 illustrates how spots 712 and 714 can both be located in a line with spot 710, but spot 714 is on one side of spot 710 and spot 712 is on the other side of spot 710. It should be noted that while arrays 702 and 704 show spots 710-714 positioned along the x-axis as shown, this could easily be changed so that spots 710-714 are positioned along the y-axis or along some other axis. Array 704 could also be inverted so that spots 712 and 714 are positioned on opposite sides of spot 710. Array 706 shows how spots 710-714 could be arranged in a two-dimensional pattern, in this example perpendicular to one another. Array 708 shows another possible two-dimensional pattern that could be formed by spots 710-714. Other examples are contemplated.

[0084]

[0095] The number of optical elements shown in FIG. 6 and illumination spots shown in FIG. 7 are not intended to be limiting. The principles described herein may be extended in some embodiments such that system 600 includes additional optical elements configured to receive reflected illumination transmitted by the previous optical elements and to at least partially reflect the received illumination along additional axes to generate additional illumination spots directed toward a target. FIG. 6 also illustrates various diffraction orders 675 for phase intensity measurements. A similar arrangement of components similar and / or the same as those described above (e.g., components of system 600) may be formed for a detection axis of a metrology system (e.g., system 10 shown in FIG. 3). The components may be configured such that the detection axis radiation is split by multiple optical elements.

[0085]

[0096] 8 illustrates a method 800 for generating an illumination spot configured to be directed at a target. In some embodiments, method 800 is performed as part of an alignment sensing operation, for example, in a semiconductor device manufacturing process. In some embodiments, one or more operations of method 800 may be performed in or by, for example, system 600 shown in FIG. 6 and / or system 10 shown in FIG. 3, a computer system (e.g., shown in FIG. 9 and described below), and / or in or by other systems. In some embodiments, the method 800 includes receiving illumination from an illumination source along a first axis with a first optical element (OPERATION 802), reflecting a first portion of the illumination away from the first axis and transmitting a second portion of the illumination along the first axis, receiving the reflected first portion of the illumination with a second optical element (OPERATION 804), and at least partially reflecting a third portion of the illumination along a second axis at an angle different from the first axis, receiving and completely reflecting a fourth portion of the illumination transmitted by the second optical element along a third axis at an angle different from the first axis and the second axis with a third optical element (OPERATION 806), reflecting the illumination received along the first axis, the second axis, and the third axis in a column direction substantially perpendicular to the first axis with a fourth optical element (OPERATION 808), and receiving the illumination beam formed by the optical element with a lens (OPERATION 810) and focusing the illumination spot on the target. The second, third, and fourth portions of the illumination are directed toward the target at different angles relative to one another in the pupil plane to generate three different illumination spots on the target.

[0086]

[0097] The operations of method 800 are intended to be illustrative. In some embodiments, method 800 may be accomplished with one or more additional operations not described and / or without one or more operations discussed. For example, in some embodiments, method 800 may include additional operations including determining adjustments to a semiconductor device manufacturing process. Additionally, the order in which the operations of method 800 are illustrated in FIG. 8 and described herein is not intended to be limiting.

[0087]

[0098] In some embodiments, one or more portions of method 800 may be implemented and / or controlled by one or more processing devices (e.g., digital processors, analog processors, digital circuits designed for processing information, analog circuits designed for processing information, state machines, and / or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices that perform some or all of the operations of method 800 in response to instructions that are electronically stored on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and / or software to be specifically designed to perform one or more of the operations of method 800 (e.g., see the discussion of FIG. 9 below).

[0088]

[0099] In operation 802, a first optical element receives illumination from an illumination source along a first axis. The first optical element reflects a first portion of the illumination away from the first axis and transmits a second portion of the illumination along the first axis. In some embodiments, the first optical element is the same as or similar to element 602 shown in FIG. 6 and described above. In some embodiments, operation 802 includes providing an illumination source (e.g., radiation source 2 shown in FIG. 3). The illumination source includes a single radiation source configured to generate illumination along the first axis.

[0089]

[0100] In operation 804, a second optical element receives a first portion of the reflected illumination and at least partially reflects a third portion of the illumination along a second axis that is at a different angle from the first axis. In some embodiments, the second optical element is the same as or similar to element 604 shown in FIG. 6 and described above.

[0090]

[0101] In operation 806, a third optical element receives and completely reflects a fourth portion of the illumination along a third axis that is at a different angle than the first axis and the second axis. The fourth portion of the illumination is transmitted by the second optical element. In some embodiments, the third optical element is the same as or similar to element 606 shown in FIG. 6 and described above.

[0091]

[0102] In some embodiments, the first optical element, the second optical element, and the third optical element each comprise a spot mirror, hi some embodiments, the first optical element is partially reflective, the second optical element is at least partially reflective, and the third optical element is fully reflective.

[0092]

[0103] At operation 808, a fourth optical element reflects the illumination received along the first axis, the second axis, and the third axis in a column direction substantially perpendicular to the first axis. In some embodiments, the fourth optical element comprises a spot mirror cube. In some embodiments, the fourth optical element is the same as or similar to element 608 shown in FIG. 6 and described above.

[0093]

[0104] In operation 810, a lens receives the illumination beam formed by the optical element and focuses the illumination spot onto the target. In some embodiments, the lens is the same as or similar to lens 610 shown in FIG. 6 and described above. The second, third, and fourth portions of the illumination are directed to the target at different angles relative to each other in the pupil plane to generate three different illumination spots on the target. The illumination spots corresponding to the illumination from the first axis include on-axis spots, and the illumination spots corresponding to the illumination from the second and third axes include off-axis spots. The off-axis spots are configured to reduce or eliminate ghost reflections.

[0094]

[0105] In some embodiments, the illumination spots are aligned in a line, hi some embodiments, the illumination spots are arranged in a two-dimensional pattern.

[0095]

[0106] In some embodiments, the first optical element, the second optical element, and the third optical element are movable relative to each other. The movement of the first optical element, the second optical element, and / or the third optical element is configured to adjust the position of the corresponding illumination spot on the target. In some embodiments, the movement includes tilting the first optical element, the second optical element, and / or the third optical element, and / or changing the distance between one or more of the first optical element, the second optical element, and the third optical element. In some embodiments, the illumination spot corresponding to the illumination from the first axis comprises an on-axis spot, and the illumination spot corresponding to the illumination from the second and third axes comprises an off-axis spot. The on-axis spot and the off-axis spot are movable relative to each other. The illumination spots directed at the target are configured to be moved relative to each other based on the movement of the first, second, third, and / or fourth optical elements.

[0096]

[0107] In some embodiments, the method 800 includes illuminating (and / or irradiating) a target in a patterned substrate (e.g., target 30 shown in Figures 3 and 6) with radiation. The radiation includes light and / or other radiation that is separated into illumination spots as described above. The target may include one or more structures in the patterned substrate that can provide a diffraction signal. The target may be included in a layer of the substrate, for example, in a semiconductor device structure. In some embodiments, the features include geometric features, such as 1D or 2D features, and / or other geometric features. As some non-limiting examples, the features may include gratings, lines, edges, a series of fine pitch lines and / or edges, and / or other features.

[0097]

[0108] The radiation may have a target wavelength and / or wavelength range, a target intensity, and / or other characteristics. The target wavelength and / or wavelength range, target intensity, etc. may be input and / or selected by a user, determined by a system (e.g., system 10 shown in FIG. 3) based on previous alignment measurements, and / or otherwise determined. In some embodiments, the radiation includes light and / or other radiation. In some embodiments, the light includes visible light, infrared light, near infrared light, and / or other light. In some embodiments, the radiation may be any radiation suitable for interferometry.

[0098]

[0109] The radiation may be generated by a radiation source (e.g., radiation source 2 shown in FIG. 3 and described above). In some embodiments, the radiation may be directed by the radiation source onto a target, a sub-portion of the target (e.g., less than the entire target), multiple targets, and / or otherwise onto a substrate. In some embodiments, the radiation may be directed by the radiation source onto the target in a time-varying manner. For example, the radiation may be rastered across the target (e.g., by moving the target under the radiation) such that different portions of the target are illuminated at different times. As another example, the characteristics of the radiation (e.g., wavelength, intensity, etc.) may be varied. This may create a time-varying data envelope, or window, for analysis. The data envelope may facilitate analysis of individual sub-portions of the target, comparison of one portion of the target to another portion and / or other targets, and / or other analysis.

[0099]

[0110] In some embodiments, the method 800 includes detecting reflected radiation from the target. Detecting the reflected radiation includes detecting one or more phase and / or amplitude (intensity) shifts of the reflected radiation from one or more geometric features of the target. The one or more phase and / or amplitude shifts correspond to one or more dimensions of the target. For example, the phase and / or amplitude of the reflected radiation from one side of the target is different relative to the phase and / or amplitude of the reflected radiation from another side of the target.

[0100]

[0111] Detecting one or more phase and / or amplitude (intensity) shifts of the reflected radiation from the target includes measuring local phase shifts (e.g., local phase delta) and / or amplitude variations corresponding to different portions of the target. For example, reflected radiation from a particular area of ​​the target may include a sinusoidal waveform having a particular phase and / or amplitude. Reflected radiation from a different area of ​​the target (or a target in a different layer) may also include a sinusoidal waveform, but with a different phase and / or amplitude. Detecting the reflected radiation also includes measuring the phase and / or amplitude differences of the reflected radiation of different diffraction orders. Detecting one or more local phase and / or amplitude shifts may be performed using, for example, the Hilbert transform and / or other techniques. Interferometry and / or other operations may be used to measure the phase and / or amplitude differences of the reflected radiation of different diffraction orders.

[0101]

[0112] In some embodiments, the method 800 includes generating a metrology signal based on the detected reflected radiation from the target. The metrology signal is generated by a sensor (such as detector 4 of FIG. 3, a camera, and / or other sensor) based on light received by the sensor. The metrology signal includes measurement information about the target. For example, the metrology signal may be an alignment signal including alignment measurement information and / or other metrology signals. The measurement information (e.g., alignment values ​​and / or other information) may be determined using principles of interferometry and / or other principles.

[0102]

[0113] The metrology signal includes an electronic signal representative of and / or corresponding to the radiation reflected from the target. The metrology signal may be indicative of, for example, an alignment value associated with the target, and / or other information. Generating the metrology signal includes sensing the reflected radiation and converting the sensed reflected radiation into an electronic signal. In some embodiments, generating the metrology signal includes sensing different portions of the reflected radiation from different areas and / or different geometric shapes of the target and / or multiple targets, and combining the different portions of the reflected radiation to form the metrology signal. This sensing and conversion may be performed by similar and / or the same components as the detector 4 and / or processor PRO shown in FIG. 3, and / or other components.

[0103]

[0114] In some embodiments, the method 800 includes determining an adjustment to a semiconductor device manufacturing process. In some embodiments, the method 800 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on one or more detected phase and / or amplitude variations, alignment values ​​indicated by metrology signals, and / or other like systems, and / or other information. The one or more parameters may include a parameter of the radiation (radiation used to determine the alignment), an alignment value, an alignment inspection position on a layer of a semiconductor device structure, a trajectory of a radiation beam across a target, and / or other parameters. In some embodiments, the process parameters may be broadly interpreted to include a stage position, a mask design, a metrology target design, a semiconductor device design, an intensity of radiation (e.g., used to expose a resist), an angle of incidence of radiation (e.g., used to expose a resist), a wavelength of radiation (e.g., used to expose a resist), a pupil size and / or shape, a resist material, and / or other parameters.

[0104]

[0115] In some embodiments, method 800 includes determining process adjustments based on the one or more determined semiconductor device manufacturing process parameters, adjusting semiconductor device manufacturing equipment based on the determined adjustments, and / or other operations. For example, if the determined alignment is not within process tolerances, one or more manufacturing processes may cause out-of-tolerance alignment, and process parameters of one or more manufacturing processes may have drifted and / or changed such that the process no longer produces acceptable devices (e.g., alignment measurements may exceed a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the alignment determination. The new or adjusted process parameters may be configured to cause the manufacturing process to again produce acceptable devices.

[0105]

[0116] For example, new or adjusted process parameters may adjust previously unacceptable alignment values ​​back to within tolerance. The new or adjusted process parameters may be compared to existing parameters for a given process. If there is a difference, the difference may be used, for example, to determine an adjustment to an apparatus used to manufacture the device (e.g., parameter "x" needs to be increased / decreased / changed to match the new or adjusted version of parameter "x" determined as part of method 800). In some embodiments, method 800 may include electronically adjusting the apparatus (e.g., based on the determined process parameters). Electronically adjusting the apparatus may include, for example, sending an electronic signal and / or other communication to the apparatus that causes a change in the apparatus. The electronic adjustment may include, for example, changing settings on the apparatus and / or other adjustments.

[0106]

[0117] 9 is a diagram of an exemplary computer system CS that may be used for one or more of the operations described herein. The computer system CS comprises a bus BS or other communication mechanism for communicating information, and a processor PRO (or a plurality of processors similar or the same as the processor PRO shown in FIG. 3) coupled to the bus BS for processing information. The computer system CS also comprises a main memory MM, such as a random access memory (RAM) or other dynamic storage device, for storing information and instructions executed by the processor PRO coupled to the bus BS. The main memory MM may also be used to store temporary variables or other intermediate information during execution of instructions by the processor PRO. The computer system CS further comprises a read-only memory (ROM) ROM or other static storage device for storing static information and instructions for the processor PRO coupled to the bus BS. A storage device SD, such as a magnetic or optical disk, for storing information and instructions is provided and coupled to the bus BS.

[0107]

[0118] The computer system CS may be coupled via a bus BS to a display DS, such as a cathode ray tube (CRT) or flat panel or touch panel display, for displaying information to a computer user. Input devices ID, including alphanumeric and other keys, are coupled to the bus BS for communicating information and command selections to the processor PRO. Another type of user input device is a cursor control CC, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor PRO and for controlling cursor movement on the display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), allowing the device to be located in a plane. Touch panel (screen) displays may also be used as input devices.

[0108]

[0119] In some embodiments, all or part of one or more operations described herein may be performed by the computer system CS in response to the processor PRO executing one or more sequences of one or more instructions contained in the main memory MM. Such instructions may be read into the main memory MM from another computer-readable medium, such as a storage device SD. Execution of the sequences of instructions contained in the main memory MM causes the processor PRO to perform the process steps (operations) described herein. One or more processors of a multiprocessing device may also be used to execute the sequences of instructions contained in the main memory MM. In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0109]

[0120] The term "computer-readable medium" or "machine-readable medium" as used herein refers to any medium that participates in providing instructions to a processor PRO for execution. Such media may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as a storage device SD. Volatile media include dynamic memory, such as a main memory MM. Transmission media include coaxial cables, copper wires, and optical fibers (including the wires that comprise the bus BS). Transmission media may also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. The computer-readable medium may be a non-transitory computer-readable medium, such as a floppy disk, a flexible disk, a hard disk, a magnetic tape, any other magnetic medium, a CD-ROM, a DVD, any other optical medium, a punch card, a paper tape, any other physical medium with a pattern of holes, a RAM, a PROM, and an EPROM, a FLASH-EPROM, any other memory chip or cartridge. The non-transitory computer-readable medium may record instructions. The instructions, when executed by a computer, can perform any of the operations described herein. The transitory computer-readable medium may include, for example, a carrier wave or other propagating electromagnetic signal.

[0110]

[0121] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to the processor PRO for execution. For example, the instructions may initially reside on a magnetic disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to the computer system CS may receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to the bus BS may receive the data carried in the infrared signal and place the data on the bus BS. The bus BS carries the data to the main memory MM, from which the processor PRO retrieves and executes the instructions. The instructions received by the main memory MM may optionally be stored in a storage device SD before or after execution by the processor PRO.

[0111]

[0122] The computer system CS may also comprise a communication interface CI coupled to a bus BS. The communication interface CI provides a two-way data communication coupling to a network link NDL, which is connected to a local network LAN. For example, the communication interface CI may be an Integrated Services Digital Network (ISDN) card or a modem providing a data communication connection to a corresponding telephone line type. As another example, the communication interface CI may be a Local Area Network (LAN) card providing a data communication connection to a compatible LAN. A wireless link may also be implemented. In such implementations, the communication interface CI transmits and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0112]

[0123] The network link NDL typically provides data communication through one or more networks to other data devices. For example, the network link NDL may provide a connection to a host computer HC through a local network LAN. This may include data communication services provided through a World Wide Packet Data Communication Network (now commonly referred to as the "Internet" INT). The local network LAN (Internet) may use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks as well as the signals on the network data link NDL and through the communication interface CI that carry digital data to the computer system CS are exemplary forms of carrier waves transporting information.

[0113]

[0124] The computer system CS can send messages and receive data including program code through the network, the network data link NDL, and the communication interface CI. In the Internet example, the host computer HC may send a request code of an application program through the Internet INT, the network data link NDL, the local network LAN, and the communication interface CI. One such downloaded application may provide, for example, all or part of the methods described herein. The received code may be executed by the processor PRO when received and / or stored in the storage device SD or other non-volatile storage for later execution. The computer system CS may thus obtain the application code in the form of a carrier wave.

[0114]

[0125] Figure 10 shows a schematic diagram of an exemplary lithographic projection apparatus similar and / or the same as the apparatus shown in Figure 1 that may be used in conjunction with the techniques described herein. The apparatus 1000 comprises an illumination system IL for conditioning a radiation beam B. In this particular case, the illumination system also comprises a radiation source SO, a first object table (e.g., patterning device table) MT provided with a patterning device holder for holding a patterning device MA (e.g., a reticle) and connected to a first positioner PM (working in conjunction with a first position sensor PS1) for accurately positioning the patterning device, a second object table (substrate table) WT provided with a substrate holder for holding a substrate W (e.g., a resist-coated silicon wafer) and connected to a second positioner PW (working in conjunction with a second position sensor PS2) for accurately positioning the substrate, and a projection system ("lens") PS (e.g., a refractive, reflective or catadioptric optical system) for imaging an illuminated portion of the patterning device MA onto a target portion C of the substrate W (e.g., comprising one or more dies).

[0115]

[0126] As depicted herein, the apparatus is of a transmissive type (i.e. has a transmissive patterning device). In general, however, the apparatus may be of a reflective type (e.g. has a reflective patterning device). The apparatus may employ other types of patterning device than a conventional mask; examples include a programmable mirror array or an LCD matrix.

[0116]

[0127] A radiation source SO (e.g. a mercury lamp or excimer laser, LPP (Laser Produced Plasma) EUV source) produces a beam of radiation. This beam is fed into an illumination system (illuminator) IL, either directly or after having traversed conditioning means, such as a beam expander Ex. The illuminator IL may comprise conditioning means for setting the outer and / or inner extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution of the beam. The illuminator IL will generally also comprise various other components, such as an integrator and a condenser. In this way, the beam B impinging on the patterning device MA has a desired uniformity and intensity distribution in its cross-section.

[0117]

[0128] It should be noted with regard to Figure 10 that the source SO can be within the housing of the lithographic projection apparatus (as is the case when the source SO is, for example, a mercury lamp), but it may also be remote from the lithographic projection apparatus and the radiation beam it generates can be directed into the apparatus (for example by means of suitable directing mirrors), this latter scenario being typical when the source SO is an excimer laser (for example based on KrF, ArF or F2 lasing).

[0118]

[0129] The beam B is then intercepted by the patterning device MA, which is held on a patterning device table MT. After traversing the patterning device MA, the beam B passes through a lens, which focuses the beam B onto a target portion C of the substrate W. Using the second positioning means (and interferometry means), the substrate table WT can be accurately moved to, for example, position different target portions C in the path of the beam B. Similarly, the first positioning means may be used to accurately position the patterning device MA with respect to the path of the beam B, for example after mechanical retrieval of the patterning device MA from a patterning device library or during a scan. Typically, movement of the object tables MT, WT will be realized with the aid of not explicitly stated long-stroke modules (coarse positioning) and short-stroke modules (fine positioning). However, in the case of a stepper (as opposed to a step-and-scan tool) the patterning device table MT may simply be connected to a short-stroke actuator, or may be fixed.

[0119]

[0130] The depicted tool (similar or the same as that shown in FIG. 1 ) can be used in two different modes. In step mode, the patterning device table MT is kept essentially stationary and the entire patterning device image is projected onto the target portion C in one movement (i.e. in a single "flash"). The substrate table WT is then shifted in the x and / or y direction so that a different target portion C can be irradiated with the beam B. In scan mode, essentially the same scenario applies, but a given target portion C is not exposed in a single "flash". Instead, the patterning device table MT is movable in a given direction (the so-called "scan direction", e.g. the y direction) with a speed v, such that the projection beam B scans the patterning device image while the substrate table WT is simultaneously moved in the same or opposite direction with a speed V=Mv, in which M is the magnification of the lens PL (typically M=¼ or ⅕). In this way, a relatively large target portion C can be exposed, without having to compromise on resolution.

[0120]

[0131] FIG. 11 shows the apparatus 1000 with the source collector module SO, the illumination system IL and the projection system PS in more detail. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained within the closed structure 220 of the source collector module SO. The EUV radiation emitting plasma 210 may be formed by a discharge produced plasma source. The EUV radiation may be generated by a gas or vapor, for example Xe gas, Li vapor or Sn vapor, in which a high temperature plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The plasma 210 is for example created by an electric discharge that produces an at least partially ionized plasma. For example, a partial pressure of 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required for efficient generation of radiation. In an embodiment, a plasma of excited tin (Sn) is provided to generate the EUV radiation.

[0121]

[0132] Radiation emitted by the plasma 210 passes from the source chamber 211 into the collector chamber 212 via an optional gas barrier or contamination trap 230 (sometimes called a contamination barrier or foil trap) located in or behind the opening of the source chamber 211. The contamination trap 230 may comprise a channel structure. The contamination trap 230 may also comprise a gas barrier or a combination of a gas barrier and a channel structure. The contamination trap 230 as further illustrated herein comprises at least a channel structure.

[0122]

[0133] The source chamber 211 may comprise a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected off a grating spectral filter 240 and focused to a virtual source point IF along an optical axis indicated by line "O". The virtual source point IF is commonly referred to as an intermediate focus, and the source collector module is configured such that the intermediate focus IF is located at or near the opening 221 of the enclosure structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

[0123]

[0134] The radiation subsequently traverses an illumination system IL, which may comprise a faceted field mirror device 22 and a facetted pupil mirror device 24 configured to provide a desired angular distribution of the radiation beam 21 at the patterning device MA, and a desired uniformity of the radiation intensity at the patterning device MA. Upon reflection of the radiation beam 21 off the patterning device MA, held by a support structure MT, a patterned beam 26 is formed, which is imaged by the projection system PS via reflective elements 28, 330 onto a substrate W held by a substrate table WT.

[0124]

[0135] Generally, more elements than shown may be present in the illumination optics unit IL and projection system PS. A grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Further, there may be more mirrors than shown, for example 1-6 additional reflective elements may be present in the projection system PS than shown in Figure 11.

[0125]

[0136] 11 is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255 as just one example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically about the optical axis O, and this type of collector optic CO is sometimes used in combination with a discharge produced plasma source, often referred to as a DPP source.

[0126]

[0137] Alternatively, the source collector module SO may be part of an LPP radiation system as shown in Fig. 12. A laser LA is configured to impart laser energy to a fuel such as xenon (Xe), tin (Sn) or lithium (Li) to generate a highly ionized plasma 210 with an electron temperature of tens of eV. Energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma and collected by a near-normal incidence collector system CO and focused into an opening 221 in a confining structure 220.

[0127]

[0138] The embodiments may be further described using the following clauses. 1. A system for generating an illumination spot configured to be directed toward a target, the system comprising: a first optical element configured to receive illumination from an illumination source along a first axis, reflect a first portion of the illumination away from the first axis, and transmit a second portion of the illumination along the first axis; and a second optical element configured to receive the reflected first portion of the illumination and at least partially reflect a third portion of the illumination along a second axis that is at a different angle from the first axis, wherein the second and third portions of the illumination are directed toward the target at an angle relative to each other in a pupil plane to generate two distinct illumination spots on the target. 2. The system of clause 1, further comprising a third optical element configured to receive and completely reflect a fourth portion of the illumination transmitted by the second optical element along a third axis that is angled differently from the first axis and the second axis, and wherein the second portion, the third portion, and the fourth portion of the illumination are directed toward the target at different angles relative to one another in the pupil plane to generate three distinct illumination spots on the target. 3. The system of clause 1 or 2, wherein the illumination spot corresponding to illumination from the first axis includes an on-axis spot, and the illumination spots corresponding to illumination from the second axis and the third axis include off-axis spots. 4. The system of any one of clauses 1 to 3, wherein the off-axis spot is configured to reduce or eliminate ghost reflections. 5. The system of any one of clauses 1 to 4, wherein the first optical element, the second optical element and the third optical element are movable relative to each other. 6. The system of any one of clauses 1 to 5, wherein movement of the first optical element, the second optical element, and / or the third optical element is configured to adjust a position of a corresponding illumination spot on the target. 7. The system of any one of clauses 1 to 6, wherein the movement includes tilting the first optical element, the second optical element, and / or the third optical element, and / or changing a distance between one or more of the first optical element, the second optical element, and the third optical element. 8. The system of any one of clauses 1 to 7, wherein the first optical element, the second optical element, and the third optical element each comprise a spot mirror. 9. The system of any one of clauses 1 to 8, wherein the first optical element is partially reflective, the second optical element is at least partially reflective, and the third optical element is fully reflective. 10. The system of any one of clauses 1 to 9, further comprising a fourth optical element. 11. The system of any one of clauses 1 to 10, wherein the fourth optical element is configured to reflect illumination received along the first axis in a column direction substantially perpendicular to the first axis. 12. The system of any one of clauses 1 to 11, wherein the fourth optical element comprises a spot mirror cube. 13. The system of any one of clauses 1 to 12, wherein the illumination spots corresponding to illumination from a first axis include on-axis spots, and the illumination spots corresponding to illumination from a second axis and a third axis include off-axis spots, and the on-axis spots and off-axis spots are movable relative to each other. 14. The system of any one of clauses 1 to 13, wherein the illumination spots directed at the target are configured to be moved relative to one another based on movement of the first, second, third and / or fourth optical elements. 15. A system according to any one of clauses 1 to 14, wherein the illumination spots are aligned in a line. 16. The system of any one of clauses 1 to 15, wherein the illumination spots are arranged in a two-dimensional pattern. 17. The system of any one of clauses 1 to 16, further comprising an illumination source including a single radiation source configured to generate illumination along a first axis. 18. The system of any one of clauses 1 to 17, further comprising a lens configured to receive the illumination beam formed by the optical element and focus the illumination spot on a target. 19. The system of any one of clauses 1 to 18, wherein the first, second, third and fourth optical elements form part of an alignment sensor, and the alignment sensor is a wafer alignment sensor used in a semiconductor manufacturing process. 20. The system of any one of clauses 1 to 19, further comprising an additional optical element configured to receive reflected illumination transmitted by the previous optical element and configured to at least partially reflect the received illumination along an additional axis to generate an additional illumination spot directed towards the target. 21. A method for generating an illumination spot configured to be directed toward a target, the method including: receiving illumination from an illumination source along a first axis with a first optical element, reflecting a first portion of the illumination away from the first axis, and transmitting a second portion of the illumination along the first axis, and receiving the reflected first portion of the illumination with a second optical element and at least partially reflecting a third portion of the illumination along a second axis that differs in angle from the first axis, wherein the second and third portions of the illumination are directed toward the target at an angle relative to each other in a pupil plane to generate two distinct illumination spots on the target. 22. The method of clause 21, further comprising receiving and totally reflecting, using a third optical element, a fourth portion of the illumination transmitted by the second optical element along a third axis that is angularly distinct from the first axis and the second axis, wherein the second portion, the third portion, and the fourth portion of the illumination are directed toward the target at different angles relative to one another in the pupil plane to generate three distinct illumination spots on the target. 23. The method of clause 21 or 22, wherein the illumination spots corresponding to illumination from the first axis include on-axis spots, and the illumination spots corresponding to illumination from the second axis and the third axis include off-axis spots. 24. The method of any one of clauses 21 to 23, wherein the off-axis spot is configured to reduce or eliminate ghost reflections. 25. The method of any one of clauses 21 to 24, wherein the first optical element, the second optical element and the third optical element are movable relative to each other. 26. The method of any one of clauses 21 to 25, wherein movement of the first optical element, the second optical element, and / or the third optical element is configured to adjust a position of a corresponding illumination spot on the target. 27. The method of any one of clauses 21 to 26, wherein the movement includes tilting the first optical element, the second optical element, and / or the third optical element, and / or changing a distance between one or more of the first optical element, the second optical element, and the third optical element. 28. The method of any one of clauses 21 to 27, wherein the first optical element, the second optical element, and the third optical element each comprise a spot mirror. 29. The method of any one of clauses 21 to 28, wherein the first optical element is partially reflective, the second optical element is at least partially reflective, and the third optical element is fully reflective. 30. The method of any one of clauses 21 to 29, further comprising providing a fourth optical element. 31. The method of any one of clauses 21 to 30, further comprising reflecting, with a fourth optical element, illumination received along the first axis in a column direction substantially perpendicular to the first axis. 32. The method of any one of clauses 21 to 31, wherein the fourth optical element comprises a spot mirror cube. 33. The method of any one of clauses 21 to 32, wherein the illumination spots corresponding to illumination from a first axis include on-axis spots, and the illumination spots corresponding to illumination from a second axis and a third axis include off-axis spots, and the on-axis spots and off-axis spots are movable relative to each other. 34. The method of any one of clauses 21 to 33, wherein the illumination spots directed at the target are configured to be moved relative to one another based on movement of the first, second, third and / or fourth optical elements. 35. The method of any one of clauses 21 to 34, wherein the illumination spots are aligned in a line. 36. The method of any one of clauses 21 to 35, wherein the illumination spots are arranged in a two-dimensional pattern. 37. The method of any one of clauses 21 to 36, further comprising providing an illumination source comprising a single radiation source configured to generate illumination along a first axis. 38. The method of any one of clauses 21 to 37, further comprising providing a lens configured to receive the illumination beam formed by the optical element and focus the illumination spot on the target. 39. The method of any one of clauses 21 to 38, wherein the first, second, third and fourth optical elements form part of an alignment sensor, and the alignment sensor is a wafer alignment sensor used in a semiconductor manufacturing process. 40. The method of any one of clauses 21 to 39, further comprising providing an additional optical element configured to receive reflected illumination transmitted by the previous optical element and configured to at least partially reflect the received illumination along an additional axis to generate an additional illumination spot directed towards the target. 41. A non-transitory computer readable medium having instructions that, when executed by a computer, cause operations including receiving, with a first optical element, illumination from an illumination source along a first axis, reflecting a first portion of the illumination away from the first axis, and transmitting a second portion of the illumination along the first axis, and receiving, with a second optical element, the reflected first portion of the illumination and at least partially reflecting a third portion of the illumination along a second axis that differs in angle from the first axis, such that the second and third portions of the illumination are directed toward a target at an angle relative to each other in a pupil plane to generate two distinct illumination spots on the target. 42. The medium of clause 41, wherein the operations further include receiving and totally reflecting, with a third optical element, a fourth portion of the illumination transmitted by the second optical element along a third axis that differs in angle from the first axis and the second axis, and the second portion, the third portion, and the fourth portion of the illumination are directed toward the target at different angles relative to one another in the pupil plane to generate three distinct illumination spots on the target. 43. The medium of clause 41 or 42, wherein the illumination spots corresponding to illumination from the first axis include on-axis spots, and the illumination spots corresponding to illumination from the second axis and the third axis include off-axis spots. 44. The medium of any one of clauses 41 to 43, wherein the off-axis spot is configured to reduce or eliminate ghost reflections. 45. The medium of any one of clauses 41 to 44, wherein the first optical element, the second optical element and the third optical element are movable relative to each other. 46. ​​The medium of any one of clauses 41 to 45, wherein movement of the first optical element, the second optical element, and / or the third optical element is configured to adjust the position of a corresponding illumination spot on the target. 47. The medium of any one of clauses 41 to 46, wherein the movement includes tilting the first optical element, the second optical element, and / or the third optical element, and / or changing a distance between one or more of the first optical element, the second optical element, and the third optical element. 48. The medium of any one of clauses 41 to 47, wherein the first optical element, the second optical element, and the third optical element each comprise a spot mirror. 49. The medium of any one of clauses 41 to 48, wherein the first optical element is partially reflective, the second optical element is at least partially reflective, and the third optical element is fully reflective. 50. The medium of any one of clauses 41 to 49, wherein the operation further includes controlling a fourth optical element. 51. The medium of any one of clauses 41 to 50, wherein the operations further include reflecting, with a fourth optical element, illumination received along the first axis in a column direction substantially perpendicular to the first axis. 52. The medium of any one of clauses 41 to 51, wherein the fourth optical element comprises a spot mirror cube. 53. The medium of any one of clauses 41 to 52, wherein the illumination spots corresponding to illumination from a first axis include on-axis spots, and the illumination spots corresponding to illumination from a second axis and a third axis include off-axis spots, and the on-axis spots and off-axis spots are movable relative to each other. 54. The medium of any one of clauses 41 to 53, wherein the illumination spots directed at the target are configured to be moved relative to one another based on movement of the first, second, third, and / or fourth optical elements. 55. The medium of any one of clauses 41 to 54, wherein the illumination spots are aligned in a line. 56. The medium of any one of clauses 41 to 55, wherein the illumination spots are arranged in a two-dimensional pattern. 57. The medium of any one of clauses 41 to 56, wherein the operations further include controlling an illumination source including a single radiation source configured to generate illumination along a first axis. 58. The medium of any one of clauses 41 to 57, wherein the operations further include controlling a lens configured to receive the illumination beam formed by the optical element and focus the illumination spot on the target. 59. The medium of any one of clauses 41 to 58, wherein the first, second, third and fourth optical elements form part of an alignment sensor, and the alignment sensor is a wafer alignment sensor used in a semiconductor manufacturing process. 60. The operations further include controlling an additional optical element configured to receive reflected illumination transmitted by the previous optical element and configured to at least partially reflect the received illumination along an additional axis to generate an additional illumination spot directed toward the target; A medium according to any one of clauses 41 to 59. 61. A system for generating an illumination spot configured to be directed at a target for a wafer alignment sensor used in a semiconductor manufacturing process, the system configured to generate multiple illumination spots from a single illumination source, the system configured to reduce or eliminate ghost reflections common to other wafer alignment sensors, the system comprising: a single illumination source; a first spot mirror included in a first glass plate configured to receive illumination from the single illumination source along a first axis, reflect a first portion of the illumination away from the first axis, and transmit a second portion of the illumination along the first axis; and a second spot mirror included in a second glass plate configured to receive illumination from the single illumination source along a first axis, reflect a first portion of the illumination away from the first axis, and transmit a second portion of the illumination along the first axis. a second spot mirror configured to receive a first portion of the reflected illumination and at least partially reflect a third portion of the illumination along a second axis different from the first axis; and a third spot mirror included in a third glass plate configured to receive and completely reflect a fourth portion of the illumination transmitted by the second spot mirror along a third axis, the third axis being at an angle different from the first axis and the second axis, wherein the second portion, the third portion, and the fourth portion of the illumination are directed toward the target at different angles relative to each other in a pupil plane to generate three distinct illumination spots on the target corresponding to the illumination on the first axis, the second axis, and the third axis. 62. The system of clause 61, wherein the first spot mirror is partially reflective, the second spot mirror is at least partially reflective, and the third spot mirror is fully reflective. 63. The system of clause 61 or 62, wherein the first glass plate, the second glass plate, and the third glass plate are movable relative to one another, and movement of the first glass plate, the second glass plate, and / or the third glass plate is configured to adjust positions of illumination spots on the target, and wherein the illumination spots corresponding to illumination along the first axis include on-axis spots, and the illumination spots corresponding to illumination along the second axis and the third axis include off-axis spots. 64. The system of any one of clauses 61 to 63, wherein a third spot mirror is configured to reflect illumination received along the first axis and the second axis in a column direction substantially perpendicular to the first axis. 65. The system of any one of clauses 61 to 64, further comprising a detection axis, the detection axis being configured to be split by a plurality of optical elements. 66. The system of any one of clauses 61 to 65, further comprising an additional optical element configured to receive reflected illumination transmitted by the previous optical element and configured to at least partially reflect the received illumination along an additional axis to generate an additional illumination spot directed towards the target.

[0128]

[0139] The concepts disclosed herein may be associated with any general imaging system for imaging sub-wavelength features, and may be particularly useful with new imaging techniques capable of producing ever-shorter wavelengths. New techniques already in use include EUV (Extreme Ultraviolet), DUV lithography capable of producing 193 nm wavelengths with ArF lasers, and even 157 nm wavelengths with Fluorine lasers. EUV lithography can also produce wavelengths in the range of 20-5 nm by using synchrotrons or by bombarding materials (either solids or plasmas) with high energy electrons to produce photons in this range.

[0129]

[0140] Although the concepts disclosed herein may be used for imaging onto substrates such as silicon wafers, it is to be understood that the disclosed concepts may be used with any type of lithographic imaging system, for example, those used for imaging onto substrates other than silicon wafers. Additionally, combinations and subcombinations of the disclosed elements may constitute separate embodiments.

[0130]

[0141] The above description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications can be made as described without departing from the scope of the claims set forth below.

Claims

1. 1. A system for generating an illumination spot configured to be directed at a target, the system comprising: a first optical element configured to receive illumination from an illumination source along a first axis, reflect a first portion of the illumination away from the first axis, and transmit a second portion of the illumination along the first axis; a second optical element configured to receive the first portion of the reflected illumination and to at least partially reflect a third portion of the illumination along a second axis that is at a different angle from the first axis; The system wherein the second and third portions of the illumination are directed toward the target at angles relative to one another in a pupil plane to generate two distinct illumination spots on the target.

2. a third optical element configured to receive and totally reflect a fourth portion of the illumination transmitted by the second optical element along a third axis that is angularly distinct from the first axis and the second axis; 2. The system of claim 1 , wherein the second portion, the third portion, and the fourth portion of the illumination are directed toward the target at different angles relative to one another in the pupil plane to generate three distinct illumination spots on the target.

3. 3. The system of claim 2, wherein the illumination spots corresponding to the illumination from the first axis include on-axis spots, and the illumination spots corresponding to the illumination from the second axis and the third axis include off-axis spots.

4. The system of claim 3 , wherein the off-axis spot is configured to reduce or eliminate ghost reflections.

5. The system of claim 2 , wherein the first optical element, the second optical element and the third optical element are movable relative to each other.

6. The system of claim 5 , wherein movement of the first optical element, the second optical element, and / or the third optical element is configured to adjust a position of a corresponding illumination spot on the target.

7. 7. The system of claim 5 or 6, wherein movement includes tilting the first optical element, the second optical element, and / or the third optical element, and / or changing a distance between one or more of the first optical element, the second optical element, and the third optical element.

8. The system of claim 1 , wherein the first optical element, the second optical element, and the third optical element each comprise a spot mirror.

9. The system of claim 8 , wherein the first optical element is partially reflective, the second optical element is at least partially reflective, and the third optical element is fully reflective.

10. The system of claim 1 , further comprising a fourth optical element.

11. The system of claim 10 , wherein the fourth optical element is configured to reflect the illumination received along the first axis in a column direction substantially perpendicular to the first axis.

12. The system of claim 10 or 11, wherein the fourth optical element comprises a spot mirror cube.

13. 13. The system of claim 2, wherein an illumination spot corresponding to the illumination from the first axis comprises an on-axis spot, and an illumination spot corresponding to the illumination from the second axis and the third axis comprises an off-axis spot, and the on-axis spot and the off-axis spot are movable relative to each other.

14. The system of claim 13 , configured such that the illumination spots directed at the target are moved relative to one another based on movement of the first, second, third, and / or fourth optical elements.

15. The system of claim 1 , wherein the illumination spots are aligned in a line.

16. The system of claim 1 , wherein the illumination spots are arranged in a two-dimensional pattern.

17. 17. The system of claim 1, further comprising the illumination source comprising a single radiation source configured to generate the illumination along the first axis.

18. 18. The system of claim 1, further comprising a lens configured to receive an illumination beam formed by the optical element and to focus the illumination spot on the target.

19. 19. The system of claim 10, wherein the first, second, third and fourth optical elements form part of an alignment sensor, the alignment sensor being a wafer alignment sensor used in a semiconductor manufacturing process.

20. 20. The system of claim 1, further comprising an additional optical element configured to receive reflected illumination transmitted by the previous optical element and configured to at least partially reflect the received illumination along an additional axis to generate an additional illumination spot directed towards the target.

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