WO2024146741A1

WO2024146741A1 - Improved dynamics geometry for one dimensional leaf spring guiding

Info

Publication number: WO2024146741A1
Application number: PCT/EP2023/084798
Authority: WO
Inventors: Perry SCHEIN; Apoorv GARG; Nicholas Christian SMITH; Jin-Won Lee; Christopher William REED
Original assignee: Asml Netherlands B.V.
Priority date: 2023-01-05
Filing date: 2023-12-07
Publication date: 2024-07-11

Abstract

Embodiments described herein include a guiding stage and a lithographic system configured to measure a position of an objective on the guiding stage by controlling the position of the objective. The guiding stage can comprise a flexure that reduces stiffness of the guiding stage in the z-axis when the objective is positioned to improve overall focus accuracy of the objective. A flexure guiding mechanism may be used to position the objective for making an overlay measurement.

Description

IMPROVED DYNAMICS GEOMETRY FOR ONE DIMENSIONAL LEAF SPRING GUIDING

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of US application 63/437,293 which was filed on 05 January 2023 and which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] This disclosure is generally directed to a lithographic system configured to measure a position of an objective on a guiding stage by controlling the position of the objective. The guiding stage can comprise a flexure that reduces stiffness of the guiding stage in the z-axis when the objective is positioned.

BACKGROUND

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

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

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

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

[0007] A lithographic system can have a performance issues due to the motion of a guiding stage. The motion can cause focus control issues, which affects the beam.

SUMMARY

[0008] A lithographic system is configured to measure a position of an objective on a guiding stage, wherein the guiding stage can comprise a flexure arrangement that reduces stiffness of the guiding stage in the z-axis when the objective is positioned. A flexure guiding mechanism may be used to position the objective for making an overlay measurement.

[0009] In some embodiments, a guiding stage is provided. An objective can be disposed on the guiding stage. The objective can include optics configured to focus a beam. A plurality of Lorentz motors can be disposed on the guiding stage and be configured to position the objective. A magnet assembly can include at least two magnets, wherein the at least two magnets can be configured balance the guiding stage. An encoder can be disposed on a bracket assembly disposed on the guiding stage, wherein the encoder can be configured to measure a position of the objective. At least one flexure and at least one leaf spring can be attached to the guiding stage and configured to provide stiffness of the guiding stage in x- and y- axes when the objective is being positioned, and the at least one flexure has a length that reduces stiffness of the guiding stage in the z-axis when the objective is being positioned.

[0010] In some embodiments, the at least one flexure is configured to limit motion in the z-axis.

[0011] In some embodiments, the at least one flexure has a rotational mode in the x-axis (R_x), wherein the R_x mode limits rocking of the guiding stage about the x-axis.

[0012] In some embodiments, the R_x mode is minimized. [0013] In some embodiments, the guiding stage further comprises a heat sink, wherein the heat sink provides additional stiffness to the flexure.

[0014] In some embodiments, the flexure comprises an L-shape.

[0015] In some embodiments, the L-shape is anchored at the objective to provide a stiff connection point.

[0016] In some embodiments, a method includes focusing a beam using an objective disposed on a guiding stage, wherein the objective includes optics. The objective can be positioned using a plurality of Lorentz motors mounted on the guiding stage. A magnet assembly can be mounted including at least two magnets and configured to balance the guiding stage. A position of the objective can be measured with an encoder on a bracket assembly mounted on the guiding stage, at least one flexure and at least one leaf spring can be attached and can be configured to provide stiffness of the guiding stage in the x- and y- axes when the objective is being positioned and the at least one flexure has a length that reduces stiffness of the guiding stage in the z-axis when the objective is positioned.

[0017] In some embodiments, a lithographic apparatus can include an illumination system configured to illuminate a pattern of a patterning device. A support can be configured to support the patterning device and include a substrate. A projection system can be configured to project an image of the pattern onto a substrate. A metrology system with a guiding stage can include an objective disposed on the guiding stage, wherein the objective comprises optics configured to focus a beam. A plurality of Lorentz motors can be disposed on the guiding stage configured to position the objective. A magnet assembly can include at least two magnets, wherein the at least two magnets are configured to balance to the guiding stage. An encoder can be disposed on a bracket assembly disposed on the guiding stage, wherein the encoder is configured to measure a position of the objective. At least one flexure and at least one leaf spring can be attached to the guiding stage and configured to providing stiffness of the guiding stage in x- and y- axes when the objective is being positioned and the at least one flexure has a length that reduces stiffness of the guiding stage in the z-axis when the objective is further positioned. [0018] Further features of the present disclosure, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE FIGURES

[0019] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable a person skilled in the relevant art(s) to make and use embodiments described herein. [0020] FIG. 1A shows a schematic of a reflective lithographic apparatus, according to some embodiments.

[0021] FIG. IB shows a schematic of a transmissive lithographic apparatus, according to some embodiments.

[0022] FIG. 2 shows a more detailed schematic of the reflective lithographic apparatus, according to some embodiments.

[0023] FIG. 3 shows a schematic of a lithographic cell, according to some embodiments.

[0024] FIGS. 4A and 4B show schematics of inspection apparatuses, according to some embodiments. [0025] FIG. 5 depicts a front perspective view of a flexure in a guiding stage for use in lithographic systems, according to some embodiments.

[0026] FIG. 6A depicts a side perspective view of a flexure in a guiding stage for use in lithographic systems, according to some embodiments.

[0027] FIG. 6B depicts a side perspective view of the leaf spring for use in lithographic systems, according to some embodiments.

[0028] FIG. 7 depicts a cross section embodiment of a flexure 730 in a guiding stage 710 for use in lithographic systems 700, according to some embodiments.

[0029] FIG. 8 describes a method 800 for positioning an objective, according to some embodiments.

[0030] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.

DETAILED DESCRIPTION

[0031] This specification discloses one or more embodiments that incorporate the features of the present disclosure. The disclosed embodiment(s) are provided as examples. The scope of the present disclosure is not limited to the disclosed embodiment(s). Claimed features are defined by the claims appended hereto.

[0032] The embodiment(s) described, and references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0033] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0034] The term “about” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the term “about” can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0035] Embodiments of the disclosure can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the disclosure may also be implemented as instructions stored on a machine-readable medium, which can be read and executed by one or more processors. A machine- readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, and/or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0036] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present disclosure can be implemented.

[0037] Example Lithographic Systems

[0038] FIGS. 1A and IB show schematic illustrations of a lithographic apparatus 100 and lithographic apparatus 100’, respectively, in which embodiments of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100’ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100’ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0039] The illumination system IL can include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0040] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus 100 and 100’, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable, as required. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0041] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0042] The terms “inspection apparatus,” “metrology system,” or the like may be used herein to refer to, e.g., a device or system used for measuring a property of a structure (e.g., overlay error, critical dimension parameters) or used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment apparatus).

[0043] The patterning device MA can be transmissive (as in lithographic apparatus 100’ of FIG. IB) or reflective (as in lithographic apparatus 100 of FIG. 1 A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by a matrix of small mirrors.

[0044] The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0045] Lithographic apparatus 100 and/or lithographic apparatus 100’ can be of a type having two (dual stage) or more substrate tables WT (and/or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.

[0046] The lithographic apparatus can also be of a type wherein at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0047] Referring to FIGS. 1A and IB, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100’ can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100’, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (in FIG. IB) including, for example, suitable directing mirrors and/or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100’ , for example, when the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, can be referred to as a radiation system.

[0048] The illuminator IL can include an adjuster AD (in FIG. IB) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as “o-outer” and “o-inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (in FIG. IB), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0049] Referring to FIG. 1A, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.

[0050] Referring to FIG. IB, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0051] The projection system PS projects an image of the mask pattern MP, where the image is formed by diffracted beams produced from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP can include an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction generates diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) traverse the pattern without any change in propagation direction. The zeroth order diffracted beams traverse an upper lens or upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD, for example, is disposed at or substantially at a plane that includes the pupil conjugate PPU of the projection system PS.

[0052] The projection system PS is arranged to capture, by means of a lens or lens group L, not only the zeroth order diffracted beams, but also first-order or first- and higher-order diffracted beams (not shown). In some embodiments, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first-order diffracted beams interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some embodiments, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some embodiments, astigmatism aberration can be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0053] With the aid of the second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in FIG. IB) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

[0054] In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short-stroke actuator only or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0055] Mask table MT and patterning device MA can be in a vacuum chamber V, where an in-vacuum robot IVR can be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot can be used for various transportation operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0056] The lithographic apparatus 100 and 100’ can be used in at least one of the following modes: [0057] 1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed.

[0058] 2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de- )magnification and image reversal characteristics of the projection system PS.

[0059] 3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

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

[0061] In a further embodiment, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0062] FIG. 2 shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. EUV radiation can be produced by a gas or vapor, for example Xe gas, Li vapor, or Sn vapor in which the very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is created by, for example, an electrical discharge causing at least a partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor can be required for efficient generation of the radiation. In some embodiments, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[0063] The radiation emitted by the hot plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap), which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 can include a channel structure. Contamination trap 230 can also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure.

[0064] The collector chamber 212 can include a radiation collector CO, which can be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point INTF. The virtual source point INTF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus INTF is located at or near an opening 219 in the enclosing structure 220. The virtual source point INTF is an image of the radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infra-red (IR) radiation.

[0065] Subsequently the radiation traverses the illumination system IL, which can include a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 221 at the patterning device MA, held by the support structure MT, a patterned beam 226 is formed and the patterned beam 226 is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by the wafer stage or substrate table WT.

[0066] More elements than shown can generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 can optionally be present, depending upon the type of lithographic apparatus. Further, there can be more mirrors present than those shown in the FIG. 2, for example there can be one to six additional reflective elements present in the projection system PS than shown in FIG. 2.

[0067] Collector optic CO, as illustrated in FIG. 2, is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[0068] Exemplary Lithographic Cell

[0069] FIG. 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some embodiments. Lithographic apparatus 100 or 100’ can form part of lithographic cell 300. Lithographic cell 300 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. In some examples, these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input/output ports I/O I , I/O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100 or 100’. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0070] Exemplary Inspection Apparatus

[0071] In order to control the lithographic process to place device features accurately on the substrate, alignment marks are generally provided on the substrate, and the lithographic apparatus includes one or more inspection apparatuses for accurate positioning of marks on a substrate. These alignment apparatuses are effectively position measuring apparatuses. Different types of marks and different types of alignment apparatuses and/or systems are known from different times and different manufacturers. A type of system widely used in current lithographic apparatus is based on a self-referencing interferometer as described in U.S. Patent No. 6,961,116 (den Boef et al.). Generally marks are measured separately to obtain X- and Y-positions. A combined X- and Y-measurement can be performed using the techniques described in U.S. Publication No. 2009/195768 A (Bijnen et al.), however. The full contents of both of these disclosures are incorporated herein by reference. [0072] FIG. 4A shows a schematic of a cross-sectional view of an inspection apparatus

[0073] 400 that can be implemented as a part of lithographic apparatus 100 or 100’, according to some embodiments. In some embodiments, inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Inspection apparatus 400 can be further configured to detect positions of alignment marks on the substrate and to align the substrate with respect to the patterning device or other components of lithographic apparatus 100 or 100’ using the detected positions of the alignment marks. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0074] In some embodiments, inspection apparatus 400 can include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and an overlay calculation processor 432. Illumination system 412 can be configured to provide an electromagnetic narrow band radiation beam 413 having one or more passbands. In an example, the one or more passbands can be within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the one or more passbands can be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. Illumination system 412 can be further configured to provide one or more passbands having substantially constant center wavelength (CWL) values over a long period of time (e.g., over a lifetime of illumination system 412). Such configuration of illumination system 412 can help to prevent the shift of the actual CWL values from the desired CWL values, as discussed above, in current alignment systems. And, as a result, the use of constant CWL values can improve long-term stability and accuracy of alignment systems (e.g., inspection apparatus 400) compared to the current alignment apparatuses.

[0075] In some embodiments, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 can be split into radiation sub-beams 415 and 417, as shown in FIG. 4A. Beam splitter 414 can be further configured to direct radiation sub-beam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 is movable along direction 424. Radiation sub-beam 415 can be configured to illuminate an alignment mark or a target 418 located on substrate 420. Alignment mark or target 418 can be coated with a radiation sensitive film. In some embodiments, alignment mark or target 418 can have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to a plane of alignment mark or target 418, rotated alignment mark or target 418 can be substantially identical to an unrotated alignment mark or target 418. The target 418 on substrate 420 can be (a) a resist layer grating comprising bars that are formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on a product layer grating. The bars can alternatively be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberrations will manifest themselves in a variation in the printed grating. One in- line method used in device manufacturing for measurements of line width, pitch, and critical dimension makes use of a technique known as “scatterometry”. Methods of scatterometry are described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry”, J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography”, SPIE, Vol. 3677 (1999), which are both incorporated by reference herein in their entireties. In scatterometry, light is reflected by periodic structures in the target, and the resulting reflection spectrum at a given angle is detected. The structure giving rise to the reflection spectrum is reconstructed, e.g. using Rigorous Coupled-Wave Analysis (RCWA) or by comparison to a library of patterns derived by simulation. Accordingly, the scatterometry data of the printed gratings is used to reconstruct the gratings. The parameters of the grating, such as line widths and shapes, can be input to the reconstruction process, performed by processing unit PU, from knowledge of the printing step and/or other scatterometry processes.

[0076] In some embodiments, beam splitter 414 can be further configured to receive diffraction radiation beam 419 and split diffraction radiation beam 419 into at least two radiation sub-beams, according to an embodiment. Diffraction radiation beam 419 can be split into diffraction radiation subbeams 429 and 439, as shown in FIG. 4A.

[0077] It should be noted that even though beam splitter 414 is shown to direct radiation sub-beam 415 towards alignment mark or target 418 and to direct diffracted radiation sub-beam 429 towards interferometer 426, the disclosure is not so limiting. It would be apparent to a person skilled in the relevant art that other optical arrangements can be used to obtain the similar result of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418. [0078] As illustrated in FIG. 4A, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414. In an example embodiment, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In an example of this embodiment, interferometer 426 comprises any appropriate set of optical-elements, for example, a combination of prisms that can be configured to form two images of alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be appreciated that a good quality image need not be formed, but that the features of alignment mark 418 should be resolved. Interferometer 426 can be further configured to rotate one of the two images with respect to the other of the two images 180° and recombine the rotated and unrotated images interfero metrically.

[0079] In some embodiments, detector 428 can be configured to receive the recombined image via interferometer signal 427 and detect interference as a result of the recombined image when alignment axis 421 of inspection apparatus 400 passes through a center of symmetry (not shown) of alignment mark or target 418. Such interference can be due to alignment mark or target 418 being 180° symmetrical, and the recombined image interfering constructively or destructively, according to an example embodiment. Based on the detected interference, detector 428 can be further configured to determine a position of the center of symmetry of alignment mark or target 418 and consequently, detect a position of substrate 420. According to an example, alignment axis 421 can be aligned with an optical beam perpendicular to substrate 420 and passing through a center of image rotation interferometer 426. Detector 428 can be further configured to estimate the positions of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

[0080] In a further embodiment, detector 428 determines the position of the center of symmetry of alignment mark or target 418 by performing one or more of the following measurements:

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

2. measuring position variations for various orders (position shift between diffraction orders); and

3. measuring position variations for various polarizations (position shift between polarizations).

[0081] This data can for example be obtained with any type of alignment sensor, for example a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Patent No. 6,961,116 that employs a self-referencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment), as described in U.S. Patent No. 6,297,876, which directs each of seven diffraction orders to a dedicated detector, which are both incorporated by reference herein in their entireties.

[0082] In some embodiments, beam analyzer 430 can be configured to receive and determine an optical state of diffracted radiation sub-beam 439. The optical state can be a measure of beam wavelength, polarization, or beam profile. Beam analyzer 430 can be further configured to determine a position of stage 422 and correlate the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420 can be accurately known with reference to stage 422. Alternatively, beam analyzer 430 can be configured to determine a position of inspection apparatus 400 or any other reference element such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400 or any other reference element. Beam analyzer 430 can be a point or an imaging polarimeter with some form of wavelength-band selectivity. In some embodiments, beam analyzer 430 can be directly integrated into inspection apparatus 400, or connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other embodiments.

[0083] In some embodiments, beam analyzer 430 can be further configured to determine the overlay data between two patterns on substrate 420. One of these patterns can be a reference pattern on a reference layer. The other pattern can be an exposed pattern on an exposed layer. The reference layer can be an etched layer already present on substrate 420. The reference layer can be generated by a reference pattern exposed on the substrate by lithographic apparatus 100 and/or 100’ . The exposed layer can be a resist layer exposed adjacent to the reference layer. The exposed layer can be generated by an exposure pattern exposed on substrate 420 by lithographic apparatus 100 or 100’. The exposed pattern on substrate 420 can correspond to a movement of substrate 420 by stage 422. In some embodiments, the measured overlay data can also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus 100 or 100’, such that after the calibration, the offset between the exposed layer and the reference layer can be minimized.

[0084] In some embodiments, beam analyzer 430 can be further configured to determine a model of the product stack profile of substrate 420, and can be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement. The product stack profile contains information on the stacked product such as alignment mark, target 418, or substrate 420, and can include mark process variation-induced optical signature metrology that is a function of illumination variation. The product stack profile can also include product grating profile, mark stack profile, and mark asymmetry information. An example of beam analyzer 430 is Yieldstar™, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, which is incorporated by reference herein in its entirety. Beam analyzer 430 can be further configured to process information related to a particular property of an exposed pattern in that layer. For example, beam analyzer 430 can process an overlay parameter (an indication of the positioning accuracy of the layer with respect to a previous layer on the substrate or the positioning accuracy of the first layer with respective to marks on the substrate), a focus parameter, and/or a critical dimension parameter (e.g., line width and its variations) of the depicted image in the layer. Other parameters are image parameters relating to the quality of the depicted image of the exposed pattern.

[0085] In some embodiments, an array of detectors (not shown) can be connected to beam analyzer 430, and allows the possibility of accurate stack profile detection as discussed below. For example, detector 428 can be an array of detectors. For the detector array, a number of options are possible: a bundle of multimode fibers, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of a bundle of multimode fibers enables any dissipating elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range but each need separate pre-amps. The number of elements is therefore limited. CCD linear arrays offer many elements that can be read-out at high speed and are especially of interest if phase- stepping detection is used.

[0086] In some embodiments, a second beam analyzer 430’ can be configured to receive and determine an optical state of diffracted radiation sub-beam 429, as shown in FIG. 4B. The optical state can be a measure of beam wavelength, polarization, or beam profile. Second beam analyzer 430’ can be identical to beam analyzer 430. Alternatively, second beam analyzer 430’ can be configured to perform at least all the functions of beam analyzer 430, such as determining a position of stage 422 and correlating the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420, can be accurately known with reference to stage 422. Second beam analyzer 430’ can also be configured to determine a position of inspection apparatus 400, or any other reference element, such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400, or any other reference element. Second beam analyzer 430’ can be further configured to determine the overlay data between two patterns and a model of the product stack profile of substrate 420. Second beam analyzer 430’ can also be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement.

[0087] In some embodiments, second beam analyzer 430’ can be directly integrated into inspection apparatus 400, or it can be connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other embodiments. Alternatively, second beam analyzer 430’ and beam analyzer 430 can be combined to form a single analyzer (not shown) configured to receive and determine the optical states of both diffracted radiation sub-beams 429 and 439.

[0088] In some embodiments, processor 432 receives information from detector 428 and beam analyzer 430. For example, processor 432 can be an overlay calculation processor. The information can comprise a model of the product stack profile constructed by beam analyzer 430. Alternatively, processor 432 can construct a model of the product mark profile using the received information about the product mark. In either case, processor 432 constructs a model of the stacked product and overlay mark profile using or incorporating a model of the product mark profile. The stack model is then used to determine the overlay offset and minimizes the spectral effect on the overlay offset measurement. Processor 432 can create a basic correction algorithm based on the information received from detector 428 and beam analyzer 430, including but not limited to the optical state of the illumination beam, the alignment signals, associated position estimates, and the optical state in the pupil, image, and additional planes. The pupil plane is the plane in which the radial position of radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor 432 can utilize the basic correction algorithm to characterize the inspection apparatus 400 with reference to wafer marks and/or alignment marks 418.

[0089] In some embodiments, processor 432 can be further configured to determine printed pattern position offset error with respect to the sensor estimate for each mark based on the information received from detector 428 and beam analyzer 430. The information includes but is not limited to the product stack profile, measurements of overlay, critical dimension, and focus of each alignment marks or target 418 on substrate 420. Processor 432 can utilize a clustering algorithm to group the marks into sets of similar constant offset error, and create an alignment error offset correction table based on the information. The clustering algorithm can be based on overlay measurement, the position estimates, and additional optical stack process information associated with each set of offset errors. The overlay is calculated for a number of different marks, for example, overlay targets having a positive and a negative bias around a programmed overlay offset. The target that measures the smallest overlay is taken as reference (as it is measured with the best accuracy). From this measured small overlay, and the known programmed overlay of its corresponding target, the overlay error can be deduced. Table 1 illustrates how this can be performed. The smallest measured overlay in the example shown is -1 nm. However this is in relation to a target with a programmed overlay of -30 nm. The process may have introduced an overlay error of 29 nm.

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

[0091] In some embodiments, processor 432 can confirm that all or most members of the group have similar offset errors, and apply an individual offset correction from the clustering algorithm to each mark, based on its additional optical stack metrology. Processor 432 can determine corrections for each mark and feed the corrections back to lithographic apparatus 100 or 100’ for correcting errors in the overlay, for example, by feeding corrections into the inspection apparatus 400.

[0092] Exemplary Flexure Embodiments

[0093] Exemplary lithographic systems as described above can be configured to measure a position of an objective on a guiding stage. The guiding stage can comprise a flexure arrangement to reduce stiffness of the guiding stage in the z-axis when the objective is positioned.

[0094] For example, a typical lithographic system can include a guiding stage and within the guiding stage, utilize a flexure leaf spring structure to guide an objective in a vertical direction. Any parasitic motion or tilts in random directions can be limited over an operating range. This parasitic motion enables focus control of the lithographic system as the sensor can measure many points on a substrate. [0095] Optics to improve sensor transmission and throughput can be positioned close to the sensor objective. For example, a quad non-polarizing beam splitter (NPBS) prism can be used to improve optical transmission and sensor throughput. However, the prism must be positioned close to the sensor objective, which requires a change in a leaf spring guiding geometry, such as a cutout of a top flexure. With the prism positioned closer to the objective, higher optical transmission is enable through the sensor, which results in a higher throughput.

[0096] But z-stage dynamics can impact the bandwidth of a focus controller. And removing a part of the quad NPBS can have a negative impact on the z-stage dynamics and the focus control bandwidth. Also, because the dynamics can be improved, such as better focus control bandwidth, faster focus control of the sensor can result. And such focus control also contributes to a higher throughput.

[0097] Hence, the leaf spring design can be altered, which can improve the performance of the lithographic system. The leaf spring can be optimized for dynamics and can incorporate new constraints from the quad NPBS cutout.

[0098] The leaf spring design can anchor a foreshortening flexure, which can reduce motion in the x- direction towards where the objective is located as opposed to the outside of the z-stage. This leaf spring design can result in a stiffer connection point, which can limit the motion in the dynamic performance limiting R_x mode. This limitation does not increase the overall stiffness, such as increasing the difficulty of movement in the z-direction. Additionally, the guiding accuracy of the flexure mechanism is not affected.

[0099] The frequency of the z mode of the actuator is between 20 and 35 Hz. A theoretical frequency of the z-stage rigid body can be achieved by shifting resonance modes or lowering the amplitude of these modes with a stiffer encoder bracket for the z mode. Improvements for the R_x mode can be achieved by adding damping, optimizing the moving mass, or flexure changes, which is proposed herein.

[0100] FIG. 5 shows a front perspective view of a flexure 530 in a guiding stage 510 for use in lithographic systems 500, according to some embodiments.

[0101] A guiding stage 510 is shown. A sensor objective 520 is below an objective (not pictured). The sensor objective 520 can be mounted to the guiding stage 510. The guiding stage can include at least one actuator motor 540, such as Lorentz motors or a similar actuator motor as would become apparent to persons skilled in the art, to enable fine adjustment movements for focusing the objective. Additionally, a piezoelectric actuator can be used. The actuator motor 540 can also assist in moving mass of the system in general. A portion of the guiding stage 510 has been removed to make room for different sizes of optical elements, such as objectives, but by changing the length of the flexures 530, there is no loss in performance.

[0102] A flexure 530 can have a shortened length in the x-axis and a long length in the y-axis. The shortened length of the flexure 530 reduces stress from deformation in the x-axis. The longer length reduces stiffness and allows for motion in the z-axis. The flexure 530 described herein can assist in limiting the rotation when the objective (not pictured) moves for focusing of the beam. The flexure 530 has been partially removed due to the change in optics. By partially removing the flexure 530, the remaining flexure 530 can act as an anchor such that less movement occurs and rotation is minimized. The flexure 530 is moved closer to the objective, which allows for controlling R_x mode better, but at the same time does not affect stiffness in the z-axis. Typically, R_x mode is difficult to control, so this change provides better control.

[0103] The R_x mode is a dynamic mode and describes the rocking motion about the x-axis. The amplitude of the rocking motion is decreased and the mode is no longer limited motion in the system. Additionally, the rotation about the x-axis is minimized.

[0104] The flexure 530 has been shortened and can be anchored at the objective side. This anchoring allows for a stiffer connection point, while limiting the amplitude of the R_x mode and improving dynamics. However, this change in the flexure 530 improves dynamics without sacrificing the guiding accuracy or the z- actuation. By guiding in one direction, the z-direction, parasitic motion can be prevented. Additionally, this allows for a fine movement in the z-direction and enables a finer focus of the objective.

[0105] At least one flexure 530 is described, but up to six flexures can be included. However, if the flexure 530 is too stiff, then the guiding stage cannot move in the up and down direction as easily. The flexure 530 has an L-shape that allows a prevention in overstressing. If the flexure is overstrained without some give, then too much pressure is put on the guiding stage. The stress of the system overall should be low due to the number of cycles performed by the lithographic apparatus.

[0106] Guiding accuracy is one of the most important aspects of the objective as the objective should not be moving around the system during measurements as the whole system would be more difficult to control. The flexure 530 and stiffness thereof provides an overall improved focus of the objective.

[0107] A magnet assembly 550 is provided to balance the guiding stage 510. The magnet assembly 550 can provide force to counteract gravity and provide, for example, emergency retract force. Additionally, a leaf spring 560 is provided, which can provide the flexure 530 with control. Specifically, the leaf spring 560 assists the flexure 530 in providing guiding stiffness in the x- and y- directions. The flexure 530 can be anchored at the leaf spring 560.

[0108] A heat sink can be used in addition to the proposed embodiment of FIG. 5. A heat sink (not pictured) can act as a passive heat exchanger that transfers heat. Here, the heat sink can also add stiffness in certain modes. The certain modes can include but are not limited to the resonant modes of the objective guiding stage. This allows for in sensor throughput, enabling more measurements made per hour by the system. By increasing the frequencies of these resonant modes and/or decreasing their magnitude, the bandwidth of the focus controller can be increased, which enables faster stage moves and therefore reducing the time between measurements.

[0109] FIG. 6A shows a side perspective view of the flexure 530 in a guiding stage 510 for use in lithographic systems 500, according to some embodiments.

[0110] The guiding stage 510 is shown with the sensor objective 520. A flexure 530 is shown, which provides stiffness to the guiding stage 510. The guiding stage 510 includes actuator motors 540. A magnet assembly 550 is provided to balance the guiding stage 510. A leaf spring 560 is provided with an encoder 570.

[0111] FIG. 6B shows a side perspective view of the leaf spring 560 for use in lithographic systems 500, according to some embodiments.

[0112] The guiding stage 560 has the flexure 530 attached to it. The objective (not pictured) can be inserted in hole 590. The offset view of flexure 530 depicts the flexure 530 in a L-shaped that can be anchored at the objective to provide a stiff connection point.

[0113] FIG. 7 shows a cross section embodiment of a flexure 730 in a guiding stage 710 for use in lithographic systems 700, according to some embodiments.

[0114] A guiding stage 710 is shown with a sensor objective 720. The sensor objective 720 can receive beam from the objective 722. The objective 722 contains optics, which can be used for focusing the beam. Additionally, the objective 722 is one of the main masses of the system that needs to be controlled. A flexure 730 is shown, which provides stiffness to the guiding stage 710. The guiding stage 710 includes Lorentz motors 740 to focus the objective 722. A magnet assembly 750 is provided to balance the guiding stage 710. A leaf spring 760 is provided with an encoder 770. The encoder 770 can assist in measuring the z-position of the objective 722. Due to the cross-section view of FIG. 7, the leaf spring 760 is shown behind the Lorentz motors 740 and the magnet assembly 750.

[0115] FIG. 8 describes a method 800 for positioning an objective, according to some embodiments.

[0116] In step 802, a beam is focused using an objective mounted on a guiding stage. The objective can include optics.

[0117] In step 804, the objective is positioned using Lorentz motors. The Lorentz motors can be mounted on the guiding stage and assist in providing fine adjustment moves for focusing the objective. The Lorentz motors can also move mass of the system.

[0118] In step 806, a magnet assembly is mounted on the guiding stage and configured to balance the guiding stage. The magnet assembly can include at least two magnets. These two magnets provide force to counteract gravity.

[0119] In step 808, the position of the objective can be measured. The measurement can be taken with an encoder on a bracket assembly, which can be mounted on the guiding stage.

[0120] In step 810, at least one flexure and at least one leaf spring is attached to the guiding stage. The leaf spring can be configured to provide stiffness of the guiding stage in the x- and y- axes when the objective is positioned. The flexure has a length that can reduce the stiffness of the guiding stage in the z-axis once the objective is positioned.

[0121] In step 812, the stiffness of the guiding stage can be reduced.

[0122] The embodiments may further be described using the following clauses

1. A guiding stage comprising: an objective disposed on the guiding stage, wherein the objective comprises optics configured to focus a beam; a plurality of actuator motors disposed on the guiding stage configured to position the objective; a magnet assembly comprising at least two magnets, wherein the at least two magnets are configured balance the guiding stage; and an encoder disposed on a bracket assembly disposed on the guiding stage, wherein the encoder is configured to measure a position of the objective; and at least one flexure and at least one leaf spring attached to the guiding stage and configured to provide stiffness of the guiding stage in x- and y- axes when the objective is being positioned, and the at least one flexure has a length that reduces stiffness of the guiding stage in the z-axis when the objective is being positioned.

2. The guiding stage of clause 1, wherein the at least one flexure is configured to limit motion in the z- axis.

3. The guiding stage of clause 1, wherein the at least one flexure has an rotational mode (R_x), wherein the R_x mode limits rocking of the guiding stage about the x-axis.

4. The guiding stage of clause 1, wherein the guiding stage further comprises a heat sink, wherein the heat sink provides additional stiffness to the flexure.

5. The guiding stage of clause 1, wherein the flexure comprises an L-shape.

6. The guiding stage of clause 1, wherein the L-shape is anchored at the objective to provide a stiff connection point.

7. A method comprising: focusing a beam using an objective disposed on a guiding stage, wherein the objective comprises optics; positioning the objective using a plurality of actuator motors mounted on the guiding stage; mounting a magnet assembly comprising at least two magnets and configured to balance the guiding stage; and measuring a position of the objective with an encoder on a bracket assembly mounted on the guiding stage; and attaching at least one flexure and at least one leaf spring configured to provide stiffness of the guiding stage in the x- and y- axes when the objective is being positioned and the at least one flexure has a length that reduces stiffness of the guiding stage in the z-axis when the objective is positioned.

8. The method of clause 7, further comprising limiting motion of the guiding stage in the z-axis with the flexure.

9. The method of clause 8, further comprising limiting rocking of the guiding stage about the x-axis with an R_x mode of the flexure.

10. The method of clause 9, further comprising minimizing the R_x mode.

11. The method of clause 8, further comprising attaching a heat sink to the guiding stage to provide additional stiffness to the flexure.

12. The method of clause 8, wherein the flexure comprises an L-shape. 13. The method of clause 8, further comprising positing the flexure on the objected to provide a stiff connection point.

14. A lithographic apparatus comprising: an illumination system configured to illuminate a pattern of a patterning device; a support configured to support the patterning device; a substrate; a projection system configured to project an image of the pattern onto a substrate; and a metrology system with a guiding stage comprising: an objective disposed on the guiding stage, wherein the objective comprises optics configured to focus a beam; a plurality of actuator motors disposed on the guiding stage configured to position the objective; a magnet assembly comprising at least two magnets, wherein the at least two magnets are configured to balance to the guiding stage; and an encoder disposed on a bracket assembly disposed on the guiding stage, wherein the encoder is configured to measure a position of the objective; and at least one flexure and at least one leaf spring attached to the guiding stage and configured to providing stiffness of the guiding stage in x- and y- axes when the objective is being positioned and the at least one flexure has a length that reduces stiffness of the guiding stage in the z- axis when the objective is further positioned.

15. The lithographic apparatus of clause 14, wherein the at least one flexure is configured to limit motion in the z-axis.

16. The lithographic apparatus of clause 15, wherein the at least one flexure has an R_x mode, wherein the R_x mode limits rocking of the guiding stage about the x-axis.

17. The lithographic apparatus of clause 16, wherein the R_x mode is minimized.

18. The lithographic apparatus of clause 15, wherein the guiding stage further comprises a heat sink, wherein the heat sink provides stiffness to the flexure.

19. The lithographic apparatus of clause 15, wherein the flexure comprises an L-shape.

20. The lithographic apparatus of clause 15, wherein the L-shape is anchored at the objective to provide a stiff connection point.

[0123] Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein can be processed, before or after exposure, in for example a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and/or a metrology unit. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0124] Although specific reference may have been made above to the use of embodiments of the present disclosure in the context of optical lithography, it will be appreciated that the present disclosure can be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0125] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present disclosure is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0126] The terms “radiation,” “beam of radiation” or the like as used herein may encompass all types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-20 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as matter beams, such as ion beams or electron beams. The terms “light,” “illumination,” or the like may refer to non-matter radiation (e.g., photons, UV, X-ray, or the like). Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G- line 436 nm; H-line 405 nm; and/or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some embodiments, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

[0127] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. [0128] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0129] While specific embodiments of the disclosure have been described above, it will be appreciated that embodiments of the present disclosure may be practiced otherwise than as described. The descriptions are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the disclosure as described without departing from the scope of the claims set out below.

[0130] The foregoing description of the specific embodiments will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0131] The breadth and scope of the protected subject matter should not be limited by any of the abovedescribed exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

2. The guiding stage of claim 1, wherein the at least one flexure is configured to limit motion in the z- axis.

3. The guiding stage of claim 1, wherein the at least one flexure has an rotational mode (R_x), wherein the R_x mode limits rocking of the guiding stage about the x-axis.

4. The guiding stage of claim 1, wherein the guiding stage further comprises a heat sink, wherein the heat sink provides additional stiffness to the flexure.

5. The guiding stage of claim 1, wherein the flexure comprises an L-shape.

6. The guiding stage of claim 1, wherein the L-shape is anchored at the objective to provide a stiff connection point.

8. The method of claim 7, further comprising limiting motion of the guiding stage in the z-axis with the flexure.

9. The method of claim 8, further comprising limiting rocking of the guiding stage about the x-axis with an R_x mode of the flexure.

10. The method of claim 9, further comprising minimizing the R_x mode.

11. The method of claim 8, further comprising attaching a heat sink to the guiding stage to provide additional stiffness to the flexure.

12. The method of claim 8, wherein the flexure comprises an L-shape.

13. The method of claim 8, further comprising positing the flexure on the objected to provide a stiff connection point.

15. The lithographic apparatus of claim 14, wherein the at least one flexure is configured to limit motion in the z-axis.