IL297796A - High pressure and vacuum level sensor in metrology radiation systems - Google Patents

Description

1 HIGH PRESSURE AND VACUUM LEVEL SENSOR IN METROLOGY RADIATION SYSTEMS CROSS REFERENCE TO RELATED APPLICATIONS id="p-1" id="p-1" id="p-1" id="p-1" id="p-1"

[0001] This application claims priority to U.S. Application No. 63/032,187 filed May 29, 2020 and titled HIGH PRESSURE AND VACUUM LEVEL SENSOR IN METROLOGY RADIATION SYSTEMS, which is incorporated herein in its entirety by reference.

FIELD id="p-2" id="p-2" id="p-2" id="p-2" id="p-2"

[0002] The present disclosure relates to feed mechanisms for delivering source material within extreme ultraviolet (EUV) radiation systems used in lithographic processes to fabricate semiconductor devices.

BACKGROUND id="p-3" id="p-3" id="p-3" id="p-3" id="p-3"

[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 may be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC being formed. This pattern can be transferred onto a target portion (e.g., including 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 (e.g., resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Traditional lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the scanning direction) while synchronously scanning the target portions in a direction parallel to this scanning direction or in a direction parallel to, and opposite the scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. id="p-4" id="p-4" id="p-4" id="p-4" id="p-4"

[0004] Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having wavelengths of around 50 nanometers (nm) or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in or with a lithographic apparatus to produce extremely small features in substrates such as, for example, silicon wafers. Methods to produce EUV light include, but are not necessarily limited to, converting a material that has an element, for example, xenon (Xe), lithium (Li), or tin (Sn), with an emission line in the EUV range, to a plasma state. For example, in one such method called laser produced plasma (EPP), the plasma can be produced by irradiating a target material, which is interchangeably referred to as fuel in the context of EPP sources, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an amplified light beam that can be 2 referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment. id="p-5" id="p-5" id="p-5" id="p-5" id="p-5"

[0005] Inside a traditional tin-based radiation source vessel, many functions such as protective hydrogen (H2) gases, heat shielding, and precise shroud mounting must also allow for metrology field of view (FOV) and droplet path clearance while preventing Sn accumulation. Moreover, current systems do not properly monitor the source available for supplying source material to the EUV droplet generator. Accordingly, there is a need to improve source availability and to eliminate down time associated with a lack of high quality source supply (e.g., Sn supply) to a droplet generator (DGen).

SUMMARY id="p-6" id="p-6" id="p-6" id="p-6" id="p-6"

[0006] The present disclosure describes various aspects of systems, apparatuses, and methods to provide for optical metrology and various other aspects in an extreme ultraviolet (EUV) radiation system. More specifically, the current disclosure describes an inline refill (IR) system, which allows for continuous monitoring and continuous supply of high purity Sn into a droplet generator assembly (DGA). id="p-7" id="p-7" id="p-7" id="p-7" id="p-7"

[0007] According to one aspect, a method for measuring a fuel feed level includes directing an inspection beam through a fuel tank view port at a top surface of the radiation fuel at a predetermined incident angle. The method can further include receiving a portion of the inspection beam reflected by the top surface of the radiation fuel at a sensor located adjacent to the view port. In other aspects, the method includes measuring a distance from the sensor to the top surface of the radiation fuel, and calculating a fill level of the radiation fuel in the fuel tank based on the measured distance. id="p-8" id="p-8" id="p-8" id="p-8" id="p-8"

[0008] According to one aspect, a measurement device and method for measuring a fuel fill level are disclosed. According to some embodiments, the measurement device is disclosed for measuring fuel fill level of a radiation fuel in an extreme ultraviolet (EUV) radiation system, the measurement device being located within a fuel tank. According to some aspects, the measurement device includes a plurality of probes extending within the fuel tank and each one of the plurality of probes generates a signal in response to having contact with the radiation fuel. According to some aspects, the plurality of probes connect to the fuel tank through a plurality of hermetic high pressure seals. According to some aspects, the measurement device may further include a controller including processing circuitry. According to some aspects, the controller calculates a fuel fill level within the fuel tank in response to receiving one or more generated signals, generate an output signal indicative of the calculated fill level, and transmits the output signal to at least one other controller. id="p-9" id="p-9" id="p-9" id="p-9" id="p-9"

[0009] According to some embodiments, there may be provided a lithographic radiation system. In some aspects, the lithographic radiation system may include a first fuel tank coupled to a first sensor device and a first controller. In some aspects, the lithographic radiation system may include a second fuel tank coupled to a second sensor device and a second controller. In some aspects, the second fuel 3 tank is located upstream from the first fuel tank in a fuel fill system and provides radiation fuel to the lithographic radiation system. According to some aspects, the first controller calculates a fuel fill level within the first fuel tank, generates an output signal indicative of the calculated fill level, and transmits the output signal to the second controller. id="p-10" id="p-10" id="p-10" id="p-10" id="p-10"

[0010] Further features, as well as the structure and operation of various aspects, are described in detail below with reference to the accompanying drawings. It is noted that the disclosure is not limited to the specific aspects described or illustrated herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS id="p-11" id="p-11" id="p-11" id="p-11" id="p-11"

[0011] 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 aspects of this disclosure and to enable a person skilled in the relevant art(s) to make and use the aspects of this disclosure. id="p-12" id="p-12" id="p-12" id="p-12" id="p-12"

[0012] FIG. 1A is a schematic illustration of an example reflective lithographic apparatus according to some aspects of the present disclosure. id="p-13" id="p-13" id="p-13" id="p-13" id="p-13"

[0013] FIG. IB is a schematic illustration of an example transmissive lithographic apparatus according to some aspects of the present disclosure. id="p-14" id="p-14" id="p-14" id="p-14" id="p-14"

[0014] FIGS. 2A, 2B, and 3 show more detailed schematics of a reflective lithographic apparatus, according to some embodiments. id="p-15" id="p-15" id="p-15" id="p-15" id="p-15"

[0015] FIG. 4 shows a schematic of a lithographic cell, according to some embodiments. id="p-16" id="p-16" id="p-16" id="p-16" id="p-16"

[0016] FIG. 5 is a schematic illustration of an example radiation source for an example reflective lithographic apparatus according to some aspects of the present disclosure . id="p-17" id="p-17" id="p-17" id="p-17" id="p-17"

[0017] FIGS. 6A and 6B illustrate schematic architecture for in-tank level sensors, according to some embodiments; id="p-18" id="p-18" id="p-18" id="p-18" id="p-18"

[0018] FIG. 7 illustrates a schematic architecture for inline refill system, according to some embodiments; id="p-19" id="p-19" id="p-19" id="p-19" id="p-19"

[0019] FIGS. 8A-8B illustrate non-invasive triangulation sensor deployment for detecting source levels in vacuum tanks, according to some embodiments; id="p-20" id="p-20" id="p-20" id="p-20" id="p-20"

[0020] FIG. 8C is a temperature-time plot that illustrates shift in average Sn level and noise level measured by an optical device; id="p-21" id="p-21" id="p-21" id="p-21" id="p-21"

[0021] FIGS. 9A-9D illustrate another example of non-invasive triangulation sensor deployment for detecting source levels in vacuum tanks, according to some embodiments; id="p-22" id="p-22" id="p-22" id="p-22" id="p-22"

[0022] FIG. 10 is a graphical representation of signal detected at a receiver array of a sensor, according to some embodiments; and 4 id="p-23" id="p-23" id="p-23" id="p-23" id="p-23"

[0023] FIG. 11 is a flow diagram showing an example of a detection method of source levels in an inline refill system, according to some embodiments. id="p-24" id="p-24" id="p-24" id="p-24" id="p-24"

[0024] The features and advantages 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, unless otherwise indicated, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. Additionally, generally, the left-most 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 id="p-25" id="p-25" id="p-25" id="p-25" id="p-25"

[0025] This specification discloses one or more embodiments that incorporate the features of the present disclosure. The disclosed embodiment(s) merely describe the present disclosure. The scope of the disclosure is not limited to the disclosed embodiment(s). The breadth and scope of the disclosure are defined by the claims appended hereto and their equivalents. id="p-26" id="p-26" id="p-26" id="p-26" id="p-26"

[0026] The embodiment(s) described, and references in the specification to "one embodiment," "an embodiment," "an example embodiment," "an exemplary embodiment," etc., indicate that the embodiment(s) described can 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 affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. id="p-27" id="p-27" id="p-27" id="p-27" id="p-27"

[0027] Spatially relative terms, such as "beneath," "below," "lower," "above," "on," "upper" and the like, may 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. id="p-28" id="p-28" id="p-28" id="p-28" id="p-28"

[0028] 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). id="p-29" id="p-29" id="p-29" id="p-29" id="p-29"

[0029] There are many advantages and benefits to the radiation source vessel and CFR disclosed herein. For example, the various aspects of the present disclosure provide for: modularity (e.g., improved serviceability, improved upgradeability); improved performance (e.g., more functions included in a single apparatus); improved availability (e.g., less Sn deposition and faster serviceability than conventional radiation source vessels); and reduced cost (e.g., building the perimeter flow function into the CFR can be cheaper than building the perimeter flow function into the radiation collector as in conventional designs). id="p-30" id="p-30" id="p-30" id="p-30" id="p-30"

[0030] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented. id="p-31" id="p-31" id="p-31" id="p-31" id="p-31"

[0031] Example Lithographic Systems id="p-32" id="p-32" id="p-32" id="p-32" id="p-32"

[0032] FIGS. 1A and IB are schematic illustrations of a lithographic apparatus 100 and lithographic apparatus 100’, respectively, in which aspects of the present disclosure can be implemented. As shown in FIGS. 1A and IB, the lithographic apparatuses 100 and 100’ are illustrated from a point of view (e.g., a side view) that is normal to the XZ plane (e.g., the X-axis points to the right and the Z-axis points upward), while the patterning device MA and the substrate W are presented from additional points of view (e.g., a top view) that are normal to the XY plane (e.g., the X-axis points to the right and the Y- axis points upward). id="p-33" id="p-33" id="p-33" id="p-33" id="p-33"

[0033] Lithographic apparatus 100 and lithographic apparatus 100’ each include the following: an illumination system IL (e.g., an illuminator) configured to condition a radiation beam B (e.g., a deep ultra violet (DUV) radiation beam or an extreme ultra violet (EUV) radiation beam); a support structure MT (e.g., a mask table) configured to support a patterning device MA (e.g., a mask, a reticle, or a dynamic patterning device) and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate holder such as a substrate table WT (e.g., a wafer table) configured to hold a substrate W (e.g., a resist-coated wafer) and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatuses 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 C (e.g., a portion including one or more dies) 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. id="p-34" id="p-34" id="p-34" id="p-34" id="p-34"

[0034] 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. id="p-35" id="p-35" id="p-35" id="p-35" id="p-35"

[0035] 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 apparatuses 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, 6 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. id="p-36" id="p-36" id="p-36" id="p-36" id="p-36"

[0036] 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. id="p-37" id="p-37" id="p-37" id="p-37" id="p-37"

[0037] The patterning device MA can be transmissive (as in lithographic apparatus 100’ of FIG. IB) or reflective (as in lithographic apparatus 100 of FIG. 1A). Examples of patterning devices MA include reticles, masks, programmable minor arrays, or programmable LCD panels. Masks 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 minor 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 minors impart a pattern in the radiation beam B, which is reflected by a matrix of small minors. id="p-38" id="p-38" id="p-38" id="p-38" id="p-38"

[0038] 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. id="p-39" id="p-39" id="p-39" id="p-39" id="p-39"

[0039] 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. id="p-40" id="p-40" id="p-40" id="p-40" id="p-40"

[0040] 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 provide 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. id="p-41" id="p-41" id="p-41" id="p-41" id="p-41"

[0041] Referring to FIGS. 1A and IB, the illumination system IL receives a radiation beam B from a radiation source SO. The radiation source SO and the lithographic apparatus 100 or 100’ can be separate physical entities, for example, when the radiation source SO is an excimer laser. In such cases, the 7 radiation source SO is not considered to form part of the lithographic apparatus 100 or 100’, and the radiation beam B passes from the radiation source SO to the illumination system IL with the aid of a beam delivery system BD (e.g., shown in FIG. IB) including, for example, suitable directing mirrors and/or a beam expander. In other cases, the radiation source SO can be an integral part of the lithographic apparatus 100 or 100’, for example, when the radiation source SO is a mercury lamp. The radiation source SO and the illuminator IL, together with the beam delivery system BD, if required, can be referred to as a radiation system. id="p-42" id="p-42" id="p-42" id="p-42" id="p-42"

[0042] The illumination system IL can include an adjuster AD (e.g., shown 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 illumination system IL can include various other components (e.g., shown in FIG. IB), such as an integrator IN and a radiation collector CO (e.g., a condenser or collector optic). The illumination system IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section. id="p-43" id="p-43" id="p-43" id="p-43" id="p-43"

[0043] Referring to FIG. 1A, the radiation beam B is incident on the patterning device MA (e.g., a mask), which is held on the support structure MT (e.g., a mask table), and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device MA. After being reflected from the patterning device 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 IFD2 (e.g., an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (e.g., 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 IFD1 (e.g., an interferometric device, linear encoder, or capacitive sensor) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B. Patterning device MA and substrate W can be aligned using mask alignment marks Ml and M2 and substrate alignment marks Pl and P2. id="p-44" id="p-44" id="p-44" id="p-44" id="p-44"

[0044] Referring to FIG. IB, the radiation beam B is incident on the patterning device MA, which is held on the support structure MT, and is patterned by the patterning device MA. Having traversed the patterning device 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. id="p-45" id="p-45" id="p-45" id="p-45" id="p-45"

[0045] The projection system PS projects an image MP’ of the mask pattern MP, where image MP’ is formed by diffracted beams produced from the mask pattern MP by radiation from the intensity distribution, onto a resist layer coated on the substrate W. For example, the mask pattern MP can include 8 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 (e.g., 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. id="p-46" id="p-46" id="p-46" id="p-46" id="p-46"

[0046] With the aid of the second positioner PW and position sensor IFD (e.g., an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (e.g., 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 patterning device MA with respect to the path of the radiation beam B (e.g., after mechanical retrieval from a mask library or during a scan). id="p-47" id="p-47" id="p-47" id="p-47" id="p-47"

[0047] In general, movement of the support structure MT can be realized with the aid of a long-stroke positioner (coarse positioning) and a short-stroke positioner (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke positioner and a short-stroke positioner, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT can be connected to a short-stroke actuator only or can be fixed. Patterning device 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 (e.g., scribe- lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the mask alignment marks can be located between the dies. id="p-48" id="p-48" id="p-48" id="p-48" id="p-48"

[0048] Support structure 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 support structure 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. In some instances, both the in-vacuum and out-of-vacuum robots need to be calibrated for a smooth transfer of any payload (e.g., a mask) to a fixed kinematic mount of a transfer station. id="p-49" id="p-49" id="p-49" id="p-49" id="p-49"

[0049] The lithographic apparatuses 100 and 100’ can be used in at least one of the following modes: id="p-50" id="p-50" id="p-50" id="p-50" id="p-50"

[0050] 1. In step mode, the support structure 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 9 at one time (e.g., 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. id="p-51" id="p-51" id="p-51" id="p-51" id="p-51"

[0051] 2. In scan mode, the support structure 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 (e.g., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT (e.g., mask table) can be determined by the (de-)magnification and image reversal characteristics of the projection system PS. id="p-52" id="p-52" id="p-52" id="p-52" id="p-52"

[0052] 3. In another mode, the support structure MT is kept substantially stationary holding a programmable patterning device MA, 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 MA, such as a programmable minor array. id="p-53" id="p-53" id="p-53" id="p-53" id="p-53"

[0053] Combinations and/or variations on the described modes of use or entirely different modes of use can also be employed. id="p-54" id="p-54" id="p-54" id="p-54" id="p-54"

[0054] In a further aspect, lithographic apparatus 100 includes an 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. id="p-55" id="p-55" id="p-55" id="p-55" id="p-55"

[0055] FIG. 2A shows the lithographic apparatus 100 in more detail, including the radiation source SO (e.g., a source collector apparatus), the illumination system IL, and the projection system PS. As shown in FIG. 2A, the lithographic apparatus 100 is illustrated from a point of view (e.g., a side view) that is normal to the XZ plane (e.g., the X-axis points to the right and the Z-axis points upward). id="p-56" id="p-56" id="p-56" id="p-56" id="p-56"

[0056] The radiation source SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220. The radiation source SO includes a source chamber 211 and a collector chamber 212 and is configured to produce and transmit EUV radiation. EUV radiation can be produced by a gas or vapor, for example xenon (Xe) gas, lithium (Li) vapor, or tin (Sn) vapor in which an EUV radiation emitting plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The EUV radiation emitting plasma 210, at least partially ionized, can be created by, for example, an electrical discharge or a laser beam. Partial pressures of, for example, about .0 pascals (Pa) of Xe gas, Li vapor, Sn vapor, or any other suitable gas or vapor can be used for efficient generation of the radiation. In some aspects, a plasma of excited Sn is provided to produce EUV radiation. id="p-57" id="p-57" id="p-57" id="p-57" id="p-57"

[0057] The radiation emitted by the EUV radiation emitting plasma 210 is passed from the source chamber 211 into the collector chamber 212 via an optional gas barrier or contaminant trap 230 (e.g., 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 230 further indicated herein at least includes a channel structure. id="p-58" id="p-58" id="p-58" id="p-58" id="p-58"

[0058] The collector chamber 212 can include a radiation collector CO (e.g., a condenser or collector optic), 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 radiation collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point IF. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the virtual source point IF is located at or near an opening 219 in the enclosing structure 220. The virtual source point IF is an image of the EUV radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infrared (IR) radiation. id="p-59" id="p-59" id="p-59" id="p-59" id="p-59"

[0059] Subsequently the radiation traverses the illumination system IL, which can include a faceted field minor device 222 and a faceted pupil minor 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 radiation beam 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. id="p-60" id="p-60" id="p-60" id="p-60" id="p-60"

[0060] More elements than shown can generally be present in illumination system IL and projection system PS. Optionally, the grating spectral filter 240 can be present depending upon the type of lithographic apparatus. Further, there can be more minors 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. 2A. id="p-61" id="p-61" id="p-61" id="p-61" id="p-61"

[0061] Radiation collector CO, as illustrated in FIG. 2A, is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, just as an example of a collector (or collector minor). The grazing incidence reflectors 253, 254, and 255 are disposed axially symmetric around an optical axis O and a radiation collector CO of this type is preferably used in combination with a discharge produced plasma (DPP) source. id="p-62" id="p-62" id="p-62" id="p-62" id="p-62"

[0062] FIG. 2B shows a schematic view of selected portions of lithographic apparatus 100 (e.g., FIG. 1), but with alternative collection optics in the source collector apparatus SO, according to some embodiments. It should be appreciated that structures shown in FIG. 2A that do not appear in FIG. 2B (for drawing clarity) may still be included in embodiments refening to FIG. 2B. Elements in FIG. 2B having the same reference numbers as those in FIG. 2A have the same or substantially similar structures and functions as described in reference to FIG. 2A. 11 id="p-63" id="p-63" id="p-63" id="p-63" id="p-63"

[0063] In some embodiments, the lithographic apparatus 100 can be used, for example, to expose a substrate W such as a resist coated wafer with a patterned beam of EUV light. In FIG. 2B, the illumination system IL and the projection system PS are represented combined as an exposure device 256 (e.g., an integrated circuit lithography tool such as a stepper, scanner, step and scan system, direct write system, device using a contact and/or proximity mask, etc.) that uses EUV light from the source collector apparatus SO. The lithographic apparatus 100 can also include collector optic 258 that reflects EUV light from the hot plasma 210 along a path into the exposure device 256 to irradiate the substrate W. Collector optic 258 can comprise a near-normal incidence collector mirror having a reflective surface in the form of a prolate spheroid (i.e., an ellipse rotated about its major axis) having, e.g., a graded multi-layer coating with alternating layers of Molybdenum and Silicon, and in some cases, one or more high temperature diffusion barrier layers, smoothing layers, capping layers and/or etch stop layers. id="p-64" id="p-64" id="p-64" id="p-64" id="p-64"

[0064] FIG. 3 shows a detailed view of a portion of lithographic apparatus 100 (e.g., FIGS. 1, 2A, and 2B), according to one or more embodiments. Elements in FIG. 3 having the same reference numbers as those in FIGS. 1,2A, and 2B have the same or substantially similar structures and functions as described in reference to FIGS. 1, 2A, and 2B. In some embodiments, lithographic apparatus 100 can include a source collector apparatus SO having an LPP EUV light radiator. As shown, the source collector apparatus SO may include a laser system 302 for generating a train of light pulses and delivering the light pulses into a light source chamber 212. For the lithographic apparatus 100, the light pulses may travel along one or more beam paths from the laser system 302 and into the chamber 212 to illuminate a source material at an irradiation region 304 to generate a plasma (e.g., plasma region where hot plasma 210 is in FIG. 2B) that produces EUV light for substrate exposure in the exposure device 256. id="p-65" id="p-65" id="p-65" id="p-65" id="p-65"

[0065] In some embodiments, suitable lasers for use in the laser system 302 can include a pulsed laser device, e.g., a pulsed gas discharge CO2 laser device producing radiation at 9.3 pm or 10.6 pm, e.g., with DC or RE excitation, operating at relatively high power, e.g., 10 kW or higher and high pulse repetition rate, e.g., 50 kHz or more. In some embodiments, the laser may be an axial-flow RF-pumped CO2 laser having an oscillator amplifier configuration (e.g., master oscillator/power amplifier (MOPA) or power oscillator/power amplifier (POPA)) with multiple stages of amplification and having a seed pulse that is initiated by a Q-switched oscillator with relatively low energy and high repetition rate, e.g., capable of 100 kHz operation. From the oscillator, the laser pulse may then be amplified, shaped and/or focused before reaching the irradiation region 304. Continuously pumped CO2 amplifiers may be used for the laser system 302. Alternatively, the laser may be configured as a so-called "self-targeting" laser system in which the droplet serves as one minor of the optical cavity of the laser. id="p-66" id="p-66" id="p-66" id="p-66" id="p-66"

[0066] In some embodiments, depending on the application, other types of lasers may also be suitable, e.g., an excimer or molecular fluorine laser operating at high power and high pulse repetition rate. Some examples include, a solid state laser, e.g., having a fiber, rod, slab, or disk-shaped active media, other 12 laser architectures having one or more chambers, e.g., an oscillator chamber and one or more amplifying chambers (with the amplifying chambers in parallel or in series), a master oscillator/power oscillator (MOPO) arrangement, a master oscillator/power ring amplifier (MOPRA) arrangement, or a solid state laser that seeds one or more excimer, molecular fluorine or CO2 amplifier or oscillator chambers, may be suitable. Other suitable designs may be envisioned. id="p-67" id="p-67" id="p-67" id="p-67" id="p-67"

[0067] In some embodiments, a source material may first be irradiated by a pre-pulse and thereafter irradiated by a main pulse. Pre-pulse and main pulse seeds may be generated by a single oscillator or two separate oscillators. One or more common amplifiers may be used to amplify both the pre-pulse seed and main pulse seed. In some embodiments, separate amplifiers may be used to amplify the pre- pulse and main pulse seeds. id="p-68" id="p-68" id="p-68" id="p-68" id="p-68"

[0068] In some embodiments, the lithographic apparatus 100 can include a beam conditioning unit 306 having one or more optics for beam conditioning such as expanding, steering, and/or focusing the beam between the laser system 302 and irradiation region 304. For example, a steering system, which may include one or more mirrors, prisms, lenses, etc., may be provided and arranged to steer the laser focal spot to different locations in the chamber 212. For example, the steering system may include a first flat mirror mounted on a tip-tilt actuator which may move the first mirror independently in two dimensions, and a second flat minor mounted on a tip-tilt actuator which may move the second mirror independently in two dimensions. With the described arrangement(s), the steering system may controllably move the focal spot in directions substantially orthogonal to the direction of beam propagation (beam axis or optical axis). id="p-69" id="p-69" id="p-69" id="p-69" id="p-69"

[0069] The beam conditioning unit 306 can include a focusing assembly to focus the beam to the irradiation region 304 and adjust the position of the focal spot along the beam axis. For the focusing assembly, an optic, such as a focusing lens or mirror, may be used that is coupled to an actuator for movement in a direction along the beam axis to move the focal spot along the beam axis. id="p-70" id="p-70" id="p-70" id="p-70" id="p-70"

[0070] In some embodiments, the source collector apparatus SO may also include a source material delivery system 308, e.g., delivering source material, such as Sn droplets, into the interior of chamber 212 to an irradiation region 304, where the droplets will interact with light pulses from the laser system 302, to ultimately produce plasma and generate an EUV emission to expose a substrate such as a resist coated wafer in the exposure device 256. More details regarding various droplet dispenser configurations may be found in, e.g., U.S. Pat. No. 7,872,245, issued on January 18, 2011, titled "Systems and Methods for Target Material Delivery in a Laser Produced Plasma EUV Light Source", U.S. Pat. No. 7,405,416, issued on July 29,2008, titled "Method and Apparatus For EUV Plasma Source Target Delivery", U.S. Pat. No. 7,372,056, issued on May 13, 2008, titled "LPP EUV Plasma Source Material Target Delivery System", and International Appl. No. WO 2019/137846, titled "Apparatus for and Method of Controlling Coalescence of Droplets In a Droplet Stream", published on July 18, 2019, the contents of each of which are incorporated by reference herein in their entirety. 13 id="p-71" id="p-71" id="p-71" id="p-71" id="p-71"

[0071] In some embodiments, the source material for producing an EUV light output for substrate exposure may include, but is not necessarily limited to, a material that includes tin, lithium, xenon or combinations thereof. The EUV emitting element, e.g., tin, lithium, xenon, etc., may be in the form of liquid droplets and/or solid particles contained within liquid droplets. For example, the element tin may be used as pure tin, as a tin compound, e.g., SnBr4, SnBr2, SnH4, as a tin alloy, e.g., tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or a combination thereof. Depending on the material used, the source material may be presented to the irradiation region at various temperatures including room temperature or near room temperature (e.g., tin alloys, SnBr4), at an elevated temperature, (e.g., pure tin) or at temperatures below room temperature, (e.g., SnH4), and in some cases, can be relatively volatile, e.g., SnBr4. id="p-72" id="p-72" id="p-72" id="p-72" id="p-72"

[0072] In some embodiments, the lithographic apparatus 100 can also include a controller 310, which can also include a drive laser control system 312 for controlling devices in the laser system 302 to thereby generate light pulses for delivery into the chamber 212, and/or for controlling movement of optics in the beam conditioning unit 306. The lithographic apparatus 100 can also include a droplet position detection system which may include one or more droplet imagers 314 that provide an output signal indicative of the position of one or more droplets, e.g., relative to the irradiation region 304. The droplet imager(s) 314 can provide this output to a droplet position detection feedback system 316, which can, e.g., compute a droplet position and trajectory, from which a droplet error can be computed, e.g., on a droplet-by-droplet basis, or on average. The droplet error may then be provided as an input to the controller 310, which can, for example, provide a position, direction and/or timing correction signal to the laser system 302 to control laser trigger timing and/or to control movement of optics in the beam conditioning unit 306, e.g., to change the location and/or focal power of the light pulses being delivered to the irradiation region 304 in the chamber 212. Also for the source collector apparatus SO, the source material delivery system 308 can have a control system operable in response to a signal (which in some implementations may include the droplet error described above, or some quantity derived therefrom) from the controller 310, to e.g., modify the release point, initial droplet stream direction, droplet release timing and/or droplet modulation to correct for errors in the droplets arriving at the irradiation region 304. id="p-73" id="p-73" id="p-73" id="p-73" id="p-73"

[0073] In some embodiments, the lithographic apparatus 100 can also include a collector optic a gas dispenser device 320. Gas dispenser device 320 can dispense gas in the path of the source material from the source material delivery system 308 (e.g., irradiation region 304). Gas dispenser device 320 can comprise a nozzle through which dispensed gas may exit. Gas dispenser device 320 can be structured (e.g., having an aperture) such that, when placed near the optical path of laser system 302, light from laser system 302 is not blocked by gas dispenser device 320 and is allowed to reach the irradiation region 304. A buffer gas such as hydrogen, helium, argon or combinations thereof, may be introduced into, replenished and/or removed from the chamber 212. The buffer gas may be present in the chamber 14 212 during plasma discharge and may act to slow plasma created ions, to reduce degradation of optics, and/or increase plasma efficiency. Alternatively, a magnetic field and/or electric field (not shown) may be used alone, or in combination with a buffer gas, to reduce fast ion damage. id="p-74" id="p-74" id="p-74" id="p-74" id="p-74"

[0074] In some embodiments, the lithographic apparatus 100 can also include a collector optic 258 such as a near-normal incidence collector minor having a reflective surface in the form of a prolate spheroid (i.e., an ellipse rotated about its major axis) having, e.g., a graded multi-layer coating with alternating layers of Molybdenum and Silicon, and in some cases, one or more high temperature diffusion barrier layers, smoothing layers, capping layers and/or etch stop layers. Collector optic 258 can be formed with an aperture to allow the light pulses generated by the laser system 302 to pass through and reach the irradiation region 304. The same, or another similar aperture, may be used to allow gas from the gas dispenser device 320 to flow into chamber 212. As shown, the collector optic 258 can be, e.g., a prolate spheroid minor that has a first focus within or near the irradiation region 304 and a second focus at a so-called intermediate region 318, where the EUV light may be output from the source collector apparatus SO and input to an exposure device 256 utilizing EUV light, e.g., an integrated circuit lithography tool. It is to be appreciated that other optics may be used in place of the prolate spheroid minor for collecting and directing light to an intermediate location for subsequent delivery to a device utilizing EUV light. Embodiments using the collector optic CO (FIG. 2A) with structures and functions described in reference to FIG. 3 may also be envisioned. id="p-75" id="p-75" id="p-75" id="p-75" id="p-75"

[0075] Example Lithographic Cell id="p-76" id="p-76" id="p-76" id="p-76" id="p-76"

[0076] FIG. 4 shows a lithographic cell 400, also sometimes referred to a lithocell or cluster.

Lithographic apparatus 100 or 100’ can form part of lithographic cell 400. Lithographic cell 400 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. For example, these apparatuses can include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler RO (e.g., a robot) picks up substrates from input/output ports I/O I and 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. id="p-77" id="p-77" id="p-77" id="p-77" id="p-77"

[0077] Example Radiation Source id="p-78" id="p-78" id="p-78" id="p-78" id="p-78"

[0078] An example of the radiation source SO (such as shown in FIG. 3) for an example reflective lithographic apparatus is shown in FIG. 5. As shown in FIG. 5, the radiation source SO is illustrated from a point of view (e.g., a top view) that is normal to the XY plane as described below. id="p-79" id="p-79" id="p-79" id="p-79" id="p-79"

[0079] The radiation source SO shown in FIG. 5 is of a type which can be referred to as a laser produced plasma (LPP) source. A laser system 501, which can for example include a carbon dioxide (CO2) laser, is arranged to deposit energy via one or more laser beams 502 into fuel targets 503’, such as one or more discrete Sn droplets, which are provided from a fuel target generator 503 (e.g., example, fuel emitter, droplet generator). According to some aspects, laser system 401 can be, or can operate in the fashion of, a pulsed, continuous wave or quasi-continuous wave laser. The trajectory of fuel targets 503’ (e.g., example, droplets) emitted from the fuel target generator 503 can be parallel to an X-axis.

According to some aspects, the one or more laser beams 502 propagate in a direction parallel to a Y- axis. A Z-axis is perpendicular to both the X-axis and the Y-axis and extends generally into (or out of) the plane of the page, but in other aspects, other configurations are used. id="p-80" id="p-80" id="p-80" id="p-80" id="p-80"

[0080] Although Sn is referred to in the following description, any suitable target material can be used.

The target material can for example be in liquid form, and can for example be a metal or alloy. Fuel target generator 503 can include a nozzle configured to direct tin, e.g., in the form of fuel targets 503’ (e.g., discrete droplets) along a trajectory towards a plasma formation region 504. Throughout the remainder of the description, references to "fuel", "fuel target" or "fuel droplet" are to be understood as referring to the target material (e.g., droplets) emitted by fuel target generator 503. Fuel target generator 503 can include a fuel emitter. The one or more laser beams 502 are incident upon the target material (e.g., tin) at the plasma formation region 504. The deposition of laser energy into the target material creates a plasma 507 at the plasma formation region 404. Radiation, including EUV radiation, is emitted from the plasma 507 during de-excitation and recombination of ions and electrons of the plasma. id="p-81" id="p-81" id="p-81" id="p-81" id="p-81"

[0081] The EUV radiation is collected and focused by a collector 505 (e.g., radiation collector CO). In some aspects, collector 505 can include a near normal-incidence radiation collector (sometimes referred to more generally as a normal-incidence radiation collector). The collector 505 can have a multilayer structure, which is arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as about 13.5 nm). According to some aspects, collector 505 can have an ellipsoidal configuration, having two focal points. A first focal point can be at the plasma formation region 504, and a second focal point can be at an intermediate focus 506, as discussed herein. id="p-82" id="p-82" id="p-82" id="p-82" id="p-82"

[0082] In some aspects, laser system 501 can be located at a relatively long distance from the radiation source SO. Where this is the case, the one or more laser beams 502 can be passed from laser system 501 to the radiation source SO with the aid of a beam delivery system (not shown) including, for example, suitable directing mirrors and/or a beam expander, and/or other optics. Laser system 501 and the radiation source SO can together be considered to be a radiation system. id="p-83" id="p-83" id="p-83" id="p-83" id="p-83"

[0083] Radiation that is reflected by collector 505 forms a radiation beam B. The radiation beam B is focused at a point (e.g., the intermediate focus 506) to form an image of plasma formation region 504, which acts as a virtual radiation source for the illumination system IL (see FIGS. 2A and 2B). The point 16 at which the radiation beam B is focused can be referred to as the intermediate focus (e.g., intermediate focus 506). The radiation source SO is arranged such that the intermediate focus 506 is located at or near to an opening 508 in an enclosing structure 509 of the radiation source SO. id="p-84" id="p-84" id="p-84" id="p-84" id="p-84"

[0084] Similarly to FIGS 2A and 2B, the radiation beam B passes from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam B. The radiation beam B passes from the illumination system IL and is incident upon the patterning device MA held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. Following reflection from the patterning device MA the patterned radiation beam B enters the projection system PS. The projection system includes a plurality of minors, which are configured to project the radiation beam B onto a substrate W held by the substrate table WT. The projection system PS can apply a reduction factor to the radiation beam, forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of four can be applied. Although the projection system PS is shown as having two mirrors in FIGS. 2A and 2B, the projection system can include any number of minors (e.g., six mirrors). id="p-85" id="p-85" id="p-85" id="p-85" id="p-85"

[0085] The radiation source SO can include components which are not illustrated in FIG. 5. For example, a spectral filter can be provided in the radiation source SO. The spectral filter can be substantially transmissive for EUV radiation but substantially blocking for other wavelengths of radiation such as infrared radiation. id="p-86" id="p-86" id="p-86" id="p-86" id="p-86"

[0086] The radiation source SO (or radiation system) further includes a fuel target imaging system to obtain images of fuel targets (e.g., droplets) in the plasma formation region 504 or, more particularly, to obtain images of shadows of the fuel targets. The fuel target imaging system can detect light diffracted from the edges of the fuel targets. References to images of the fuel targets in the following text should be understood also to refer to images of shadows of the fuel targets or diffraction patterns caused by the fuel targets. id="p-87" id="p-87" id="p-87" id="p-87" id="p-87"

[0087] The fuel target imaging system can include a photodetector such as a CCD array or a CMOS sensor, but it will be appreciated that any imaging device suitable for obtaining images of the fuel targets can be used. It will be appreciated that the fuel target imaging system can include optical components, such as one or more lenses, in addition to a photodetector. For example, the fuel target imaging system can include a camera 510, e.g., a combination of a photosensor (or: photodetector) and one or more lenses. The optical components can be selected so that the photosensor or camera 510 obtains near-field images and/or far-field images. The camera 510 can be positioned within the radiation source SO at any appropriate location from which the camera has a line of sight to the plasma formation region 504 and one or more markers (not shown in Fig. 5) provided on the collector 505. It may be necessary, however, to position the camera 510 away from the propagation path of the one or more laser beams 502 and from the trajectory of the fuel targets emitted from fuel target generator 503 so as to avoid damage to the camera 510. According to some aspects, the camera 510 is configured to provide images of the fuel 17 targets to a controller 511 via a connection 512. The connection 512 is shown as a wired connection, though it will be appreciated that the connection 512 (and other connections referred to herein) can be implemented as either a wired connection or a wireless connection or a combination thereof. id="p-88" id="p-88" id="p-88" id="p-88" id="p-88"

[0088] As shown in FIG. 5, the radiation source SO can include a fuel target generator 503 configured to generate and emit fuel targets 503’ (e.g., discrete Sn droplets) towards a plasma formation region 504. The radiation source SO can further include a laser system 501 configured to hit one or more of the fuel targets 503’ with one or more laser beams 502 for generating a plasma 507 at the plasma formation region 504. The radiation source SO can further include a collector 505 (e.g., a radiation collector CO) configured to collect radiation emitted by the plasma 507. In some aspects, a collector flow ring CFR (not shown in FIG. 5) can be disposed adjacent to the collector 505 to mitigate an accumulation of fuel debris (e.g., tin) in the radiation source SO, among other features. The collector flow ring CFR can be disposed along an axis parallel to the X-axis (e.g., near the trajectory of fuel targets 503’ emitted from the fuel target generator 503). id="p-89" id="p-89" id="p-89" id="p-89" id="p-89"

[0089] In order for the radiation source to function properly, a continuous supply of fuel is required.

This means that measurement, monitoring, and maintenance is required to ensure a continuous inline supply of fuel. id="p-90" id="p-90" id="p-90" id="p-90" id="p-90"

[0090] As will be further described herein with regard to FIGS. 6-11, an inline refill system may be provided. According to some aspects, in the inline refill system, Sn level may be measured indirectly by releasing a certain amount of gas from pressurized reservoir through an orifice of known size. The rate at which the pressure drops inside the reservoir may then be measured for the volume of pressurized gas. The Sn volume can then be determined by subtracting the gas volume from the total reservoir volume. Such methodology may be used along with a pressure fluctuation on the reservoir in order to determine the Sn volume inside the reservoir. The disclosure provides other embodiments for the measurement of the Sn volume when the pressure vessel is supplying Sn to the droplet generator (DG) such that avoids any issues associated with the Sn running dry, and getting gas bubbles in the transfer line due to the dryness. It is useful to accurately monitor the volume of Sn in the pressurized reservoirs to avoid a gas volume reaching a freeze valve, at which condition the system may become uncontrollable, since it would be difficult to close the gas filled freeze valve. id="p-91" id="p-91" id="p-91" id="p-91" id="p-91"

[0091] Figs. 6A and 6B illustrate schematic architecture 600 for in-tank level sensors, according to some embodiments. Architecture 600 can include passive level sensors, which do not require pressure fluctuations in the Sn reservoir, as will be further described herein. id="p-92" id="p-92" id="p-92" id="p-92" id="p-92"

[0092] Architecture 600 can include a plurality of molybdenum rods 602 that can be housed within fuel tank 604 and secured with glass/ceramic seal 606. Fuel tank 604 may be constructed of various metals, ceramics, polymers, or other suitable rigid materials. In some aspects, the seal may be constructed using a short length of borosilicate tubing. The borosilicate tubing can provide a favorable coefficient of linear expansion (GTE) with respect to the molybdenum, and thus, may provide better 18 hold and seal of the molybdenum rods. According to some aspects, a chemical bond may be provided between the borosilicate and the molybdenum for added seal. In a non-limiting manner, it can be understood that other bonding material may be utilized, including, for example, aluminum silicate (A12SiO5). id="p-93" id="p-93" id="p-93" id="p-93" id="p-93"

[0093] According to some aspects, the plurality of molybdenum rods 602 can detect a full state 608 or an empty state 610 based on a combination of detection methodologies. In some aspects, two molybdenum rods (A and B) can be utilized to determine low levels of Sn in tank 604. In this regard, a closed circuit status may be monitored, and when Sn levels drop below a minimum threshold (in which the molybdenum rods are no longer in contact with the Sn), an open circuit results, and a signal may be transmitted to controller/processor (such as controller 310) indicating low levels of Sn in the tank. id="p-94" id="p-94" id="p-94" id="p-94" id="p-94"

[0094] According to some embodiments illustrated in Fig. 6B, the molybdenum rods 612 can be arranged horizontally. In this implementation, molybdenum rod E can be designated as a low level threshold in which when Sn levels drop below, an empty indication may be provided. In one example, when continuity between rods A and E is detected (e.g., closed circuit), a full signal may be relayed back indicating a "full" status. When no continuity between D and E is detected, an "empty" status may be indicated. Moreover, when there is continuity between E and B, C, or D, a proportional level indication may be provided. id="p-95" id="p-95" id="p-95" id="p-95" id="p-95"

[0095] The embodiments described in Figs. 6A and 6B eliminate the need for pressure fluctuations as a means to measure the Sn level. Moreover, level indications, e.g., full, empty, 50%, or the like, may be provided immediately after that level is reached. This allows for simpler and therefore faster control systems, because this is a passive signal being sent to a control system, as opposed to an active measurement that requires certain system states. Additionally, the present implementations illustrated in Figs. 6A and 6B enable further simplification of the inline refill system. id="p-96" id="p-96" id="p-96" id="p-96" id="p-96"

[0096] FIG. 7 illustrates a schematic architecture for inline refill system 700, according to some embodiments. To improve source availability in EUV lithography systems, there is a drive to reduce or even eliminate the downtime associated with a lack of high quality Sn supply to a droplet generator (DG). According to aspects of the present embodiment, the described inline refill system (IR) allows for a continuous supply of high purity Sn into the droplet generator assembly (DGA). Moreover, without knowing the status of the Sn supply (e.g., amount left, cleanliness, and state of the Sn (e.g., liquid or solid)), it would be unproductive to operate an inline refill system. id="p-97" id="p-97" id="p-97" id="p-97" id="p-97"

[0097] To allow for implementation of an IR, there may be a need to determine a status of Sn across two or more IR sub modules, as will be further described herein. System 700 may include a Sn priming tank (TFT) 702 that holds an initial level of solid Sn. TPT 702 may be configured to receive and prime Sn solids and melt the Sn. TPT 702 may further be configured to feed the melted Sn into Sn refill tank (TRT) 704. TRT 704 may be configured to supply the new-clean liquid Sn to refill reservoir (RR) 708.

According to some aspects, RR 708 may then supply the liquid Sn to primary reservoir (PR) 714 and/or 19 to the DGA 722. The transfer of liquid Sn may be done through a flow system including a combination of flow valves and conduits (710a-e). It is to be understood that flow system 710a-e may be comprise physical properties that can withstand the safe, constant, and uniform transfer of melted Sn, within system 700. id="p-98" id="p-98" id="p-98" id="p-98" id="p-98"

[0098] According to some aspects, RR 708 may supply Sn for droplets, and supplies more Sn to PR 714, and PR 714 may supply the liquid Sn to the DGA 722. The liquid Sn housed in RR 708 and PR 714 may be illustrated as liquid Sn 712. It is noted that the number of tanks and reservoirs described herein is illustrative, and different combinations thereof and numbers may be implemented for greater efficiency and cost measures. id="p-99" id="p-99" id="p-99" id="p-99" id="p-99"

[0099] According to some aspects, one or more of the tanks/reservoirs in system 700 may be coupled to an optical sensor 716, 718, or 720 configured to measure Sn properties contained within each tank/reservoir. In one example, TPT 702, TRT 704, RR 708 and PR 714 can each be coupled to an associated optical sensor (e.g. TPT 702 coupled to optical sensor 716) that can measure properties of the Sn located inside each tank/reservoir. Among the properties that the optical sensors can measure are Sn levels, Sn contamination levels, sight glass contamination and the like as will be further described herein. It is to be understood that optical sensor may also be referred to herein as sensor, optical device, measuring device, or optical measuring device. id="p-100" id="p-100" id="p-100" id="p-100" id="p-100"

[0100] According to some embodiments, TPT 702 sensor 716 can be configured to detect when solid Sn is loaded, and monitors a melt operation into TRT 704. According to some embodiments, sensor 718 at TRT 704 can monitor the Sn level in TRT 704, and provide a request for more Sn from TPT 702 when needed. According to some aspects, such need for Sn may be determined based on measurements taken by sensor 718, or may be based on request signals received from other sensors (e.g., sensor 720 or an optical sensor on RR 708, not shown). Sensor 718 can also monitor the amount of Sn being pushed/suppled to RR 708. According to some aspects, sensor 720 can monitor the Sn level in PR 714, and request more Sn to be delivered from TRT 704 to RR 708 and subsequently PR 714. id="p-101" id="p-101" id="p-101" id="p-101" id="p-101"

[0101] According to some aspects, the Sn may be pushed via a pressured gas mixture (e.g., ~ 98% Ar (argon), 2% H (hydrogen)) applied at TRT 704 delivering Sn through flow valve 710a and conduit 710b, into RR 708 which is held at a low pressure (not deep vacuum). According to some aspects, TRT 704 can be filled via TPT 702. Additionally, PR 714 can operate the entire time under high pressure to supply DGA 722. In one example, once RR 708 is full, flow valve 710c can be closed off; pressure can then be applied to RR 708 to match pressure in PR 714. Once pressure is at a level matching PR 714, flow valve 710c can be opened so that fuel can flow from RR 708 to PR 714, when PR 714 is near empty, for example. Accordingly, level measurements taken by sensor 720 can dictate when flow valves, such as flow valve 724 may open and close. Sensor 720 may also be referred to as optical device 720, and these terms may be used interchangeably herein. As previously noted, each sensor may be configured to monitor Sn level changes (and subsequent volume changes), Sn purity levels, and Sn state status (e.g., liquid or solid). id="p-102" id="p-102" id="p-102" id="p-102" id="p-102"

[0102] According to some aspects, pressure manipulation of reservoirs throughout the system can provide different functions. For example, according to some aspects, deep vacuum and low pressure gas can be employed, which is known as cycle purging. According to some aspects, the Sn can be kept under deep vacuum, while high pressure can be used to maintain Sn droplet velocity at the nozzle (e.g., DGA 722). PR 714, or any other reservoir/tank that may be positioned directly prior to DGA 722, can maintain high pressure to be able to supply the Sn to produce EUV. Additionally, TRT 704 and TPT 702 can maintain environments for clean Sn. For example, switching from solid Sn to liquid Sn may introduce opportunities for Sn contamination due to environments the Sn and TPT 702 were exposed to prior to TPT 702 being sealed. According to some aspects, the manner in which Sn is heated may have an effect on Sn cleanliness. Additionally, Sn cleanliness is desired for long lifetime droplet generation with accurate droplet positioning. id="p-103" id="p-103" id="p-103" id="p-103" id="p-103"

[0103] According to some aspects, RR 708 can employ a transition from low to high pressure, and thus, switch to low pressure to receive Sn from TRT 704, and switch back to high pressure when supplying Sn to PR 714. According to some aspects, optical device 720 may include a processor that can generate control signals to control the flow of Sn through the reservoirs. Additionally, or in the alternative, optical device 720 may transmit active measurements to a controller (e.g., controller 310 in FIG. 3) for further processing and control of the Sn flow. Similar operations can be carried out by other optical devices in system 700. For example, each of optical devices 716, 718, and 720 may include its own processing capabilities for monitoring and reporting the above-noted properties, and taking actions based on the monitoring. Taking actions in this context may mean providing control signals to facilitate actions for transfer, or feed of Sn for example. According to some aspects, each sensor can monitor and report data to a central processor (e.g., controller 310), or to one or to another sensor (e.g., sensors reporting upstream or downstream depending on which sensor may be configured to provide the instructions/control signals). id="p-104" id="p-104" id="p-104" id="p-104" id="p-104"

[0104] In one example, sensor 720 may be configured to determine the Sn properties within PR 714.

Additionally, based on the determined properties, and processing what sensors 716 and 718 have reported with regards to upstream availability of Sn, sensor 720 can provide instructions for other tanks to take certain actions. For example, sensor 720 may send instructions to any or each of TPT 702, TRT 704 and/or RR 708 to take an action. Such actions may include melting more Sn, or providing certain levels of Sn from one reservoir to another. Such instructions may take into account thermodynamic considerations related to the heating and transfer of Sn, conduit properties, tank properties, and the like.

It is to be appreciated that sensor 720 can send action commands to one or more tanks, one or more sensors, and one or more processors that can perform the necessary actions to ensure continuous supply of Sn. According to other aspects, sensor 720 may be one a plurality of sensors that report to a central 21 processor (e.g., controller 310) and controller 310 can provide further instructions to any and all the sensors/tanks in system 700. id="p-105" id="p-105" id="p-105" id="p-105" id="p-105"

[0105] According to some aspects, PR 714 can be the primary supplier of Sn to DGA 722. As such, monitoring Sn levels in PR 714 may be a beneficial aspect to achieve constant supply of Sn to DGA 722. According to some aspects, sensor 720 (or controller 310) may place a greater weighting factor to readings of PR 714. For example, a low Sn level at PR 714 may be more critical than low Sn level at TPT 702 or TRT 704, due to the immediacy of need for Sn to feed DGA 722. Similarly, contamination readings at different tanks/reservoirs may be assigned different weighting based on their location in the inline assembly. id="p-106" id="p-106" id="p-106" id="p-106" id="p-106"

[0106] FIGS. 8A-8B illustrate non-invasive triangulation sensor assembly 800 deployment within system 700 for detecting source levels in vacuum tanks such as the primary and refill reservoirs 714, 708 in system 700, according to some embodiments. According to some embodiments, assembly 800 can include an optical device 802 that both transmits and receives light signals 804 into tank 806 to measure a level and other properties of Sn 808. As will be further described herein, optical device 802 may also be referred to as optical sensor, optical measuring device, sensor device, measurement device, and the like. According to some aspects, optical device 802 can include an optical transmitter 816 and an optical receiver 818. Optical transmitter 816 can be configured to transmit a light beam 804. Light beam 804 can be a laser light beam. In some aspects, the transmitted and received light 804 can enter and exit tank 806 through flange 810 that includes one or more view ports. id="p-107" id="p-107" id="p-107" id="p-107" id="p-107"

[0107] According to some aspects, optical device 802 can be configured to determine Sn level, quality, and state of the Sn in the can by using triangulation. According to some aspects, optical device 802 can include an optical transmitter 816 including a light source and an optical receiver 818 including a detector array. According to some aspects, optical transmitter 816 transmits an incident light beam (e.g., laser beam, or the like) and optical receiver 818 is configured to receive a reflected light beam. After the reflected light beam is received, optical device 802 can perform triangulation calculations to determine properties associated with the Sn and the tank to which optical device 802 is mounted. id="p-108" id="p-108" id="p-108" id="p-108" id="p-108"

[0108] According to some embodiments, optical transmitter 816 can transmit a beam at a known angle 9. Based on the Sn level in the tank, the transmitted beam is reflected at a certain point and is reflected back into optical receiver 818. According to some aspects, the height of the Sn level can determine where, on optical receiver 818, a reflected light beam is received. Accordingly, to determine a Sn level 814, optical device 802 measures a horizontal distance 812, from a point on optical receiver 818 where the reflected light beam is received to a point of irradiation within optical transmitter 816. According to some aspects, distance 812 can be measured from the point light is transmitted to a point on the detector array (e.g., a predetermined pixel location, or predetermined sensor in the array) that receives the reflected light. According to some aspects, reflected light may be received at multiple locations on the detector array. Accordingly, for purposes of measuring horizontal distance 812, the location within 22 the array that receives the strongest signal (e.g., signal with highest amplitude) may be utilized. Given the measurement 812, and the known angle of incidence, 9, the level 814 can be calculated. id="p-109" id="p-109" id="p-109" id="p-109" id="p-109"

[0109] According to some aspects, the feedback form the sensors allows for multi-functionality in the measurements of the Sn level, and quality, with no adverse effects to the high pressure, high vacuum, and high purity environment. According to some aspects, optical device 802 can measure a light intensity across an array of sensors on optical receiver 818. Using raw data from the optical receiver 818, a light intensity graph can be generated as a function of position on optical receiver 818 (e.g., location vs. intensity, as illustrated in FIG. 10). This light intensity graph can include multiple peaks, as will be further described herein. According to some aspects, when optical device 802 is used with the Sn and the reservoir is in the vertical configuration, as illustrated in FIG. 8A, the extra peaks can be negligible, and the main function can be to monitor the Sn level, and Sn phase changes (e.g., solid, liquid). id="p-110" id="p-110" id="p-110" id="p-110" id="p-110"

[0110] According to some aspects, optical device 802 can be used as a stand-alone device to detect phase change. According to some aspects, a pairing between optical device 802 and a thermocouple device (e.g., a probe - not shown) that can generate thermocouple readings can further enhance phase shift readings of Sn. id="p-111" id="p-111" id="p-111" id="p-111" id="p-111"

[0111] FIG. 8C is a temperature-time plot that illustrates shift in average Sn level and noise level measured by optical device 802 plotted with measured temperature. In one example, the shift can happen at a predetermined temperature range of Sn melting (e.g., about 232°C), as depicted by 820.

Based on the optical properties of solid Sn and liquid Sn, determining phase change of Sn can factor in calculation of supply of Sn, (e.g., how much Sn is melted, vs. how much Sn is solid). For example, melted Sn may be readily available, whereas solid Sn may require additional time to be melted and fed through system 700. id="p-112" id="p-112" id="p-112" id="p-112" id="p-112"

[0112] According to some aspects, optical device 802 can detect the largest spike on the graph, and determine that as being the most dominant reflection received, which is then correlated to the distance measurement of the Sn level, as described herein. Other information can be derived from the secondary and tertiary light intensity spikes. This can be the case when the reservoir 806 is upright or in an angled configuration. id="p-113" id="p-113" id="p-113" id="p-113" id="p-113"

[0113] According to one example, Sn purity levels can be detected based on one or more data points illustrated in the graph. According to one aspect, a light spike found just before the distance measurement between the detector point (i.e., location where the reflected light is received at optical receiver 818) and the illumination point (i.e., location where the light signal is transmitted from optical transmitter 816) changes as a function of Sn purity. This is caused due to a reduced reflection of light off the Sn as the Sn surface becomes more contaminated (e.g., the light spot becomes more dominant on the Sn itself.) According to some aspects, the effects of contamination and the like can be amplified when the reservoir is in an angular configuration as illustrated in FIG. 9 23 id="p-114" id="p-114" id="p-114" id="p-114" id="p-114"

[0114] FIG. 9A illustrates another example of non-invasive triangulation sensor deployment 900 for detecting source levels in vacuum tanks within system 700, according to some embodiments. In deployment 900, optical device 802 can transmit and receive a light beam and generate a reading of Sn level and other physical properties of the Sn based on certain parameters as further described herein.

According to some aspects, entry and exit site 902 can be at glass ports within a viewing window 810 located at an end of a tank/reservoir. According to some aspects, a clean glass port will show minimal light intensity at an entry and exit point from which incident light enters and exits. Conversely, an increase in the light intensity at these entry and exit points indicates that the sight glass is getting dirty, or becoming more contaminated and requires further attention/maintenance. Depictions of the received light/intensities at optical device 802 are further illustrated in FIGS. 9B-9D described herein below. id="p-115" id="p-115" id="p-115" id="p-115" id="p-115"

[0115] According to some aspects, light intensity measured at 904 is indicative of Sn level detection.

According to some embodiments, as illustrated in FIGS. 8A and 8B for example, liquid Sn can act as a minor, and with Sn at an angle, the distance can be calculated from the reflected dot 904, reflected from the reservoir wall. According to other aspects, point 906 can indicate a Sn purity detection location. At 904 as this location becomes more visible, the Sn is reflected less which means that tin-oxide build-up is increasing. id="p-116" id="p-116" id="p-116" id="p-116" id="p-116"

[0116] FIGS. 9B-9D illustrate intensities received and measured at the sensor (e.g., optical device 802).

For example, FIG. 9B illustrates light signals received at optical device 802 in a situation where both, the viewport and the Sn are clean. FIG. 9C illustrates light signals received at optical device 802 in a situation where the viewport is dirty, and the Sn is clean. Fig. 9D illustrates light signals received at optical device 802 in a situation where the viewport is clean and the Sn is dirty. It can be appreciated that the designation of "clean" and "dirty" may reflect a level of detected contamination, above which, the viewport/Sn can be deemed "dirty" and, below which, the viewport/Sn can be deemed "clean." id="p-117" id="p-117" id="p-117" id="p-117" id="p-117"

[0117] According to some aspects, the general locations of the received signals/light may be known.

For example, viewport entry point 902 and return point 908 can be fixed locations. Variations can occur for reflected dot 904 and point 906. The correlation between these two signals relates to the determination of Sn level and purity levels. For example, reflected dot 904 may be the point of highest intensity, indicating the reflection off of the Sn (either at Sn surface or the reservoir wall), and therefore, its location is correlated with the Sn level. However, as Sn contamination levels increase, the intensity at 906 increases while intensity at reflected dot 904 decreases. This can continue until intensity at point 906 is greater than intensity at reflected dot 904. In this case, optical device 802 can use reflected dot 906 as the location corresponding to the Sn level instead of reflected dot 904. Moreover, optical device 802 may further generate a warning indicative of a high contamination level. It can be appreciated that such warning may be transmitted to an operator through a graphical user interface (GUI), or other methodologies indicating the detected contamination of the Sn. 24 id="p-118" id="p-118" id="p-118" id="p-118" id="p-118"

[0118] FIG. 10 is a graphical representation of signal detected at a receiver array of a sensor, according to some embodiments. According to some aspects, the receiver array of optical receiver 818, for example, can receive a light with different intensity profiles at different locations, indicated as peaks (at different locations within the receiver array). According to some embodiments, peak 1002 can be indicative of a light intensity of a view port cleanliness detection. Peak 1004 can be indicative of a light intensity of Sn purity detection, in which this intensity grows as the Sn gets dirtier. Peak 1006 can be indicative of a light intensity of Sn level detection, and peak 1008 can be indicative of light intensity of viewport return beam. According to some aspects, the location of the peaks and the relationship to one another is not arbitrary. As described in FIGS. 9B-9D, for example, the main signal output (highest peak - peak 1006) can designated as the peak indicative of the Sn level detection. It is further determined that the peak right before (or right after as illustrated in FIGS. 9B-9D) the highest peak 1006 (peak 1004) can be indicative of a light intensity of the Sn purity. Moreover, according to some aspects, the first and last intensity peaks can be determined as the peaks associated with the light intensity of the view port and thus, viewport cleanliness detection can be determined. id="p-119" id="p-119" id="p-119" id="p-119" id="p-119"

[0119] According to some aspects, the detector array of receiver 818 can correlate distance measurements of received signals based on known 9. For example, since the system geometries are known (e.g., location of optical device 802, viewport entry and return points, and reservoir dimensions), the expected location of the relative peaks can be expected to be within certain location range.

Accordingly, detector array readings may focus on 904 and 906 to determine depth and contamination levels. In some aspects, when the light intensity switches from 904 to 906 (e.g., FIG. 9C to 9D), optical device 802 may include further programming that can switch to using the 906 measurement as that associated with the depth of the Sn. Additionally, optical device 802 (through its own controller or controller 310) may transmit a message to an operator, letting the operator know that high contamination levels are detected that warrant investigation. id="p-120" id="p-120" id="p-120" id="p-120" id="p-120"

[0120] FIG. 11 illustrates a flow diagram showing an example of a detection method 1100 of source levels in an inline refill system, according to some embodiments. id="p-121" id="p-121" id="p-121" id="p-121" id="p-121"

[0121] According to some aspects, method 1100 can be a method for measuring inline feed of a radiation fuel in an extreme ultraviolet (EUV) radiation system. Method 1100 can include directing an inspection beam through a fuel tank view port at a top surface of the radiation fuel at a predetermined incident angle, as illustrated in step 1102. Method 1100 can also include receiving a portion of the inspection beam reflected by the top surface of the radiation fuel at a sensor located adjacent to the view port, as illustrated in step 1104. Method 1100 can also include measuring a distance to the top surface of the radiation fuel, as illustrated in step 1106. Moreover, method 1100 can also include calculating a fill level of the radiation fuel in the fuel tank based on the measured distance, as illustrated in step 1108. id="p-122" id="p-122" id="p-122" id="p-122" id="p-122"

[0122] Although not illustrated in Fig. 11, method 1100 can further include the inspection beam being directed at plural irradiation points and the calculation is based on one or more reflections having the highest signal intensity. Moreover, method 1100 can further include transmitting a signal indicative of the calculated fill level to a first upstream tank (e.g., RR 708) supplying the radiation fuel to the fuel tank (e.g., PR 714). According to some aspects, the transmitted signal further includes a maintain course of action command to the first upstream tank (e.g. RR 708) to maintain a course of action in response to the fill level being within a predetermined threshold. For example, if the fill level of PR 714 is within a predetermined fill range where the tank is not full and not nearing empty, sensor 720 may transmit a sensor associated with RR 708 or controller 310 indicating that a course of action should be maintained. id="p-123" id="p-123" id="p-123" id="p-123" id="p-123"

[0123] According to some aspects, method 1100 can further include transmitting a second signal indicative of the calculated fill level to a second upstream tank (e.g., TPT 702) supplying the Sn to the first upstream tank (e.g., RR 708), the second upstream tank being tank configured to collect and heat the radiation fuel to a predetermined temperature. According to some aspects, TPT 702 may directly provide Sn to RR 708, or provide the Sn initially to TRT 704. As noted herein, any number/combination of tanks and reservoirs in the system can be deployed based on system requirements and required need of DGA 722. According to some aspects, method 1100 can further include transmitting a time parameter for supplying the Sn, taking into account a required time for heating the Sn. In one example, the signal received at TPT 702 (i.e., via controller 310 or sensor 716) can include a timing parameter. The timing parameter can take in system factors into account, including, for example, how long Sn may be required to be heated and melted, length of the conduits in flow system 710a-e, and a number of tanks in the system (e.g., RR 708, TRT 704). Moreover, the second signal can further instruct the second upstream tank (e.g., TPT 702) when to supply the collected and heated radiation fuel to the first upstream tank (e.g., TRT 704 or RR 708). Additionally, method 1100 can further include measuring, by sensor 716, an amount of Sn being heated, and transmitting, to sensor 720, the measured amount indicative of an amount of Sn entering the inline feed of the EUV radiation system. id="p-124" id="p-124" id="p-124" id="p-124" id="p-124"

[0124] According to some aspects, method 1100 can further include processing one other reflected signal from the one or more reflections (e.g., 1002, 1004, or 1008), the one other reflected signal having a lower intensity than the one or more reflections having the highest signal intensity, and generating an operator message, the message indicating a level of contamination associated with the view port (e.g., view port too dirty). In yet another aspect, the message may indicate a level of contamination associated with the Sn (e.g., Sn contamination too high). id="p-125" id="p-125" id="p-125" id="p-125" id="p-125"

[0125] 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 apparatuses described herein can 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 synonymous with the more general terms "substrate" or "target portion", respectively. The substrate referred to herein can be processed, before or after 26 exposure, in for example a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit and/or an inspection 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 can also refer to a substrate that already contains multiple processed layers. id="p-126" id="p-126" id="p-126" id="p-126" id="p-126"

[0126] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein. id="p-127" id="p-127" id="p-127" id="p-127" id="p-127"

[0127] The examples disclosed herein are illustrative, but not limiting, of the embodiments of this disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the relevant art(s), are within the spirit and scope of the disclosure. id="p-128" id="p-128" id="p-128" id="p-128" id="p-128"

[0128] While specific aspects of the disclosure have been described above, it will be appreciated that the aspects can be practiced otherwise than as described. The description is not intended to limit the embodiments of the disclosure. id="p-129" id="p-129" id="p-129" id="p-129" id="p-129"

[0129] It is to be appreciated that the Detailed Description section, and not the Background, 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 example embodiments as contemplated by the inventor(s), and thus, are not intended to limit the present embodiments and the appended claims in any way. id="p-130" id="p-130" id="p-130" id="p-130" id="p-130"

[0130] Some aspects of the disclosure have 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. id="p-131" id="p-131" id="p-131" id="p-131" id="p-131"

[0131] The foregoing description of the specific aspects of the disclosure will so fully reveal the general nature of the aspects that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific aspects, without undue experimentation, without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein. id="p-132" id="p-132" id="p-132" id="p-132" id="p-132"

[0132] Other aspects of the invention are set out in the following numbered clauses. 1. A method for measuring a fuel fill level of a radiation fuel in an extreme ultraviolet (EUV) radiation system, the method comprising: directing an inspection beam through a fuel tank view port at a top surface of the radiation fuel at a predetermined incident angle; 27 receiving a portion of the inspection beam reflected by the top surface of the radiation fuel at a sensor located adjacent to the view port; determining a transmission coordinate of a transmission location of the inspection beam; determining a reception coordinate of a reception location of the received portion of the inspection beam; measuring a distance between the reception coordinate and the transmission coordinate; and calculating the fill level of the radiation fuel in the fuel tank based on the measured distance. 2. The method of clause 1, wherein the inspection beam is directed at plural irradiation points and the calculation is based on one or more reflections having the highest signal intensity. 3. The method of clause 1, further comprising: transmitting a signal indicative of the calculated fill level to a first upstream tank supplying the radiation fuel to the fuel tank. 4. The method of clause 3, wherein the transmitted signal further includes a maintain course of action command to the first upstream tank to maintain a course of action in response to the fill level being within a predetermined threshold.

. The method of clause 3, further comprising: transmitting a second signal indicative of the calculated fill level to a second upstream tank supplying the radiation fuel to the first upstream tank, the second upstream tank being tank configured to collect and heat the radiation fuel to a predetermined temperature. 6. The method of clause 5, wherein the radiation fuel is tin (Sn), and wherein the transmitting the second signal further comprises transmitting a time parameter for supplying the tin, taking into account a required time for heating the tin. ר. The method of clause 5, wherein the second signal further instructs the second upstream tank to supply the collected and heated radiation fuel to the first upstream tank. 8. The method of clause 7, further comprising: measuring an amount of radiation fuel being heated; and transmitting, to the sensor, the measured amount indicative of an amount of radiation fuel entering the fuel feed level of the EUV radiation system. 9. The method of clause 3, further comprising: processing one other reflected signal from the one or more reflections, the one other reflected signal having a lower intensity than the one or more reflections having the highest signal intensity; and generating an operator message, the message indicating a level of contamination associated with the view port.

. The method of clause 1, further comprising: measuring a tank light intensity reflection of the received portion of the inspection beam from a tank wall in response to the fuel tank being positioned at an angular deviation from an upright position, the tank light intensity reflection being indicative of fuel level in the tank; and 28 measuring a fuel light intensity reflection from the fuel in the fuel tank, the fuel light intensity reflection being indicative of a purity level of the fuel. 11. A measurement device for measuring fuel fill level of a radiation fuel in an extreme ultraviolet (EUV) radiation system, the measurement device being located adjacent to a fuel tank view port, the measurement device comprising: a transmitter configured to direct an inspection beam through the fuel tank view port at a top surface of the radiation fuel at a predetermined incident angle; a receiver configured to receive a portion of the inspection beam reflected by the top surface of the radiation fuel; and processing circuitry configured to determine a transmission coordinate of a transmission location of the inspection beam, determine a reception coordinate of a reception location of the received portion of the inspection beam, measure a distance between the reception coordinate and the transmission coordinate, and calculate a fill level of the radiation fuel in the fuel tank based on the measured distance. 12. The measurement device of clause 11, wherein the inspection beam is directed at plural irradiation points and the calculation is based on one or more reflections having the highest signal intensity. 13. The measurement device of clause 11, wherein the processing circuitry is further configured to transmit a signal indicative of the calculated fill level to a first upstream tank supplying the radiation fuel to the fuel tank. 14. The measurement device of clause 13, wherein the transmitted signal further includes a maintain course of action command to the first upstream tank to maintain a course of action in response to the fill level being within a predetermined threshold.

. The measurement device of clause 13, wherein the processing circuitry is further configured to transmit a second signal indicative of the calculated fill level to a second upstream tank supplying the radiation fuel to the first upstream tank, the second upstream tank being a tank configured to collect and heat the radiation fuel to a predetermined temperature. 16. The measurement device of clause 15, wherein the radiation fuel is tin (Sn), and the processing circuitry is further configured to transmit, within the second signal, a time parameter for supplying the tin, taking into account a required time for heating the tin. 17. The measurement device of clause 15, wherein the second signal further instructs the second upstream tank to supply the collected and heated radiation fuel to the first upstream tank. 18. The measurement device of clause 17, wherein the processing circuitry is further configured to: receive, from a sensor associated with the second upstream tank, a measured amount of radiation fuel being heated and supplied to the first upstream tank; 29 update a measurement indicative of an amount of radiation fuel entering the fuel fill level of the EUV radiation system; and calculate a time interval at which the heated radiation fuel is expected to arrive at the fuel tank. 19. The measurement device of clause 13, wherein the processing circuitry is further configured to: process one other reflected signal from the one or more reflections, the one other reflected signal having a lower intensity than the one or more reflections having the highest signal intensity; and generate an operator message, the message indicating a level of contamination associated with the view port.

. The measurement device of clause 11, wherein the processing circuitry is further configured to: measure a tank light intensity reflection from a tank wall in response to the fuel tank being positioned at an angular deviation from an upright position, the tank light intensity reflection being indicative of fuel level in the fuel tank; and measure a fuel light intensity reflection from the fuel in the fuel tank, the fuel light intensity reflection being indicative of a purity level of the fuel. 21. A measurement device for measuring fuel fill level of a radiation fuel in an extreme ultraviolet (EUV) radiation system, the measurement device being located within a fuel tank, the measurement device comprising: a measurement sensor comprising a plurality of probes extending within the fuel tank, each one of the plurality of probes being configured to generate a signal in response to having contact with the radiation fuel, wherein the plurality of probes connect to the fuel tank through a plurality of hermetic high pressure seals; and a controller including processing circuitry, the controller being configured to calculate a fuel fill level within the fuel tank in response to receiving one or more generated signals, generate an output signal indicative of the calculated fill level, and transmit the output signal to at least one other controller. 22. The measurement device of clause 21, wherein the at least one other controller is a first upstream controller associated with a first upstream tank supplying the radiation fuel to the fuel tank. 23. The measurement device of clause 22, wherein the transmitted output signal includes a maintain course of action command to the first upstream controller to maintain a course of feed action in response to the fill level being within a predetermined threshold. 24. The measurement device of clause 22, wherein the controller is further configured to transmit a second signal indicative of the calculated fill level to a second upstream controller associated with a second upstream tank supplying the radiation fuel to the first upstream tank, the second upstream tank being a tank configured to collect and heat the radiation fuel to a predetermined temperature.

. The measurement device of clause 24, wherein the radiation fuel is tin (Sn), and the controller is further configured to transmit, within the second signal, a time parameter for supplying the Sn based on a required time for heating the Sn. 26. The measurement device of clause 24, wherein the second signal further instructs the second upstream controller to supply the collected and heated radiation fuel to the first upstream tank. 27. The measurement device of clause 26, wherein the controller is further configured to: receive, from the second upstream controller, a measured amount of radiation fuel being heated and supplied to the first upstream tank; update a measurement indicative of an amount of radiation fuel entering the fuel fill level of the EUV radiation system; and calculate a time interval at which the heated radiation fuel is expected to arrive at the fuel tank. 28. The measurement device of clause 21, wherein the plurality of probes extend downwardly to different depths within the fuel tank. 29. The measurement device of clause 21, wherein the plurality of probes extend laterally into the tank at different vertical locations.

. A lithographic radiation system comprising: a first fuel tank coupled to a first sensor device and a first controller; and a second fuel tank coupled to a second sensor device and a second controller, the second fuel tank located upstream from the first fuel tank in a fuel fill system and providing radiation fuel to the lithographic radiation system, the first controller is configured to calculate a fuel fill level within the first fuel tank, generate an output signal indicative of the calculated fill level, and transmit the output signal to the second controller. 31. The lithographic radiation system of clause 30, wherein the first sensor device is an optical sensor. 32. The lithographic radiation system of clause 31, wherein the optical sensor is configured to: direct an inspection beam through a first tank view port at a top surface of the radiation fuel at a predetermined incident angle, and receive a portion of the inspection beam reflected by the top surface of the radiation. 33. The lithographic radiation system of clause 32, wherein the optical sensor is further configured to: determine a transmission coordinate of a transmission location of the inspection beam, determine a reception coordinate of a reception location of the received portion of the inspection beam, and measure a distance between the reception coordinate and the transmission coordinate. 34. The lithographic radiation system of clause 33, wherein the optical sensor is further configured to calculate the fill level of the radiation fuel in the fuel tank based on the measured distance. 31 . The lithographic radiation system of clause 30, wherein the first sensor device is located within a fuel tank. 36. The lithographic radiation system of clause 35, wherein the measurement sensor comprises: a plurality of probes extending within the fuel tank, each one of the plurality of probes being configured to generate a signal in response to having contact with the radiation fuel. 37. The lithographic radiation system of clause 36, wherein the plurality of probes connect to the fuel tank through a plurality of hermetic high pressure seals. 38. The lithographic radiation system of clause 35, further comprising a controller including processing circuitry, the controller being configured to calculate a fuel fill level within the fuel tank in response to receiving one or more generated signals, generate an output signal indicative of the calculated fill level, and transmit the output signal to at least one other controller. 39. The lithographic radiation system of clause 38, wherein the at least one other controller is a first upstream controller associated with a first upstream tank supplying the radiation fuel to the fuel tank. 40. The lithographic radiation system of clause 39, wherein the transmitted signal includes a maintain course of action command to the first upstream controller to maintain a course of feed action in response to the fill level being within a predetermined threshold. 41. The lithographic radiation system of clause 37, wherein the plurality of probes extend downwardly to different depths within the fuel tank. 42. The lithographic radiation system of clause 37, wherein the plurality of probes extend laterally into the tank at different vertical locations. [01 33] The breadth and scope of the present disclosure should not be limited by any of the above- described example aspects or embodiments, but should be defined only in accordance with the following claims and their equivalents.

HIGH PRESSURE AND VACUUM LEVEL SENSOR IN METROLOGY RADIATION SYSTEMS

Claims (21)

CLAIMS 5

1. A method for measuring a fuel fill level of a radiation fuel in an extreme ultraviolet (EUV) radiation system, the method comprising: directing an inspection beam through a fuel tank view port at a top surface of the radiation fuel at a predetermined incident angle; 10 receiving a portion of the inspection beam reflected by the top surface of the radiation fuel at a sensor located adjacent to the view port; determining a transmission coordinate of a transmission location of the inspection beam; determining a reception coordinate of a reception location of the received portion of the inspection beam; 15 measuring a distance between the reception coordinate and the transmission coordinate; and calculating the fill level of the radiation fuel in the fuel tank based on the measured distance.

2. The method of claim 1, wherein the inspection beam is directed at plural irradiation points and the calculation is based on one or more reflections having the highest signal intensity. 20

3. The method of claim 1, further comprising: transmitting a signal indicative of the calculated fill level to a first upstream tank supplying the radiation fuel to the fuel tank. 25

4. The method of claim 3, further comprising: transmitting a second signal indicative of the calculated fill level to a second upstream tank supplying the radiation fuel to the first upstream tank, the second upstream tank being tank configured to collect and heat the radiation fuel to a predetermined temperature. 30

5. The method of claim 4, wherein the second signal further instructs the second upstream tank to supply the collected and heated radiation fuel to the first upstream tank.

6. The method of claim 1, further comprising: measuring a tank light intensity reflection of the received portion of the inspection beam from 35 a tank wall in response to the fuel tank being positioned at an angular deviation from an upright position, the tank light intensity reflection being indicative of fuel level in the tank; and Company Secret 2019P00335WO 33 measuring a fuel light intensity reflection from the fuel in the fuel tank, the fuel light intensity reflection being indicative of a purity level of the fuel.

7. A measurement device for measuring fuel fill level of a radiation fuel in an extreme 5 ultraviolet (EUV) radiation system, the measurement device being located adjacent to a fuel tank view port, the measurement device comprising: a transmitter configured to direct an inspection beam through the fuel tank view port at a top surface of the radiation fuel at a predetermined incident angle; a receiver configured to receive a portion of the inspection beam reflected by the top surface 10 of the radiation fuel; and processing circuitry configured to determine a transmission coordinate of a transmission location of the inspection beam; determine a reception coordinate of a reception location of the received portion of the inspection beam; 15 measure a distance between the reception coordinate and the transmission coordinate; and calculate a fill level of the radiation fuel in the fuel tank based on the measured distance.

8. The measurement device of claim 7, wherein the inspection beam is directed at plural irradiation points and the calculation is based on one or more reflections having the highest signal 20 intensity.

9. The measurement device of claim 7, wherein the processing circuitry is further configured to transmit a signal indicative of the calculated fill level to a first upstream tank supplying the radiation fuel to the fuel tank and to transmit a second signal indicative of the calculated fill level to a second 25 upstream tank supplying the radiation fuel to the first upstream tank, the second upstream tank being a tank configured to collect and heat the radiation fuel to a predetermined temperature.

10. The measurement device of claim 9, wherein the second signal further instructs the second upstream tank to supply the collected and heated radiation fuel to the first upstream tank and the 30 processing circuitry is further configured to: receive, from a sensor associated with the second upstream tank, a measured amount of radiation fuel being heated and supplied to the first upstream tank; update a measurement indicative of an amount of radiation fuel entering the fuel fill level of the EUV radiation system; and 35 calculate a time interval at which the heated radiation fuel is expected to arrive at the fuel tank.

11. The measurement device of claim 7, wherein the processing circuitry is further configured to: Company Secret 2019P00335WO 34 measure a tank light intensity reflection from a tank wall in response to the fuel tank being positioned at an angular deviation from an upright position, the tank light intensity reflection being indicative of fuel level in the fuel tank; and measure a fuel light intensity reflection from the fuel in the fuel tank, the fuel light 5 intensity reflection being indicative of a purity level of the fuel.

12. A measurement device for measuring fuel fill level of a radiation fuel in an extreme ultraviolet (EUV) radiation system, the measurement device being located within a fuel tank, the measurement device comprising: 10 a measurement sensor comprising a plurality of probes extending within the fuel tank, each one of the plurality of probes being configured to generate a signal in response to having contact with the radiation fuel, wherein the plurality of probes connect to the fuel tank through a plurality of hermetic high pressure seals; and 15 a controller including processing circuitry, the controller being configured to calculate a fuel fill level within the fuel tank in response to receiving one or more generated signals, generate an output signal indicative of the calculated fill level, and transmit the output signal to at least one other controller. 20

13. The measurement device of claim 21, wherein the at least one other controller is a first upstream controller associated with a first upstream tank supplying the radiation fuel to the fuel tank and the controller is further configured to transmit a second signal indicative of the calculated fill level to a second upstream controller associated with a second upstream tank supplying the radiation 25 fuel to the first upstream tank, the second upstream tank being a tank configured to collect and heat the radiation fuel to a predetermined temperature.

14. The measurement device of claim 12, wherein the plurality of probes extend downwardly to different depths within the fuel tank. 30

15. The measurement device of claim 12, wherein the plurality of probes extend laterally into the tank at different vertical locations.

16. A lithographic radiation system comprising: 35 a first fuel tank coupled to a first sensor device and a first controller; and a second fuel tank coupled to a second sensor device and a second controller, Company Secret 2019P00335WO 35 the second fuel tank located upstream from the first fuel tank in a fuel fill system and providing radiation fuel to the lithographic radiation system, the first controller is configured to calculate a fuel fill level within the first fuel tank, 5 generate an output signal indicative of the calculated fill level, and transmit the output signal to the second controller.

17. The lithographic radiation system of claim 16, wherein the first sensor device is an optical sensor and the optical sensor is configured to: 10 direct an inspection beam through a first tank view port at a top surface of the radiation fuel at a predetermined incident angle, and receive a portion of the inspection beam reflected by the top surface of the radiation.

18. The lithographic radiation system of claim 17, wherein the optical sensor is further configured 15 to: determine a transmission coordinate of a transmission location of the inspection beam, determine a reception coordinate of a reception location of the received portion of the inspection beam, measure a distance between the reception coordinate and the transmission coordinate, and to 20 calculate the fill level of the radiation fuel in the fuel tank based on the measured distance.

19. The lithographic radiation system of claim 17, further comprising a controller including processing circuitry, the controller being configured to calculate a fuel fill level within the fuel tank in response to receiving one or more generated 25 signals, generate an output signal indicative of the calculated fill level, and transmit the output signal to at least one other controller, wherein the at least one other controller is a first upstream controller associated with a first upstream tank supplying the radiation fuel to the fuel tank. 30

20. The lithographic radiation system of claim 16, wherein the first sensor device comprises a plurality of probes extending within the fuel tank, each one of the plurality of probes being configured to generate a signal in response to having contact with the radiation fuel and wherein the plurality of probes extend downwardly to different depths within the fuel tank. 35

21. The lithographic radiation system of claim 16, wherein the first sensor device comprises a plurality of probes extending within the fuel tank, each one of the plurality of probes being configured Company Secret 2019P00335WO 36 to generate a signal in response to having contact with the radiation fuel and wherein the plurality of probes extend laterally into the tank at different vertical locations. Company Secret