High pressure and vacuum level sensors in metrology radiation systems

Abstract

Systems, apparatus, and methods are provided for measuring the level of radiant fuel in an extreme ultraviolet (EUV) radiation system. In one example, a method for measuring the fuel level includes directing an inspection beam through a fuel tank viewport at a predetermined angle of incidence to a top surface of the radiant fuel. The method may further include receiving a portion of the inspection beam reflected from the top surface of the radiant fuel with a sensor positioned adjacent the viewport. The method may also include measuring a distance to the top surface of the radiant fuel and calculating a fill level of the radiant fuel in the fuel tank based on the measured distance.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

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

[0002] FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to a supply mechanism for delivering source materials within an extreme ultraviolet (EUV) radiation system used in lithography processes for manufacturing semiconductor devices. [Background technology]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device, alternatively referred to as a mask or 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. comprising part of one or several dies) on the substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern with a radiation beam in a given direction (the "scan" direction) while the substrate is scanned synchronously parallel or anti-parallel to the given direction (the "scan" direction). It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] Extreme ultraviolet (EUV) light, e.g., electromagnetic radiation having wavelengths of approximately 50 nanometers (nm) or less (sometimes referred to as soft x-rays), including light with wavelengths of about 13 nm, can be used to generate extremely small features in or on substrates, e.g., silicon wafers. Methods for generating EUV light include, but are not necessarily limited to, converting a material having elements, e.g., xenon (Xe), lithium (Li), or tin (Sn), with an emission line in the EUV range into a plasma state. For example, in one such method, called laser-produced plasma (LPP), plasma can be generated by irradiating a target material, e.g., in the form of droplets, plates, tapes, streams, or clusters of material, which in the context of the LPP source is interchangeably referred to as a fuel, with an amplified light beam, which may be referred to as a drive laser. For this process, the plasma is typically generated in a sealed vessel, e.g., a vacuum chamber, and monitored using various types of metrology instruments.

[0005]

[0005] Inside a traditional tin-based radiation source vessel, many features, such as protective hydrogen (H2) gas, thermal shielding, and precise shroud installation, must be considered while preventing tin buildup and also taking into account the field of view (FOV) and droplet path clearance. Furthermore, current systems do not accurately monitor the sources available to deliver source material to the EUV droplet generator. Therefore, there is a need to improve source availability and eliminate downtime associated with a lack of high-quality source supply (e.g., Sn supply) to the droplet generator (DGen). Summary of the Invention

[0006] This disclosure describes various aspects of systems, apparatus, and methods for performing optical metrology and various other aspects in extreme ultraviolet (EUV) radiation systems. More specifically, this disclosure describes an in-line replenishment (IR) system that enables continuous monitoring and supply of high-purity Sn to a droplet generator assembly (DGA).

[0007] According to one aspect, a method for measuring a fuel supply level includes directing an inspection beam through a fuel tank viewport at a top surface of a radiant fuel at a predetermined angle of incidence. The method may further include receiving a portion of the inspection beam reflected from the top surface of the radiant fuel with a sensor positioned adjacent the viewport. In another aspect, the method includes measuring a distance from the sensor to the top surface of the radiant fuel and calculating a fill level of the radiant fuel in the fuel tank based on the measured distance.

[0008] According to one aspect, a measurement device and method for measuring a fuel fill level are disclosed. According to some embodiments, a measurement device located within a fuel tank for measuring a fuel fill level of a radiant fuel in an extreme ultraviolet (EUV) radiation system is disclosed. According to some aspects, the measurement device includes a plurality of probes extending into the fuel tank, each one of the plurality of probes generating a signal in response to contacting the radiant fuel. According to some aspects, the plurality of probes connect to the fuel tank via a plurality of gas-tight high-pressure seals. According to some aspects, the measurement device may further include a controller having processing circuitry. According to some aspects, the controller calculates a fuel fill level in the fuel tank in response to receiving the one or more generated signals, generates an output signal indicative of the calculated fill level, and transmits the output signal to at least one other controller.

[0009] According to some embodiments, a lithographic radiation system may be provided. 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 tank is located upstream of the first fuel tank in a fuel filling system and provides radiation fuel to the lithographic radiation system. According to some aspects, the first controller calculates a fuel fill level in the first fuel tank, generates an output signal indicative of the calculated fill level, and sends the output signal to the second controller.

[0010]

[0010] Further features and the structure and operation of various embodiments are described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific embodiments described or illustrated herein. Such embodiments are shown herein for illustrative purposes only. Further embodiments will be apparent to those skilled in the art based on the teachings contained herein. [Brief explanation of the drawings]

[0011]

[0011] The accompanying drawings, which are incorporated in and form part of this specification, illustrate the present invention and, together with the description, serve to further explain the principles of aspects of the present disclosure and to enable those skilled in the art to make and use aspects of the present disclosure.

[0012] [Figure 1A]

[0012] FIG. 1 is a schematic diagram of an exemplary reflective lithographic apparatus according to some aspects of the present disclosure. [Figure 1B]

[0013] 1 is a schematic diagram of an exemplary transmissive lithographic apparatus according to some aspects of the present disclosure; [Figure 2A]

[0014] 2 shows a more detailed schematic of a reflective lithographic apparatus according to some embodiments; [Figure 2B]1 shows a more detailed schematic of a reflective lithographic apparatus according to some embodiments; [Figure 3] 1 shows a more detailed schematic of a reflective lithographic apparatus according to some embodiments; [Figure 4]

[0015] 1 illustrates a schematic of a lithographic cell according to some embodiments. [Figure 5]

[0016] 1 is a schematic diagram of an exemplary radiation source for an exemplary reflective lithographic apparatus according to some aspects of the present disclosure; [Figure 6A]

[0017] 1 illustrates a schematic architecture of an in-tank level sensor according to some embodiments. [Figure 6B] 1 illustrates a schematic architecture of an in-tank level sensor according to some embodiments. [Figure 7]

[0018] 1 illustrates a schematic architecture of an in-line replenishment system according to some embodiments. [Figure 8A]

[0019] 1 illustrates a non-invasive triangulation sensor deployment for detecting source level in a vacuum tank according to some embodiments. [Figure 8B]

[0019] Figure 1 illustrates a non-invasive triangulation sensor deployment for detecting source level in a vacuum tank in accordance with some embodiments. [Figure 8C]

[0020] 1 is a temperature time plot showing the change in average Sn level and noise level measured by an optical device. [Figure 9A]

[0021] 10 illustrates another example of a non-invasive triangulation sensor deployment for detecting source level in a vacuum tank according to some embodiments. [Figure 9B]

[0021] Another example of a non-invasive triangulation sensor deployment for detecting source level in a vacuum tank according to some embodiments is shown. [Figure 9C]

[0021] Another example of a non-invasive triangulation sensor deployment for detecting source level in a vacuum tank according to some embodiments is shown. [Figure 9D]

[0021] Another example of a non-invasive triangulation sensor deployment for detecting source level in a vacuum tank according to some embodiments is shown. [Figure 10]

[0022] 1 is a graphical representation of signals detected at a receiver array of a sensor according to some embodiments. [Figure 11]

[0023] 1 is a flowchart illustrating an example method for detecting a source level in an in-line replenishment system according to some embodiments.

[0013]

[0024] The features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements, unless otherwise indicated. Furthermore, the leftmost digit(s) of a reference number generally identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as drawings to scale. DETAILED DESCRIPTION OF THE INVENTION

[0014]

[0025] This specification discloses one or more embodiments that incorporate features of the present disclosure. The disclosed embodiment or embodiments are merely illustrative of the present disclosure. The scope of the present disclosure is not limited to the disclosed embodiment or embodiments. The breadth and scope of the present disclosure are defined by the claims appended hereto and their equivalents.

[0015]

[0026] References to one or more described embodiments, and to "one embodiment," "an embodiment," "an exemplary embodiment," "exemplary embodiment," etc., herein indicate that the described embodiments may include a particular feature, structure, or characteristic, but each embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it is understood that it is within the knowledge of one of ordinary skill in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0016]

[0027] Spatially relative terms such as "beneath," "below," "lower," "above," "on," "upper," and the like may be used herein to facilitate describing the relationship of one element or feature to another element or features, as shown in the figures. Spatially relative terms are intended to encompass various orientations of the device in use or operation in addition to the orientation shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0017]

[0028] As used herein, the term "about" refers to a given quantity value that can vary based on a particular technique. Based on a particular technique, the term "about" can refer to a given quantity value that can vary, for example, within 10-30% of that value (e.g., ±10%, ±20%, or ±30% of that value).

[0018]

[0029] The radiation source enclosures and CFRs disclosed herein have many advantages and benefits. For example, various aspects of the present disclosure provide modularity (e.g., improved maintainability, increased upgradability), improved performance (e.g., more functionality contained in a single device), increased availability (e.g., less tin buildup and faster maintainability than conventional radiation source enclosures), and cost savings (e.g., incorporating peripheral flow functionality into a CFR can be less expensive than incorporating peripheral flow functionality into the radiation collector as in conventional designs).

[0019]

[0030] Before describing such aspects in detail, it will be useful to present an exemplary environment in which embodiments of the present invention may be practiced.

[0020]

[0031] Exemplary Lithography System

[0032] 1A and 1B are schematic diagrams of lithographic apparatus 100 and lithographic apparatus 100', respectively, in which aspects of the present disclosure may be implemented. As shown in Figures 1A and 1B, lithographic apparatuses 100 and 100' are shown from a perspective (e.g., a side view) that is perpendicular to the XZ plane (e.g., the X axis points to the right and the Z axis points up), while patterning device MA and substrate W are shown from another perspective (e.g., a top view) that is perpendicular to the XY plane (e.g., the X axis points to the right and the Y axis points up).

[0021]

[0033] Lithographic apparatus 100 and lithographic apparatus 100' each comprise: an illumination system IL (e.g., an illuminator) configured to condition a radiation beam B (e.g., a deep ultraviolet (DUV) radiation beam or an extreme ultraviolet (EUV) radiation beam), a support structure MT (e.g., a mask table) configured to support a patterning device MA (e.g., a mask, 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 comprise a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (e.g., a portion comprising one or more dies). 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.

[0022]

[0034] The illumination system IL may 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.

[0023]

[0035] The support structure MT holds the patterning device MA in a manner that depends on conditions such as the orientation of the patterning device MA relative to a reference frame, the design of at least one of lithographic apparatuses 100 and 100′, and whether or not the patterning device is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may, for example, be a frame or a table, and may be fixed or movable as required. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS.

[0024]

[0036] The term "patterning device" MA should be interpreted broadly to refer 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 a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0025]

[0037] Patterning device MA may be transmissive (as in lithographic apparatus 100′ of FIG. 1B) or reflective (as in lithographic apparatus 100 of FIG. 1A). Examples of patterning device MA include a reticle, a mask, a programmable mirror array, or a programmable LCD panel. Masks include mask types such as binary, alternating phase-shift, or attenuated phase-shift masks, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam B in different directions. The tilted mirrors impart a pattern to a radiation beam B that is reflected by the matrix of small mirrors.

[0026]

[0038] As used herein, the term "projection system" PS may include any type of projection system, including refractive, reflective, magnetic, electromagnetic, electrostatic, or any combination thereof, appropriate to the exposure radiation used or other factors such as the use of an immersion liquid or the use of a vacuum. A vacuum environment may be used for EUV or electron beam radiation, as other gases may be too absorbing of the radiation or electrons. A vacuum environment may therefore be provided throughout the beam path using a vacuum wall and vacuum pumps.

[0027]

[0039] Lithographic apparatus 100 and / or lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, the additional substrate tables WT may be used in parallel, or one or more substrate tables WT may be used for exposure while preparation steps are performed on one or more other tables. In some circumstances, the additional tables may not be substrate tables WT.

[0028]

[0040] The lithographic apparatus may be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system and the substrate. Immersion liquids may 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. As used herein, the term "immersion" does not mean that a structure such as the substrate must be submerged in liquid, but rather that a liquid is present between the projection system and the substrate during exposure.

[0029]

[0041] 1A and 1B, the illumination system IL receives a radiation beam B from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be separate physical entities, for example if the source SO is an excimer laser. In this case, the source SO is not considered to form part of the lithographic apparatus 100 or 100' and the radiation beam B passes from the source SO to the illumination system IL via a beam delivery system BD (shown in FIG. 1B), which may comprise, for example, appropriate directing mirrors and / or beam expanders. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100', for example if the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, may be referred to as a radiation system.

[0030]

[0042] The illumination system IL may comprise an adjuster AD (e.g. as shown in FIG. 1B ) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. The illumination system IL may also comprise various other components (e.g. as shown in FIG. 1B ), such as an integrator IN and a radiation collector CO (e.g. a condenser or collector system). The illumination system IL may be used to adjust the radiation beam B to obtain a desired uniformity and intensity distribution in its cross-section.

[0031]

[0043] Referring to Figure 1A, a radiation beam B is incident on a patterning device MA (e.g., a mask), which is held on a 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 reflecting from the patterning device MA, the radiation beam B passes through a projection system PS. The projection system PS focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IFD2 (e.g., an interferometric device, a linear encoder, or a capacitance sensor), the substrate table WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IFD1 (e.g., an interferometric device, a linear encoder, or a capacitance sensor) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. Mask alignment marks M1 and M2 and substrate alignment marks P1 and P2 may be used to align patterning device MA and substrate W.

[0032]

[0044] Referring to Figure 1B, a radiation beam B is incident on a patterning device MA held on a support structure MT and is patterned by the patterning device MA. After traversing the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The projection system has a pupil PPU that is conjugate with the illumination system pupil IPU. A portion of the radiation arises from the intensity distribution in the illumination system pupil IPU and traverses the mask pattern without being affected by diffraction at the mask pattern, creating an image of the intensity distribution in the illumination system pupil IPU.

[0033]

[0045] The projection system PS projects an image MP' of the mask pattern MP. The image MP' is formed on a resist layer coated on the substrate W by diffracted beams generated from the mask pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Non-zero-order diffraction of radiation at the array produces stimulated diffraction beams whose direction is changed perpendicular to the lines. Non-diffracted beams (e.g., so-called zero-order diffraction beams) traverse the pattern without changing their direction of propagation. The zero-order diffraction beams traverse the upper lens or upper lens group of the projection system PS, which is upstream of the conjugate pupil PPU of the projection system PS, and reach the conjugate pupil PPU. The portion of the intensity distribution in the plane of the conjugate pupil PPU associated with the zero-order diffraction beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD is, for example, arranged in a plane or substantially in a plane containing the conjugate pupil PPU of the projection system PS.

[0034]

[0046] With the aid of the second positioner PW and a position sensor IFD (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. to position different target portions C in the path of the radiation beam B). Similarly, the patterning device MA can be accurately positioned with respect to the path of the radiation beam B using the first positioner PM and a further position sensor (not shown in FIG. 1B ) (e.g. after mechanical removal of the mask library or during a scan).

[0035]

[0047] In general, movement of the support structure MT may 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 may be realized using long-stroke and short-stroke positioners, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to short-stroke actuators only, or may be fixed. The patterning device MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks as illustrated occupy dedicated target portions, but may also be located in spaces between the 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 may be located between the dies.

[0036]

[0048] The support structure MT and patterning device MA may be within a vacuum chamber V. An in-vacuum robot IVR may be used to move a patterning device, such as a mask, in and out of the vacuum chamber. Alternatively, if the support structure MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot may be used for various transport operations, similar to the in-vacuum robot IVR. In some cases, both the in-vacuum and out-of-vacuum robots may need to be calibrated for smooth movement of any payload (e.g., a mask) to a fixed kinematic mount in the transfer station.

[0037]

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

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

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

[0052] 3. In another mode, the support structure MT holds the programmable patterning device MA substantially stationary, 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 used, with the programmable patterning device MA being updated as required with each movement of the substrate table WT, or between successive pulses of radiation during a scan. This mode of operation is readily adaptable to maskless lithography using a programmable patterning device such as a programmable mirror array.

[0038]

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

[0039]

[0054] In a further aspect, the lithographic apparatus 100 comprises an EUV source configured to generate a beam of EUV radiation for EUV lithography. Typically, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0040]

[0055] Figure 2A shows lithographic apparatus 100 in more detail, including a radiation source SO (e.g., a source collector apparatus), an illumination system IL, and a projection system PS. As shown in Figure 2A, lithographic apparatus 100 is shown from a perspective (e.g., a side view) perpendicular to the XZ plane (e.g., with the X axis pointing to the right and the Z axis pointing up).

[0041]

[0056] The radiation source SO is constructed and arranged to maintain a vacuum environment within the enclosure 220. The radiation source SO includes a source chamber 211 and a collector chamber 212 and is configured to generate and transmit EUV radiation. The EUV radiation may be generated by a gas or vapor, such as xenon (Xe) gas, lithium (Li) vapor, or tin (Sn) vapor, from which an EUV radiation-emitting plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. The at least partially ionized EUV radiation-emitting plasma 210 may be generated by, for example, an electric discharge or a laser beam. For efficient radiation generation, for example, Xe gas, Li vapor, Sn vapor, or any other suitable gas or vapor may be used, with a partial pressure of about 10.0 Pascals (Pa). In some embodiments, an excited tin plasma is provided to generate the EUV radiation.

[0042]

[0057] Radiation emitted by the EUV radiation-emitting plasma 210 is delivered from the source chamber 211 into the collector chamber 212 through an optional gas barrier or contaminant trap 230 (e.g., sometimes referred to as a contaminant barrier or foil trap) located in or after an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap 230 illustrated further herein includes at least a channel structure.

[0043]

[0058] The collector chamber 212 may comprise a radiation collector CO (e.g. a condenser or collector system), which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the radiation collector CO may be reflected by a grating spectral filter 240 and focused into a virtual source point IF. The virtual source point IF is commonly called the intermediate focus, and the source collector arrangement is arranged such that the virtual source point IF is located at or near the opening 219 of the enclosure structure 220. The virtual source point IF is an image of the EUV radiation emitting plasma 210. The grating spectral filter 240 is used to suppress, in particular, infrared (IR) radiation.

[0044]

[0059] The radiation then traverses the illumination system IL, which may comprise a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA, and to provide a desired radiation intensity uniformity at the patterning device MA. When the radiation beam 221 is reflected from the patterning device MA, which is held by the support structure MT, a patterned beam 226 is formed which is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by a wafer stage or substrate table WT.

[0045]

[0060] In general, there may be more elements in the illumination system IL and the projection system PS than are shown. A grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Furthermore, there may be more mirrors than are shown in Figure 2. For example, there may be one to six additional reflective elements in the projection system PS compared to what is shown in Figure 2A.

[0046]

[0061] 2A is shown as just one example of a collector (or collector mirror), as a nested collector with grazing incidence reflectors 253, 254 and 255. Grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically about optical axis O, and this type of radiation collector CO is suitable for use in combination with a discharge produced plasma (DPP) source.

[0047]

[0062] Figure 2B shows a schematic diagram of selected portions of lithographic apparatus 100 (e.g., Figure 1) with alternative collection optics in the source collector device SO, according to some embodiments. It should be understood that structures shown in Figure 2A that do not appear in Figure 2B (for clarity of the drawing) may still be included in the embodiment referring to Figure 2B. Elements in Figure 2B that have the same reference numbers as elements in Figure 2A have the same or substantially similar structure and function as those described with reference to Figure 2A.

[0048]

[0063] In some embodiments, lithographic apparatus 100 may be used to expose a substrate W, such as a resist-coated wafer, with a patterned beam of EUV light. In FIG. 2B , illumination system IL and projection system PS are depicted 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, or device using contact and / or proximity masks) that uses EUV light from a source collector apparatus SO. Lithographic apparatus 100 may also include collector optics 258 that reflects EUV light from hot plasma 210 along a path to exposure device 256 for irradiating substrate W. Collector optics 258 may include a near-normal incidence collector mirror having a reflective surface in the shape of a prolate spheroid (i.e., an ellipse rotated about its major axis) with a graded multilayer coating, for example, including alternating layers of molybdenum and silicon, and possibly one or more high-temperature diffusion barrier layers, smoothing layers, capping layers, and / or etch stop layers.

[0049]

[0064] FIG. 3 shows a detailed view of a portion of a 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 elements in FIGS. 1, 2A, and 2B have the same or substantially similar structure and function as those described with reference to FIGS. 1, 2A, and 2B. In some embodiments, the lithographic apparatus 100 may include a source collector apparatus SO having an LPP EUV light emission device. 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 the light source chamber 212. In the lithographic apparatus 100, the light pulses may travel along one or more beam paths from the laser system 302 into the chamber 212 to illuminate a source material at an irradiation region 304 (e.g., the plasma region where the hot plasma 210 in FIG. 2B is located) to generate a plasma that generates EUV light for substrate exposure in the exposure device 256.

[0050]

[0065] In some embodiments, a laser suitable for use in laser system 302 may include a pulsed laser device, such as a pulsed gas discharge CO laser device operating at relatively high power (e.g., 10 kW or greater) and high pulse repetition rate (e.g., 50 kHz or greater) generating radiation at 9.3 pm or 10.6 pm with DC or RF excitation. In some embodiments, the laser may be an axially RF-pumped CO laser with a seed pulse initiated by a Q-switched oscillator having an oscillator-amplifier configuration with multiple gain stages (e.g., a master oscillator / power amplifier (MOPA) or a power oscillator / power amplifier (POPA)) capable of operation at relatively low energy and high repetition rate, e.g., 100 kHz. After leaving the oscillator, the laser pulse may be amplified, shaped, and / or focused before reaching the irradiation region 304. A continuously pumped CO amplifier may be used in laser system 302. Alternatively, the laser may be configured as a so-called "self-targeted" laser system, in which a droplet acts as one mirror of the laser's optical cavity.

[0051]

[0066] In some embodiments, depending on the application, other types of lasers may be suitable, such as excimer or molecular fluorine lasers operating at high power and high pulse repetition rates. Some examples include solid-state lasers with fiber-, rod-, slab-, or disk-shaped active media, other laser architectures with one or more chambers, such as an oscillator chamber and one or more amplifier chambers (arranged in parallel or series), master oscillator / power oscillator (MOPO) configurations, master oscillator / power ring amplifier (MOPRA) configurations, or solid-state lasers seeding one or more excimer, molecular fluorine, or CO amplifier or oscillator chambers may be suitable. Other suitable designs may be envisioned.

[0052]

[0067] In some embodiments, the source material may be first irradiated with a pre-pulse and then with a main pulse. The pre-pulse seed and the main pulse seed 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 the main pulse seed. In some embodiments, separate amplifiers may be used to amplify the pre-pulse seed and the main pulse seed.

[0053]

[0068] In some embodiments, the lithographic apparatus 100 may include a beam conditioning unit 306 having one or more optical components for beam conditioning, such as expanding, steering, and / or focusing, between the laser system 302 and the 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 positions within the chamber 212. For example, the steering system may include a first plane mirror mounted on a tip-tilt actuator that can independently move the first mirror in two dimensions, and a second plane mirror mounted on a tip-tilt actuator that can independently move the second mirror in two dimensions. With the above configuration, the steering system may controllably move the focal spot in a direction substantially perpendicular to the beam propagation direction (beam axis or optical axis).

[0054]

[0069] The beam conditioning unit 306 may comprise a focusing assembly for focusing the beam onto the illumination region 304 and adjusting the position of the focal spot along the beam axis. The focusing assembly may use optical components such as focusing lenses or mirrors coupled to actuators that move in a direction along the beam axis to move the focal spot along the beam axis.

[0055]

[0070] In some embodiments, the source collector apparatus SO may also include a source material delivery system 308 that delivers source material, such as Sn droplets, to an irradiation region 304 within the chamber 212 where the droplets interact with light pulses from the laser system 302 to ultimately generate a plasma and generate EUV emissions for exposing a substrate, such as a resist-coated wafer, in the exposure device 256. Further details regarding various droplet dispenser configurations may be found in, for example, U.S. Pat. No. 7,872,245, entitled "Systems and Methods for Target Material Delivery in a Laser Produced Plasma EUV Light Source," issued January 18, 2011; U.S. Pat. No. 7,405,416, entitled "Method and Apparatus For EUV Plasma Source Target Delivery," issued July 29, 2008; U.S. Pat. No. 7,372,056, entitled "LPP EUV Plasma Source Material Target Delivery System," issued May 13, 2008; and International Application No. WO2019 / 137846, entitled "Apparatus for and Method of Controlling Coalescence of Droplets in a Droplet Stream," published July 18, 2019, the contents of each of which are incorporated herein by reference in their entirety.

[0056]

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

[0057]

[0072] In some embodiments, lithographic apparatus 100 may also include a controller 310, which may also include a drive laser control system 312 for controlling devices in laser system 302 to generate light pulses for delivery into chamber 212 and / or for controlling movement of optical components in beam conditioning unit 306. Lithographic apparatus 100 may also include a droplet position detection system, which may include, for example, one or more droplet imagers 314 that provide output signals indicative of the position of one or more droplets relative to irradiation area 304. Droplet imagers 314 may provide this output to droplet position detection feedback system 316, which may calculate droplet positions and trajectories from which droplet errors may be calculated, for example, on a droplet-by-droplet basis or on an average. The droplet error may then be provided as an input to controller 310, which may, for example, provide position, direction, and / or timing correction signals to laser system 302 to control laser trigger timing and / or control movement of optical components in beam conditioning unit 306, for example, to change the position and / or focusing power of the light pulses delivered to irradiation region 304 in chamber 212. Also, with respect to source collector apparatus SO, source material delivery system 308 may have a control system operable in response to signals from controller 310 (which in some implementations may include the droplet error, or some quantity derived therefrom), for example, to modify the ejection point, initial droplet stream direction, droplet ejection timing, and / or droplet modulation to correct for errors in droplets reaching irradiation region 304.

[0058]

[0073] In some embodiments, the lithographic apparatus 100 may also include a collector optic, a gas dispenser device 320. The gas dispenser device 320 may distribute gas from the source material delivery system 308 to the path of the source material (e.g., the irradiation region 304). The gas dispenser device 320 may include a nozzle through which the dispensed gas exits. The gas dispenser device 320 may be configured (e.g., with an opening) such that, when positioned near the optical path of the laser system 302, light from the laser system 302 is not blocked by the gas dispenser device 320 and is allowed to reach the irradiation region 304. A buffer gas, such as hydrogen, helium, argon, or a combination thereof, may be introduced into, replenished with, and / or removed from the chamber 212. The buffer gas may be present in the chamber 212 during plasma discharge and may serve to slow ions generated by the plasma to reduce degradation of optical components and / or increase plasma efficiency. Alternatively, magnetic and / or electric fields (not shown) may be used alone or in combination with a buffer gas to reduce fast ion damage.

[0059]

[0074] In some embodiments, lithographic apparatus 100 may also include collector optics 258, such as a near-normal incidence collector mirror having a reflective surface in the shape of a prolate spheroid (i.e., an ellipse rotated about its major axis) with a graded multilayer coating, for example, including alternating layers of molybdenum and silicon, and possibly one or more high-temperature diffusion barrier layers, smoothing layers, capping layers, and / or etch stop layers. Collector optics 258 may have an aperture formed therein to allow light pulses generated by laser system 302 to pass through and reach irradiation region 304. The same or another similar aperture may be used to allow gas from gas dispenser device 320 to enter chamber 212. As shown, collector optics 258 may be, for example, a prolate spheroid mirror with a first focal point in or near irradiation region 304 and a second focal point in a so-called intermediate region 318, and EUV light may be output from source collector apparatus SO and input to exposure device 256, for example, an integrated circuit lithography tool, that utilizes EUV light. It should be understood that instead of a prolate spheroidal mirror, other optical components may be used to collect and direct the light to an intermediate location for subsequent delivery to a device utilizing EUV light. Embodiments may also be envisioned using a collector optic CO (FIG. 2A) with the structure and functionality described with reference to FIG.

[0060]

[0075] Exemplary Lithography Cell

[0076] FIG. 4 illustrates a lithography cell 400, sometimes referred to as a lithocell or cluster. Lithography apparatus 100 or 100′ may form part of lithography cell 400. Lithography cell 400 may also include one or more devices for performing pre-exposure and post-exposure processes on substrates. For example, these devices may include a spin coater SC for depositing a resist layer, a developer DE for developing exposed resist, a chill plate CH, and a bake plate BK. A substrate handler RO (e.g., a robot) retrieves substrates from input / output ports I / O1 and I / O2, moves them between various process tools, and delivers them to a loading bay LB of lithography apparatus 100 or 100′. These devices are often collectively referred to as a track and are under the control of a track control unit TCU. The TCU itself is controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, these various tools may be operated to maximize throughput and processing efficiency.

[0061]

[0077] Exemplary Radiation Sources

[0078] An example of a radiation source SO (as shown in Figure 3) for an exemplary reflective lithographic apparatus is shown in Figure 5. As shown in Figure 5, the radiation source SO is shown from a perspective that is perpendicular to the XY plane below (e.g., a top view).

[0062]

[0079] The radiation source SO shown in FIG. 5 is of a type that may be referred to as a laser-produced plasma (LPP) source. A laser system 501, which may comprise, for example, a carbon dioxide (CO) laser, is arranged to impart energy via one or more laser beams 502 to a fuel target 503′, such as one or more individual Sn droplets, provided from a fuel target generator 503 (e.g., a fuel emitter, a droplet generator). According to some embodiments, the laser system 401 may be a pulsed continuous wave or quasi-continuous wave laser or may operate like a pulsed continuous wave or quasi-continuous wave laser. The trajectory of the fuel target 503′ (e.g., droplets) emitted from the fuel target generator 503 may be parallel to the X-axis. According to some embodiments, the one or more laser beams 502 propagate in a direction parallel to the Y-axis. The Z-axis is perpendicular to both the X-axis and the Y-axis and extends generally into (or out of) the page, although other configurations are used in other embodiments.

[0063]

[0080] Although the following description refers to tin, any suitable target material can be used. The target material can be, for example, in liquid form and can be, for example, a metal or alloy. The fuel target generator 503 can include a nozzle configured to direct tin, for example, in the form of fuel targets 503′ (e.g., individual droplets) along a trajectory toward the plasma formation region 504. Throughout the remainder of the description, references to “fuel,” “fuel target,” or “fuel droplets” should be understood to refer to the target material (e.g., droplets) emitted by the fuel target generator 503. The fuel target generator 503 can include a fuel emitter. One or more laser beams 502 are incident on the target material (e.g., tin) in the plasma formation region 504. Deposition of laser energy in the target material generates a plasma 507 in the plasma formation region 404. Radiation, including EUV radiation, is emitted from the plasma 507 during de-excitation and recombination of the plasma's ions and electrons.

[0064]

[0081] The EUV radiation is collected and focused by a collector 505 (e.g., radiation collector CO). In some embodiments, collector 505 may include a near-normal incidence radiation collector (which may be more commonly referred to as a normal incidence radiation collector). Collector 505 may be a multi-layer mirror structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength, such as about 13.5 nm). According to some embodiments, collector 505 may have an elliptical configuration with two foci. As discussed herein, the first focus may be at plasma formation region 504 and the second focus may be at intermediate focus 506.

[0065]

[0082] In some embodiments, the laser system 501 may be located relatively far away from the radiation source SO. In such cases, one or more laser beams 502 may be passed from the laser system 501 to the radiation source SO with the aid of a beam delivery system (not shown), e.g., comprising appropriate directing mirrors and / or beam expanders and / or other optics. The laser system 501 and the radiation source SO may collectively be considered a radiation system.

[0066]

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

[0067]

[0084] Similar to Figures 2A and 2B, a radiation beam B passes from a radiation source SO into an illumination system IL. The illumination system IL is configured to condition the radiation beam B. The radiation beam B travels from the illumination system IL and is incident on a patterning device MA held by a support structure MT. The patterning device MA reflects and patterns the radiation beam B. After reflecting from the patterning device MA, the patterned radiation beam B enters a projection system PS. The projection system comprises a number of mirrors configured to project the radiation beam B onto a substrate W held on a substrate table WT. The projection system PS may apply a demagnification factor to the radiation beam to form an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of 4 may be applied. Although Figures 2A and 2B show the projection system PS as having two mirrors, the projection system may comprise any number of mirrors (for example, six mirrors).

[0068]

[0085] The radiation source SO may include components not shown in Figure 5. For example, the radiation source SO may be provided with a spectral filter that is substantially transparent to EUV radiation but substantially blocks other radiation wavelengths, such as infrared radiation.

[0069]

[0086] The radiation source SO (or radiation system) further comprises a fuel target imaging system for obtaining an image of the fuel target (e.g., droplets) in the plasma formation region 504, and more particularly for obtaining a shadow image of the fuel target. The fuel target imaging system is capable of detecting light diffracted from the edge of the fuel target. References in the following description to an image of the fuel target should be understood to also refer to a shadow image of the fuel target or a diffraction pattern produced by the fuel target.

[0070]

[0087] The fuel target imaging system may include a photodetector, such as a CCD array or a CMOS sensor, although it will be understood that any imaging device suitable for obtaining an image of the fuel target may be used. It will be understood that the fuel target imaging system may include optical components, such as one or more lenses, in addition to the photodetector. For example, the fuel target imaging system may include a camera 510, such as a combination of a light sensor (i.e., a photodetector) and one or more lenses. The optical components may be selected such that the light sensor or camera 510 obtains near-field and / or far-field images. The camera 510 may be positioned in any suitable location within the radiation source SO such that the camera has a line of sight to the plasma formation region 504 and one or more markers (not shown in FIG. 5 ) disposed on the collector 505. However, to avoid damage to the camera 510, it may be necessary to position the camera 510 away from the propagation path of the one or more laser beams 502 and the trajectory of the fuel target emitted from the fuel target generator 503. According to some embodiments, the camera 510 is configured to provide an image of the fuel target to a controller 511 via a connection 512. Although connection 512 is shown as a wired connection, it will be understood that connection 512 (and other connections mentioned herein) may be implemented as a wired connection, a wireless connection, or a combination thereof.

[0071]

[0088] As shown in FIG. 5 , the radiation source SO may include a fuel target generator 503 configured to generate and emit fuel targets 503′ (e.g., individual tin droplets) toward a plasma formation region 504. The radiation source SO may further include a laser system 501 configured to impinge one or more of the fuel targets 503′ with one or more laser beams 502 to generate a plasma 507 in the plasma formation region 504. The radiation source SO may further include a collector 505 (e.g., a radiation collector CO) configured to collect radiation emitted by the plasma 507. In some embodiments, a collector flow ring CFR (not shown in FIG. 5 ) may be disposed adjacent to the collector 505 to mitigate fuel debris (e.g., tin) accumulation in the radiation source SO, among other features. The collector flow ring CFR may be disposed along an axis parallel to the X-axis (e.g., near the trajectory of the fuel targets 503′ emitted from the fuel target generator 503).

[0072]

[0089] To function properly, radiation sources require a continuous supply of fuel, which means that measurements, monitoring, and maintenance are required to ensure a continuous in-line supply of fuel.

[0073]

[0090] As further described herein with respect to FIGS. 6 through 11 , an inline refill system may be provided. According to some embodiments, the inline refill system may indirectly measure Sn levels by releasing a fixed amount of gas from a pressure reservoir through an opening of a known size. The rate at which pressure drops in the reservoir may then be measured for the amount of pressurized gas. The amount of Sn may then be determined by subtracting the amount of gas from the total volume of the reservoir. Such a method may be used in conjunction with reservoir pressure fluctuations to determine the amount of Sn in the reservoir. The present disclosure provides other embodiments for measuring Sn content that avoid problems associated with Sn drying out and becoming water-free and bubbling in the transfer line when the pressure vessel is supplying Sn to a droplet generator (DG). Because it is difficult to close a gas-filled freeze valve, it is useful to accurately monitor the amount of Sn in the pressure reservoir to avoid a situation in which a gas amount reaches the freeze valve, which could cause the system to become uncontrollable.

[0074]

[0091] 6A and 6B show a schematic architecture 600 of an in-tank level sensor according to some embodiments. The architecture 600 may comprise a passive level sensor that does not require pressure fluctuations in a Sn reservoir, as described further herein.

[0075]

[0092] The architecture 600 may include multiple molybdenum rods 602 that may be housed within a fuel tank 604 and secured with a glass / ceramic seal 606. The fuel tank 604 may be constructed of various metals, ceramics, polymers, or other suitable rigid materials. In some embodiments, the seal may be constructed using short borosilicate tubing. The borosilicate tubing may provide a favorable coefficient of linear expansion (CTE) for molybdenum and therefore may better retain and seal the molybdenum rods. According to some embodiments, a chemical bond may be formed between the borosilicate and the molybdenum for additional sealing. It may be understood that other bonding materials may be used, including, but not limited to, aluminum silicate (Al2SiO5).

[0076]

[0093] According to some embodiments, multiple molybdenum rods 602 can detect a full condition 608 or an empty condition 610 based on a combination of detection methods. In some embodiments, two molybdenum rods (A and B) may be used to measure low levels of Sn in tank 604. In this regard, a closed circuit condition may be monitored, and when the Sn level falls below a minimum threshold (the molybdenum rods are no longer in contact with the Sn), an open circuit occurs and a signal may be sent to a controller / processor (e.g., controller 310) indicating a low level of Sn in the tank.

[0077]

[0094] According to some embodiments shown in FIG. 6B, the molybdenum rod 612 may be positioned horizontally. In this implementation, the molybdenum rod E may be designated a low level threshold below which an empty indication may be shown when the Sn level falls. In one example, if continuity between rods A and E is detected (e.g., a closed circuit), a full signal may be relayed back indicating a "full" condition. If no continuity is detected between D and E, an "empty" condition may be indicated. Additionally, when there is continuity between E and B, C, or D, a proportional level indication may be provided.

[0078]

[0095] The embodiment described in Figures 6A and 6B eliminates the need for pressure fluctuations as a means of measuring Sn level. Furthermore, a level indication, such as full, empty, 50%, etc., may be shown immediately after the level is reached. This allows for a simpler, and therefore faster, control system because it is a passive signal sent to the control system, as opposed to active measurement requiring several system states. Additionally, the present implementation shown in Figures 6A and 6B allows for further simplification of in-line refill systems.

[0079]

[0096] 7 illustrates a schematic architecture of an in-line replenishment system 700 according to some embodiments. To improve source availability in EUV lithography systems, there is an incentive to reduce or eliminate downtime associated with a lack of high-quality Sn supply to the droplet generator (DG). According to aspects of this embodiment, the in-line replenishment system (IR) described above enables a continuous supply of high-purity Sn to the droplet generator assembly (DGA). Furthermore, it would be counterproductive to operate the in-line replenishment system without knowing the status of the Sn supply (e.g., remaining amount, cleanliness, and state of the Sn (e.g., liquid or solid)).

[0080]

[0097] To enable implementation of the IR, it may be necessary to determine the status of Sn across two or more IR sub-modules, as described further herein. The system 700 may include a Sn priming tank (TPT) 702 that maintains an initial level of solid Sn. The TPT 702 may be configured to receive and prime Sn solids to dissolve the Sn. The TPT 702 may further be configured to pump the dissolved Sn to a Sn replenishment tank (TRT) 704. The TRT 704 may be configured to provide fresh, clean liquid Sn to a replenishment reservoir (RR) 708. According to some embodiments, the RR 708 may then provide the liquid Sn to a primary reservoir (PR) 714 and / or a DGA 722. The transfer of the liquid Sn may occur via a flow system including a combination of flow valves and conduits (710a-e). It should be understood that flow systems 710 a - e may have physical properties that are capable of supporting safe, continuous, and uniform transport of molten Sn within system 700 .

[0081]

[0098] According to some embodiments, RR 708 may provide Sn as droplets, providing more Sn to PR 714, which may provide liquid Sn to DGA 722. The liquid Sn contained in RR 708 and PR 714 may be referred to as liquid Sn 712. It should be noted that the number of tanks and reservoirs described herein are exemplary, and various combinations and numbers of these may be implemented for increased efficiency and cost savings.

[0082]

[0099] According to some embodiments, one or more of the tanks / reservoirs of system 700 may be coupled to optical sensors 716, 718, or 720 configured to measure a characteristic of the Sn contained within each tank / reservoir. In one example, TPT 702, TRT 704, RR 708, and PR 714 may each be coupled to an associated optical sensor (e.g., TPT 702 is coupled to optical sensor 716) that may measure a characteristic of the Sn located within each tank / reservoir. The characteristics that the optical sensor may measure include Sn level, Sn contamination level, sight glass contamination, etc., as described further herein. It should be understood that an optical sensor may also be referred to herein as a sensor, optical device, measurement device, or optical measurement device.

[0083]

[0100] According to some embodiments, the TPT 702 sensor 716 may be configured to detect when solid Sn is loaded and monitors the dissolving action on the TRT 704. According to some embodiments, a sensor 718 in the TRT 704 monitors the Sn level in the TRT 704 and can request more Sn from the TPT 702 when needed. According to some aspects, the need for such Sn may be determined based on measurements made by the sensor 718 or may be based on a request signal received from another sensor (e.g., sensor 720 or an optical sensor, not shown, on the RR 708). The sensor 718 may also monitor the amount of Sn being pushed / fed to the RR 708. According to some aspects, the sensor 720 monitors the Sn level in the PR 714 and can request that more Sn be delivered from the TRT 704 to the RR 708 and thus to the PR 714.

[0084]

[0101] According to some embodiments, Sn may be forced through a pressurized gas mixture (e.g., approximately 98% Ar (argon), 2% H (hydrogen)) applied by the TRT 704 and delivering the Sn through flow valve 710a and conduit 710b to the RR 708, which is held at low pressure (not deep vacuum). According to some embodiments, the TRT 704 may be filled through the TPT 702. The PR 714 may also operate under high pressure all the while to supply the DGA 722. In one example, when the RR 708 is full, the flow valve 710c may be closed, and then pressure may be applied to the RR 708 to match the pressure in the PR 714. Once the pressure is at a level that matches the PR 714, the flow valve 710c may be opened to allow fuel to flow from the RR 708 to the PR 714, for example, when the PR 714 is nearly empty. Thus, level measurements made by sensor 720 can indicate when a flow valve, such as flow valve 724, can open or close. Sensor 720 may also be referred to as optical device 720, and these terms may be used interchangeably herein. As previously mentioned, each sensor may be configured to monitor Sn level changes (and subsequent volume changes), Sn purity levels, and Sn condition status (e.g., liquid or solid).

[0085]

[0102] According to some embodiments, pressure manipulation of reservoirs throughout the system can serve various functions. For example, in some embodiments, deep vacuum and low-pressure gas can be used, known as cycle purging. In some embodiments, high pressure can be used to maintain Sn droplet velocity at the nozzle (e.g., DGA722) while keeping the Sn under deep vacuum. PR714, or any other reservoir / tank that may be located immediately before DGA722, can maintain high pressure that can supply Sn for EUV generation. TRT704 and TPT702 can also maintain a clean environment for Sn. For example, the conversion of solid Sn to liquid Sn can introduce opportunities for Sn contamination from the Sn and the environment to which TPT702 was exposed before it was sealed. According to some embodiments, the method of heating the Sn can affect Sn cleanliness. Clean Sn is also desirable for long-life droplet generation with accurate droplet positioning.

[0086]

[0103] According to some embodiments, the RR 708 can use a low-to-high pressure transition, i.e., switching to low pressure to receive Sn from the TRT 704 and switching back to high pressure to supply Sn to the PR 714. According to some embodiments, the optical device 720 can include a processor that can generate control signals to control the flow of Sn through the reservoir. Additionally or alternatively, the optical device 720 can transmit active measurements to a controller (e.g., controller 310 of FIG. 3 ) for further processing and control of the Sn flow. Similar operations can be performed by other optical devices in the system 700. For example, each of the optical devices 716, 718, and 720 can include its own processing capabilities to monitor and report the above characteristics and take action based on the monitoring. Taking action here can mean, for example, providing a control signal to facilitate the movement or supply of Sn. According to some embodiments, each sensor can monitor and report data to a central processing unit (e.g., controller 310) or to one or another sensor (e.g., a sensor reporting upstream or downstream depending on which sensor is configured to provide an indication / control signal).

[0087]

[0104] In one example, sensor 720 may be configured to measure Sn characteristics within PR 714. Based on the measured characteristics and processing what sensors 716 and 718 report about the upstream availability of Sn, sensor 720 can instruct other tanks to take certain actions. For example, sensor 720 may send instructions to one or each of TPT 702, TRT 704, and / or RR 708 to take certain actions. Such actions may include melting more Sn or providing a certain level of Sn from one reservoir to another. Such instructions may take into account thermodynamic considerations related to Sn heating and movement, conduit characteristics, tank characteristics, etc. Sensor 720 may send operational commands to one or more tanks, one or more sensors, and one or more processors, which may perform the actions necessary to ensure a continuous supply of Sn. According to other embodiments, sensor 720 may be one of multiple sensors reporting to a central processing unit (e.g., controller 310), which can provide further instructions to each and every sensor / tank in system 700.

[0088]

[0105] According to some embodiments, the PR 714 may be the primary supplier of Sn to the DGA 722. Therefore, monitoring the Sn level in the PR 714 may be advantageous for achieving a stable supply of Sn to the DGA 722. According to some embodiments, the sensor 720 (or controller 310) may place a greater weighting factor on the measurement of the PR 714. For example, a low Sn level in the PR 714 may be more critical than a low Sn level in the TPT 702 or TRT 704 due to the immediacy of the need to deliver Sn to the DGA 722. Similarly, contamination measurements in various tanks / reservoirs may be assigned different weights based on their location within the in-line assembly.

[0089]

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

[0090]

[0107] According to some embodiments, the optical device 802 can be configured to measure the Sn level, quality, and condition within the can by using triangulation. According to some embodiments, the optical device 802 can include an optical transmitter 816 with a light source and an optical receiver 818 with a detector array. According to some embodiments, the optical transmitter 816 transmits an incident light beam (e.g., a laser beam, etc.), and the optical receiver 818 is configured to receive the reflected light beam. After the reflected light beam is received, the optical device 802 can perform triangulation calculations to measure Sn and properties associated with the tank to which the optical device 802 is attached.

[0091]

[0108] According to some embodiments, the optical transmitter 816 can transmit a beam at a known angle θ. Based on the Sn level in the tank, the transmitted beam is reflected at a point and reflected back into the optical receiver 818. According to some aspects, the height of the Sn level can determine where the reflected light beam is received on the optical receiver 818. Thus, to determine the Sn level 814, the optical device 802 measures the horizontal distance 812 from a point on the optical receiver 818 where the reflected light beam is received to an illumination point in the optical transmitter 816. According to some aspects, the distance 812 from the point where the light is transmitted to a point on the detector array that receives the reflected light (e.g., a predetermined pixel location or a predetermined sensor in the array) may be measured. According to some aspects, the reflected light may be received at multiple locations on the detector array. Thus, the location in the array that receives the strongest signal (e.g., the signal with the highest amplitude) may be used to measure the horizontal distance 812. Given the measurement 812 and the known angle of incidence θ, the level 814 may be calculated.

[0092]

[0109] According to some embodiments, the sensor feedback format allows for versatility in measuring Sn levels and quality without adversely affecting high-pressure, high-vacuum, and high-purity environments. According to some embodiments, the optical device 802 can measure light intensity across an array of sensors on the optical receiver 818. Using raw data from the optical receiver 818, a light intensity graph can be generated as a function of position on the optical receiver 818 (e.g., position vs. intensity as shown in FIG. 10 ). This light intensity graph can include multiple peaks as described further herein. According to some embodiments, when the optical device 802 is used with Sn and the reservoir is in a vertical configuration as shown in FIG. 8A , the extra peaks can be negligible, and the primary function can be to monitor Sn levels and Sn phase changes (e.g., solid, liquid).

[0093]

[0110] According to some embodiments, the optical device 802 may be used as a standalone device to detect phase changes. According to some embodiments, pairing the optical device 802 with a thermocouple device (e.g., a probe (not shown)) that can generate thermocouple measurements can further improve the phase shift measurements of Sn.

[0094]

[0111] 8C is a temperature-time plot showing the change in the average Sn level and noise level measured by optical device 802 with the measured temperature plotted. In one example, the change can occur at a predetermined temperature range of Sn melting (e.g., about 232°C), as indicated by 820. Determining the phase change of Sn based on the optical properties of solid and liquid Sn can allow for calculation of the amount of Sn delivered (e.g., dissolved amount of Sn vs. solid amount of Sn). For example, molten Sn is readily available, whereas solid Sn may require additional time to melt and deliver through system 700.

[0095]

[0112] According to some embodiments, the optical device 802 can detect the largest spike on the graph and determine this to be the most dominant reflection received, which is correlated to the Sn level distance measurement, as described herein. Other information can be obtained from secondary and tertiary light intensity spikes. This can be the case when the reservoir 806 is in an upright or angled configuration.

[0096]

[0113] According to one example, the Sn purity level may be detected based on one or more data points shown on the graph. According to one embodiment, the light spike found just before the distance measurement between the detector point (i.e., the location where the reflected light is received by the optical receiver 818) and the illumination point (i.e., the location where the optical signal is transmitted from the optical transmitter 816) varies as a function of Sn purity. This is caused by the reduction in light reflection from the Sn as the Sn surface becomes more contaminated (e.g., the light spot becomes more dominant on the Sn itself). According to some embodiments, the effects of contamination may be amplified when the reservoir is in an angle configuration such as that shown in FIG. 9.

[0097]

[0114] FIG. 9A illustrates another example of a non-invasive triangulation sensor deployment 900 for detecting source levels in a vacuum tank in system 700, according to some embodiments. In the deployment 900, an optical device 802 can transmit and receive light beams to generate measurements of Sn levels and other physical characteristics of Sn based on several parameters, as described further herein. According to some embodiments, the access points 902 can be glass ports in a sight glass 810 located at the end of the tank / reservoir. According to some embodiments, a clean glass port will exhibit minimal light intensity at the access points where incident light enters and exits. Conversely, an increase in light intensity at these access points indicates that the sight glass is becoming dirty or increasingly contaminated and requires further attention / maintenance. Representations of the light / intensity received by the optical device 802 are shown in more detail in FIGS. 9B-9D, described herein below.

[0098]

[0115] According to some aspects, the light intensity measured at 904 indicates Sn level detection. According to some embodiments, the liquid Sn may act as a mirror, and with the Sn tilted, distance may be calculated from the reflective dot 904 reflected from the reservoir wall, as shown in Figures 8A and 8B. According to other aspects, dot 906 may indicate a Sn purity detection location. As this location becomes more visible at 904, the Sn becomes less reflective, and therefore, tin oxide buildup increases.

[0099]

[0116] 9B-9D show the intensities received and measured by a sensor (e.g., optical device 802). For example, FIG. 9B shows the optical signal received by optical device 802 when both the viewport and Sn are clean. FIG. 9C shows the optical signal received by optical device 802 when the viewport is dirty and Sn is clean. FIG. 9D shows the optical signal received by optical device 802 when the viewport is clean and Sn is dirty. It may be understood that the designations "clean" and "dirty" reflect the level of contamination detected, above which the viewport / Sn is considered "dirty" and below which the viewport / Sn is considered "clean."

[0100]

[0117] According to some embodiments, the approximate location of the received signal / light may be known. For example, the viewport entry point 902 and return point 908 may be fixed locations. The reflective dot 904 and point 906 may vary. The correlation between these two signals is relevant to determining the Sn level and purity level. For example, the reflective dot 904 may be the point of highest intensity indicating the reflection of Sn (at the Sn surface or reservoir wall), and therefore its location correlates with the Sn level. However, as the Sn contamination level increases, the intensity at 906 increases while the intensity at reflective dot 904 decreases. This may continue until the intensity at point 906 is greater than the intensity at reflective dot 904. In this case, the optical device 802 may use the reflective dot 906, rather than the reflective dot 904, as the location corresponding to the Sn level. The optical device 802 may also generate an alert indicating a high contamination level. Such an alert may be transmitted to an operator via a graphical user interface (GUI) or other method indicating the detected Sn contamination.

[0101]

[0118] FIG. 10 is a graphical representation of a signal detected at a receiver array of a sensor according to some embodiments. According to some aspects, the receiver array of the optical receiver 818 can receive light having different intensity profiles at different locations, e.g., depicted as peaks (at different locations within the receiver array). According to some embodiments, peak 1002 can represent the light intensity of viewport cleanliness detection. Peak 1004 can represent the light intensity of Sn purity detection, which increases as Sn becomes more contaminated. Peak 1006 can represent the light intensity of Sn level detection, and peak 1008 can represent the light intensity of the viewport return beam. According to some aspects, the locations of the peaks and their relationship to each other are not arbitrary. For example, as depicted in FIGS. 9B-9D, the main signal output (highest peak - peak 1006) can be designated as the peak indicative of Sn level detection. It is further determined that the peak (peak 1004) immediately preceding (or immediately following as shown in FIGS. 9B-9D) the highest peak 1006 can represent the light intensity of Sn purity. Further, according to some aspects, the first and last intensity peaks may be determined to be peaks associated with the light intensity of the viewport, and thus, a cleanliness detection of the viewport may be measured.

[0102]

[0119] According to some embodiments, the detector array of receiver 818 can correlate distance measurements of received signals based on a known θ. For example, because the system geometry (e.g., the position of optical device 802, the viewport entry and return points, and the reservoir dimensions) is known, the expected locations of relative peaks may be expected within a certain range of locations. Thus, the detector array measurements may emphasize 904 and 906 to determine depth and contamination level. In some embodiments, when the light intensity switches from 904 to 906 (e.g., from FIG. 9C to FIG. 9D), optical device 802 may include further programming that can switch to using the 906 measurement as associated with Sn depth. Optical device 802 may also send a message (via its own controller, i.e., controller 310) to an operator informing them that a high contamination level has been detected that requires investigation.

[0103]

[0120] FIG. 11 shows a flow chart illustrating an example method 1100 for detecting source levels in an in-line replenishment system according to some embodiments.

[0104]

[0121] According to some aspects, method 1100 may be a method of measuring an in-line supply of radiant fuel in an extreme ultraviolet (EUV) radiation system. Method 1100 may include directing an inspection beam through a fuel tank viewport at a top surface of the radiant fuel at a predetermined angle of incidence, as shown in step 1102. Method 1100 may also include receiving a portion of the inspection beam reflected from the top surface of the radiant fuel with a sensor positioned adjacent to the viewport, as shown in step 1104. Method 1100 may also include measuring a distance to the top surface of the radiant fuel, as shown in step 1106. Furthermore, method 1100 may also include calculating a fill level of the radiant fuel in the fuel tank based on the measured distance, as shown in step 1108.

[0105]

[0122] 11 , method 1100 may further include directing the inspection beam to multiple illumination points and basing the calculation on one or more reflections having the highest signal strength. Method 1100 may also include transmitting a signal indicative of the calculated fill level to a first upstream tank (e.g., RR 708) that supplies radiant fuel to the fuel tank (e.g., PR 714). According to some aspects, the transmitted signal may further include a maintain operation policy command to the first upstream tank (e.g., RR 708) to maintain the operation policy 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 neither full nor approaching empty, sensor 720 may signal to RR 708 or a sensor associated with controller 310 that the operation policy should be maintained.

[0106]

[0123] According to some embodiments, the method 1100 may further include transmitting a second signal indicating the calculated fill level to a second upstream tank (e.g., TPT 702) that supplies Sn to the first upstream tank (e.g., RR 708), which may be a tank configured to collect and heat radiant fuel to a predetermined temperature. According to some embodiments, the TPT 702 may provide Sn directly to the RR 708 or may first provide Sn to the TRT 704. As noted herein, the number / combination of tanks and reservoirs in the system may be developed based on system requirements and the needs of the desired DGA 722. According to some embodiments, the method 1100 may further include transmitting a time parameter for providing Sn, taking into account the time required to heat the Sn. In one example, the signal received at the TPT 702 (i.e., via the controller 310 or the sensor 716) may include a timing parameter. The timing parameters may take into account system factors including, for example, how long the Sn may need to be heated and melted, the length of the conduits in the flow systems 710a-e, and the number of tanks (e.g., RR 708, TRT 704) in the system. The second signal may also instruct a second upstream tank (e.g., TPT 702) when to supply collected and heated radiant fuel to the first upstream tank (e.g., TRT 704 or RR 708). The method 1100 may also include measuring the amount of Sn being heated with sensor 716 and transmitting the measurement to sensor 720 indicative of the amount of Sn entering the in-line supply of the EUV radiation system.

[0107]

[0124] According to some aspects, method 1100 may include processing one other reflected signal (e.g., 1002, 1004, or 1008) from the one or more reflections that has a lower intensity than the one or more reflections having the highest signal intensity, and generating an operator message indicating a contamination level associated with the viewport (e.g., the viewport is too dirty). In yet another aspect, the message may indicate a contamination level associated with Sn (e.g., the Sn contamination is too high).

[0108]

[0125] Although specific reference is made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein 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. In light of these alternative applications, those skilled in the art will recognize that when the terms "wafer" or "die" are used herein, they may be considered synonymous with the more general terms "substrate" or "target portion," respectively. The substrates described herein may be processed, before or after exposure, in, for example, a track unit (a tool that typically applies a layer of resist to the substrate and develops the exposed resist), a metrology unit, and / or an inspection unit. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to produce multi-layer ICs, and thus the term substrate, as used herein, may also refer to a substrate that already includes multiple processed layers.

[0109]

[0126] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, and thus should be interpreted by one of ordinary skill in the art in light of the teachings herein.

[0110]

[0127] The examples disclosed herein are illustrative but not limiting of embodiments of the disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the art and obvious to those skilled in the art are within the spirit and scope of the disclosure.

[0111]

[0128] While certain aspects of the disclosure have been described above, it will be understood that these aspects may be practiced otherwise than as described, and this description is not intended to limit the embodiments of the disclosure.

[0112]

[0129] It is understood that the Detailed Description section, and not the Background, Overview, and Abstract sections, is intended to be used to interpret the claims. The Overview and Abstract sections may describe one or more, but not all, example embodiments contemplated by the inventors, and thus are not intended to limit the scope of embodiments of the present invention and the appended claims in any way.

[0113]

[0130] Some aspects of the present disclosure have been described above using functional building blocks illustrating the implementation of specific functions and relationships thereof. In this specification, the boundaries of these functional building blocks have been arbitrarily defined for the convenience of description. Alternative boundaries may be defined as long as the specific functions and relationships thereof are appropriately implemented.

[0114]

[0131] The foregoing description of particular embodiments of the present disclosure sufficiently reveals the general nature of the embodiments, so that those skilled in the art can readily modify and / or adapt such particular embodiments to various uses without undue experimentation and without departing from the general concept of the disclosure. Accordingly, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0115]

[0132] Other aspects of the invention are described in the following numbered clauses. 1. A method for measuring a fuel fill level of a radiant fuel in an extreme ultraviolet (EUV) radiation system, comprising: directing an inspection beam through a fuel tank viewport onto an upper surface of the radiant fuel at a predetermined angle of incidence; receiving a portion of the inspection beam reflected from the top surface of the radiating fuel with a sensor positioned adjacent the viewport; determining transmit coordinates of a transmit position of the inspection beam; determining receive coordinates of a receive location of the received portion of the interrogation beam; measuring the distance between the receiving coordinates and the transmitting coordinates; and calculating a fill level of the radiated fuel in the fuel tank based on the measured distance; A method comprising: 2. The method of clause 1, wherein the inspection beam is directed at multiple illumination points and the calculation is based on the one or more reflections having the highest signal strength. 3. The method of clause 1, further comprising transmitting a signal indicative of the calculated fill level to a first upstream tank that supplies radiant fuel to the fuel tank. 4. The method of clause 3, wherein the transmitted signal further includes a maintain operating policy command to the first upstream tank to maintain the operating policy in response to the fill level being within a predetermined threshold. 5. The method of clause 3, further comprising sending a second signal indicative of the calculated fill level to a second upstream tank that supplies radiant fuel to the first upstream tank, the second upstream tank being a tank that collects and heats the radiant fuel to a predetermined temperature. 6. The method of clause 5, wherein the radiant fuel is tin (Sn), and transmitting the second signal further comprises transmitting a time parameter for supplying the tin, taking into account the time required to heat the tin. 7. The method of clause 5, wherein the second signal further instructs the second upstream tank to supply the collected and heated radiant fuel to the first upstream tank. 8. Measuring the amount of radiant fuel heated; and transmitting a measured quantity to a sensor indicative of an amount of radiant fuel entering a fuel supply level of the EUV radiation system; The method of clause 7 further comprises: 9. 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 indicating a contamination level associated with the viewport; 3. The method of clause 3, further comprising: 10. Responsive to the fuel tank being positioned at an angle away from an upright position, measuring a tank light intensity reflection of a received portion of the inspection beam from a tank wall, indicative of a fuel level within the tank; and measuring fuel light intensity reflection from the fuel in the fuel tank, which is indicative of the purity level of the fuel; 2. The method of clause 1, further comprising: 11. A measurement device positioned adjacent a fuel tank viewport for measuring a fuel fill level of a radiant fuel in an extreme ultraviolet (EUV) radiation system, comprising: a transmitter for directing an inspection beam through a fuel tank viewport onto the top surface of the radiating fuel at a predetermined angle of incidence; a receiver for receiving a portion of the interrogation beam reflected from the top surface of the radiating fuel; a processing circuit that determines transmit coordinates of a transmission location of the inspection beam, determines receive coordinates of a reception location of a received portion of the inspection beam, measures a distance between the receive coordinates and the transmit coordinates, and calculates a fill level of the radiated fuel in the fuel tank based on the measured distance; A measuring device comprising: 12. A measuring device according to clause 11, in which the inspection beam is directed at a plurality of illumination points and the calculation is based on the one or more reflections having the highest signal strength. 13. The measuring device of clause 11, wherein the processing circuitry further transmits a signal indicative of the calculated fill level to a first upstream tank that supplies radiant fuel to the fuel tank. 14. The measurement device of clause 13, wherein the transmitted signal further comprises a maintain operating policy command to the first upstream tank to maintain the operating policy in response to the fill level being within a predetermined threshold. 15. The measuring device of clause 13, wherein the processing circuitry further transmits a second signal indicative of the calculated fill level to a second upstream tank that supplies radiant fuel to the first upstream tank, the second upstream tank being a tank that collects and heats the radiant fuel to a predetermined temperature. 16. The radiant fuel is tin (Sn); 16. The measuring device of clause 15, wherein the processing circuitry further transmits in the second signal a time parameter for supplying the tin, taking into account the time required to heat the tin. 17. The measuring device of clause 15, wherein the second signal further instructs the second upstream tank to supply collected and heated radiant fuel to the first upstream tank. 18. The processing circuit further comprises: receiving a measured amount of radiant fuel from a sensor associated with the second upstream tank, the amount of radiant fuel being heated and delivered to the first upstream tank; Update the measurements showing the amount of radiation fuel entering the fuel fill level of the EUV radiation system; Clause 17 measuring device that calculates the time interval during which heated radiant fuel is expected to reach the fuel tank. 19. The processing circuit further comprises: 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; A Clause 13 measuring device that generates an operator message indicating the level of contamination associated with the viewport. 20. The processing circuit further comprises: measuring a tank light intensity reflection from a tank wall in response to the fuel tank being angled away from an upright position, the reflection being indicative of a fuel level within the tank; Clause 11 measuring device that measures fuel light intensity reflection from the fuel in the fuel tank, indicating the purity level of the fuel. 21. A measurement device located in a fuel tank for measuring a fuel fill level of a radiant fuel in an extreme ultraviolet (EUV) radiation system, comprising: a measurement sensor; and a controller having processing circuitry; a measurement sensor including a plurality of probes, each one generating a signal in response to contact with the radiated fuel, the probes extending into the fuel tank and connecting to the fuel tank via a plurality of gas-tight high-pressure seals; a measuring device, wherein the controller calculates a fuel fill level in the fuel tank in response to receiving one or more generated signals, generates an output signal indicative of the calculated fill level, and transmits the output signal to at least one other controller; 22. The measuring device of clause 21, wherein the at least one other controller is a first upstream controller associated with a first upstream tank that supplies radiant fuel to the fuel tank. 23. The measurement device of clause 22, wherein the transmitted output signal comprises a maintain operating policy command to the first upstream controller to maintain the supply operating policy in response to the fill level being within a predetermined threshold. 24. The measuring device of clause 22, wherein the controller further sends a second signal indicative of the calculated fill level to a second upstream controller associated with a second upstream tank that supplies radiant fuel to the first upstream tank, the second upstream tank being a tank that collects and heats the radiant fuel to a predetermined temperature. 25. The radiant fuel is tin (Sn); 25. The measuring device of clause 24, wherein the controller further transmits in the second signal a time parameter for supplying the tin based on the time required to heat the tin. 26. The measurement device of clause 24, wherein the second signal further instructs the second upstream controller to supply the collected and heated radiant fuel to the first upstream tank. 27. The controller further receiving a measured amount of radiant fuel from the second upstream controller to be heated and delivered to the first upstream tank; Update the measurements showing the amount of radiation fuel entering the fuel fill level of the EUV radiation system; Clause 26 measuring device that calculates the time interval during which heated radiant fuel is expected to reach the fuel tank. 28. A measuring device of clause 21 in which multiple probes extend downward to different depths within the fuel tank. 29. A measuring device according to clause 21 in which a number of probes extend laterally into the tank at different vertical positions. 30. 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; a second fuel tank located upstream of the first fuel tank in the fuel filling system for providing radiation fuel to the lithography radiation system; a first controller calculating a fuel fill level in the first fuel tank, generating an output signal indicative of the calculated fill level, and transmitting the output signal to a second controller; Lithography radiation system. 31. The lithographic radiation system of clause 30, wherein the first sensor device is an optical sensor. 32. The optical sensor directing the inspection beam through the first tank viewport onto the top surface of the radiating fuel at a predetermined angle of incidence; 32. The lithographic radiation system of clause 31, receiving a portion of the inspection beam reflected from the top surface of the radiation. 33. The optical sensor further determining transmit coordinates of a transmit location of the inspection beam; determining receive coordinates of a receive location of the received portion of the inspection beam; 33. The lithographic radiation system of clause 32, measuring the distance between the receiving coordinate and the transmitting coordinate. 34. The lithography radiation system of clause 33, wherein the optical sensor further calculates a fill level of radiation fuel in the fuel tank based on the measured distance. 35. The lithographic radiation system of clause 30, wherein the first sensor device is located within the fuel tank. 36. The lithographic radiation system of clause 35, wherein the measurement sensor comprises a plurality of probes extending into the fuel tank, each one generating a signal in response to contact with the radiation fuel. 37. A lithography radiation system according to clause 36, wherein the plurality of probes connect to the fuel tank via a plurality of gas-tight high-pressure seals. 38. Further comprising a controller having a processing circuit; The controller calculating a fuel fill level in the fuel tank in response to receiving the one or more generated signals; generating an output signal indicative of the calculated fill level; 36. The lithographic radiation system of clause 35, wherein the output signal is sent 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 that supplies radiation fuel to the fuel tank. 40. A lithographic radiation system according to clause 39, wherein the transmitted signal comprises a maintain operating policy command to the first upstream controller to maintain the supply operating policy in response to the fill level being within a predetermined threshold. 41. The lithography radiation system of clause 37, wherein the multiple probes extend downward to different depths within the fuel tank. 42. A lithography radiation system according to clause 37, wherein a plurality of probes extend laterally into the tank at different vertical positions.

[0116]

[0133] The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary aspects or embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. 1. A method for measuring a fuel fill level of a radiant fuel in an extreme ultraviolet (EUV) radiation system, comprising: directing an inspection beam through a fuel tank viewport onto a top surface of the radiating fuel at a predetermined angle of incidence; receiving a portion of the inspection beam reflected from the top surface of the radiating fuel with a sensor positioned adjacent to the viewport; determining transmit coordinates of a transmit position of the inspection beam; determining receive coordinates of a receive location of the received portion of the interrogation beam; measuring the distance between the receiving coordinates and the transmitting coordinates; calculating the fill level of the radiant fuel in the fuel tank based on the measured distance; 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 angled away from an upright position, the reflection being indicative of a fuel level within the tank; measuring a fuel light intensity reflection from the fuel in the fuel tank, the reflection indicating a purity level of the fuel; A method comprising:

2. the inspection beam is directed to a plurality of illumination points; The method of claim 1 , wherein the calculation is based on one or more reflections having the highest signal strength.

3. The method of claim 1 , further comprising transmitting a signal indicative of the calculated fill level to a first upstream tank that supplies the radiant fuel to the fuel tank.

4. transmitting a second signal indicative of the calculated fill level to a second upstream tank that supplies the radiant fuel to the first upstream tank; 4. The method of claim 3, wherein the second upstream tank is a tank that collects and heats the radiant fuel to a predetermined temperature.

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

6. 1. A measurement device positioned adjacent a fuel tank viewport for measuring a fuel fill level of a radiant fuel in an extreme ultraviolet (EUV) radiation system, comprising: a transmitter for directing an inspection beam through the fuel tank viewport onto the top surface of the radiating fuel at a predetermined angle of incidence; a receiver for receiving a portion of the interrogation beam reflected from the top surface of the radiant fuel; a processing circuit for determining transmit coordinates of a transmission location of the inspection beam, determining receive coordinates of a reception location of the received portion of the inspection beam, measuring a distance between the receive coordinates and the transmit coordinates, calculating a fill level of the radiated fuel in the fuel tank based on the measured distance, measuring a tank light intensity reflection from a tank wall indicative of a fuel level in the tank in response to the fuel tank being angled from an upright position, and measuring a fuel light intensity reflection from the fuel in the fuel tank indicative of a purity level of the fuel; A measuring device comprising:

7. the inspection beam is directed to a plurality of illumination points; The measurement device of claim 6 , wherein the calculation is based on the one or more reflections having the highest signal strength.

8. the processing circuitry further transmits a signal indicative of the calculated fill level to a first upstream tank supplying the radiant fuel to the fuel tank, and transmits a second signal indicative of the calculated fill level to a second upstream tank supplying the radiant fuel to the first upstream tank; 7. The measurement device of claim 6, wherein the second upstream tank is a tank that collects and heats the radiant fuel to a predetermined temperature.

9. A measurement device positioned adjacent to a fuel tank viewport for measuring a fuel fill level of a radiant fuel in an extreme ultraviolet (EUV) radiation system, comprising: a transmitter for directing an inspection beam through the fuel tank viewport onto the top surface of the radiating fuel at a predetermined angle of incidence; a receiver for receiving a portion of the interrogation beam reflected from the top surface of the radiant fuel; a processing circuit that determines transmit coordinates of a transmission location of the inspection beam, determines receive coordinates of a reception location of the received portion of the inspection beam, measures a distance between the receive coordinates and the transmit coordinates, calculates a fill level of the radiant fuel in the fuel tank based on the measured distance, transmits a signal indicative of the calculated fill level to a first upstream tank that supplies the radiant fuel to the fuel tank, and transmits a second signal indicative of the calculated fill level to a second upstream tank that supplies the radiant fuel to the first upstream tank; the second upstream tank is a tank that collects and heats the radiant fuel to a predetermined temperature; the second signal further instructs the second upstream tank to supply the collected and heated radiant fuel to the first upstream tank; The processing circuitry further comprises a measurement device that receives a measured amount of radiant fuel that is heated and supplied to the first upstream tank from a sensor associated with the second upstream tank, updates a measurement value indicative of the amount of radiant fuel entering the fuel fill level of the EUV radiation system, and calculates a time interval at which the heated radiant fuel is expected to reach the fuel tank.

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