Extreme ultraviolet source temperature monitoring using a confocal sensor

Abstract

The broadband light source includes a confocal sensor assembly configured to measure a surface of a rotatable drum covered with a plasma formation target material. The broadband light source includes a laser source configured to direct pulsed illumination at the rotatable drum to excite the plasma formation target material and emit broadband light as the drum is angularly rotated and axially translated. The broadband light source includes a controller configured to direct the confocal sensor assembly to transmit a confocal light signal to the rotatable drum, record a calibrated measurement of the distance from the confocal sensor assembly to the rotatable drum, direct a cryogenic cooling subsystem to cryogenically cool the rotatable drum, record one or more distance measurements from the sensor head to the rotatable drum, convert the distance measurements to temperature values, and determine whether a target process condition temperature has been achieved.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 63 / 432,772, entitled "EUV Source Temperature Monitoring Using Confocal Sensor," filed December 15, 2022, with Patrick Tae and Caijun Su as inventors, and is hereby incorporated by reference in its entirety.

[0002] The present disclosure relates generally to generating broadband illumination, and more particularly to a system and method for generating broadband illumination with a pulsed laser and a rotating drum covered with a target material. [Background technology]

[0003] As the demand for lithography-based device structures with increasingly miniaturized features continues to grow, the need for improved illumination sources used to inspect the associated reticles that lithographically print these ever-shrinking devices continues to grow. One such illumination source includes extreme ultraviolet (EUV) light sources. One method of generating EUV light involves spinning a drum covered with a uniformly thick layer of a solid (frozen) plasma-forming target material, such as xenon, and exposing the xenon-covered portion of the cylinder to a pulsed laser suitable for exciting the xenon to generate a plasma. Inspection tools used in this context typically operate at the same wavelengths used for imaging, creating the challenge of providing a reliable source of short-wavelength EUV light that meets system-level specifications. Traditionally, drum inspection at EUV sources has relied on infrared pyrometry and thermocouples combined with thermal modeling. However, infrared pyrometry encounters limitations due to the low emissivity of the copper drum target material. Furthermore, this technique has proven difficult to obtain accurate temperature readings at extremely low temperatures, especially below -50 degrees Celsius. Another approach, combining thermocouples with thermal modeling, presents its own challenges. The inherent difficulty stems from the lack of effective coupling between the thermocouples and the dynamically moving drum target, which operates along two independent axes. This makes it difficult to establish a reliable correlation between the temperature measurements and the actual temperature of the drum target, hindering the accuracy and efficiency of the inspection process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0136903 [Patent Document 2] U.S. Patent Application Publication No. 2017 / 0248416 Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be desirable to provide a method and system that overcomes the above-identified shortcomings of previous approaches. [Means for solving the problem]

[0006] A broadband light source is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the broadband light source includes a rotatable drum at least partially covered with a plasma formation target material. In another exemplary embodiment, the broadband light source includes a confocal sensor assembly including a sensor head and a light source for measuring the surface of the rotatable drum. In another exemplary embodiment, the broadband light source includes a laser source configured to direct pulsed illumination to a portion of the rotatable drum covered with the material to excite the plasma formation target material and emit broadband light as the rotatable drum is angularly rotated and axially translated. In another exemplary embodiment, the broadband light source includes a controller having one or more processors configured to execute program instructions stored in a memory. In another exemplary embodiment, the program instructions are configured to cause the one or more processors to direct the confocal sensor assembly to transmit a confocal light signal to the rotatable drum. In another exemplary embodiment, the program instructions are configured to cause the one or more processors to record a calibration measurement of the distance from the confocal sensor assembly to the rotatable drum at a first temperature. In another exemplary embodiment, the program instructions are configured to cause the one or more processors to direct a cryogenic cooling subsystem to cryogenically cool the rotatable drum. In another exemplary embodiment, the program instructions are configured to cause the one or more processors to record one or more distance measurements from the sensor head to the rotatable drum during cryogenic cooling of the rotatable drum. In another exemplary embodiment, the program instructions are configured to cause the one or more processors to convert the one or more distance measurements to one or more temperature values ​​representative of a temperature of the material on the rotatable drum during cryogenic cooling of the rotatable drum. In another exemplary embodiment, the program instructions are configured to cause the one or more processors to determine, based on the converted temperature values, whether a target process condition temperature of the rotatable drum has been achieved.

[0007] A characterization system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the characterization system includes an illumination subsystem. In another exemplary embodiment, the illumination subsystem includes a rotatable drum at least partially covered with a plasma-forming target material. In another exemplary embodiment, the illumination subsystem includes a confocal sensor assembly including a sensor head and a light source for measuring the surface of the rotatable drum. In another exemplary embodiment, the illumination subsystem includes a laser source configured to direct pulsed illumination to a portion of the rotatable drum covered with the material to excite the plasma-forming target material and emit broadband light as the rotatable drum is angularly rotated and axially translated. In another exemplary embodiment, the characterization system includes one or more collection optics configured to collect illumination emitted from plasma generated in response to excitation of the plasma-forming target material. In another exemplary embodiment, the characterization system includes a set of illumination optics configured to direct illumination from the one or more collection optics to one or more samples disposed on a stage. In another exemplary embodiment, the characterization system includes a detector. In another exemplary embodiment, a characterization system includes a set of projection optics configured to receive illumination from surfaces of one or more samples and direct illumination from the one or more samples to a detector.

[0008] A method is disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the method may include, but is not limited to, rotating a rotatable drum covered with a plasma-forming target material. In another exemplary embodiment, the method may include, but is not limited to, instructing a confocal sensor assembly to transmit a confocal optical signal to the rotatable drum. In another exemplary embodiment, the method may include, but is not limited to, recording a calibration measurement of a distance from the confocal sensor assembly to the rotatable drum at a first temperature. In another exemplary embodiment, the method may include, but is not limited to, instructing a cryogenic cooling subsystem to cryogenically cool the rotatable drum. In another exemplary embodiment, the method may include, but is not limited to, recording one or more distance measurements from a sensor head to the rotatable drum during cryogenic cooling of the rotatable drum. In another exemplary embodiment, the method may include, but is not limited to, converting the one or more distance measurements to one or more temperature values ​​representing a temperature of the material on the rotatable drum during cryogenic cooling of the rotatable drum. In another exemplary embodiment, the method may include, but is not limited to, determining whether a target process condition temperature of the rotatable drum has been achieved based on the converted temperature values.

[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplary embodiments of the invention, and the general description together therewith serve to explain the principles of the invention.

[0010] The many advantages of the present disclosure may be better understood by those skilled in the art by reference to the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1A] FIG. 1 is a conceptual diagram of a confocal sensor assembly integrated within a rotating drum-based broadband light source in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a conceptual diagram of a confocal sensor assembly integrated within a cryogenically cooled, rotating drum-based broadband light source, in accordance with one or more embodiments of the present disclosure. [Figure 2] FIG. 1 is a conceptual diagram of a drum-based broadband light source with a confocal sensor assembly in accordance with one or more embodiments of the present disclosure. [Figure 3] FIG. 1 is a block diagram of an inspection system incorporating a broadband light source in accordance with one or more embodiments of the present disclosure. [Figure 4] FIG. 1 is a flow diagram illustrating a method for determining the temperature of a drum target by a confocal sensor assembly in accordance with one or more embodiments of the present disclosure. [Figure 5] FIG. 1 is a flow diagram illustrating a method for determining when the temperature of a drum target exceeds the atmospheric dew point by a confocal sensor assembly in accordance with one or more embodiments of the present disclosure. [Figure 6] 10 illustrates continuous temperature metrics determined for a drum target based on the confocal length of a confocal sensor assembly, in accordance with one or more embodiments of the present disclosure. [Figure 7] 10 illustrates a drum target temperature metric for determining when the temperature of the drum target exceeds the atmospheric dew point, in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with reference to certain embodiments and certain features thereof. The embodiments described herein are to be construed as illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made therein without departing from the spirit and scope of the present disclosure.

[0013] 1A-7 generally illustrate embodiments of systems and methods for determining a drum target temperature in accordance with one or more embodiments of the present disclosure.

[0014] Embodiments of the present disclosure are directed to the exposure of a rotating drum (e.g., a cylinder) covered with a plasma-forming material (e.g., frozen xenon or carbon dioxide), which can be excited by an illumination source (e.g., a pulsed laser) to emit broadband light (e.g., broadband EUV light or soft x-ray light). Embodiments of the present disclosure are directed to a confocal sensor assembly integrated within a xenon ice-based EUV source to improve productivity and uptime in semiconductor photomask inspection, particularly those designed for use in EUV lithography. These masks are complex in their geometries and require sophisticated inspection systems operating at the same wavelengths employed for imaging. This creates the challenge of providing a reliable source of short-wavelength extreme ultraviolet (EUV) light that meets system-level specifications. To mitigate downtime and optimize operational efficiency, embodiments of the present disclosure introduce metrology techniques that determine the process condition temperature of a plasma-based rotating drum in real time, even in the absence of ice. This capability has proven valuable during various critical stages of tool operation. For example, during the source ramp-up phase, the drum temperature can serve as a dynamic indicator, enabling accurate determination of when the drum has reached the temperature required for ice growth and maintenance. This real-time measurement eliminates the need to rely on temperature sensors that may not be directly coupled to the drum. As another example, measuring the drum temperature during a source maintenance phase can help reduce green-to-green time by determining a safe point to vent the chamber and expose the drum to atmosphere. This improves upon traditional approaches that rely on predetermined wait times that include sufficient margin to accommodate variations in tool and environmental conditions. As another example, during unplanned downtime, drum temperature measurements can provide important information for assessing the health of the system. This allows for informed decisions to be made about whether to vent the drum or continue operating it, facilitating faster system recovery than would be possible without such feedback.As another example, determining the temperature of a rotating drum as it rotates and translates can provide valuable insight for research and development purposes, as it can provide characterization of thermally induced stresses and strains in the drum during cooling and warming processes. Understanding the relationship between drum deformation and temperature can provide the basis for hardware design iterations and optimization of process conditions for source operation.

[0015] 1A-1B are conceptual diagrams of a confocal sensor assembly 100 integrated within a rotating drum-based broadband light source, in accordance with one or more embodiments of the present disclosure.

[0016] In an embodiment, the broadband source 200 includes a confocal sensor assembly 100, a rotatable drum 108, and a controller 106 including one or more processors and memory. For example, the confocal sensor assembly 100 may be positioned proximate to the rotatable drum 108 to measure the surface of the drum 108. In an embodiment, the confocal sensor assembly 100 may include a sensor head 102. For example, the sensor head 102 may be mounted in a vacuum environment while remaining proximate to the rotatable drum 108.

[0017] In an embodiment, the confocal sensor assembly 100 may include a light source 104. For example, the light source 104 may be positioned outside the sensor head 102 and the vacuum environment. In an embodiment, the light source 104 is configured to emit light in a direction toward the surface of the rotating drum 108. For example, the light source 104 is designed to generate light of a particular wavelength suitable for confocal metrology measurements. For example, the wavelength may be tuned to the characteristics of the drum material and the measurement environment.

[0018] In embodiments, the light source 104 may include, but is not limited to, one or more broadband light sources. For example, the one or more light sources may include, but are not limited to, one or more flash lamps or one or more LEDs. Note that the confocal assembly 100 may measure the distance from the sensor head 102 to the surface of the drum 108 by utilizing controlled chromatic aberration observed within the broadband light source of the confocal assembly 100. Furthermore, the particular type of light source 104 selected may be adapted to optimize performance under cryogenic conditions and other operating conditions of the rotating drum 108. As another example, the sensor head 102 may be configured to emit and receive optical signals. In embodiments, the sensor head 102 includes confocal optics used to ensure that the emitted and received optical signals share a common focal point at the surface of the drum 108. This confocal arrangement enhances measurement accuracy by selectively capturing only light reflected from the focal plane. In embodiments, the sensor head 102 may employ various configurations to optimize its performance under various operating conditions. For example, the sensor head 102 may include adaptive optics or variable focal length elements to accommodate variations in the rotation and translation of the rotatable drum 108 .

[0019] In an embodiment, the confocal sensor assembly 100 is communicatively coupled to a controller 106 that includes one or more processors and a memory. For example, the one or more processors may be communicatively coupled to a memory such that the one or more processors are configured to execute a set of program instructions stored in the memory. In an embodiment, the one or more processors are configured to direct the sensor head 102 to transmit a confocal optical signal toward the surface of the rotatable drum 108. In an embodiment, the one or more processors are configured to direct the light source to emit light in a direction toward the surface of the rotatable drum 108.

[0020] FIG. 2 is a conceptual diagram of a drum-based broadband light source 200 with a confocal sensor assembly 100 in accordance with one or more embodiments of the present disclosure.

[0021] In an embodiment, the broadband source 200 includes a rotating drum 108 suitable for rotation about an axis. For example, the drum 108 may be a cylinder, as shown in FIG. 1A . In other embodiments, the drum 108 includes any cylindrically symmetric shape known in the art. For example, the drum 108 may include, but is not limited to, a cylinder, a cone, a sphere, an ellipsoid, and the like. Furthermore, the drum 108 may include a composite shape consisting of two or more shapes. For convenience of explanation, embodiments of the present disclosure are described herein in the context of a rotating drum or rotating drum 108, as shown in FIG. 1A , but it should be noted that this embodiment should not be construed as limiting the scope of the present disclosure.

[0022] In an embodiment, the drum 108 is covered with a plasma-forming target material. For example, the target material may include a solid disposed on the surface of the drum 108. The plasma-forming target material may include any material known in the art that, when excited by an illumination source, generates a plasma and subsequently emits broadband light. The broadband light emitted by the plasma may include, but is not limited to, broadband soft x-ray light, broadband EUV light, broadband DUV light, broadband VUV light, broadband UV light, broadband visible light, and / or broadband IR light. As another example, the target material may include, but is not limited to, xenon frozen on the surface of the drum 108. It is noted that the use of frozen xenon as a target material may be particularly useful in situations where broadband EUV light is to be generated. As another example, the target material may include, but is not limited to, carbon dioxide frozen on the surface of the drum 108. It is noted that the use of frozen carbon dioxide as a target material may be particularly useful in situations where broadband soft x-ray light is to be generated.

[0023] In an embodiment, broadband source 200 includes a pulsed illumination source 202. Pulsed illumination source 202 may include any pulsed or modulated illumination source known in the art. For example, pulsed source 202 may include a pulsed laser. Furthermore, pulsed illumination source 202 is suitable for initiating and / or sustaining a plasma within the material of the rotating drum. For example, pulsed illumination source 202 may include, but is not limited to, one or more infrared (IR) lasers. For example, pulsed illumination source 202 may include, but is not limited to, one or more CO lasers.

[0024] In an embodiment, the broadband source 200 includes one or more actuators configured to actuate the drum 108 rotationally and axially. In an embodiment, the broadband source 200 includes a rotary actuator 206 configured to rotate the drum 108 about an axis. The rotary actuator 206 may include any rotary actuator known in the art, including, but not limited to, one or more servo motors. Additionally, the broadband source 200 may include a linear actuator 208 configured to translate the drum 108 along an axial direction (e.g., vertically in the example shown in FIG. 1A ). It is recognized herein that the present disclosure is not limited to the rotary and linear actuators 206, 208 of FIG. 2 . Thus, the above description should be construed as merely exemplary. For example, the pulsed source 202 may be disposed on an actuation stage (not shown) that provides translation of the pulsed illumination 204 relative to the drum 108.

[0025] The axial motion imparted by the linear actuator 208 and the rotational motion of the drum 108 caused by the rotary actuator 206 enable tracking of the pulsed illumination 204 across the surface of the drum 108. In embodiments, the controller 106 may control the triggering of the pulsed laser source 202 and / or the actuation of the drum 108 along the rotational and / or axial directions. In this regard, the controller 106 may direct the actuators 206, 208, and the drum 108 to track the pulsed illumination 204 across the surface of the cylinder as it rotates and translates axially in any manner described in this disclosure.

[0026] In an embodiment, the broadband source 200 may include a cryogenic cooling subsystem for cooling the rotating drum 108. For example, the cryogenic cooling subsystem may include a heat exchanger, a cryogenic fluid, and / or a circulation system. In an embodiment, the cryogenic fluid may include, but is not limited to, liquid nitrogen, liquid helium, liquid argon, liquid carbon dioxide, liquid hydrogen, and / or liquid oxygen. For example, one or more processors of the controller 106 may be configured to direct the cryogenic cooling subsystem to circulate a selected cryogenic fluid through a heat exchanger. For example, the heat exchanger may absorb heat from the rotating drum and vaporize the cryogenic fluid. As the cryogenic fluid vaporizes, it absorbs heat from the rotating drum 108, thereby lowering the temperature of the drum. The vaporized coolant is then returned to the circulation system for re-cooling.

[0027] In an embodiment, the broadband source 200 may include a heating subsystem. For example, the heating subsystem may include one or more heating elements configured to heat the rotating drum back to a calibration temperature or other desired level. The one or more heating elements may include, but are not limited to, electric heating elements (e.g., one or more resistive heaters), radiant heating elements (e.g., one or more quartz infrared heaters), or inductive heating elements (e.g., one or more induction heating coils). In an embodiment, the one or more heating elements may be positioned around the rotating drum 108.

[0028] In embodiments, broadband source 200 may include multiple controllers for managing various operations of broadband source 200. For example, the multiple controllers may include at least one of a motion controller, a process controller, and / or a laser controller for collectively handling functions including, but not limited to, drum actuation, process control, and laser triggering. It should be noted herein that broadband source 200 is not limited to multiple controllers, although a single controller 106 may be configured to perform the functions of multiple controllers described above, as needed.

[0029] FIG. 3 is a block diagram of an inspection system 300 incorporating a plasma-based illumination source 200 in accordance with one or more embodiments of the present disclosure. In an embodiment, the system 300 includes an illumination subsystem 302. The illumination subsystem 302 may incorporate the broadband source 200 described throughout this disclosure. In an embodiment, although not shown in FIG. 3, the system 300 includes a set of illumination optics. In an embodiment, the illumination optics may direct illumination 109 emitted from the broadband source 200 to one or more samples 304 disposed on a sample stage 306. For example, the one or more samples 304 may include, but are not limited to, wafers (e.g., semiconductor wafers). As another example, the one or more samples 304 may include, but are not limited to, a reticle or a photomask. In an embodiment, the system 300 includes one or more detectors 310. In an embodiment, system 300 includes a set of projection optics 308 suitable for collecting light scattered, reflected, diffracted, or otherwise diverging from the sample and directing the light to one or more detectors (e.g., CCD, TDI-CCD, PMT, etc.). In an embodiment, controller 106 may be integrated within system 300 to receive and / or analyze measurements from detector 310.

[0030] It is noted herein that one or more components of system 300 may be communicatively coupled to various other components of system 300 in any manner known in the art. For example, broadband light source 200, detector 310, controller 106, and one or more processors may be communicatively coupled to each other and to the other components via wires (e.g., copper wire and fiber optic cables, etc.) or wireless connections (e.g., RF coupling, IR coupling, data network communications (e.g., WiFi, WiMax, Bluetooth, etc.)).

[0031] In an embodiment, inspection system 300 is configured as a wafer inspection system or a reticle / photomask inspection system. For example, inspection system 300 may include any wafer or reticle / photomask inspection optical architecture known in the art that is suitable for operating in the EUV spectral range. As another example, inspection system 300 may include any wafer or reticle / photomask inspection optical architecture known in the art that is suitable for operating in the soft x-ray spectral range. It is further recognized that inspection system 300 may be configured as an EUV mask or mask blank inspection system. EUV-based mask blank inspection is generally described in U.S. Patent No. 8,711,346 to Stokowski, issued April 29, 2014, which is incorporated herein by reference in its entirety. EUV-based mask blank inspection is generally described in U.S. Patent No. 8,785,082 to Xiong et al., issued July 22, 2014, which is incorporated herein by reference in its entirety. EUV-based reticle inspection is generally described in U.S. Patent No. 8,953,869 to Nasser-Ghodsi et al., issued February 10, 2015, which is incorporated herein by reference in its entirety.

[0032] In embodiments, the broadband source 200 described throughout this disclosure may be implemented within an optical lithography system. In embodiments, the optical lithography system may include a set of illumination optics configured to direct output light from the broadband source 200 to an EUV-compatible lithography mask (e.g., an EUV reflective mask) or a soft X-ray-compatible lithography mask. In embodiments, the optical lithography system includes a set of projection optics configured to receive illumination reflected from the mask and direct the reflected illumination from the mask to one or more wafers disposed on a wafer stage. The optical lithography system may include any broadband lithography system known in the art. EUV-based lithography is generally described in U.S. Patent No. 8,916,831 to Wang, issued December 23, 2014, the entire contents of which are incorporated herein by reference.

[0033] FIG. 4 is a flow diagram illustrating a method 400 for determining the temperature of a drum target with a confocal sensor assembly, in accordance with one or more embodiments of the present disclosure.

[0034] In step 402, a confocal optical signal is transmitted from the confocal sensor assembly to the surface of the rotatable drum. For example, the controller 106 may instruct the sensor head 102 of the confocal sensor assembly 100 to transmit the confocal optical signal to the rotatable drum 108.

[0035] In step 404, calibration measurements of the distance from the sensor head to the surface of the rotatable drum at the first temperature are recorded. For example, the sensor head 102 may be configured to communicate the calibration measurements with the controller 106. Further, the memory of the controller 206 may be configured to store the recorded calibration measurements and corresponding temperatures associated with the calibration measurements.

[0036] The rotatable drum is cryogenically cooled in step 406. For example, one or more processors of the controller 106 may be configured to direct the cryogenic cooling subsystem to cool the rotatable drum 108 to a predetermined temperature.

[0037] In step 408, the sensor head is configured to continuously monitor the confocal distance from the sensor head to the rotating drum during cryogenic cooling. For example, the sensor head 102 is configured to transmit continuous confocal optical signals to the rotating drum 108 to monitor the temperature of the surface of the rotating drum 108. Furthermore, the sensor head 102 is configured to communicate the continuous measurements to the controller 106, which is configured to store the data in memory.

[0038] In step 410, the continuously recorded distance measurements are converted into temperature values ​​representing the temperature of the drum material during cryogenic cooling. For example, one or more processors of the controller 106 are configured to derive the temperature of the rotatable drum 108 from the communication distance measurements received from the sensor head 102.

[0039] In step 412, it is determined whether a target process condition temperature of the surface of the rotatable drum has been achieved based on the converted temperature values. For example, the controller 106 may be configured to continuously monitor the temperature readings provided by the confocal sensor assembly. Furthermore, when a temperature reading is received that meets or exceeds a predetermined target temperature of the rotatable drum 108, the controller 106 may interpret this as the target condition being achieved.

[0040] FIG. 5 is a flow diagram illustrating a method for determining when the temperature of a drum target exceeds the atmospheric dew point by a confocal sensor assembly in accordance with one or more embodiments of the present disclosure.

[0041] In step 502, the rotatable drum is warmed back to the first temperature. For example, the drum 108 is warmed by a heating subsystem, which may include one or more heating elements configured to heat the rotatable drum 108. As another example, the one or more heating elements may include at least one of an electric heating element, a radiant heating element, or an induction heating system.

[0042] In step 504, the rotary drum is cryogenically cooled. For example, cryogenic cooling of the rotary drum 108 is achieved by a cryogenic fluid, which is a cryogenic fluid including at least one of liquid nitrogen, liquid helium, liquid argon, liquid carbon dioxide, liquid hydrogen, or liquid oxygen.

[0043] In step 506, distance measurements from the sensor head to the rotating drum are continuously recorded during cryogenic cooling. For example, the sensor head 102 is configured to transmit continuous confocal optical signals to the rotating drum 108 to monitor the temperature of the surface of the rotating drum 108. Further, the sensor head 102 is configured to communicate the continuous measurements to the controller 106, which is configured to store the data in memory.

[0044] In an embodiment, the controller 106 analyzes the intensity of the confocal optical signal for one or more temperature values ​​to determine the presence of ice on the rotatable drum. For example, the controller 106 may determine the presence of ice based on fluctuations in the intensity of the confocal optical signal.

[0045] In step 508, the continuous distance measurements are converted to temperature values ​​representing the temperature of the drum material during cryogenic cooling. For example, program instructions stored in the memory of the controller 106 are configured to cause one or more processors to derive the temperature of the rotatable drum 108 from the recorded distance measurements.

[0046] The atmospheric dew point temperature of the rotatable drum is determined in step 510. For example, the controller 106 may be configured to determine when the surface of the rotatable drum 108 exceeds a temperature corresponding to the atmospheric dew point.

[0047] 6 illustrates continuous temperature metrics determined for a drum target based on the confocal distance of a confocal sensor assembly, in accordance with one or more embodiments of the present disclosure. For example, as the rotating drum is cryogenically cooled, the confocal distance from the sensor head 102 to the surface of the rotating drum 108 changes due to deformation of the rotating drum 108. Furthermore, the temperature of the rotating drum 108 can be derived from the recorded confocal distance measurements of the rotating drum 108.

[0048] 7 illustrates a drum target temperature metric for determining when the temperature of the drum target exceeds the atmospheric dew point, in accordance with one or more embodiments of the present disclosure. In an embodiment, the atmospheric dew point temperature may be stored in a memory of the controller 106. For example, when the temperature of the rotatable drum 108 reaches or exceeds the atmospheric dew point temperature, the chamber may be safely vented for maintenance.

[0049] The subject matter described herein may depict different components contained within or connected to other components. It should be understood that any architectures depicted are merely exemplary, and that in fact, many other architectures that achieve the same functionality may be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Thus, any two components herein that are combined to achieve a particular function can be considered to be “associated” with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be “connected” or “coupled” to each other to achieve the desired functionality, and any two components that can be associated in this manner can also be considered to be “couplable” to each other to achieve the desired functionality. Specific examples of combinable components include, but are not limited to, components that are physically interactable and / or physically interacting, components that are wirelessly interactable and / or wirelessly interacting, and / or components that are logically interactable and / or logically interacting.

[0050] As used throughout this disclosure, the term "sample" generally refers to a substrate formed of a semiconductor or non-semiconductor material (e.g., a wafer, etc.). For example, the semiconductor or non-semiconductor material may include, but is not limited to, monocrystalline silicon, gallium arsenide, and indium phosphide.

[0051] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes in form, construction, and arrangement of the elements may be made without departing from the disclosed subject matter or sacrificing all of its material advantages. The described forms are merely illustrative, and it is the intent of the following claims to embrace and include such modifications. It will further be understood that the invention is defined by the appended claims.

Claims

1. a rotating drum at least partially covered with a plasma-forming target material; a confocal sensor assembly including a sensor head and a light source for measuring the surface of the rotatable drum; a laser source configured to direct pulsed illumination onto a material-covered portion of the rotatable drum to excite the plasma-forming target material and emit broadband light as the rotatable drum is angularly rotated and axially translated; a controller comprising one or more processors configured to execute program instructions stored in a memory, the program instructions causing the one or more processors to: directing the confocal sensor assembly to transmit a confocal optical signal to the rotatable drum; recording a calibration measurement of the distance from the confocal sensor assembly to the rotatable drum at a first temperature; directing a cryogenic cooling subsystem to cryogenically cool the rotatable drum; recording one or more distance measurements from the sensor head to the rotatable drum during the cryogenic cooling of the rotatable drum; converting the one or more distance measurements into one or more temperature values ​​representative of a temperature of the material of the rotatable drum during the cryogenic cooling of the rotatable drum; and determining whether a target process condition temperature of the rotary drum has been achieved based on the converted temperature value; configured to cause Broadband light source.

2. 10. The broadband light source of claim 1, wherein recording the one or more distance measurements to the rotatable drum comprises continuously recording the one or more distance measurements during the cryogenic cooling of the rotatable drum.

3. The broadband light source of claim 1 , further comprising a heating subsystem for the rotatable drum, the heating subsystem comprising one or more heating elements configured to heat the rotatable drum.

4. The broadband light source of claim 3 , wherein the one or more heating elements include at least one of an electric heating element, a radiant heating element, or an induction heating system.

5. the one or more processors: directing the heating subsystem to heat the rotatable drum back to the first temperature with the one or more heating elements; directing the cryogenic cooling subsystem to cryogenically cool the rotary drum; recording the one or more distance measurements from the sensor head to the rotary drum during the cryogenic cooling of the rotary drum; converting the one or more distance measurements into one or more temperature values ​​representing the temperature of the material on the rotating drum during the cryogenic cooling of the rotating drum; and Determining when the rotating drum exceeds the atmospheric dew point 4. The broadband light source of claim 3, further configured as follows:

6. the one or more processors: analyzing the intensity of the confocal optical signal for the one or more temperature values; and determining the presence of ice on the rotating drum based on the variations in the intensity of the confocal optical signal; The broadband light source of claim 1 further configured as follows:

7. 2. The broadband light source of claim 1, wherein the first temperature is set to a calibration temperature for the calibration measurements.

8. 10. The broadband light source of claim 1, wherein the cryogenic cooling of the rotating drum is achieved by a cryogenic fluid, the cryogenic fluid comprising at least one of liquid nitrogen, liquid helium, liquid argon, liquid carbon dioxide, liquid hydrogen, or liquid oxygen.

9. An illumination subsystem, the illumination subsystem comprising: a rotating drum at least partially covered with a plasma-forming target material; a confocal sensor assembly including a sensor head and a light source for measuring the surface of the rotating drum; and a laser source configured to direct pulsed illumination onto a material-covered portion of the rotatable drum to excite the plasma-forming target material and emit broadband light as the rotatable drum is angularly rotated and axially translated. a lighting subsystem comprising: one or more collection optics configured to collect illumination emitted from a plasma generated in response to excitation of the plasma-forming target material; a set of illumination optics configured to direct the illumination from the one or more collection optics to one or more samples disposed on a stage; A detector; a set of projection optics configured to receive the illumination from a surface of the one or more samples and direct the illumination from the one or more samples to the detector; A characterization system comprising:

10. a controller comprising one or more processors configured to execute program instructions stored in memory, the program instructions causing the one or more processors to: directing the confocal sensor assembly to transmit a confocal optical signal to the rotatable drum; recording a calibration measurement of the distance from the confocal sensor assembly to the rotatable drum at a first temperature; directing a cryogenic cooling subsystem to cryogenically cool the rotatable drum; recording one or more distance measurements from the sensor head to the rotatable drum during the cryogenic cooling of the rotatable drum; converting the one or more distance measurements into one or more temperature values ​​representative of a temperature of the material of the rotatable drum during the cryogenic cooling of the rotatable drum; and determining whether a target process condition temperature of the rotary drum has been achieved based on the converted one or more temperature values; configured to cause The characterization system of claim 9 .

11. 11. The characterization system of claim 10, wherein recording the one or more distance measurements to the rotatable drum comprises continuously recording the one or more distance measurements during the cryogenic cooling of the rotatable drum.

12. The characterization system of claim 10 , further comprising a heating subsystem for the rotatable drum, the heating subsystem comprising one or more heating elements configured to heat the rotatable drum.

13. The characterization system of claim 12 , wherein the one or more heating elements include at least one of an electric heating element, a radiant heating element, or an induction heating system.

14. the one or more processors: directing the heating subsystem to heat the rotatable drum back to the first temperature with the one or more heating elements; directing the cryogenic cooling subsystem to cryogenically cool the rotary drum; recording the one or more distance measurements from the sensor head to the rotary drum during the cryogenic cooling of the rotary drum; converting the one or more distance measurements into one or more temperature values ​​representative of a temperature of the material on the rotatable drum during the cryogenic cooling of the rotatable drum; and Determining when the rotating drum exceeds the atmospheric dew point The characterization system of claim 12 further configured to:

15. the one or more processors: analyzing the intensity of the confocal optical signal for the one or more temperature values; and determining the presence of ice on the rotating drum based on the variations in the intensity of the confocal optical signal; The characterization system of claim 10 further configured to:

16. The characterization system of claim 10 , wherein the first temperature is set to a calibration temperature for the calibration measurements.

17. 11. The characterization system of claim 10, wherein the cryogenic cooling of the rotatable drum is achieved by a cryogenic fluid, the cryogenic fluid comprising at least one of liquid nitrogen, liquid helium, liquid argon, liquid carbon dioxide, liquid hydrogen, or liquid oxygen.

18. directing a confocal sensor assembly to transmit a confocal optical signal to a rotatable drum; recording a calibration measurement of the distance from the confocal sensor assembly to the rotatable drum at a first temperature; directing a cryogenic cooling subsystem to cryogenically cool the rotatable drum; recording one or more distance measurements from a sensor head to the rotary drum during the cryogenic cooling of the rotary drum; converting the one or more distance measurements into one or more temperature values ​​representative of a temperature of the material of the rotatable drum during the cryogenic cooling of the rotatable drum; determining whether a target process condition temperature of the rotatable drum has been achieved based on the converted one or more temperature values; A method comprising:

19. directing the heating subsystem to heat the rotatable drum back to the first temperature with the one or more heating elements; directing the cryogenic cooling subsystem to cryogenically cool the rotary drum; recording the one or more distance measurements from the sensor head to the rotary drum during the cryogenic cooling of the rotary drum; converting the one or more distance measurements into the one or more temperature values ​​representing the temperature of the material on the rotatable drum during the cryogenic cooling of the rotatable drum; determining when the rotatable drum exceeds the atmospheric dew point; 20. The method of claim 18, further comprising:

20. 20. The method of claim 18, wherein the cryogenic cooling of the rotatable drum is achieved by a cryogenic fluid, the cryogenic fluid comprising at least one of liquid nitrogen, liquid helium, liquid argon, liquid carbon dioxide, liquid hydrogen, or liquid oxygen.

21. analyzing the intensity of the confocal optical signal for the one or more temperature values; determining the presence of ice on the rotatable drum based on the variations in the intensity of the confocal optical signal; 20. The method of claim 18, further comprising:

22. 20. The method of claim 18, wherein the first temperature is set to a calibration temperature for the calibration measurement.

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