Extreme ultraviolet light source temperature monitoring using confocal sensors

Abstract

A broadband light source includes a confocal sensor assembly configured to measure a surface of a rotatable drum coated with a plasma forming target. The broadband light source includes a laser source configured to direct pulsed illumination to the rotatable drum for exciting the plasma forming target and emitting broadband light as the rotatable drum rotates in an angular direction and translates in an axial direction. The broadband light source includes a controller configured to direct the confocal sensor assembly to transmit a confocal optical signal to the rotatable drum, to record a calibrated measurement of a distance from the confocal sensor assembly to the rotatable drum, to direct a cryocooling subsystem to cryocool the rotatable drum, and to record a calibrated measurement of a distance from the confocal sensor assembly to the rotatable drum. One or more distance measurements from a sensor head to the rotatable drum are recorded, the distance measurements are converted into temperature values, and whether a target process condition temperature is achieved is determined.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 63 / 432,772, filed on December 15, 2022, entitled “EUV Source Temperature Monitoring Using Confocal Sensor,” naming Patrick Tae and Caijun Su as inventors, the entire text of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to the generation of broadband illumination, and more particularly, to a system and method for generating broadband illumination via a pulsed laser and a rotatable drum covered with a target material. Background Art

[0004] As the demand for lithography-based device structures with smaller and smaller features continues to increase, there is a growing need for improved illumination sources for inspecting the associated masks of these shrinking devices for lithography printing. One such illumination source includes an extreme ultraviolet (EUV) light source. A method for generating EUV light includes spin coating a roller coated with a uniform thickness layer of a solid (frozen) plasma-forming target material (e.g., xenon), and exposing the xenon-coated portion of the cylinder with a pulsed laser suitable for exciting the xenon to produce the plasma. The inspection tools used in this context typically operate at the same wavelength used for imaging, which creates the challenge of providing a reliable short-wavelength EUV light source that meets system-level specifications. Traditionally, inspection of rollers in EUV light sources relies on infrared high-temperature measurements and thermocouples combined with thermal modeling. However, infrared high-temperature measurements encounter limitations originating from the low emissivity of copper roller targets. In addition, this method has proven to be challenging to obtain accurate temperature readings at low temperatures (specifically, below -50 degrees Celsius). Alternative methods involving thermocouples combined with thermal modeling bring their own set of challenges. The inherent difficulty stems from the lack of effective coupling between the thermocouple and the dynamically moving drum target (which operates along two independent axes). This makes it difficult to establish a reliable correlation between the temperature measurement and the actual temperature of the drum target, thereby hindering the accuracy and efficiency of the inspection process.

[0005] Therefore, it is desirable to provide a method and system that solves the deficiencies of the above-mentioned previous methods. Summary of the invention

[0006] According to one or more illustrative embodiments of the present disclosure, a broadband light source is disclosed. In one illustrative embodiment, the broadband light source includes a rotatable drum, the rotatable drum being at least partially coated with a plasma-forming target. In another illustrative embodiment, the broadband light source includes a confocal sensor assembly, the confocal sensor assembly including a sensor head and a light source for measuring the surface of the rotating drum. In another illustrative embodiment, the broadband light source includes a laser light source configured to direct pulsed illumination to the material-coated portion of the rotatable drum for exciting the plasma-forming target and emitting broadband light when the rotatable drum rotates in an angular direction and translates in an axial direction. In another illustrative embodiment, the broadband light source includes a controller, the controller including one or more processors configured to execute program instructions stored in a memory. In another illustrative embodiment, the program instructions are configured to cause the one or more processors to direct the confocal sensor assembly to transmit a confocal optical signal to the rotating drum. In another illustrative embodiment, the program instructions are configured to cause the one or more processors to record a calibration measurement of a distance from the confocal sensor assembly to the rotating drum at a first temperature. In another illustrative 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 illustrative 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 the cryogenic cooling of the rotatable drum. In another illustrative embodiment, the program instructions are configured to cause the one or more processors to convert the one or more distance measurements into one or more temperature values ​​representing the temperature of the material of the rotatable drum during the cryogenic cooling of the rotatable drum. In another illustrative embodiment, the program instructions are configured to cause the one or more processors to determine whether a target process condition temperature of the rotating drum is achieved based on the converted temperature values.

[0007] According to one or more illustrative embodiments of the present disclosure, a characterization system is disclosed. In one illustrative embodiment, the characterization system includes an illumination subsystem. In another illustrative embodiment, the illumination subsystem includes a rotatable drum at least partially coated with a plasma-forming target. In another illustrative 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 illustrative embodiment, the illumination subsystem includes a laser light source configured to direct pulsed illumination to the material-coated portion of the rotatable drum for exciting the plasma-forming target and emitting broadband light when the rotatable drum rotates in an angular direction and translates in an axial direction. In another illustrative embodiment, the characterization system includes one or more collection optics configured to collect illumination radiated from a plasma generated in response to the excitation of the plasma-forming target. In another illustrative embodiment, the characterization system includes a set of illuminator optics configured to direct illumination from the one or more collection optics to one or more samples disposed on a stage. In another illustrative embodiment, the characterization system includes a detector.In another illustrative embodiment, the characterization system includes a set of projection optics configured to receive illumination from a surface of the one or more samples and direct the illumination from the one or more samples to the detector.

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

[0009] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and do not necessarily limit the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Those skilled in the art may better appreciate the numerous advantages of the present disclosure with reference to the accompanying drawings.

[0011] Figure 1A A conceptual diagram illustrating a confocal sensor assembly integrated within a rotatable drum based broadband light source in accordance with one or more embodiments of the present disclosure.

[0012] Figure 1B A conceptual diagram illustrating a confocal sensor assembly integrated within a cryogenically cooled rotatable drum based broadband light source in accordance with one or more embodiments of the present disclosure.

[0013] Figure 2 A conceptual diagram illustrating a drum-based broadband light source equipped with a confocal sensor assembly according to one or more embodiments of the present disclosure.

[0014] Figure 3 A block diagram illustration of an inspection system incorporating a broadband light source according to one or more embodiments of the present disclosure is shown.

[0015] Figure 4 Description A flow chart depicts a method for determining the temperature of a drum target via a confocal sensor assembly according to one or more embodiments of the present disclosure.

[0016] Figure 5 The description depicts a flow chart of a method for determining when the temperature of a drum target exceeds the atmospheric dew point via a confocal sensor assembly in accordance with one or more embodiments of the present disclosure.

[0017] Figure 6 A continuous temperature metric determined for a drum target based on a confocal distance of a confocal sensor assembly in accordance with one or more embodiments of the present disclosure is described.

[0018] Figure 7 A temperature metric of a drum target for determining when the temperature of the drum target is above the atmospheric dew point is described in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0019] 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 respect to certain embodiments and specific features thereof. The embodiments set forth herein are to be regarded as illustrative and not restrictive. It should be readily apparent to one of ordinary skill in the art that various changes and modifications may be made in form and detail without departing from the spirit and scope of the present disclosure.

[0020] Figures 1A to 7 Systems and methods for determining drum target temperature in accordance with one or more embodiments of the present disclosure are generally described.

[0021] Embodiments of the present disclosure relate to exposure of a rotating drum (e.g., a cylinder) covered with a plasma-forming material (e.g., frozen xenon or carbon dioxide) that can be excited via an illumination light 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 relate to a confocal sensor assembly integrated within a xenon ice-based EUV light source to enhance productivity and uptime in semiconductor photomask inspection, and in particular, a confocal sensor assembly designed for use in EUV lithography. These masks, which have complex geometries, require advanced inspection systems operating at the same wavelength used for imaging. This creates the challenge of providing a reliable short-wavelength extreme ultraviolet (EUV) light source that meets system-level specifications. To reduce downtime and optimize operational efficiency, embodiments of the present disclosure introduce a metrology method that can determine the process status temperature of a plasma-based rotatable drum in real time, even in the absence of ice. This capability proves valuable during various critical stages of tool operation. For example, during the light source incubation stage, the temperature of the drum acts as a dynamic indicator, allowing precise determination of when the drum has reached the required temperature for growing and maintaining ice. This real-time measurement eliminates reliance on temperature sensors that cannot be directly coupled to the drum. As another example, during the light source maintenance phase, determining the temperature of the drum can help reduce the green-to-green time by determining a safe time point to empty the chamber and expose the drum to the atmosphere. This improves the traditional method that relies on predetermined waiting times (which include significant margins to accommodate changes in tool and environmental conditions). As another example, during unexpected downtime, temperature measurements of the drum can provide critical information to assess the state of the system. This allows for an informed decision to be made on whether to empty or continue to operate the drum, thereby facilitating faster system recovery compared to the lack of this feedback. As another example, determining the temperature of a rotatable drum while rotating and translating can provide valuable insights for research and development purposes because it can provide a characterization of thermally induced stresses and strains in the drum during cooling and heating processes. Understanding the relationship between drum deformation and temperature can provide a basis for hardware design iterations and optimization of process conditions for light source operation.

[0022] Figure 1A to 1B A conceptual view illustrating a confocal sensor assembly 100 integrated within a rotatable drum based broadband illumination source in accordance with one or more embodiments of the present disclosure.

[0023] In an embodiment, the broadband light source 200 includes a confocal sensor assembly 100, a rotatable drum 108, and a controller 106 including one or more processors and a memory. For example, the confocal sensor assembly 100 can be positioned near the rotatable drum 108 for measuring the surface of the drum 108. In an embodiment, the confocal sensor assembly 100 can include a sensor head 102. For example, the sensor head 102 can be installed in a vacuum environment while remaining near the rotating drum 108.

[0024] 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 specific wavelength suitable for confocal metrology measurements. For example, this wavelength may be tailored according to the characteristics of the drum material and the measurement environment.

[0025] In an embodiment, 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. It should be noted that the confocal assembly 100 may measure the distance from the sensor head 102 to the surface of the drum 108 using the controlled chromatic aberration observed within the broadband light source of the confocal assembly 100. In addition, the selected specific type of light source 104 may be adapted to optimize the performance of the rotating drum 108 in low temperature conditions and other operating conditions. For another example, the sensor head 102 may be configured to transmit and receive light signals. In an embodiment, the sensor head 102 includes a confocal optical device for ensuring that the transmitted and received light signals share a common focus at the surface of the drum 108. This confocal arrangement enhances measurement accuracy by selectively capturing only light reflected from the focal plane. In an embodiment, the sensor head 102 may adopt various configurations to optimize its performance in different operating conditions. For example, the sensor head 102 may include an adaptive optical device or a variable focal length element for adapting to changes in the rotation and translational movement of the rotatable drum 108.

[0026] In an embodiment, the confocal sensor assembly 100 is communicatively coupled to a controller 106 including one or more processors and a memory. For example, the one or more processors may be communicatively coupled to the memory such that the one or more processors are configured to execute a set of program instructions stored on the memory. In an embodiment, the one or more processors are configured to direct the sensor head 102 to transmit the confocal optical signal to 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.

[0027] Figure 2 A conceptual diagram illustrating a drum-based broadband light source 200 equipped with a confocal sensor assembly 100 in accordance with one or more embodiments of the present disclosure.

[0028] In an embodiment, the broadband light source 200 includes a rotatable drum 108 adapted to rotate about an axis. For example, the drum 108 may be a cylinder, such as Figure 1A In other embodiments, the drum 108 includes any cylindrical symmetrical 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. In addition, the drum 108 may include a composite shape composed of two or more shapes. It should be noted herein that for the purpose of ease of description, embodiments of the present disclosure are described in the context of a rotatable drum or a rotating drum 108, such as Figure 1A However, this embodiment should not be construed as limiting the scope of the present disclosure.

[0029] In an embodiment, the drum 108 is coated with a plasma-forming target. For example, the target may include a solid disposed on the surface of the drum 108. The plasma-forming target may include any material known in the art that produces a plasma and subsequently emits broadband light when excited by an illumination light source. 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 may include, but is not limited to, xenon gas frozen onto the surface of the drum 108. It should be noted that using frozen xenon gas as a target may be particularly useful in the context of generating broadband EUV light. As another example, the target may include, but is not limited to, carbon dioxide frozen onto the surface of the drum 108. It should be noted that using frozen carbon dioxide as a target may be particularly useful in the context of generating broadband soft x-ray light.

[0030] In an embodiment, the broadband light source 200 includes a pulsed illumination light source 202. The pulsed illumination light source 202 may include any pulsed or modulated illumination light source known in the art. For example, the pulsed illumination light source 202 may include a pulsed laser. Furthermore, the pulsed illumination light source 202 is suitable for exciting and / or maintaining a plasma in the material of the rotatable drum. For example, the pulsed illumination light source 202 may include, but is not limited to, one or more infrared (IR) lasers. For example, the pulsed illumination light source 202 may include, but is not limited to, one or more CO2 lasers.

[0031] In an embodiment, the broadband light source 200 includes one or more actuators configured to rotationally and axially actuate the drum 108. In an embodiment, the broadband light 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 light source 200 may include a rotary actuator configured to rotate the drum 108 in an axial direction (e.g., Figure 1A The linear actuator 208 of the roller 108 is used to translate the roller 108 in the vertical direction in the example shown in FIG. Figure 2 The rotary and linear actuators 206, 208 in the drum 108 are shown. Thus, the description provided above should be interpreted as merely illustrative. For example, the pulsed light source 202 may be disposed on an actuation stage (not shown) that provides translation of the pulsed illumination 204 relative to the drum 108.

[0032] The axial motion imparted by the linear actuator 208 and the rotational motion of the drum 108 caused by the rotary actuator 206 allow the pulsed illumination 204 to pass across the surface of the drum 108. In embodiments, the controller 106 may control the triggering of the pulsed laser light source 202 and / or the actuation of the drum 108 in a rotational direction and / or an axial direction. In this regard, the controller 106 may direct the actuators 206, 208, and the drum 108 to pass the pulsed illumination 204 across the surface of the cylinder as the cylinder rotates and translates axially in any manner described in the present disclosure.

[0033] In an embodiment, the broadband light 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, thereby evaporating the cryogenic fluid. When the cryogenic fluid evaporates, it absorbs heat from the rotating drum 108, thereby reducing the temperature of the drum. The evaporated coolant is then returned to the circulation system for recooling.

[0034] In an embodiment, the broadband light source 200 may include a heating subsystem. For example, the heating subsystem may include one or more heating elements configured to heat the rotatable 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.

[0035] In an embodiment, the broadband light source 200 may include multiple controllers for managing various operations of the broadband light 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 co-handling functions including, but not limited to, drum actuation, process control, and laser triggering. It should be noted herein that the broadband light source 200 is not limited to multiple controllers; however, a single controller 106 may be configured to perform the functions of the multiple controllers described above as desired.

[0036] Figure 3 A block diagram view of an inspection system 300 incorporating a plasma-based illumination source 200 according to one or more embodiments of the present disclosure is illustrated. In an embodiment, the system 300 includes an illumination subsystem 302. The illumination subsystem 302 may be incorporated into the broadband light source 200 described throughout the present disclosure. In an embodiment, although Figure 3300. In an embodiment, the system 300 includes a set of illuminator optics. In an embodiment, the illuminator optics may direct illumination 109 emitted from the broadband light 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, a wafer (e.g., a semiconductor wafer). As another example, the one or more samples 304 may include, but are not limited to, a mask or a photomask. In an embodiment, the system 300 includes one or more detectors 310. In an embodiment, the system 300 includes a set of projection optics 308 adapted to collect light scattered, reflected, diffracted, or otherwise emitted from a sample and direct the light to one or more detectors (e.g., a CCD, TDI-CCD, PMT, and the like). In an embodiment, the controller 106 may be integrated within the system 300 for receiving and / or analyzing measurements from the detector 310.

[0037] It should be noted herein that one or more components of the system 300 may be communicatively coupled to various other components of the system 300 in any manner known in the art. For example, the broadband light source 200, the detector 310, the controller 106, and the one or more processors may be communicatively coupled to each other and other components via wires (e.g., copper wires, fiber optic cables, and the like) or wireless connections (e.g., RF couplings, IR couplings, data network communications (e.g., WiFi, WiMax, Bluetooth, and the like)).

[0038] In an embodiment, the inspection system 300 is configured as a wafer inspection system or a reticle / photomask inspection system. For example, the 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, the 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 should be further recognized that the inspection system 300 may be configured as an EUV mask or blank mask inspection system. EUV-based blank mask inspection is generally described in U.S. Patent No. 8,711,346 issued to Stokowski on April 29, 2014, which is incorporated herein by reference in its entirety. EUV-based blank mask inspection is generally described in U.S. Patent No. 8,785,082 issued to Xiong et al. on July 22, 2014, which is incorporated herein by reference in its entirety. EUV-based reticle inspection is generally described in US Pat. No. 8,953,869, issued on Feb. 10, 2015 to Nasser-Ghodsi et al., which is incorporated herein by reference in its entirety.

[0039] In an embodiment, the broadband light source 200 described throughout the present disclosure may be implemented within an optical lithography system. In an embodiment, the optical lithography system may include a set of illuminator optics configured to direct output light from the broadband light source 200 to an EUV compatible lithography mask (e.g., an EUV reflective mask) or a soft x-ray compatible lithography mask. In an embodiment, 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. Pat. No. 8,916,831 issued to Wang on Dec. 23, 2014, which is incorporated herein by reference in its entirety.

[0040] Figure 4 The description depicts a flow chart of a method 400 for determining the temperature of a drum target via a confocal sensor assembly in accordance with one or more embodiments of the present disclosure.

[0041] 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 direct the sensor head 102 of the confocal sensor assembly 100 to transmit the confocal optical signal to the rotatable drum 108 .

[0042] In step 404, a calibration measurement of the distance from the sensor head to the surface of the rotatable drum at the first temperature is recorded. For example, the sensor head 102 may be configured to communicate the calibration measurement to the controller 106. In addition, the memory of the controller 206 may be configured to store the recorded calibration measurement and the corresponding temperature associated with the calibration measurement.

[0043] In step 406, the rotatable drum is cryogenically cooled. 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.

[0044] 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 a continuous confocal optical signal to the rotatable drum 108 to monitor the temperature of the surface of the rotating drum 108. In addition, the sensor head 102 is configured to communicate the continuous measurements to the controller 106, which is configured to store the data in a memory.

[0045] In step 410 , the continuously recorded distance measurements are converted to temperature values ​​representative of 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 communicated distance measurements received from the sensor head 102 .

[0046] In step 412, it is determined whether the target process condition temperature of the surface of the rotatable drum is achieved based on the converted temperature value. For example, the controller 106 can be configured to continuously monitor the temperature readings provided by the confocal sensor assembly. In addition, once a temperature reading that meets or exceeds the predefined target temperature of the rotatable drum 108 is received, the controller 106 can interpret this as achieving the target condition.

[0047] Figure 5 The description depicts a flow chart of a method for determining when the temperature of a drum target is above the atmospheric dew point via a confocal sensor assembly in accordance with one or more embodiments of the present disclosure.

[0048] In step 502, the rotating drum is warmed back to the first temperature. For example, the drum 108 is warmed via 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 element.

[0049] In step 504, the rotatable drum is cryogenically cooled. For example, cryogenic cooling of the rotatable drum 108 is achieved via a cooling fluid comprising at least one of liquid nitrogen, liquid helium, liquid argon, liquid carbon dioxide, liquid hydrogen, or liquid oxygen.

[0050] 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 a continuous confocal optical signal to the rotatable drum 108 to monitor the temperature of the surface of the rotating drum 108. In addition, the sensor head 102 is configured to communicate the continuous measurements to the controller 106, which is configured to store the data in a memory.

[0051] In an embodiment, the controller 106 analyzes the intensity of the confocal optical signal for one or more temperature values ​​and determines the presence of ice on the rotatable drum. For example, the controller 106 may determine the presence of ice based on changes in the intensity of the confocal optical signal.

[0052] The continuous distance measurements are converted to temperature values ​​representative of the temperature of the drum material during cryogenic cooling in step 508. For example, program instructions stored in a memory of controller 106 are configured to cause one or more processors to derive the temperature of rotatable drum 108 from the recorded distance measurements.

[0053] In step 510, the atmospheric dew point temperature of the rotatable drum is determined. For example, the controller 106 may be configured to determine when the surface of the rotating drum 108 exceeds a temperature corresponding to the atmospheric dew point.

[0054] Figure 6 A continuous temperature metric determined for a drum target based on the confocal distance of a confocal sensor assembly according to one or more embodiments of the present disclosure is illustrated. For example, upon cryogenically cooling a rotatable drum, the confocal distance from the sensor head 102 to the surface of the rotatable drum 108 changes due to deformation of the rotatable drum 108. Furthermore, the temperature of the rotatable drum 108 can be derived from the recorded confocal distance measurements of the rotatable drum 108.

[0055] Figure 7 A temperature metric of a drum target for determining when the temperature of the drum target is above the atmospheric dew point in accordance with one or more embodiments of the present disclosure is described. In an embodiment, the atmospheric dew point temperature may be stored in a memory of the controller 106. For example, once the temperature of the rotatable drum 108 reaches or exceeds the atmospheric dew point temperature, the chamber may be safely evacuated for service.

[0056] The themes described herein sometimes illustrate different components contained in or connected to other components. It should be understood that such depicted architectures are merely exemplary, and in fact, many other architectures that realize the same functionality can be implemented. In a conceptual sense, any arrangement of components for realizing the same functionality is effectively "associated" so as to realize the desired functionality. Therefore, any two components combined to realize a specific functionality herein can be considered to be "associated" with each other so as to realize the desired functionality, regardless of the architecture or intermediate components. Similarly, any two components so associated can be considered to be "connected" or "coupled" to each other to realize the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to realize the desired functionality. Specific examples that can be coupled include, but are not limited to, physically interactive and / or physically interactive components and / or wirelessly interactive and / or wirelessly interactive components and / or logically interactive and / or logically interactive components.

[0057] As used throughout this disclosure, the term "sample" generally refers to a substrate (eg, a wafer or the like) formed of semiconductor or non-semiconductor materials. For example, the semiconductor or non-semiconductor materials may include, but are not limited to, single crystal silicon, gallium arsenide, and indium phosphide.

[0058] It is believed that from the foregoing description, the present disclosure and its many attendant advantages will be understood, and it will be apparent that various changes may be made in the form, construction and arrangement of components without departing from the disclosed subject matter or without sacrificing all of its substantial advantages. The described form is merely illustrative and it is intended that such changes be covered and included by the appended claims. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A broadband light source, comprising: a rotatable drum at least partially coated with a plasma-forming target material; a confocal sensor assembly comprising a sensor head and a light source for measuring the surface of the rotatable drum; a laser light source configured to direct pulsed illumination to a material-coated portion of the rotatable drum for exciting the plasma to form a target material and emit broadband light as the rotatable drum rotates in an angular direction and translates in an axial direction; and A controller comprising one or more processors configured to execute program instructions stored in a memory, wherein the program instructions are configured to cause 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 a distance from the confocal sensor assembly to the rotatable drum at a first temperature; directing the 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 material of the rotatable drum during the cryogenic cooling of the rotatable drum; and A determination is made based on the converted temperature value whether a target process condition temperature of the rotatable drum is achieved. 2 . 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 comprise at least one of an electric heating element, a radiant heating element, or an induction heating system.

5. The broadband light source of claim 3, wherein the one or more processors are further configured to: directing the heating subsystem to warm the rotatable drum back to the first temperature via the one or more heating elements; directing the cryogenic cooling subsystem to cryogenically cool the rotatable drum; recording the 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 the one or more temperature values ​​representative of the temperature of the material of the rotatable drum during the cryogenic cooling of the rotatable drum; and It is determined when the rotatable drum is above the atmospheric dew point.

6. The broadband light source of claim 1, wherein the one or more processors are further configured to: analyzing the intensity of the confocal optical signal at the one or more temperature values; and The presence of ice on the rotatable drum is determined based on a change in the intensity of the confocal optical signal.

7. The broadband light source of claim 1, wherein the first temperature is set at a calibration temperature for the calibration measurement.

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

9. A characterization system comprising: A lighting subsystem, wherein the lighting subsystem comprises: a rotatable drum at least partially coated with a plasma-forming target material; a confocal sensor assembly comprising a sensor head and a light source for measuring the surface of the rotatable drum; and a laser light source configured to direct pulsed illumination to a material-coated portion of the rotatable drum for exciting the plasma to form a target material and emit broadband light as the rotatable drum rotates in an angular direction and translates in an axial direction; one or more collection optics configured to collect illumination emitted from a plasma generated in response to excitation of the plasma-forming target; a set of illuminator optics configured to direct the illumination from the one or more collection optics to one or more samples disposed on a stage; detector; and A set of projection optics is configured to receive the illumination from the surface of the one or more samples and direct the illumination from the one or more samples to the detector.

10. The characterization system of claim 9, further comprising a controller comprising one or more processors configured to execute program instructions stored in a memory, wherein the program instructions are configured to cause 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 a distance from the confocal sensor assembly to the rotatable drum at a first temperature; directing the 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 material of the rotatable drum during the cryogenic cooling of the rotatable drum; and A determination is made as to whether a target process condition temperature of the rotatable drum is achieved based on the converted one or more temperature values.

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 comprise at least one of an electric heating element, a radiant heating element, or an induction heating system.

14. The characterization system of claim 12, wherein the one or more processors are further configured to: directing the heating subsystem to warm the rotatable drum back to the first temperature via the one or more heating elements; directing the 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 material of the rotatable drum during the cryogenic cooling of the rotatable drum; and It is determined when the rotatable drum is above the atmospheric dew point.

15. The characterization system of claim 10, wherein the one or more processors are further configured to: analyzing the intensity of the confocal optical signal at the one or more temperature values; and The presence of ice on the rotatable drum is determined based on a change in the intensity of the confocal optical signal.

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

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

18. A method comprising: directing the confocal sensor assembly to transmit the confocal optical signal to the rotatable drum; recording a calibration measurement of a distance from the confocal sensor assembly to the rotatable drum at a first temperature; directing the cryogenic cooling subsystem to cryogenically cool the rotatable drum; recording one or more distance measurements from a 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 material of the rotatable drum during the cryogenic cooling of the rotatable drum; and A determination is made as to whether a target process condition temperature of the rotatable drum is achieved based on the converted one or more temperature values.

19. The method according to claim 18, further comprising: directing a heating subsystem to warm the rotatable drum back to the first temperature via one or more heating elements; directing the cryogenic cooling subsystem to cryogenically cool the rotatable drum; recording the 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 the one or more temperature values ​​representative of the temperature of the material of the rotatable drum during the cryogenic cooling of the rotatable drum; and It is determined when the rotatable drum is above the atmospheric dew point.

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

21. The method of claim 18, further comprising: analyzing the intensity of the confocal optical signal at the one or more temperature values; and The presence of ice on the rotatable drum is determined based on a change in the intensity of the confocal optical signal.

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

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