Confocal chromatic metrology for EUV light source status monitoring

Abstract

A light source includes a rotatable drum to be coated with xenon ice and illuminated by a laser beam to generate a plasma. The drum can also be translatable. The light source further includes a confocal color sensor to measure a distance from the confocal color sensor to the rotatable drum. The confocal color sensor can include a sensor head to focus light onto the rotatable drum and detect reflected light from the rotatable drum. The sensor head and the rotatable drum can be disposed within a vacuum chamber.

Description

Technical Field

[0001] This disclosure relates to metrology for a xenon ice-coated cylinder in an extreme ultraviolet (EUV) light source, and more specifically, to performing this metrology using a confocal color sensor. Background Technology

[0002] An EUV light source may comprise a rotating cylinder with an outer surface coated with xenon (Xe) ice (i.e., solid Xe). A plasma emitting EUV light is formed by irradiating the Xe ice with a laser beam. Optical imaging using a camera can be performed to determine parameters of the Xe ice, such as its thickness and surface quality. The camera images segments of the Xe ice, and image processing algorithms extract relevant information from the images. However, the extracted information is limited in terms of spatial resolution and bandwidth. Therefore, identifying parameters of the Xe ice using optical imaging (e.g., for real-time feedback) is challenging. Summary of the Invention

[0003] Therefore, there is a need for improved systems and methods for monitoring Xe ice on the rotating drum of an EUV light source. Such systems and methods may involve confocal color sensors, also known simply as confocal sensors.

[0004] In some embodiments, a light source includes a rotatable cylinder to be coated with Xe ice and irradiated by a laser beam to generate plasma. The light source also includes a confocal color sensor to measure the distance from the confocal color sensor to the rotatable cylinder.

[0005] In some embodiments, a method of operating a light source includes: rotating a cylinder; coating the cylinder with Xe ice while rotating the cylinder; and irradiating the cylinder with a laser beam to generate plasma while rotating the cylinder and coating it with the Xe ice. The method further includes: monitoring the cylinder using a confocal color sensor to detect defects in the Xe ice on the cylinder while irradiating it with the laser beam; and shutting off the laser beam in response to detecting defects in the Xe ice on the cylinder. Attached Figure Description

[0006] To better understand the various described implementation schemes, please refer to the detailed implementation methods below in conjunction with the following diagram.

[0007] Figure 1 This is a cross-sectional side view of an EUV light source according to some embodiments.

[0008] Figure 2 A confocal color sensor according to some embodiments is shown.

[0009] Figure 3A and 3B Components of an EUV light source according to some embodiments are shown.

[0010] Figure 4A and 4B This demonstrates components of an EUV light source according to some embodiments, including... Figures 3A to 3B Components of the EUV light source and their placement Figures 3A to 3B The outer shell of the rotatable cylinder.

[0011] Figure 5 It is a graph showing the time trajectory data of the thickness of Xe ice on a rotatable and translational cylinder according to some embodiments.

[0012] Figure 6 and 7 It is a graph showing the variation in the thickness of Xe ice on a rotatable and translatable cylinder according to some embodiments.

[0013] Figure 8A and 8B A flowchart illustrating a method for operating a light source according to some embodiments.

[0014] Figure 9 This is a block diagram of an EUV light source system according to some embodiments.

[0015] Figure 10A and 10B This demonstrates components of an EUV light source according to some embodiments, including... Figures 4A to 4B The components of the EUV light source and the electric translation stage on which the sensor head is mounted.

[0016] The same component symbols refer to the corresponding parts that are used throughout the drawings and instructions. Detailed Implementation

[0017] Examples of various embodiments will now be described in detail with reference to the accompanying drawings. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the various described embodiments. However, those skilled in the art will appreciate that the various described embodiments can be practiced without these specific details. In other instances, well-known methods, processes, components, circuits, and networks have not been described in detail to avoid unnecessarily obscuring aspects of the embodiments.

[0018] Figure 1This is a cross-sectional side view of an extreme ultraviolet (EUV) light source 100 according to some embodiments. The EUV light source 100 includes a vacuum chamber 102 (e.g., an aluminum billet chamber). A vacuum pump 110 (e.g., a turbopump) provides a vacuum in the vacuum chamber 102. A laser beam 103 is introduced into the vacuum chamber 102 through a laser objective 104 and an accompanying thin film. The laser objective 104 focuses the laser beam 103 onto the outer surface of a cylinder 118 (e.g., a copper cylinder) coated with xenon (Xe) ice (i.e., solid Xe). The laser beam 103 irradiates the cylinder 118, thereby impacting the Xe ice on the outer surface of the cylinder 118. When the laser beam 103 impacts the Xe ice on the outer surface of the cylinder 118, it triggers a plasma that emits EUV light 105. A mirror 106 collects a portion of the EUV light 105 and guides the collected EUV light 105 through a window 108 in the vacuum chamber 102. The cylinder 118 is rotated and also translated vertically to allow different areas (i.e., portions) of the Xe ice on its outer surface to be exposed to the laser beam 103. As the cylinder 118 rotates and translates, Xe can be sprayed onto the outer surface of the cylinder 118 via the sprayer 117 to maintain the Xe ice coating.

[0019] The feedthrough assembly 112 supplies liquid nitrogen into the interior of the cylinder 118 to keep the surface of the cylinder 118 cool and thus maintain the Xe ice coating on the cylinder 118. The liquid nitrogen evaporates during operation of the EUV light source 100. The feedthrough assembly 112 vents the resulting nitrogen gas from the cylinder 118.

[0020] Cylinder 118 is housed within cylinder assembly 114, which is coupled to feedthrough assembly 112. Cylinder assembly 114 also includes a rotary motor 116 for rotating cylinder 118. Rotary motor 116 is coupled to cylinder 118 independently of feedthrough assembly 112. Cylinder assembly 114 further includes a sprayer 117. Cylinder assembly 114 has a water-cooled cylinder cap for receiving water from water-cooled input 126. Below cylinder assembly 114 and therefore below cylinder 118 is translation motor 120, which linearly translates cylinder 118 in the vertical direction (i.e., moves cylinder 118 up and down). Translation motor 120 is also coupled to cylinder 118 independently of feedthrough assembly 112. A corresponding linear stage actuator 124 actuates translation motor 120. Weight-compensating bellows 122 is also located below cylinder assembly 114.

[0021] For the EUV light source 100 to operate properly, the Xe ice coating on the cylinder 118 should be defect-free. For example, the Xe ice should have a minimum thickness at every point on the cylinder 118. This minimum thickness should be sufficient to ensure that the laser beam 103 does not impact the exposed outer surface of the cylinder 118; such impact could damage the cylinder 118 and lead to contamination of the vacuum chamber 102. The Xe ice should also have a relatively uniform thickness (e.g., within a specified uniformity). To allow for this Xe ice coating, the exposed outer surface of the cylinder 118 on which Xe will be deposited should be smooth. A confocal color sensor (i.e., a confocal sensor) is used to monitor the cylinder 118, if coated with Xe ice and / or its exposed outer surface is exposed, to determine whether these criteria are met.

[0022] Figure 2 A confocal color sensor 200 according to some embodiments is illustrated. The confocal color sensor 200 includes a sensor head 206, a controller 202, and an optical fiber 204 coupled between the sensor head 206 and the controller 202. The controller 202 includes circuitry for controlling the sensor head 206 and also includes a light source (e.g., one or more light-emitting diodes (LEDs)) to generate broadband light (e.g., white light) to be provided to the sensor head 206. The broadband light is transmitted from the controller 202 to the sensor head 206 via the optical fiber 204. The sensor head 206 includes optics for dispersing and emitting the broadband light, thereby focusing the emitted light along an optical axis 220 such that different wavelengths of emitted light have different focal lengths. Figure 2 In the example, the dispersed emitted light includes violet light 208, blue light 210, green light 212, yellow light 214, orange light 216, and red light 218. The focal length of violet light 208 is shorter than that of blue light 210, the focal length of blue light 210 is shorter than that of green light 212, the focal length of green light 212 is shorter than that of yellow light 214, the focal length of yellow light 214 is shorter than that of orange light 216, and the focal length of orange light 216 is shorter than that of red light 218.

[0023] If an object is positioned in front of the tip of sensor head 206 (i.e., in front of the end of sensor head 206 from which it emits diffused light) such that the object intersects optical axis 220, then sensor head 206 receives light initially emitted by the sensor head and subsequently reflected from the object. Based on the wavelength of the received light, confocal color sensor 200 determines the distance from sensor head 206 (e.g., from the tip) to the object. Confocal color sensor 200 may also determine the reflectivity of the object and the roughness (or equivalent, uniformity) of a portion of the object's surface illuminated by the emitted light from sensor head 206. Confocal color sensor 200 operates at a sampling rate. In some embodiments, the sampling rate is in the range between 100 Hz and 70 kHz.

[0024] Figure 3A and 3BThis demonstrates an EUV light source 300 (e.g., EUV light source 100) according to some embodiments. Figure 1 The component includes a cylinder 302 (e.g., cylinder 118). Figure 1 ) and confocal color sensor 200 ( Figure 2 The confocal color sensor 200 includes a sensor head 206, an optical fiber 204, and a controller 202. The cylinder 302 can rotate about its central vertical axis, enabling rotational movement 314, and can also translate vertically, enabling translational movement 316. Figure 3A In the middle, the outer surface of cylinder 302 is exposed and therefore bare. Figure 3B In the middle, the outer surface of the cylinder 302 is coated with Xe ice 316. The cylinder 302 coated with Xe ice 316 can be powered by a laser beam (e.g., laser beam 103). Figure 1 Irradiation to generate plasma that emits EUV light.

[0025] The cylinder 302 and sensor head 206 are housed within a vacuum chamber 304 (e.g., within vacuum chamber 102). The controller 202 is housed in an atmosphere 308 outside the vacuum chamber 304 (e.g., outside vacuum chamber 102). An optical fiber 204, providing broadband light from the controller 202 to the sensor head 206, passes through a feedthrough 310 in the wall 306 of the vacuum chamber 304. Thus, the optical fiber 204 is partially located outside and partially located inside the vacuum chamber 304.

[0026] Figure 4A and 4B This illustrates components of an EUV light source 400 according to some embodiments, the EUV light source 400 being an EUV light source 300 (e.g., and an EUV light source 100), Figure 1 An example of an EUV light source 400. The assembly of the EUV light source 400 includes the assembly of the EUV light source 300, and further includes a housing 402 enclosing a cylinder 302. In some embodiments, the housing 402 is a cylinder assembly 114 ( Figure 1 The sensor head 206 is positioned outside the housing 402 (but inside the vacuum chamber 304) when the cylinder 302 is housed within the housing 402. The housing 402 has a window 404 located between the cylinder 302 and the sensor head 206. Light 312 from the sensor head 206 passes through the window 404 to the cylinder 302, and corresponding reflected light from the cylinder 302 passes through the window 404 to the sensor head 206. The housing 402 accommodates the pressure difference between the area inside the housing 402 and the area outside the housing 402 but inside the vacuum chamber 304. For example, during operation of the EUV light source 400, the area inside the housing 402 has a higher pressure than the area outside the housing 402 but inside the vacuum chamber 304.

[0027] Figure 10A and10B This illustrates components of an EUV light source 1000 according to some embodiments, the EUV light source 1000 being an EUV light source 400 (e.g., and EUV light source 100, ...). Figure 1 An example of an EUV light source 1000 is provided. The components of the EUV light source 400 include the components of the EUV light source 400, and further include an electrically powered translation stage 1002 on which a sensor head 206 is mounted. The electrically powered translation stage 1002 is housed within a vacuum chamber 304. The electrically powered translation stage 1002 is translational and therefore can translate the sensor head 206 vertically (e.g., according to the translational movement 316 of the cylinder 302) and / or horizontally (i.e., moving the sensor head toward or away from the cylinder 302 and the window 404). For example, the electrically powered translation stage 1002 can be vertically translated to align the sensor head 206 with a laser point (e.g., the point where the laser beam 103 illuminates Xe ice 316), such that the sensor head 206 monitors a portion of Xe ice 316 newly illuminated by the laser beam (e.g., where the newly illuminated portion rotates from the laser point into the field of view of the sensor head 206 in less than one full rotation of the cylinder 302). This alignment between the sensor head 206 and the laser spot allows the sensor head 206 to detect defects (e.g., pits) newly induced in the Xe ice 316 by the laser beam. In some embodiments, to achieve this alignment, the vertical position of the sensor head 206 is adjusted relative to the vertical position of the cylinder 302 by the motorized translation stage 1002 to take into account the translational velocity of the cylinder 302 and the relative angular positions of the laser spot and the sensor head 206 about the cylinder 302. The position of the motorized translation stage 1002 can be measured using an encoder (not shown).

[0028] In some embodiments, the cylinder 302 has a groove 1004 around its outer surface at a designated vertical position along the cylinder 302 (e.g., around the center of the cylinder 302). The groove 1004 can be detected by the confocal color sensor 200 to align the sensor head 206 and the vertical position of the cylinder 302. This alignment is performed based on the detection of the groove 1004 by the confocal color sensor 200, for example, during calibration and / or at the start of operation of the EUV light source 1000.

[0029] In some embodiments, the confocal color sensor 200 measures the distance from the confocal color sensor 200 to the cylinder 302. For example, a sensor head 206 disposed within a vacuum chamber 304 focuses light 312 onto the cylinder 302 and detects the corresponding light reflected from the cylinder 302. The light 312 is dispersed into different wavelengths (e.g., colors 208 to 218). Figure 2The wavelength of the light reflected from the cylinder 302 and detected by the sensor head 206 corresponds to and is used to determine the distance from the confocal color sensor 200 (e.g., from the sensor head 206) to the cylinder 302. The distance from the confocal color sensor 200 (e.g., from the sensor head 206) to the cylinder 302, as measured by the confocal color sensor 200, includes a first distance from the confocal color sensor 200 (e.g., from the sensor head 206) to the corresponding portion of the exposed outer surface of the cylinder 302 before the cylinder 302 is coated with Xe ice 316 (as shown in...). Figure 3A and 4A (in the middle) and / or when the cylinder 302 is coated with Xe Ice 316, the second distance from the confocal color sensor 200 (e.g., from the sensor head 206) to the corresponding portion of the outer surface of the Xe Ice 316 (as in the middle) and / or when the cylinder 302 is coated with Xe Ice 316. Figure 3B and 4B The distance from the confocal color sensor 200 (e.g., from sensor head 206) to different portions of the exposed outer surface of the cylinder 302 can vary due to variations in the surface roughness (i.e., lack of surface uniformity) of the exposed outer surface of the cylinder 302. The distance from the confocal color sensor 200 (e.g., from sensor head 206) to different portions of the outer surface of the Xe ice 316 can vary due to variations in the thickness of the Xe ice 316 and / or the surface roughness of the exposed outer surface of the cylinder 302. The thickness of a corresponding portion of the Xe ice 316 can be determined by subtracting a corresponding first distance from a corresponding second distance: the thickness of a particular portion of the Xe ice 316 is equal to the difference between the second distance of said portion and the first distance of said portion. In this way, variations in the thickness of the Xe ice 316 on the cylinder 302 are identified. This can be achieved through a computer system associated with the EUV light source 300 or 400 (e.g., through the computer system of the EUV light source system 900). Figure 9 To calculate distance and thickness.

[0030] The thickness of Xe Ice 316 (e.g., the thickness of a corresponding portion of Xe Ice 316) is one example of a parameter of the cylinder 302 that can be measured using the confocal color sensor 200. Other examples include the roughness of Xe Ice 316 and the reflectivity of Xe Ice 316. On a large (e.g., global) scale of the cylinder 302, when the cylinder 302 is coated with Xe Ice 316, the roughness (as shown in the figure) can be measured by measuring a second distance from the confocal color sensor 200 (e.g., from the sensor head 206) to a corresponding portion of the outer surface of the Xe Ice 316. Figure 3B and 4BThe change in the second distance provides an indication of the roughness of the Xe ice. At a smaller local scale, the confocal color sensor 200 can provide an indication of the roughness within a specific portion of the Xe ice 316 (e.g., where the specific portion corresponds to a specific measurement sample of the confocal color sensor 200). The confocal color sensor 200 can also provide an indication of the reflectance of a corresponding portion of the Xe ice 316 (e.g., where the specific portion corresponds to a specific measurement sample of the confocal color sensor 200). In these ways, the confocal color sensor 200 can be used to monitor changes and / or absolute values ​​of the thickness, roughness, and reflectance of the Xe ice 316. This can be achieved through a computer system associated with the EUV light source 300 or 400 (e.g., through the computer system of the EUV light source system 900). Figure 9 This is used to calculate roughness and reflectivity values ​​(such as distance and thickness).

[0031] Parameters measured using the confocal color sensor 200 (e.g., the thickness, roughness, and / or reflectivity of Xe ice 316) can be used to provide real-time feedback to control the operation of the EUV light source 400. For example, the laser beam (e.g., laser beam 103) of the irradiation tube 302 can be shut off in response to the detection of defects in the Xe ice 316 (e.g., pits in Xe ice 316, which are areas with insufficient thickness and resulting in excessive roughness). Figure 1 (For example, by deactivating the laser that generates it or by tilting the laser beam). For example, if the thickness of one or more portions of Xe Ice 316 (i.e., the thickness of one or more corresponding portions of Xe Ice 316) does not meet a threshold (e.g., less than, or less than or equal to a minimum thickness), if the roughness of Xe Ice 316 (or one or more portions of Xe Ice 316) meets a threshold (e.g., greater than, or equal to, or greater than a maximum roughness), and / or if the reflectivity of one or more portions of Xe Ice 316 (i.e., the reflectivity of one or more corresponding portions of Xe Ice 316) is not within a specified range (e.g., less than, or less than or equal to a minimum reflectivity, or greater than, or greater than or equal to a maximum reflectivity, wherein the range is between the minimum and maximum reflectivity), then a defect is detected and the laser beam is turned off. The decision to turn off the laser beam can be made by a computer system associated with EUV light source 300 or 400 (e.g., by the computer system of EUV light source system 900). Figure 9 ) made.

[0032] Once the laser beam has been switched off, parameters measured using the confocal color sensor 200 (e.g., the thickness, roughness, and / or reflectivity of the Xe ice 316) can be used to determine whether to reactivate the laser beam. For example, the laser beam may be reactivated in response to determining that a detected defect has been eliminated (e.g., by regrowth of the Xe ice 316 on the cylinder 302). For example, the laser beam may be reactivated in response to determining that the thickness of the Xe ice 316 (e.g., the thickness of a corresponding portion of the Xe ice 316) meets a threshold (e.g., greater than, or greater than or equal to a minimum thickness), that the roughness of the Xe ice 316 (or a corresponding portion of the Xe ice 316) does not meet a threshold (e.g., less than, or less than or equal to a maximum roughness), and / or that the reflectivity of the corresponding portion of the Xe ice 316 is within a specified range (e.g., greater than, or equal to, or greater than a minimum reflectivity and less than, or less than or equal to a maximum reflectivity). The decision to reactivate the laser beam can be made by the computer system associated with EUV source 300 or 400 (e.g., via the computer system of EUV source system 900). Figure 9 ) made.

[0033] In some embodiments, the suitability for use of the cartridge 302 is determined at least in part by measuring the roughness of its exposed outer surface. For example, a first distance is measured from the confocal color sensor 200 (e.g., from the sensor head 206) to a corresponding portion of the exposed outer surface of the cartridge 302, and its variation is analyzed. This variation is an indication of the surface roughness of the outer surface of the cartridge 302. Based on this variation (e.g., the difference between the maximum and minimum values, standard deviation, etc.), a decision is made as to whether the cartridge 302 is suitable for use. If the variation of the first distance does not meet a threshold (e.g., less than, or less than or equal to the maximum variation), then the cartridge 302 is considered suitable for use and is therefore deemed suitable. In some embodiments, a computer system associated with the EUV light source 300 or 400 (e.g., the computer system of the EUV light source system 900, ...) Figure 9 The EUV source 300 or 400 is determined to be suitable for use, and activation of the EUV source 300 or 400 is authorized based at least in part on this determination (and therefore at least in part on the roughness of the exposed outer surface of the cylinder 302). If the variation (and therefore the roughness of the exposed outer surface of the cylinder) meets a threshold (e.g., exceeds, is equal to or exceeds the maximum variation), then the cylinder 302 may be considered defective.

[0034] In some embodiments, maintenance of the EUV light source 300 or 400 is triggered in response to the detection of a defect in the Xe ice 316 or on the cylinder 302 (e.g., scheduled or enforced before operation can begin or continue).

[0035] Generally, the results of one or more parameters of the confocal color sensor 200 measuring cylinder 302 can be used to improve (e.g., optimize) other process parameters of the EUV light source 300 or 400.

[0036] Figure 5 This is a graph 500 showing time-track data 502 of the thickness of Xe ice 316 on the cylinder 302 according to some embodiments. The time-track data 502 is generated using a confocal color sensor 200 attached to an EUV light source system having the cylinder 302. The x-axis of graph 500 is time measured in seconds, and the y-axis of graph 500 is the thickness of Xe ice 316 measured in millimeters. The confocal color sensor 200 (e.g., for...) is used... Figures 3A to 3B (As described in 4A to 4B) the thickness values ​​of time trajectory data 502 are obtained. The thickness of Xe ice 316 on most of the cylinder 302 remains stable at slightly above 0.9 mm, but specific portions (i.e., areas) of Xe ice 316 on the cylinder 302 have a lower thickness. This specific portion may be a pit in Xe ice 316. As the cylinder 302 rotates and translates, the low thickness is repeatedly measured, resulting in repeated examples of low-measured thickness in time trajectory data 502 over time. The low thickness decreases from about 0.8 mm at about 6.2 seconds to about 0.35 mm at about 6.5 seconds, remains stable until about 7.3 seconds, and then recovers to 0.9 mm immediately after 7.4 seconds. The low thickness of Xe ice 316 between about 6.3 seconds and 7.4 seconds corresponds to defects in Xe ice 316. Therefore, Figure 5 This section explains the formation and subsequent elimination of defects in Xe316.

[0037] Figure 6 and 7 These are corresponding graphs 600 and 700 illustrating the variation in the thickness of Xe ice 316 on an example of cylinder 302 according to some embodiments. The data in graphs 600 and 700 are generated using a confocal color sensor 200 attached to an EUV light source system having cylinder 302. Graphs 600 and 700 show the thickness of Xe ice 316 on corresponding portions of cylinder 302 as defined by corresponding rotational positions (in radians) and vertical positions (in millimeters) on cylinder 302. Each of graphs 600 and 700 is for different time points. The rotational positions are shown on the x-axis of graphs 600 and 700, and the vertical positions are shown on the y-axis of graphs 600 and 700. When cylinder 302 is irradiated with a laser beam to generate plasma (and thus EUV light), the confocal color sensor 200 (e.g., for...) is used... Figures 3A to 3B (and descriptions from 4A to 4B) to obtain data for charts 600 and 700.

[0038] The majority of Xe ice 316 on cylinder 302 has a thickness of approximately 0.9 mm. However, some portions on the top and bottom of cylinder 302 have a lower thickness. The portion 602 on the top of cylinder 302 and the portion 604 on the bottom of cylinder 302 have a thickness as low as approximately 0.4 mm. These portions 602 and 604 with lower thicknesses are considered defects. In response to the detection of these defects (e.g., as described above for...), Figures 3A to 3B (as described in 4A to 4B), the laser beam can be turned off, thereby allowing Xe ice 316 to regrow in portions of 602 and 604, and thus become thicker. Figure 7 Showing the results of this regrowth: portions of 602 and 604 ( Figure 6 The thickness of Xe ice 316 in ) has been Figure 7 The number of cases has increased to the point where they are no longer considered defective.

[0039] Figure 8A and 8B Demonstrating an operating light source (e.g., EUV light source 100) according to some embodiments. Figure 1 300, Figures 3A to 3B 400, Figures 4A to 4B The flowchart of method 800 is shown. In method 800, rotation (802, Figure 8A ) cylinder (e.g., cylinder 118, Figure 1 ;Cylinder 302, Figures 3A to 4B In some embodiments, the cylinder is vertically translated (804) while being rotated. While being rotated (e.g., and while being vertically translated), the cylinder is coated (806) with Xe ice. While being rotated (e.g., and while being vertically translated) and coated with Xe ice, a laser beam (e.g., laser beam 103) is used. Figure 1 Irradiate (808) tube to generate plasma.

[0040] When irradiating with a laser beam, a confocal color sensor (e.g., confocal color sensor 200) is used. Figures 2 to 4B (810) Monitor the cylinder to detect defects in the Xe ice on the cylinder. In some embodiments, a (812) confocal color sensor is used to measure the thickness of the corresponding portion of the Xe ice on the cylinder (e.g., as for...). Figures 3A to 3B (as described in 4A to 4B). In some embodiments (e.g., in addition to or in lieu of step 812), a confocal color sensor (814) is used to measure the roughness of the Xe ice on the cylinder. In some embodiments (e.g., in addition to or in lieu of steps 812 and / or 814), a confocal color sensor (816) is used to measure the reflectance of a corresponding portion of the Xe ice on the cylinder (i.e., to measure the reflectance of the corresponding portion).

[0041] A monitoring cylinder is used to detect defects in the Xe ice. If no defect is detected (818 - No), monitoring continues (810). However, if a defect is detected (818 - Yes), the laser beam is switched off (820) in response to the defect detection. According to steps 802, 804 and / or 806, while the laser beam is switched off, the cylinder continues to rotate, translate and / or be coated with Xe ice to allow the Xe ice to properly regrow on the cylinder.

[0042] After the laser beam is turned off, while rotating the cylinder (e.g., translating the cylinder and coating it with Xe ice), a confocal color sensor is used to monitor (822, Figure 8B The cylinder is used to detect defects in the Xe ice on the cylinder. In some embodiments, a (824) confocal color sensor is used to measure the thickness of the corresponding portion of the Xe ice on the cylinder (e.g., as for...). Figures 3A to 3B (and 4A to 4B are described). In some embodiments (e.g., other than or alternative to step 824), a (826) confocal color sensor is used to measure the roughness of the Xe ice on the cylinder. In some embodiments (e.g., other than or alternative to steps 824 and 826), a (828) confocal color sensor is used to measure the reflectance of a corresponding portion of the Xe ice on the cylinder (i.e., to measure the reflectance of the corresponding portion).

[0043] After the laser beam is turned off, monitoring (822) of the cylinder is performed to determine whether the detected defects have been eliminated (e.g., by the regrowth of Xe ice) and whether any other defects exist. If a defect is detected (830 - Yes), monitoring (822) of the cylinder continues while the laser beam is still off, during rotation (802), translation (804), and / or coating (806) of the cylinder with Xe ice. However, if no defect is detected (830 - No), the laser beam (832) is reactivated in response to the detection that no defects are present in the Xe ice on the cylinder: the cylinder is irradiated again with the laser beam during rotation (802) and / or translation (804) and coating (806) of the cylinder with Xe ice (e.g., during coating (806) of the cylinder with Xe ice). The operation of method 800 returns to step 810. Figure 8A ).

[0044] In some embodiments, the cylinder is mounted on an electric translation stage (e.g., electric translation stage 1002). Figures 10A to 10B During the monitoring in steps 810 and 822, the electric translation stage can be translated to align the confocal color sensor with the laser spot, at which the laser beam illuminates the Xe ice (e.g., to detect new pits in the Xe ice).

[0045] Therefore, method 800 allows for control of the EUV light source operation in response to real-time feedback from the confocal color sensor. The real-time feedback provides an indication of the quality of the Xe ice on the cylinder and allows for a real-time determination of whether to continue EUV light source operation or allow for the reconstruction of the Xe ice coating on the cylinder.

[0046] Although Figure 8 shows the operations of method 800 in a specific order, the execution of the operations may overlap. For example, steps 802, 804, and / or 806 may be executed throughout method 800, and steps 808 and 810 may be executed simultaneously. Method 800 may contain more or fewer operations. Two or more operations may be combined into a single operation.

[0047] Figure 9 This is a block diagram of an EUV light source system 900 according to some embodiments. System 900 includes an EUV light source 930 (e.g., EUV light source 100). Figure 1 300, Figures 3A to 3B 400, Figures 4A to 4B ), which includes cylinder 932 (e.g., cylinder 118, Figure 1 ;Cylinder 302, Figures 3A to 4B ), laser 934 (for example, used to generate laser beam 103, Figure 1 ) and confocal color sensor 936 (e.g., confocal color sensor 200, Figures 2 to 4B The confocal color sensor 936 can be mounted on an electric translation stage (e.g., electric translation stage 1002). Figures 10A to 10B The system 900 also includes a computer system communicatively coupled to the EUV light source 930. The computer system includes one or more processors 902 (e.g., CPUs), an optional user interface 906, a memory 910, and a communication bus 904 interconnecting these components. In some embodiments, the EUV light source 930 is communicatively coupled to the computer system via one or more wired and / or wireless networks. The computer system may further include one or more wired and / or wireless network interfaces for communicating with the EUV light source 930 and / or a remote computer system.

[0048] User interface 906 may include display 907 and one or more input devices 908 (e.g., keyboard, mouse, touch-sensitive surface of display 907, etc.). Display 907 may display the status of EUV light source 930, including the results of monitoring tube 932 using confocal color sensor 936. For example, display 907 may display something similar to graph 500 (…). Figure 5 ), 600 (Chart 6) and / or 700 ( Figure 7 (Charts)

[0049] Memory 910 includes volatile and / or non-volatile memory. Memory 910 (e.g., non-volatile memory within memory 910) includes non-transitory computer-readable storage media. Memory 910 optionally includes one or more storage devices located remotely from processor 902 and / or non-transitory computer-readable storage media removably inserted into the computer system of system 900. Memory 910 (e.g., non-transitory computer-readable storage media of memory 910) includes features for implementing the functionality described herein (e.g., for...). Figures 3A to 3B Instructions (and the functional ones described in 4A to 4B). For example, memory 910 (e.g., a non-transitory computer-readable storage medium of memory 910) contains instructions for performing method 800 (and the functional ones described in 4A to 4B). Figures 8A to 8B (instructions).

[0050] In some embodiments, memory 910 (e.g., a non-transitory computer-readable storage medium of memory 910) stores the following modules and data, or subsets or supersets thereof: operating system 912, which includes processes for handling various basic system services and for performing hardware-related tasks; cylinder control module 914, which controls the rotation and translation of cylinder 932; confocal color sensor control module 916, which controls and receives data from confocal color sensor 936 (e.g., and controls an electric translation stage on which confocal color sensor 936 is mounted); laser beam control module 918, which controls laser 934 and corresponding laser beams irradiating Xe ice-coated cylinder 932 (e.g., for turning off and reactivating laser beams); defect detection module 918, which uses data from confocal color sensor 936 to detect defects in Xe ice on cylinder 932; and maintenance module 920, which triggers maintenance of EUV light source 930 (e.g., scheduling or enforcement).

[0051] Each of the modules stored in memory 910 corresponds to a set of instructions to be executed by one or more processors 902 for performing one or more functions described herein. Separate modules need not be implemented as separate software programs. Modules and various subsets of modules can be combined or otherwise reconfigured. In some embodiments, memory 910 stores a subset or superset of the modules and / or data structures identified above.

[0052] Figure 9 It is intended to serve as a functional description of various features that can exist in an EUV light source system rather than as a structural diagram. For example, the functionality of the computer system in the EUV light source system 900 can be divided among multiple devices. A portion of the modules stored in the memory 910 may alternatively be stored in one or more other computer systems communicatively coupled to the computer system of the EUV light source system 900 via one or more networks.

[0053] For illustrative purposes, the foregoing description has been referenced to specific embodiments. However, the illustrative statements above are not intended to be exhaustive or to limit the claims to the precise form disclosed. In view of the teachings above, many modifications and variations are possible. The embodiments have been selected to best explain the basic principles of the claims and their practical application, so that those skilled in the art can best use the embodiments with various modifications suitable for the particular purpose that has been carefully considered.

Claims

1. A light source, comprising: A rotatable cylinder, coated with xenon (Xe) ice and irradiated by a laser beam to generate plasma; A confocal color sensor is used to measure the distance from the confocal color sensor to the rotatable cylinder; One or more processors; and A memory storing one or more programs executed by the one or more processors, the one or more programs including instructions for: When the rotatable cylinder is coated with the xenon (Xe) ice, the confocal color sensor is used to detect defects in the xenon (Xe) ice on the rotatable cylinder; and The laser beam is shut off in response to the detection of a defect in the xenon (Xe) ice on the rotatable cylinder using the confocal color sensor.

2. The light source according to claim 1, further comprising a vacuum chamber, wherein: The rotatable cylinder is placed inside the vacuum chamber; and The confocal color sensor includes a sensor head disposed within the vacuum chamber to focus light onto the rotatable cylinder and detect reflected light from the rotatable cylinder.

3. The light source according to claim 2, wherein the confocal color sensor further includes a controller disposed outside the vacuum chamber to control the operation of the confocal color sensor and generate broadband light to be provided to the sensor head.

4. The light source of claim 3, wherein the confocal color sensor further comprises an optical fiber coupled between the sensor head and the controller to provide the broadband light to the sensor head, wherein: The vacuum chamber includes a wall with feedthrough; and The optical fiber passes through the feedthrough.

5. The light source according to claim 2, further comprising a housing within the vacuum chamber, wherein: The rotatable cylinder is housed within the outer casing; The sensor head is mounted outside the housing; and The housing includes a window located between the rotatable cylinder and the sensor head.

6. The light source according to claim 2, wherein the distance from the confocal color sensor to the rotatable cylinder, measured by the confocal color sensor, comprises: The first distance from the sensor head to the corresponding portion of the exposed outer surface of the rotatable cylinder before the xenon (Xe) ice is coated on the rotatable cylinder; and The second distance from the sensor head to a corresponding portion of the outer surface of the xenon (Xe) ice when the rotatable cylinder is coated with the xenon (Xe) ice.

7. The light source according to claim 1, wherein: The instructions for detecting defects include instructions for the following: The thickness of the corresponding portion of the xenon (Xe) ice on the rotatable cylinder is measured using the confocal color sensor, and Determine whether the thickness of the corresponding portion of the xenon (Xe) ice on the rotatable cylinder meets a threshold; and The instructions for shutting down the laser beam include instructions for shutting down the laser beam in response to determining that the thickness of one or more corresponding portions of the xenon (Xe) ice on the rotatable cylinder does not meet the threshold.

8. The light source according to claim 7, further comprising a vacuum chamber, wherein: The rotatable cylinder is placed inside the vacuum chamber; The confocal color sensor includes a sensor head disposed within the vacuum chamber to focus light onto the rotatable cylinder and detect reflected light from the rotatable cylinder; and The instructions for measuring the thickness of the corresponding portion of the xenon (Xe) ice on the rotatable cylinder include instructions for the following: Before the rotatable cylinder is coated with the xenon (Xe) ice, a first distance from the sensor head to a corresponding portion of the exposed outer surface of the rotatable cylinder is measured using the confocal color sensor. When the rotatable cylinder is coated with the xenon (Xe) ice, the confocal color sensor is used to measure a second distance from the sensor head to a corresponding portion of the outer surface of the xenon (Xe) ice, and Subtract the corresponding first distance from the corresponding second distance.

9. The light source according to claim 1, wherein: The instructions for detecting defects include instructions for the following: The roughness of the xenon (Xe) ice on the rotatable cylinder was measured using the confocal color sensor. Determine whether the roughness meets the threshold; and The instructions for shutting down the laser beam include instructions for shutting down the laser beam in response to determining that the roughness meets the threshold.

10. The light source according to claim 9, wherein: The instructions for determining whether the roughness meets the threshold include instructions for using the confocal color sensor to identify pits in the xenon (Xe) ice on the rotatable cylinder; and The instruction for shutting off the laser beam in response to determining that the roughness meets the threshold includes an instruction for shutting off the laser beam in response to identifying the pit.

11. The light source according to claim 1, wherein: The instructions for detecting defects include instructions for the following: The reflectance of a corresponding portion of the xenon (Xe) ice on the rotatable cylinder was measured using the confocal color sensor, and Determine whether the reflectivity of the corresponding portion of the xenon (Xe) ice on the rotatable cylinder is within a specified range; and The instructions for shutting off the laser beam include instructions for shutting off the laser beam in response to determining that the reflectivity of one or more corresponding portions of the xenon (Xe) ice on the rotatable cylinder is not within the specified range.

12. The light source of claim 1, wherein the one or more procedures further include instructions for: After shutting off the laser beam in response to the detection of the defect, the confocal color sensor is used to monitor for defects in the xenon (Xe) ice within the rotatable cylinder; and The laser beam is reactivated in response to the identification that there are no defects in the xenon (Xe) ice on the rotatable cylinder.

13. The light source according to claim 12, wherein: The instructions for monitoring the rotatable cylinder include instructions for the following: The thickness of the corresponding portion of the xenon (Xe) ice on the rotatable cylinder is measured using the confocal color sensor, and Determine whether the thickness of the corresponding portion of the xenon (Xe) ice on the rotatable cylinder meets a threshold. and The instructions for reactivating the laser beam include instructions for reactivating the laser beam based at least in part on a determination that the thickness satisfies the threshold.

14. The light source according to claim 12, wherein: The instructions for monitoring the rotatable cylinder include instructions for the following: The roughness of the xenon (Xe) ice on the rotatable cylinder was measured using the confocal color sensor. Determine whether the roughness meets the threshold; and The instructions for reactivating the laser beam include instructions for reactivating the laser beam based at least in part on the determination that the roughness does not meet a threshold.

15. The light source according to claim 12, wherein: The instructions for monitoring the rotatable cylinder include instructions for the following: The reflectance of a corresponding portion of the xenon (Xe) ice on the rotatable cylinder was measured using the confocal color sensor, and Determine whether the reflectivity of the corresponding portion of the xenon (Xe) ice on the rotatable cylinder is within a specified range; and The instructions for reactivating the laser beam include instructions for reactivating the laser beam based at least in part on a determination of the reflectivity of the corresponding portion of the xenon (Xe) ice on the rotatable cylinder within the specified range.

16. The light source of claim 1, wherein the one or more procedures further include instructions for triggering maintenance based at least in part on the detection of the defects in the xenon (Xe) ice on the rotatable cylinder.

17. The light source of claim 1, wherein the one or more procedures further include instructions for: Before the rotatable cylinder is coated with the xenon (Xe) ice, the roughness of the exposed outer surface of the rotatable cylinder is measured; and The suitability of the rotatable cylinder for use is determined at least in part based on the roughness.

18. A light source comprising: A rotatable cylinder, coated with xenon (Xe) ice and irradiated by a laser beam to generate plasma; A confocal color sensor is used to measure the distance from the confocal color sensor to the rotatable cylinder; Electric translation stage; One or more processors; as well as A memory that stores one or more programs executed by the one or more processors; in: The confocal color sensor includes a sensor head mounted on the motorized translation stage; and The one or more procedures include instructions for translating the electrified translation stage to align the sensor head with the laser spot illuminating the xenon (Xe) ice.

19. The light source according to claim 18, wherein: The rotatable cylinder has grooves surrounding its outer surface; and The one or more procedures further include instructions for aligning the vertical position of the rotatable cylinder and the sensor head based on the detection of the groove by the confocal color sensor.

20. A method of operating a light source according to any one of claims 1-19, comprising: Rotate the rotatable cylinder; While rotating the rotatable cylinder, the rotatable cylinder is coated with xenon (Xe) ice; While rotating the rotatable cylinder and coating it with xenon (Xe) ice, the rotatable cylinder is irradiated with the laser beam to generate the plasma; When the rotatable cylinder is irradiated with the laser beam, the confocal color sensor is used to monitor the rotatable cylinder to detect defects in the xenon (Xe) ice on the rotatable cylinder; and In response to the detection of a defect in the xenon (Xe) ice on the rotatable cylinder, the laser beam is turned off.

21. The method of claim 20, wherein monitoring the rotatable cylinder comprises using the confocal color sensor to measure a parameter selected from the group consisting of the thickness of a corresponding portion of the xenon (Xe) ice on the rotatable cylinder, the roughness of the xenon (Xe) ice on the rotatable cylinder, and the reflectivity of a corresponding portion of the xenon (Xe) ice on the rotatable cylinder.

22. The method of claim 20, further comprising: After the laser beam is turned off, the confocal color sensor is used to monitor the rotatable cylinder while rotating it to detect defects in the xenon (Xe) ice on the rotatable cylinder. and In response to the detection that there are no defects in the xenon (Xe) ice on the rotatable cylinder, the laser beam is reactivated to irradiate the rotatable cylinder to generate the plasma while the rotatable cylinder is rotated and coated with the xenon (Xe) ice.

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