Confocal color metrology for EUV light source state monitoring

Abstract

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

Description

Technical Field

[0001] The present disclosure relates to metrology of xenon ice coated cartridges used in extreme ultraviolet (EUV) light sources, and more particularly to such metrology using a confocal color sensor. Background Art

[0002] An EUV light source may include a drum having 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 may be performed to determine parameters of the Xe ice, such as the thickness and surface quality of the Xe ice. The camera images a section of the Xe ice and an image processing algorithm extracts relevant information from the image. However, the extracted information is limited in terms of spatial resolution and bandwidth. Therefore, it is challenging to identify parameters of the Xe ice (e.g., for real-time feedback) using optical imaging. Summary of the invention

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

[0004] In some embodiments, a light source includes a rotatable drum 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 drum.

[0005] In some embodiments, a method of operating a light source includes: rotating a barrel; coating the barrel with Xe ice while rotating the barrel; and irradiating the barrel with a laser beam to generate plasma while rotating the barrel and coating the barrel with the Xe ice. The method also includes: monitoring the barrel using a confocal color sensor to detect defects in the Xe ice on the barrel while irradiating the barrel with the laser beam; and shutting off the laser beam in response to detecting defects in the Xe ice on the barrel. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] For a better understanding of the various described embodiments, reference should be made to the following detailed description in conjunction with the following figures.

[0007] Figure 1 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 An assembly of an EUV light source according to some embodiments is shown, comprising Figures 3A to 3B Components of EUV light source and placement thereof Figures 3A to 3B The outer shell of the rotatable drum.

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

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

[0013] Fig. 8A and 8B A flow chart showing a method of operating a light source according to some embodiments.

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

[0015] Fig. 10A and 10B An assembly of an EUV light source according to some embodiments is shown, comprising Figures 4A to 4B Components of an EUV light source and the motorized translation stage on which the sensor head is mounted.

[0016] Like reference numerals refer to corresponding parts throughout the drawings and description. DETAILED DESCRIPTION

[0017] Reference will now be made in detail to various embodiments, examples of which are illustrated in 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, it will be apparent to one of ordinary skill in the art that the various described embodiments may be practiced without these specific details. In other instances, well-known methods, processes, components, circuits, and networks are not described in detail to avoid unnecessarily obscuring aspects of the described embodiments.

[0018] Figure 11 is a cross-sectional side view of an extreme ultraviolet (EUV) light source 100 according to some embodiments. EUV light source 100 includes a vacuum chamber 102 (e.g., an aluminum billet chamber). A vacuum pump 110 (e.g., a turbo pump) provides a vacuum in vacuum chamber 102. A laser beam 103 is introduced into vacuum chamber 102 through a laser objective lens 104 and accompanying thin films. Laser objective lens 104 focuses laser beam 103 on the outer surface of a cylinder 118 (e.g., a copper cylinder) coated with xenon (Xe) ice (i.e., solid Xe). Laser beam 103 irradiates cylinder 118, thereby striking the Xe ice on the outer surface of cylinder 118. When laser beam 103 strikes the Xe ice on the outer surface of cylinder 118, it triggers a plasma that emits EUV light 105. Mirror 106 collects a portion of EUV light 105 and directs the collected EUV light 105 through a window 108 in vacuum chamber 102. The barrel 118 is rotated and also translated vertically to allow different areas (ie, portions) of the Xe ice on its outer surface to be exposed to the laser beam 103. As the barrel 118 rotates and translates, Xe may be sprayed onto the outer surface of the barrel 118 by the sprayer 117 to maintain a coating of Xe ice.

[0019] Feedthrough assembly 112 provides liquid nitrogen to the interior of barrel 118 to keep the surface of barrel 118 cool and thus maintain the coating of Xe ice on barrel 118. The liquid nitrogen evaporates during operation of EUV light source 100. Feedthrough assembly 112 exhausts the resulting nitrogen from barrel 118.

[0020] The barrel 118 is housed in the barrel assembly 114, which is coupled to the feed-through assembly 112. The barrel assembly 114 also includes a rotary motor 116 that rotates the barrel 118. The rotary motor 116 is coupled to the barrel 118 independently of the feed-through assembly 112. The barrel assembly 114 further includes a sprayer 117. The barrel assembly 114 has a water-cooled barrel cover that receives water from a water-cooled input 126. Below the barrel assembly 114 and therefore below the barrel 118 is a translation motor 120 that linearly translates the barrel 118 in a vertical direction (i.e., moves the barrel 118 up and down). The translation motor 120 is also coupled to the barrel 118 independently of the feed-through assembly 112. A corresponding linear stage actuator 124 actuates the translation motor 120. A weight compensation bellows 122 is also located below the barrel assembly 114.

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

[0022] Figure 2 A confocal color sensor 200 is shown in accordance with some embodiments. 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 to control 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 to disperse the broadband light and emit the dispersed light, thereby focusing the emitted light along an optical axis 220 so that emitted light of different wavelengths has different focal lengths. Figure 2 In the example of , the scattered 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 placed in front of the tip of the sensor head 206 (i.e., in front of the end of the sensor head 206 from which the scattered light is emitted) so that the object intersects the optical axis 220, the sensor head 206 receives light that was initially emitted by the sensor head and then reflected from the object. Based on the wavelength of the received light, the confocal color sensor 200 determines the distance from the sensor head 206 (e.g., from the tip) to the object. The confocal color sensor 200 can also determine the reflectivity of the object and the roughness (or equivalently, uniformity) of a portion of the surface of the object illuminated by the emitted light from the sensor head 206. The confocal color sensor 200 operates at a sampling rate. In some embodiments, the sampling rate is in a range between 100 Hz and 70 kHz.

[0024] Figure 3A and 3BAn EUV light source 300 (eg, EUV light source 100, Figure 1 ) component. The component includes a cartridge 302 (e.g., cartridge 118, Figure 1 ) and confocal color sensor 200( Figure 2 ), the confocal color sensor 200 has a sensor head 206, an optical fiber 204, and a controller 202. The barrel 302 can rotate around a central vertical axis so that it can achieve a rotational motion 314, and can translate in a vertical direction so that it can achieve a translational motion 316. Figure 3A In , the outer surface of the barrel 302 is bare and thus exposed. Figure 3B In the embodiment, the outer surface of the cylinder 302 is coated with Xe ice 316. The cylinder 302 coated with Xe ice 316 can be laser beamed (e.g., laser beam 103, Figure 1 ) to produce a plasma that emits EUV light.

[0025] The cartridge 302 and the sensor head 206 are disposed in a vacuum chamber 304 (e.g., in the vacuum chamber 102). The controller 202 is disposed in an atmosphere 308 outside the vacuum chamber 304 (e.g., outside the vacuum chamber 102). The optical fiber 204 that provides 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 disposed partially outside the vacuum chamber 304 and partially inside the vacuum chamber 304.

[0026] Figure 4A and 4B Components of an EUV light source 400 are shown, according to some embodiments, and the EUV light source 400 is an EUV light source 300 (eg, and EUV light source 100, Figure 1 ). The components of EUV light source 400 include the components of EUV light source 300, and further include a housing 402 enclosing barrel 302. In some embodiments, housing 402 is barrel assembly 114 ( Figure 1 ). When the barrel 302 is disposed within the housing 402, the sensor head 206 is disposed outside the housing 402 (but within the vacuum chamber 304). The housing 402 has a window 404 located between the barrel 302 and the sensor head 206. Light 312 from the sensor head 206 passes through the window 404 to the barrel 302, and corresponding reflected light from the barrel 302 passes through the window 404 to the sensor head 206. The housing 402 accommodates a pressure difference between an area inside the housing 402 and an area outside the housing 402 but inside the vacuum chamber 304. For example, during operation of the EUV light source 400, an area inside the housing 402 has a higher pressure than an area outside the housing 402 but inside the vacuum chamber 304.

[0027] Fig. 10A and10B Components of an EUV light source 1000 are shown, according to some embodiments, where the EUV light source 1000 is an EUV light source 400 (eg, and EUV light source 100, Figure 1 ). The components of EUV light source 1000 include the components of EUV light source 400, and further include a motorized translation stage 1002 on which sensor head 206 is mounted. Motorized translation stage 1002 is disposed within vacuum chamber 304. Motorized translation stage 1002 is translatable, and thus can translate sensor head 206 vertically (e.g., in accordance with translational motion 316 of barrel 302) and / or horizontally (i.e., moving sensor head toward or away from barrel 302 and window 404). For example, motorized translation stage 1004 can translate vertically to align sensor head 206 with a laser spot (e.g., a spot where laser beam 103 illuminates Xe ice 316) so that 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 spot to the field of view of sensor head 206 in less than one full rotation of barrel 302). This alignment between the sensor head 206 and the laser spot allows the sensor head 206 to detect defects (e.g., pits) in the Xe ice 316 newly induced by the laser beam. In some embodiments, to achieve this alignment, the motorized translation stage 1004 adjusts the vertical position of the sensor head 206 relative to the vertical position of the barrel 302 to account for the translation speed of the barrel 302 and the relative angular positions of the laser spot and the sensor head 206 about the barrel 302. The position of the motorized translation stage 1002 can be measured using an encoder (not shown).

[0028] In some embodiments, barrel 302 has grooves 1004 around its outer surface at specified vertical positions along barrel 302 (e.g., around the center of barrel 302). Grooves 1004 may be detected by confocal color sensor 200 to align the vertical positions of sensor head 206 and barrel 302. Such alignment is performed, for example, during calibration and / or at the beginning of operation of EUV light source 1000 based on detection of grooves 1004 by confocal color sensor 200.

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

[0030] The thickness of Xe ice 316 (e.g., the corresponding thickness of a corresponding portion of Xe ice 316) is one example of a parameter of barrel 302 that can be measured using 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 barrel 302, when barrel 302 is coated with Xe ice 316, the roughness (e.g., the thickness of a corresponding portion of Xe ice 316) can be measured by measuring a second distance from confocal color sensor 200 (e.g., from sensor head 206) to a corresponding portion of the outer surface of Xe ice 316. Figure 3B and 4BThe change in the second distance provides an indication of the roughness of the Xe ice. On a smaller local scale, the confocal color sensor 200 may 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 may provide an indication of the reflectivity 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 may be used to monitor changes and / or absolute values ​​of the thickness, roughness, and reflectivity of the Xe ice 316. The information may be acquired by a computer system associated with the EUV light source 300 or 400 (e.g., by a computer system of the EUV light source system 900, Fig. 9 ) to calculate roughness and reflectivity values ​​(such as distance and thickness).

[0031] Parameters measured using the confocal color sensor 200 (e.g., thickness, roughness, and / or reflectivity of the Xe ice 316) can be used to provide real-time feedback to control the operation of the EUV light source 400. For example, a laser beam (e.g., laser beam 103, laser beam 104) irradiating the barrel 302 can be turned off in response to detecting a defect in the Xe ice 316 (e.g., a pit in the Xe ice 316, which is an area with insufficient thickness and resulting in excessive roughness). Figure 1 ) (e.g., by deactivating a laser that generates it or by dumping a laser beam. For example, if the thickness of one or more portions of the Xe ice 316 (i.e., the thickness of one or more corresponding portions of the Xe ice 316) does not satisfy a threshold value (e.g., is less than, or is less than or equal to a minimum thickness), if the roughness of the Xe ice 316 (or one or more portions of the Xe ice 316) satisfies a threshold value (e.g., exceeds, is equal to, or exceeds a maximum roughness), and / or if the reflectivity of one or more portions of the Xe ice 316 (i.e., the reflectivity of one or more portions of the Xe ice 316) is not within a specified range (e.g., is less than, or is less than or equal to a minimum reflectivity, or is greater than, or is greater than or equal to a maximum reflectivity, where the range is between the minimum reflectivity and the maximum reflectivity), then a defect is detected and the laser beam is turned off. The decision whether to turn off the laser beam may be made by a computer system associated with the EUV light source 300 or 400 (e.g., by a computer system of the EUV light source system 900, Fig. 9 ) made.

[0032] Once the laser beam has been turned off, the parameters measured using the confocal color sensor 200 (e.g., the thickness, roughness, and / or reflectivity of the Xe ice 316) may be used to determine whether to reactivate the laser beam. For example, the laser beam may be reactivated in response to determining that the detected defect has been eliminated (e.g., by regrowth of the Xe ice 316 on the barrel 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 the corresponding portion of the Xe ice 316) satisfies a threshold value (e.g., greater than, or greater than or equal to a minimum thickness), the roughness of the Xe ice 316 (or the corresponding portion of the Xe ice 316) does not satisfy a threshold value (e.g., less than, or less than or equal to a maximum roughness), and / or 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 whether to reactivate the laser beam may be made by a computer system associated with EUV light source 300 or 400 (e.g., by a computer system of EUV light source system 900, Fig. 9 ) made.

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

[0034] In some embodiments, maintenance of EUV light source 300 or 400 is triggered in response to detecting a defect in Xe ice 316 or on cartridge 302 (eg, scheduled or enforced before operations can begin or continue).

[0035] In general, the results of measuring one or more parameters of barrel 302 using confocal color sensor 200 may be used to improve (eg, optimize) other process parameters of EUV light source 300 or 400 .

[0036] Figure 5 5 is a graph 500 showing time trajectory data 502 of the thickness of Xe ice 316 on barrel 302 according to some embodiments. The time trajectory data 502 is generated using a confocal color sensor 200 attached to an EUV light source system having barrel 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. Figures 3A to 3B 4A to 4B) to obtain the thickness values ​​of the time trajectory data 502. The thickness of the Xe ice 316 on most of the barrel 302 remains stable at slightly above 0.9 mm, but a specific portion (i.e., an area) of the Xe ice 316 on the barrel 302 has a lower thickness. This specific portion may be a pit in the Xe ice 316. As the barrel 302 rotates and translates, the low thickness is repeatedly measured, resulting in repeated examples of low measured thickness in the time trajectory data 502 over time. The low thickness drops from about 0.8 mm at 6.2 seconds to about 0.35 mm at about 6.5 seconds, remains stable at the thickness until about 7.3 seconds, and then returns to 0.9 mm immediately after 7.4 seconds. The low thickness of the Xe ice 316 between about 6.3 seconds and 7.4 seconds is equivalent to a defect in the Xe ice 316. Therefore, Figure 5 The formation and subsequent elimination of defects in Xe ice 316 are described.

[0037] Figure 6 and 7 6 and 700 are respective graphs 600 and 700 showing the variation of the thickness of Xe ice 316 on an example of a barrel 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 the barrel 302. Graphs 600 and 700 show the thickness of the Xe ice 316 of respective portions of the barrel 302 as defined by respective rotational positions (in radians) and vertical positions (in millimeters) on the barrel 302. Each of the graphs 600 and 700 is for a different point in time. The rotational position is shown on the x-axis of the graphs 600 and 700, and the vertical position is shown on the y-axis of the graphs 600 and 700. When the barrel 302 is irradiated with a laser beam to generate plasma (and thus EUV light), the confocal color sensor 200 (e.g., as for Figures 3A to 3B and 4A to 4B) to obtain the data of Figures 600 and 700.

[0038] Xe ice 316 on most of barrel 302 has a thickness of about 0.9 mm. However, some portions on the top and bottom of barrel 302 have a lower thickness. Portion 602 on the top of barrel 302 and portion 604 on the bottom of barrel 302 have a thickness as low as about 0.4 mm. Portions 602 and 604 having these low thicknesses are equivalent to defects. In response to detecting these defects (e.g., as described above for Figures 3A to 3B 4A to 4B ), the laser beam may be turned off, thereby allowing the Xe ice 316 to regrow in portions 602 and 604 and thereby become thicker. Figure 7 The results of this regrowth are shown: sections 602 and 604 ( Figure 6 ) has a thickness of Xe ice 316 Figure 7 to the point where it is no longer considered defective.

[0039] Fig. 8A and 8B An operation light source (e.g., EUV light source 100, Figure 1 ; 300, Figures 3A to 3B ; 400, Figures 4A to 4B ) is a flowchart of method 800. In method 800, rotating (802, Fig. 8A ) cartridge (e.g., cartridge 118, Figure 1 ; Cylinder 302, Figures 3A to 4B ). In some embodiments, the barrel is vertically translated (804) while being rotated. While being rotated (e.g., and while being vertically translated), the barrel is coated (806) with Xe ice. While being rotated (e.g., and while being vertically translated) and while being coated with Xe ice, a laser beam (e.g., laser beam 103, Figure 1 ) irradiates (808) the cylinder to generate plasma.

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

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

[0042] After the laser beam is turned off, while the barrel is being rotated (eg, and the barrel is translated and coated with Xe ice), the confocal color sensor is used to monitor (822, Figure 8B ) cylinder to detect defects in the Xe ice on the cylinder. In some embodiments, a confocal color sensor is used (824) to measure the thickness of a corresponding portion of the Xe ice on the cylinder (e.g., as for Figures 3A to 3B 4A to 4B). In some embodiments (e.g., in addition to or in place of step 824), a confocal color sensor is used (826) to measure the roughness of the Xe ice on the barrel. In some embodiments (e.g., in addition to or in place of steps 824 and 826), a confocal color sensor is used (828) to measure the reflectivity of a corresponding portion of the Xe ice on the barrel (i.e., measure the reflectivity of the corresponding portion).

[0043] Monitoring (822) the barrel is performed after the laser beam is turned off to determine whether the detected defect has been eliminated (e.g., by regrowth of Xe ice) and whether any other defects exist. If a defect is detected (830-yes), the barrel continues to be monitored (822) while the barrel is rotated (802), translated (804), and / or coated (806) with Xe ice with the laser beam still turned off. However, if no defect is detected (830-no), the laser beam is reactivated (832) in response to detecting that the absence of defects in the Xe ice on the barrel: the barrel is again irradiated with the laser beam while the barrel is rotated (802) and / or translated (804) and coated with Xe ice (e.g., while the barrel is coated (806) with Xe ice). Operation of method 800 returns to step 810 ( Fig. 8A ).

[0044] In some embodiments, the barrel is mounted on a motorized translation stage (e.g., motorized translation stage 1002, Figures 10A to 10B During the monitoring of steps 810 and 822, the motorized translation stage may be translated to align the confocal color sensor with the laser spot where the laser beam illuminates the Xe ice (e.g., to detect new pits in the Xe ice).

[0045] Thus, method 800 allows operation of the EUV light source to be controlled 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 barrel and allows a determination to be made in real time whether to continue operation of the EUV light source or allow the coating of Xe ice on the barrel to rebuild.

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

[0047] Fig. 9 is a block diagram of an EUV light source system 900 according to some embodiments. The 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 a cartridge 932 (e.g., cartridge 118, Figure 1 ; Cylinder 302, Figures 3A to 4B ), laser 934 (for example, to generate laser beam 103, Figure 1 ) and a confocal color sensor 936 (e.g., confocal color sensor 200, Figures 2 to 4B The confocal color sensor 936 may be mounted on a motorized translation stage (eg, motorized 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., a keyboard, a mouse, a touch-sensitive surface of display 907, etc.). Display 907 may display the status of EUV light source 930, including the results of monitoring barrel 932 with confocal color sensor 936. For example, display 907 may display a graph similar to graph 500 ( Figure 5 ), 600 (Figure 6) and / or 700 ( Figure 7 ) in the table below.

[0049] Memory 910 includes volatile and / or nonvolatile memory. Memory 910 (e.g., nonvolatile 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 a computer system of system 900. Memory 910 (e.g., non-transitory computer-readable storage media of memory 910) includes functions for implementing the functionality described herein (e.g., for processing the processing of ... Figures 3A to 3B 4A to 4B). For example, memory 910 (e.g., a non-transitory computer-readable storage medium of memory 910) includes instructions for executing method 800 ( Figures 8A to 8B ) instruction.

[0050] In some embodiments, the memory 910 (e.g., a non-transitory computer-readable storage medium of the memory 910) stores the following modules and data, or a subset or superset thereof: an operating system 912, which includes processes for handling various basic system services and for performing hardware-related tasks; a barrel control module 914, which is used to control the rotation and translation of the barrel 932; a confocal color sensor control module 916, which is used to control and receive data from the confocal color sensor 936 (e.g., and for controlling a motorized translation stage on which the confocal color sensor 936 is mounted); a laser beam control module 918, which is used to control the laser 934 and the corresponding laser beam that irradiates the barrel 932 coated with Xe ice (e.g., for shutting down and reactivating the laser beam); a defect detection module 918, which is used to detect defects in the Xe ice on the barrel 932 using data from the confocal color sensor 936; and a maintenance module 920, which is used to trigger maintenance of the EUV light source 930 (e.g., scheduling or forcing).

[0051] Each of the modules stored in the 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. The separate modules need not be implemented as separate software programs. Modules and various subsets of modules may be combined or otherwise reconfigured. In some embodiments, the memory 910 stores a subset or superset of the modules and / or data structures identified above.

[0052] Fig. 9 Rather, it is intended as a functional description of various features that may be present in an EUV light source system rather than as a schematic diagram of a structure. For example, the functionality of the computer system in EUV light source system 900 may be divided between multiple devices. A portion of the modules stored in memory 910 may alternatively be stored in one or more other computer systems that are communicatively coupled to the computer system of EUV light source system 900 via one or more networks.

[0053] For purposes of illustration, the foregoing description has been described with reference to specific embodiments. However, the above illustrative discussion is not intended to be exhaustive or to limit the claims to the precise forms disclosed. In light of the above teachings, many modifications and variations are possible. The embodiments are selected to best explain the underlying principles of the claims and their practical application, so as to enable those skilled in the art to best use the embodiments with various modifications suitable for the particular use under consideration.

Claims

1. A light source, comprising: A rotatable drum to be coated with xenon (Xe) ice and irradiated by a laser beam to generate plasma; and A confocal color sensor is used to measure the distance from the confocal color sensor to the rotatable barrel.

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

3. The light source of claim 2, wherein the confocal color sensor further comprises a controller disposed outside the vacuum chamber to control operation of the confocal color sensor and to 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 having a feedthrough; and The optical fiber passes through the feed-through.

5. The light source of claim 2, further comprising a housing within the vacuum chamber, wherein: The rotatable drum is disposed in the housing; The sensor head is disposed outside the housing; and The housing includes a window between the rotatable barrel and the sensor head.

6. The light source of claim 2, wherein the distance from the confocal color sensor to the rotatable barrel to be measured by the confocal color sensor comprises: a first distance from the sensor head to a corresponding portion of an exposed outer surface of the rotatable drum before the rotatable drum is coated with the Xe ice; and A second distance from the sensor head to a corresponding portion of the outer surface of the Xe ice when the rotatable drum is coated with the Xe ice.

7. The light source according to claim 1, further comprising: 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: detecting defects in the Xe ice on the rotatable drum using the confocal color sensor when the rotatable drum is coated with the Xe ice; and The laser beam is turned off in response to detecting a defect in the Xe ice on the rotatable drum using the confocal color sensor.

8. The light source of claim 7, wherein: The instructions for detecting defects include instructions for: measuring the thickness of a corresponding portion of the Xe ice on the rotatable drum using the confocal color sensor, and determining whether the thickness of the corresponding portion of the Xe ice on the rotatable drum satisfies a threshold; and The instructions for shutting off the laser beam include instructions for shutting off the laser beam in response to determining that one or more thicknesses of one or more corresponding portions of the Xe ice on the rotatable drum do not satisfy the threshold value.

9. The light source of claim 8, further comprising a vacuum chamber, wherein: The rotatable drum is disposed in the vacuum chamber; The confocal color sensor includes a sensor head disposed within the vacuum chamber to focus light onto the rotatable drum and detect reflected light from the rotatable drum; and The instructions for measuring the thickness of the corresponding portion of the Xe ice on the rotatable drum include instructions for: measuring a first distance from the sensor head to a corresponding portion of an exposed outer surface of the rotatable drum using the confocal color sensor before the rotatable drum is coated with the Xe ice, measuring a second distance from the sensor head to a corresponding portion of an outer surface of the Xe ice using the confocal color sensor while the rotatable drum is coated with the Xe ice, and The corresponding first distance is subtracted from the corresponding second distance.

10. The light source of claim 7, wherein: The instructions for detecting defects include instructions for: measuring the roughness of the Xe ice on the rotatable drum using the confocal color sensor, and determining whether the roughness satisfies a threshold; and The instructions for turning off the laser beam include instructions for turning off the laser beam in response to determining that the roughness satisfies the threshold.

11. The light source of claim 10, wherein: The instructions for determining whether the roughness satisfies the threshold include instructions for identifying pits in the Xe ice on the rotatable cartridge using the confocal color sensor; and The instructions for turning off the laser beam in response to determining that the roughness satisfies the threshold include instructions for turning off the laser beam in response to identifying the pit.

12. The light source of claim 7, wherein: The instructions for detecting defects include instructions for: measuring the reflectivity of corresponding portions of the Xe ice on the rotatable drum using the confocal color sensor, and determining whether the reflectivity of the corresponding portion of the Xe ice on the rotatable drum is within a specified range; and The instructions for shutting down the laser beam include instructions for shutting down the laser beam in response to determining that one or more reflectivities of one or more corresponding portions of the Xe ice on the rotatable drum are not within the specified range.

13. The light source of claim 7, wherein the one or more programs further comprise instructions for: monitoring the rotatable drum for defects in the Xe ice using the confocal chromatic sensor after shutting off the laser beam in response to detecting the defect; and The laser beam is reactivated in response to identifying the absence of defects in the Xe ice on the rotatable drum.

14. The light source of claim 13, wherein: The instructions for monitoring the rotatable drum include instructions for: measuring the thickness of a corresponding portion of the Xe ice on the rotatable drum using the confocal color sensor, and determining whether the thickness of the corresponding portion of the Xe ice on the rotatable drum satisfies 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.

15. The light source of claim 13, wherein: The instructions for monitoring the rotatable drum include instructions for: measuring a roughness of the Xe ice on the rotatable drum using the confocal color sensor, and determining whether the roughness satisfies 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 roughness does not satisfy a threshold.

16. The light source of claim 13, wherein: The instructions for monitoring the rotatable drum include instructions for: measuring the reflectivity of corresponding portions of the Xe ice on the rotatable drum using the confocal color sensor, and determining whether the reflectivity of the corresponding portion of the Xe ice on the rotatable drum 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 that the reflectivity of the corresponding portion of the Xe ice on the rotatable drum is within the specified range.

17. The light source of claim 7, wherein the one or more programs further comprise instructions for triggering maintenance based at least in part on detecting the defect in the Xe ice on the rotatable drum.

18. The light source of claim 7, wherein the one or more programs further comprise instructions for: measuring the roughness of an exposed outer surface of the rotatable drum before the rotatable drum is coated with the Xe ice; and A determination is made as to whether the rotatable drum is suitable for use based at least in part on the roughness.

19. The light source of claim 7, further comprising a motorized translation stage, wherein: The confocal color sensor includes a sensor head mounted on the motorized translation stage; and The one or more programs further include instructions for translating the motorized translation stage to align the sensor head with a laser spot where the laser beam illuminates the Xe ice.

20. The light source of claim 19, wherein: The rotatable drum has grooves around its outer surface; and The one or more programs further include instructions for aligning a vertical position of the rotatable barrel and the sensor head based on detection of the grooves by the confocal color sensor.

21. A method of operating a light source, comprising: Rotating drum; coating the cylinder with xenon (Xe) ice while rotating the cylinder; irradiating the barrel with a laser beam to generate plasma while the barrel is rotated and coated with the Xe ice; monitoring the barrel using a confocal color sensor to detect defects in the Xe ice on the barrel while irradiating the barrel with the laser beam; and In response to detecting a defect in the Xe ice on the cartridge, the laser beam is turned off.

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

23. The method of claim 21, further comprising: After turning off the laser beam, monitoring the barrel using the confocal chromatic sensor while rotating the barrel to detect defects in the Xe ice on the barrel; and In response to detecting the absence of defects in the Xe ice on the barrel, the laser beam is reactivated to irradiate the barrel to generate the plasma while rotating the barrel and coating the barrel with the Xe ice.

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