Determination of measurement errors with etalons.

Abstract

To provide a method for determination of a measurement error in an etalon.SOLUTION: Information relating to an etalon is accessed, the etalon being associated with a calibration parameter having a pre-set default value, and the etalon being configured to produce an interference pattern including a plurality of fringes from a received light beam, where the information relating to the etalon includes first spatial information relating to a first fringe of the plurality of fringes and second spatial information relating to a second fringe of the plurality of fringes. A first wavelength value of the received light beam is determined based on the spatial information relating to the first fringe and an initial value of the calibration parameter. A second wavelength value of the received light beam is determined based on the spatial information relating to the second fringe and the initial value of the calibration parameter. The first wavelength value and the second wavelength value are compared to determine a measurement error value.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. patent application Ser. No. 63 / 043,312, entitled "DETERMINATION OF MEASUREMENT ERROR IN AN ETALON," filed Jun. 24, 2020, the entire contents of which are incorporated by reference herein.

[0002] This disclosure relates to determining measurement errors in etalons, which may be used in deep ultraviolet (DUV) optical systems. [Background technology]

[0003]

[0003] An etalon is an optical resonator made of two partially reflective optical surfaces that produces interference patterns and may be used to measure or estimate the wavelength of light incident on the etalon. Summary of the Invention

[0004]

[0004] In one aspect, a method includes accessing information related to an etalon, the etalon associated with calibration parameters having preset default values, the etalon configured to generate an interference fringe including a plurality of fringes from a received light beam, the information related to the etalon including first spatial information related to a first fringe of the plurality of fringes and second spatial information related to a second fringe of the plurality of fringes; determining a first wavelength value of the received light beam based on the spatial information related to the first fringe and an initial value of the calibration parameter; determining a second wavelength value of the received light beam based on the spatial information related to the second fringe and an initial value of the calibration parameter; and comparing the first wavelength value and the second wavelength value to determine a measurement error value.

[0005]

[0005] Implementations may include one or more of the following features.

[0006]

[0006] The method may further include determining whether to adjust a preset default value of the calibration parameter based on the measurement error value. The measurement error value may include a difference between the first wavelength value and the second wavelength value, and the preset default value may be adjusted to a value such that the magnitude of the measurement error value is less than a threshold value. The preset default value may be adjusted to a value such that the measurement error value is zero.

[0007] The calibration parameters may include a focal length of the lens at the output of the etalon, and the measurement error may include a difference between the first wavelength value and the second wavelength value.

[0008]

[0008] The first spatial information may include a diameter of the first fringe and the second spatial information may include a diameter of the second fringe.

[0009]

[0009] The method may further include sending a light beam toward the etalon. The first fringes may be generated by a first portion of the light beam, and the second fringes may be generated by a second portion of the light beam. The light beam may include a plurality of pulses, the first portion of the light beam may include a first pulse of the plurality of pulses, and the second portion of the light beam may include a second pulse of the plurality of pulses. The light beam may include a continuous wave light beam, the first portion of the light beam may include a first sample of the light beam, and the second portion of the light beam may include a second sample of the light beam. The method further includes changing an initial value of the calibration parameter to an updated value of the calibration parameter, activating an optical element to thereby change a wavelength of the received light beam, determining a first wavelength value of the received light beam based on spatial information associated with the first fringe and the updated value of the calibration parameter, determining a second wavelength value of the received light beam based on spatial information associated with the second fringe and the updated value of the calibration parameter, and comparing the first wavelength value and the second wavelength value to determine a measurement error value based on the updated value of the calibration parameter. Prior to determining the second wavelength value, the optical element may be activated to increase or decrease the wavelength. The first wavelength value and the second wavelength value may be determined two or more times each time the optical element is activated. The method may further include determining whether to adjust a preset default value of the calibration parameter by comparing an error measurement determined based on the initial value of the calibration parameter and an error measurement determined based on the updated value of the calibration parameter.

[0010]

[0010] The initial values ​​of the calibration parameters may be pre-set default values.

[0011]

[0011] The first fringe and the second fringe may exist simultaneously within the interference pattern.

[0012]

[0012] In another aspect, a method of calibrating an etalon includes accessing information related to the etalon, the etalon being associated with calibration parameters having preset default values, the etalon being configured to generate an interference fringe including a plurality of fringes from a received light beam, the information related to the etalon including first spatial information related to a first fringe of the plurality of fringes and second spatial information related to a second fringe of the plurality of fringes, determining a measurement error value of the etalon based on the first spatial information, the second spatial information, and initial values ​​of the calibration parameters, and analyzing the measurement error value to determine whether to adjust the preset default value.

[0013]

[0013] Implementations may include one or more of the following features.

[0014]

[0014] The calibration parameters may include a focal length of the lens at an output of the etalon. The method further includes determining a first wavelength value based on the first spatial information and determining a second wavelength value based on the second spatial information. The measurement error may include a difference between the first wavelength value and the second wavelength value.

[0015]

[0015] The calibration parameters may include a plurality of initial values. Determining the measurement error values ​​may include simulating a plurality of measurement error values ​​for each of the plurality of initial values. Each measurement error value may be based on the first spatial information, the second spatial information, and one of the plurality of initial values ​​of the calibration parameters. Analyzing the measurement error values ​​may include analyzing the simulated measurement error values.

[0016]

[0016] In another aspect, an optical measurement instrument for a light source includes an etalon including a focusing lens configured to focus light at an image plane, a photodetector configured to detect interference fringes generated by the etalon and generate information related to the etalon, and a control system coupled to the photodetector. The etalon is associated with calibration parameters related to the focusing lens, the calibration parameters having preset default values. The information includes first spatial information for the first fringes and second spatial information for the second fringes. The control system is configured to determine a measurement error value of the etalon based on the first spatial information from the detector, the second spatial information, and an initial value of the calibration parameter, and analyze the measurement error value to determine whether to adjust the preset default value.

[0017]

[0017] Implementations may include one or more of the following features.

[0018] The light source may comprise a deep ultraviolet (DUV) light source.

[0019]

[0019] In another aspect, the light source may include a light generating device and an optical measurement device. The optical measurement device includes an etalon including a focusing lens configured to focus light on an image plane, a photodetector configured to detect interference fringes generated by the etalon and generate information related to the etalon, and a control system coupled to the photodetector. The etalon is associated with calibration parameters related to the focusing lens, the calibration parameters having preset default values. The information includes first spatial information for the first fringes and second spatial information for the second fringes. The control system is configured to determine a measurement error value of the etalon based on the first spatial information from the detector, the second spatial information, and an initial value of the calibration parameter, and analyze the measurement error value to determine whether to adjust the preset default value.

[0020]

[0020] Implementations may include one or more of the following features.

[0021]

[0021] The light-generating device may comprise a deep ultraviolet (DUV) light source. The light-generating device may comprise a master oscillator. The light-generating device may further comprise a power amplifier. The light-generating device may comprise multiple master oscillators.

[0022]

[0022] The light source may further comprise an optical element configured to receive light from the light-generating device and transmit the light to the etalon. The optical element may be a dispersive optical element.

[0023]

[0023] Implementations of any of the techniques described above may include a system, a method, a process, an apparatus, or a device. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0024] [Figure 1A] FIG. 1 is a block diagram of an example system. [Figure 1B]

[0025] 4 shows an example of interference fringes. [Figure 1C]

[0026] FIG. 1B is a block diagram of an embodiment of the system of FIG. 1A. [Figure 2A]

[0027] FIG. 1 is a block diagram of an example of an optical measurement instrument. [Figure 2B]

[0028] Another example of interference fringes. [Figure 2C]

[0028] Regarding another example of interference fringes. [Diagram 3]

[0029] 1 is a flow diagram of an example process for determining an etalon measurement error. [Figure 4] 4 is a flow diagram of an example process for determining an etalon measurement error. [Diagram 5]

[0030] 1 shows an exemplary plot of measurement error of an etalon. [Figure 6]

[0031] 1 is a flow diagram of an example process for determining an etalon measurement error. [Figure 7]

[0032] 1 shows an exemplary plot of measurement error of an etalon. [Figure 8A]

[0033] 1 illustrates an example of a deep ultraviolet (DUV) optical system in which the optical metrology instrument can be used. [Figure 8B]

[0034] 1 is an example of a projection optical system. [Figure 9A]

[0035] FIG. 2 is a block diagram of an example of a spectral conditioning device. [Figure 9B]

[0036] An example of a prism is shown. [Figure 10]

[0037] 1 illustrates an example of a deep ultraviolet (DUV) optical system in which the optical metrology instrument can be used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025]

[0038] FIG 1A is a block diagram of a system 100. In FIG 1A, dashed lines between elements represent optical paths along which light travels, and solid lines between elements represent signal paths along which information and / or data travels. System 100 includes a light-generating module 110 that generates a light beam 116. Light beam 116 propagates on a path 114 to device 180. Device 180 is any device that uses light beam 116. Device 180 may be an optical lithography device (such as scanner device 880 of FIG 8A and FIG 10) or a power amplifier (such as power amplifier 1012_2 of FIG 10).

[0026]

[0039] The system 100 also includes a beam separator 117 that sends a portion 116' of the light beam 116 to the optical measurement instrument 160. The beam separator 117 may be, for example, a beam splitter that sends the portion 116' to the optical measurement instrument 160 while the remaining light in the light beam 116 continues to propagate to the device 180. The optical measurement instrument 160 is used to measure the wavelength of the light beam 116. The optical measurement instrument 160 includes an etalon 130, a detector 140, and a control system 150. The etalon 130 includes two parallel optical elements 133A, 133B separated by a distance 136, and an output lens 134. With further reference to FIG. 1C, the output lens 134 has a focal length 163 and focuses the incident light at an image plane 137. The image plane 137 coincides with an active area 142 of the detector 140. FIG. 1C is a block diagram of the operating region 142 and the image plane 137.

[0027]

[0040] 1B, the output of the etalon 130 is an interference fringe 139 that is focused at an image plane 137. FIG. 1B shows the interference fringes 139 at the image plane 137. In the example of FIG. 1B, the interference fringes 139 are concentric rings formed at the image plane 137. Two fringes 139_1 and 139_2 are shown in FIG. 1B. The fringe 139_1 is a first order fringe and the fringe 139_2 is a second order fringe. The first order fringe 139_1 and the second order fringe 139_2 are two consecutive fringes. The wavelength of the light in the portion 116′ is related to the diameter of the fringes in the interference fringe 139 by Equation 1:

number

[0028]

[0041] The etalon 130 is used to measure the wavelength of the light at the portion 116'. The etalon 130 is associated with a measurement error that may be absolute at a particular wavelength and may be variable as a function of wavelength. One source of wavelength-dependent measurement error may occur when a fixed detector (such as detector 140) at the image plane 137 determines a wavelength value using a different order of fringes compared to a previous wavelength determination. That is, when the same wavelength of light is measured at different orders of fringes at the same interference fringe, the wavelength measurement based on the first order fringes 139_1 and / or the second order fringes 139_2 may be inaccurate. In particular, such measurement error results in an artificial change in the wavelength determination between two different measurements, even though the true wavelength of the incident light has not changed.

[0029]

[0042] The etalon 130 is associated with at least one calibration parameter 131. The value of FD is the calibration parameter 131. The value of FD is determined when the etalon 130 is manufactured. However, the value of FD may drift or change throughout the life of the etalon 130. The value of FD may change due to, for example, alignment shifts caused by thermal cycling (heating and / or cooling) that may occur during use of the etalon 130. This alignment shift may manifest as a change in the value of FD. Techniques for determining the value of FD during use and / or during the life of the etalon 130 are described below. Before considering techniques related to determining the value of the calibration parameter 131, details of an exemplary implementation of the optical measurement instrument 160 are considered.

[0030]

[0043] 2A is a block diagram of an optical measurement instrument 260. The optical measurement instrument 260 is an example of an implementation of the optical measurement instrument 160 (FIG. 1A). The optical measurement instrument 260 includes an input lens 232, an etalon 230, an output lens 234 (i.e., a focusing lens 234), and a detector 240. The portion 116' is diffused and passes through an aperture 235 of the optical measurement instrument 260. The portion 116' may be intentionally diffused by an optical diffuser (not shown) located at a plane 237 between the beam separator 117 and the aperture 235. The aperture 235 is in the focal plane of the input lens 232. The input lens 232 collimates the portion 116' before it enters the etalon 230. The output lens 234 has a focal length 263 and focuses the light onto an image plane. The detector 240 is positioned so that the active area 242 of the detector 240 coincides with the image plane.

[0031]

[0044] In the example shown in FIG. 2A, the etalon 230 comprises a pair of partially reflective optical elements 233A and 233B. The optical elements 233A and 233B are between the input lens 232 and the output lens 234. The optical elements 233A and 233B have respective reflective surfaces 238A and 238B that are spaced apart by a distance 236. The distance 236 may be a relatively short distance (e.g., millimeters to centimeters). The optical elements 233A and 233B are wedge-shaped to prevent the back surface (opposite the front surfaces 238A and 238B) from generating interference fringes. The back surface may have an anti-reflective coating. Other implementations of the etalon 230 are also possible. For example, in other implementations, the optical elements 233A and 233B are parallel plates and are not wedge-shaped. In yet another example, the etalon 230 may comprise only a single plate having two partially reflective parallel faces.

[0032]

[0045] 2B, the etalon 230 interacts with the portion 116' and outputs an interference fringe 239. FIG. 2B shows the interference fringe 239 at a point in time in the image plane of the lens 234. The interference fringe 239 includes a number of fringes, two of which (239_1 and 239_2) are shown in FIG. 2B. The interference fringe 239 includes areas of no light created by the destructive interference of the portion 116' and areas of light created by the constructive interference of the portion 116'. The areas of constructive interference are fringes 239_1 and 239_2. The areas of no light are shown in gray shading and are between the areas of light. Fringes 239_1 and 239_2 are concentric rings of light at the image plane of the output lens 234. Each ring in the set of fringes is an order (m) of the interference fringe, where m is an integer equal to or greater than 1. The fringes 239_1 are first order fringes and the fringes 239_2 are second order fringes.

[0033]

[0046] The interference fringes 239 are detected in an active area 242 of a detector 240. The detector 240 can be any type of detector capable of detecting light at the interference fringes 239. For example, the active area 242 can be a linear photodiode array that includes multiple elements of the same size spaced equally along one dimension in a single package. Each element in the photodiode array is sensitive to the wavelength of the portion 116'. As another example, the detector 240 can be a two-dimensional sensor, such as a two-dimensional charge-coupled device (CCD) or a two-dimensional complementary metal-oxide semiconductor (CMOS) sensor.

[0034]

[0047] The detector 240 is connected to a control system 250 via a data connection 254. The control system 250 includes an electronic processing module 251, an electronic storage 252, and an I / O interface 253. The electronic processing module 251 includes one or more processors suitable for executing computer programs, such as general-purpose or special-purpose microprocessors, and any one or more processors of any type of digital computer. Typically, the electronic processor receives instructions and data from a read-only memory, a random access memory (RAM), or both. The electronic processing module 251 may include any type of electronic processor. The one or more electronic processors of the electronic processing module 251 execute instructions and access data stored in the electronic storage 252. The one or more electronic processors may also write data to the electronic storage 252.

[0035]

[0048] The electronic storage 252 is any type of computer-readable or machine-readable medium. For example, the electronic storage 252 may be a volatile memory, such as a RAM, or a non-volatile memory. In some implementations, the electronic storage 252 includes non-volatile and volatile portions or components. The electronic storage 252 may store data and information used in the operation of the control system 250. The electronic storage 252 may also store instructions (e.g., in the form of a computer program) that enable the control system 250 to interact with the optical measurement device 260. For example, the instructions may be instructions that enable the electronic processing module 251 to implement the processes discussed with respect to Figures 3, 4, and 6. The electronic storage 252 also stores information about the etalon 230, such as initial values ​​of the default calibration parameters 231, or preset values ​​of the calibration parameters 231. The default or preset values ​​may be values ​​determined during a factory calibration or values ​​determined using a process such as processes 300, 400, or 600 described below. Calibration parameter 231 may be, for example, the focal length of lens 234. In another example, electronic storage 252 may also store specifications indicating one or more ranges of values ​​associated with an acceptable amount of measurement error in etalon 230.

[0036]

[0049] I / O interface 253 is any type of interface that allows control system 250 to exchange data and signals with an operator, other equipment, and / or an automated process running on another electronic device. For example, in implementations where data or instructions stored in electronic storage 252 can be edited, the editing may occur via I / O interface 253. I / O interface 253 may include one or more of a display, a keyboard, and a communication interface, such as a parallel port, a Universal Serial Bus (USB) connection, and / or any type of network interface, e.g., Ethernet. I / O interface 253 may also enable communication without physical contact, e.g., via an IEEE 802.11, Bluetooth, or Near Field Communication (NFC) connection.

[0037]

[0050] Control system 250 is coupled to various components of device 260 via data connection 254. Data connection 254 is any type of connection that allows for the transmission of data, signals, and / or information. For example, data connection 254 may be a physical cable or other physical data conduit (such as a cable that supports data transmission according to IEEE 802.3), a wireless data connection (such as a data connection that provides data via IEEE 802.11 or Bluetooth), or a combination of wired and wireless data connections.

[0038]

[0051] 3 is a flow diagram of a process 300. Process 300 is used to determine a measurement error value. Process 300 may be performed by control system 250 (FIG. 2A). For example, process 300 may be performed by one or more electronic processors in processing module 251. Consider process 300 with respect to measurement device 260 (FIG. 2A).

[0039]

[0052] Information related to the etalon 230 is accessed (310). This information may be accessed from electronic storage 252 or via I / O interface 253. The information related to the etalon 230 includes first spatial information related to a first fringe and second spatial information related to a second fringe. The first fringe and the second fringe may be two different fringes formed at the same time. For example, the first fringe may be fringe 239_1 and the second fringe may be fringe 239_2. As mentioned above, fringes 239_1 and fringe 239_2 are two different fringes formed by a single pulse of light or the same sample of a continuous wave light beam. The process 400 discussed with respect to FIG. 4 is an example of such an approach. In other implementations, the first fringe is a fringe in an interference fringe formed at a first time and the second fringe is a fringe in an interference fringe formed at a second time. For example, in such an implementation, the first fringes may be fringes formed by a first pulse of light incident on the etalon 230, and the second fringes may be fringes formed by a second pulse of light incident on the etalon 230 after the first pulse of light. Process 600 discussed with respect to FIG. 6 is an example of such an approach. The first spatial information may be a diameter of the first fringes. The second spatial information may be a diameter of the second fringes.

[0040]

[0053] The information associated with the etalon 230 also includes initial values ​​for the calibration parameters 231. The initial values ​​for the calibration parameters 231 may be factory calibration values ​​determined when the etalon 230 was assembled. In some implementations, the initial values ​​for the calibration parameters 231 are values ​​determined in a previous execution of the process 300. The pre-set default values ​​for the calibration parameters 231 may be stored in and accessed from the electronic storage 252.

[0041]

[0054] A first wavelength value is determined (320) based on spatial information associated with the first fringe and the initial values ​​of the calibration parameters 231. A second wavelength value is determined (330) based on spatial information associated with the second fringe and the initial values ​​of the calibration parameters 231.

[0042]

[0055] The first wavelength value and the second wavelength value are compared to determine a measurement error value (340). The measurement error value is a value that represents the difference between the first wavelength value and the second wavelength value. The measurement error value may be determined, for example, by subtracting the first wavelength value from the second wavelength value, or vice versa. Other implementations are possible. For example, the measurement error value may be a ratio of the first wavelength value to the second wavelength value.

[0043]

[0056] 4 is a flow diagram of a process 400. Process 400 is another example of a process for determining measurement error values ​​and values ​​of calibration parameters 231. Consider process 400 for interference fringes 239 (FIGS. 2B and 2C), which are the output of etalon 230 at a point in time. Process 400 may be performed by control system 250.

[0044]

[0057] An initial value for the calibration parameter 231 is accessed (410). The value for the calibration parameter 231 may be accessed from electronic storage 252 or provided to the control system 250 via I / O interface 253. The calibration parameter 231 is FD in this example. The initial value for the calibration parameter 231 may be a predetermined value or a default value determined when the etalon 230 is manufactured. The initial value for the calibration parameter 231 may be the value of the calibration parameter determined in a previous iteration of process 400.

[0045]

[0058] The diameter of the first stripe 239_1 (stripe diameter d1) is determined. For example, referring to FIG. 2B and FIG. 2C, the stripe diameter d1 may be determined based on data generated by the detector 240. In this example, the stripe diameter d1 may be the number of pixels between two points on either side of the first stripe 239_1, determined from the image data generated by the detector 240. Other implementations are possible, and the stripe diameters d1 and d2 may be determined in any manner.

[0046]

[0059] Based on the determined fringe diameter d1 and the initial value of the calibration value, a first wavelength value (λ1) is determined (420). For example, the first wavelength (λ1) may be determined using the initial value of the parameter 231, the order (m) of the first fringe 239_1, the known value of ND, and the fringe diameter d1 in Equation 1. Similarly, the diameter of the second fringe 239_2 (fringe diameter d2) is determined. Based on the determined fringe diameter d2 and the initial value of the calibration value, a second wavelength value (λ2) is determined (430). The second wavelength (λ2) may be determined using the initial value of the parameter 231, the order (m) of the second fringe 239_2, the known value of ND, and the fringe diameter d2 in Equation 1. The first fringe 239_1 and the second fringe 239_2 have consecutive orders. For example, if the order (m) of the first fringe 239_1 is 10.001, the order (m) of the second fringe 239_2 is 10.002.

[0047]

[0060] The first wavelength value (λ1) and the second wavelength value (λ2) are compared to determine a measurement error (440). The measurement error may be determined by finding the difference between the first wavelength value (λ1) and the second wavelength value (λ2). In the absence of a measurement error, the first wavelength value and the second wavelength value are the same since the light used to create the first fringes 239_1 and the second fringes 239_2 is the same. Thus, the difference between the first wavelength value (λ1) and the second wavelength value (λ2) is characteristic of the measurement error. This difference may be determined by subtracting the first wavelength value (λ1) from the second wavelength value (λ2), or vice versa. Furthermore, the measurement error may be the absolute value of the difference. Thus, the measurement error may be positive, negative, or zero (if there is no measurement error).

[0048]

[0061] The measurement error is compared to a specification to determine whether the calibration parameter 231 (FD in this example) should be adjusted. The specification may be a range of values, including positive and negative values, or a single threshold that is positive. The measurement error is compared to the specification to determine whether the value of the calibration parameter 231 should be adjusted (450). If the value of the calibration parameter 231 is within the specification or less than the threshold, the value of the calibration parameter 231 is correct and the process 400 returns to (410) to continue monitoring the measurement error. If the value of the calibration parameter 231 is out of specification, the value of the calibration parameter 231 is adjusted (460). The value of the calibration parameter 231 is adjusted until the first wavelength value (λ1) and the second wavelength value (λ2) are within the specification. For example, if the specification is zero, the value of the calibration parameter 231 is adjusted according to Equation 1 until the same wavelength value is obtained in the first fringe 239_1 and the second fringe 239_2.

[0049]

[0062] After the values ​​of the calibration parameters 231 are adjusted, the process 400 may return to (410) to continue monitoring the etalon measurement error or the process 400 may end. The adjusted values ​​of the calibration parameters 231 may be stored (470) in the electronic storage 252. In implementations in which the adjusted values ​​of the calibration parameters 231 are stored, the adjusted values ​​of the calibration parameters 231 may be used as the initial values ​​of the calibration parameters 231 in subsequent executions of the process 400. In some implementations, the adjusted calibration parameters 231 are not stored and / or are not used in subsequent executions of the process 400. In such implementations, the factory determined values ​​of the calibration parameters 231 are always used as the initial values ​​of the calibration parameters 231.

[0050]

[0063] FIG. 5 is a plot of exemplary data showing the measurement error as a function of the value of the calibration parameter 231 (FD). In the example of FIG. 5, the measurement error is the difference between a first wavelength value (λ1) determined in (420) and a second wavelength value (λ2) determined in (430). The factory determined value of the calibration parameter 231 was 18352 pixels. However, as shown in FIG. 5, using the factory determined value of the calibration parameter 231 resulted in a measurement error of about 2.5 femtometers (fm). The value of the calibration parameter 231 was varied through the range of values ​​shown in FIG. 5 to determine the measurement error at various values ​​of the calibration parameter 231. As shown in FIG. 5, when the value of the calibration parameter 231 was 18353 pixels, the measurement error was zero. The value of the calibration parameter 231 was adjusted to be equal to 18353 pixels, and the wavelength of the portion 116′ was measured using the interference fringes output by the etalon 130 and Equation 1 (using the updated value of FD). By adjusting the values ​​of the calibration parameters 231, measurement errors are removed so that the wavelength values ​​determined from the output of the etalon 230 are accurate.

[0051]

[0064] 6 is a flow diagram of a process 600. Process 600 is another example of a process for determining a measurement error of an etalon, such as etalon 130 or etalon 230. Process 600 is considered with respect to etalon 230 and control system 250.

[0052]

[0065] The initial values ​​of the calibration parameters 231 are changed (610) to the updated values. The initial values ​​of the calibration parameters 231 may be factory calibrated values, values ​​determined during previous operational use of the etalon 230, values ​​generated by an automated process (such as a random process), or values ​​provided by an operator of the control system 250. The initial values ​​of the calibration parameters 231 may be changed by adding a predetermined constant amount to the initial values ​​of the calibration parameters 231. In some implementations, the initial values ​​of the calibration parameters 231 are changed by a specific amount provided by an operator of the control system 250 or by a preprogrammed recipe or formula.

[0053]

[0066] The wavelength of the light in the portion 116' is changed (620). The wavelength of the light in the portion 116' is changed by a known amount. For example, by actuating an optical element (such as prism 922, 923, 924, or 925 in FIG. 9A) associated with the light source 110, the wavelength of the light in the portion 116' is changed by a known amount, thereby changing the wavelength of the light exiting the optical element by a known amount relative to the light entering the optical element. The process 600 then estimates the wavelength value of the light in the portion 116' using one or more instances of the interference fringes 239 output by the etalon 230, where each of the two instances is output at a different time from each other. For example, the light beam 116 (and the portion 116') may be a pulsed light beam that includes pulses of light, each separated from an adjacent pulse by a finite time during which the light generating module 110 does not emit light. In this example, a first instance of interference fringes 239 is generated by irradiating etalon 230 with a first pulse in portion 116', and a second instance of interference fringes 239 is generated by irradiating etalon 230 with a second pulse in portion 116'.

[0054]

[0067] A first wavelength value (λ1) is determined (630) using fringes from the first instance of the interference fringes 239. The first wavelength value (λ1) is determined using Equation 1, where m is the order of the fringes, FD is the updated value of the calibration parameters 231 determined in (610), and d is the diameter of the fringes. The first wavelength value (λ1) may be determined from two or more instances of the interference fringes 239. For example, the first wavelength value (λ1) may be determined from 50 or more instances of the interference fringes 239. Various values ​​of the first wavelength value (λ1) may be averaged together or otherwise filtered to remove or reduce noise, and the averaged or filtered value may be used as the first wavelength value (λ1).

[0055]

[0068] The wavelength of the light in the portion 116' is again changed (640). As in (620), the wavelength of the light in the portion 116' may be changed by the same known amount. A second wavelength value (λ2) is determined (650) using fringes from one or more instances of the interference fringes 239. The second wavelength value (λ2) is determined by using Equation 1 as described in (630), where m is the order of the fringes, FD is the updated value of the calibration parameters 231 determined in (610), and d is the diameter of the fringes. The second wavelength value (λ2) may be determined from two or more instances of the interference fringes 239. For example, the second wavelength value (λ2) may be determined 10, 50, or 100 times and then averaged to reduce the effects of noise and mechanical vibrations.

[0056]

[0069] A measurement error associated with the updated value of the calibration parameter 231 is determined (660). Taking into account the nominal sensitivity (NS) of the system controlling the actual wavelength of the portion 116' (in this example, the actuated optical element), the measurement error is the difference between the determined first wavelength value (λ1) and the determined second wavelength value (λ2). The nominal sensitivity is a constant value, which may be determined by the manufacturer and stored in the electronic storage 252. The nominal sensitivity is the amount of change in wavelength for a unit amount change in the optical element that determines the wavelength of the light incident on the etalon 230. For example, if the optical element is a prism coupled to a PZT actuator, the nominal sensitivity is the amount of wavelength change for each unit amount change in the prism position. The measurement error (ME) may be determined from Equation 2. ME = (S-NS)(OA) Equation (2) where ME is the measurement error, S is the current sensitivity, NS is the nominal sensitivity, and OA is a measure of the actuation of the optical element in units of distance. OA may be determined according to Equation 3: OA=P2-P1 Equation (3) where P2 is the position of the optical element when light having a second wavelength is provided by the optical element, and P1 is the position of the optical element when light having a first wavelength is provided by the optical element. The current sensitivity (S) is calculated based on the measured wavelength and the change in position of the optical element and may be determined from Equation 4.

number

[0057]

[0070] The measurement error (ME) is stored in electronic storage 252 or output via I / O interface 253 .

[0058]

[0071] Process 600 may return (610) to determine the measurement error (ME) for different updated values ​​of calibration parameters 231 and for another wavelength of portion 116' using (610)-(660) as described above. For example, the wavelength may be increased or decreased at (620) compared to the previous iteration of (610)-(660). In some implementations, each time process 600 returns (610), a counter is incremented (665) to keep track of how many times the measurement error has been determined.

[0059]

[0072] After the measurement error has been determined for more than one value of the calibration parameter 231, or for more than a specified number of values ​​of the calibration parameter 231, the determined calibration values ​​are analyzed (670). For example, the absolute value of the measurement error may be determined and a minimum error measurement found from the absolute value. The value of the calibration parameter 231 associated with this minimum error measurement is determined.

[0060]

[0073] For example, FIG. 7 shows two sets of measurement error values ​​in femtometers (fm) determined in pixel values ​​as a function of updated values ​​of calibration parameter 231. Each measurement error value in the first set is shown as a solid circle symbol. Each measurement error value in the second set is shown as a hollow circle symbol. The first set of measurement error values ​​was determined by performing (610)-(660) for a number of different values ​​of calibration parameter 231. Each time the value of calibration parameter 231 is updated to a different value of calibration parameter 231 in (610), an optical element (such as a prism) is actuated to increase the wavelength of light in portion 116′, and a measurement error is determined in (660). The second set is shown as plot 754. The second set of measurement error values ​​was determined by performing (610)-(660) for a number of different values ​​of calibration parameter 231. Each time the value of the calibration parameter 231 was updated in (610) to a different value of the calibration parameter 231, an optical element (such as a prism) was actuated to shorten the wavelength of the light in the portion 116'.

[0061]

[0074] The first set of measurements was fitted to a linear relationship 753 and the second set of measurements was fitted to a linear relationship 754. The value of FD corresponding to where linear relationship 753 and relationship 754 intersect is the minimum measurement error. As shown in FIG. 7, the slopes of relationship 753 and relationship 754 are opposite in magnitude but may differ in absolute value as well. The difference in absolute value may result from hysteresis in the actuator that moves the optical element. In the example of FIG. 7, the actuator is a piezoelectric actuator that is first compressed from its nominal dimension to actuate the prism to lengthen the wavelength (generating a first set of measurement error values) and then expanded back to its nominal dimension to shorten the wavelength (generating a second set of measurement error values). Mechanical effects resulting from compression and expansion resulted in a slightly different absolute value of the slope of relationship 753 compared to the absolute value of the slope of relationship 754.

[0062]

[0075] 7, the value of the calibration parameter 231 corresponding to the smallest measurement error was approximately 18369. In contrast, the preset default value of the calibration parameter 231 was approximately 18362, which is associated with a relatively high measurement error.

[0063]

[0076] The preset default values ​​of the calibration parameters 231 are adjusted 680 if using the default values ​​would result in a measurement error greater than specification. In the example of Figure 7, the preset default values ​​of the calibration parameters 231 would result in a measurement error value that exceeds specification, and the value of the calibration parameters 231 is adjusted 690 to the value of the calibration parameters 231 that corresponds to the minimum value of the measurement error. Process 600 then ends.

[0064]

[0077] 8A and 10 show examples of deep ultraviolet (DUV) optical systems in which the optical metrology instruments 160 or 260 may be used. In the following example, an optical metrology instrument 260 is shown for use in a DUV optical system.

[0065]

[0078] 8A and 8B, system 800 includes a light generating module 810 that provides an exposure beam (or output light beam) 816 to a scanner device 880. Light generating module 810 and scanner device 880 are implementations of light generating module 110 and device 180 (FIG. 1A), respectively.

[0066]

[0079] System 800 also includes a beam separator 117, an optical measurement device 260, and a control system 250. Beam separator 117 sends a portion of exposure beam 816 to optical measurement device 260, which is used to measure the wavelength of exposure beam 816. Control system 250 is coupled to optical measurement device 260. In the example of FIG. 8A , control system 250 is also coupled to light generating module 810 and various components associated with light generating module 810.

[0067]

[0080] The light generating module 810 comprises an optical oscillator 812. The optical oscillator 812 generates an output light beam 816. The optical oscillator 812 comprises a discharge chamber 815, which comprises a cathode 813-a and an anode 813-b. The discharge chamber 815 also includes a gaseous gain medium 819. A potential difference between the cathode 813-a and the anode 813-b creates an electric field in the gaseous gain medium 819. This potential difference may be created by controlling a voltage source 897 to apply a voltage to the cathode 813-a and / or the anode 813-b. This electric field provides sufficient energy to the gain medium 819 to cause population inversion and enable the generation of pulses of light by stimulated emission. Repeated creation of such a potential difference creates a series of pulses that are emitted as the light beam 816. The repetition rate of the pulsed light beam 816 is determined by the rate at which voltages are applied to the electrodes 813-a and 813-b.

[0068]

[0081] Gain medium 819 is pumped by applying a voltage to electrodes 813-a and 813-b. The duration and repetition rate of the pulses in pulsed optical beam 816 are determined by the duration and repetition rate of the voltage applied to electrodes 813-a and 813-b. The repetition rate of the pulses may range, for example, between about 500 Hz and 6,000 Hz. In some implementations, the repetition rate may be faster than 6,000 Hz, for example, 12,000 Hz or higher. Each pulse emitted from optical oscillator 812 may have a pulse energy of, for example, about 1 millijoule (mJ).

[0069]

[0082] The gaseous gain medium 819 may be any gas suitable for producing a light beam at the wavelength, energy, and bandwidth required for the application. The gaseous gain medium 819 may include more than one type of gas, and the various gases are referred to as gas compositions. In an excimer radiation source, the gaseous gain medium 819 may include a noble gas, such as argon or krypton, or a halogen, such as fluorine or chlorine. In implementations where a halogen is the gain medium, the gain medium also includes traces of xenon, apart from a buffer gas such as helium.

[0070]

[0083] The gaseous gain medium 819 may be a gain medium that emits light in the deep ultraviolet (DUV) range. DUV light may include, for example, wavelengths from about 100 nanometers (nm) to about 400 nm. Examples of gaseous gain medium 819 include argon fluoride (ArF), which emits light at a wavelength of about 193 nm, krypton fluoride (KrF), which emits light at a wavelength of about 248 nm, or xenon chloride (XeCl), which emits light at a wavelength of about 351 nm.

[0071]

[0084] A resonator is formed between a spectral conditioner 895 on one side of the discharge chamber 815 and an output coupler 896 on a second side of the discharge chamber 815. The spectral conditioner 895 may include, for example, a diffractive optical element such as a diffraction grating and / or a prism that fine-tunes the spectral output of the discharge chamber 815. The diffractive optical element may be reflective or refractive. In some implementations (such as shown in FIG. 9A ), the spectral conditioner 895 includes multiple diffractive optical elements. For example, the spectral conditioner 895 may include four prisms, some of which are configured to control the center wavelength of the light beam 816 and others of which are configured to control the spectral bandwidth of the light beam 816.

[0072]

[0085] 9A, there is shown a block diagram of a spectral conditioner 995. The spectral conditioner 995 may be used in the light-generating module 810 as the spectral conditioner 895.

[0073]

[0086] The spectral conditioner 995 includes a set of optical features or components 921, 922, 923, 924, 925 arranged to optically interact with the light beam 816. The control system 250 is connected to one or more actuation systems 921A, 922A, 923A, 924A, 925A that are physically coupled to the respective optical components 921, 922, 923, 924, 925. The actuation systems 921A, 922A, 923A, 924A, 925A may include a shaft (such as shaft 926A) that rotates the components coupled to the shaft about an axis parallel to the shaft. The actuation systems 921A, 922A, 923A, 924A, 925A also include electronics and mechanical devices, such as, for example, electronic interfaces and motors for communicating with the control system 250 and for receiving power.

[0074]

[0087] The optical component 921 is a dispersive optical element, such as a diffraction grating and / or a prism. In the example of FIG. 9A, the optical component 921 is a reflective diffraction grating including a diffractive surface 902. The optical components 922, 923, 924, and 925 are refractive optical elements, which may be prisms. The optical components 922, 923, 924, and 925 form a beam expander 901 having an optical magnification OM 965. The OM 965 of the light beam 816 passing through the beam expander 901 is the ratio of the lateral width Wo of the light beam 816 leaving the beam expander 901 to the lateral width Wi of the light beam 816 entering the beam expander 901.

[0075]

[0088] Surface 902 of diffraction grating 921 is made of a material that reflects and diffracts the wavelengths of light beam 816. Each of prisms 922, 923, 924, and 925 is a prism that acts to disperse and redirect light beam 816 as it passes through the body of the prism. Each of prisms 922, 923, 924, and 925 is made of a material that transmits the wavelengths in light beam 816. For example, if light beam 816 is in the DUV range, then prisms 922, 923, 924, and 925 are made of a material that transmits light in the DUV range (e.g., calcium fluoride, etc.).

[0076]

[0089] Prism 925 is located furthest from grating 921, and prism 922 is located closest to grating 921. Light beam 816 enters the spectral conditioner through aperture 955 and then travels through prism 925, prism 924, prism 923, and prism 922 (in that order). Each time light beam 816 passes through successive prisms 925, 924, 923, and 922, light beam 816 is optically expanded and redirected (refracted at an angle) towards the next optical component. After passing through prisms 925, 924, 923, and 922, light beam 816 reflects off surface 902. Light beam 816 then passes through prism 922, prism 923, prism 924, and prism 925 (in that order). With each successive prism 922, 923, 924, 925, light beam 816 is optically compressed as it travels toward aperture 955. After passing through prisms 922, 923, 924, and 925, light beam 816 exits spectral conditioner 995 through aperture 955. After exiting spectral conditioner 995, light beam 816 passes through chamber 815 and reflects off output coupler 896 back into chamber 815 and spectral conditioner 995.

[0077]

[0090] The spectral characteristics of the light beam 816 may be adjusted by changing the relative orientation of the optical components 921, 922, 923, 924, and / or 925. Referring to Fig. 9B, rotation of a prism P (which may be any of the prisms 922, 923, 924, or 925) about an axis perpendicular to the plane of the page changes the angle of incidence at which the light beam 816 strikes the entrance surface H(P) of the rotated prism P. Furthermore, two local optical properties of the light beam 816 passing through the rotated prism P, namely the optical magnification OM(P) and the beam refraction angle δ(P), are functions of the angle of incidence of the light beam 816 striking the entrance surface H(P) of the rotated prism P. The optical magnification OM(P) of a light beam 816 passing through a prism P is the ratio of the lateral width Wo(P) of the light beam 816A exiting the prism P to the lateral width Wi(P) of the light beam 816 entering the prism P.

[0078]

[0091] A change in the local optical magnification OM(P) of the light beam 816 at one or more of the prisms P inside the beam expander 901 causes an overall change in the optical magnification OM965 of the light beam 816 through the beam expander 901. Furthermore, a change in the local beam refraction angle δ(P) through one or more of the prisms P inside the beam expander 901 causes an overall change in the incidence angle 962 ( FIG. 9A ) of the light beam 816A at the surface 902 of the diffraction grating 921. The wavelength of the light beam 816 may be adjusted by changing the incidence angle 962 ( FIG. 9A ) at which the light beam 816 hits the surface 902 of the diffraction grating 921. The spectral bandwidth of the light beam 816 may be adjusted by changing the optical magnification 965 of the light beam 816.

[0079]

[0092] Thus, the spectral characteristics of the light beam 816 may be changed or adjusted by controlling the orientation of the diffraction grating 921 and / or one or more of the prisms 922, 923, 924, 925 via the respective actuators 921A, 922A, 923A, 924A, 925A. The actuators 921A, 922A, 923A, 924A, 925A may be, for example, piezoelectric actuators that change shape in response to the application of a voltage. Other implementations of the spectral adjustment device are possible.

[0080]

[0093] 8A , the spectral characteristics of the light beam 816 may be adjusted in other ways. For example, the spectral characteristics, such as the spectral bandwidth and center wavelength, of the light beam 816 may be adjusted by controlling the pressure and / or gas concentration of the gaseous gain medium in the chamber 815. For implementations in which the light-generating module 810 is an excimer radiation source, the spectral characteristics (e.g., the spectral bandwidth or center wavelength) of the light beam 816 may be adjusted by controlling the pressure and / or concentration of, for example, fluorine, chlorine, argon, krypton, xenon, and / or helium in the chamber 815.

[0081]

[0094] The pressure and / or concentration of the gaseous gain medium 819 can be controlled using a gas supply system 890. The gas supply system 890 is fluidly coupled to the interior of the discharge chamber 815 via a fluid conduit 889. The fluid conduit 889 is any conduit capable of carrying a gas or other fluid with no or minimal fluid loss. For example, the fluid conduit 889 can be a pipe made of or coated with a material that does not react with the fluid or fluids being carried in the fluid conduit 889. The gas supply system 890 includes a chamber 891 configured to contain and / or receive a supply of one or more gases used in the gain medium 819. The gas supply system 890 also includes devices (such as pumps, valves, and / or fluidic switches) that allow the gas supply system 890 to remove gas from or inject gas into the discharge chamber 815. The gas supply system 890 is coupled to the control system 250.

[0082]

[0095] The optical oscillator 812 also includes a spectrum analysis device 898. The spectrum analysis device 898 is a measurement system that may be used to measure or monitor the wavelength of the light beam 816. In the example shown in FIG. 8A, the spectrum analysis device 898 receives light from the output coupler 896. In some implementations, the spectrum analysis device 898 is part of the optical measurement device 260.

[0083]

[0096] The light generation module 810 may include other components and systems. For example, the light generation module 810 may include a beam preparation system 899. The beam preparation system 899 may include a pulse stretcher that stretches in time each pulse that interacts with the pulse stretcher. The beam preparation system may also include other components that can act on the light, such as, for example, reflective and / or refractive optical elements (e.g., lenses, mirrors, etc.) and / or filters. In the illustrated example, the beam preparation system 899 is located in the path of the exposure beam 816. However, the beam preparation system 899 may be located elsewhere in the system 800.

[0084]

[0097] The system 800 also includes a scanner apparatus 880. The scanner apparatus 880 exposes a wafer 882 with a shaped exposure beam 816A. The shaped exposure beam 816A is formed by passing the exposure beam 816 through a projection optical system 881. The scanner apparatus 880 may be an immersion system or a dry system. The scanner apparatus 880 includes a projection optical system 881 through which the exposure beam 816 passes before reaching the wafer 882, and a sensor or metrology system 870. The wafer 882 is held or received on a wafer holder 883. The scanner apparatus 880 may also include, for example, temperature control devices (such as air conditioning and / or heating devices) and / or power sources for various electrical components.

[0085]

[0098] Metrology system 870 includes a sensor 871. Sensor 871 may be configured to measure characteristics of shaped exposure beam 816A, such as, for example, bandwidth, energy, pulse duration, and / or wavelength. Sensor 871 may be, for example, a camera or other device capable of capturing an image of shaped exposure beam 816A at wafer 882, or may be an energy detector capable of capturing data indicative of the amount of optical energy at wafer 882 in the xy plane.

[0086]

[0099] 8B, the projection optical system 881 comprises a slit 884, a mask 885, and a projection objective including a lens system 886. The lens system 886 comprises one or more optical elements. The exposure beam 816 enters the scanner device 880 and impinges on the slit 884, and at least a portion of the output light beam 816 passes through the slit 884 to form the shaped exposure beam 816A. In the example of FIGS. 8A and 8B, the slit 884 is rectangular and shapes the exposure beam 816 into an elongated rectangular shaped light beam, which becomes the shaped exposure beam 816A. The mask 885 contains a pattern that determines which portions of the shaped light beam are transmitted and which portions are blocked by the mask 885. Microelectronic features are formed on the wafer 882 by exposing a layer of radiation-sensitive photoresist material on the wafer 882 to the exposure beam 816A. The design of the pattern on the mask is dictated by the particular microelectronic circuit function desired.

[0087]

[0100] The configuration shown in Figure 8A is an example of a configuration in a DUV system. Other implementations are possible. For example, light generation module 810 may include N instances of optical oscillators 812, where N is an integer equal to or greater than 1. In such implementations, each optical oscillator 812 is configured to emit a respective optical beam towards a beam combiner that forms an exposure beam 816.

[0088]

[0101] Another exemplary configuration of a DUV system is shown in Fig. 10. Fig. 10 is a block diagram of a photolithography system 1000 including a light generation module 1010 that generates a pulsed light beam 1016 that is provided to a scanner device 880. The photolithography system 1000 also includes a beam separator 117, an optical measurement device 260, and a control system 250. The control system 250 is coupled to the optical measurement device 260, various components of the light generation module 1010, and the scanner device 1080 to control various operations of the system 1000. In the example of Fig. 10, the beam separator 117 sends a portion of the output light beam 1016 to the optical measurement device 260. Other implementations are possible. For example, the beam separator 117 may be arranged to interact with the seed light beam 1018.

[0089]

[0102] The light generation module 1010 is a two-stage laser system that includes a master oscillator (MO) 1012_1 that provides a seed light beam 1018 to a power amplifier (PA) 1012_2. The PA 1012_2 receives the seed light beam 1018 from the MO 1012_1 and amplifies the seed light beam 1018 to generate a light beam 1016 for use in the scanner device 880. For example, in some implementations, the MO 1012_1 may emit a pulsed seed light beam having a seed pulse energy of about 1 millijoule (mJ) per pulse, and these seed pulses may be amplified by the PA 1012_2 to about 10-15 mJ, although other energies may be used in other embodiments.

[0090]

[0103] The MO 1012_1 includes a discharge chamber 1015_1 having two elongated electrodes 1013a_1 and 1013b_1, a gain medium 1019_1 that is a gas mixture, and a fan (not shown) for circulating the gas mixture between the electrodes 1013a_1 and 1013b_1. A resonator is formed between a line narrowing module 1095 on one side of the discharge chamber 1015_1 and an output coupler 1096 on a second side of the discharge chamber 1015_1.

[0091]

[0104] The discharge chamber 1015_1 includes a first chamber window 1063_1 and a second chamber window 1064_1. The first chamber window 1063_1 and the second chamber window 1064_1 are on opposite sides of the discharge chamber 1015_1. The first chamber window 1063_1 and the second chamber window 1064_1 transmit light in the DUV range and allow the DUV light to enter and exit the discharge chamber 1015_1.

[0092]

[0105] The line narrowing module 1095 may include a diffractive optical component S, such as a diffraction grating or prism (as shown in FIG. 9A ), that fine-tunes the spectral output of the discharge chamber 1015_1. The light generation module 1010 also includes a line center analysis module 1068 that receives the output light beam from the output coupler 1096, and a beam combining optical system 1069. The line center analysis module 1068 is a measurement system that may be used to measure or monitor the wavelength of the seed light beam 1018. The line center analysis module 1068 may be located elsewhere in the light generation module 1010 or may be located at the output of the light generation module 1010.

[0093]

[0106] The gas mixture, which is the gain medium 1019_1, can be any gas suitable for generating a light beam at the wavelength and bandwidth required for the application. In the case of an excimer radiation source, the gas mixture may include, for example, a noble gas such as argon or krypton, a halogen such as fluorine or chlorine, and a trace amount of xenon apart from a buffer gas such as helium. Specific examples of gas mixtures include argon fluoride (ArF), which emits light at a wavelength of about 193 nm, krypton fluoride (KrF), which emits light at a wavelength of about 248 nm, or xenon chloride (XeCl), which emits light at a wavelength of about 351 nm. Thus, in this implementation, the light beams 1016 and 1018 include wavelengths in the DUV range. The excimer gain medium (gas mixture) is pumped with a high-voltage discharge by applying a voltage to the elongated electrodes 1013a_1, 1013b_1 with short (e.g., nanosecond) current pulses.

[0094]

[0107] PA 1012_2 includes a beam combining optical system 1069 that receives the seed light beam 1018 from MO 1012_1 and directs the seed light beam 1018 through discharge chamber 1015_2 to beam rotation optical element 1092, which modifies or changes the direction of the seed light beam 1018 so that it is transmitted back to discharge chamber 1015_2. The beam rotation optical element 1092 and the beam combining optical system 1069 form a circular, closed-loop optical path in which the input to the ring amplifier intersects with the output of the ring amplifier at the beam combining optical system 1069.

[0095]

[0108] The discharge chamber 1015_2 includes a pair of elongated electrodes 1013a_2, 1013b_2, a gain medium 1019_2, and a fan (not shown) for circulating the gain medium 1019_2 between the electrodes 1013a_2 and 1013b_2. The gas mixture forming the gain medium 1019_2 can be the same as the gas mixture forming the gain medium 1019_1.

[0096]

[0109] The discharge chamber 1015_2 includes a first chamber window 1063_2 and a second chamber window 1064_2. The first chamber window 1063_2 and the second chamber window 1064_2 are on opposite sides of the discharge chamber 1015_2. The first chamber window 1063_2 and the second chamber window 1064_2 transmit light in the DUV range and allow the DUV light to enter and exit the discharge chamber 1015_2.

[0097]

[0110] When the gain medium 1019_1 or 1019_2 is pumped by applying a voltage to the electrodes 1013a_1, 1013b_1, or 1013a_2, 1013b_2, respectively, the gain medium 1019_1 and / or 1019_2 emits light. When a voltage is applied to the electrodes at regular time intervals, the light beam 1016 is pulsed. The repetition rate of the pulsed light beam 1016 is therefore determined by the rate at which the voltage is applied to the electrodes. The repetition rate of the pulses may range from about 500 to 6,000 Hz for various applications. In some implementations, the repetition rate may be greater than 6,000 Hz, for example, 12,000 Hz or greater, although other repetition rates may be used in other implementations.

[0098]

[0111] The output light beam 1016 may be directed through a beam preparation system 1099 before reaching the scanner instrument 880. The beam preparation system 1099 may include a bandwidth analysis module that measures various parameters of the beam 1016 (such as bandwidth or wavelength). The beam preparation system 1099 may also include a pulse stretcher that stretches each pulse of the output light beam 1016 in time. The beam preparation system 1099 may also include other components that may act on the beam 1016, such as, for example, reflective and / or refractive optical elements (such as lenses and mirrors), filters, and optical apertures (including automatic shutters).

[0099]

[0112] The DUV light generation module 1010 also includes a gas management system 1090 in fluid communication with the interior 1078 of the DUV light generation module 1010 .

[0100]

[0113] Other aspects of the invention are described in the following numbered clauses. 1. An optical measurement instrument for a light source, comprising: an etalon comprising a focusing lens configured to focus light onto an image plane, the etalon being associated with calibration parameters related to the focusing lens, the calibration parameters having pre-set default values; a photodetector configured to detect interference fringes produced by the etalon and generate information related to the etalon, the information including first spatial information about the first fringes and second spatial information about the second fringes; a control system coupled to the photodetector, determining a measurement error value of the etalon based on the first spatial information from the detector, the second spatial information, and an initial value of the calibration parameter; a control system configured to analyze the measurement error value to determine whether to adjust the preset default value; An optical measuring instrument comprising: 2. The optical measurement instrument of claim 1, wherein the light source comprises a deep ultraviolet (DUV) light source. 3. A light generating device; an etalon comprising a focusing lens configured to focus light onto an image plane, the etalon being associated with calibration parameters related to the focusing lens, the calibration parameters having pre-set default values; a photodetector configured to detect interference fringes produced by the etalon and generate information related to the etalon, the information including first spatial information about the first fringes and second spatial information about the second fringes; and a control system coupled to the photodetector, determining a measurement error value of the etalon based on the first spatial information, the second spatial information, and an initial value of the calibration parameter; A control system configured to analyze the measurement error values ​​to determine whether to adjust the pre-set default values. Optical measuring instruments including A light source comprising: 4. The light source of claim 3, wherein the light generating instrument comprises a deep ultraviolet (DUV) light source. 5. The light source according to clause 4, wherein the light generating device comprises a master oscillator. 6. The light source according to clause 4, wherein the light generating device further comprises a power amplifier. 7. The light source according to clause 4, wherein the light generating device comprises a plurality of master oscillators. 8. The light source of claim 3, further comprising an optical element configured to receive light from the light-generating device and send the light to the etalon. 9. The light source according to clause 8, wherein the optical element is a dispersive optical element. 10. Accessing information related to an etalon, the etalon being associated with calibration parameters having preset default values, the etalon being configured to generate an interference pattern including a plurality of fringes from a received light beam, the information related to the etalon including first spatial information related to a first fringe of the plurality of fringes and second spatial information related to a second fringe of the plurality of fringes; determining a first wavelength value of the received light beam based on spatial information associated with the first fringe and an initial value of a calibration parameter; determining a second wavelength value of the received light beam based on the spatial information associated with the second fringe and the initial value of the calibration parameter; comparing the first wavelength value to the second wavelength value to determine a measurement error value; A method comprising: 11. The method of claim 10, further comprising determining whether to adjust the preset default values ​​of the calibration parameters based on the measured error values. 12. The method of claim 11, wherein the measurement error value comprises a difference between a first wavelength value and a second wavelength value, and the preset default value is adjusted to a value such that the magnitude of the measurement error value is less than a threshold value. 13. The method according to clause 12, wherein the pre-set default value is adjusted to a value such that the measurement error value is zero. 14. The method of claim 10, wherein the calibration parameters include a focal length of the lens at the output of the etalon, and the measurement error includes a difference between the first wavelength value and the second wavelength value. 15. The method of claim 10, wherein the first spatial information comprises a diameter of a first fringe and the second spatial information comprises a diameter of a second fringe. 16. The method of claim 10, further comprising sending the light beam to an etalon, wherein a first fringe is generated by a first portion of the light beam and a second fringe is generated by a second portion of the light beam. 17. The method of claim 16, wherein the light beam comprises a plurality of pulses, a first portion of the light beam comprises a first pulse of the plurality of pulses, and a second portion of the light beam comprises a second pulse of the plurality of pulses. 18. The method of claim 16, wherein the light beam comprises a continuous wave light beam, the first portion of the light beam comprises a first sample of the light beam, and the second portion of the light beam comprises a second sample of the light beam. 19. Changing the initial value of the calibration parameter to the updated value of the calibration parameter; actuating an optical element to thereby change the wavelength of the received light beam; determining a first wavelength value of the received light beam based on the spatial information associated with the first fringe and the updated value of the calibration parameter; determining a second wavelength value of the received light beam based on the spatial information associated with the second fringe and the updated value of the calibration parameter; comparing the first wavelength value to the second wavelength value to determine a measurement error value based on the updated value of the calibration parameter; 17. The method of claim 16, further comprising: 20. The method of claim 19, wherein the optical element is actuated to increase the wavelength or decrease the wavelength before determining the second wavelength value. 21. The method of claim 19, wherein the first wavelength value and the second wavelength value are determined two or more times each time the optical element is actuated. 22. The method of clause 20, further comprising determining whether to adjust a preset default value of the calibration parameter by comparing an error measure determined based on an initial value of the calibration parameter with an error measure determined based on an updated value of the calibration parameter. 23. The method of claim 10, wherein the initial values ​​of the calibration parameters are preselected default values. 24. The method of claim 10, wherein the first fringe and the second fringe are simultaneously present within the interference pattern. 25. A method for calibrating an etalon, comprising the steps of: accessing information related to an etalon, the etalon being associated with calibration parameters having preset default values, the etalon being configured to generate an interference fringe from a received light beam, the interference fringe including a plurality of fringes, the information related to the etalon including first spatial information related to a first fringe of the plurality of fringes and second spatial information related to a second fringe of the plurality of fringes; determining a measurement error value of the etalon based on the first spatial information, the second spatial information, and an initial value of the calibration parameter; Analyzing the measurement error values ​​to determine whether to adjust the preset default values; A method comprising: 26. The method of claim 25, wherein the calibration parameters include the focal length of the lens at the output of the etalon. 27. Determining a first wavelength value based on the first spatial information; determining a second wavelength value based on the second spatial information; and Further comprising: 27. The method of claim 26, wherein the measurement error comprises a difference between the first wavelength value and the second wavelength value. 28. The calibration parameters include multiple initial values; Determining the measurement error value includes simulating a plurality of measurement error values ​​for each of a plurality of initial values, each measurement error value being based on one of the first spatial information, the second spatial information, and a plurality of initial values ​​of the calibration parameter; 26. The method of claim 25, wherein analyzing the measurement error values ​​includes analyzing simulated measurement error values.

[0101]

[0114] Other implementations are within the scope of the claims.

Claims

1. 1. An optical measurement instrument for a light source, comprising: an etalon comprising a focusing lens configured to focus light onto an image plane, the etalon having an output associated with a calibration parameter related to the focusing lens, the calibration parameter indicating a focal length of the focusing lens, the calibration parameter having a preset default value; a photodetector configured to detect interference fringes produced by the etalon and generate information related to the etalon, the information including first spatial information about a first fringe and second spatial information about a second fringe; and a control system coupled to the photodetector, determining a first wavelength value and a second wavelength value based on first spatial information from the detector, the second spatial information, and an initial value of the calibration parameter; determining a measurement error value of the etalon representing a difference or ratio between the first wavelength value and the second wavelength value; analyzing the measurement error values ​​to determine whether to adjust the calibration parameters; a control system configured to adjust the calibration parameters in response to an analysis of the measurement error values ​​to values ​​such that the magnitude of the measurement error values ​​is less than a threshold value; An optical measuring instrument comprising:

2. The optical measurement instrument of claim 1 , wherein the light source comprises a deep ultraviolet (DUV) light source.

3. A light generating device; an etalon comprising a focusing lens disposed at an output of the etalon and configured to focus light onto an image plane, the etalon being associated with a calibration parameter related to the focusing lens, the calibration parameter indicating a focal length of the focusing lens, the calibration parameter having a pre-set default value; a photodetector configured to detect interference fringes produced by the etalon and generate information related to the etalon, the information including first spatial information about a first fringe and second spatial information about a second fringe; and a control system coupled to the photodetector, determining a first wavelength value and a second wavelength value based on the first spatial information, the second spatial information, and an initial value of the calibration parameter; determining a measurement error value of the etalon representing a difference or ratio between the first wavelength value and the second wavelength value; analyzing the measurement error values ​​to determine whether to adjust the calibration parameters; a control system configured to adjust the calibration parameters in response to an analysis of the measurement error values ​​such that the magnitude of the measurement error values ​​is less than a threshold value. Optical measuring instruments including A light source comprising:

4. The light source of claim 3 , wherein the light-generating instrument comprises a deep ultraviolet (DUV) light source.

5. The light source of claim 4 , wherein the light generating device comprises a master oscillator.

6. The light source of claim 4 , wherein the light generating device further comprises a power amplifier.

7. The light source of claim 4 , wherein the light generating device comprises a plurality of master oscillators.

8. The light source of claim 3 , further comprising an optical element configured to receive light from the light-generating device and transmit light to the etalon.

9. The light source of claim 8 , wherein the optical element is a dispersive optical element.

10. 1. A method comprising: calibrating an etalon, the method comprising: accessing information related to an etalon comprising a focusing lens at an output of the etalon, the etalon being associated with calibration parameters having pre-set default values, the calibration parameters indicating a focal length of the focusing lens, the etalon being configured to generate an interference pattern comprising a plurality of fringes from a received light beam, the information related to the etalon including first spatial information related to a first fringe of the plurality of fringes and second spatial information related to a second fringe of the plurality of fringes; determining a first wavelength value of the received light beam based on the spatial information associated with the first fringe and an initial value of the calibration parameter; determining a second wavelength value of the received light beam based on the spatial information associated with the second fringe and the initial value of the calibration parameter; determining a measurement error value representing a difference or ratio between the first wavelength value and the second wavelength value; adjusting the calibration parameters in response to an analysis of the measurement error values ​​such that the magnitude of the measurement error values ​​is less than a threshold value; A method comprising:

11. The method of claim 10 , further comprising determining whether to adjust the pre-set default values ​​of the calibration parameters based on the measurement error values.

12. 12. The method of claim 11, wherein the measurement error value comprises a difference between the first wavelength value and the second wavelength value, and a preset default value is adjusted to a value such that the magnitude of the measurement error value is less than a threshold value.

13. The method of claim 12 , wherein the pre-set default value is adjusted to a value such that the measurement error value is zero.

14. 11. The method of claim 10, wherein the calibration parameter comprises a focal length of the lens at an output of the etalon, and the measurement error comprises a difference between the first wavelength value and the second wavelength value.

15. The method of claim 10 , wherein the first spatial information comprises a diameter of the first fringes and the second spatial information comprises a diameter of the second fringes.

16. 11. The method of claim 10, further comprising sending a light beam to the etalon, wherein the first fringes are generated by a first portion of the light beam and the second fringes are generated by a second portion of the light beam.

17. 17. The method of claim 16, wherein the light beam comprises a plurality of pulses, the first portion of the light beam comprises a first pulse of the plurality of pulses, and the second portion of the light beam comprises a second pulse of the plurality of pulses.

18. 17. The method of claim 16, wherein the light beam comprises a continuous wave light beam, the first portion of the light beam comprises a first sample of the light beam, and the second portion of the light beam comprises a second sample of the light beam.

19. changing the initial value of the calibration parameter to an updated value of the calibration parameter; actuating an optical element to thereby change the wavelength of the received light beam; determining a first wavelength value of the received light beam based on the spatial information associated with the first fringe and the updated value of the calibration parameter; determining a second wavelength value of the received light beam based on the spatial information associated with the second fringe and the updated value of the calibration parameter; comparing the first wavelength value to the second wavelength value to determine a measurement error value based on the updated value of the calibration parameter; 20. The method of claim 16, further comprising:

20. 20. The method of claim 19, further comprising actuating the optical element to increase the wavelength or decrease the wavelength before determining the second wavelength value.

21. 20. The method of claim 19, wherein the first wavelength value and the second wavelength value are determined two or more times for each actuation of the optical element.

22. 21. The method of claim 20, further comprising determining whether to adjust the preset default value of the calibration parameter by comparing the measurement error value determined based on the initial value of the calibration parameter and the measurement error value determined based on the updated value of the calibration parameter.

23. The method of claim 10 , wherein the initial values ​​of the calibration parameters are the pre-set default values.

24. The method of claim 10 , wherein the first fringe and the second fringe are present simultaneously within the interference pattern.

25. A method comprising calibrating an etalon, the calibrating comprising: accessing information related to an etalon comprising a focusing lens at an output of the etalon, the etalon being associated with calibration parameters having pre-set default values, the calibration parameters indicating a focal length of the focusing lens, the etalon being configured to generate an interference pattern comprising a plurality of fringes from a received light beam, the information related to the etalon including first spatial information related to a first fringe of the plurality of fringes and second spatial information related to a second fringe of the plurality of fringes; determining a first wavelength value and a second wavelength value based on the first spatial information, the second spatial information, and an initial value of the calibration parameter; determining a measurement error value of the etalon representing a difference or ratio between the first wavelength value and the second wavelength value; analyzing the measurement error values ​​to determine whether to adjust the calibration parameters; adjusting the calibration parameters in response to the analysis such that the magnitude of the measurement error value is less than a threshold value; A method comprising:

26. 26. The method of claim 25, wherein the calibration parameters include a focal length of the lens at the output of the etalon.

27. determining a first wavelength value based on the first spatial information; and determining a second wavelength value based on the second spatial information; and Further comprising:

27. The method of claim 26, wherein the measurement error comprises a difference between the first wavelength value and the second wavelength value.

28. the calibration parameters include a plurality of initial values; determining a measurement error value includes simulating a plurality of measurement error values ​​for each of the plurality of initial values, each measurement error value being based on the first spatial information, the second spatial information, and one of the plurality of initial values ​​of the calibration parameter; 26. The method of claim 25, wherein analyzing the measurement error values ​​comprises analyzing the simulated measurement error values.

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