Spectrometer, laser device, and method for determining peak position of reference light

Abstract

A spectrum meter for measuring the wavelength of laser light comprises: a mercury lamp in which natural mercury containing a plurality of isotopes is sealed, and which outputs reference light; a beam splitter that is positioned on the optical path of the reference light and the laser light, inputs the reference light, and outputs a first spectral waveform; and a processor capable of accessing a template waveform of a spectrum including a plurality of peak values of a known wavelength of the reference light, performing pattern matching using the first spectrum waveform and the template waveform, and determining a first peak value position corresponding to one of the plurality of peak values in the first spectrum waveform.

Description

Technical Field

[0001] The present disclosure relates to a spectrum detector, a laser device, and a method for determining the peak position of reference light. Background Art

[0002] In recent years, in semiconductor exposure apparatuses, with the miniaturization and high integration of semiconductor integrated circuits, an improvement in resolution has been required. Therefore, the shortening of the wavelength of light emitted from an exposure light source has been developed. For example, as a gas laser device for exposure, a KrF excimer laser device that uses a laser with an output wavelength of approximately 248 nm and an ArF excimer laser device that uses a laser with an output wavelength of approximately 193 nm are used.

[0003] The spectral line widths of the spontaneous oscillation lights of KrF excimer laser devices and ArF excimer laser devices are relatively wide, being 350 to 400 pm. Therefore, when a projection lens is formed of a material that transmits ultraviolet light such as KrF and ArF lasers, chromatic aberration sometimes occurs. As a result, the resolution may decrease. Therefore, it is necessary to narrow the spectral line width of the laser output from the gas laser device to a level where chromatic aberration can be ignored. Therefore, in the laser resonator of the gas laser device, in order to narrow the spectral line width, a line narrowing module (LNM) including a narrowing element (etalon, grating, etc.) is sometimes provided. Hereinafter, a gas laser device whose spectral line width has been narrowed will be referred to as a narrowed gas laser device.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Specification of U.S. Patent No. 5,243,614

[0007] Patent Document 2: Japanese Patent Laid-Open No. 05-167168

[0008] Patent Document 3: Specification of U.S. Patent No. 5,748,316

[0009] Patent Document 4: Specification of U.S. Patent Application Publication No. 2019 / 107438 Summary of the Invention

[0010] A spectrum detector according to one aspect of the present disclosure measures the wavelength of a laser, and the spectrum detector includes: a mercury lamp that encloses natural mercury containing a plurality of isotopes and outputs reference light; a spectroscope that is located on the optical path of the reference light and the laser, inputs the reference light, and outputs a first spectral waveform; and a processor that can access a template waveform of a spectrum including a plurality of known wavelength peaks of the reference light, performs pattern matching using the first spectral waveform and the template waveform, and determines a first peak position corresponding to one of the plurality of peaks in the first spectral waveform.

[0011] A laser device according to one aspect of the present disclosure includes a spectrometer, which includes: a mercury lamp that contains natural mercury including a plurality of isotopes and outputs reference light; a spectroscope that is located on the optical paths of the reference light and the laser, inputs the reference light, and outputs a first spectral waveform; and a processor that can access a template waveform of a spectrum including a plurality of peaks of known wavelengths of the reference light, performs pattern matching using the first spectral waveform and the template waveform, and determines a first peak position in the first spectral waveform corresponding to one of the plurality of peaks.

[0012] A method for determining the peak position of reference light according to one aspect of the present disclosure includes the following steps: causing the reference light output from the mercury lamp to be incident on the spectroscope to obtain a first spectral waveform, where the mercury lamp contains natural mercury including a plurality of isotopes; reading out a template waveform of a spectrum including a plurality of peaks of known wavelengths of the reference light; and performing pattern matching using the first spectral waveform and the template waveform to determine a first peak position in the first spectral waveform corresponding to one of the plurality of peaks. Description of the Drawings

[0013] Hereinafter, several embodiments of the present disclosure will be described only as examples with reference to the drawings.

[0014] Figure 1 The structure of the exposure system in the comparative example is schematically shown.

[0015] Figure 2 The structure of the laser device in the comparative example is schematically shown.

[0016] Figure 3 It is a flowchart of the wavelength control process in the comparative example.

[0017] Figure 4 It shows Figure 3 A flowchart showing the details of the process of detecting the interference fringes of the reference light shown.

[0018] Figure 5 It is a graph showing an example of the waveform of the interference fringes of the reference light.

[0019] Figure 6 It shows Figure 3 A flowchart showing the details of the process of detecting the interference fringes of the laser shown.

[0020] Figure 7 It is a graph showing an example of the waveform of the interference fringes in the case where a mercury lamp containing natural mercury is used as the light source of the reference light.

[0021] Figure 8 It is a graph showing the resonance wavelengths of the respective plurality of isotopes contained in natural mercury and the relative light amounts of each resonance wavelength.

[0022] Figure 9 Schematically shows the structure of the laser device according to the first embodiment.

[0023] Figure 10 Is a flowchart showing the details of the process of detecting the interference fringes of the reference light in the first embodiment.

[0024] Figure 11 Is to show Figure 10 Is a flowchart showing the details of the process of calculating the matching position shown.

[0025] Figure 12 Is a diagram for explaining the process of obtaining the center position of the interference fringes of the reference light.

[0026] Figure 13 Is a diagram for explaining the process of obtaining the center position of the interference fringes of the reference light.

[0027] Figure 14 Is a diagram for explaining the process of obtaining the center position of the interference fringes of the reference light.

[0028] Figure 15 Is a diagram for explaining the process of obtaining the center position of the interference fringes of the reference light.

[0029] Figure 16 Is a graph showing the waveform with the center position of the interference fringes of the reference light set as the origin.

[0030] Figure 17 Is a graph showing an example of the deformed waveform converted into the wavelength coordinate system.

[0031] Figure 18 Is to show in Figure 17 Is a graph showing the first example of the state where the template waveform is superimposed on the deformed waveform shown.

[0032] Figure 19 Is to show in Figure 17 Is a graph showing the second example of the state where the template waveform is superimposed on the deformed waveform shown.

[0033] Figure 20 Is to show Figure 17 Is a graph showing the normalized cross-correlation function of the deformed waveform and the template waveform shown.

[0034] Figure 21 Is a graph showing the waveform of the normalized cross-correlation function and the template waveform superimposed.

[0035] Figure 22 Is a graph showing another example of the deformed waveform converted into the wavelength coordinate system.

[0036] Figure 23 It is shown in Figure 22 The graph shown is a state where a template waveform is superimposed on a deformed waveform.

[0037] Figure 24 It is shown Figure 22 Shown is a graph of the normalized cross-correlation function of the deformed waveform and the template waveform.

[0038] Figure 25 The structure of a mercury lamp used in a laser device according to a second embodiment is shown.

[0039] Figure 26 The structure of a mercury lamp used in a laser device according to a second embodiment is shown.

[0040] Figure 27 Graph showing the relationship between the light emission time from the start of light emission and the mercury vapor pressure for a mercury lamp including a getter material and a mercury lamp not including a getter material.

[0041] Figure 28 Graph showing the relationship between the light emission time from the start of light emission and the light amount of a mercury lamp including a getter material and a mercury lamp not including a getter material.

[0042] Figure 29 The waveform of interference fringes of reference light generated using a mercury lamp containing a getter material is shown.

[0043] Figure 30 The waveform of interference fringes of reference light generated using a mercury lamp containing a getter material is shown.

[0044] Figure 31 The waveform of interference fringes of reference light generated using a defective mercury lamp that does not include a getter material is shown.

[0045] Figure 32 This is a flowchart showing details of a process for detecting interference fringes of reference light in the third embodiment.

[0046] Figure 33 This is a flowchart showing details of a process for detecting interference fringes of reference light in the third embodiment.

[0047] Figure 34 This is a flowchart showing details of the process of calculating the matching position in the fourth embodiment.

[0048] Figure 35 It is a graph for explaining a method of extracting a partial waveform.

[0049] Figure 36 It is a graph for explaining a method of updating a template waveform using a partial waveform. Detailed implementation mode

[0050] <Content>

[0051] 1. Comparative example

[0052] 1.1 Structure of exposure apparatus 100

[0053] 1.2 Operation of exposure apparatus 100

[0054] 1.3 Structure of laser device 1

[0055] 1.3.1 Laser oscillator 20

[0056] 1.3.2 Spectrum detector 16

[0057] 1.4 Operation

[0058] 1.4.1 Laser control processor 30

[0059] 1.4.2 Laser oscillator 20

[0060] 1.4.3 Spectrum detector 16

[0061] 1.4.4 Wavelength measurement processor 50

[0062] 1.4.5 Wavelength control

[0063] 1.4.5.1 Detection of interference fringes of reference light

[0064] 1.4.5.2 Detection of interference fringes of laser

[0065] 1.5 Problems of comparative example

[0066] 2. Spectrum detector 16 that performs pattern matching and measures interference fringes of reference light

[0067] 2.1 Structure

[0068] 2.2 Operation

[0069] 2.2.1 Calculation of matching position (Rhg) 2 of

[0070] 2.2.1.1 Determination of center position of interference fringes of reference light

[0071] 2.2.1.2 Conversion to wavelength coordinate system

[0072] 2.2.1.3 Cross-correlation function with template waveform T(i)

[0073] 2.2.1.4 Determination of matching position

[0074] 2.2.2 Coping with aliased waveforms

[0075] 2.3 Function

[0076] 3. The spectrometer 16 includes a mercury lamp 18n enclosing natural mercury and a getter material

[0077] 3.1 Structure

[0078] 3.2 Function

[0079] 4. The spectrometer 16 with an improved SN ratio

[0080] 4.1 Operation

[0081] 4.1.1 Acquisition of background waveform

[0082] 4.1.2 Improvement of SN ratio achieved by accumulation of interference fringes based on reference light

[0083] 4.1.3 Improvement of SN ratio achieved by subtracting the background waveform

[0084] 4.1.4 Pattern matching

[0085] 4.2 Function

[0086] 5. The spectrometer 16 that updates the template waveform T(i)

[0087] 5.1 Operation

[0088] 5.2 Function

[0089] 6. Others

[0090] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments described below show several examples of the present disclosure and do not limit the content of the present disclosure. In addition, the structures and operations described in each embodiment are not necessarily all essential to the structures and operations of the present disclosure. In addition, the same reference numerals are assigned to the same structural elements and repeated descriptions are omitted.

[0091] 1. Comparative example

[0092] Figure 1 Schematically shows the structure of the exposure system in the comparative example. The comparative example of the present disclosure is a method known only to the applicant and is not a publicly known example admitted by the applicant himself.

[0093] The exposure system includes a laser device 1 and an exposure device 100. The laser device 1 includes a laser control processor 30. The laser control processor 30 is a processing device that includes a memory 32 storing a control program and a CPU (central processing unit) 31 that executes the control program. The laser control processor 30 is specifically configured or programmed to execute various processes included in the present disclosure. The laser control processor 30 constitutes the processor in the present disclosure. The laser device 1 is configured to output laser light toward the exposure device 100.

[0094] 1.1 Structure of the exposure device 100

[0095] The exposure device 100 includes an illumination optical system 101, a projection optical system 102, and an exposure control processor 110. The illumination optical system 101 illuminates a mask pattern of an unillustrated mask disposed on a mask stage RT with the laser light incident from the laser device 1. The projection optical system 102 reduces and projects the laser light that has passed through the mask and forms an image on an unillustrated workpiece disposed on a workpiece stage WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with a resist film.

[0096] The exposure control processor 110 is a processing device that includes a memory 112 storing a control program and a CPU 111 that executes the control program. The exposure control processor 110 is specifically configured or programmed to execute various processes included in the present disclosure. The exposure control processor 110 coordinates the control of the exposure device 100 and exchanges various data and various signals with the laser control processor 30.

[0097] 1.2 Operation of the exposure device 100

[0098] The exposure control processor 110 sends setting data of a target wavelength and a target pulse energy and a trigger signal to the laser control processor 30. The laser control processor 30 controls the laser device 1 according to these data and signals. The exposure control processor 110 causes the mask stage RT and the workpiece stage WT to move synchronously in opposite directions parallel to each other. Thereby, the workpiece is exposed with the laser light reflecting the mask pattern.

[0099] The mask pattern is transferred onto the semiconductor wafer through this exposure process. Then, electronic devices can be manufactured through multiple processes.

[0100] 1.3 Structure of the laser device 1

[0101] Figure 2 The structure of the laser device 1 of the comparative example is schematically shown. The laser device 1 includes a laser oscillator 20, a spectrometer 16, and a laser control processor 30. The laser device 1 can be connected to the exposure device 100.

[0102] 1.3.1 Laser oscillator 20

[0103] The laser oscillator 20 includes a laser cavity 10, discharge electrodes 11a, a power supply 12, a narrowbanding module 14, and an output coupling mirror 15.

[0104] The narrowbanding module 14 and the output coupling mirror 15 constitute a laser resonator. The laser cavity 10 is arranged on the optical path of the laser resonator. Windows 10a and 10b are provided at both ends of the laser cavity 10. Inside the laser cavity 10, a discharge electrode 11a and an unillustrated discharge electrode paired with it are arranged. The unillustrated discharge electrode is located at a position overlapping the discharge electrode 11a in the V-axis direction perpendicular to the paper surface. For example, a laser gas is enclosed in the laser cavity 10, and the laser gas includes krypton gas as a noble gas, fluorine gas as a halogen gas, neon gas as a buffer gas, and the like.

[0105] The power supply 12 includes a switch 13 and is connected to the discharge electrode 11a and an unillustrated charger.

[0106] The narrowbanding module 14 includes a plurality of prisms 14a and 14b and a grating 14c. The prisms 14a and 14b are sequentially arranged on the optical path of the light emitted from the window 10a. The surfaces of the prisms 14a and 14b for light incident and emission are both parallel to the V-axis. The prism 14b is supported by a rotary stage 14e. The rotary stage 14e is connected to a wavelength driver 51. The grating 14c is arranged on the optical path of the light that has passed through the prisms 14a and 14b. The direction of the grooves of the grating 14c is parallel to the V-axis.

[0107] The output coupling mirror 15 is a partial reflector with a partial reflection film coated on one surface and a reflection suppression film coated on the other surface.

[0108] 1.3.2 Spectrum detector 16

[0109] The spectrum detector 16 is arranged on the optical path of the laser between the output coupling mirror 15 and the exposure device 100. The spectrum detector 16 includes a beam splitter 16a and 16b, an energy sensor 16c, a shutter 17a, a condenser lens 17c, a spectroscope 18, a mercury lamp 18g, a lamp power supply 18h, and a wavelength measurement processor 50. The wavelength measurement processor 50 corresponds to the processor in the present disclosure.

[0110] The beam splitter 16a is located on the optical path of the laser output from the output coupling mirror 15. The beam splitter 16a is configured to transmit a part of the laser to the exposure device 100 with a high transmittance and reflect the other part. The beam splitter 16b is located on the optical path of the laser reflected by the beam splitter 16a. The energy sensor 16c is located on the optical path of the laser reflected by the beam splitter 16b. The energy sensor 16c is composed of a photodiode, a phototube, or a thermoelectric element.

[0111] The shutter 17a is located on the optical path of the laser after passing through the beam splitter 16b. The shutter 17a can be switched between an open state and a closed state by an actuator 17b.

[0112] The condenser lens 17c is located on the optical path of the laser after passing through the shutter 17a in the open state. The shutter 17a in the closed state does not allow the laser to pass through and does not allow the laser to reach the condenser lens 17c.

[0113] The mercury lamp 18g is a hot cathode type low-pressure mercury lamp filled with mercury in which the proportion of the isotope with a mass number of 202 is 90% or more. The mercury lamp 18g is configured to be supplied with power from the lamp power supply 18h and output reference light. The reference light output by the mercury lamp 18g contains a relatively large wavelength component of approximately 253.7 nm.

[0114] The spectroscope 18 is located on the optical paths of these lights so that both the laser after passing through the condenser lens 17c and the reference light emitted by the mercury lamp 18g are incident. The spectroscope 18 includes a diffusion plate 18a, an etalon 18b, a condenser lens 18c, a line sensor 18d, a beam splitter 18e, a filter 18f, and a housing 18i. The etalon 18b and the beam splitter 18e are housed inside the housing 18i. The diffusion plate 18a, the condenser lens 18c, and the filter 18f are mounted on the housing 18i.

[0115] The diffusion plate 18a is located on the optical path of the laser converged by the condenser lens 17c. The diffusion plate 18a has a plurality of irregularities on its surface and is configured to allow the laser to pass through from the outside of the housing 18i to the inside of the housing 18i and diffuse it.

[0116] The filter 18f is a band-pass filter that allows the wavelength components of the reference light emitted by the mercury lamp 18g to pass through. The filter 18f is configured to allow the reference light to pass through from the outside of the housing 18i to the inside of the housing 18i.

[0117] The beam splitter 18e is disposed at the position where the optical path of the laser after passing through the diffusion plate 18a and the optical path of the reference light after passing through the filter 18f intersect. The beam splitter 18e is configured to allow the laser containing the wavelength component of approximately 248.4 nm to pass through and reflect the reference light containing the wavelength component of approximately 253.7 nm.

[0118] The laser after passing through the beam splitter 18e and the reference light reflected by the beam splitter 18e have substantially the same divergence angle. These lights are incident on the etalon 18b through substantially the same optical path.

[0119] The etalon 18b includes two partial reflectors. The two partial reflectors face each other with an air gap of a specified distance and are bonded with a spacer in between. The two partial reflectors each have a specified reflectivity for a laser beam containing a wavelength component of approximately 248.4 nm and a reference light beam containing a wavelength component of approximately 253.7 nm. The condenser lens 18c is located on the optical paths of the laser beam and the reference light beam that have passed through the etalon 18b.

[0120] The line sensor 18d is located on the focal plane of the condenser lens 18c on the optical paths of the laser beam and the reference light beam that have passed through the condenser lens 18c. The line sensor 18d is a light distribution sensor including a plurality of light receiving elements arranged in a one-dimensional array. Alternatively, instead of the line sensor 18d, a photodiode array may be used, or an image sensor including a plurality of light receiving elements arranged in a two-dimensional array may be used.

[0121] The line sensor 18d receives the interference fringes formed by the etalon 18b and the condenser lens 18c. The interference fringes are an interference pattern of the laser beam or the reference light beam, have a concentric shape, and the square of the distance from the center of the concentric circles is proportional to the change in wavelength. The waveform of the interference fringes is also referred to as the fringe waveform.

[0122] The line sensor 18d is configured to send the waveform data of the interference fringes formed by the etalon 18b and the condenser lens 18c to the wavelength measurement processor 50. The line sensor 18d may also detect the integrated light amount obtained by integrating the light amount of each light receiving element over time, and set the integrated waveform representing the distribution of the integrated light amount as the waveform data of the interference fringes.

[0123] The wavelength measurement processor 50 is a processing device including a memory 61 storing a control program and a CPU 62 executing the control program. The wavelength measurement processor 50 is specifically configured or programmed to execute various processes included in the present disclosure.

[0124] In the present disclosure, the laser control processor 30 and the wavelength measurement processor 50 are described as different structural elements, but the laser control processor 30 may also serve as the wavelength measurement processor 50.

[0125] 1.4 Operations

[0126] 1.4.1 Laser Control Processor 30

[0127] The laser control processor 30 sends the set data of the applied voltage to be applied to the discharge electrode 11a to the power supply 12 according to the set data of the target pulse energy received from the exposure control processor 110. The laser control processor 30 sends a drive signal based on the set data of the target wavelength received from the exposure control processor 110 to the wavelength driver 51. In addition, the laser control processor 30 sends an oscillation trigger signal based on the trigger signal received from the exposure control processor 110 to the switch 13 included in the power supply 12.

[0128] 1.4.2 Laser oscillator 20

[0129] The switch 13 becomes in an on state when receiving the oscillation trigger signal from the laser control processor 30. When the switch 13 becomes in an on state, the power supply 12 generates a pulsed high voltage according to the electric energy charged by a charger (not shown), and applies the high voltage to the discharge electrode 11a.

[0130] When applying the high voltage to the discharge electrode 11a, a discharge occurs inside the laser cavity 10. By the energy of this discharge, the laser medium inside the laser cavity 10 is excited and transitions to a higher energy level. Then, when the excited laser medium transitions to a lower energy level, light corresponding to the energy level difference is emitted.

[0131] The light generated inside the laser cavity 10 exits to the outside of the laser cavity 10 through the windows 10a and 10b. The prism 14a and 14b expand the beam width of the light exiting from the window 10a of the laser cavity 10 and make it incident on the grating 14c. The light incident on the grating 14c from the prism 14a and 14b is reflected by the multiple grooves of the grating 14c and diffracted in the direction corresponding to the wavelength of the light. The prism 14a and 14b narrow the beam width of the diffracted light from the grating 14c and make this light return to the laser cavity 10 through the window 10a.

[0132] The output coupler mirror 15 allows a part of the light exiting from the window 10b of the laser cavity 10 to pass through and outputs it, and reflects another part and returns it to the inside of the laser cavity 10 through the window 10b.

[0133] In this way, the light exiting from the laser cavity 10 travels back and forth between the narrowbanding module 14 and the output coupler mirror 15 and is amplified each time passing through the discharge space inside the laser cavity 10. This light is narrowed each time it turns back in the narrowbanding module 14. In this way, the light that undergoes laser oscillation and is narrowed in the laser oscillator 20 is output as laser light from the output coupler mirror 15.

[0134] The rotating table 14e included in the narrowbanding module 14 rotates the prism 14b about an axis parallel to the V axis according to the drive signal output from the wavelength driver 51. By rotating the prism 14b, the selected wavelength of the narrowbanding module 14 is adjusted, and the center wavelength of the laser is adjusted.

[0135] 1.4.3 Spectrometer 16

[0136] The energy sensor 16c detects the pulse energy of the laser and outputs the data of the pulse energy to the laser control processor 30 and the wavelength measurement processor 50. The data of the pulse energy is used by the laser control processor 30 for feedback control of the set data of the applied voltage applied to the discharge electrode 11a. In addition, the electrical signal including the data of the pulse energy can be used by the wavelength measurement processor 50 to count the number of pulses of the laser.

[0137] In the beam splitter 18, data of the waveform of the interference fringe is generated based on the light quantity of each light receiving element included in the line sensor 18d that receives the interference fringe.

[0138] 1.4.4 Wavelength Measurement Processor 50

[0139] The wavelength measurement processor 50 controls the opening and closing of the shutter 17a implemented based on the actuator 17b. In addition, the wavelength measurement processor 50 controls the lighting and extinguishing of the mercury lamp 18g implemented based on the lamp power supply 18h. When the wavelength measurement processor 50 obtains the waveform of the interference fringe of the reference light, it closes the shutter 17a and lights the mercury lamp 18g. Then, the wavelength measurement processor 50 outputs a data output trigger to the line sensor 18d. Then, the wavelength measurement processor 50 receives the waveform data of the interference fringe output from the line sensor 18d. Thus, the waveform data of the interference fringe of the reference light with a known specific wavelength is obtained.

[0140] When the wavelength measurement processor 50 measures the wavelength of the laser, it extinguishes the mercury lamp 18g and opens the shutter 17a. The wavelength measurement processor 50 receives the measurement signal of the pulse energy from the energy sensor 16c, counts the number of pulses of the laser, and sends a data output trigger to the line sensor 18d according to a certain cumulative number of pulses. Then, the wavelength measurement processor 50 receives the waveform data of the interference fringe output from the line sensor 18d. Thus, the waveform data of the interference fringe of the laser with an unknown wavelength is obtained. The wavelength measurement processor 50 calculates the absolute wavelength λabs of the laser based on the radius of the interference fringe of the laser and the radius of the interference fringe of the reference light.

[0141] The wavelength measurement processor 50 transmits the calculation result of the absolute wavelength λabs of the laser to the laser control processor 30. Based on the absolute wavelength λabs of the laser received from the wavelength measurement processor 50 and the set data of the target wavelength λt received from the exposure control processor 110, the laser control processor 30 transmits a control signal to the wavelength driver 51. The rotating table 14e of the holder that supports the prism 14b is driven by the wavelength driver 51, and the prism 14b rotates about an axis parallel to the V direction. As a result, the incident angle at which the incident light enters the grating 14c changes, and the selected wavelength changes.

[0142] 1.4.5 Wavelength Control

[0143] Figure 3 This is a flowchart of the wavelength control process in the comparative example. Through the processes described below, the wavelength measurement processor 50 measures the interference fringes of the reference light and the interference fringes of the laser, calculates the absolute wavelength λabs of the laser, and the laser control processor 30 performs feedback control on the central wavelength of the laser.

[0144] In S100, the wavelength measurement processor 50 transmits a measurement start signal for the reference light to the laser control processor 30. The laser control processor 30 transmits a signal permitting the start of the measurement of the reference light to the wavelength measurement processor 50. After receiving the signal permitting the start of the measurement of the reference light, the wavelength measurement processor 50 advances the process to S200.

[0145] In S200, the wavelength measurement processor 50 resets and starts the timer T1 for the measurement interval of the reference light measurement.

[0146] In S300, the wavelength measurement processor 50 detects the interference fringes of the reference light and calculates the radius Rhg of the interference fringes of the reference light. For the details of the process in S300, refer to Figure 4 and Figure 5 which will be described later.

[0147] In S500, the wavelength measurement processor 50 transmits a measurement end signal for the reference light to the laser control processor 30. In addition, the laser control processor 30 receives the set data of the target wavelength λt of the laser from the exposure control processor 110.

[0148] In S600, the wavelength measurement processor 50 detects the interference fringes of the laser and calculates the radius Rex of the interference fringes of the laser based on the peak position of the interference fringes of the laser. The interference fringes of the laser correspond to the second spectral waveform in the present disclosure, and the peak position of the interference fringes of the laser corresponds to the second peak position in the present disclosure. For the details of the process in S600, refer to Figure 6 which will be described later.

[0149] In S700, the wavelength measurement processor 50 calculates the absolute wavelength λabs of the laser by the following formula and sends the calculation result to the laser control processor 30.

[0150] λabs = A((Rex) 2 -(Rhg) 2 ) + λc

[0151] Here, λc is the offset wavelength, which is a constant corresponding to the absolute wavelength of the laser when the radius Rex of the interference fringes of the laser is equal to the radius Rhg of the interference fringes of the reference light. A is a positive number given as a proportionality constant. When (Rex) 2 and (Rhg) 2 are given on a wavelength scale, the proportionality constant A becomes 1.

[0152] In S800, the laser control processor 30 receives the absolute wavelength λabs of the laser from the wavelength measurement processor 50 and calculates the difference Δλ between the absolute wavelength λabs of the laser and the target wavelength λt by the following formula.

[0153] Δλ = λabs - λt

[0154] The laser control processor 30 controls the turntable 14e to make the difference Δλ approach 0. In this way, the laser control processor 30 performs feedback control on the central wavelength of the laser to make the absolute wavelength λabs approach the target wavelength λt.

[0155] In S900, the wavelength measurement processor 50 determines whether the value of the timer T1 has reached the threshold K1. If the value of the timer T1 has not reached the threshold K1 (S900: No), the wavelength measurement processor 50 proceeds to S1000. In S1000, the wavelength measurement processor 50 determines whether to abort the wavelength control. If the wavelength control is aborted (S1000: Yes), the wavelength measurement processor 50 ends the processing of this flowchart. If the wavelength control is not aborted (S1000: No), the wavelength measurement processor 50 returns the processing to S600.

[0156] If the value of the timer T1 has reached the threshold K1 (S900: Yes), the wavelength measurement processor 50 returns the processing to S100 and updates the radius Rhg of the interference fringes of the reference light by performing the subsequent processing.

[0157] As described above, the frequency of detecting the interference fringes of the reference light can be lower than the frequency of detecting the interference fringes of the laser. The threshold K1 set for the period of detecting the interference fringes of the reference light can also be 5 minutes or more. If the characteristics of the etalon 18b are stable, the threshold K1 can be 1 day or more and 1 week or less.

[0158] 1.4.5.1 Detection of interference fringes of reference light

[0159] Figure 4 It shows Figure 3 The flowchart showing the details of the process for detecting the interference fringes of the reference light shown Figure 4 The process shown is used as Figure 3 A subroutine of S300 shown is performed by the wavelength measurement processor 50

[0160] In S310, the wavelength measurement processor 50 controls the actuator 17b to close the shutter 17a to limit the incidence of the laser

[0161] In S350, the wavelength measurement processor 50 resets and starts the timer T2 that measures the time from when the mercury lamp 18g starts emitting light to when the line sensor 18d starts exposure, and controls the lamp power supply 18h to cause the mercury lamp 18g to start emitting light

[0162] In S360, the wavelength measurement processor 50 determines whether the value of the timer T2 has reached the threshold K2. The threshold K2 can be, for example, 0.5 seconds or more and 2 seconds or less. If the value of the timer T2 has not reached the threshold K2 (S360: No), the wavelength measurement processor 50 waits until the value of the timer T2 reaches the threshold K2. If the value of the timer T2 has reached the threshold K2 (S360: Yes), the wavelength measurement processor 50 proceeds to S390

[0163] In S390, the wavelength measurement processor 50 starts the exposure of the line sensor 18d, and resets and starts the timer T5 for measuring the time until the exposure of the line sensor 18d ends

[0164] In S400, the wavelength measurement processor 50 determines whether the value of the timer T5 has reached the threshold K5. The threshold K5 can be, for example, 2 seconds or more and 3 seconds or less. If the value of the timer T5 has not reached the threshold K5 (S400: No), the wavelength measurement processor 50 waits until the value of the timer T5 reaches the threshold K5 and continues the exposure of the line sensor 18d. If the value of the timer T5 has reached the threshold K5 (S400: Yes), the wavelength measurement processor 50 proceeds to S410

[0165] In S410, the wavelength measurement processor 50 outputs a data output trigger to the line sensor 18d. Thereby, the wavelength measurement processor 50 ends the exposure of the line sensor 18d. In addition, the wavelength measurement processor 50 reads out the data of the interference fringes of the reference light from the line sensor 18d

[0166] In S430, the wavelength measurement processor 50 controls the lamp power supply 18h to turn off the mercury lamp 18g.

[0167] In S450, the wavelength measurement processor 50 calculates the radius Rhg of the interference fringe of the reference light based on the data of the interference fringes. The square of the radius Rhg of the interference fringe of the reference light is used in Figure 3 S700 for calculating the absolute wavelength λabs of the laser.

[0168] In S460, the wavelength measurement processor 50 controls the actuator 17b to open the shutter 17a. Then, the wavelength measurement processor 50 ends the processing of this flowchart and returns to Figure 3 the processing.

[0169] Figure 5 is a graph showing an example of the waveform of the interference fringe of the reference light. Figure 5 The horizontal axis of represents the channel number, and the vertical axis represents the light quantity. The channel number corresponds to the position of each light-receiving element included in the line sensor 18d. The light quantity is represented by the count number. When measuring the concentric interference fringes using the line sensor 18d, a waveform that is approximately symmetric about the left and right is obtained.

[0170] In Figure 5 the waveform of the interference fringe of the reference light shown, the method for calculating the radius Rhg of the interference fringe is as follows, for example. Scanning the light quantity data from the position of the approximate center of the interference fringe in the right direction, determining the pair of the first point that crosses the threshold in the upward direction and the second point that crosses the threshold in the downward direction. In Figure 5 , an arrow in the upper right direction is shown near the first point, and an arrow in the lower right direction is shown near the second point. Similarly, scanning the light quantity data from the position of the approximate center of the interference fringe in the left direction, determining the pair of the third point that crosses the threshold in the upward direction and the fourth point that crosses the threshold in the downward direction. In Figure 5 , an arrow in the upper left direction is shown near the third point, and an arrow in the lower left direction is shown near the fourth point.

[0171] The distance between the position where the light quantity becomes the peak between the first point and the second point and the position where the light quantity becomes the peak between the third point and the fourth point is equivalent to twice the radius Rhg of the interference fringe of the reference light. Therefore, the radius Rhg can be calculated based on this distance.

[0172] 1.4.5.2 Detection of the Interference Fringe of the Laser

[0173] Figure 6 is a flowchart showing the details of the process for detecting the interference fringe of the Figure 3 laser shown. Figure 6 The process shown is used as Figure 3The subroutine of S600 shown is performed by the wavelength measurement processor 50.

[0174] In S610, the wavelength measurement processor 50 determines whether laser oscillation has occurred. For example, it is determined whether laser oscillation has occurred based on whether the wavelength measurement processor 50 has received an electrical signal generated when the energy sensor 16c detects the pulse energy of the laser.

[0175] In S620, the wavelength measurement processor 50 outputs a data output trigger to the line sensor 18d. Thereby, the wavelength measurement processor 50 receives data of the interference fringes of one pulse of the laser from the line sensor 18d. Alternatively, the wavelength measurement processor 50 may also cause the line sensor 18d to perform exposure for a certain period of time, thereby receiving data of the interference fringes obtained by accumulating the light amounts of the respective light-receiving elements with multiple pulses included in the laser.

[0176] In S630, the wavelength measurement processor 50 calculates the radius Rex of the interference fringes of the laser based on the data of the interference fringes. The method for calculating the radius Rex of the interference fringes of the laser may be the same as the method described with reference to Figure 5 The square of the radius of the interference fringes of the laser (Rex) 2 In Figure 3 of S700 is used for the calculation of the absolute wavelength λabs of the laser. Then, the wavelength measurement processor 50 ends the processing of this flowchart and returns to Figure 3 the processing.

[0177] 1.5 Problems of the Comparative Example

[0178] Figure 7 is a graph showing an example of the waveform of the interference fringes in the case where a mercury lamp filled with natural mercury is used as the light source of the reference light. Figure 8 is a graph showing the resonance wavelengths of the multiple isotopes contained in natural mercury and the relative light amounts for each resonance wavelength. Figure 8 The numerical values on the horizontal axis of

[0179] represent the wavelength differences of the resonance wavelengths of other isotope mercuries with respect to the resonance wavelength of the isotope mercury with a mass number of 198. In natural mercury, six stable isotopes are contained in a component ratio with an error of approximately 1% or less. In the spectroscope 18 where the resonance wavelengths of the isotope mercuries with mass numbers 198 and 201 cannot be distinguished, the spectrum of the resonance wavelengths of natural mercury is observed as five peaks.

[0180] On the other hand, in the case of using natural mercury, it is difficult to determine the peak position of the interference fringes. For example, if referring to Figure 5If the threshold value of the described light quantity changes, which of the five peaks enters between the above-mentioned first and second points or between the third and fourth points changes, and the radius Rhg of the measured interference fringes also changes. Even if the threshold value of the light quantity is constant, if the light quantity of the interference fringes changes or noise enters, the radius Rhg of the measured interference fringes also changes. Therefore, accurate measurement cannot be performed by the existing detection method.

[0181] The embodiment described below relates to a technique for accurately determining the peak position based on the spectral waveform of reference light emitted from a mercury lamp in which natural mercury containing multiple isotopes is enclosed.

[0182] 2. A spectrometer 16 that performs pattern matching and measures the interference fringes of the reference light

[0183] 2.1 Structure

[0184] Figure 9 The structure of the laser device 1a of the first embodiment is schematically shown. In the laser device 1a of the first embodiment, as a light source that outputs reference light, a mercury lamp 18n in which natural mercury containing multiple isotopes is enclosed is used. In addition, the wavelength measurement processor 50 can access the template waveform T(i) stored inside the memory 61. The template waveform T(i) is a spectral waveform including multiple peaks of known wavelengths of the reference light, and is created based on the spectral waveform of the reference light. For example, it may also be created for each spectrometer 18 based on the waveform of the interference fringes of the reference light measured using a specific spectrometer 18. Alternatively, the template waveform T(i) may be created by averaging in such a way that the peaks of the waveforms of the interference fringes of the reference light measured using multiple spectrometers 18 are superimposed, so that it can also be used for different spectrometers 18. The template waveform T(i) is not limited to being stored in the memory 61, and the wavelength measurement processor 50 may also access the template waveform T(i) stored in other storage devices.

[0185] 2.2 Operation

[0186] Figure 10 It is a flowchart showing the details of the process of detecting the interference fringes of the reference light in the first embodiment. Figure 10 The process shown is performed by the wavelength measurement processor 50 as a subroutine of Figure 3 shown S300. The processes of S310 to S430 and S460 are the same as those of the comparative example described with reference to Figure 4 , and instead of Figure 4 S450, the process of Figure 10 S450a is performed.

[0187] In S450a, the wavelength measurement processor 50 calculates the matching position (Rhg) between the deformed waveform I(m), obtained by deforming the waveform of the interference fringes of the reference light into a waveform corresponding to the wavelength coordinate system, and the template waveform T(i). 2 . Refer to Figure 3 the square of the radius (Rhg) of the interference fringes of the reference light in the comparative example described 2 and the matching position (Rhg) 2 . The relationship will be described later. In the first embodiment, the matching position (Rhg) 2 is used in Figure 3 S700 for calculating the absolute wavelength λabs of the laser.

[0188] 2.2.1 Calculation of the matching position (Rhg) 2 is

[0189] Figure 11 a flowchart showing the details of the process for calculating the matching position (Rhg) Figure 10 shown 2 . The process shown Figure 11 is performed by the wavelength measurement processor 50 as a subroutine of Figure 10 S450a shown

[0190] 2.2.1.1 Determination of the center position of the interference fringes of the reference light

[0191] In S451, the wavelength measurement processor 50 obtains the center position of the interference fringes of the reference light to deform the waveform of the interference fringes of the reference light into a deformed waveform I(m) corresponding to the wavelength coordinate system. The center position of the interference fringes of the reference light is obtained using pattern matching as follows.

[0192] Figures 12 - 15 is a diagram for explaining the process of obtaining the center position of the interference fringes of the reference light. Figure 12 is equivalent to a diagram obtained by recording the division positions for obtaining the center position in the same curve graph as Figure 7 . As Figure 12 shown, division positions are set in the waveform of the interference fringes of the reference light. Let the initial value of the channel number of the division position be S. The initial value S is set, for example, to a channel number slightly smaller than half of the maximum value of the channel numbers. That is, the position slightly shifted to the left of the center of the line sensor 18d is set as the initial value S of the division position.

[0193] Figure 13 and Figure 14 are curve graphs showing each waveform when the waveform shown Figure 12 is divided into two at the division position. Figure 13 shows the waveform on the left side of the division position, i.e., the first part,Figure 14 The waveform to the right of the division position, i.e., the second part, is shown. In Figure 14 , the coordinates on the horizontal axis are transformed so that the coordinate at the left end of the second part becomes 0. That is, Figure 14 the coordinates in Figure 12 correspond to the coordinates obtained by subtracting the channel number at the division position from the channel number in

[0194] Figure 15 is a graph showing the waveform obtained by reversing the first part shown in Figure 13 left and right, i.e., the reversed first part. In Figure 15 , the coordinate at the left end of the reversed first part is set to 0, and the coordinates on the horizontal axis are transformed so that the coordinate at the right end becomes the channel number at the division position. That is, Figure 15 the coordinates in Figure 13 correspond to the coordinates obtained by subtracting the channel number at the division position from the coordinates in and multiplying the result by -1.

[0195] The wavelength measurement processor 50 calculates the cross-correlation value between the second part shown in Figure 14 and the reversed first part shown in Figure 15 . As the cross-correlation value, for example, any one of the following can be used: the normalized cross-correlation (NCC), the zero-mean normalized cross-correlation (ZNCC), the sum of squared differences (SSD), and the sum of absolute differences (SAD), which will be described later. The larger the calculated cross-correlation value, the higher the degree of coincidence between the two waveforms.

[0196] Furthermore, the wavelength measurement processor 50 shifts the correspondence relationship between the coordinates of the second part and the coordinates of the reversed first part by, for example, one channel, and newly calculates the cross-correlation value between the second part and the reversed first part. Shifting the correspondence relationship between the coordinates of the second part and the coordinates of the reversed first part by one channel is equivalent to shifting the division position in Figure 12 by 0.5 channels. The wavelength measurement processor 50 calculates the cross-correlation value in the case where the waveform of the divided interference fringes is divided at each division position and reversed left and right while shifting the division position to the right by 0.5 channels each time. That is, a cross-correlation function representing the change in the cross-correlation value corresponding to the division position is obtained. The division position at which the cross-correlation value is at a peak becomes the center position of the interference fringes. By interpolation, the division position at which the cross-correlation value is at a peak is obtained in a unit smaller than 0.5 channels, whereby the accuracy can be further improved.

[0197] Described is a case where the channel number at a position slightly shifted to the left of the center of the ratio line sensor 18d is set as the initial value S, and the cross-correlation value is calculated while shifting the division position to the right. However, the calculation order of the cross-correlation value can also be other than this order. In addition, in a case where a peak of the cross-correlation value is not obtained even when the division position is shifted within a predetermined range, an error signal may be output. Further, in a case where the optical alignment of the beam splitter 18 is sufficiently stable, after obtaining the center position of the interference fringe of the reference light once, when performing the processing of this flowchart thereafter, the processing of S451 may sometimes be omitted.

[0198] 2.2.1.2 Conversion to the Wavelength Coordinate System

[0199] Refer again to Figure 11 , in S452, the wavelength measurement processor 50 sets the center position of the interference fringe of the reference light as the origin, squares the coordinates of the horizontal axis of the interference fringe, and converts it into a deformed waveform I(m) corresponding to the wavelength coordinate system.

[0200] Figure 16 is a graph showing a waveform with the center position of the interference fringe of the reference light set as the origin. Figure 16 The coordinates in Figure 12 are the coordinates obtained by subtracting the channel number of the center position obtained in S451 from the channel number in

[0201] Figure 17 is a graph showing an example of the deformed waveform I(m) converted to the wavelength coordinate system. Figure 17 It is possible to square Figure 16 the coordinates of the right half of the horizontal axis in, or it is also possible to square the coordinates of the left half of the horizontal axis. By deforming according to the distance from the center position of the interference fringe, the horizontal axis and the wavelength can be made to correspond. Figure 17 One scale of the horizontal axis in Figure 17 corresponds to the free spectral range (FSR) of the etalon 18b. Figure 16 The waveform of the interference fringe shown in Figure 17 and the deformed waveform I(m) shown in

[0202] 2.2.1.3 Cross-Correlation Function with the Template Waveform T(i)

[0203] Refer again to Figure 11, in S453, the wavelength measurement processor 50 reads out the template waveform T(i) from the memory 61, and calculates the cross-correlation function between the deformed waveform I(m) converted into the wavelength coordinate system and the template waveform T(i).

[0204] Figure 18 is a graph showing the first example of the state where the template waveform T(i) is superimposed on the deformed waveform I(m) shown in Figure 17 The graph shows the first example of the state where the template waveform T(i) is superimposed on the deformed waveform I(m). Figure 19 is a graph showing the second example. In Figure 18 and Figure 19 , the offset d of the template waveform T(i) is different. Compared with the case shown in Figure 18 , in the case shown in Figure 19 , the cross-correlation value between the deformed waveform I(m) and the template waveform T(i) becomes higher. When calculating the cross-correlation value while shifting the template waveform T(i) along the horizontal axis of the deformed waveform I(m), a cross-correlation function representing the change in the cross-correlation value corresponding to the offset d of the template waveform T(i) is obtained.

[0205] Figure 20 is a graph showing the normalized cross-correlation function R Figure 17 between the deformed waveform I(m) and the template waveform T(i) shown in NCC . Figure 20 The horizontal axis of represents the offset d of the template waveform T(i).

[0206] As the cross-correlation value, for example, any one of normalized cross-correlation (NCC), zero-mean normalized cross-correlation (ZNCC), sum of squared differences (SSD), and sum of absolute differences (SAD) can be used. As the cross-correlation functions R NCC (d), R ZNCC (d), R SSD (d), R SAD (d) that respectively represent the change in the cross-correlation value corresponding to the offset d are defined as follows.

[0207] [Equation 1]

[0208]

[0209] Here, Iavg is the average value of the deformed waveform I(m) of the reference light converted into the wavelength coordinate system, and Tavg is the average value of the template waveform T(i).

[0210] As Figure 17As shown, the farther away from the center position of the interference fringes, the smaller the amount of light of the deformation waveform I(m). Therefore, the farther away from the center position of the interference fringes, the lower the cross-correlation value may be. However, in the case of using normalized cross-correlation (NCC) or zero-mean normalized cross-correlation (ZNCC), even when far from the center position of the interference fringes, the decrease in the cross-correlation value becomes gentle. In addition, here, in order to show that the peak of the cross-correlation value can be detected even when far from the center position of the interference fringes, the result of calculating the cross-correlation value within approximately the entire range of the horizontal axis of the deformation waveform I(m) is shown. However, as long as the peaks of a specified number of cross-correlation values can be detected, the calculation of the cross-correlation value can also be terminated halfway.

[0211] 2.2.1.4 Determination of the Matching Position

[0212] Refer again to Figure 11 , in S454, the wavelength measurement processor 50 sets the position of the template waveform T(i) when the cross-correlation value is at a peak as the matching position (Rhg) 2 . The value of (Rhg) 2 thus obtained is used in Figure 3 S700 for the calculation of the absolute wavelength λabs of the laser. The absolute wavelength λabs of the laser is calculated based on the matching position (Rhg) 2 and the square of the radius (Rex) of the interference fringes of the laser 2 . After S454, the wavelength measurement processor 50 ends the processing of this flowchart and returns to Figure 10 the processing shown.

[0213] Refer again to Figure 20 , and the position of the template waveform T(i) when the cross-correlation value is at a peak will be described. Scan the cross-correlation value from the left end of Figure 20 in the right direction, and determine the pair of the first point that crosses the threshold in the upward direction and the second point that crosses the threshold in the downward direction. The position where the cross-correlation value becomes a peak between the first point and the second point is determined as the matching position (Rhg) 2 .

[0214] Figure 21 is a graph showing the waveform of the normalized cross-correlation function R NCC (d) and the template waveform T(i). The position of the left end of the template waveform T(i) coincides with the peak position of the cross-correlation value, and this position is determined as the matching position (Rhg) 2 .

[0215] The template waveform T(i) includes multiple peaks of a known wavelength of the reference light. The distance Pt from the left end of the template waveform T(i) to the position of the peak at the resonance wavelength of the isotope with a mass number of 202, i.e., 253.65277 nm, can be calculated when the template waveform T(i) is created. Therefore, the matching position (Rhg) is determined through the process of S454 2 , and thus the position (Rhg) of the peak at the wavelength of 253.65277 nm in the deformed waveform I(m) of the reference light converted into the wavelength coordinate system can be determined 2 +Pt. The position of the peak at the wavelength of 253.65277 nm corresponds to the first peak position in the present disclosure

[0216] Instead of the square (Rhg) of the radius Rhg of the interference fringes of the reference light in the comparative example 2 , the matching position (Rhg) is used in the first embodiment 2 , and correspondingly, the definition of the offset wavelength λc is different in the comparative example and the first embodiment. In the comparative example, the offset wavelength λc is defined as the absolute wavelength of the laser when the radius Rex of the interference fringes of the laser is equal to the radius Rhg of the interference fringes of the reference light. However, in the first embodiment, the offset wavelength λc is defined as the absolute wavelength of the laser when the square (Rex) of the radius of the interference fringes of the laser 2 and the matching position (Rhg) 2 are equal. The difference between the offset wavelength λc in the comparative example and the offset wavelength λc in the first embodiment corresponds to the value obtained by converting the distance Pt into a wavelength

[0217] 2.2.2 Coping with the distorted waveform

[0218] Figure 22 is a graph showing another example of the deformed waveform I(m) converted into the wavelength coordinate system Figure 22 The shown deformed waveform I(m) compared with Figure 17 the shown deformed waveform I(m), cannot be said to necessarily clearly show 5 peaks, but becomes a flattened waveform. When the finesse of the etalon 18b is low, or when noise enters due to some reasons, it sometimes becomes Figure 22 the waveform shown like this

[0219] Figure 23 is a graph showing the state where the template waveform T(i) is superimposed on the deformed waveform I(m) shown in Figure 22 , and Figure 24 is a graph showing Figure 22 the normalized cross-correlation function R NCC (d) of the deformed waveform I(m) shown and the template waveform T(i) Figure 22 ​The deformed waveform I(m) shown looks very different in shape from the template waveform T(i). However, the peak intervals of the five peaks and the ratio of their respective light amounts are similar to those of the template waveform T(i). Therefore, regarding Figure 24 the normalized cross-correlation function R NCC (d), the peaks represented according to each free spectral range are clear, and the matching position (Rhg) can be clearly determined 2 . Therefore, even for Figure 22 a deformed waveform I(m) such as that shown, the matching position (Rhg) can be determined by pattern matching with the template waveform T(i) 2 .

[0220] 2.3 Function

[0221] (1) According to the first embodiment, the spectrum detector 16 for measuring the wavelength of the measurement laser has: a mercury lamp 18n that encloses natural mercury containing multiple isotopes and outputs reference light; a spectroscope 18 that is located on the optical paths of the reference light and the laser and outputs the waveform of the interference fringes of the reference light; and a wavelength measurement processor 50 that can access the template waveform T(i) of the spectrum including multiple peaks of the known wavelength of the reference light, performs pattern matching using the waveform of the interference fringes of the reference light and the template waveform T(i), and determines the position (Rhg) of the peak corresponding to one of the multiple peaks 2 +Pt.

[0222] In addition, the method for determining the peak position of the reference light in the first embodiment includes the following steps: making the reference light output from the mercury lamp 18n incident on the spectroscope 18 to obtain the waveform of the interference fringes of the reference light, where the mercury lamp 18n encloses natural mercury containing multiple isotopes; reading out the template waveform T(i) of the spectrum including multiple peaks of the known wavelength of the reference light; and performing pattern matching using the waveform of the interference fringes of the reference light and the template waveform T(i) to determine the position (Rhg) of the peak corresponding to one of the multiple peaks 2 +Pt.

[0223] Thus, by performing pattern matching using the waveform of the interference fringes of the reference light having multiple peaks corresponding to the resonance wavelengths of multiple isotopes and the template waveform T(i), the position (Rhg) of the peak corresponding to the known wavelength of 253.65277 nm can be accurately determined 2 +Pt.

[0224] (2)According to the first embodiment, the optical splitter 18 outputs the waveform of the interference fringes of the reference light formed by the etalon 18b, and the wavelength measurement processor 50 converts the waveform of the interference fringes of the reference light into a deformed waveform I(m) corresponding to the wavelength coordinate system, thereby deforming the waveform of the interference fringes of the reference light. In the deformed waveform I(m), the matching position (Rhg) that matches the template waveform T(i) is determined 2 , thereby determining the position of the peak (Rhg) 2 +Pt.

[0225] Thus, the waveform of the interference fringes whose scale changes according to the distance from the center is converted into the deformed waveform I(m) of the wavelength coordinate system, and pattern matching with the template waveform T(i) is performed. Thus, the position of the peak (Rhg) can be efficiently determined 2 +Pt.

[0226] (3)According to the first embodiment, the wavelength measurement processor 50 divides the waveform of the interference fringes of the reference light into a first part and a second part, determines the center position of the interference fringes of the reference light according to the cross-correlation function between the inverted first part and the second part after inverting the first part, and converts the waveform of the interference fringes of the reference light according to the distance from the center position.

[0227] Thus, by inverting the first part to investigate the relationship with the second part, the symmetry between the two can be determined, the center position of the waveform of the interference fringes can be determined, and the waveform of the interference fringes can be converted.

[0228] (4)According to the first embodiment, the wavelength measurement processor 50 determines the center position according to the cross-correlation value between the inverted first part and the second part.

[0229] Thus, by using the cross-correlation value, the center position of the waveform of the interference fringes can be obtained by calculation.

[0230] (5)According to the first embodiment, the wavelength measurement processor 50 obtains the relationship between the division position where the waveform of the interference fringes of the reference light is divided into two parts and the cross-correlation value, and determines the center position according to this relationship.

[0231] Thus, according to the relationship between the division position and the cross-correlation value, the center position of the waveform of the interference fringes can be accurately obtained.

[0232] (6)According to the first embodiment, the wavelength measurement processor 50 determines the matching position (Rhg) according to the cross-correlation value between the deformed waveform I(m) and the template waveform T(i) 2 .

[0233] Thus, by using the cross-correlation value, the matching position (Rhg) can be obtained by calculation. 2 .

[0234] (7)According to the first embodiment, the wavelength measurement processor 50 obtains the relationship between the offset d between the deformed waveform I(m) and the template waveform T(i) and the cross-correlation value, and determines the matching position (Rhg) based on this relationship. 2 .

[0235] Thereby, based on the relationship between the offset d between the deformed waveform I(m) and the template waveform T(i) and the cross-correlation value, the matching position (Rhg) can be accurately obtained. 2 .

[0236] (8)According to the first embodiment, the optical splitter 18 outputs the waveform of the interference fringes of the laser, and the wavelength measurement processor 50 measures the absolute wavelength λabs of the laser based on the matching position (Rhg) 2 and the peak position in the waveform of the interference fringes of the laser.

[0237] Thereby, the peak position corresponding to the known wavelength of the reference light can be determined by the matching position (Rhg). Therefore, based on the matching position (Rhg) 2 and the peak position in the waveform of the interference fringes of the laser, the absolute wavelength λabs of the laser can be calculated. 2

[0238] (9)According to the first embodiment, the optical splitter 18 outputs the waveform of the interference fringes of the laser, and the wavelength measurement processor 50 obtains the matching position (Rhg) 2 and the square of the radius (Rex) of the interference fringes of the laser 2 When they are consistent, the wavelength of the laser is used as the bias wavelength λc. Based on the matching position (Rhg) 2 , the square of the radius (Rex) of the interference fringes of the laser 2 and the bias wavelength λc, the absolute wavelength λabs of the laser is measured.

[0239] Thereby, by using the bias wavelength λc, the absolute wavelength λabs of the laser can be obtained by simple calculation.

[0240] In other aspects, the first embodiment is the same as the comparative example.

[0241] 3. The spectrometer 16 including the mercury lamp 18n encapsulating natural mercury and the getter material

[0242] 3.1 Structure

[0243] Figure 25 and Figure 26Shows the structure of the mercury lamp 18n used in the laser device 1a of the second embodiment. Regarding the structure and operation of the laser device 1a of the second embodiment, aspects other than the mercury lamp 18n described below are the same as those of the first embodiment. The mercury lamp 18n includes a quartz tube 80, a lamp base 81, a flared portion 82, two stem pins 83, a filament 84, a mercury alloy plate 85, and a support rod 86.

[0244] Natural mercury is enclosed inside the quartz tube 80. The opening of the quartz tube 80 is sealed by the lamp base 81. The flared portion 82 is fixed to the lamp base 81 inside the quartz tube 80. The two stem pins 83 are fixed to the flared portion 82. The two stem pins 83 penetrate the flared portion 82 and the lamp base 81 and are exposed to the outside of the quartz tube 80 as two electrode pins. The filament 84, which is a hot cathode, is installed and fixed to the two stem pins 83 inside the quartz tube 80. The current path inside the quartz tube 80 is formed by the two stem pins 83 and the filament 84.

[0245] Inside the quartz tube 80, a mercury alloy plate 85 is arranged as a getter material for adsorbing natural mercury. For example, a support rod 86 is fixed to the flared portion 82, and the mercury alloy plate 85 is fixed to the support rod 86 by brazing. The mercury alloy plate 85 is brazed to the support rod 86 on the side opposite to the surface on the filament 84 side of the mercury alloy plate 85. Mercury alloy means an alloy containing mercury. The mercury alloy plate 85 is composed of, for example, an alloy of indium, silver, and natural mercury. The mercury alloy plate 85 has a plurality of concavities and convexities on its surface to increase the surface area. The mercury alloy plate 85 is arranged such that the shortest distance g from the filament 84, for example, becomes a value of 2 mm or more and 6 mm or less. The shortest distance refers to the minimum value of the gap between objects. For example, the shortest distance between two spheres is the value obtained by subtracting the sum of the radii of these spheres from the distance between the centers of these spheres. The mercury alloy plate 85 is located on the side opposite to the traveling direction X of the light from the approximate center of the mercury lamp 18n toward the etalon 18b.

[0246] At the same ambient temperature, the vapor pressure of mercury contained in the mercury alloy is lower than that of pure mercury. Therefore, most of the mercury enclosed inside the mercury lamp 18n is absorbed by the mercury alloy plate 85 when the mercury lamp 18n is extinguished. When the mercury lamp 18n is lit, mercury is released from the mercury alloy plate 85, but an excessive increase in vapor pressure is suppressed. The appropriate range of the mercury vapor pressure is in the range of 0.8 Pa to 1.0 Pa. When the shortest distance g from the filament 84 to the mercury alloy plate 85 is shortened, the time to reach the appropriate vapor pressure becomes shorter, and when the shortest distance g is extended, the time to reach the appropriate vapor pressure becomes longer.

[0247] Figure 27It is a graph showing the relationship between the emission time and the mercury vapor pressure of a mercury lamp 18n containing a gettering material and a mercury lamp 18n not containing a gettering material starting from the start of emission. The mercury lamp 18n not containing a gettering material includes a mercury lamp 18n in good condition and a mercury lamp 18n in poor condition.

[0248] When the mercury lamp 18n not containing a gettering material starts to emit light, the inside of the mercury lamp 18n is heated by the hot cathode, and the mercury vapor pressure inside the mercury lamp 18n rises sharply. In any state of good condition and poor condition, at the point of about 2 seconds after the start of emission, the mercury vapor pressure is within the appropriate vapor pressure range of 0.8 Pa to 1.0 Pa. Then, the mercury vapor pressure also rises and becomes supersaturated beyond the appropriate vapor pressure range. Thus, when the mercury vapor pressure exceeds the appropriate range in a short time, it is difficult to obtain a stable light quantity and stable interference fringes. As a reason for the sharp rise in mercury vapor pressure, it is considered that when the mercury lamp 18n is extinguished, mercury dew condenses near the hot cathode or on the hot cathode itself and is rapidly heated after the start of emission. After about 6 seconds from the start of emission, the mercury vapor pressure gradually decreases. However, as Figure 27 shown as the poor condition, at the point of about 20 seconds after the start of emission, the deviation from the appropriate vapor pressure is sometimes large.

[0249] In the mercury lamp 18n internally provided with a gettering material, the rise in mercury vapor pressure from the start of emission becomes gentle, and further, from the point of about 5 seconds after the start of emission, the rise in mercury vapor pressure becomes even gentler. As a result, during the period from about 5 seconds after the start of emission to about 10 seconds after the start of emission, the mercury vapor pressure becomes the appropriate vapor pressure of 0.8 Pa to 1.0 Pa.

[0250] Figure 28 It is a graph showing the relationship between the emission time and the light quantity of a mercury lamp 18n containing a gettering material and a mercury lamp 18n not containing a gettering material starting from the start of emission.

[0251] In the mercury lamp 18n not containing a gettering material, at the point of about 2 seconds after the start of emission, the light quantity reaches the maximum value, and then the light quantity temporarily decreases. After about 6 seconds from the start of emission, the light quantity gradually rises. In particular, it is known that in the poor condition, the reduction amplitude of the light quantity after about 2 seconds from the start of emission is large. In the poor condition, after about 6 seconds from the start of emission, even if the light quantity gradually rises, sometimes only less than half of the light quantity in the good condition can be obtained.

[0252] In the mercury lamp 18n internally provided with a gettering material, the rise in light quantity from the start of emission becomes slightly gentle, but during the period from about 5 seconds after the start of emission to about 12 seconds after the start of emission, a high light quantity is stably obtained.

[0253] Figure 29 and Figure 30 shows the waveform of the interference fringes of the reference light generated using the mercury lamp 18n containing the gettering material. Figure 29 is Figure 27 and Figure 28 the waveform 8 seconds after the start of light emission at F29 of Figure 30 is Figure 27 and Figure 28 the waveform 19 seconds after the start of light emission at F30 of Figure 31 shows the waveform of the interference fringes of the reference light generated using the defective mercury lamp 18n that does not contain the gettering material. Figure 31 is Figure 27 and Figure 28 the waveform 7 seconds after the start of light emission at F31 of

[0254] According to the mercury lamp 18n containing the gettering material, during at least 8 seconds from the start of light emission, a waveform with almost no obvious distortion is obtained (refer to Figure 29 ). At the point in time 19 seconds after the start of light emission, distortion of the waveform is seen (refer to Figure 30 ), however, 5 peaks can be distinguished.

[0255] In the mercury lamp 18n that does not contain the gettering material, due to the excessive mercury vapor pressure, self-absorption occurs, and almost no 5 peaks that should be included in the reference light can be seen (refer to Figure 31 ). In addition, when the defective mercury lamp 18n is continuously lit for about 10 minutes, for example, the amount of mercury condensed near the filament 84 during subsequent extinguishing can be reduced. When starting to emit light again in this state, a large amount of mercury can be prevented from evaporating all at once, and thus, the mercury lamp 18n can be made into a good state.

[0256] 3.2 Function

[0257] (10) According to the second embodiment, the mercury lamp 18n is a low-pressure mercury lamp in which a mercury alloy plate 85 is enclosed as a gettering material together with natural mercury.

[0258] Thereby, by enclosing the gettering material together with natural mercury, the attenuation of multiple peaks based on multiple isotopes due to self-absorption is suppressed, and the accuracy of matching based on multiple peaks is improved. In addition, by using natural mercury for the matching of 5 peaks, compared with the case of calculating only using the resonance wavelengths of specific isotopes, the amount of information increases, and high-precision detection can be performed.

[0259] In other aspects, the second embodiment is the same as the first embodiment.

[0260] 4. Spectrometer 16 with improved SN ratio

[0261] 4.1 Operation

[0262] Figure 32 and Figure 33 is a flowchart showing details of the process of detecting interference fringes of reference light in the third embodiment. Figure 32 and Figure 33 The processes shown are performed by the wavelength measurement processor 50 as a subroutine of S300 shown in Figure 3 The illustration of the laser device 1a of the third embodiment is omitted. However, except that the memory 61 includes a background memory and a light amount accumulation memory, it is the same as the laser device 1a of the first embodiment described with reference to Figure 9

[0263] Referring to Figure 32 , in S310, the wavelength measurement processor 50 controls the actuator 17b to close the shutter 17a to limit the incidence of laser light. This is the same as the comparative example described with reference to Figure 4

[0264] 4.1.1 Acquisition of Background Waveform

[0265] In S320b, the wavelength measurement processor 50 starts the exposure of the line sensor 18d, resets and starts the timer T5 for measuring the time until the exposure of the line sensor 18d ends. Different from S390, the mercury lamp 18n is not lit in S320b.

[0266] In S330b, the wavelength measurement processor 50 determines whether the value of the timer T5 has reached the threshold K0. The threshold K0 corresponds to the second exposure time in the present disclosure and can be, for example, 0.5 seconds or more and 1 second or less. When the value of the timer T5 has not reached the threshold K0 (S330b: No), the wavelength measurement processor 50 waits until the value of the timer T5 reaches the threshold K0 and continues the exposure of the line sensor 18d. When the value of the timer T5 has reached the threshold K0 (S330b: Yes), the wavelength measurement processor 50 advances the process to S340b.

[0267] In S340b, the wavelength measurement processor 50 outputs a data output trigger to the line sensor 18d. Thereby, the wavelength measurement processor 50 ends the exposure of the line sensor 18d. In addition, the wavelength measurement processor 50 reads the observation data of the light amount in the unlit state from the line sensor 18d as the background waveform and stores the background waveform in the background memory. The background waveform corresponds to the third spectral waveform in the present disclosure.

[0268] 4.1.2 Improvement of SN Ratio by Accumulation of Interference Fringes Based on Reference Light

[0269] In S350, the wavelength measurement processor 50 resets and starts the timer T2 that measures the time from when the mercury lamp 18n starts emitting light until the line sensor 18d starts exposure, and controls the lamp power supply 18h to cause the mercury lamp 18n to start emitting light. Further, in S360, the wavelength measurement processor 50 determines whether the value of the timer T2 has reached the threshold K2. These aspects are the same as in the comparative example described with reference to Figure 4 The threshold K2 may also be 0 seconds or more and 2 seconds or less.

[0270] In S370b, the wavelength measurement processor 50 sets the value of the counter N that counts the number of measurements of the reference light to the initial value 0. Further, the wavelength measurement processor 50 deletes the data stored in the light quantity accumulation memory.

[0271] With reference to Figure 33 , in S380b, the wavelength measurement processor 50 increments the value of the counter N and updates the value of N.

[0272] In S390, the wavelength measurement processor 50 starts the exposure of the line sensor 18d and resets and starts the timer T5 that measures the time until the exposure of the line sensor 18d ends. This is the same as in the comparative example described with reference to Figure 4 The comparative example described.

[0273] In S400b, the wavelength measurement processor 50 determines whether the value of the timer T5 has reached the threshold K0. The threshold K0 is the same as the threshold K0 used in S330b. When the value of the timer T5 has not reached the threshold K0 (S400b: No), the wavelength measurement processor 50 waits until the value of the timer T5 reaches the threshold K0 and continues the exposure of the line sensor 18d. When the value of the timer T5 has reached the threshold K0 (S400b: Yes), the wavelength measurement processor 50 proceeds to S410b.

[0274] In S410b, the wavelength measurement processor 50 outputs a data output trigger to the line sensor 18d. Thereby, the wavelength measurement processor 50 ends the exposure of the line sensor 18d. Further, the wavelength measurement processor 50 reads out the data of the interference fringes of the reference light from the line sensor 18d and accumulates it for each channel of the line sensor 18d in the data stored in the light quantity accumulation memory, and updates the data in the light quantity accumulation memory. Thereby, the accumulated interference fringes of the reference light are stored in the light quantity accumulation memory.

[0275] In S420b, the wavelength measurement processor 50 determines whether the maximum value among the light amounts of each channel of the interference fringes of the accumulated reference light has reached the threshold S1. When the maximum value is less than the threshold S1 (S420b: No), the wavelength measurement processor 50 returns the process to S380b. When the maximum value is equal to or greater than the threshold S1 (S420b: Yes), the wavelength measurement processor 50 advances the process to S430.

[0276] In S430, the wavelength measurement processor 50 controls the lamp power supply 18h to turn off the mercury lamp 18n. This is the same as the comparative example described with reference to Figure 4 The value N×K0 obtained by multiplying the value of the counter N accumulated up to this point by the threshold K0 is the total exposure time of the interference fringes of the reference light, which corresponds to the first exposure time of the present disclosure.

[0277] 4.1.3 Improvement of the SN ratio achieved by subtracting the background waveform

[0278] In S440b, the wavelength measurement processor 50 subtracts the light amount of each channel of the background waveform from the value obtained by dividing the light amount of each channel of the accumulated interference fringes of the reference light by N, thereby deforming the accumulated interference fringes of the reference light. Dividing the light amount of the accumulated interference fringes of the reference light by N is to make the exposure time consistent before subtracting the light amount of the background waveform. Instead of dividing the light amount of the accumulated interference fringes of the reference light by N, the light amount of the background waveform can be multiplied by N. In addition, when the processes of S320b to S340b are executed between S430 and S440b, the exposure time in S330b can also be set to N×K0. In this case, it is also possible not to divide the light amount of the accumulated interference fringes of the reference light by N. Furthermore, the processes of S320b to S340b and S440b can be omitted. In addition, instead of the processes of S370b to S420b, the Figure 10 processes of S390 to S410 can be performed, and instead of S440b, the background waveform can be subtracted from the interference fringes of the reference light. The interference fringes obtained as described above are set as the interference fringes of the reference light in the subsequent processes.

[0279] 4.1.4 Pattern matching

[0280] In S450a, the wavelength measurement processor 50 deforms the waveform of the interference fringes of the reference light into a deformed waveform I(m) corresponding to the wavelength coordinate system, and calculates the matching position (Rhg) between the deformed waveform I(m) and the template waveform T(i) 2 . This is the same as the first embodiment described with reference to Figures 10 - 21 .

[0281] In S460, the wavelength measurement processor 50 controls the actuator 17b to open the shutter 17a. Then, the wavelength measurement processor 50 ends the processing of this flowchart and returns Figure 3 to the processing of Figure 4 . These aspects are the same as the comparative example described with reference to

[0282] 4.2 Effects

[0283] (11) According to the third embodiment, the wavelength measurement processor 50 acquires a background waveform, reduces the noise included in the waveform of the interference fringes of the reference light based on the background waveform, and performs pattern matching using the waveform of the interference fringes of the reference light with the reduced noise.

[0284] Thereby, by reducing the noise using the background waveform, accurate determination in pattern matching can be performed.

[0285] (12) According to the third embodiment, the wavelength measurement processor 50 acquires a spectral waveform output from the spectroscope 18 when the incidence of the reference light and the laser to the spectroscope 18 is restricted as the background waveform, deforms the waveform of the interference fringes of the reference light using the background waveform, and performs pattern matching using the deformed waveform of the interference fringes of the reference light.

[0286] Thereby, by using the spectral waveform output from the spectroscope 18 when the incidence of the reference light and the laser to the spectroscope 18 is restricted, the noise caused by the deviation of the bias signal when light is not incident on the plurality of light receiving elements included in the line sensor 18d can be reduced, and accurate determination can be performed.

[0287] (13) According to the third embodiment, the wavelength measurement processor 50 accumulates the light amount of the waveform of the interference fringes of the reference light for each channel, and when the maximum value of the accumulated light amount reaches the threshold S1, performs pattern matching using the accumulated waveform of the interference fringes of the reference light.

[0288] Thereby, by accumulating the light amount until the threshold S1 of the light amount is reached, insufficient light amount and excessive light amount can be suppressed. Therefore, it is not necessary to adjust the threshold K5 of the exposure time (refer to Figure 4 ) in order to suppress insufficient light amount and excessive light amount.

[0289] (14) According to the third embodiment, the wavelength measurement processor 50 integrates the light amount of the waveform of the interference fringes of the reference light for each channel while measuring the first exposure time N×K0 of the reference light, obtains the background waveform when the incidence of the reference light and the laser light on the spectrometer 18 is limited and the exposure is performed with the second exposure time, i.e., the threshold value K0, and reduces the noise included in the waveform of the interference fringes of the integrated reference light based on the waveform of the interference fringes of the integrated reference light, the first exposure time N×K0, the background waveform, and the second exposure time, i.e., the threshold value K0, and performs pattern matching using the waveform of the interference fringes of the reference light after the noise is reduced.

[0290] Thus, based on the first exposure time N×K0 for integrating the light amount of the interference fringes of the reference light and the second exposure time, namely the threshold value K0, the interference fringes of the reference light or the background waveform is adjusted to reliably remove noise.

[0291] The third embodiment is the same as the first embodiment in other respects. Also, similarly to the second embodiment, a mercury lamp 18n containing natural mercury and a getter material may be used.

[0292] 5. Spectrum measuring device 16 for updating the template waveform T(i)

[0293] 5.1 Action

[0294] Figure 34 is a diagram showing the calculated matching position (Rhg) in the fourth embodiment. 2 Flowchart of the details of the processing. Figure 34 The processing shown as Figure 10 The subroutine of S450a shown in FIG. 4 is executed by the wavelength measurement processor 50. The processing and reference of S451 to S454 Figure 11 The same as the first embodiment described.

[0295] In S455c, the wavelength measurement processor 50 extracts a partial waveform P(i) of a wavelength band corresponding to the wavelength band of the template waveform T(i) from the deformed waveform I(m) of the interference fringes of the reference light deformed into a waveform corresponding to the wavelength coordinate system.

[0296] Figure 35 is a graph for explaining a method of extracting a partial waveform P(i). Figure 35 In the figure, the deformation waveform I(m) of the interference fringes of the reference light and the normalized cross-correlation function R are shown with the same wavelength scale. NCC (d) The starting point of the partial waveform P(i) extracted from the deformed waveform I(m) is set as the normalized cross-correlation function R NCCThe peak position Pe of (d). The end point of the partial waveform P(i) is determined such that the wavelength width of the partial waveform P(i) is the same as the wavelength width of the template waveform T(i). For example, the wavelength width of the partial waveform P(i) is the same as the free spectral range of the etalon 18b.

[0297] Referring again to Figure 34 in S456c, the wavelength measurement processor 50 updates the template waveform T(i) stored in the memory 61 using the partial waveform P(i).

[0298] Figure 36 is a graph for explaining a method of updating the template waveform T(i) using the partial waveform P(i). The template waveform T(i) stored in the memory 61 and the partial waveform P(i) extracted in S455c are multiplied by weights r and 1-r respectively, the weighted waveforms T(i)×r and P(i)×(1-r) are calculated, and the waveform obtained by adding these weighted waveforms is set as the new template waveform Tn(i).

[0299] 5.2 Function

[0300] (15) According to the fourth embodiment, the wavelength measurement processor 50 updates the template waveform T(i) based on the waveform of the interference fringes of the reference light deformed into the deformation waveform I(m) corresponding to the wavelength coordinate system.

[0301] Thus, by updating the template waveform T(i) using the measured value of the interference fringes of the reference light, accurate measurement can be performed even if the characteristics of the mercury lamp 18n change.

[0302] (16) According to the fourth embodiment, the wavelength measurement processor 50 extracts the partial waveform P(i) corresponding to the band of the template waveform T(i) from the deformation waveform I(m), and updates the template waveform T(i) based on the partial waveform P(i).

[0303] Thus, by making the band of the partial waveform P(i) the same as the band of the template waveform T(i), reliable update of the template waveform T(i) can be performed.

[0304] (17) According to the fourth embodiment, the wavelength measurement processor 50 obtains the relationship between the offset d between the deformation waveform I(m) and the template waveform T(i) and the cross-correlation value between the deformation waveform I(m) and the template waveform T(i), and extracts, based on this relationship, the portion of the deformation waveform I(m) having a width corresponding to the width of the template waveform T(i) as the partial waveform P(i).

[0305] Thus, an appropriate partial waveform P(i) corresponding to the width of the template waveform T(i) can be extracted from the deformation waveform I(m).

[0306] (18) According to the fourth embodiment, the wavelength measurement processor 50 weights the partial waveform P(i) and the template waveform T(i) and adds them together, thereby updating the template waveform T(i).

[0307] Thus, by taking into account the partial waveform P(i) and the template waveform T(i) before updating, it is possible to suppress a sudden change in the template waveform T(i).

[0308] In other respects, the fourth embodiment is the same as the first embodiment. In addition, as in the second embodiment, a mercury lamp 18n containing natural mercury and a getter material may be used. In addition, as in the third embodiment, the interference fringes of the reference light may be accumulated until the accumulated light amount exceeds a certain value, or the background waveform may be subtracted.

[0309] 6. Others

[0310] The above description is not limiting but merely illustrative. Therefore, it is clear to those skilled in the art that changes can be made to the embodiments of the present disclosure without departing from the claims. In addition, it is also clear to those skilled in the art that the embodiments of the present disclosure can be used in combination.

[0311] Unless explicitly stated otherwise, the terms used in this specification and claims as a whole should be interpreted as "non-limiting" terms. For example, terms such as "including", "having", "having", and "having" should be interpreted as "excluding the existence of structural elements other than the structural elements to be recorded". In addition, the modifier "one" should be interpreted as meaning "at least one" or "one or more". In addition, terms such as "at least one of A, B, and C" should be interpreted as "A", "B", "C", "A+B", "A+C", "B+C", or "A+B+C". Furthermore, it should be interpreted as also including combinations of them and parts other than "A", "B", and "C".

Claims

1. A spectrum detector that measures the wavelength of a laser, wherein, The spectrum detector has: a mercury lamp that encloses natural mercury containing multiple isotopes and outputs reference light; a spectroscope that is located on the optical path of the reference light and the laser, inputs the reference light, and outputs a first spectral waveform; and a processor that can access a template waveform of a spectrum including multiple peaks of known wavelengths of the reference light, performs pattern matching using the first spectral waveform and the template waveform, and determines a first peak position corresponding to one of the multiple peaks in the first spectral waveform.

2. The spectrum detector according to claim 1, wherein the spectroscope outputs a waveform of an interference fringe of the reference light formed using an etalon as the first spectral waveform, the processor converts the waveform of the interference fringe of the reference light into a waveform corresponding to a wavelength coordinate system, thereby deforming the first spectral waveform, the processor determines a matching position that matches the template waveform in the deformed first spectral waveform, thereby determining the first peak position.

3. The spectrum detector according to claim 2, wherein the processor divides the waveform of the interference fringe of the reference light into a first part and a second part, and determines the center position of the interference fringe of the reference light based on the relationship between the inverted first part after inverting the first part and the second part, the processor converts the waveform of the interference fringe of the reference light according to the distance from the center position.

4. The spectrum detector according to claim 3, wherein the processor determines the center position based on the cross-correlation value between the inverted first part and the second part.

5. The spectrum detector according to claim 4, wherein the processor obtains the relationship between the division position that divides the waveform of the interference fringe of the reference light into two parts and the cross-correlation value, the processor determines the center position based on the relationship between the division position and the cross-correlation value.

6. The spectrum detector according to claim 2, wherein the processor determines the matching position based on the cross-correlation value between the deformed first spectral waveform and the template waveform.

7. The spectrum detector according to claim 6, wherein the processor obtains the relationship between the offset amount between the deformed first spectral waveform and the template waveform and the cross-correlation value, the processor determines the matching position based on the relationship between the offset amount and the cross-correlation value.

8. The spectrum detector according to claim 2, wherein the spectroscope inputs the laser and outputs a second spectral waveform, the processor measures the absolute wavelength of the laser based on the matching position and a second peak position in the second spectral waveform.

9. The spectrum detector according to claim 2, wherein the spectroscope inputs the laser and outputs a second spectral waveform, the processor obtains the wavelength of the laser when the square of the radius of the interference fringe of the laser is consistent with the matching position as a bias wavelength, the processor measures the absolute wavelength of the laser based on the matching position, the square of the radius of the interference fringe of the laser, and the bias wavelength.

10. The spectral detector according to claim 1, wherein, the mercury lamp is a low-pressure mercury lamp in which getter material is enclosed together with natural mercury.

11. The spectral detector according to claim 1, wherein, the processor obtains a third spectral waveform, the processor reduces noise included in the first spectral waveform based on the third spectral waveform, the processor performs the pattern matching using the first spectral waveform with the reduced noise.

12. The spectral detector according to claim 1, wherein, the processor obtains a spectral waveform output from the spectroscope when incidence of the reference light and the laser to the spectroscope is restricted, as the third spectral waveform, the processor deforms the first spectral waveform using the third spectral waveform, the processor performs the pattern matching using the deformed first spectral waveform.

13. The spectral detector according to claim 1, wherein, the processor accumulates the light quantity of the first spectral waveform for each channel, when the maximum value of the accumulated light quantity reaches a threshold value, the processor performs the pattern matching using the accumulated first spectral waveform.

14. The spectral detector according to claim 1, wherein, the processor accumulates the light quantity of the first spectral waveform for each channel while measuring a first exposure time of the reference light, the processor obtains a third spectral waveform when incidence of the reference light and the laser to the spectroscope is restricted and exposure is performed with a second exposure time, the processor reduces noise included in the accumulated first spectral waveform based on the accumulated first spectral waveform, the first exposure time, the third spectral waveform, and the second exposure time, the processor performs the pattern matching using the first spectral waveform with the reduced noise.

15. The spectral detector according to claim 1, wherein, the processor updates the template waveform based on the first spectral waveform deformed into a waveform corresponding to a wavelength coordinate system.

16. The spectral detector according to claim 15, wherein, the processor extracts a partial waveform corresponding to a band of the template waveform from the deformed first spectral waveform, the processor updates the template waveform based on the partial waveform.

17. The spectral detector according to claim 16, wherein, the processor obtains a relationship between an offset amount between the deformed first spectral waveform and the template waveform and a cross-correlation value between the deformed first spectral waveform and the template waveform, the processor extracts, as the partial waveform, a portion having a width corresponding to the width of the template waveform from the deformed first spectral waveform based on the relationship between the offset amount and the cross-correlation value.

18. The spectral detector according to claim 16, wherein, the processor updates the template waveform by respectively weighting and adding the partial waveform and the template waveform.

19. A laser device having a spectral detector, the spectral detector including: a mercury lamp that encloses natural mercury containing a plurality of isotopes and outputs reference light; A spectroscope, which is located on the optical paths of the reference light and the laser, inputs the reference light and outputs a first spectral waveform; and A processor, which can access a template waveform of a spectrum containing multiple peaks of known wavelengths of the reference light, performs pattern matching using the first spectral waveform and the template waveform, and determines a first peak position corresponding to one of the multiple peaks in the first spectral waveform.

20. A method for determining the peak position of a reference light, comprising the following steps: Causing the reference light output from a mercury lamp, in which natural mercury containing multiple isotopes is enclosed, to be incident on a spectroscope to obtain a first spectral waveform; Reading out a template waveform of a spectrum containing multiple peaks of known wavelengths of the reference light; and Performing pattern matching using the first spectral waveform and the template waveform, and determining a first peak position corresponding to one of the multiple peaks in the first spectral waveform.

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