Extreme ultraviolet light generation device, droplet generation control method, and method for manufacturing electronic devices

Abstract

There was a need for an EUV light generator that could adjust the duty cycle while suppressing droplet misalignment. [Solution] The extreme ultraviolet light generating device comprises a piezoelectric element that generates droplets of a target material by applying vibrations that reflect an electrical signal to a target material output from a nozzle; a first sensor that measures the passage interval of the droplets output from the nozzle; a second sensor that measures parameters related to the droplets; and a processor configured to set a duty cycle ban band based on data that associates the duty cycle of an electrical signal with parameters in the duty cycle, and to set the duty cycle of the electrical signal applied to the piezoelectric element while avoiding the ban band.

Description

[Technical Field]

[0001] This disclosure relates to an extreme ultraviolet light generation apparatus, a droplet generation control method, and a method for manufacturing an electronic device. [Background technology]

[0002] In recent years, with the miniaturization of semiconductor processes, the miniaturization of transfer patterns in semiconductor photolithography has been rapidly progressing. In the next generation, microfabrication of 10 nm or less will be required. For this reason, the development of semiconductor exposure equipment that combines a device for generating extreme ultraviolet (EUV) light with a wavelength of approximately 13 nm with a reduction projection reflection optical system is expected. As for EUV light generation devices, development is progressing on laser-produced plasma (LPP) type devices that use plasma generated by irradiating a target material with laser light. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent No. 10225917 [Patent Document 2] Summary of U.S. Patent No. 7,154,922

[0004] An extreme ultraviolet light generator according to one aspect of the present disclosure is an extreme ultraviolet light generator that generates extreme ultraviolet light by irradiating a droplet with laser light, and comprises: a tank for containing a liquid target substance; a nozzle for outputting the target substance contained in the tank; a piezoelectric element for generating droplets of the target substance by applying vibrations that reflect an electrical signal to the target substance output from the nozzle; a first sensor for measuring the passage interval of the droplets output from the nozzle; a second sensor for measuring parameters related to the droplets; and a processor configured to set a duty cycle ban band based on data relating the duty cycle of an electrical signal and parameters in the duty cycle, and to set the duty cycle of the electrical signal applied to the piezoelectric element while avoiding the ban band.

[0005] A droplet generation control method relating to one aspect of this disclosure is a droplet generation control method in an extreme ultraviolet light generation device that generates extreme ultraviolet light by irradiating a droplet with laser light, and includes: applying an electrical signal to a piezoelectric element to generate droplets of a target material by causing vibrations that reflect the electrical signal to a liquid target material output from a nozzle; measuring the passage interval of the droplets output from the nozzle with a first sensor; measuring parameters related to the droplets with a second sensor different from the first sensor; setting a duty cycle no-go band based on data relating the duty cycle of the electrical signal and the parameters in the duty cycle; and setting the duty cycle of the electrical signal to be output to the piezoelectric element while avoiding the no-go band.

[0006] A method for manufacturing an electronic device according to one aspect of the present disclosure is an extreme ultraviolet light generating apparatus that generates extreme ultraviolet light by irradiating droplets with laser light, the apparatus comprising: a tank containing a liquid target substance; a nozzle for outputting the target substance contained in the tank; a piezoelectric element that generates droplets of the target substance by applying vibrations reflecting an electrical signal to the target substance output from the nozzle; a first sensor for measuring the passage interval of the droplets output from the nozzle; a second sensor for measuring parameters related to the droplets; and a processor configured to set a duty cycle no-go band based on data relating the duty cycle of an electrical signal and parameters in the duty cycle, and to set the duty cycle of the electrical signal applied to the piezoelectric element while avoiding the no-go band; the apparatus generates extreme ultraviolet light, outputs the extreme ultraviolet light to an exposure apparatus, and exposes a photosensitive substrate with the extreme ultraviolet light in the exposure apparatus in order to manufacture an electronic device.

[0007] A method for manufacturing an electronic device according to one aspect of the present disclosure is an extreme ultraviolet light generating apparatus that generates extreme ultraviolet light by irradiating a droplet with laser light, the apparatus comprising: a tank containing a liquid target substance; a nozzle for outputting the target substance contained in the tank; a piezoelectric element that generates droplets of the target substance by applying vibrations reflecting an electrical signal to the target substance output from the nozzle; a first sensor for measuring the passage interval of the droplets output from the nozzle; a second sensor for measuring parameters related to the droplets; and a processor configured to set a duty cycle no-go zone based on data relating the duty cycle of an electrical signal and parameters in the duty cycle, and to set the duty cycle of the electrical signal applied to the piezoelectric element while avoiding the no-go zone; generating extreme ultraviolet light with the extreme ultraviolet light generating apparatus; irradiating a reticle with the extreme ultraviolet light to inspect the reticle for defects; selecting a reticle using the inspection results; and exposing and transferring the pattern formed on the selected reticle onto a photosensitive substrate. [Brief explanation of the drawing]

[0008] Some embodiments of this disclosure are described below, merely as examples, with reference to the accompanying drawings. [Figure 1] Figure 1 is a schematic diagram showing a configuration for measuring the droplet passage interval. [Figure 2] Figure 2 is a schematic diagram of the output signal of the photodetector of the droplet detection sensor. [Figure 3] Figure 3 shows an example of an electrical signal applied to a piezoelectric element. [Figure 4] Figure 4 is a schematic diagram showing an example configuration of an LPP-type EUV light generation system related to a comparative example. [Figure 5] Figure 5 is a flowchart showing the main operation flow of the EUV light generator. [Figure 6] Figure 6 is a flowchart showing an example of a DL coupling adjustment subroutine applied to step S3 in Figure 5. [Figure 7] Figure 7 is a graph showing an example of the DL passage interval σ measured during DL coupling adjustment. [Figure 8] Figure 8 is a flowchart showing an example of a DL coupling control subroutine applied in step S4 of Figure 5. [Figure 9] Figure 9 is a graph illustrating the process of changing the duty cycle in a way that improves performance. [Figure 10] Figure 10 is a graph showing an example of the change in DL passage interval σ and duty cycle with respect to control time in DL coupling control. [Figure 11] Figure 11 is a graph showing an example of DL position shift caused by piezo duty. [Figure 12] Figure 12 is a graph showing EUV performance when DL misalignment occurs. [Figure 13] Figure 13 is a graph showing DL position shifts originating from piezo duty. [Figure 14] Figure 14 is a schematic diagram of the DL generation operation corresponding to each of the enclosed areas in Figure 13. [Figure 15]FIG. 15 is a diagram schematically showing the configuration of the EUV light generation apparatus according to Embodiment 1. [Figure 16] FIG. 16 is an example of a droplet position detection image as image data acquired via the DL position sensor. [Figure 17] FIG. 17 shows an example of the piezo Duty operation in the EUV light generation apparatus. [Figure 18] FIG. 18 is a flowchart showing an example of the DL coupling adjustment subroutine according to Embodiment 1. [Figure 19] FIG. 19 is a graph showing an example of the prohibited Duty set based on the data showing the relationship between the piezo Duty and the DL position deviation. [Figure 20] FIG. 20 is a flowchart showing an example of the subroutine of the DL coupling control applied to step S4 in FIG. 5. [Figure 21] FIG. 21 is a conceptual diagram of an operation in which setting to the piezo Duty is prohibited. [Figure 22] FIG. 22 is a flowchart showing an example of the DL coupling control subroutine according to a modification of Embodiment 1. [Figure 23] FIG. 23 is a diagram schematically showing an example of the configuration of the EUV light generation apparatus according to Embodiment 2. [Figure 24] FIG. 24 is a flowchart showing the main flow of the operation of the EUV light generation apparatus. [Figure 25] FIG. 30 is a flowchart showing an example of the subroutine of the DL coupling control based on the EUV light applied to step S6. [Figure 26] FIG. 26 is a graph showing the relationship between the Duty acquired in step S73 and the index value based on CE. [Figure 27] FIG. 27 is a graph for explaining the process of changing the Duty in the improvement direction. [Figure 28] FIG. 28 is a graph showing an example of the CE measurement value, the CE difference, and the frequency distribution of the CE difference when a coupling failure of the DL occurs. [Figure 29]Figure 29 is a graph showing an example of CE measurement values, CE difference, and frequency distribution of the CE difference when DL binding is normal. [Figure 30] Figure 30 is a schematic diagram showing the configuration of an exposure apparatus connected to an EUV light generator. [Figure 31] Figure 31 is a schematic diagram showing the configuration of the inspection device connected to the EUV light generator. Embodiment

[0009] -table of contents- 1. Explanation of Terms 1.1 DL passing interval σ 1.2 Duty 2. Overview of the EUV light generation system related to the comparative example 2.1 Configuration 2.2 Operation 2.2.1 Example of DL binding adjustment 2.2.2 Example of DL coupling control 2.3 Challenges 2.4 Mechanism of DL positional misalignment (Mechanism of the problem) 3. Embodiment 1 3.1 Configuration 3.2 Operation 3.2.1 Example of DL binding adjustment 3.2.2 Example of DL coupling control 3.3 Action and Effects 3.4 Variations 3.4.1 Configuration 3.4.2 Operation 3.4.3 Action and Effects 4. Embodiment 2 4.1 Configuration 4.2 Operation 4.3 Examples of index values ​​based on CE 4.4 Action and Effects 5. Combinations of indicators for determining prohibited duties 6. Methods for Manufacturing Electronic Devices 7. About the processor 8. Other

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. The embodiments described below are examples of the disclosure and are not intended to limit the scope of this disclosure. Furthermore, not all configurations and operations described in each embodiment are necessarily essential to the configurations and operations of this disclosure. The same reference numerals are used for identical components, and redundant descriptions are omitted.

[0011] 1. Explanation of Terms 1.1 DL passing interval σ Figure 1 is a schematic diagram showing a configuration for measuring the droplet passage interval σ, which is the time interval over which a droplet passes through. Figure 1 shows a nozzle for ejecting a target substance, a droplet formed by the target substance ejected from the nozzle, and a droplet detection sensor, which is a timing sensor for detecting the timing of the droplet's passage. The droplet detection sensor is positioned opposite the position through which the droplet passes. The droplet detection sensor includes a photodetector (not shown) and detects the change in the output voltage of the photodetector as the droplet passes through. The voltage of the photodetector is set to a detection threshold for light emission triggering for the pulse laser device. The droplet detection sensor may also include an illumination light source (not shown) for illuminating the droplet.

[0012] Note that "droplet" refers to a form of target supplied into the chamber. A droplet can mean a drop-shaped target that has become nearly spherical due to the surface tension of the molten target material. In the specification and drawings, "DL" is an abbreviation for "droplet".

[0013] The jet of target material ejected from the nozzle separates into droplets, and multiple droplets combine to form a droplet-like particle (DL). A DL that is properly output and has combined in the specified number of droplets casts a relatively large shadow. Therefore, when a properly output DL passes through the droplet detection sensor, the voltage of the photodetector drops significantly. As a result, the voltage of the photodetector falls below the detection threshold for light emission triggering, which becomes the trigger point for the pulsed laser device.

[0014] On the other hand, depending on the DL generation conditions, DLs with insufficient bonding and unbonded droplets may occur. While poorly bonded DLs result in smaller shadows and a smaller voltage drop on the photodetector, the voltage on the photodetector may fall below the detection threshold for light emission triggering, potentially triggering the pulsed laser device.

[0015] To avoid such phenomena, DL generation conditions are determined using the detection interval (hereinafter referred to as "DL pass interval") as an indicator, where the voltage at the photodetector falls below the detection threshold for light emission triggering. When DL coupling is normal, the DL pass interval becomes a predetermined DL generation period, and DL coupling is evaluated using the DL pass interval variation σ, calculated by the following equation 1.

[0016]

number

[0017] In Equation 1, n is the number of calculated samples, Ii is the i-th DL pass interval, and Iave is the average DL pass interval for the number of calculated samples. Hereafter, the DL pass interval variability σ is referred to as "DL pass interval σ". The unit of DL pass interval σ is, for example, nanoseconds [ns].

[0018] Figure 2 is a schematic diagram of the output signal (pass-through timing signal) of the photodetector of a droplet detection sensor. In Figure 2, the horizontal axis represents time, and the vertical axis represents, for example, voltage. Figure 2, left F2A, shows the case where the DL pass-through interval is stable. Figure 2, right F2B, shows the case where the DL pass-through interval is unstable. When DL coupling is normal, the DL pass-through interval is stable and the DL pass-through interval σ is small, as shown in Figure 2A. In contrast, when DL coupling is poor, the DL pass-through interval becomes unstable and the DL pass-through interval σ is large, as shown in Figure 2B.

[0019] 1.2 Duty Figure 3 shows an example of an electrical signal applied to a piezoelectric element for generating a droplet. Figure 3 is an example of a square wave with a predetermined period. In Figure 3, the horizontal axis represents time and the vertical axis represents voltage. "Duty" is the percentage [%] of the on-time (high-potential voltage time) Ts within one period T of the square wave.

[0020] 2. Overview of the EUV light generation system related to the comparative example 2.1 Configuration Figure 4 is a schematic diagram showing an example configuration of an LPP-type EUV light generation system related to a comparative example. The comparative example in this disclosure is a form that the applicant recognizes as being known only to the applicant, and is not a prior art example acknowledged by the applicant. The term "EUV light" is an abbreviation for "extreme ultraviolet light."

[0021] The EUV light generator 10 comprises a target generation system 20, a chamber 22, an EUV light generation processor 24, and a droplet detection device 50. The EUV light generator 10 is used together with a pulsed laser device 90. In this disclosure, the system including the EUV light generator 10 and the pulsed laser device 90 is referred to as the EUV light generation system.

[0022] The target generation system 20 includes a target supply unit 32, an inert gas supply unit 34, a piezo power supply 37, and a heater power supply 38.

[0023] The target supply unit 32 includes a nozzle 42 with a hole for outputting molten target material 40, a filter 43, a tank 44 for containing the target material 40, a heater 45, a temperature sensor 46, a piezoelectric element 47, and a pressure regulator 48.

[0024] Nozzle 42 corresponds to the nozzle shown in Figure 1. Filter 43 is located upstream of nozzle 42 and removes impurities contained in the target substance 40. The target substance 40 is, for example, tin (Sn). Nozzle 42, heater 45, and temperature sensor 46 are fixed to tank 44. Piezo element 47 is fixed to nozzle 42.

[0025] The pressure regulator 48 is installed in the piping 49 between the inert gas supply unit 34 and the tank 44. The inert gas supplied from the inert gas supply unit 34 may be, for example, Ar or He gas.

[0026] The target substance 40 inside the tank 44 is output as a jet 81 from the nozzle 42 due to the pressure difference between the inert gas supplied from the pressure regulator 48 and the pressure inside the chamber 22. When the nozzle 42 is vibrated by the piezoelectric element 47, the jet 81 output from the nozzle 42 separates into droplets, becoming droplets 82 (hereinafter referred to as DL82).

[0027] Chamber 22 comprises a droplet detection device 50, a laser focusing optical system 54, a biaxial stage 55, and a target retrieval unit 56.

[0028] The droplet detection device 50 (hereinafter referred to as DL detection device 50) corresponds to the droplet detection sensor shown in Figure 1. The DL detection device 50 comprises a light source unit 61 and a light receiving unit 62. The light source unit 61 comprises a CW laser 63 which is a light source, an illumination optical system 64 which is a focusing lens, and a window 65. The light source unit 61 is positioned to illuminate the DL 82 at a predetermined position P on the target trajectory between the nozzle 42 of the target supply unit 32 and the plasma generation region 80. The DL detection device 50 is an example of the "first sensor" in this disclosure.

[0029] The light-receiving unit 62 comprises a photosensor 66, which is a light-receiving element, a window 67 that guides CW laser light to the photosensor 66, and a light-receiving optical system 68. The light-receiving unit 62 is positioned to receive CW laser light output from the light source unit 61. When DL82 blocks the CW laser light, the output of the photosensor 66 fluctuates. Based on this fluctuation, the light-receiving unit 62 outputs a passing timing signal TS that indicates the timing when DL82 will pass through position P. The passing timing signal TS is input to the EUV light generation processor 24.

[0030] The EUV photogeneration processor 24 includes a control program 25 and a delay circuit 26. The pass-through timing signal TS is input to the delay circuit 26 via the EUV photogeneration processor 24. The EUV photogeneration processor 24 sets the delay time of the delay circuit 26. The delay circuit 26 may be configured separately from the EUV photogeneration processor 24, and a signal line for setting the delay time of the delay circuit 26 may be connected from the EUV photogeneration processor 24 to the delay circuit 26.

[0031] The delay circuit 26 generates a light emission trigger signal Tr by adding a delay time to the passing timing signal TS. The light emission trigger signal Tr output from the delay circuit 26 is input to the pulse laser device 90.

[0032] The pulsed laser device 90 outputs pulsed laser light based on the light emission trigger signal Tr. The pulsed laser device 90 may be, for example, a CO2 laser device. Alternatively, the pulsed laser device 90 may be a solid-state laser device that uses a crystal doped with impurities from one of the following as the laser medium: YVO4 (yttrium vanadium oxide), YLF (yttrium lithium fluoride), or YAG (yttrium aluminum garnet).

[0033] The laser focusing optical system 54 is an optical system that focuses the pulsed laser light output from the pulsed laser device 90 and guided into the chamber 22 onto the plasma generation region 80. The laser focusing optical system 54 is supported by a biaxial stage 55. The biaxial stage 55 can move the laser focusing optical system 54 in two directions: a first axis direction and a second axis direction. For example, the first axis direction may be the Z-axis direction and the second axis direction may be the Y-axis direction.

[0034] By adjusting the position of the laser focusing optical system 54 using the two-axis stage 55, the focusing position of the pulsed laser beam can be adjusted to the plasma generation region 80. The laser focusing optical system 54 may include multiple optical elements.

[0035] The target retrieval unit 56 is positioned on the orbit of DL82 and retrieves DL82 when it is not irradiated with pulsed laser light.

[0036] Furthermore, an EUV light focusing mirror (not shown) is positioned within the chamber 22. The EUV light focusing mirror has a spheroidal reflective surface. A multilayer reflective film is formed on the reflective surface of the EUV light focusing mirror, with alternating layers of molybdenum and silicon. The EUV light focusing mirror has a first focal point and a second focal point, and is positioned so that the first focal point is located in the plasma generation region 80. The EUV light focusing mirror selectively reflects EUV light from the synchrotron radiation emitted from the plasma generated in the plasma generation region 80. The EUV light focusing mirror focuses the selectively reflected EUV light at the second focal point (intermediate focal point). An aperture (not shown) is positioned at the intermediate focal point, and the EUV light that passes through the aperture is incident on an exposure apparatus or inspection apparatus (not shown).

[0037] 2.2 Operation Figure 5 is a flowchart showing the main flow of operation of the EUV light generation device 10. In step S1, the EUV light generation processor 24 executes a control program 25 when it receives a command to generate EUV light from an operator or an external device (not shown). As the EUV light generation processor 24 starts executing the control program 25, DL82 is discharged from the target supply unit 32 in step S2.

[0038] In step S2, the EUV photogeneration processor 24 controls the heater power supply 38 based on the temperature sensor 46's detection value so that the Sn in the target supply unit 32 reaches a temperature above its melting point, thereby melting the Sn stored in the tank 44. For example, the EUV photogeneration processor 24 controls the heater power supply 38 so that the Sn in the target supply unit 32 reaches a predetermined temperature of 232°C to 300°C. The EUV photogeneration processor 24 also controls the inert gas to a predetermined pressure, for example, 0.2 MPa to 40 MPa, using the pressure regulator 48, and outputs the liquid Sn in the tank 44 to the outside of the nozzle 42.

[0039] The EUV photogeneration processor 24 vibrates the nozzle 42 so that the jet 81 of liquid Sn output from the nozzle 42 forms droplets, and then multiple droplets combine to generate coupled DL of a predetermined diameter and period. For example, the EUV photogeneration processor 24 applies a square wave voltage waveform of a predetermined frequency and duty cycle to the piezoelectric element 47 via the piezoelectric power supply 37, causing the nozzle 42 to vibrate at a predetermined frequency. The piezoelectric element 47 is an example of an excitation element that vibrates the liquid target material 40.

[0040] Hereafter, in this specification, when "DL" refers to generating a DL or generating a DL, unless otherwise specified, it refers to a coupled DL. In this specification, the duty cycle of the rectangular voltage waveform applied to the piezoelectric element 47 is referred to as the "duty cycle of the piezoelectric element 47," "piezo duty cycle," or simply "duty cycle." Duty cycle is one of the vibration parameters related to the vibration of the piezoelectric element 47, and the value of Duty cycle is referred to as the "duty cycle value."

[0041] In step S3, the EUV photogeneration processor 24 performs DL coupling adjustment. DL coupling adjustment is a process that adjusts the DL passage interval σ to an appropriate duty cycle. Specific examples of the DL coupling adjustment subroutine applied in step S3 will be described later with reference to Figures 6 and 7.

[0042] Subsequently, in step S4, the EUV light generation processor 24 starts DL coupling control to maintain the DL coupling state by fine-tuning the Duty cycle. Note that DL coupling control may be performed regardless of whether pulsed laser light is irradiating DL82 (no EUV emission) or irradiating it (EUV emission). A specific example of the subroutine applied to the DL coupling control in step S4 will be described later with reference to Figure 8.

[0043] Once step S4 is completed, the EUV photogeneration processor 24 terminates the flowchart shown in Figure 5.

[0044] 2.2.1 Example of DL binding adjustment Figure 6 is a flowchart showing an example of a DL coupling adjustment subroutine applied to step S3 in Figure 5. This subroutine is executed during DL ejection when EUV emission is not occurring.

[0045] When the processing in step S3 begins, in step S11, the EUV light generation processor 24 reads the initial parameters and sets the duty cycle of the piezoelectric element 47 to the initial lower limit D. LL Set to the lower limit D in the initial parameters. LL In addition, upper limit D UL This includes the step amount d, the number of samples used to calculate the DL passage interval σ, the moving average number Nσ of the DL passage interval σ, the threshold S1 of the DL passage interval σ, and the threshold B for determining the continuous duty cycle.

[0046] Typical values ​​for initial parameters include the lower bound D. LL is 1[%], upper limit D UL The step size d may be 99%, the step size d may be 0.1%, the number of samples used to calculate the DL pass interval σ may be 10000, the number of moving averages Nσ for the DL pass interval σ may be 0.6%, and the threshold S1 for the DL pass interval σ may be 170ns. If the step size d is 0.1%, then a moving average Nσ of 0.6% for the DL pass interval σ means that the number of intervals for the moving average is 0.6 ÷ 0.1 = 6. Furthermore, the threshold B for continuous duty cycle determination should be set after determining a value that allows the connection to be maintained for a long time through experiments or other means. The threshold B for continuous duty cycle determination may be 0.6% or greater; for example, threshold B may be 0.6%.

[0047] The EUV light generation processor 24 sets the duty cycle to a lower limit D LL From upper limit D UL Within the numerical range up to [value], it can be changed in units of the step amount d.

[0048] In step S12, the EUV light generation processor 24 measures the DL passing interval σ of the set Duty value. That is, the EUV light generation processor 24 controls the piezo power supply 37 to apply the voltage waveform of the rectangular wave of the set Duty value to the piezo element 47, and drives the piezo element 47 through the piezo power supply 37 to generate the DL82. Further, the EUV light generation processor 24 acquires the passing timing signal TS through the EUV light generation processor 24, and calculates the DL passing interval σ based on the passing timing signal TS and Equation 1. The number of DLs for each Duty value, which is the number of calculation samples of the DL passing interval σ, may be, for example, 10,000. Then, the EUV light generation processor 24 associates the Duty and the DL passing interval σ and stores them in the memory.

[0049] In step S13, the EUV light generation processor 24 determines whether the set Duty value is less than the upper limit value D UL If the determination result in step S13 is a Yes determination, the EUV light generation processor 24 proceeds to step S14, sets a new Duty value obtained by adding the step amount d to the set Duty value, and then returns to step S12.

[0050] Until the Duty value reaches the upper limit value D UL The loop of steps S12 to S14 is repeated. In this way, while increasing the Duty from the lower limit value D LL to the upper limit value D UL in increments of the step amount d, the characteristic data (see FIG. 7) showing the relationship between the Duty and the DL passing interval σ is obtained by measuring the DL passing interval σ for each Duty value.

[0051] When the Duty value reaches the upper limit value D UL and the determination result in step S13 is a No determination, the EUV light generation processor 24 proceeds to step S15. In step S15, the EUV light generation processor 24 selects a region candidate in which the condition that the DL passing interval σ is less than the threshold value S1 is satisfied and the width of the continuous Duty region (continuous region) is equal to or greater than the threshold value B.

[0052] In step S16, the EUV photogeneration processor 24 calculates a moving average of the DL pass interval σ with respect to the duty cycle for each candidate region selected in step S15. Alternatively, the EUV photogeneration processor 24 may perform a filter operation on the data sequence to smooth out any outliers instead of using a moving average.

[0053] In step S17, the EUV photogeneration processor 24 sets the operating duty cycle to the duty cycle that minimizes the moving average calculated in step S16. After step S16, the EUV photogeneration processor 24 returns to the flowchart in Figure 5.

[0054] Figure 7 is a graph showing an example of the DL pass-through interval σ measured during DL coupling adjustment. In Figure 7, the horizontal axis represents Duty, and the vertical axis represents the DL pass-through interval σ. Figure F7A in the upper part of Figure 7 is an example of the DL pass-through interval σ obtained by scanning the Duty value from 1% to 99% in increments of 0.1% while the pulsed laser light irradiation was stopped.

[0055] In Figure F7A above, the four candidate regions CA11, CA12, CA13, and CA14 satisfy the conditions that the DL passage interval σ is less than the threshold S1 and the width of the continuous region is greater than or equal to the continuous duty width determination threshold B. Candidate regions CA11, CA12, CA13, and CA14 are regions near duty values ​​of 3[%], 53[%], 56[%], and 93[%], respectively.

[0056] Here, for each of the four candidate regions CA11, CA12, CA13, and CA14, a moving average of the DL passage interval σ against the duty cycle is calculated, and the duty cycle value that minimizes the moving average is set as the operating duty cycle value. Figure 7, lower section F7B, is an enlarged graph of candidate region CA12, showing an example of an operating duty cycle value set from the moving average.

[0057] 2.2.2 Example of DL coupling control Figure 8 is a flowchart showing an example of a DL coupling control subroutine applied to step S4 in Figure 5. In the DL coupling control subroutine in Figure 8, the duty cycle is controlled using the DL passage interval σ as an indicator. This subroutine can be implemented both when EUV is not emitting light and when EUV is emitting light.

[0058] When the processing in step S4 begins, in step S21, the EUV photogeneration processor 24 reads the initial settings. The parameters to be initialized include the search width ΔDu of the Duty value, the number of search levels N of the Duty, the amount of movement da of the Duty, and the number of samples Ns for calculating the DL passage interval σ. The EUV photogeneration processor 24 reads the initial settings for each of these parameters. Typical values ​​for the parameters include, for example, the search width ΔDu is preferably 0.02[%], the number of search levels N is preferably 2 or more, for example 5, the amount of movement da of the Duty is 0.02[%], and the number of samples for calculating the DL passage interval σ may be 10000.

[0059] In step S22, the EUV light generation processor 24 generates DLs by driving the piezoelectric elements 47 at each N duty cycle value on the positive and negative sides, centered around the current duty cycle value, based on the initial settings read in step S21. Furthermore, the EUV light generation processor 24 obtains the DL pass interval σ for the generated DLs and calculates the correlation between the duty cycle and the DL pass interval σ. The intervals of the number of search levels N may be the search width ΔDu, and the order in which the duty cycle values ​​are set when changing levels can be arbitrary. It is also desirable that the search range determined by the search width ΔDu be set to a width that produces a significant difference in DL coupling performance.

[0060] In step S23, the EUV light generation processor 24 calculates a linear approximation line with Duty on the horizontal axis and DL passage interval σ on the vertical axis based on the correlation between Duty and DL passage interval σ obtained in step S22, and identifies its slope (see Figure 9).

[0061] In step S24, the EUV photogeneration processor 24 changes the Duty Cycle in the direction of performance improvement, i.e., in the direction that reduces the DL passage interval σ, based on the gradient of the approximate straight line identified in step S23. For example, if the gradient is positive, the EUV photogeneration processor 24 changes the Duty Cycle in the negative direction from the current value (position 0). If the gradient is negative, the EUV photogeneration processor 24 changes the Duty Cycle in the positive direction from the current value. The amount of change in Duty Cycle at this time may be set to a Duty Cycle value that differs by a displacement amount da from the current value, or to any Duty Cycle value in the direction of performance improvement. The amount of change in Duty Cycle may also differ depending on the value of the gradient. From this point onward, the piezoelectric element 47 is driven by a Duty Cycle value that results in a smaller DL passage interval σ.

[0062] Furthermore, if the absolute value of the gradient can be considered as 0, the EUV light generation processor 24 does not need to change the Duty Cycle.

[0063] After step S24, the EUV light generation processor 24 returns to step S22 and repeats the same process (steps S22 to S24) with the modified Duty value as the current value.

[0064] The processing in steps S22 to S24 is a process to maintain the coupling state of the DL by fine-tuning the duty cycle using the DL passage interval σ as an indicator, and is repeated as long as it is necessary to maintain the coupling state of the DL. When it is no longer necessary to maintain the coupling state of the DL due to the stopping of the DL output by a stop command from the operator or an external device (not shown), the EUV light generation processor 24 terminates the repeated processing and exits this subroutine.

[0065] Figure 9 is a graph illustrating the process of changing the Duty Cycle in a direction that improves performance. In Figure 9, the horizontal axis represents the Duty Cycle, and the vertical axis represents the DL passage interval σ. The circles in Figure 9 represent the plotted positions of the DL passage interval σ relative to the Duty Cycle, and the numbers inside the circles represent the search order. In the example shown in Figure 9, the Duty Cycle values ​​for search orders 1, 2, 3, 4, and 5 are "current value," "current value - ΔDu," "current value - ΔDu × 2," "current value + ΔDu," and "current value + ΔDu × 2," respectively. From these five plotted points, the approximate straight line AL1, shown as a dashed line in Figure 9, can be obtained by a first-order approximation.

[0066] In the example in Figure 9, the gradient G of the approximate line AL1 is 0, and reducing the Duty cycle relative to the current value improves the value of the DL passage interval σ. Therefore, in this case, the process in step S24 is to change the Duty cycle value by a displacement amount da in the negative direction from the current value.

[0067] Figure 10 is a graph showing an example of the change in DL passage interval σ and duty cycle with respect to control time in DL coupling control. In this example, the DL passage interval σ is improved by controlling the duty cycle to increase over the long term.

[0068] 2.3 Challenges In the comparative example, duty cycle adjustment is performed based on a time-based indicator using the DL detection device 50. Therefore, if the DL performance deterioration is due to "space" originating from the duty cycle that cannot be detected by the DL detection device 50, the duty cycle cannot be adjusted.

[0069] For example, one instance of DL performance degradation due to "space" that cannot be detected by the DL detection device 50 is the phenomenon of horizontal DL positional displacement (so-called "lateral displacement") occurring at certain piezo duties.

[0070] Figure 11 is a graph showing an example of DL position deviation caused by piezo duty. The middle section of Figure 11 shows the piezo duty setting, the upper section shows the DL position deviation, and the lower section shows the DL passage interval σ. DL position deviation refers to the amount of deviation of the DL from the target position (DL position deviation). The horizontal axis of each graph is time, and the time axes are coincident.

[0071] As shown in Figure 11, when a specific piezo duty cycle is used, a relative misalignment occurs between the DL and the laser beam irradiation position, leading to deterioration of EUV energy stability (see Figure 12) and fragmentation.

[0072] Figure 12 is a graph showing the EUV performance (in this case, EUV energy) when DL positional misalignment occurs.

[0073] If the EUV collector mirror becomes contaminated due to fragmentation, maintenance will be required, raising concerns about reduced equipment operating time and increased costs due to frequent maintenance.

[0074] Therefore, there was a need for an EUV light generator that could adjust the duty cycle while suppressing DL positional shift.

[0075] 2.4 Mechanism of DL positional misalignment (Mechanism of the problem) The mechanism of DL displacement originating from piezo duty will be explained with reference to Figures 13 and 14. Figure 13 is a graph showing DL displacement originating from piezo duty.

[0076] Figure 14 is a schematic diagram of the DL generation operation corresponding to the areas enclosed by the box lines 13A and 13B in Figure 13, respectively. The left figure F14A in Figure 14 shows the DL generation operation corresponding to the area enclosed by the box line 13A in Figure 13, and the right figure F14B shows the DL generation operation corresponding to the area enclosed by the box line 13B in Figure 13.

[0077] As shown in Figure 14, left diagram F14A, when the DL generation operation is normal, the main DL (laser-irradiated DL) ejected from nozzle 42 combines with the motion components of the microdroplets before coupling and passes along a predetermined trajectory (hereinafter referred to as the DL trajectory).

[0078] Therefore, as shown in Figure F14B on the right, if there are unbound microdroplets (extra droplets), according to the law of conservation of momentum, the horizontal motion component of the extra droplets is removed, giving the main DL an opposite horizontal motion component, and thus a deviation from the DL trajectory in the case without extra droplets occurs.

[0079] 3. Embodiment 1 3.1 Configuration Figure 15 is a schematic diagram showing the configuration of the EUV light generation apparatus 10A according to Embodiment 1. The differences between the configuration shown in Figure 15 and the EUV light generation apparatus 10 shown in Figure 4 will be explained below.

[0080] The EUV light generator 10A includes a droplet position sensor (DL position sensor) 76. The DL position sensor 76 is positioned to observe the DL trajectory between the target supply unit 32 and the plasma generation region 80. The DL position sensor 76 is configured to include an image sensor such as a CCD camera. The DL position sensor 76 is an example of the "second sensor" in this disclosure.

[0081] The EUV light generator 10A may include a light source (not shown) that illuminates DL82 within the field of view of the DL position sensor 76. The chamber 22 includes a window 77, and the DL position sensor 76 can image DL82 within the field of view through the window 77. The DL position sensor 76 is connected to the EUV light generator processor 24. Other configurations may be the same as those of the EUV light generator 10 shown in Figure 4. The field of view of the DL position sensor 76 is an example of a "droplet passage position" in this disclosure.

[0082] 3.2 Operation The operation of the EUV light generation device 10A will be described. The DL position sensor 76 images DL82 and acquires image data. The image data obtained by the DL position sensor 76 is transmitted to the EUV light generation processor 24.

[0083] The EUV light generation processor 24 calculates the DL position from the acquired image data.

[0084] Figure 16 shows an example of a droplet position detection image as image data acquired via the DL position sensor 76. For example, the DL position sensor 76 is positioned to observe the DL trajectory from the positive X-axis side to image DL82, and the Z-direction position of DL82 is determined by associating the image with coordinates.

[0085] Furthermore, the X-direction position of DL82 may be obtained by positioning a DL position sensor (not shown) to observe the DL trajectory from the positive Z-axis side.

[0086] Figure 17 shows an example of piezo duty cycle operation in the EUV light generator 10A. The EUV light generator 10A stores piezo duty cycles in which DL position shift occurs during DL coupling adjustment. The EUV light generation processor 24 then does not set piezo duty cycles in which DL position shift occurs during duty cycle adjustment operations such as DL coupling control. In other words, the EUV light generation processor 24 provides a prohibited duty cycle region (prohibited band) in which setting of piezo duty cycles is prohibited. The prohibited band may be a series of consecutive duty cycle regions or a collection of discrete duty cycle regions. The prohibited duty cycle region is an example of a "prohibited duty cycle" in this disclosure.

[0087] The thick line in the graph in the middle of Figure 17 represents the duty cycle that causes DL positional shift.

[0088] The EUV light generation processor 24 sets the piezo duty cycle while avoiding the forbidden zone where DL position shift occurs. As a result, DL position shift is suppressed, which is clear when compared with Figure 11.

[0089] The main operation flow of the EUV light generator 10A is the same as in Figure 5, but it differs from the operation of the comparative example in that, in step S3, DL coupling adjustment, not only is the DL passage interval σ used as an indicator, but the DL position is also used as an indicator.

[0090] In other words, the operation of the EUV light generator 10A differs from that of the EUV light generator 10 in the comparative example in that the DL coupling adjustment subroutine and the DL coupling control subroutine are different.

[0091] 3.2.1 Example of DL binding adjustment Figure 18 is a flowchart showing an example of a DL coupling adjustment subroutine according to Embodiment 1. The differences between Figure 18 and Figure 6 will be explained below.

[0092] The flowchart shown in Figure 18 includes step S31 instead of step S12 in Figure 6, and steps S32 and S33 instead of step S15.

[0093] In the DL coupling adjustment subroutine shown in Figure 18, the duty cycle is adjusted based on the DL passage interval σ and the DL position. Therefore, the initial parameters read in step S11 of Figure 18 include, in addition to those described in Figure 6, the DL target position, the number of DL position calculation samples, and the DL position deviation threshold P1. Typical values ​​for these initial parameters are, for example, a DL target position of 0 [μm], a DL position calculation sample count of 5, and a threshold P1 of 2 [μm].

[0094] In step S31, following step S11, the EUV light generation processor 24 measures the DL position deviation from the target position and the DL passage interval σ at the set duty cycle. Specifically, the EUV light generation processor 24 controls the piezoelectric power supply 37 to apply a rectangular voltage waveform of the set duty cycle to the piezoelectric element 47 to generate DL82, and measures the DL position deviation from the image data obtained from the DL position sensor 76. The method by which the EUV light generation processor 24 measures the DL passage interval σ is the same as in step S15. The EUV light generation processor 24 then associates (links) the duty cycle, DL position deviation, and DL passage interval σ and stores them in memory.

[0095] If multiple DL position sensors 76 are arranged, the DL position deviation from the target position of the detected position at each DL position sensor is stored. The EUV light generation processor 24 measures the DL passage interval σ while keeping conditions other than the duty cycle constant. After step S31, the process proceeds to step S13.

[0096] Duty Value upper limit D UL Steps S31, S13, and S14 are repeated until the lower limit D of Duty is reached. LL From upper limit D UL By increasing the step amount d in increments up to a certain point, and measuring the DL position deviation and DL passage interval σ at each duty cycle value, characteristic data showing the relationship between duty cycle, DL position deviation, and DL passage interval σ can be obtained.

[0097] If the result of step S13 is No, the EUV light generation processor 24 proceeds to step S32.

[0098] In step S32, the EUV photogenerator 24 stores piezoDuty periods in which the DL position deviation is greater than or equal to threshold P1 as prohibited Duty periods, based on the characteristic data acquired in step S31 (see Figure 19). If multiple DL position sensors are arranged, any DL position deviation of any of the sensors is greater than or equal to threshold P1 and is therefore prohibited Duty. Furthermore, the prohibited Duty periods stored in step S32 may be updated at predetermined time intervals or with each DL coupling adjustment. Threshold P1 or greater is an example of "greater than or equal to the first threshold" in this disclosure.

[0099] In step S33, the EUV light generation processor 24 selects candidate regions where the DL position deviation is less than threshold P1 and the DL passage interval σ is less than threshold S1, and the width of the continuous duty region (continuous region) is greater than or equal to the continuous duty width determination threshold B. Such conditions are an example of the "predetermined conditions" in this disclosure.

[0100] After step S33, the EUV photogeneration processor 24 proceeds to step S16.

[0101] The other steps are the same as in Figure 6.

[0102] Figure 19 is a graph showing an example of a prohibited duty cycle set based on data illustrating the relationship between piezo duty cycle and DL position deviation. In Figure 19, the area of ​​duty cycles indicated by the filled pattern is the prohibited zone, and duty cycles belonging to the prohibited zone are prohibited duty cycles that cannot be set. In Figure 19, duty cycles where the DL position deviation is greater than or equal to the threshold P1 of 2 [μm] are stored as prohibited duty cycles.

[0103] 3.2.2 Example of DL coupling control Figure 20 is a flowchart showing an example of a DL coupling control subroutine applied to step S4 in Figure 5. The differences between Figure 20 and Figure 8 will be explained below.

[0104] In step S21 of Figure 20, the EUV photogeneration processor 24 reads the parameters described in step S21 of Figure 8, as well as the information on the prohibited duty cycle obtained in DL coupling adjustment (Figure 18) where the DL position deviation ≥ threshold P1.

[0105] The flowchart shown in Figure 20 includes step S51 instead of step S22 in Figure 8.

[0106] In step S51 following step S21, the EUV light generation processor 24 changes the Duty cycle by a search width ΔDu on both the positive and negative sides, centered on the current Duty cycle value, and obtains the DL passage interval σ at each level (see Figure 9). However, in step S51, if the Duty cycle value after the change by the search width ΔDu falls within the prohibited Duty cycle, or crosses the prohibited Duty cycle, the EUV light generation processor 24 will not set the Duty cycle to a value beyond the Duty cycle value of the level before the change on the positive (or negative) side.

[0107] Furthermore, in step S24, if the destination Duty to which the Duty is moved by da is a prohibited Duty, or if it crosses a prohibited Duty, the piezo Duty will not be set. Other operations are the same as in the flowchart of Figure 8. The approximate line AL1 (Figure 9) in step S23 of Figure 20 is an example of the "first approximate line" in this disclosure.

[0108] Figure 21 is a conceptual diagram of the operation in which setting to a prohibited duty cycle or a piezo duty cycle that crosses a prohibited duty cycle is prohibited. In Figure 21, the horizontal axis represents the piezo duty cycle, and the vertical axis represents the average DL pass interval σ. When changing the piezo duty cycle within the DL coupling control operation, for example, the piezo duty cycle is changed in units of the search width ΔDu from the initial level, and the DL pass interval σ is measured. However, as shown in Figure 21, even if the DL coupling performance is improved, the EUV photogeneration processor 24 does not set to a prohibited duty cycle that causes DL misalignment, or a piezo duty cycle that crosses a prohibited duty cycle.

[0109] The droplet generation control method in Embodiment 1 is an example of a "droplet generation control method" in this disclosure.

[0110] 3.3 Action and Effects According to the EUV light generator 10A of Embodiment 1, setting the piezoDuty to one that causes DL position shift is prevented, thus preventing DL position shift originating from the piezoDuty. As a result, the relative irradiation position between DL82 and the laser light is stabilized, and EUV energy stability is maintained. Furthermore, fragment generation caused by relative position shift between DL82 and the laser light is suppressed, and contamination of the EUV collector mirror is suppressed.

[0111] 3.4 Variations 3.4.1 Configuration The configuration of the EUV light generation apparatus according to a modified example of Embodiment 1 may be the same as that of the EUV light generation apparatus 10A shown in Figure 15.

[0112] 3.4.2 Operation In the modified EUV light generator according to Embodiment 1, the DL position [μm] is also evaluated during DL coupling control in step S4 of Figure 5. The operation of the modified Embodiment 1 differs from that of Embodiment 1 in that, when there is a piezoDuty that satisfies DL position deviation ≥ threshold P1 during DL coupling control, the duty that satisfies this condition is added to the prohibited duty and the prohibited duty data is updated. Other operations may be the same as in Embodiment 1.

[0113] Figure 22 is a flowchart showing an example of a DL coupling control subroutine according to a modified embodiment of Embodiment 1. The differences between the flowchart shown in Figure 22 and Figure 20 will be explained below.

[0114] In step S21 in Figure 22, the EUV photogeneration processor 24 reads the initial settings described in step S21 of Figure 20, as well as the initial settings for the DL target position, the number of DL position calculation samples, and the DL position deviation threshold P1. Typical values ​​for each of these initial parameters are the same as those described in the example in step S21 of Figure 8.

[0115] Figure 22 includes step S61 instead of step S51 in Figure 20. In step S61, the EUV light generation processor 24 changes the Duty cycle by a search width ΔDu on both the positive and negative sides, centered on the current Duty cycle value, and obtains the DL passage interval σ and DL position deviation at each level.

[0116] The EUV light generation processor 24 stores the current piezo duty cycle and adds it to the prohibited duty cycle if the DL position deviation is greater than or equal to the threshold P1. Furthermore, if the target duty cycle for the search width ΔDu is a prohibited duty cycle, or crosses the prohibited duty cycle, the EUV light generation processor 24 does not set the piezo duty cycle on the positive or negative side beyond that point. Other operations are the same as those shown in the flowchart in Figure 20.

[0117] 3.4.3 Action and Effects According to a modified embodiment of Embodiment 1, even if a DL position deviation occurs in a piezoDuty that was below threshold P1 during DL coupling adjustment due to changes over time, the next DL coupling control operation prevents setting the piezoDuty to one that will cause a DL position deviation. This further improves EUV energy stability.

[0118] 4. Embodiment 2 4.1 Configuration Figure 23 is a schematic diagram showing an example configuration of the EUV photogenerator 10B according to Embodiment 2. The differences between the configuration shown in Figure 23 and the EUV photogenerator 10A shown in Figure 15 will be explained. The EUV photogenerator 10B is equipped with an EUV energy sensor 78 instead of a DL position sensor 76. The EUV energy sensor 78 is positioned to observe the plasma generation region 80, measures the EUV energy and transmits it to the EUV photogenerator processor 24.

[0119] Furthermore, the EUV light generator 10B includes a beam splitter BS and a laser energy sensor 79.

[0120] The beam splitter BS is positioned in the optical path of the laser beam between the pulsed laser device 90 and the laser focusing optical system 54. The beam splitter BS is configured to transmit a portion of the incident laser beam and reflect the other portion.

[0121] The laser energy sensor 79 is positioned to receive light transmitted or reflected from the beam splitter BS. The laser energy sensor 79 illustrated in Figure 23 is positioned to receive light transmitted from the beam splitter BS. An optical system (not shown) may be placed between the beam splitter BS and the laser energy sensor 79. This optical system may be a collimating optical system or a focusing optical system. The laser energy sensor 79 measures the laser energy and transmits it to the EUV light generation processor 24. Other configurations may be the same as those of the EUV light generation device 10A.

[0122] 4.2 Operation Figure 24 is a flowchart showing the main operation flow of the EUV light generator 10B. The differences between the flowchart in Figure 24 and that in Figure 5 will be explained below.

[0123] In Figure 24, steps S5 to S7 are included after DL coupling control (step S4). That is, in the EUV light generator 10B, DL coupling control (step S4) is performed before EUV emission to finely adjust the duty cycle with high precision. DL coupling adjustment (step S3) and DL coupling control (step S4) may be the same as in Embodiment 1 or a modified example of Embodiment 1.

[0124] Maintaining the DL-coupled state after step S4 is performed by DL-coupled control based on EUV light (step S6).

[0125] In step S5, the EUV light generation processor 24 generates EUV light.

[0126] In step S6, the EUV light generation processor 24 performs DL coupling control based on EUV light. Specific examples of the processing applied in step S6 will be described later with reference to Figures 25-29, but during EUV light generation, the DL coupling state is controlled by manipulating the duty cycle of the piezoelectric element 47 using CE (Conversion Efficiency), an indicator of EUV performance, as a guide. CE is an example of the "ratio of EUV energy to laser energy" in this disclosure.

[0127] CE is the conversion efficiency of EUV energy to laser energy, and is calculated using the following formula.

[0128] CE = (EUV energy / laser energy) × 100 [%] An index value based on CE (CE index value) is, for example, the outlier rate of the CE difference. Other useful CE index values ​​include the standard deviation of the CE difference and the rate of data occurring outside the normal range (outlier rate) [%].

[0129] If a piezo duty cycle exists during the operation of DL coupling control based on EUV light (step S6) where the CE index value is greater than or equal to the threshold E1, that piezo duty cycle is added as a prohibited duty cycle, and the prohibited duty cycle setting is updated. Note that stored piezo duty cycles may be updated after a predetermined period of time has elapsed. A threshold of E1 or higher is an example of "greater than or equal to the second threshold" in this disclosure.

[0130] In step S7, the EUV light generation processor 24 determines whether to continue EUV light generation. If the result of the determination in step S7 is Yes, the process returns to step S5. If the result of the determination in step S7 is No, the EUV light generation processor 24 terminates the flowchart shown in Figure 24.

[0131] Figure 25 is a flowchart showing an example of a subroutine for DL ​​coupling control based on EUV light applied in step S6. The DL coupling control based on EUV light shown in Figure 25 is performed when EUV light is emitted.

[0132] In step S71, the EUV photogeneration processor 24 reads the initial settings. For example, the parameters to be set may be: search width ΔDu is 0.02[%], number of search levels N is 5, duty cycle shift da is 0.02[%], number of index samples is 20000, and index threshold E1 is 0.05.

[0133] The processes in steps S72 to S74 are repeated processes. In step S72, the EUV light generation processor 24 changes the Duty cycle N times on both the positive and negative sides, centered around the current Duty cycle value, based on the read initial settings, and obtains an index value based on CE (CE index value) for each Duty cycle including the current value. The interval between N levels may be the search width ΔDu, and the order in which the Duty cycles are set when changing levels is arbitrary. Here, the number of search levels N is 2 or more, for example, 5. It is desirable to set the search width ΔDu to a width that produces a significant difference in the index values ​​based on CE.

[0134] If the index value exceeds the threshold E1, the EUV light generation processor 24 stores the current piezo duty cycle (see Figure 26). If the target duty cycle when changing the level is a prohibited duty cycle (piezo duty cycle with index value σ ≥ E1), or if it crosses the prohibited duty cycle, the EUV light generation processor 24 does not set the piezo duty cycle to the positive or negative side beyond that point.

[0135] In step S73, the EUV photogeneration processor 24 calculates a linear approximation line in the correlation between the Duty and CE-based index values ​​obtained in step S72 and identifies its slope (see Figure 27).

[0136] In step S74, the EUV photogeneration processor 24 changes the Duty Cycle in the direction of improving the index value (performance) based on the gradient of the linear approximation line created in step S73. For example, if the gradient is positive, the Duty Cycle is changed in the negative direction from the current value (0 position). The change in Duty Cycle at this time may be set to the amount of movement da or to any Duty Cycle in the direction of improvement. The amount of change in Duty Cycle may also be changed depending on the value of the gradient.

[0137] After step S74, the EUV light generation processor 24 returns to step S72 and repeats the same process with the modified Duty as the current value.

[0138] When the conditions for the repetition termination of steps S72 to S74 are met, the EUV light generation processor 24 exits the flowchart in Figure 25 and returns to the flowchart in Figure 24.

[0139] Figure 26 is a graph showing the relationship between the Duty obtained in step S73 and the index value based on CE. The horizontal axis represents Duty, and the vertical axis represents the index value. The index value here is the rate of occurrence of outliers in the CE difference. If this index value is 0%, it indicates that the DL coupling is in a good state. As shown in Figure 26, Dutys whose index value exceeds the threshold E1 are stored as prohibited Dutys that cannot be set.

[0140] Figure 27 is a graph illustrating the process of changing the Duty cycle in the direction of improvement of the indicator. In Figure 27, the horizontal axis represents the Duty cycle, and the vertical axis represents the indicator value based on the CE. The notation rules for Figure 27 are the same as in Figure 9, with the circles in Figure 27 representing the plotted positions of the indicator value relative to the Duty cycle, and the numbers inside the circles representing the search order. From these five plotted points, the approximate straight line AL2, shown as a dashed line in Figure 27, can be obtained by first-order approximation. The approximate straight line AL2 is an example of a "second approximate straight line" in this disclosure.

[0141] In the example in Figure 27, the slope of the approximation line AL2 is positive, and reducing the Duty relative to the current value improves the index value. Therefore, in this case, as the process in step S74, the Duty value is changed by a displacement of da in the negative direction from the current value.

[0142] 4.3 Examples of index values ​​based on CE The indicators used to evaluate CE may include, for example, the 3σ of CE, the 3σ of the CE difference, the outlier rate of CE, or the outlier rate of the CE difference, all of which are indicators for evaluating the variability of CE. Here, "σ" represents the standard deviation.

[0143] The CE difference is the difference in CE between two consecutive pulses. The CE difference dCE(k), where k is an integer representing the pulse number, is defined by the following equation.

[0144] dCE(k) = CE(k) - CE(k-1) CE(k) represents the CE of pulse number k.

[0145] The outlier rate for CE or CE difference refers to the rate of data occurrence outside the acceptable range (normal range), and can be defined as the percentage [%] obtained by dividing the number of events in which CE or CE difference is distributed outside the acceptable range by the number of samples n. The number of samples n used to determine the index value may be, for example, 20,000 pulses.

[0146] In the EUV light generator 10B according to Embodiment 2, the duty cycle of the piezoelectric element 47 is controlled based on an evaluation value (index value) of CE calculated based on the output of the EUV energy sensor 78 and the output of the laser energy sensor 79. Evaluating the variation in CE is equivalent to evaluating the energy stability of the generated EUV light, that is, evaluating the EUV light generation performance.

[0147] Figure 28 is a graph showing an example of CE measurement values, CE difference, and frequency distribution of CE difference when DL coupling failure occurs. In the upper part of Figure 28, graph G1 shows the pulse number on the horizontal axis and the CE measurement value in arbitrary units on the vertical axis. In the middle part of Figure 28, graph G2 shows the pulse number on the horizontal axis and the CE difference in arbitrary units on the vertical axis. In the lower part of Figure 28, graph G3 is the frequency distribution (histogram) of CE difference. Note that the vertical axis of graph G3 is displayed on a logarithmic scale (LOG).

[0148] Further, FIG. 29 is a graph showing an example of the CE measurement value, the CE difference, and the frequency distribution of the CE difference when the DL connection is normal. The graph G11 shown in the upper part of FIG. 29 is the CE measurement value, the graph G12 shown in the middle part is the CE difference, and the graph G13 shown in the lower part is the frequency distribution of the CE difference. The horizontal and vertical axes of each graph are the same as those of the corresponding graph in FIG. 28.

[0149] As is clear from comparing FIGS. 28 and 29, when a connection defect occurs, the variations in the CE measurement value and the CE difference measured in pulse order are larger than those in the normal state. The 3σ of the CE measurement value in the normal state shown in the example of FIG. 29 is 7%. In contrast, the 3σ of the CE measurement value when a connection defect occurs shown in the example of FIG. 28 is 11%. Also, the 3σ of the CE difference in the normal state shown in the example of FIG. 29 is 0.1%, while the 3σ of the CE difference when a connection defect occurs shown in the example of FIG. 28 is 0.15%.

[0150] As shown in the lower parts of FIGS. 28 and 29, when, for example, a range where the absolute value of the CE difference is less than 0.2 (-0.2 < dCE < 0.2) is set as the allowable range (normal range) of the CE difference, the abnormal value occurrence rate of the CE difference in the normal state shown in the example of FIG. 29 is 0%, while the abnormal value occurrence rate of the CE difference when a connection defect occurs shown in the example of FIG. 28 is 1.7%.

[0151] Thus, by controlling the Duty of the piezoelectric element 47 using an index for evaluating the variation in CE, such as the 3σ of the CE measurement value, the 3σ of the CE difference, or the abnormal value occurrence rate of the CE difference, which reflects the DL connection state, it is possible to suppress the occurrence of a DL connection defect state that is difficult to detect with the DL passing interval σ. The index for evaluating the variation in CE is an example of the "abnormal value occurrence rate of the difference between the ratio to the laser energy and the past ratio" in the present disclosure.

[0152] 4.4 Operations and Effects According to the EUV light generator 10B of Embodiment 2, the operation of DL coupling control based on EUV light prevents setting the piezoDuty to one that causes deterioration of EUV performance, thereby improving EUV energy stability. Fragment generation is also suppressed.

[0153] 5. Combinations of indicators for determining prohibited duties In Embodiment 1, the prohibited duty cycle is determined using DL position deviation as an indicator, and in Embodiment 2, the prohibited duty cycle is determined using the outlier occurrence rate of the CE difference, which is an indicator value for evaluating the variability of CE. However, a prohibited duty cycle range may be set by combining multiple indicators.

[0154] 6. Methods for Manufacturing Electronic Devices Figure 30 is a schematic diagram showing the configuration of an exposure apparatus 660 connected to an EUV light generator 10A. The exposure apparatus 660 includes a mask irradiation unit 668 and a workpiece irradiation unit 669. The mask irradiation unit 668 illuminates the reticle pattern of the reticle table MT via a reflective optical system using EUV light incident from the EUV light generator 10A. The workpiece irradiation unit 669 images the EUV light reflected by the reticle table MT onto a workpiece (not shown) placed on a workpiece table WT via a reflective optical system. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist.

[0155] The exposure apparatus 660 exposes the workpiece to EUV light reflecting the reticle pattern by synchronously moving the reticle table MT and the workpiece table WT in parallel. By transferring the device pattern to the semiconductor wafer through this exposure process, an electronic device can be manufactured. In the configuration shown in Figure 30, the EUV light generator 10B can be used instead of the EUV light generator 10A.

[0156] Figure 31 is a schematic diagram showing the configuration of the inspection device 661 connected to the EUV light generator 10A. The inspection device 661 includes an illumination optical system 663 and a detection optical system 666. The illumination optical system 663 reflects the EUV light incident from the EUV light generator 10A and irradiates the reticle 665 placed on the reticle stage 664. The reticle 665 here includes mask blanks before a pattern is formed. The detection optical system 666 reflects the EUV light from the illuminated reticle 665 and images it onto the light-receiving surface of the detector 667. The detector 667, having received the EUV light, acquires an image of the reticle 665. The detector 667 is, for example, a TDI (Time Delay Integration) camera.

[0157] The image of the reticle 665 obtained through the inspection process described above is used to inspect for defects in the reticle 665, and the results of the inspection are used to select a reticle suitable for the manufacture of an electronic device. Then, the pattern formed on the selected reticle is exposed and transferred onto a photosensitive substrate using the exposure apparatus 660 to manufacture the electronic device. In the configuration shown in Figure 31, the EUV light generator 10B can be used instead of the EUV light generator 10A.

[0158] 7. About the processor A processor such as the EUV photogeneration processor 24 may be physically configured in hardware form to perform the various processes included in this disclosure. For example, the processor may be a computer including a memory storing a control program that defines the various processes, and a processing unit that executes the control program. The control program may be stored in a single memory, or it may be stored in multiple physically separate memories, and the various processes may be defined by the control program as a collection of these memories. The processing unit may be a general-purpose processing unit such as a CPU, or a purpose-specific processing unit such as a GPU.

[0159] Furthermore, the processor may be programmed in software form to perform the various processes included in this disclosure. For example, the processor may have functions for performing the various processes implemented in a dedicated device such as an ASIC or a programmable device such as an FPGA.

[0160] The various processes included in this disclosure may be performed by one computer, one dedicated device, or one programmable device, or by the cooperation of multiple computers, multiple dedicated devices, or multiple programmable devices located physically separately. The various processes may be performed by at least two combinations of one or more computers, one or more dedicated devices, and one or more programmable devices.

[0161] 8. Other The above description is intended to be illustrative and not restrictive. It will therefore be apparent to those skilled in the art that modifications can be made to the embodiments of this disclosure without departing from the claims. It will also be apparent to those skilled in the art that the embodiments of this disclosure can be used in combination.

[0162] Terms used in this specification and throughout the claims should be interpreted as "non-limiting" unless otherwise specified. For example, terms such as "includes," "have," "equip," and "possess" should be interpreted as "not excluding the existence of components other than those described." Also, the modifier "one" should be interpreted as "at least one" or "one or more." Furthermore, the term "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." In addition, it should be interpreted as including combinations of these with anything other than "A," "B," and "C."

Claims

1. An extreme ultraviolet light generation device that generates extreme ultraviolet light by irradiating a droplet with laser light, A tank for containing the liquid target substance, A nozzle that outputs the target substance contained in the tank, A piezoelectric element that generates droplets of the target material by applying vibrations that reflect an electrical signal to the target material output from the nozzle, A first sensor for measuring the passage interval of the droplet output from the nozzle, A second sensor for measuring parameters related to the droplet, A processor configured to set a prohibited band for the duty cycle based on data relating the duty cycle of the electrical signal and the parameters in the duty cycle, and to set the duty cycle of the electrical signal applied to the piezoelectric element while avoiding the prohibited band, An extreme ultraviolet light generating device equipped with [a specific feature].

2. An extreme ultraviolet light generating apparatus according to claim 1, The processor outputs the electrical signal to the piezoelectric element with a duty cycle such that it avoids the prohibited band and reduces the variation in the pass-through interval. Extreme ultraviolet light generator.

3. An extreme ultraviolet light generating apparatus according to claim 1, The aforementioned processor, A first approximate straight line is calculated in the correlation between the duty cycle and the variation in the passing interval. Based on the gradient of the first approximate straight line, the duty cycle is changed in a direction that reduces the variation in the passing interval. Extreme ultraviolet light generator.

4. An extreme ultraviolet light generating apparatus according to claim 1, The second recovery described above is This is a sensor that detects the position the droplet passes through. The aforementioned parameter includes the deviation of the passing position from the target position. Extreme ultraviolet light generator.

5. An extreme ultraviolet light generating device according to claim 4, The second recovery described above is It is configured to include an image sensor, Positioned to observe the trajectory of the aforementioned droplet, Extreme ultraviolet light generator.

6. An extreme ultraviolet light generating device according to claim 4, The processor stores the duty cycles whose deviation is greater than or equal to a first threshold as prohibited duty cycles belonging to the prohibited zone. Extreme ultraviolet light generator.

7. An extreme ultraviolet light generating apparatus according to claim 1, The processor outputs the electrical signal to the piezoelectric element with a duty cycle such that the parameters satisfy predetermined conditions, while avoiding the prohibited band. Extreme ultraviolet light generator.

8. An extreme ultraviolet light generating apparatus according to claim 1, The second recovery described above is The system includes an EUV energy sensor that detects the EUV energy of extreme ultraviolet light generated by irradiating the droplet with laser light, and a laser energy sensor that measures the laser energy of the laser light. The aforementioned parameter is an index based on the ratio of the EUV energy to the laser energy. Extreme ultraviolet light generator.

9. An extreme ultraviolet light generating apparatus according to claim 8, The aforementioned parameters are, This is the rate of occurrence of an anomaly in the difference between the ratio of the EUV energy and the laser energy and the ratio in the past. Extreme ultraviolet light generator.

10. An extreme ultraviolet light generating device according to claim 9, The aforementioned processor, The duty cycle in which the rate of occurrence of abnormal values ​​in the difference exceeds the second threshold is stored as a prohibited duty cycle belonging to the prohibited zone. Extreme ultraviolet light generator.

11. An extreme ultraviolet light generating apparatus according to claim 1, The aforementioned processor, A second approximation line is calculated in the correlation between the duty cycle and the parameter. Based on the gradient of the second approximate line, the duty cycle is changed in the direction of performance improvement indicated by the parameter. Extreme ultraviolet light generator.

12. A method for controlling droplet generation in an extreme ultraviolet light generation device that generates extreme ultraviolet light by irradiating a droplet with laser light, By applying an electrical signal to a piezoelectric element, the liquid target substance output from the nozzle is subjected to vibrations that reflect the electrical signal, thereby generating droplets of the target substance. The passage interval of the droplet output from the nozzle is measured by the first sensor, Measuring parameters related to the droplet using a second sensor different from the first sensor, Setting the duty cycle prohibition band based on data relating the duty cycle of the electrical signal and the parameters in the duty cycle, Setting the duty cycle of the electrical signal output to the piezoelectric element while avoiding the prohibited band, A droplet generation control method including the following.

13. A method for manufacturing electronic devices, A tank for containing the liquid target substance, A nozzle that outputs the target substance contained in the tank, A piezoelectric element generates droplets of the target material by applying vibrations that reflect an electrical signal to the target material output from the nozzle, A first sensor for measuring the passage interval of the droplet output from the nozzle, A second sensor for measuring parameters related to the droplet, A processor configured to set a prohibited band for the duty cycle based on data relating the duty cycle of the electrical signal and the parameters in the duty cycle, and to set the duty cycle of the electrical signal applied to the piezoelectric element while avoiding the prohibited band, Equipped with, Extreme ultraviolet light is generated by an extreme ultraviolet light generation device that generates extreme ultraviolet light by irradiating the droplet with laser light, The aforementioned extreme ultraviolet light is output to the exposure device, To manufacture an electronic device, the process involves exposing a photosensitive substrate to extreme ultraviolet light in the exposure apparatus, A method for manufacturing electronic devices.

14. A method for manufacturing electronic devices, A tank for containing the liquid target substance, A nozzle that outputs the target substance contained in the tank, A piezoelectric element generates droplets of the target material by applying vibrations that reflect an electrical signal to the target material output from the nozzle, A first sensor for measuring the passage interval of the droplet output from the nozzle, A second sensor for measuring parameters related to the droplet, A processor configured to set a prohibited band for the duty cycle based on data relating the duty cycle of the electrical signal and the parameters in the duty cycle, and to set the duty cycle of the electrical signal applied to the piezoelectric element while avoiding the prohibited band, Equipped with, Extreme ultraviolet light is generated by an extreme ultraviolet light generation device that generates extreme ultraviolet light by irradiating the droplet with laser light, The reticle is irradiated with the aforementioned extreme ultraviolet light to inspect for defects in the reticle. Using the results of the above inspection, a reticle is selected. This includes exposing and transferring the pattern formed on the selected reticle onto a photosensitive substrate. A method for manufacturing electronic devices.

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