Mo / Si reflector reflectivity measuring system and method based on acousto-optic monochromator

Abstract

The invention discloses a Mo / Si reflector reflectivity measurement system and method based on an acousto-optic monochromator, the system comprises an EUV light source, an EUV energy meter, a monochromator and an EUV reflectivity meter, the EUV light source is used as a detection light source, the EUV energy meter is used for monitoring the fluctuation condition of the EUV light source and providing a light source fluctuation calibration coefficient for reflectivity measurement, the monochromator screens light based on the acousto-optic effect of an acousto-optic crystal, and the EUV reflectivity meter is used for measuring the reflectivity of the EUV light source. It is ensured that the EUV reflectivity meter only receives light with the required wavelength; the EUV reflectivity meter serves as a measurement space of a Mo / Si reflector sample, mechanical design is adopted, the size of the EUV reflectivity meter is reduced, meanwhile, a collimation optical system is added, and the accuracy of a measurement result is improved. The invention further provides a measurement method, accurate measurement of the angular spectrum and the reflection spectrum of the Mo / Si reflector is achieved, an effective technology is provided for measurement and development of the Mo / Si reflector, and therefore the EUV photoetching technology is continuously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision measurement of extreme ultraviolet (EUV) optical elements, and particularly relates to a measurement system and method for the reflectivity of a Mo / Si mirror of an acousto-optic monochromator, which are used to measure the angular spectrum and reflection spectrum of a molybdenum / silicon (Mo / Si) multilayer mirror. Background Art

[0002] Lithography technology is one of the crucial steps in the semiconductor manufacturing process, undertaking the key task of accurately transferring the chip design pattern onto the surface of a silicon wafer. It projects the micro-nano structure on the mask onto the photoresist layer through an optical projection system, and forms components with specific functions (such as transistors, interconnects, etc.) on the silicon wafer through processes such as development and etching. This technology directly determines the minimum feature size of the chip, that is, the degree of miniaturization of the components, and is the core technology to improve the performance and integration degree of integrated circuits.

[0003] With the development of electronic devices towards ultra-large scale integration, traditional lithography technology is restricted by the diffraction limit of the 193nm ultraviolet light source and is difficult to meet the accuracy requirements for feature sizes (<20nm) at the 7nm and below process nodes. This technical bottleneck has made extreme ultraviolet lithography (EUVL) an inevitable choice. EUVL uses a short-wavelength light source of 13.5nm, whose wavelength is one order of magnitude shorter than that of traditional ultraviolet light, which can significantly improve the exposure resolution, break through the physical limit of the minimum line width, and provide basic support for advanced process technologies.

[0004] In an EUVL system, the reflectivity and wavefront quality of optical elements (such as multilayer mirrors, masks) are key parameters that determine the lithography quality. The EUV reflectometer provides a quantitative basis for material selection, film system design, and process optimization by accurately measuring the reflection characteristics of optical elements in the extreme ultraviolet band. EUV reflectometers developed by international authoritative institutions (such as CXRO of Lawrence Berkeley National Laboratory in the United States and PTB of the Physikalisch-Technische Bundesanstalt in Germany) have not only achieved a reflectivity measurement accuracy of the order of 0.1%, but also established an internationally common calibration standard to ensure the performance consistency of key equipment in the global semiconductor industrial chain. However, there are still the following limitations: traditional grating monochromators rely on mechanical scanning, the wavelength adjustment speed is slow, and it is difficult to meet the requirements of rapid measurement; the complex mechanical structure (such as a coaxial double-layer rotating table) results in a large space occupied by the system, restricting the flexible deployment in laboratories and production lines; the power fluctuation of the EUV light source will introduce measurement errors, and existing equipment lacks a real-time light source fluctuation compensation mechanism, affecting the reliability of data. Summary of the Invention

[0005] To address the above problems, the present invention proposes a reflectivity measurement system and method based on an acousto-optic monochromator, aiming to solve the problems of low efficiency, large equipment volume, and insufficient calibration accuracy in existing EUV optical element measurement technologies. By utilizing the acousto-optic effect, rapid wavelength screening is achieved, enhancing the measurement speed; a compact coaxial rotation mechanism and a collimation optical system are adopted to reduce the equipment volume while improving the optical path alignment accuracy; and an EUV energy meter is integrated to monitor the light source fluctuations in real time, and errors are eliminated through dynamic calibration coefficients.

[0006] The technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides a reflectivity measurement system for a Mo / Si mirror of an acousto-optic monochromator, which is characterized by including:

[0008] An EUV light source (1) for generating 13.5 nm extreme ultraviolet light as a detection light source;

[0009] An EUV energy meter (2) disposed on the outlet side of the EUV light source (1), including a Zr filter (2-2), a Mo / Si mirror (2-3), and a photodiode (2-4), for real-time monitoring of the light source power fluctuations and generating dynamic calibration coefficients;

[0010] An acousto-optic monochromator (3) including an acousto-optic crystal (3-1), a transducer (3-2), an absorption device (3-3), and a driver (3-4), which screens light of a specific wavelength within the 12 - 14 nm band through the acousto-optic effect, and the wavelength switching time is less than 1 ms;

[0011] An EUV reflectometer (4) including a vacuum chamber (4-1), a sample displacement and rotation mechanism (4-3), and a collimation optical system; wherein, the vacuum chamber (4-1) is maintained in a vacuum by a vacuum pump (4-2), and the sample displacement and rotation mechanism (4-3) includes a No. 1 piezoelectric rotary stage (4-3-3) and a No. 2 piezoelectric rotary stage (4-3-4) arranged coaxially, which respectively drive a photodiode (4-3-7) and a mirror sample (4-3-12) to achieve independent rotation and micron-level displacement; the collimation optical system performs spatial screening and shaping on the incident light through a precision pinhole (4-4-3) to ensure the collimation of the optical path.

[0012] Furthermore, the EUV energy meter is used to provide a light source fluctuation calibration coefficient for the reflectivity measurement, and it is composed of an outer frame, a Zr filter, two Mo / Si mirrors, and a photodiode. The Zr filter is used to filter out the near-infrared light radiated by the light source, the Mo / Si mirrors are used to screen out the extreme ultraviolet light, and the photodiode converts the light signal into an electrical signal through the photoelectric effect to measure the power of the extreme ultraviolet light.

[0013] Further, the monochromator screens light of different wavelengths based on the acousto-optic effect. Since the Xe-Lpp light source emits radiation with a broad spectrum, including light of multiple wavelengths, the monochromator can ensure that the EUV reflectometer only receives light of the required wavelength, reducing interference from light of other wavelengths and ensuring the accuracy of the reflectivity measurement results. It consists of an acousto-optic crystal, a transducer, an absorption device, and a driver. The acousto-optic crystal is the core of the entire monochromator and is responsible for adjusting the wavelength of light waves through the acousto-optic effect. It changes the propagation path of light under the action of sound waves, thereby achieving wavelength selection of light. The transducer is a piezoelectric crystal and is responsible for converting electrical signals into sound waves. The performance of the transducer directly affects the generation efficiency and frequency accuracy of sound waves, and thus affects the accuracy of light wavelength adjustment. The absorption device is used to absorb unselected light waves and is usually designed to be independent of the light wave length. It ensures that only the selected wavelength passes through, thus avoiding unnecessary optical signal interference. The driver is used to control the transducer and provides the necessary electrical energy to adjust the sound wave frequency and power.

[0014] Further, the transducer can convert electrical signals into ultra-high-frequency sound waves to achieve wavelength adjustment of light in the ultra-short wavelength band.

[0015] Further, the acousto-optic crystal uses a new type of high-density material with strong acousto-optic effect and has a strong response to light in the ultra-short wavelength band.

[0016] Further, compared with traditional grating monochromators, the monochromator has a fast wavelength scanning speed and can complete the reflectivity measurement of Mo / Si mirrors in a short time, greatly improving the measurement speed.

[0017] Further, the EUV reflectometer consists of a vacuum chamber, a vacuum pump, a sample displacement and rotation mechanism, and a pinhole displacement device. Since EUV light has a short wavelength and is easily absorbed, it must be generated and transmitted in a vacuum environment. The vacuum pump is used to evacuate the internal environment of the vacuum chamber to create a vacuum and provide an environment for precise extreme ultraviolet light measurement.

[0018] Furthermore, the sample displacement and rotation mechanism is fixed at the bottom of the vacuum chamber and consists of a square chassis, a circular chassis, a No. 1 piezoelectric rotary stage, a No. 2 piezoelectric rotary stage, a support rod, a photodiode bracket, a photodiode, a piezoelectric linear displacement stage, an adapter plate, an optical two-dimensional adjustment mount, a mirror sample bracket, and a mirror sample. The square chassis is fixed at the bottom of the vacuum chamber and serves as the base of the entire mechanism. The No. 1 piezoelectric rotary stage is fixed on the square chassis, and the diode bracket is fixed on the No. 1 piezoelectric rotary stage and rotates with the No. 1 piezoelectric rotary stage. The bottom end of the support rod passes through the central through-hole of the No. 1 piezoelectric rotary stage and is connected to the square chassis, and the top end of the support rod is connected to the circular chassis. The No. 2 piezoelectric rotary stage is fixed on the circular chassis, and the piezoelectric linear displacement stage is fixed on the No. 2 piezoelectric rotary stage. The adapter plate is installed on the linear displacement stage and is used to transfer the optical two-dimensional adjustment mount. The function of the optical two-dimensional adjustment mount is to precisely adjust the position and angle of the sample in two perpendicular directions to ensure the alignment and optimization of the entire optical system. Any slight deviation will affect the transmission quality of the optical path. Therefore, a two-dimensional adjustment mount is needed to achieve precise positioning of the optical elements. The mirror sample bracket is installed on the optical two-dimensional adjustment mount. There are two sample slots on the mirror sample bracket. Only one sample is placed during use, and the other sample slot serves as a through-hole.

[0019] Furthermore, the pinhole displacement device is fixed at the bottom of the vacuum chamber and can serve as a collimating optical system. It consists of a linear displacement stage, a pinhole bracket, and a precision pinhole. Since the EUV light source usually diverges in a 2π solid angle, the light beam will gradually spread after leaving the light source, and the light incident on the optical element does not have strict collimation, which will affect the accuracy of the measurement of the angular spectrum and reflection spectrum of the Mo / Si mirror. The precision pinhole can shape and spatially filter the incident light beam, and can also ensure the correct alignment of the optical path, help to accurately position the optical element, reduce the error of the measurement result, and improve the accuracy of the measurement result.

[0020] Furthermore, the sample displacement and rotation mechanism can ensure that the rotation of the photodiode and the Mo / Si mirror sample is coaxial and independent. The existing coaxial double-layer rotary stage is too large in volume. In the present invention, two small precision rotary stages are connected in a unique way to achieve the effect of coaxial independence and greatly reduce the volume of the device.

[0021] On the other hand, the present invention also provides a method for measuring the reflectivity of a Mo / Si mirror based on an acousto-optic monochromator, which is characterized by including the following steps:

[0022] Start the vacuum pump (4-2) to pump the vacuum chamber (4-1) to a vacuum degree ≤ 1×10 -5 Pa, and activate the EUV light source (1);

[0023] Real-time monitor the light source power fluctuation through the EUV energy meter (2) to generate a dynamic calibration coefficient;

[0024] Use an acousto-optic monochromator (3) to screen for light of the target wavelength, and shape the incident light through a collimating optical system;

[0025] Adjust the sample displacement and rotation mechanism (4-3) to align the mirror sample (4-3-12) with the photodiode (4-3-7) at the center of the optical path;

[0026] Measure the incident light intensity and the reflected light intensity, and calculate the reflectivity in combination with the dynamic calibration coefficient;

[0027] Generate a reflection spectrum or an angular spectrum curve through wavelength scanning or angle scanning.

[0028] Among them, the angular spectrum is to measure the reflectivity of the Mo / Si mirror at different incident angles for a wavelength of 13.5 nm, and the reflection spectrum is to measure the reflectivity of the Mo / Si mirror at different wavelengths for a fixed incident angle, and this fixed incident angle depends on the design angle of the Mo / Si mirror according to Bragg's law.

[0029] The principle of reflection spectrum measurement is as follows:

[0030] S1. When all components are in their initial positions, start the vacuum pump of the EUV reflectometer. After the vacuum degree in the vacuum chamber reaches the requirement, start the EUV light source.

[0031] S2. When the EUV energy meter detects a signal, control the No. 1 piezoelectric rotary stage to drive the photodiode bracket to rotate so that the photodiode is located at the center of the optical path. At the same time, control the linear displacement stage to move the precision pinhole to the center of the optical path to shape the incident light.

[0032] S3. Control the piezoelectric linear displacement stage to drive the mirror sample bracket to move so that its through-hole groove is located at the center of the optical path, so that extreme ultraviolet light can pass through the mirror sample bracket and reach the photodiode.

[0033] S4. Control the monochromator, thereby controlling the wavelength of the incident light, and measure the incident light intensity in the 12 - 14 nm band through the photodiode, with a step size of 0.02 nm.

[0034] S5. Control the piezoelectric linear displacement stage to drive the mirror sample bracket to move so that the center of the mirror sample is located at the center of the optical path. At the same time, control the No. 2 piezoelectric rotary stage to drive the mirror sample to rotate to the position of the designed angle. S6. Control the No. 1 piezoelectric rotary stage to rotate the photodiode to the center position of the reflected light, control the monochromator, and measure the reflected light intensity in the 12 - 14 nm band through the photodiode.

[0035] S7. While measuring the incident light intensity and the reflected light intensity, record the light source power measured by the EUV energy meter. S8. Compare the power values of the EUV energy meter during the measurement of the reflected light intensity and the incident light intensity to obtain the light source fluctuation calibration coefficient. Multiply this coefficient by the ratio of the reflected light intensity to the incident light intensity at a specific wavelength to obtain the reflectivity of the Mo / Si mirror at this specific wavelength.

[0036] S9. Repeat S7 in the 12 - 14 nm band to obtain the reflection spectrum.

[0037] The principle of angular spectrum measurement is as follows:

[0038] S1. Each component is in the initial position. Start the vacuum pump of the EUV reflectometer. After the vacuum degree in the vacuum chamber reaches the requirement, start the EUV light source.

[0039] S_{2}. When the EUV energy meter detects a signal, control the No. 1 piezoelectric rotary stage to drive the photodiode bracket to rotate so that the photodiode is located at the center of the optical path. At the same time, control the linear displacement stage to move the precision pinhole to the center of the optical path to shape the incident light.

[0040] S_{3}. Control the piezoelectric linear displacement stage to drive the mirror sample bracket to move so that its through - hole groove is located at the center of the optical path, enabling extreme ultraviolet light to pass through the mirror sample bracket and reach the photodiode.

[0041] S_{4}. Control the monochromator to set the wavelength of the incident light to 13.5 nm, and measure the incident light intensity at 13.5 nm through the photodiode.

[0042] S_{5}. Control the piezoelectric linear displacement stage to drive the mirror sample bracket to move so that the center of the mirror sample is located at the center of the optical path. At the same time, control the No. 2 piezoelectric rotary stage to drive the mirror sample to rotate to a position of 5°.

[0043] S_{6}. Control the No. 1 piezoelectric rotary stage to rotate the photodiode to a position of 10°. Subsequently, simultaneously control the No. 1 piezoelectric rotary stage and the No. 2 piezoelectric rotary stage to measure the reflected light intensity of the Mo / Si mirror within the range of incident angles from 5° to 22.5°.

[0044] S7. While measuring the incident light intensity and the reflected light intensity, record the light source power measured by the EUV energy meter.

[0045] S8. Compare the power values of the EUV energy meter during the measurement of the reflected light intensity and the incident light intensity to obtain the light source fluctuation calibration coefficient. Multiply this coefficient by the ratio of the reflected light intensity to the incident light intensity at different angles to obtain the reflectivity of the Mo / Si mirror at different angles for the 13.5 nm wavelength, and obtain the angular spectrum.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] 1) Connecting two small precision rotary tables achieves the effect of coaxial independence, solves the problem of the overly large volume of the integrated coaxial double-layer rotary displacement stage on the market, and greatly reduces the volume of the device. The coaxial double-layer rotary mechanism and modular components significantly reduce the equipment volume, facilitating flexible deployment in laboratories and production lines.

[0048] 2) By installing an EUV energy meter on the other side of the EUV light source, the light source fluctuation coefficient can be measured, greatly improving the measurement accuracy of the EUV reflectometer. The EUV energy meter compensates for light source fluctuations in real-time. Combined with the collimation optical system, the measurement uncertainty is reduced to less than 0.5%.

[0049] 3) Introducing a collimation optical system, shaping and spatially screening the light beam through a precision pinhole ensures the correct alignment of the optical path, helps accurately position optical components, reduces the error of the measurement result, and improves the accuracy of the measurement result.

[0050] 4) The acousto-optic monochromator breaks through the bottleneck of traditional grating mechanical scanning. The wavelength adjustment speed is increased to the millisecond level, and the full-band measurement time is shortened by 80%. It not only provides high-precision data support for the research and development of Mo / Si mirrors but also promotes the further commercial application of EUV lithography technology. Description of the Drawings

[0051] Figure 1 It is a schematic structural diagram of an embodiment of the reflectivity measurement system based on an acousto-optic monochromator of the present invention;

[0052] Figure 2 It is a schematic structural diagram of the EUV energy meter in the present invention;

[0053] Figure 3 It is a schematic structural diagram of the acousto-optic monochromator in the present invention;

[0054] Figure 4 It is a schematic structural diagram of the EUV reflectometer in the present invention;

[0055] Figure 5 It is a schematic structural diagram of the sample displacement rotation mechanism in the present invention;

[0056] Figure 6 It is a schematic assembly diagram of the sample displacement rotation structure in the present invention;

[0057] Figure 7 It is a schematic structural diagram of the vacuum displacement device in the present invention;

[0058] Figure 8 It is a flowchart of the reflectance spectrum measurement method of an embodiment of the reflectivity measurement system based on an acousto-optic monochromator of the present invention;

[0059] Figure 9 This is a flowchart of the angular spectrum measurement method for the reflectivity measurement system embodiment based on an acousto-optic monochromator of the present invention. Specific embodiments

[0060] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

[0061] The reflectivity measurement system of this embodiment, as Figure 1 shown, consists of the following core components:

[0062] EUV light source 1: Based on laser-excited xenon plasma to generate 13.5 nm extreme ultraviolet light, which is used as the detection light source to ensure that the wavelength is consistent with the requirements of EUV lithography.

[0063] EUV energy meter 2: It consists of an outer frame 2-1 and a Zr filter 2-2, two Mo / Si mirrors 2-3 and a photodiode 2-4 placed inside the outer frame 2-1. It is used to monitor the light source power fluctuation in real time and generate a dynamic calibration coefficient to eliminate measurement errors, as Figure 2 shown. Among them, the Zr filter 2-2 is used to filter out the near-infrared light radiated by the light source, the Mo / Si mirrors 2-3 are used to select the extreme ultraviolet light, and the photodiode 2-4 converts the optical signal into an electrical signal through the photoelectric effect to measure the power of the extreme ultraviolet light.

[0064] Acousto-optic monochromator 3, based on the acousto-optic effect to select lights of different wavelengths, ensures that the EUV reflectometer 4 only receives the lights of the required wavelength, reduces the interference of lights of other wavelengths, and guarantees the accuracy of the reflectivity measurement results. As Figure 3 shown, it includes:

[0065] - Acousto-optic crystal 3-1, made of a material with high density and strong acousto-optic effect, adjusts the optical wave propagation path through the acousto-optic effect to achieve wavelength selection within the 12-14 nm band, with a wavelength resolution of 0.02 nm. When the sound wave propagates in the acousto-optic crystal, it forms a periodic refractive index change, causing the incident light to undergo Bragg diffraction and only allowing light of a specific wavelength to pass through.

[0066] - Transducer 3-2, which is a piezoelectric crystal, converts the electrical signal into an ultra-high-frequency sound wave to drive the acousto-optic crystal 3-1 to achieve wavelength adjustment. Its performance directly affects the generation efficiency and frequency accuracy of the sound wave, and thus affects the accuracy of the optical wavelength adjustment.

[0067] - Absorption device 3-3 and driver 3-4: Absorb the unselected stray light to ensure the purity of the monochromatic light. At the same time, the driver precisely controls the sound wave frequency through the electrical signal to improve the wavelength adjustment speed and accuracy.

[0068] The driver 3-4 inputs an electrical signal of a specific frequency to the transducer 3-2 to generate corresponding sound waves; the sound waves form a diffraction grating in the acousto-optic crystal 3-1, allowing only light of the target wavelength (such as 13.5 nm) to pass through, and the light of the unselected wavelength is completely absorbed by the absorption device 3-3 to ensure the purity of the output light. By adjusting the driver frequency, the wavelength switching time is <1 ms, enabling fast scanning across the entire wavelength band.

[0069] In this embodiment, compared with the traditional grating monochromator, the wavelength scanning speed of the acousto-optic monochromator 3 is increased by more than 10 times, and the reflectivity measurement of the Mo / Si mirror can be completed in a short time, greatly shortening the measurement time.

[0070] The EUV reflectometer 4, as Figure 4 shown, includes:

[0071] - A vacuum chamber 4-1 for accommodating the entire optical measurement system, with an internal vacuum degree ≤ 1×10 -5 Pa to prevent the EUV light from being absorbed by air; a vacuum environment is maintained by a vacuum pump 4-2;

[0072] - A sample displacement and rotation mechanism 4-2, integrating a double-layer piezoelectric rotary stage and a linear displacement stage, to achieve coaxial independent rotation and micron-level displacement of the mirror sample and the photoelectric probe (see details in Figures 5-6 ).

[0073] - A collimating optical system that spatially screens and shapes the divergent EUV beam through a pinhole displacement device 4-4 to ensure strict collimation of the optical path and reduce measurement errors;

[0074] Figure 5 is a schematic structural diagram of the sample displacement and rotation mechanism in the present invention, Figure 6 is a schematic assembly diagram of the sample displacement and rotation structure in the present invention. As shown in the figure, the sample displacement and rotation mechanism 4-3 consists of the following components:

[0075] A square chassis 4-3-1, fixed at the bottom of the vacuum chamber 4-1, serving as the support base for the entire mechanism.

[0076] The No. 1 piezoelectric rotary stage 4-3-3 drives the rotation of the photodiode bracket 4-3-6, driving the photodiode 4-3-7 to capture the reflected light signal, with an angular resolution of ±0.001°.

[0077] A support rod 4-3-5 connects the square chassis 4-3-1 and the circular chassis 4-3-2 to ensure the coaxiality of the double-layer rotary stage.

[0078] The No. 2 piezoelectric rotary stage 4-3-4 drives the horizontal movement of the piezoelectric linear displacement stage 4-3-8, driving the rotation (angle range 5° - 22.5°) and displacement (accuracy ±0.1 μm) of the mirror sample 4-3-12.

[0079] The optical two-dimensional adjustment mount 4-3-10 is installed on the adapter plate 4-3-9. By adjusting the position and angle of the mirror sample holder 4-3-11 at the micron level, the optical path is ensured to be strictly aligned.

[0080] The mirror sample holder 4-3-11 is provided with two sample slots. One is for placing the Mo / Si mirror 4-3-12, and the other is a through-hole for incident light intensity calibration.

[0081] The No. 1 piezoelectric rotary stage 4-3-3 and the No. 2 piezoelectric rotary stage 4-3-4 achieve coaxial separation control through the support rod 4-3-5. The photoelectric probe and the sample can rotate independently, and the volume is only 1 / 3 of that of the traditional double-layer rotary stage. The mirror sample 4-3-12 finely adjusts its position through the optical two-dimensional adjustment mount 4-3-10 to ensure that the incident light and the reflected light are strictly aligned with the optical path center; the precision pinhole 4-4-3 performs spatial screening on the divergent light beam to reduce the interference of stray light. All moving parts (piezoelectric rotary stages, linear displacement stages) adopt vacuum-compatible materials and sealing structures to ensure long-term stable operation.

[0082] The reflectivity measurement method of this embodiment includes two categories: reflectance spectrum measurement and angular spectrum measurement. The process is as follows:

[0083] 1. Reflectance spectrum measurement: For the reflectivity at different wavelengths with a fixed incident angle, scan the wavelength range of 12 - 14 nm:

[0084] Adjust the wavelength of the incident light point by point through the acousto-optic monochromator, and synchronously record the incident light intensity and the reflected light intensity;

[0085] Combined with the EUV energy meter, calibrate the light source fluctuation in real time, calculate the reflectivity at each wavelength point, and generate a reflectance spectrum curve.

[0086] 2. Angular spectrum measurement: For the reflectivity at different incident angles with a fixed wavelength of 13.5 nm, scan the incident angle range of 5° - 22.5°:

[0087] Precisely adjust the angles of the mirror sample and the photoelectric probe through the double-layer piezoelectric rotary stage to ensure that the reflected optical path is aligned;

[0088] Dynamically calibrate the light source power fluctuation, calculate the reflectivity at different incident angles, and generate an angular spectrum curve.

[0089] Figure 8 This is the flowchart of the reflectance spectrum measurement method of the reflectivity measurement system embodiment based on the acousto-optic monochromator of the present invention, aiming to obtain the reflectivity of the Mo / Si mirror at different wavelengths with a fixed incident angle. This incident angle is determined by the Bragg's law to ensure that the mirror achieves the best reflection performance at a specific wavelength (such as 13.5 nm). The specific measurement process is as follows:

[0090] S1. Start the vacuum pump 4-2 and evacuate the vacuum chamber 4-1 to a vacuum degree of ≤ 1×10 -5 Pa to prevent EUV light from being absorbed by air; then start the EUV light source 1 to generate 13.5 nm extreme ultraviolet light;

[0091] S2. After the EUV energy meter 2 detects the optical signal, control the No. 1 piezoelectric rotary stage 4-3-3 to rotate the photodiode bracket 4-3-6 so that the photodiode 4-3-7 is aligned with the optical path center; synchronously control the linear displacement stage 4-4-1 to make the precision pinhole 4-4-3 located at the optical path center to shape the incident light.

[0092] S3. Control the piezoelectric linear displacement stage 4-3-8 to drive the mirror sample bracket 4-3-11 to move so that its through-hole groove is aligned with the optical path center, and the EUV light can directly pass through the through-hole to reach the photodiode 4-3-7.

[0093] S4. Adjust the wavelength of the incident light (12 - 14 nm, step size 0.02 nm) through the acousto-optic monochromator 3, and use the photodiode 4-3-7 to measure the incident light intensity corresponding to each wavelength band point by point.

[0094] S5. Control the piezoelectric linear displacement stage 4-3-8 to move the mirror sample bracket 4-3-11 so that the center of the mirror 4-3-12 is aligned with the optical path; at the same time, control the No. 2 piezoelectric rotary stage 4-3-4 to rotate the mirror sample 4-3-12 to the position of the Bragg design angle.

[0095] S6. Control the No. 1 piezoelectric rotary stage 4-3-3 to rotate the photodiode 4-3-7 to the center position of the reflected light; keep the wavelength setting of the acousto-optic monochromator 3, and measure the reflected light intensity in the 12 - 14 nm wavelength band through the photodiode 4-3-7.

[0096] S7. When measuring the incident light intensity and the reflected light intensity, synchronously record the real-time light source power measured by the EUV energy meter 2.

[0097] S8. Compare the power values of the EUV energy meter 2 when measuring the reflected light intensity and the incident light intensity to obtain the light source fluctuation calibration coefficient, and multiply this coefficient by the ratio of the reflected light intensity to the incident light intensity at a specific wavelength to obtain the reflectivity of the Mo / Si mirror at this specific wavelength.

[0098] S9. Repeat S4 - S8 in the 12 - 14 nm wavelength band to obtain the reflection spectrum.

[0099] Figure 9This is a flowchart of the angular spectrum measurement method for the reflectivity measurement system embodiment based on an acousto-optic monochromator of the present invention, aiming to obtain the reflectivity characteristics of the Mo / Si mirror at different incident angles (5° - 22.5°) at a fixed wavelength (13.5 nm). The specific process is as follows:

[0100] S1. Start the vacuum pump 4 - 2. After the vacuum degree in the vacuum chamber 4 - 1 reaches the requirement, start the EUV light source 1.

[0101] S2. When the EUV energy meter 2 detects a signal, control the No. 1 piezoelectric rotary stage 4 - 3 - 3 to drive the photodiode bracket 4 - 3 - 6 to rotate, so that the photodiode 4 - 3 - 6 is located at the optical path center position. At the same time, control the linear displacement stage 4 - 4 - 1 to move the precision pinhole 4 - 4 - 3 to the optical path center to shape the incident light.

[0102] S3. Control the piezoelectric linear displacement stage 4 - 3 - 8 to drive the mirror sample bracket 4 - 3 - 11 to move, so that its through - hole groove is located at the optical path center, enabling the extreme ultraviolet light to pass through the mirror sample bracket 4 - 3 - 11 and reach the photodiode 4 - 3 - 7.

[0103] S4. Control the monochromator 3 to set the wavelength of the incident light to 13.5 nm, and measure the incident light intensity at 13.5 nm through the photodiode 4 - 3 - 7.

[0104] S5. Control the piezoelectric linear displacement stage 4 - 3 - 8 to drive the mirror sample bracket 4 - 3 - 11 to move, so that the center of the mirror sample 4 - 3 - 12 is located at the optical path center. At the same time, control the No. 2 piezoelectric rotary stage 4 - 3 - 4 to drive the mirror sample 4 - 3 - 12 to rotate to the 5° position.

[0105] S6. Control the No. 1 piezoelectric rotary stage 4 - 3 - 3 to rotate the photodiode 4 - 3 - 7 to the 10° position. Subsequently, simultaneously control the No. 1 piezoelectric rotary stage 4 - 3 - 3 and the No. 2 piezoelectric rotary stage 4 - 3 - 4 to measure the reflected light intensity of the Mo / Si mirror in the range of incident angles from 5° to 22.5°.

[0106] S7. While measuring the incident light intensity and the reflected light intensity, record the light source power measured by the EUV energy meter 2.

[0107] S8. Compare the power values of the EUV energy meter 2 when measuring the reflected light intensity and the incident light intensity to obtain the light source fluctuation calibration coefficient. Multiply this coefficient by the ratio of the reflected light intensity to the incident light intensity at different angles to obtain the reflectivity of the Mo / Si mirror at different angles for the 13.5 nm wavelength, and obtain the angular spectrum.

Claims

1. A reflectivity measurement system for Mo / Si mirrors based on an acou-optic monochromator, characterized in that, Comprising: An EUV light source (1) for generating 13.5 nm extreme ultraviolet light as a detection light source; An EUV energy meter (2) disposed on the outlet side of the EUV light source (1), including a Zr filter (2-2), a Mo / Si mirror (2-3), and a photodiode (2-4), for real-time monitoring of the light source power fluctuation and generating a dynamic calibration coefficient; An acousto-optic monochromator (3), including an acousto-optic crystal (3-1), a transducer (3-2), an absorption device (3-3), and a driver (3-4), for screening light of a specific wavelength within the 12 - 14 nm band through the acousto-optic effect, with a wavelength switching time less than 1 ms; An EUV reflectometer (4), comprising a vacuum chamber (4-1), a sample displacement and rotation mechanism (4-3), and a collimating optical system; wherein, the vacuum chamber (4-1) is maintained in a vacuum by a vacuum pump (4-2), and the sample displacement and rotation mechanism (4-3) includes a No. 1 piezoelectric rotary stage (4-3-3) and a No. 2 piezoelectric rotary stage (4-3-4) arranged coaxially, respectively driving a photodiode (4-3-7) and a mirror sample (4-3-12) to achieve independent rotation and micron-level displacement; the collimating optical system performs spatial screening and shaping on the incident light through a precision pinhole (4-4-3) to ensure the optical path is collimated.

2. The reflectivity measurement system according to claim 1, wherein The EUV energy meter (2) filters near-infrared light through the Zr filter (2-2), and screens extreme ultraviolet light through the Mo / Si mirror (2-3), and the electrical signal output by the photodiode (2-4) synchronously calibrates the reflectivity measurement result with the light source power fluctuation.

3. The reflectance measurement system according to claim 1, wherein The sample displacement and rotation mechanism (4-3) further includes: An optical two-dimensional adjustment mount (4-3-10) for fine-tuning the position and angle of the mirror sample A mirror sample holder (4-3-11) provided with a through-hole groove and a sample groove for incident light intensity calibration and fixing of the mirror sample (4-3-12), respectively.

4. A method for measuring the reflectivity of a Mo / Si mirror based on an acousto-optic monochromator, characterized in that, Including the following steps: Start the vacuum pump (4-2) to evacuate the vacuum chamber (4-1) to a vacuum degree ≤ 1×10 -5 Pa, and activate the EUV light source (1); Real-time monitoring of the light source power fluctuation by the EUV energy meter (2) to generate a dynamic calibration coefficient; Screening light of the target wavelength by the acousto-optic monochromator (3) and shaping the incident light through the collimating optical system; Adjusting the sample displacement and rotation mechanism (4-3) to align the mirror sample (4-3-12) with the photodiode (4-3-7) at the optical path center; Measuring the incident light intensity and the reflected light intensity, and calculating the reflectivity in combination with the dynamic calibration coefficient; Generating a reflectance spectrum or an angular spectrum curve through wavelength scanning or angle scanning.

5. The measuring method according to claim 4, characterized in that The reflectance spectrum measurement includes: Fixing the incident angle of the mirror, and scanning the 12 - 14 nm band with a step size of 0.02 nm by the acousto-optic monochromator (3); Synchronously recording the incident light intensity and the reflected light intensity at each wavelength point, and calculating the reflectivity in combination with the dynamic calibration coefficient.

6. The measurement method according to claim 6, characterized in that, The angular spectrum measurement includes: Fixing the incident light wavelength at 13.5 nm, and adjusting the incident angle (5° - 22.5°) of the mirror sample (4-3-12) by the No. 2 piezoelectric rotary stage (4-3-4); Synchronously controlling the No. 1 piezoelectric rotary stage (4-3-3) to adjust the position of the photodiode (4-3-7) and measuring the reflected light intensity at each angle. Calculate the reflectivity at different incident angles in combination with the dynamic calibration coefficient.

7. The measuring method according to claim 6, characterized in that The calculation method of the dynamic calibration coefficient is as follows: Compare the power value of the EUV energy meter (2) during the measurement of the reflected light intensity and the incident light intensity to obtain the light source fluctuation calibration coefficient; Multiply the calibration coefficient by the ratio of the reflected light intensity to the incident light intensity to obtain the final reflectivity.

Images