Energy monitoring device for a 13.5nm extreme ultraviolet light source based on a spherical mirror

Abstract

This invention relates to the field of optical system design technology, and more particularly to an energy monitoring device for a 13.5nm extreme ultraviolet (EUV) light source based on a spherical mirror. The device comprises, sequentially along the optical path, an aperture stop, a thin-film filter, a first spherical mirror, a second spherical mirror, and a detector. Broadband radiation emitted by the EUV light source first passes through the aperture stop and then is incident on the thin-film filter. The EUV beam passing through the thin-film filter illuminates the first spherical mirror at an incident angle of 5-10°, where it undergoes narrowband filtering and beam focusing, initially reducing the beam divergence angle and spot size. The reflected beam from the first spherical mirror is incident on the second spherical mirror at an incident angle of 5-10°, where the beam undergoes a second focusing and spot shaping. The filtered and focused EUV radiation is received by the detector located at the end of the optical path. The advantages are: significantly improved energy measurement accuracy; and a more compact structure.

Description

Technical Field

[0001] This invention relates to the field of optical system design technology, and in particular to a 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror. Background Technology

[0002] In extreme ultraviolet (EUV) lithography, the light source needs to provide high-power (greater than several hundred watts) and highly stable 13.5nm (center wavelength, bandwidth approximately 2%) radiation. To precisely control the lithography process (such as exposure dose control) and monitor and optimize the performance of the light source itself, accurate and real-time absolute intensity measurements of the EUV pulse energy output by the light source are essential. Therefore, developing high-performance, miniaturized EUV energy monitoring devices is a crucial step in the research and integration of EUV lithography machines.

[0003] Currently, E-MON type EUV energy monitoring devices exist on the market. The core of this device uses a planar multilayer film mirror combined with filters to achieve spectral selection, and is detected by an EUV-sensitive photodiode (IRD SXUV 100 or IRD AXUV100). Its main drawback is that the planar mirror cannot effectively control the spot size, and the photosensitive area of ​​the detector used is typically 100mm². 2 The above. Furthermore, to avoid optical path interference, it is difficult to further compress the design space of the optical system. EUV energy monitoring devices (such as E-MON) based on existing technologies using planar multilayer film mirrors have the following main shortcomings:

[0004] Weak light spot control capability: Plane mirrors lack focusing or beam-constricting functions, making it impossible to effectively control the size of the light spot incident on the photosensitive surface of the photodiode. This necessitates the use of devices with a large photosensitive area (typically ≥100mm²). 2 EUV photodiodes are used to ensure that the entire light spot can be effectively received by the detector.

[0005] Detector uniformity issues: The uniformity of materials in large-area photodiodes is relatively poor. Since the light spot may cover a large area of ​​the detector's photosensitive surface, material inhomogeneity introduces additional measurement errors, limiting the accuracy of the final energy measurement.

[0006] System size limitations: In order to avoid beam blocking or interference between different mirrors in the optical path, the optical path design using planar mirrors usually requires a large space layout, making it difficult to achieve further compaction of the optical system layout and hindering integration inside the space-constrained EUV lithography machine.

[0007] In summary, while existing EUV energy monitoring devices can achieve basic EUV pulse energy measurement, they have significant shortcomings in areas such as spot control, detector uniformity, and system size, limiting their application in high-precision, miniaturized, and high-performance EUV lithography machines. Therefore, there is an urgent need to develop a new EUV energy monitoring device that can effectively solve the above problems. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical reflector.

[0009] The purpose of this invention is to provide a 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror, which includes, in sequence along the optical path, an aperture stop, a thin film filter, a first spherical mirror, a second spherical mirror, and a detector;

[0010] The broadband radiation emitted by the EUV source first passes through the aperture stop and then enters the thin-film filter. The EUV beam passing through the thin-film filter illuminates the first spherical mirror at an incident angle of 5° to 10°, where the incident beam undergoes narrowband filtering and focusing, initially reducing the beam divergence angle and spot size. The reflected beam from the first spherical mirror enters the second spherical mirror at an incident angle of 5° to 10°, where the beam undergoes a second focusing and spot shaping. The filtered and focused EUV radiation is then received by the detector located at the end of the optical path.

[0011] Preferably, the aperture size of the aperture stop is adjustable, ranging from 3mm to 8mm; the EUV light source emits broadband radiation with wavelengths greater than 25nm, including far-ultraviolet, ultraviolet, visible, and infrared long-wave radiation.

[0012] Preferably, the thin-film filter is a zirconium film or beryllium film with a thickness of 100nm~200nm, used to filter the broadband EUV light source and allow EUV radiation near 13.5nm to pass through.

[0013] Preferably, the thin-film filter is a zirconium film with a thickness of 200 nm.

[0014] Preferably, both the first spherical reflector and the second spherical reflector are spherical concave structures, with molybdenum / silicon periodic multilayer films deposited on their surfaces, and the film thickness period is 6.8~7.2nm.

[0015] Preferably, the reflectivity of the first spherical mirror is >60%, and it has a bandwidth of ±2% at the center wavelength of 13.5nm; after the light passes through the second spherical mirror, the detection spectral width has a bandwidth of ±1.4% at the center wavelength of 13.5nm.

[0016] Preferably, the detector has a photosensitive area ≥25mm².2 A silicon-based or wide-bandgap semiconductor detector is used to receive the reflected beam from the second spherical mirror, convert the received EUV photon energy into a photocurrent signal, and then transmit it to the signal processing unit for analysis.

[0017] Preferably, the detector is an EUV photodiode based on silicon, diamond, GaN, SiC or AlN.

[0018] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0019] This invention provides a 13.5nm extreme ultraviolet (EUV) light source energy monitoring device based on a spherical mirror. To better control the spot size and optimize the device layout, two spherical multilayer film mirrors are used to achieve in-band filtering and transmission in the 13.5nm band. While achieving 13.5nm±1.4% bandpass filtering, the spherical mirrors also have focusing / beam-shrinking functions, which can effectively control the spot diameter within 5mm. This allows the use of EUV photodiodes with smaller photosensitive areas and better material uniformity (such as silicon-based or wide-bandgap semiconductor detectors with a diameter ≤5mm), significantly improving the energy measurement accuracy. At the same time, the optical path design of the spherical mirrors optimizes the spatial layout, making the EUV energy monitoring device structure more compact. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the optical path of a 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror according to an embodiment of the present invention.

[0021] Figure 2 This is the transmittance curve of the thin-film filter provided according to an embodiment of the present invention.

[0022] Figure 3 This is a reflectivity curve of light passing through a first spherical mirror and light passing through a second spherical mirror, provided according to an embodiment of the present invention.

[0023] Figure 4 This is the optical system design and spot diagram of an extreme ultraviolet energy monitoring device based on a plane mirror.

[0024] Figure 5 This is an optical system design and spot diagram of a 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror, provided according to an embodiment of the present invention.

[0025] Figure label:

[0026] 1. Aperture stop;

[0027] 2. Thin-film filters;

[0028] 3. First spherical reflecting mirror;

[0029] 4. Second spherical reflecting mirror;

[0030] 5. Detector. Detailed Implementation

[0031] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0033] This invention provides a 13.5nm extreme ultraviolet (EUV) light source energy monitoring device based on a spherical mirror. Its core function is to accurately measure the energy of EUV radiation pulses output from an EUV lithography machine, with a center wavelength of 13.5nm and a bandwidth of 2% within a specific solid angle. This monitoring device needs to efficiently filter out out-of-band stray light from a broadband light source containing extreme ultraviolet, deep ultraviolet (DUV), ultraviolet (UV), visible light (VIS), and infrared (IR) radiation, and measure the absolute energy of the target EUV band with high precision.

[0034] like Figure 1 As shown, the device includes, in sequence along the optical path, an aperture stop 1, a thin film filter 2, a first spherical mirror 3, a second spherical mirror 4, and a detector 5;

[0035] The aperture size of aperture stop 1 is adjustable. Aperture stop 1 determines the solid angle of the collected light source radiation. Users can adjust the incident light flux according to actual needs to prevent detector saturation or improve the signal-to-noise ratio. In a specific embodiment, the aperture size of aperture stop 1 is adjustable from 3mm to 8mm.

[0036] Thin-film filter 2 uses a metal thin-film material of a specific thickness, such as a zirconium (Zr) film or a beryllium (Be) film, typically about 100nm~200nm thick. Its function is to filter broadband EUV light sources (high absorption, extremely low transmittance), while maintaining relatively high transmittance for EUV radiation near the target 13.5nm, effectively filtering out most out-of-band radiation and reducing the thermal load and non-EUV background noise received by subsequent optical components and detectors. Specifically, the broadband EUV light source is long-wave radiation with wavelengths greater than 25nm, including far-ultraviolet, ultraviolet, visible, and infrared. In a specific embodiment, thin-film filter 2 is a zirconium film with a thickness of approximately 200nm, and the transmittance curve is shown below. Figure 2 As shown.

[0037] The reflecting surface of the first spherical mirror 3 is a concave spherical structure, and its surface is coated with a periodic multilayer molybdenum / silicon (Mo / Si) film specifically optimized for 13.5nm. The film thickness period is 6.8~7.2nm. This multilayer film has high reflectivity (typically >60%) near the center wavelength of 13.5nm (bandwidth of about ±2%), while having low reflectivity for other wavelengths. Therefore, the first spherical mirror 3 first achieves the first narrowband filtering (spectral selection) of the target 13.5nm EUV radiation; at the same time, it utilizes the geometric optical focusing characteristics of its spherical surface to perform the first focusing and beam contraction of the reflected 13.5nm beam, initially reducing the beam divergence angle and spot size.

[0038] The second spherical mirror 4 has a concave spherical reflective surface coated with a periodic multilayer molybdenum / silicon (Mo / Si) film specifically optimized for 13.5nm, providing a bandwidth of ±2% at the center wavelength of 13.5nm. The second spherical mirror 4 performs a second focusing and beam shaping of the light beam. Combined with the first spherical mirror 3, the second spherical mirror 4 forms a more stringent bandpass filtering characteristic (center wavelength 13.5nm, bandwidth ±1.4%), further suppressing out-of-band radiation and ensuring that the light incident on the detector 5 is primarily pure target EUV radiation.

[0039] The reflectivity curves of the first spherical mirror 3 and the second spherical mirror 4 are as follows: Figure 3 As shown.

[0040] Detector 5 has a photosensitive area ≥25mm² 2 A silicon-based or wide-bandgap semiconductor detector is used to receive the reflected beam from the second spherical mirror 4 and convert the received EUV photon energy into a photocurrent signal, which is then transmitted to the signal processing unit for analysis. Specifically, the detector 5 is an EUV photodiode based on silicon-based materials, preferably a Si photodiode; or an EUV photodiode based on wide-bandgap semiconductor materials, preferably an EUV photodiode made of diamond, GaN, SiC, AlN, etc.; or other commercial or custom EUV detectors that meet the requirements of small size and high uniformity, such as the optimized small-area AXUV / SXUV series.

[0041] The broadband radiation emitted by the EUV source first passes through an adjustable aperture stop 1, and then the beam is incident on a thin-film filter 2. The EUV beam passing through the thin-film filter 2 illuminates the first spherical mirror 3 at an incident angle of 5° to 10°, where the incident beam undergoes narrowband filtering and focusing, initially reducing the beam divergence angle and spot size. The reflected beam from the first spherical mirror 3 is incident on the second spherical mirror 4 at an incident angle of 5° to 10°, where the beam undergoes a second focusing and spot shaping. The purified 13.5nm ± 1% EUV radiation, after rigorous filtering and focusing, is received by the detector 5 located at the end of the optical path. The detector 5 converts the received EUV photon energy into a photocurrent signal, the intensity of which is proportional to the incident 13.5nm EUV radiation power (or pulse energy).

[0042] Because the light spot is significantly reduced to within 5 mm in diameter, this invention allows for the use of EUV photodiodes with smaller photosensitive areas (e.g., 5 mm or smaller in diameter) and better material uniformity. The use of a small-area, highly uniform detector is because the light spot completely covers the more uniform central region of its photosensitive surface, significantly reducing measurement errors introduced by detector response non-uniformity, thereby greatly improving the absolute measurement accuracy of EUV pulse energy. Furthermore, the focusing characteristics of the spherical mirror allow for a more compact optical path design. Compared to planar mirror solutions that require more space to avoid beam obstruction, the spherical mirror solution of this invention optimizes the spatial layout, significantly reducing the overall size of the monitoring device, making its structure more compact and facilitating integration into the space-constrained interior of an EUV lithography machine.

[0043] Optical system simulation designs for the extreme ultraviolet energy monitoring device based on a spherical mirror and the extreme ultraviolet energy monitoring device based on a plane mirror (replacing the spherical mirror with a plane mirror) of this invention were performed using optical design analysis software. The results are shown in […]. Figure 4 and Figure 5 It can be seen that the spot size of the extreme ultraviolet energy monitoring device based on the spherical reflector of this invention is reduced from 7.6 mm ( Figure 4 Shrink to 4.8mm Figure 5 This indicates that spherical mirrors have significant advantages in focusing light rays, improving light intensity concentration, and optimizing optical path design, thereby improving the accuracy and efficiency of energy monitoring.

[0044] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0045] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror, characterized in that: Along the optical path, it includes, in sequence, an aperture stop, a thin-film filter, a first spherical mirror, a second spherical mirror, and a detector; The broadband radiation emitted by the EUV source first passes through the aperture stop and then enters the thin-film filter. The EUV beam passing through the thin-film filter illuminates the first spherical mirror at an incident angle of 5° to 10°, where the incident beam undergoes narrowband filtering and focusing, initially reducing the beam divergence angle and spot size. The reflected beam from the first spherical mirror enters the second spherical mirror at an incident angle of 5° to 10°, where the beam undergoes a second focusing and spot shaping. The filtered and focused EUV radiation is then received by the detector located at the end of the optical path.

2. The 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror according to claim 1, characterized in that: The aperture size of the aperture stop is adjustable, ranging from 3mm to 8mm; the EUV light source emits broadband radiation, which includes long-wave radiation with wavelengths greater than 25nm, including far-ultraviolet, ultraviolet, visible, and infrared radiation.

3. The 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror according to claim 1, characterized in that: The thin-film filter is a zirconium or beryllium film with a thickness of 100nm~200nm, used to filter broadband EUV light sources and allow EUV radiation near 13.5nm to pass through.

4. The 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror according to claim 3, characterized in that: The thin-film filter is a zirconium film with a thickness of 200 nm.

5. The 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror according to claim 1, characterized in that: Both the first and second spherical reflectors have a concave spherical structure and are coated with a periodic multilayer molybdenum / silicon film with a film thickness period of 6.8~7.2nm.

6. The 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror according to claim 5, characterized in that: The first spherical mirror has a reflectivity of >60% and a bandwidth of ±2% at the center wavelength of 13.5nm; after the light passes through the second spherical mirror, the detection spectral width has a bandwidth of ±1.4% at the center wavelength of 13.5nm.

7. The 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror according to claim 1, characterized in that: The detector has a photosensitive area ≥25mm². 2 A silicon-based or wide-bandgap semiconductor detector is used to receive the reflected beam from the second spherical mirror, convert the received EUV photon energy into a photocurrent signal, and then transmit it to the signal processing unit for analysis.

8. The 13.5nm extreme ultraviolet light source energy monitoring device based on a spherical mirror according to claim 7, characterized in that: The detector is an EUV photodiode based on silicon, diamond, GaN, SiC, or AlN.

Images