Multi-layer antireflection film preparation device capable of regulating and controlling photomultiplier cathode performance and preparation method

Abstract

The invention relates to the technical field of photomultipliers, in particular to a device and method for preparing a multi-layer antireflection film capable of regulating and controlling the cathode performance of a photomultiplier, and the device comprises a vacuum chamber which is used for bearing and sealing a glass bulb, and maintaining a preset pressure environment required by preparation; the atmosphere system is connected with the vacuum chamber and is used for introducing at least two different process gases into the vacuum chamber; and each target material carrying table is independently provided with a target material, and is constructed to be capable of generating plasma to sputter the corresponding target material so as to form a film layer on the inner wall of the glass shell. According to the invention, the total optical thickness of the multi-layer antireflection film is accurately controlled to be within the predetermined range, so that a user can actively design and accurately prepare the PMT according to the required target wave band, the user can customize the most adaptive PMT according to specific application, and the diversified requirements of the PMT are met.

Description

Technical Field

[0001] This invention relates to the field of photomultiplier tube technology, and more specifically to an apparatus and method for preparing a multilayer antireflection film with adjustable cathode performance of a photomultiplier tube. Background Technology

[0002] A photomultiplier tube (PMT) is a vacuum electronic device that converts and amplifies weak light signals into electrical signals. It is widely used in optical measurement, nuclear medicine, high-energy physics, and other fields. A PMT typically consists of an optical window, a photocathode, a dynode, and an anode. Based on the photoelectric effect and the principle of secondary electron emission, when photons are incident on the photocathode, photoelectrons are excited. These photoelectrons enter the multiplication system under the influence of an electric field, and through multiple collisions with the dynode (such as a dynode), secondary electrons are generated. Finally, these secondary electrons are collected by the anode and converted into an electrical signal.

[0003] The core performance indicators of a photomultiplier tube (PMT) include quantum efficiency and its spectral response characteristics, which directly determine the performance and applicable fields of the entire detection system. With the rapid development of cutting-edge scientific exploration and precision measurement technologies, the performance requirements for PMTs have shifted from general-purpose high performance to optimization within specific wavelength bands. In different advanced application areas, due to significant differences in the intrinsic wavelength of the measured optical signal or the emission spectrum of the scintillator used, drastically different customized requirements are placed on the spectral response of the PMT.

[0004] However, existing PMT antireflection film preparation technologies fundamentally limit the realization of such customized requirements. Current mainstream technologies, such as thermal evaporation followed by oxidation / nitriding (as shown in CN111261488A) or electron beam evaporation of specific bilayer films (as shown in CN111463103A), cannot meet customized requirements.

[0005] The antireflective membranes prepared using the aforementioned technologies have their materials, number of layers, and total thickness fixed during the process design stage. The resulting PMTs have fixed spectral response curves and are essentially general-purpose or standard products. Users can only find approximately matching models from a series of PMTs with fixed performance, and cannot customize the spectral response of the PMT according to their specific target wavelength. Moreover, existing equipment and processes struggle to achieve flexible and efficient preparation of complex membrane systems with three or more layers.

[0006] Clearly, existing preparation technologies, due to their inherent functional immobilization and rigid processes, cannot meet the diverse needs of PMT. Summary of the Invention

[0007] To address the technical problems existing in the fabrication of photomultiplier tubes in the prior art, the first aspect of this invention proposes a technical solution: a multilayer antireflection film fabrication apparatus for tunable photomultiplier tube cathode performance, comprising: A vacuum chamber is used to support and seal the glass shell and maintain the predetermined pressure environment required for the preparation. An atmosphere system, connected to the vacuum chamber, is used to introduce at least two different process gases into it; Multiple target stages, each independently configured with a target and constructed to generate plasma to sputter its corresponding target, for forming a film on the inner wall of the glass shell; A transfer unit, disposed within the vacuum chamber, is configured to selectively move any of the target stages to a sputtering station opposite the inner wall of the glass shell; The monitoring system is configured to monitor the coating status of the inner wall of the glass shell in real time, and trigger the transfer component to perform the target stage switching operation and the atmosphere system to perform the process gas switching operation based on the monitoring signal. Through the coordinated control of the monitoring system, the matching and coordinated switching of target materials and process gases for different membrane layers are realized, thereby completing the automated and continuous preparation of multilayer antireflection membranes on the inner wall of the glass shell within a predetermined pressure range in the vacuum chamber.

[0008] Preferably, the target stage is a magnetron sputtering assembly, which includes an anode base, a cathode base, a magnet, and a target. The anode base and the cathode base are separated by an insulating ring, and the three are fixed to each other. The first end of the anode base is connected to the transfer component, and the second end is connected to the target cover. The magnet and the target are both connected to the cathode base, and the target corresponds to the window position of the magnet and the target cover. The anode base and cathode base are connected to a power source, which is used to apply a negative high voltage to the cathode base.

[0009] Preferably, the insulating ring is a ceramic ring made of alumina, zirconium oxide, silicon nitride, or boron nitride, and the target material is one of Mg, Al, Be, Hf, Si, or Mn metal targets.

[0010] Preferably, the magnet comprises one of the following three configurations: a) The first central magnet is cylindrical and exhibits a first type of magnetism, and the first outer ring magnets are multiple cylindrical objects equidistantly distributed around the outer periphery of the first central magnet and exhibit a second type of magnetism opposite to the first type of magnetism. b) The second central magnet is cylindrical and exhibits the first magnetic field, and the second outer ring magnet is a ring-shaped magnet that fits around the second central magnet and exhibits the second magnetic field that is opposite to the first magnetic field. c) The third central magnet is a ring and exhibits a first magnetic field, and the third outer ring magnet is a ring that fits around the third central magnet and exhibits a second magnetic field opposite to the first magnetic field.

[0011] Preferably, the atmosphere system includes: The vacuum pumping unit includes a mechanical pump, a molecular pump, and a valve group that isolates the mechanical pump, the molecular pump, and the vacuum chamber. The valve group includes a gate valve, which is used to control the vacuum chamber to be between 0.1 and 50 Pa. At least two independent process gas input lines, each including an inlet valve and a mass flow meter, are used to precisely control the flow rates of argon, oxygen, and nitrogen respectively.

[0012] Preferably, the vacuum chamber is provided with multiple stations for supporting glass shells, and the transfer component is configured to synchronously or sequentially transfer multiple target stages on it to sputtering stations opposite to the inner walls of different glass shells, so as to realize the one-time preparation of multilayer antireflection films for multiple glass shells.

[0013] Preferably, the transfer component includes a lifting mechanism and a rotating mechanism. The multiple target platforms located on the vacuum chamber are arranged in a ring. The lifting mechanism can raise the target platform connected to it as a whole into the interior of the target platform or lower it out of the target platform. The rotating mechanism can rotate all the target platforms connected to it by a predetermined angle to transfer the multiple target platforms synchronously or sequentially to the sputtering stations opposite to the inner walls of different target platforms.

[0014] Preferably, the monitoring system includes a reflectivity monitoring component. The probe of the reflectivity monitoring component is in perpendicular contact with the top of the glass shell and can emit and receive probe light. The reflectivity monitoring component can monitor the change in the reflectivity of the film layer in real time based on the received probe light. When the reflectivity of the currently prepared film layer reaches a preset target value, the following sequence of actions is triggered: A1. Disconnect the sputtering power supply of the current target stage; A2. Control the transfer component to lower the current target stage to exit the glass shell, and transfer the target stage of the next film layer corresponding to the target to the current position, and then raise it into the glass shell; A3. Control the atmosphere system to shut down the current process gas pipeline and open the process gas pipeline corresponding to the preparation of the next film layer, so that the glass shell has the atmosphere environment required for the preparation of the next film layer.

[0015] The second aspect of this invention provides a technical solution: a method for preparing a multilayer antireflection film with tunable photomultiplier tube cathode performance, using the aforementioned apparatus for preparing a multilayer antireflection film with tunable photomultiplier tube cathode performance, comprising the following steps: Step S1: Seal the glass shell in the vacuum chamber and evacuate to the target vacuum level; Step S2: Position the target stage carrying the current target material to the sputtering station inside the glass shell using the transfer component; Step S3: Introduce the process gas corresponding to the nth film layer, start the target stage carrying the corresponding nth film layer for sputtering, so that an antireflection film is deposited inside the glass shell, and monitor the coating status in real time through the monitoring system. Step S4: When the current film layer reaches the preset thickness, stop sputtering and the current process gas is introduced, and switch the target stage carrying the target material corresponding to the (n+1)th film layer to the sputtering station through the transfer component. Step S5: Introduce the process gas corresponding to the (n+1)th film layer and start the target stage for sputtering; Step S6: Repeat steps S3 to S5 until all film layers are deposited. The entire process is completed continuously within a single vacuum cycle. In the magnetron sputtering process, reflectivity is used to monitor the change in film thickness, and the total optical thickness of the multilayer antireflection film is controlled within the range of 70% to 250% to change the peak response band of the photocathode.

[0016] Preferably, during magnetron sputtering, the sputtering working pressure is 0.1~10Pa, a high voltage DC current of 300~800V is applied to the cathode base for glow discharge sputtering, or a radio frequency power supply with a frequency of 13.56 MHz is applied for radio frequency sputtering, and the anode base and the transfer component are grounded simultaneously.

[0017] Compared with the prior art, the advantages of the present invention are as follows: This invention allows users to actively design and precisely fabricate PMTs according to the target wavelength required by precisely controlling the total optical thickness of the multilayer antireflection film within a predetermined range. This enables users to customize the most suitable PMT for specific applications and meet the diverse needs of PMTs. This invention employs reactive magnetron sputtering technology combined with a high vacuum environment to prepare oxide or nitride films with high density, strong adhesion, and uniform composition. Compared with existing thermal evaporation technology, the films have fewer internal defects, superior optical performance, and are less prone to peeling off during subsequent high-temperature baking, ensuring high performance and long-life reliability of the products. This invention enables the entire multilayer film preparation process to be completed automatically and continuously within a single vacuuming cycle through the coordination of the monitoring system, transfer components and atmosphere system, without the need for manual intervention, thus ensuring production efficiency and process consistency. Furthermore, the combination of multi-glass shell station and annular transfer layout enables batch parallel processing capability, allowing the device to balance the flexibility of the R&D stage with the economies of scale of the industrialization stage. Attached Figure Description

[0018] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the structure of the multilayer antireflection film preparation device with adjustable photomultiplier tube cathode performance shown in an embodiment of the present invention; Figure 2 This is a schematic diagram of a sputtering station where the target stage is located inside a glass shell, as shown in an embodiment of the present invention. Figure 3(a) is a schematic diagram of the first structure of the magnet shown in the embodiment of the present invention; Figure 3(b) is a schematic diagram of the second structure of the magnet shown in the embodiment of the present invention; Figure 3(c) is a schematic diagram of the third structure of the magnet shown in the embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the multilayer film layer prepared on the surface of the glass shell as shown in the embodiment of the present invention; Figure 5 These are the spectral response curves of photomultiplier tube cathodes prepared using antireflection films of different thicknesses, as shown in the embodiments of the present invention. Detailed Implementation

[0019] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0020] Combination Figure 1 As shown, the first aspect of the present invention proposes a technical solution: a multilayer antireflection film preparation device with adjustable photomultiplier tube cathode performance, comprising a vacuum chamber 20, an atmosphere system, multiple target stages, a transfer component 40, and a monitoring system 30.

[0021] Combination Figure 1 As shown, the vacuum chamber 20 can be a cylindrical structure, and the top of the cylindrical structure is provided with multiple holes as points for supporting the glass shell 10.

[0022] Specifically, the glass shell 10 of the photomultiplier tube is sealed to the aperture placed in the vacuum chamber 20 by a fluororubber ring, so that the glass shell 10 and the vacuum chamber 20 form the same pressure environment.

[0023] As described above, the vacuum chamber 20 is used to support and seal the glass shell 10, while also maintaining the predetermined pressure environment required for the preparation.

[0024] Furthermore, the atmosphere system is connected to the vacuum chamber 20 for introducing at least two different process gases into it.

[0025] Combination Figure 1 As shown, the atmosphere system includes a vacuum unit and at least two independent process gas input lines.

[0026] The vacuum pumping unit includes a mechanical pump 84, a molecular pump 82, and a valve assembly that isolates the mechanical pump 84 and the molecular pump 82 from the vacuum chamber 20. The valve assembly includes a gate valve 81, which is used to control the vacuum chamber 20 to maintain a pressure between 0.1 and 50 Pa. The vacuum chamber 20 is also equipped with a full-range vacuum gauge 60 for monitoring its internal pressure and a vent valve 80, which is used to ensure that the pressure inside the vacuum chamber 20 is the same as the atmospheric pressure.

[0027] Specifically, the mechanical pump 84 is connected to the vacuum chamber 20 via a bypass valve 83, the molecular pump 82 is connected to the vacuum chamber 20 via a gate valve 81, and the mechanical pump 84 and the molecular pump 82 are connected by a shut-off valve 85.

[0028] Preliminary vacuuming can be performed by turning on the mechanical pump 84 and the bypass valve 83. Once the full-range vacuum gauge 60 shows a vacuum level below 20 Pa, close the bypass valve 83, open the shut-off valve 85 and the molecular pump 82, and after the molecular pump 82 starts, fully open the slide gate valve 81 to evacuate the chamber to a high vacuum state.

[0029] Furthermore, during the preparation process, the pressure of the vacuum chamber 20 can be controlled within the range of 0.1~50 Pa by controlling the opening and closing ratio of the slide valve 81 as needed.

[0030] Furthermore, each process gas input line includes an inlet valve and a mass flow meter. The mass flow meter can control the flow rate into the vacuum chamber 20. Therefore, different process gas input lines can be used to precisely control the flow rates of argon, oxygen and nitrogen into the vacuum chamber 20 respectively.

[0031] Combination Figure 1 As shown, in an optional embodiment, the vacuum chamber 20 is connected to three process gas paths, namely the first gas path (including the first inlet valve 70 and the first mass flow meter 71), the second gas path (including the second inlet valve 72 and the second mass flow meter 73), and the third gas path (including the third inlet valve 74 and the third mass flow meter 75).

[0032] The first gas path is used to introduce argon gas into the vacuum chamber 20, the second gas path is used to introduce oxygen gas into the vacuum chamber 20, and the third gas path is used to introduce nitrogen gas into the vacuum chamber 20.

[0033] Furthermore, each of the multiple target stages is independently configured with a target 505 and is constructed to generate plasma to sputter its corresponding target 505 for forming a film on the inner wall of the glass shell 10.

[0034] Combination Figure 2 As shown, the target stage is a magnetron sputtering assembly 50. The magnetron sputtering assembly 50 includes an anode base 501, a cathode base 503, a magnet 504, and a target 505. The anode base 501 and the cathode base 503 are separated by an insulating ring 502 and the three are fixed to each other. The first end of the anode base 501 is connected to the transfer component 40, and the second end is connected to the target cover 506.

[0035] The magnet 504 and the target 505 are both connected to the cathode base 503, and the target 505 corresponds to the window position of the magnet 504 and the target cover 506.

[0036] Furthermore, the anode base 501 and the cathode base 503 are connected to a power source, which is used to apply a negative high voltage to the cathode base 503.

[0037] Thus, by applying a negative high voltage of 300~800V to the cathode base 503, magnetron sputtering can be performed. The magnetic field generated by the magnet 504 confines electrons to the vicinity of the target surface, increasing the probability of collisions between electrons and argon atoms, thereby generating and maintaining a high-density plasma. In a mixed atmosphere of inert gas (Ar) and reactive gas (O2 / N2), the target 505 is bombarded with plasma, and the sputtered metal atoms and reactive gas directly combine and deposit on the surface of the glass shell 10 to form an antireflection film layer.

[0038] In an optional embodiment, the insulating ring 502 is a ceramic ring made of alumina, zirconium oxide, silicon nitride, or boron nitride, and the target 505 is one of Mg, Al, Be, Hf, Si, or Mn metal targets.

[0039] Furthermore, to accommodate different glass shell types, the magnet 504 includes one of the following three configurations: As shown in Figure 3(a), the first central magnet 5041 is cylindrical and exhibits first magnetism, while the first outer ring magnet 5042 consists of multiple cylindrical magnets equidistantly distributed around the outer periphery of the first central magnet 5041 and exhibits second magnetism opposite to the first magnetism.

[0040] Thus, the distribution of these magnets forms a balanced magnetron target, with the magnetic field lines tightly confined to the surface of the target material, making it suitable for coating planar substrates and small-diameter glass shells.

[0041] As shown in Figure 3(b), the second central magnet 5043 is cylindrical and exhibits the first magnetic property, while the second outer ring magnet 5044 is a ring-shaped magnet surrounding the second central magnet 5043 and exhibits the second magnetic property opposite to the first magnetic property.

[0042] Thus, the distribution of these magnets constitutes an unbalanced magnetron target, and some magnetic field lines can extend from the target surface and penetrate into the coating cavity. Therefore, when the magnetron sputtering assembly 50 extends into the glass shell 10 for sputtering, the plasma can better cover the curved surface of the inner wall of the glass shell, thereby obtaining a film layer with a more uniform thickness.

[0043] As shown in Figure 3(c), the third central magnet 5045 is a ring and exhibits a first magnetic field, while the third outer ring magnet 5046 is a ring that fits around the third central magnet 5045 and exhibits a second magnetic field opposite to the first magnetic field.

[0044] Thus, the distribution of these magnets constitutes an enhanced unbalanced magnetron target, forming a stronger and farther magnetic field extension, which can be applied to the internal coating of PMT glass shells with deep holes and high aspect ratios.

[0045] Furthermore, the transfer component 40 is disposed within the vacuum chamber 20 and is configured to selectively move any target stage to a sputtering station opposite the inner wall of the glass shell 10.

[0046] like Figure 1 As shown, the vacuum chamber 20 is provided with multiple stations for carrying glass shells 10. The transfer component 40 is configured to transfer multiple target stages on it synchronously or sequentially to sputtering stations opposite to the inner walls of different glass shells 10, so as to realize the one-time preparation of multilayer antireflection films of multiple glass shells 10.

[0047] In an optional embodiment, the transfer component 40 includes a lifting mechanism and a rotating mechanism. The multiple carrier glass shells 10 on the vacuum chamber 20 are arranged in a ring. The lifting mechanism can raise the target stage connected to it as a whole into the glass shell 10 or lower it out of it. The rotating mechanism can rotate all the target stages connected to it by a predetermined angle so as to transfer the multiple target stages synchronously or sequentially to the sputtering station opposite to the inner wall of different glass shells 10.

[0048] In this way, the combination of the annular glass shell station layout and the rotating mechanism allows a set of target carriers to serve multiple glass shells in sequence, achieving batch processing to improve production efficiency. It also allows for the deposition of the same or different customized film systems for different glass shells within the same vacuum cycle, improving equipment utilization and production flexibility to adapt to different needs of R&D and production.

[0049] In addition, the lifting mechanism ensures precise control of the distance between the sputtering source (target 505) and the inner wall of the glass shell 10, which is beneficial to obtaining a uniform film layer in the above-mentioned batch processing. Furthermore, the high-precision rotating mechanism can ensure the spatial consistency of the sputtering process after each target switching, avoiding film thickness and composition fluctuations caused by positioning deviations.

[0050] Furthermore, the monitoring system 30 is configured to monitor the coating status of the inner wall of the glass shell 10 in real time, and trigger the transfer component 40 to perform the target stage switching operation and the atmosphere system to perform the process gas switching operation based on the monitoring signal.

[0051] Through the coordinated control of the monitoring system 30, the matching and coordinated switching of target materials and process gases for different membrane layers are realized, thereby completing the automated continuous preparation of multilayer antireflection membranes on the inner wall of the glass shell 10 at a predetermined pressure range in the vacuum chamber 20.

[0052] In this way, by monitoring the coating status in real time through the monitoring system 30, the most tedious and critical process of stop-switch-restart in the preparation of multilayer films is automated, eliminating errors, delays and accidental mistakes introduced by human intervention, ensuring the absolute repeatability of the process, and minimizing contamination and interval time between layers through rapid and programmed automatic switching, ensuring a clear and clean interface between multilayer films, which is crucial for achieving the expected optical interference effect.

[0053] Furthermore, by monitoring and coordinating the control of film thickness, the termination point of each film layer is determined by an objective optical signal (reflectivity) rather than a fixed time. Therefore, it is possible to execute the film thickness design determined in advance through optical simulation, laying the foundation for precise control of spectral response.

[0054] Specifically, the monitoring system 30 includes a reflectivity monitoring component. The probe of the reflectivity monitoring component is in vertical contact with the top of the glass shell 10 and can emit and receive probe light. The reflectivity monitoring component can monitor the change in the reflectivity of the film layer in real time based on the received probe light. When the reflectivity of the currently prepared film layer reaches the preset target value, the following action sequence is triggered: A1. Disconnect the sputtering power supply of the current target stage; A2. The control transfer component 40 lowers the current target stage to exit the glass shell 10, and transfers the target stage of the next film layer corresponding to the target to the current position, and then raises it into the glass shell 10. A3. The control atmosphere system shuts down the current process gas pipeline and opens the process gas pipeline corresponding to the preparation of the next film layer, so that the glass shell 10 has the atmosphere environment required for the preparation of the next film layer.

[0055] Thus, the above switching process stops sputtering before switching gases, ensuring that the residue of the previous reaction gas will not contaminate or pre-react the subsequent target material, and ensuring that each target material works only in the pure atmosphere designed for it, which is conducive to maintaining the stability and reliability of the multilayer film preparation process.

[0056] In a specific embodiment, taking a magnetron sputtering assembly 50 with 6 stations as an example, the 6 stations are numbered C1, C2, C3, C4, C5, and C6 in a clockwise direction. The glass shells 10 are correspondingly numbered B1, B2, B3, B4, B5, and B6. The magnets 504 adopt the structure shown in Figure 3(b), as follows... Figure 4 As shown, the photomultiplier tube multilayer antireflection film structure to be prepared is specifically a three-layer film, including a glass shell 10 substrate, a first antireflection film 101, a second antireflection film 102, and a photocathode 103.

[0057] First, the glass shell to be coated and the chamber 20 are vacuum sealed with a fluororubber ring. Then, the mechanical pump 84 and the bypass valve 83 are turned on to perform preliminary vacuuming. When the full-range vacuum gauge 60 shows that the vacuum reaches below 20 Pa, the bypass valve 83 is closed, and the shut-off valve 85 and the molecular pump 82 are opened. After the molecular pump starts, the slide gate valve 81 is fully opened to pump the chamber to a high vacuum state.

[0058] Once the chamber vacuum reaches 2×10 -5 Pa, align the laser probe of the reflectivity monitoring component 30 with the center of the top of the glass shell 10, and install the target material 505 in advance according to the plan for the antireflection film layer. In this embodiment, three antireflection films (magnesium oxide, beryllium nitride, and beryllium oxide) are prepared. Therefore, the targets in the magnetron sputtering components C1 to C6 are three sets of alternating magnesium metal targets and beryllium metal targets.

[0059] The control transfer component 40 inserts the magnetron sputtering assembly 50 into the glass shell 10, closes the insert valve 81, sets the argon flow rate of the first mass flow meter 71 to 100 sccm and the oxygen flow rate of the second mass flow meter 73 to 20 sccm, sequentially opens the second inlet valve 72 and the first inlet valve 70, adjusts the opening ratio of the insert valve 81 to control the vacuum gauge 60 reading to 0.3 Pa, turns on the cathode power supply of the magnetron sputtering assemblies numbered C1, C3, and C5 (target material 505 is a magnesium metal target) to apply a negative high voltage of 400V for sputtering, monitors the reflectivity increase of 50%, turns off the power supply, closes the second inlet valve 72 and the first inlet valve 70, and fully opens the insert valve 81 to complete the preparation of the first antireflection film of the glass shell 10 numbered B1, B3, and B5.

[0060] The control transfer component 40 lowers the magnetron sputtering assembly 50 out of the glass shell 10 and rotates 60° clockwise to raise the magnetron sputtering assembly 50 into the glass shell. At this time, the glass shells 10 numbered B1, B3, and B5 contain the magnetron sputtering assemblies 50 numbered C6, C2, and C4, and the preparation of the second antireflection film beryllium nitride is started.

[0061] First, close the gate valve 81, set the argon flow rate of the first mass flow meter 71 to 100 sccm, and the nitrogen flow rate of the third mass flow meter 75 to 40 sccm. Then, sequentially open the third inlet valve 74 and the first inlet valve 70, adjust the opening ratio of the gate valve 81 to control the reading of the vacuum gauge 60 to 0.5 Pa, turn on the cathode power supply of the magnetron sputtering components 50 (target 505 is a beryllium metal target) numbered C6, C2, and C4 to apply a negative high voltage of 400V for sputtering, monitor the reflectivity increase to 80%, turn off the power supply, close the third inlet valve 74 and the first inlet valve 70, and fully open the gate valve 81 to complete the preparation of the second antireflection film of glass shells B1, B3, and B5.

[0062] The third antireflection film still uses a beryllium metal target, so there is no need to replace the magnetron sputtering assembly 50. Close the gate valve 81, set the argon flow rate of the first mass flow meter 71 to 100 sccm, and the oxygen flow rate of the second mass flow meter 73 to 20 sccm. Open the second inlet valve 72 and the first inlet valve 70 in sequence, adjust the opening ratio of the gate valve 81 to control the reading of the vacuum gauge 60 to 0.3 Pa, turn on the cathode power supply of the magnetron sputtering assemblies (C6, C2, and C4, with the target material 505 being a beryllium metal target) to apply a negative high voltage of 400V for sputtering, monitor the reflectivity increase to 10%, turn off the power, close the second inlet valve 72 and the first inlet valve 70, and fully open the gate valve 81 to complete the preparation of the third antireflection film of the glass shell 10, numbered B1, B3, and B5.

[0063] At this point, the remaining three-layer antireflection membranes for glass shells 10, numbered B2, B4, and B6, can be prepared by following the steps above. Close the insert valve 81, open the vent valve 80 to restore the chamber pressure to atmospheric pressure (vacuum gauge 60 shows 1E5 Pa), and remove the glass shells to complete the antireflection membrane preparation.

[0064] like Figure 5 As shown, in this example, the total thickness of the three-layer antireflection film is 50% + 80% + 10% = 140%. The relationship between the cathode spectral response and the thickness of the antireflection film is as follows. Figure 5 As shown in Table 1, the peak position and the corresponding QE are given. The data show that as the thickness of the antireflection film increases, the peak response shifts from 0% at 395nm to the longer wavelength direction. When the thickness of the antireflection film reaches 250%, the cathode peak response position is 430nm, and the quantum efficiency is improved in the range of 120%~200% of the thickness of the antireflection film.

[0065] Table 1 curve 1 2 3 4 5 thickness 0% 120% 140% 200% 250% Peak band 395nm 390nm 400nm 420nm 430nm Peak QE 32.2% 34.9% 34.6% 32.5% 30.3% {Example 2} The second aspect of this invention provides a technical solution: a method for preparing a multilayer antireflection film with tunable photomultiplier tube cathode performance, using the aforementioned apparatus for preparing a multilayer antireflection film with tunable photomultiplier tube cathode performance, comprising the following steps: Step S1: Seal the glass shell 10 inside the vacuum chamber 20 and evacuate to the target vacuum level; Step S2: Position the target stage carrying the current target material to the sputtering station inside the glass shell 10 using the transfer component 40; Step S3: Introduce the process gas corresponding to the nth film layer, start the target stage carrying the corresponding nth film layer for sputtering, so that an antireflection film is deposited in the glass shell 10, and at the same time, the coating status is monitored in real time through the monitoring system 30. Step S4: When the current film layer reaches the preset thickness, stop sputtering and the current process gas is introduced, and switch the target stage carrying the target material corresponding to the (n+1)th film layer to the sputtering station through the transfer component 40. Step S5: Introduce the process gas corresponding to the (n+1)th film layer and start the target stage for sputtering; Step S6: Repeat steps S3 to S5 until all film layers are deposited. The entire process is completed continuously within a single vacuum cycle. In the magnetron sputtering process, reflectivity is used to monitor the change in film thickness, and the total optical thickness of the multilayer antireflection film is controlled within the range of 70% to 250% to change the peak response band of the photocathode.

[0066] It should be understood that light will be reflected at the interfaces of the multilayer film, and these reflected lights will interfere with each other. The choice between enhancing interference or destructive interference depends on the phase difference of the light waves, and the phase difference is directly determined by the optical thickness.

[0067] Therefore, by precisely controlling the total optical effect (i.e., total optical thickness) of the multilayer film stack to fall within the specific range of 70% to 250%, the peak response band of the photocathode can be controllably adjusted from about 390nm to about 430nm to meet the customized needs of different application scenarios.

[0068] Furthermore, during the magnetron sputtering process, the sputtering working pressure is 0.1~10Pa, and a high voltage DC current of 300~800V is applied to the cathode base 503 for glow discharge sputtering, or a radio frequency power supply with a frequency of 13.56 MHz is applied for radio frequency sputtering. The anode base 503 and the transfer component 40 are grounded simultaneously.

[0069] In a specific embodiment, taking a magnetron sputtering assembly 50 with 6 stations as an example, the 6 stations are numbered C1, C2, C3, C4, C5, and C6 in a clockwise direction. The glass shells 10 are correspondingly numbered B1, B2, B3, B4, B5, and B6. The magnets 504 adopt the structure shown in Figure 3(b), as follows... Figure 4As shown, the photomultiplier tube multilayer antireflection film structure to be prepared is specifically a three-layer film, including a glass shell 10 substrate, a first antireflection film 101, a second antireflection film 102, and a photocathode 103.

[0070] First, the glass shell to be coated and the chamber 20 are vacuum sealed with a fluororubber ring. Then, the mechanical pump 84 and the bypass valve 83 are turned on to perform preliminary vacuuming. When the full-range vacuum gauge 60 shows that the vacuum reaches below 20 Pa, the bypass valve 83 is closed, and the shut-off valve 85 and the molecular pump 82 are opened. After the molecular pump starts, the slide gate valve 81 is fully opened to pump the chamber to a high vacuum state.

[0071] Once the chamber vacuum reaches 2×10 -5 Pa, align the laser probe of the reflectivity monitoring component 30 with the center of the top of the glass shell 10, and install the target material 505 in advance according to the plan for the antireflection film layer. In this embodiment, three antireflection films (magnesium oxide, beryllium nitride, and beryllium oxide) are prepared. Therefore, the targets in the magnetron sputtering components C1 to C6 are three sets of alternating magnesium metal targets and beryllium metal targets.

[0072] The control transfer component 40 inserts the magnetron sputtering assembly 50 into the glass shell 10, closes the insert valve 81, sets the argon flow rate of the first mass flow meter 71 to 100 sccm and the oxygen flow rate of the second mass flow meter 73 to 20 sccm, sequentially opens the second inlet valve 72 and the first inlet valve 70, adjusts the opening ratio of the insert valve 81 to control the vacuum gauge 60 reading to 0.3 Pa, turns on the cathode power supply of the magnetron sputtering assemblies numbered C1, C3, and C5 (target material 505 is a magnesium metal target) to apply a negative high voltage of 400V for sputtering, monitors the reflectivity increase of 50%, turns off the power supply, closes the second inlet valve 72 and the first inlet valve 70, and fully opens the insert valve 81 to complete the preparation of the first antireflection film of the glass shell 10 numbered B1, B3, and B5.

[0073] The control transfer component 40 lowers the magnetron sputtering assembly 50 out of the glass shell 10 and rotates 60° clockwise to raise the magnetron sputtering assembly 50 into the glass shell. At this time, the glass shells 10 numbered B1, B3, and B5 contain the magnetron sputtering assemblies 50 numbered C6, C2, and C4, and the preparation of the second antireflection film beryllium nitride is started.

[0074] First, close the gate valve 81, set the argon flow rate of the first mass flow meter 71 to 100 sccm, and the nitrogen flow rate of the third mass flow meter 75 to 40 sccm. Then, sequentially open the third inlet valve 74 and the first inlet valve 70, adjust the opening ratio of the gate valve 81 to control the reading of the vacuum gauge 60 to 0.5 Pa, turn on the cathode power supply of the magnetron sputtering components 50 (target 505 is a beryllium metal target) numbered C6, C2, and C4 to apply a negative high voltage of 400V for sputtering, monitor the reflectivity increase to 80%, turn off the power supply, close the third inlet valve 74 and the first inlet valve 70, and fully open the gate valve 81 to complete the preparation of the second antireflection film of glass shells B1, B3, and B5.

[0075] The third antireflection film still uses a beryllium metal target, so there is no need to replace the magnetron sputtering assembly 50. Close the gate valve 81, set the argon flow rate of the first mass flow meter 71 to 100 sccm, and the oxygen flow rate of the second mass flow meter 73 to 20 sccm. Open the second inlet valve 72 and the first inlet valve 70 in sequence, adjust the opening ratio of the gate valve 81 to control the reading of the vacuum gauge 60 to 0.3 Pa, turn on the cathode power supply of the magnetron sputtering assemblies (C6, C2, and C4, with the target material 505 being a beryllium metal target) to apply a negative high voltage of 400V for sputtering, monitor the reflectivity increase to 10%, turn off the power, close the second inlet valve 72 and the first inlet valve 70, and fully open the gate valve 81 to complete the preparation of the third antireflection film of the glass shell 10, numbered B1, B3, and B5.

[0076] At this point, the remaining three-layer antireflection membranes for glass shells 10, numbered B2, B4, and B6, can be prepared by following the steps above. Close the insert valve 81, open the vent valve 80 to restore the chamber pressure to atmospheric pressure (vacuum gauge 60 shows 1E5 Pa), and remove the glass shells to complete the antireflection membrane preparation.

[0077] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A device for preparing a multilayer antireflection film with adjustable photomultiplier tube cathode performance, characterized in that, The application relates to a vacuum chamber (20) for carrying and sealing the glass bulb (10) and maintaining a predetermined pressure environment required for preparation; an atmosphere system connected with the vacuum chamber (20) for introducing at least two different process gases into the vacuum chamber (20); a plurality of target material carriers, each of which is independently provided with a target material (505) and is configured to generate plasma to sputter the corresponding target material (505) for forming a film layer on the inner wall of the glass bulb (10); a transfer component (40) arranged in the vacuum chamber (20) and configured to selectively move any of the target material carriers to a sputtering station opposite the inner wall of the glass bulb (10); and a monitoring system (30) configured to monitor the film forming state of the inner wall of the glass bulb (10) in real time and trigger the transfer component (40) to perform a switching operation of the target material carrier and the atmosphere system to perform a switching operation of the process gas based on a monitoring signal; wherein through the cooperative control of the monitoring system (30), the matching and coordinated switching of the target material and the process gas for different film layers are realized, and the automatic continuous preparation of a multilayer antireflection film on the inner wall of the glass bulb (10) in the vacuum chamber (20) is completed in a predetermined pressure range. The target material carrier is a magnetron sputtering assembly (50) comprising an anode base (501), a cathode base (503), a magnet (504) and a target material (505), the anode base (501) and the cathode base (503) are separated by an insulating ring (502) and are fixed to each other, the first end of the anode base (501) is connected to the transfer component (40), and the second end is connected to a target cover (506), the magnet (504) and the target material (505) are connected to the cathode base (503), and the target material (505) corresponds to the window position of the magnet (504) and the target cover (506). The anode base (501) and the cathode base (503) are connected to a power supply for applying a negative high voltage to the cathode base (503). The insulating ring (502) is a ceramic ring, and the material is alumina, zirconia, silicon nitride or boron nitride, and the target material (505) is one of Mg, Al, Be, Hf, Si and Mn metal target materials. The magnet (504) comprises one of the following three configurations: a) the first center magnet (5041) is cylindrical and has a first magnetism, and the first outer ring magnet (5042) is cylindrical and has a second magnetism opposite to the first magnetism and is equidistantly distributed on the outer periphery of the first center magnet (5041); b) the second center magnet (5043) is cylindrical and has a first magnetism, and the second outer ring magnet (5044) is a circular ring and has a second magnetism opposite to the first magnetism and is sleeved outside the second center magnet (5043); 2. The device for preparing multilayer antireflection coating of controllable performance of photomultiplier tube cathode according to claim 1, characterized in that, c) the third center magnet (5045) is a circular ring and has a first magnetism, and the third outer ring magnet (5046) is a circular ring and has a second magnetism opposite to the first magnetism and is sleeved outside the third center magnet (5045). The atmosphere system comprises:

3. The device for preparing multilayer antireflection coating of controllable performance of photomultiplier tube cathode according to claim 2, characterized in that, ​ 4. The device for preparing multilayer antireflection coating of controllable performance of photomultiplier tube cathode according to claim 2, characterized in that, ​ ​ ​ ​ 5. The apparatus for preparing multilayer antireflection film for controllable photomultiplier tube cathode performance according to claim 1, wherein ​ The vacuum pumping unit comprises a mechanical pump (84), a molecular pump (82), and a valve group for isolating the mechanical pump (84) and the molecular pump (82) from the vacuum chamber (20), wherein the valve group comprises a flapper valve (81) for controlling the vacuum chamber (20) to be at 0.1-50 Pa; At least two independent process gas input pipelines, each including an inlet valve and a mass flow meter, are used to accurately control the flow rates of argon, oxygen, and nitrogen, respectively.

6. The apparatus for preparing multilayer antireflection coating of controllable performance of photomultiplier tube cathode according to claim 1, characterized in that, The vacuum chamber (20) is provided with a plurality of workstations for carrying the glass bulb (10), and the transfer component (40) is configured to synchronously or sequentially transfer a plurality of target material carriers thereon to the sputtering workstations opposite the inner walls of different glass bulbs (10) to realize one-time preparation of multi-layer anti-reflection films for a plurality of glass bulbs (10).

7. The apparatus for preparing multilayer antireflection coating of controllable performance of photomultiplier tube cathode according to claim 1, characterized in that, The transfer component (40) comprises a lifting mechanism and a rotating mechanism, and the plurality of workstations for carrying the glass bulbs (10) on the vacuum chamber (20) are arranged in a ring shape. The lifting mechanism can lift or lower the target material carriers connected thereto as a whole to the inside or outside of the glass bulb (10), and the rotating mechanism can rotate all the target material carriers connected thereto by a predetermined angle to synchronously or sequentially transfer a plurality of target material carriers to the sputtering workstations opposite the inner walls of different glass bulbs (10).

8. The apparatus for preparing multilayer antireflection film for controllable photomultiplier tube cathode performance according to claim 1, wherein The monitoring system (30) comprises a reflectivity monitoring assembly, a probe of the reflectivity monitoring assembly is in direct contact with the top of the glass bulb (10) and can emit and receive probe light, and the reflectivity monitoring assembly can monitor the change of the reflectivity of the film layer in real time according to the received probe light. When it is monitored that the reflectivity of the current prepared film layer reaches a preset target value, the following action sequence is triggered: A1, cutting off the sputtering power supply of the current target material carrier; A2, controlling the transfer component (40) to lower the current target material carrier to exit the glass bulb (10) and transfer the target material carrier corresponding to the next film layer to the current position, and then lift it into the glass bulb (10); A3, controlling the atmosphere system to close the current process gas pipeline and open the process gas pipeline corresponding to the preparation of the next layer of film to make the glass bulb (10) have the atmosphere environment required for the preparation of the next layer of film.

9. A method for preparing a multilayer antireflection coating for regulating the properties of a photomultiplier cathode, characterized in that, The multi-layer anti-reflection film preparation device for controllable photomultiplier cathode performance according to any one of claims 1-8 comprises the following steps: Step S1, sealing the glass bulb (10) in the vacuum chamber (20) and pumping to a target vacuum degree; Step S2, positioning the target material carrier carrying the current target material to the sputtering workstation in the glass bulb (10) by the transfer component (40); Step S3, introducing the process gas corresponding to the nth layer of film, starting the sputtering of the target material carrier carrying the nth layer of film to deposit the anti-reflection film in the glass bulb (10), and monitoring the film deposition state in real time by the monitoring system (30); Step S4, when it is monitored that the current film layer reaches a preset thickness, stopping the sputtering and the introduction of the current process gas, and switching the target material carrier carrying the target material corresponding to the n+1 layer of film to the sputtering workstation by the transfer component (40). Step S5, the process gas corresponding to the n+1 layer is introduced, and the target carrier is started to sputter; Step S6, repeating steps S3 to S5 until all film layers are deposited, the whole process is completed in a single vacuum cycle; In the magnetron sputtering process, the reflectivity is monitored to control the thickness change of the film layer, and the total optical thickness of the multilayer antireflection film is controlled in the range of 70% to 250% to change the peak response waveband of the photocathode.

10. The method for preparing a multilayer antireflection film for regulating the performance of a photomultiplier tube cathode according to claim 9, characterized in that, In the magnetron sputtering process, the sputtering working pressure is 0.1~10Pa, the cathode base (503) applies a voltage of 300~800V to perform glow sputtering, or a radio frequency power source with a frequency of 13.56 MHz is used for radio frequency sputtering, and the anode base (503) and the transfer component (40) are grounded at the same time.

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