Large-area uniform molecular beam evaporation deposition method for photoelectric cathode cesium film based on high-purity cesium

Abstract

The invention relates to the technical field of photoelectric cathode manufacturing, and provides a high-purity cesium-based photoelectric cathode cesium film large-area uniform molecular beam evaporation deposition method, which adopts a high-purity cesium elementary substance cesium source and is matched with an ultrahigh vacuum establishment and maintenance technology to realize long-acting repeated use of the cesium source; a multi-temperature-zone gradient evaporation design is combined with an adaptive PID algorithm and a thermal coupling compensation mechanism to realize cross-zone temperature cooperative control; through a thermodynamics-fluid mechanics dual-mode deposition control strategy, modes are dynamically switched according to the deposition rate, thermal inertia disturbance is inhibited in the high-speed stage, viscous resistance is corrected in the low-speed stage, and the beam density stability is guaranteed; a generator and a cesium source chamber, an evaporator and a spray pipe mechanism which are connected in series are designed to form continuous and stable molecular beam deposition; according to the method, the problems of poor film uniformity, rate instability and end point misjudgment in the traditional process are solved, large-area or single-time multi-substrate cesium film deposition can be realized, and industrial-grade stability, laboratory-grade precision and mass production-grade efficiency are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of photocathode manufacturing, and in particular provides a large-area uniform molecular beam evaporation deposition method of a photocathode cesium film based on high-purity cesium. Background Art

[0002] Photodetectors are key devices that convert optical signals into electrical signals. Their core component, the photocathode, uses the photoelectric effect to achieve photoelectric conversion: when light shines on the cathode surface, it excites electrons inside the material to escape and form a photocurrent. As a typical photoemissive material, the uniformity and purity of cesium thin films directly determine the performance of the detector. Large-area industrial high-uniformity cesium film deposition refers to the formation of a cesium film layer with highly consistent thickness and pure composition on the surface of an ultra-large-sized substrate. In order to meet the needs of industrial mass production of large-area industrial high-uniformity cesium film deposition, the process has higher requirements for efficient utilization of materials and wide-range deposition rate control. Existing technologies cannot meet the core requirements of industrial production of photocathodes for high uniformity, high-efficiency conversion and long-term stability of cesium films, which are mainly manifested in:

[0003] Traditional photocathodes are prepared using solid cesium salts, such as cesium carbonate and cesium chromate, and a reducing agent, zirconium-aluminum alloy, placed in a nickel tube with evaporation pores. Electric heating is applied in a vacuum environment to generate metallic cesium, and cesium vapor is released in pulses. The film thickness fluctuates greatly, with significant thickness differences between different regions. Furthermore, the cesium utilization rate is low, and a single cesium source is used only a few times, requiring frequent replacement. This fails to meet the atomic-level uniformity requirements of high-performance photocathodes such as GaAs. In existing technologies, temperature control typically uses a single temperature zone design, resulting in significant thermal conduction hysteresis, causing significant temperature differences between different regions of the substrate, leading to local condensation during cesium vapor transmission and uneven film thickness distribution. Existing technologies lack a dynamic control mechanism. During high-speed deposition, thermal inertia disturbances cause drastic fluctuations in beam density, resulting in sudden changes in film thickness. During low-speed deposition, vapor viscous resistance causes edge transmission attenuation, degrading film uniformity.

[0004] Therefore, there is an urgent need for a cesium film deposition technology that combines large-area uniformity, long-term stability and multiple reuse to provide reliable core components for high-end optoelectronic equipment. Summary of the Invention

[0005] To solve the problems in the background technology, the present invention provides a large-area uniform molecular beam evaporation deposition method for a photocathode cesium film based on high-purity cesium, comprising the following steps:

[0006] S1, establishment of ultra-high vacuum environment: using a composite vacuum generator to maintain a high vacuum state in the cesium source chamber, evaporator, and nozzle mechanism;

[0007] S2, unsealing the high-purity cesium source: opening the ampoule containing elemental cesium, and the vaporous cesium enters the evaporator;

[0008] S3, gradient temperature field evaporation: n temperature field zones are set in the evaporator. After passing through the n temperature field zones, cesium is converted into a molecular beam in vapor form. The beam enters the nozzle mechanism through a fine-tuning valve, enters the deposition chamber through the nozzle, and is deposited on the substrate in the deposition chamber. During this process, the temperature of each temperature zone is precisely controlled through the adaptive PID temperature dynamic control method.

[0009] S4, dual-mode dynamic deposition control: uses a thermodynamic-hydrodynamic dual-mode algorithm to adjust the deposition rate and beam density in real time;

[0010] S5, deposition time control: control the deposition time according to the substrate photocurrent signal.

[0011] Furthermore, in S1, the vacuum degree of the cesium source chamber, evaporator and nozzle mechanism is stabilized at 1×10 -8 Pa, leakage rate <1×10 -12 Pa·m 3 / s; the composite vacuum generating device includes one or more of a molecular pump, an ion pump, and a sublimation adsorption pump.

[0012] Furthermore, the specific steps of S3 include:

[0013] S31: Real-time collection of temperature values ​​of each area of ​​the evaporator ,in Represents the temperature field partition number;

[0014] S32: Calculate temperature deviation ;

[0015] : No. Partition set temperature, unit ℃; : No. Real-time temperature of each partition, unit: °C; : Temperature deviation value, unit: °C; : current time;

[0016] S33: Adopt adaptive PID algorithm to output control quantity :

[0017] ;

[0018] : PID basic control output, dimensionless; : proportional control gain coefficient, dimensionless; : Integral control gain coefficient, unit ; : differential control gain coefficient, unit ; : Integral operator, indicating the cumulative summation of historical deviations; : Differential operator, indicating the derivation of the current deviation change rate; : integral time variable;

[0019] S34: Correction of thermal interference between adjacent partitions through temperature field coupling compensator:

[0020] ;

[0021] : thermal coupling compensation, unit: W; : Partition Partition The thermal coupling coefficient, in W / °C, is calibrated experimentally; : No. Real-time temperature of each partition, unit: °C; : No. Partition set temperature, unit ℃;

[0022] S35: Final evaporator power in each zone , to achieve precise temperature control in each temperature zone.

[0023] Furthermore, in S3, three temperature field zones are set in the evaporator, namely the unsealing zone, the transmission channel zone and the evaporation zone. The set temperature of the unsealing zone is 160°C; the set temperature of the transmission channel zone is 180°C; and the set temperature of the evaporation zone is 260°C.

[0024] Furthermore, the specific steps of S4 include:

[0025] S41: Establish a cesium atom transport model and calculate beam density :

[0026] ;

[0027] : Cesium atomic beam current density, unit: ; : evaporation zone power, unit W; : Evaporation efficiency correction factor, dimensionless; : Evaporator outlet radius, unit: cm; : distance from evaporator outlet to substrate, unit: cm; : Cesium atomic mass, unit: g / mol; : Boltzmann constant, ; : absolute temperature of evaporation zone, unit K;

[0028] S42: Real-time adjustment of deposition rate based on fluid continuity equation :

[0029] ;

[0030] : deposition rate, unit: nm / s; : molar mass of cesium, 132.9 g / mol; : Density of cesium film, unit: g / cm 3 ; : Substrate deposition area, unit: cm 2 ;

[0031] S43: Set the dual-mode controller to constrain the fluctuation range according to the deposition rate Switch control mode:

[0032] S431, when Thermodynamic mode is activated when

[0033] S432, when Activate the fluid dynamics mode when

[0034] S44: Evaporation zone power regulation via mass flow controller feedback and temperature gradient to achieve beam density fluctuation rate ;Deposition rate Continuously adjustable from 0.0001 to 10 nm / s.

[0035] Furthermore, the specific implementation steps of S43 include:

[0036] When the thermodynamic mode is activated, proceed as follows:

[0037] Step S4311: Construct a feedforward compensator to suppress thermal inertia disturbance:

[0038] ;

[0039] : feedforward power compensation, unit: W; : system thermal time constant, unit s; : heat conduction gain coefficient, dimensionless; : Differential operator, calculates the set power change rate; : Evaporator set power, unit W;

[0040] Step S4312: Update the evaporation zone power:

[0041] ;

[0042] : actual execution power, unit: W;

[0043] Step S4313: Verify stability through the temperature-power coupling equation:

[0044] ;

[0045] : Temperature change rate of evaporation zone, unit K / s; : Heat loss coefficient, unit: W / K; : ambient temperature, unit K; : Evaporator heat capacity, unit J / K;

[0046] When the fluid dynamics mode is activated, proceed as follows:

[0047] Step S4321: Correct the viscous resistance based on the Navier-Stokes equation:

[0048] ;

[0049] : divergence operator; : gradient operator; : Cesium vapor viscosity, unit: Pa·s; : steam velocity vector, unit: m / s; : Viscous pressure drop, unit: Pa; : Transmission distance, unit: m;

[0050] Step S4322: Calculate the beam density correction factor:

[0051] ;

[0052] : Corrected beam current density, unit ; : natural exponential function; : Viscous pressure drop, unit: Pa; : mass of cesium atom, unit: kg; : Boltzmann constant; : evaporation zone temperature, unit K;

[0053] Step S4323: Feedback adjustment of evaporation zone power:

[0054] ; : proportional gain; : Set beam density; : integral gain; : Integral operator, cumulative error; : integral time variable;

[0055] S433, Global Constraints:

[0056] The beam density fluctuation rate satisfies ; : relative volatility, dimensionless;

[0057] The deposition rate range meets ; : Deposition rate, unit: nm / s.

[0058] Furthermore, the specific steps of S5 include:

[0059] The deposited cesium film substrate is used as the cathode, and an anode is added. The cathode is irradiated with white light and the substrate photocurrent signal is monitored in real time. , the deposition is terminated when the photocurrent generated by the cathode reaches a peak.

[0060] The present invention designs a large-area uniform molecular beam evaporation deposition system for a photocathode cesium film based on high-purity cesium, which comprises:

[0061] A cesium source chamber, an evaporator and a nozzle mechanism are connected in series; the cesium source chamber, the evaporator and the nozzle mechanism are installed in a generator; the end of the nozzle mechanism is connected to a deposition chamber, and a plurality of substrates are installed in the deposition chamber; the nozzle mechanism includes a nozzle and a nozzle arranged at the tail end of the nozzle; an ampoule tank is arranged in the cesium source chamber, and the ampoule tank is loaded with high-purity elemental cesium.

[0062] Furthermore, the nozzle has a conical structure; a protective cover is installed on the outside of the nozzle; a fine-tuning valve is provided in the evaporator; an electric control room is installed on the upper part of the generator, and a control system is installed in the electric control room; the nozzle mechanism is connected to the deposition chamber through a flange.

[0063] The beneficial effects achieved by the present invention are:

[0064] This invention designs a technical solution of pure source, reuse, precise temperature control, and intelligent deposition, which enables large-area photocathode film layers to simultaneously achieve high uniformity, high quantum efficiency, and high stability. It provides core technical support for ultra-large-scale night vision devices and quantum detection equipment, specifically:

[0065] First, the present invention designs a large-area uniform molecular beam evaporation deposition system for cesium films on photocathode based on high-purity cesium, adopts ultra-high vacuum establishment and maintenance technology to ensure that the core components maintain stable performance under continuous operation, and the design of the jar chamber and the high-purity cesium single-substance cesium source avoids frequent replacement of the cesium source, and the system can achieve a service cycle of several years; a conical nozzle is designed to achieve precise molecular beam control, so that cesium atoms can continuously and uniformly escape and cover the surface of large-size substrates; a gradient temperature field and a dynamic adjustment mechanism are designed, and the three temperature zones work together to achieve directional transmission of cesium atoms without condensation loss. The dual-mode algorithm automatically switches the control strategy according to the deposition rate, eliminates thermal inertia disturbances in the high-speed stage, and compensates for viscous resistance in the low-speed stage, greatly improving the utilization rate of the cesium source and ensuring zero interruption of the deposition process. At the same time, it can realize large-area or single-time multi-substrate cesium film deposition, achieving industrial-grade stability, laboratory-grade precision and mass production-grade efficiency.

[0066] Second, the present invention designs a temperature field partitioning structure, combining an adaptive PID algorithm with a temperature field coupling compensation mechanism. By real-time sampling of temperature deviations in each partition, the thermal interference between adjacent temperature zones is dynamically corrected, achieving coordinated cross-regional temperature control. This overcomes the bottleneck of uneven heat distribution in large cavities and eliminates the lag effect of heat conduction at the edges. Multiple temperature zones maintain stable temperature differences with ultra-high precision, ensuring directional transmission of cesium vapor without condensation and improving the spatial uniformity of the atomic beam by an order of magnitude.

[0067] Third, the present invention proposes a dual-mode deposition dynamic tuning technology solution, establishes a self-sensing control mode for deposition rate, activates thermodynamic feedforward compensation in the high-speed stage, and suppresses thermal inertia disturbances; adapts to full-rate deposition scenarios through seamless mode switching, and solves the contradiction between high-speed deposition fluctuations and low-speed transmission attenuation; the thermodynamic mode eliminates the film thickness mutation caused by power delay, and the fluid mechanics mode repairs the edge airflow attenuation, so that large-area substrates can obtain sub-nanometer thickness consistency.

[0068] Fourth, this invention employs a closed-loop control solution for photocurrent peak value, constructing an in-situ photoelectric response monitoring system that uses the substrate photocurrent signal during deposition as the termination criterion. Through white light excitation and real-time signal analysis, the peak point of photoelectric conversion efficiency is captured, resolving the problem of film performance fluctuations associated with traditional timed deposition. Using the quantum efficiency peak as the closed-loop control node ensures that each batch of cathodes achieves the optimal band structure, maximizing both the spectral responsivity and the electron escape probability. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a schematic structural diagram of a large-area uniform molecular beam evaporation deposition system for a photocathode cesium film based on high-purity cesium according to the present invention;

[0070] Figure 2 The present invention provides a flow chart of a large-area uniform molecular beam evaporation deposition method for a photocathode cesium film based on high-purity cesium.

[0071] Figure 3 This is a three-zone adaptive PID temperature control diagram in Example 1, showing the temperature control accuracy and stability of the unsealing zone, transmission zone, and evaporation zone.

[0072] Figure 4 This is the beam density control diagram in Example 1, which shows the fluctuation relationship between the measured beam density and the set value during the deposition process and the control effect.

[0073] Figure 5 This is a thermal diagram of the cesium film thickness on a 300mm GaAs substrate in Example 1.

[0074] Numbers in the figure:

[0075] 1. Generator; 2. Stop valve; 3. Ampoule chamber; 4. Cesium source chamber; 5. Evaporator; 6. Fine-tuning valve; 7. Nozzle mechanism; 71. Nozzle; 72. Nozzle; 8. Deposition chamber; 9. Substrate; 10. Electronic control room. DETAILED DESCRIPTION

[0076] The technical solutions of the present invention will be described clearly and completely below in conjunction with the drawings in the present invention. In addition, the forms of the various structures described in the following embodiments are merely examples. The present invention is not limited to the various structures described in the following embodiments. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0077] Reference Figure 1The present invention designs a large-area uniform molecular beam evaporation deposition system for photocathode cesium film based on high-purity cesium, which realizes the continuous output and deposition process of cesium. The system can be reused multiple times after being loaded with a cesium source. The generator 1 serves as the core sealed environment, and is internally connected in series with the cesium source chamber 4, the evaporator 5 and the nozzle mechanism 7. A portion of the nozzle mechanism 7 extends below the generator 1, and the end is connected to the deposition chamber 8. The nozzle mechanism 7 and the deposition chamber 8 are preferably connected by a flange; at the same time, a stop valve 2 is installed at the rear end of the cesium source chamber 4 to prevent cesium from escaping to the rear end. An ampoule tank 3 is provided in the cesium source chamber for loading high-purity cesium element. A fine-tuning valve 6 is configured inside the evaporator 5 to accurately control the steam flow; the nozzle mechanism 7 includes a conical nozzle 71 and a 90-degree conical nozzle 72. The molecular beam jet is formed through precise geometric design. A protective cover is installed outside the nozzle 71 to isolate interference such as heat radiation. The end of the nozzle 72 is connected to the deposition chamber 8 through a flange to ensure that the molecular beam is directional and delivered to the surface of the substrate 9. The deposition chamber 8 is equipped with several substrates 9. For example, using substrates with a diameter of 15-20 mm, this system can simultaneously load 16 substrates and deposit cesium films on all 16 substrates. The cesium vapor forms an ultra-uniform cesium film on each substrate 9. An independent electrical control room is located above the generator 1. The built-in control system executes a dual-mode deposition algorithm and photocurrent monitoring program in real time, dynamically adjusting the deposition rate by switching between thermodynamic and hydrodynamic modes. The vacuum system utilizes a combination of molecular and ion pumps to maintain an ultra-high vacuum within the cesium source chamber 4, evaporator 5, and nozzle mechanism 7.

[0078] Reference Figure 2 The present invention provides a large-area uniform molecular beam evaporation deposition method for a photocathode cesium film based on high-purity cesium, comprising the following steps:

[0079] S1, establishment of ultra-high vacuum environment: using a composite vacuum generator to maintain a high vacuum state in the cesium source chamber, evaporator, and nozzle mechanism;

[0080] S2, unsealing the high-purity cesium source: opening the ampoule containing elemental cesium, and the vaporous cesium enters the evaporator;

[0081] S3, gradient temperature field evaporation: n temperature field zones are set in the evaporator. After passing through the n temperature field zones, cesium is converted into a molecular beam in vapor form. The beam enters the nozzle mechanism through a fine-tuning valve, enters the deposition chamber through the nozzle, and is deposited on the substrate in the deposition chamber. During this process, the temperature of each temperature zone is precisely controlled through the adaptive PID temperature dynamic control method.

[0082] S4, dual-mode dynamic deposition control: uses a thermodynamic-hydrodynamic dual-mode algorithm to adjust the deposition rate and beam density in real time;

[0083] S5, deposition time control: control the deposition time according to the substrate photocurrent signal.

[0084] In S1, the vacuum degree of the cesium source chamber, evaporator and nozzle mechanism is stable at 1×10 -8 Pa, leakage rate <1×10 -12 Pa·m 3 / s; the composite vacuum generating device includes one or more of a molecular pump, an ion pump, and a sublimation adsorption pump.

[0085] In S2, the ampoule containing elemental cesium is opened by a crushing mechanism, and the vaporous cesium enters the evaporator;

[0086] The specific steps of S3 include:

[0087] S31: Real-time collection of temperature values ​​of each area of ​​the evaporator ,in Represents the temperature field partition number;

[0088] S32: Calculate temperature deviation ;

[0089] : No. Partition set temperature, unit ℃; : No. Real-time temperature of each partition, unit: °C; : Temperature deviation value, unit: °C; : current time;

[0090] S33: Adopt adaptive PID algorithm to output control quantity :

[0091] ;

[0092] : PID basic control output, dimensionless; : proportional control gain coefficient, dimensionless; : Integral control gain coefficient, unit ; : differential control gain coefficient, unit ; : Integral operator, indicating the cumulative summation of historical deviations; : Differential operator, indicating the derivation of the current deviation change rate; : integral time variable;

[0093] S34: Correction of thermal interference between adjacent partitions through temperature field coupling compensator:

[0094] ;

[0095] : thermal coupling compensation, unit W; : Partition Partition The thermal coupling coefficient, in W / °C, is calibrated experimentally; : No. Real-time temperature of each partition, unit: °C; : No. Partition set temperature, unit ℃;

[0096] S35: Final evaporator power in each zone , to achieve precise temperature control in each temperature zone.

[0097] In S3, three temperature field zones are set in the evaporator, namely the unsealing zone, the transmission channel zone and the evaporation zone. The set temperature of the unsealing zone is 160°C; the set temperature of the transmission channel zone is 180°C; and the set temperature of the evaporation zone is 260°C.

[0098] The specific steps of S4 include:

[0099] S41: Establish a cesium atom transport model and calculate beam density :

[0100] ;

[0101] : Cesium atomic beam current density, unit: ; : evaporation zone power, unit W; : Evaporation efficiency correction factor, dimensionless; : Evaporator outlet radius, unit: cm; : distance from evaporator outlet to substrate, unit: cm; : Cesium atomic mass, unit: g / mol; : Boltzmann constant, ; : absolute temperature of evaporation zone, unit K;

[0102] S42: Real-time adjustment of deposition rate based on fluid continuity equation :

[0103] ;

[0104] : deposition rate, unit: nm / s; : molar mass of cesium, 132.9 g / mol; : Density of cesium film, unit: g / cm 3 ; : Substrate deposition area, unit: cm 2 ;

[0105] S43: Set the dual-mode controller to constrain the fluctuation range according to the deposition rate Switch control mode:

[0106] S431, when Thermodynamic mode is activated when

[0107] S432, when Activate the fluid dynamics mode when

[0108] S44: Evaporation zone power regulation via mass flow controller feedback and temperature gradient to achieve beam density fluctuation rate ;Deposition rate Continuously adjustable from 0.0001 to 10 nm / s.

[0109] The specific implementation steps of S43 include:

[0110] When the thermodynamic mode is activated, proceed as follows:

[0111] Step S4311: Construct a feedforward compensator to suppress thermal inertia disturbance:

[0112] ;

[0113] : feedforward power compensation, unit: W; : system thermal time constant, unit s; : heat conduction gain coefficient, dimensionless; : Differential operator, calculates the set power change rate; : Evaporator set power, unit W;

[0114] Step S4312: Update the evaporation zone power:

[0115] ;

[0116] : actual execution power, unit: W;

[0117] Step S4313: Verify stability through the temperature-power coupling equation:

[0118] ;

[0119] : Temperature change rate of evaporation zone, unit K / s; : Heat loss coefficient, unit: W / K; : ambient temperature, unit K; : Evaporator heat capacity, unit J / K;

[0120] When the fluid dynamics mode is activated, proceed as follows:

[0121] Step S4321: Correct the viscous resistance based on the Navier-Stokes equation:

[0122] ;

[0123] : divergence operator; : gradient operator; : Cesium vapor viscosity, unit: Pa·s; : steam velocity vector, unit: m / s; : Viscous pressure drop, unit: Pa; : Transmission distance, unit: m;

[0124] Step S4322: Calculate the beam density correction factor:

[0125] ;

[0126] : Corrected beam current density, unit ; : natural exponential function; : Viscous pressure drop, unit: Pa; : mass of cesium atom, unit: kg; : Boltzmann constant; : evaporation zone temperature, unit K;

[0127] Step S4323: Feedback adjustment of evaporation zone power:

[0128] ; : proportional gain; : Set beam density; : integral gain; : Integral operator, cumulative error; : integral time variable;

[0129] S433, Global Constraints:

[0130] The beam density fluctuation rate satisfies ; : relative volatility, dimensionless;

[0131] The deposition rate range meets ; : Deposition rate, unit: nm / s.

[0132] The specific steps of S5 include:

[0133] The deposited cesium film substrate is used as the cathode, and an anode is added. The cathode is irradiated with white light and the substrate photocurrent signal is monitored in real time. , the deposition is terminated when the photocurrent generated by the cathode reaches a peak.

[0134] Example 1: In this example, cesium film deposition is performed on a 300 mm diameter GaAs substrate.

[0135] 1. Equipment configuration:

[0136] A molecular pump and ion pump are combined in a configuration; a high-purity cesium source is sealed in an alumina ceramic ampoule with a purity of 99.997%; the evaporator system is equipped with a three-zone gradient control; the unsealing zone is set at 160°C; the transfer zone is set at 180°C; and the evaporation zone is set at 260°C; the monitoring unit uses an in-situ photocurrent detection platform, including a white light LED light source and a picoampere ammeter.

[0137] 2. The deposition process is performed as follows:

[0138] Step 1: Start the molecular pump and ion pump composite system and pump the cesium source chamber, evaporator, and nozzle mechanism to 4.2×10 -8 Pa, the cavity leakage rate is reduced to <1×10 -12 Pa·m 3 / s, and monitor the vacuum degree of the cesium source chamber, evaporator, and nozzle mechanism in real time, maintaining a stable vacuum of 1×10 -8 Pa magnitude;

[0139] Step 2: Open the ampoule chamber to release the cesium source;

[0140] Step 3: Three-temperature zone gradient evaporation control;

[0141] Desealing zone: 160°C, realizing the transformation of solid cesium to molten state; transmission zone: 180°C, realizing directional transmission of cesium vapor; evaporation zone: 260°C, forming atomic beam; temperature control accuracy of ±0.08°C is achieved through adaptive PID algorithm.

[0142] Figure 3 This is the three-zone adaptive PID temperature control diagram of this embodiment, from Figure 3As shown in the figure, the adaptive PID control algorithm demonstrates excellent temperature control performance in the photocathode deposition system, successfully achieving precise temperature management in the deblocking, transfer, and evaporation zones. The system rapidly responds from an initial room temperature state, reaching stable setpoints for each zone within 200 seconds. The deblocking zone remains at 160.00±0.015°C, the transfer zone at 180.00±0.018°C, and the critical evaporation zone remains precisely controlled within 260.00±0.024°C. Actual temperature fluctuations in the evaporation zone during the stabilization phase are strictly limited to the design requirement of ±0.08°C, with an average temperature deviation of only -0.0031°C, a standard deviation of 0.0238°C, and a maximum instantaneous deviation of 0.0763°C. All data points remain within the permissible fluctuation range, demonstrating the reliability of the control algorithm under extreme precision requirements. The thermal coupling compensation mechanism plays a key role in maintaining stability in multiple zones, minimizing the impact of thermal interference between them. The system maintains a precise temperature gradient of 20.00±0.02°C between the deblocking and transfer zones, and a temperature gradient of 80.00±0.03°C between the transfer and evaporation zones. This temperature control system demonstrates strong anti-interference capabilities, remaining stable under the noise and periodic thermal disturbances of simulated industrial environments. Even when subjected to a disturbance of 0.05°C, the system recovers to a stable state within 5 seconds. This rapid response ensures the continuity and reliability of the production process. 300 seconds of continuous stable operation demonstrates the system's robustness and durability, providing reliable support for ultra-large-area uniform thin film deposition technology.

[0143] Step 4: Dynamic adjustment of dual-mode deposition; initial stage v = 0.5 nm / s: activate the fluid dynamics mode; correct the viscous resistance, cesium vapor viscosity μ = 1.2 × 10 -5 Pa·s, beam density correction factor Jcorr=0.983J;

[0144] Peak deposition stage v = 5.2nm / s: switch to thermodynamic mode; feedforward compensation ΔPff offsets 83% of thermal inertia disturbance; finally achieves beam density fluctuation rate ΔJ / J = 1.2%, see Figure 4 ;

[0145] Figure 4 is the beam density control diagram of this embodiment, Figure 4 The blue solid line in the figure shows the measured beam current density curve, which is always around the set value of 5.00 represented by the red dotted line during the 42-second deposition process. g / (cm 2 ·s) fluctuates, and its variation is strictly limited to the ±1.2% fluctuation range indicated by the light green filled area. The white background box in the upper left corner clearly marks the key performance parameters: the system sets the beam current density to 5.00 g / (cm 2 ·s), the average volatility in actual operation was only 0.0958%, and the maximum instantaneous volatility was controlled at 0.3098%. These values ​​were significantly lower than the preset control target of 1.2%, and the entire process met The technical requirements of the dual-mode control algorithm are met, indicating that the dual-mode control algorithm effectively suppresses thermal inertia disturbances and system noise. The entire curve trajectory is smooth and completely within the fluctuation band, proving that the beam stability during the deposition process meets the expected indicators and verifies the thermodynamic-hydrodynamic dual-mode control scheme described in the patent document in the high-speed deposition stage. These data together confirm that this technical solution can achieve better than the design indicator volatility. The beam control accuracy of this embodiment actually reaches 1.2%, providing reliable guarantee for large-area uniform deposition of the photocathode.

[0146] Step 5: Real-time monitoring of photocurrent; during the deposition process, the photocurrent I(t) continues to rise, and the deposition is terminated when it reaches the peak.

[0147] Test Example 1:

[0148] This test example is a film thickness uniformity test. Method: The film thickness at 49 points on the substrate (7×7 grid) was measured using an ellipsometer. Test results: average thickness d = 8.6nm, standard deviation σ = 0.3113nm; coefficient of variation CV = (σ / d) × 100% = 3.62%, see Figure 5 ,from Figure 5As can be seen in the image, the substrate surface exhibits a distinct cesium film thickness distribution pattern, with the central region displaying darker red and yellow colors, indicating a thickness range of 8.8-9.0nm, while the edge regions display blue and green, corresponding to thickness values ​​between 8.2-8.4nm. This color gradient reveals the distribution characteristic of the film gradually becoming thinner from the center to the edge. The specific values ​​from the 49 measurement points show that the thickness at the center reaches 8.92nm, while the thickness at the four corner points decreases to between 8.22-8.25nm. The average thickness is 8.60nm, and the standard deviation is 0.3113nm. The calculated coefficient of variation (CV) is 3.62%, a key indicator that quantifies the uniformity of the film thickness. This test example demonstrates that the deposition process of the present invention successfully achieves high-quality, uniform film deposition on a large 300mm substrate. The coefficient of variation of only 3.62% is far lower than the typical value of 31.7% for traditional methods. Analysis shows that the three-zone gradient control and dual-mode deposition algorithm effectively overcome edge effects. The thickness varies by approximately 0.7 nm from center to edge, indicating that the spatial distribution of the evaporation source remains the primary factor affecting uniformity, but process optimization has minimized its impact. No significant abnormal spots or irregular areas appear in the thermal map, demonstrating the excellent stability and repeatability of the deposition process. The coefficient of variation of 3.62% fully meets the stringent film thickness uniformity requirements of photocathode manufacturing, demonstrating the combined application of core technologies such as adaptive PID temperature control and thermodynamic-fluid dynamics dual-mode control.

[0149] Verification in Example 1 and test examples demonstrates that the present invention utilizes a gradient temperature field design and staged temperature increase to prevent cesium vapor condensation, significantly improving transmission efficiency. A dual-mode control algorithm reduces the power delay response time of the thermodynamic mode compensation to 0.3s during high-speed deposition. During low-speed deposition, viscous drag correction reduces film thickness deviation in the edge region by 89%. This invention utilizes quantum tunneling deblocking to ensure cesium source purity, three-temperature zone coupled PID control to eliminate thermal interference, and a dual-mode algorithm to overcome deposition uniformity bottlenecks. The invention successfully achieved a CV of 3.62% on a 300mm GaAs substrate, continuously controlled deposition rate from 0.001–8.7nm / s, and a beam density fluctuation rate of ≤1.2%, providing a reliable technical path for the manufacture of ultra-large-scale photocathodes.

[0150] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A large-area uniform molecular beam evaporation deposition method for a photocathode cesium film based on high-purity cesium, characterized in that: The following steps are involved: S1, establishment of ultra-high vacuum environment: using a composite vacuum generator to maintain a high vacuum state in the cesium source chamber, evaporator, and nozzle mechanism; S2, unsealing the high-purity cesium source: opening the ampoule containing elemental cesium, and the vaporous cesium enters the evaporator; S3, gradient temperature field evaporation: n temperature field zones are set in the evaporator. After passing through the n temperature field zones, cesium is converted into a molecular beam in vapor form. The beam enters the nozzle mechanism through a fine-tuning valve, enters the deposition chamber through the nozzle, and is deposited on the substrate in the deposition chamber. During this process, the temperature of each temperature zone is precisely controlled through the adaptive PID temperature dynamic control method. S4, dual-mode dynamic deposition control: uses a thermodynamic-hydrodynamic dual-mode algorithm to adjust the deposition rate and beam density in real time; S5, deposition time control: control the deposition time according to the substrate photocurrent signal.

2. The method according to claim 1, wherein: In S1, the vacuum degree of the cesium source chamber, evaporator and nozzle mechanism is stable at 1×10 -8 Pa, leakage rate <1×10 -12 Pa·m 3 / s; the composite vacuum generating device includes one or more of a molecular pump, an ion pump, and a sublimation adsorption pump.

3. The method according to claim 1, wherein: The specific steps of S3 include: S31: Real-time collection of temperature values ​​of each area of ​​the evaporator ,in Represents the temperature field partition number; S32: Calculate temperature deviation ; : No. Partition set temperature, unit ℃; : No. Real-time temperature of each partition, unit: °C; : Temperature deviation value, unit: °C; : current time; S33: Adopt adaptive PID algorithm to output control quantity : ； : PID basic control output, dimensionless; : proportional control gain coefficient, dimensionless; : Integral control gain coefficient, unit ; : differential control gain coefficient, unit ; : Integral operator, indicating the cumulative summation of historical deviations; : Differential operator, indicating the derivation of the current deviation change rate; : integral time variable; S34: Correction of thermal interference between adjacent partitions through temperature field coupling compensator: ； : thermal coupling compensation, unit: W; : Partition Partition The thermal coupling coefficient, in W / °C, is calibrated experimentally; : No. Real-time temperature of each partition, unit: °C; : No. Partition set temperature, unit ℃; S35: Final evaporator power in each zone , to achieve precise temperature control in each temperature zone.

4. The method according to claim 3, wherein: In S3, three temperature field zones are set in the evaporator, namely the unsealing zone, the transmission channel zone and the evaporation zone. The set temperature of the unsealing zone is 160°C; the set temperature of the transmission channel zone is 180°C; and the set temperature of the evaporation zone is 260°C.

5. The method according to claim 4, characterized in that: The specific steps of S4 include: S41: Establish a cesium atom transport model and calculate beam density : ； : Cesium atomic beam current density, unit: ; : evaporation zone power, unit W; : Evaporation efficiency correction factor, dimensionless; : Evaporator outlet radius, unit: cm; : distance from evaporator outlet to substrate, unit: cm; : Cesium atomic mass, unit: g / mol; : Boltzmann constant, ; : absolute temperature of evaporation zone, unit K; S42: Real-time adjustment of deposition rate based on fluid continuity equation : ； : deposition rate, unit: nm / s; : molar mass of cesium, 132.9 g / mol; : Density of cesium film, unit: g / cm 3 ; : Substrate deposition area, unit: cm 2 ; S43: Set the dual-mode controller to constrain the fluctuation range according to the deposition rate Switch control mode: S431, when Thermodynamic mode is activated when S432, when Activate the fluid dynamics mode when S44: Evaporation zone power regulation via mass flow controller feedback and temperature gradient to achieve beam density fluctuation rate ;Deposition rate Continuously adjustable from 0.0001 to 10 nm / s.

6. The method according to claim 5, characterized in that: The specific implementation steps of S43 include: When the thermodynamic mode is activated, proceed as follows: Step S4311: Construct a feedforward compensator to suppress thermal inertia disturbance: ； : feedforward power compensation, unit: W; : system thermal time constant, unit s; : heat conduction gain coefficient, dimensionless; : Differential operator, calculates the set power change rate; : Evaporator set power, unit W; Step S4312: Update the evaporation zone power: ； : actual execution power, unit: W; Step S4313: Verify stability through the temperature-power coupling equation: ； : Temperature change rate of evaporation zone, unit K / s; : Heat loss coefficient, unit: W / K; : ambient temperature, unit K; : Evaporator heat capacity, unit J / K; When the fluid dynamics mode is activated, proceed as follows: Step S4321: Correct the viscous resistance based on the Navier-Stokes equation: ； : divergence operator; : gradient operator; : Cesium vapor viscosity, unit: Pa·s; : steam velocity vector, unit: m / s; : Viscous pressure drop, unit: Pa; : Transmission distance, unit: m; Step S4322: Calculate the beam density correction factor: ； : Corrected beam current density, unit ; : natural exponential function; : Viscous pressure drop, unit: Pa; : mass of cesium atom, unit: kg; : Boltzmann constant; : Evaporation zone temperature, unit K; Step S4323: Feedback adjustment of evaporation zone power: ; : proportional gain; : Set beam density; : integral gain; : Integral operator, cumulative error; : integral time variable; S433, Global Constraints: The beam density fluctuation rate satisfies ; : relative volatility, dimensionless; The deposition rate range meets ; : Deposition rate, unit: nm / s.

7. The method according to claim 1, wherein: The specific steps of S5 include: The deposited cesium film substrate is used as the cathode, and an anode is added. The cathode is irradiated with white light and the substrate photocurrent signal is monitored in real time. , the deposition is terminated when the photocurrent generated by the cathode reaches a peak.

8. A large-area uniform molecular beam evaporation deposition system for a high-purity cesium photocathode cesium film for implementing the method according to any one of claims 1 to 7, characterized in that: It includes: A cesium source chamber, an evaporator and a nozzle mechanism are connected in series; the cesium source chamber, the evaporator and the nozzle mechanism are installed in a generator; the end of the nozzle mechanism is connected to a deposition chamber, and a plurality of substrates are installed in the deposition chamber; the nozzle mechanism includes a nozzle and a nozzle arranged at the tail end of the nozzle; an ampoule tank is arranged in the cesium source chamber, and the ampoule tank is loaded with high-purity elemental cesium.

9. The system according to claim 8, characterized in that The nozzle has a conical structure; a protective cover is installed on the outside of the nozzle; a fine-tuning valve is provided in the evaporator; an electric control room is installed on the upper part of the generator, and a control system is installed in the electric control room; the nozzle mechanism is connected to the deposition chamber through a flange.

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