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

Abstract

The application relates to the technical field of photoelectric cathode manufacturing, and provides a large-area uniform molecular beam evaporation and deposition method for a cesium film of a photoelectric cathode based on high-purity cesium, which adopts high-purity cesium cesium source and cooperates with ultrahigh vacuum establishment and maintenance technology to realize long-term repeated use of the cesium source; a multi-temperature-zone gradient evaporation design is combined with a self-adaptive PID algorithm and a thermal coupling compensation mechanism to realize cross-regional temperature collaborative control; through a thermodynamics-fluid mechanics dual-mode deposition control strategy, the mode is dynamically switched according to a deposition rate, thermal inertia disturbance is inhibited in a high-speed stage, and viscous drag is corrected in a low-speed stage, so that the beam current density stability is guaranteed; a generator and a cesium source chamber, an evaporator and a nozzle mechanism connected in series are designed, and a continuous and stable molecular beam flow deposition is formed; the application solves the problems of poor film uniformity, unstable rate and difficult end point misjudgment in traditional processes, can realize large-area or single-time multi-substrate cesium film deposition, and achieves industrial-grade stability, laboratory-grade precision and mass production efficiency.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of photoelectric cathode manufacturing, and particularly provides a large-area uniform molecular beam evaporation deposition method for a cesium film of a photoelectric cathode based on high-purity cesium. BACKGROUND

[0002] A photoelectric detector is a key device for converting optical signals into electrical signals, and a photoelectric cathode, a core component of the photoelectric detector, realizes photoelectric conversion by using a photoelectric effect: when light irradiates a cathode surface, electrons inside the material are excited to escape to form a photocurrent. Cesium is a typical photoelectric emission material, and the uniformity and purity of a cesium film directly determine the performance of the detector. Large-area industrial high-uniformity cesium film deposition refers to forming a cesium film layer with high consistency in thickness and high purity in composition on a surface of an ultra-large-size substrate. To meet the demand for large-area industrial high-uniformity cesium film deposition for industrial mass production, the process involves higher requirements for efficient use of materials and wide-range deposition rate regulation. The prior art cannot meet the core requirements of high uniformity, high efficiency conversion and long-term stability of the cesium film for industrial production of photoelectric cathodes, mainly in the following aspects:

[0003] Traditional photoelectric cathode preparation adopts solid cesium salt, such as cesium carbonate and cesium chromate, and a reducing agent, zirconium-aluminum alloy, is loaded in a nickel tube with evaporation apertures, and metal cesium is generated by electric heating in a vacuum environment. Cesium vapor is released in a pulse mode, the thickness of the film layer fluctuates greatly, the thickness difference between different regions is obvious, the utilization rate of cesium is low, the cesium source is used for a small number of times, and the cesium source needs to be frequently replaced, which cannot meet the requirement of atomic-level uniformity for high-performance photoelectric cathodes such as GaAs. In the prior art, temperature control usually adopts a single-temperature-zone design, and the thermal conduction hysteresis effect is significant, so that the temperature difference between different regions of the substrate is obvious, leading to local condensation of cesium vapor in the transmission process, and causing uneven distribution of the film layer thickness. The prior art lacks a dynamic regulation mechanism, and the thermal inertia disturbance causes a dramatic fluctuation of the beam density during high-speed deposition, and forms a film thickness mutation; during low-speed deposition, the vapor stick resistance causes transmission attenuation at the edge, and the uniformity of the film layer is deteriorated.

[0004] Therefore, there is an urgent need for a cesium film deposition technology with large-area uniformity, long-term stability and multiple repeated use, to provide reliable core components for high-end photoelectric equipment. SUMMARY

[0005] To solve the problems in the background art, the application provides a large-area uniform molecular beam evaporation deposition method for a cesium film of a photoelectric cathode based on high-purity cesium, which comprises the following steps:

[0006] S1, establishing an ultra-high vacuum environment: a composite vacuum generating device is used to maintain a high vacuum state of a cesium source chamber, an evaporator and a nozzle mechanism;

[0007] S2, unsealing a high-purity cesium source: opening an ampoule warehouse containing elemental cesium, and allowing the cesium in a vapor state to enter the evaporator;

[0008] S3, gradient temperature field evaporation: n temperature field partitions are arranged in the evaporator, cesium is converted into a molecular beam stream in vapor form through the n temperature field partitions, enters the nozzle mechanism through the fine tuning valve, and enters the deposition chamber through the nozzle to deposit on the substrate in the deposition chamber; in this process, the temperature of each temperature zone is precisely controlled through an adaptive PID temperature dynamic control method;

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

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

[0011] Further, in S1, the vacuum degree of the cesium source chamber, the evaporator and the nozzle mechanism is stabilized at 1×10 -8 Pa, the leakage rate is less than 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] Further, the specific steps of S3 include:

[0013] S31: real-time acquisition of temperature values of each region of the evaporator , wherein represents the temperature field partition number;

[0014] S32: calculation of temperature deviation ;

[0015] : the set temperature of the first temperature field partition, in units of ℃; : the real-time temperature of the first temperature field partition, in units of ℃; : the temperature deviation value, in units of ℃; : the current time; S33: output of the control amount using the adaptive PID algorithm :

[0016]

[0017] ;

[0018] : the PID basic control output, dimensionless; : the proportional control gain coefficient, dimensionless; : the integral control gain coefficient, in units of ; : the differential control gain coefficient, in units of ; : the integral operator, indicating the summation of the cumulative history deviation;​​ : differential operator, representing the derivation of the current deviation rate; : integral time variable;

[0019] S34: Correcting the adjacent partition thermal interference by the temperature field coupling compensator:

[0020] ;

[0021] : thermal coupling compensation amount, unit W; : partition The thermal coupling coefficient of the partition , unit W / ℃, calibrated by experiment; : the Partition real-time temperature, unit ℃; : the Partition set temperature, unit ℃;

[0022] S35: Final evaporator zone power , realizing accurate temperature control of each temperature zone.

[0023] Further, in S3, three temperature field partitions are set in the evaporator, which are unsealing zone, transmission channel zone and evaporation zone, respectively. The set temperature of the unsealing zone is 160℃; The set temperature of the transmission channel zone is 180℃; The set temperature of the evaporation zone is 260℃.

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

[0025] S41: Establishing cesium atom transmission model, calculating beam density :

[0026] ;

[0027] : Cesium atom beam density, unit: ; : Evaporation zone power, unit W; : Evaporation efficiency correction coefficient, dimensionless; : Evaporator outlet radius, unit cm; : Distance from evaporator outlet to substrate, unit cm; : Cesium atom mass, unit g / mol; : Boltzmann constant, ; : Evaporation zone absolute temperature, 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; : cesium film density, unit g / cm 3 ; : substrate deposition area, unit cm 2 ;

[0031] S43: set the dual-mode controller constraint fluctuation range, according to the deposition rate switch the control mode:

[0032] S431, when the thermodynamic mode is activated;

[0033] S432, when the hydrodynamic mode is activated;

[0034] S44: adjust the evaporation zone power through the mass flow controller feedback and temperature field gradient, achieve beam current density fluctuation rate ; deposition rate is continuously adjustable from 0.0001-10 nm / s.

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

[0036] When the thermodynamic mode is activated, the following steps are taken:

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

[0038] ;

[0039] : feedforward power compensation amount, unit W; : system thermal time constant, unit s; : thermal conduction gain coefficient, dimensionless; : differential operator, calculate 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 temperature-power coupling equation:

[0044] ;

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

[0046] When the fluid dynamics mode is activated, the following steps are taken:

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

[0048] ;

[0049] : divergence operator; : gradient operator; : viscosity of cesium vapor, unit Pa·s; : vapor flow velocity vector, unit m / s; : viscous pressure drop, unit Pa; : transmission distance, unit m;

[0050] Step S4322: calculate the beam current 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; : temperature of evaporation zone, unit K;

[0053] Step S4323: feedback adjust the evaporation zone power:

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

[0055] S433, global constraints:

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

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

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

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

[0060] The application designs a large-area uniform molecular beam evaporation deposition system for a cesium film of a photoelectric cathode based on high-purity cesium, which comprises:

[0061] The cesium source chamber, the evaporator and the nozzle mechanism are connected in series; the cesium source chamber, the evaporator and the nozzle mechanism are installed in the generator; the nozzle mechanism is connected with the deposition chamber at the end; the nozzle mechanism comprises a nozzle and a nozzle opening arranged at the tail of the nozzle; the ampoule warehouse is arranged in the cesium source chamber, and the high-purity elemental cesium is loaded in the ampoule warehouse.

[0062] Further, the nozzle opening is a conical structure; the nozzle is externally installed with a protective cover; the evaporator is internally provided with a fine adjustment valve; the electric control chamber is installed at the upper part of the generator, and the control system is installed in the electric control chamber; the nozzle mechanism and the deposition chamber are connected through flanges.

[0063] The application achieves the following beneficial effects:

[0064] The application designs a technical scheme of a pure source, repeated use, precise temperature control and intelligent deposition, so that the large-area photoelectric cathode film layer simultaneously achieves three characteristics of high uniformity, high quantum efficiency and high stability, provides core technical support for super-large size night vision devices and quantum detection equipment, and specifically has the following advantages:

[0065] Firstly, the application designs a large-area uniform molecular beam evaporation deposition system of cesium film of photoelectric cathode based on high-purity cesium, adopts ultra-high vacuum establishment and maintenance technology, so that the core components remain stable in the continuous operation state, the design of the cell bin and high-purity cesium elemental cesium source avoids frequent replacement of the cesium source, and the system can be used for a period of several years; a conical nozzle is designed to realize accurate molecular beam flow control, so that cesium atoms can continuously and uniformly escape and cover the surface of a large-size substrate; a gradient temperature field and a dynamic adjustment mechanism are designed, three temperature zones cooperatively realize directional transmission of cesium atoms without condensation loss, a double-mode algorithm automatically switches the control strategy according to the deposition rate, eliminates thermal inertia disturbance in the high-speed stage, compensates viscous resistance in the low-speed stage, greatly improves the utilization rate of the cesium source, simultaneously guarantees zero interruption in the deposition process, and simultaneously realizes deposition of cesium film on a large area or multiple substrates at a time, and achieves industrial-level stability, laboratory-level precision and mass production-level efficiency.

[0066] Secondly, the application designs a temperature field partition structure, combines a self-adaptive PID algorithm and a temperature field coupling compensation mechanism, dynamically corrects adjacent temperature zone thermal interference by real-time acquisition of temperature deviation of each partition, realizes cross-region temperature collaborative regulation, breaks through the bottleneck of uneven heat distribution of a large-size cavity, and eliminates the edge heat conduction hysteresis effect. The multiple temperature zones maintain stable temperature difference under ultra-high precision, ensure directional transmission of cesium vapor without condensation, and improve the spatial distribution uniformity of the atomic beam by one order of magnitude.

[0067] Thirdly, the application provides a double-mode deposition dynamic optimization technical scheme, establishes a deposition rate self-sensing control mode, activates thermodynamic feedforward compensation in the high-speed stage to suppress thermal inertia disturbance, seamlessly switches modes to adapt to full-rate deposition scenarios, solves the contradiction between high-speed deposition fluctuation and low-speed transmission attenuation, and thermodynamic mode eliminates film thickness mutation caused by power delay, and fluid mechanics mode repairs edge airflow attenuation, so that a large-area substrate obtains sub-nanometer level thickness consistency.

[0068] Fourthly, the application adopts a photocurrent peak closed-loop control technical scheme, constructs an in-situ photoelectric response monitoring system, and takes the substrate photocurrent signal in the deposition as a termination criterion. Through white light excitation and real-time signal analysis, the highest point of photoelectric conversion efficiency is captured, and the film performance fluctuation problem of traditional timed deposition is solved. The quantum efficiency peak is taken as a closed-loop control node to ensure that each batch of cathode obtains the best energy band structure, so that the spectral response rate and the electron escape probability are maximized synchronously. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 is a structural schematic diagram of the large-area uniform molecular beam evaporation deposition system of cesium film of photoelectric cathode based on high-purity cesium of the application;

[0070] Figure 2 The application is a flowchart of the large-area uniform molecular beam evaporation deposition method of cesium film of photoelectric cathode based on high-purity cesium.

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

[0072] Figure 4 is the beam density control chart in Example 1, showing the fluctuation relationship and control effect of the actual measured beam density and the set value during the deposition process.

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

[0074] Marked in the figure:

[0075] 1, generator; 2, stop valve; 3, ampoule bin; 4, cesium source chamber; 5, evaporator; 6, fine adjustment valve; 7, spray pipe mechanism; 71, spray pipe; 72, spray port; 8, deposition chamber; 9, substrate; 10, electric control chamber. DETAILED DESCRIPTION

[0076] The technical solutions in the present application will be described clearly and completely below in combination with the drawings in the present application, and additionally, the forms of each structure described in the following embodiments are only examples, and the present application is not limited to each structure described in the following embodiments, and all other embodiments obtained by those skilled in the art without making creative efforts belong to the scope of protection of the present application.

[0077] Reference Figure 1The application designs a large-area uniform molecular beam evaporation deposition system of cesium film of photoelectric cathode based on high-purity cesium, realizes continuous output and deposition process of cesium, and the system can be repeatedly used after the cesium source is loaded. The generator 1 is used as a core sealed environment, and the cesium source chamber 4, the evaporator 5 and the nozzle mechanism 7 are connected in series inside the generator 1, part of the nozzle mechanism 7 extends out of the generator 1, and the tail end is connected with the deposition chamber 8, and the nozzle mechanism 7 and the deposition chamber 8 are preferably connected through flanges; at the same time, the stop valve 2 is installed at the rear end of the cesium source chamber 4 to prevent cesium from escaping to the rear end. The ampoule warehouse 3 is arranged in the cesium source chamber and is used for loading high-purity cesium single element. The evaporator 5 is internally configured with a fine adjustment valve 6 to accurately control the vapor flow; the nozzle mechanism 7 comprises a conical nozzle 71 and a 90-degree conical nozzle 72, and a molecular beam jet is formed through accurate geometric design, the nozzle 71 is externally installed with a protective cover to isolate interference such as thermal radiation, and the nozzle 72 is connected with the deposition chamber 8 through flanges at the tail end, so that the molecular beam is ensured to be delivered to the surface of the substrate 9 in a directional manner. The deposition chamber 8 is installed with a plurality of substrates 9, for example, the substrates with a diameter of 15-20 mm, the system can realize loading of 16 substrates at a time, and deposition of cesium film on the 16 substrates is simultaneously completed; the cesium vapor forms a super-uniform cesium film on each substrate 9. The electric control chamber is independently arranged at the upper part of the generator 1, the built-in control system realizes real-time execution of a double-mode deposition algorithm and a photocurrent monitoring program, and the deposition rate is dynamically adjusted through a thermodynamics-hydrodynamics mode switching.

[0078] Reference Figure 2 The application provides a large-area uniform molecular beam evaporation deposition method of cesium film of photoelectric cathode based on high-purity cesium, which comprises the following steps.

[0079] S1, ultra-high vacuum environment establishment: a composite vacuum generating device is used to maintain high vacuum states of the cesium source chamber, the evaporator and the nozzle mechanism;

[0080] S2, unsealing of high-purity cesium source: the ampoule warehouse containing single cesium is opened, and the cesium in vapor state enters the evaporator;

[0081] S3, gradient temperature field evaporation: n temperature field partitions are arranged in the evaporator, the cesium is converted into a molecular beam flow in vapor form through the n temperature field partitions, enters the nozzle mechanism through the fine adjustment valve, enters the deposition chamber through the nozzle, and is deposited on the substrate of the deposition chamber; in this process, the self-adaptive PID temperature dynamic control method is used to realize accurate control of the temperature of each temperature zone;

[0082] S4, double-mode dynamic deposition control: a thermodynamics-hydrodynamics double-mode algorithm is used to realize real-time adjustment of the deposition rate and the beam density;

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

[0084] In S1, the vacuum level of the cesium source chamber, evaporator, and nozzle mechanism is stabilized at 1×10⁻⁶. -8 Pa, leakage rate < 1×10 -12 Pa·m 3 / s; The composite vacuum generating device includes one or more of the following: molecular pump, ion pump, and sublimation adsorption pump.

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

[0086] The specific steps of S3 include:

[0087] S31: Real-time acquisition of temperature values ​​in various zones of the evaporator ,in Represents the temperature field zone number;

[0088] S32: Calculate temperature deviation ;

[0089] : No. Temperature settings for each zone, in °C; : No. Real-time temperature of each zone, in °C; Temperature deviation value, in °C; Current time;

[0090] S33: Uses an adaptive PID algorithm to output control quantity. :

[0091] ;

[0092] : PID basic control output quantity, dimensionless; : Proportional control gain coefficient, dimensionless; Integral control gain coefficient, unit ; Differential control gain coefficient, unit ; The integral operator represents the cumulative summation of historical deviations; The differential operator represents taking the derivative with respect to the current rate of change of deviation; Integration time variable;

[0093] S34: Correcting thermal interference between adjacent zones using a temperature field coupling compensator:

[0094] ;

[0095] Thermal coupling compensation amount, in W; Partition For partitions The thermal coupling coefficient, in W / ℃, is determined experimentally. : No. Real-time temperature of each zone, in °C; : No. Temperature settings for each zone, in °C;

[0096] S35: Power of each zone of the final evaporator This enables precise temperature control in each temperature zone.

[0097] In S3, three temperature zones are set inside the evaporator: the unsealing zone, the transmission channel zone, and the evaporation zone. The set temperature of the unsealing zone is 160℃; the set temperature of the transmission channel zone is 180℃; and the set temperature of the evaporation zone is 260℃.

[0098] The specific steps of S4 include:

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

[0100] ;

[0101] Cesium atomic beam current density, unit: ; Evaporation zone power, in watts (W). Evaporation efficiency correction factor, dimensionless; Evaporator outlet radius, in cm; Distance from evaporator outlet to substrate, in cm; Cesium atomic mass, in g / mol; Boltzmann constant ; : Absolute temperature of the evaporation zone, in K;

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

[0103] ;

[0104] : Deposition rate, unit: nm / s; The molar mass of cesium is 132.9 g / mol. Cesium film density, unit: g / cm³ 3 ; Substrate deposition area, in cm² 2 ;

[0105] S43: Set the fluctuation range of the dual-mode controller according to the deposition rate. Switching control mode:

[0106] S431, when thermodynamic mode is activated;

[0107] S432, when hydrodynamic mode is activated;

[0108] S44: Feedback regulation of evaporation zone power by mass flow controller and temperature field gradient to achieve beam current density fluctuation rate ; deposition rate is continuously adjustable from 0.0001-10 nm / s.

[0109] The specific implementation steps of S43 include:

[0110] When the thermodynamic mode is activated, the following steps are taken:

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

[0112] ;

[0113] : Feedforward power compensation amount, unit W; : System thermal time constant, unit s; : Thermal conduction gain coefficient, dimensionless; : Differential operator, calculate 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 temperature-power coupling equation:

[0118] ;

[0119] : Evaporation zone temperature change rate, unit K / s; : Heat loss coefficient, unit W / K; : Ambient temperature, unit K; : Evaporator heat capacity, unit J / K;

[0120] When the hydrodynamic mode is activated, the following steps are taken:

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

[0122] ;

[0123] : divergence operator; : gradient operator; : cesium vapor viscosity, unit Pa·s; : vapor flow velocity vector, unit m / s; : viscous pressure drop, unit Pa; : transmission distance, unit m;

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

[0125] ;

[0126] : corrected beam current density, unit ; : natural exponential function; : viscous pressure drop, unit Pa; : cesium atomic mass, unit kg; : Boltzmann constant; : evaporation zone temperature, unit K;

[0127] Step S4323: Feedback adjust the evaporation zone power:

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

[0129] S433, global constraint:

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

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

[0132] The specific steps of S5 include:

[0133] The deposited cesium film substrate is used as a cathode, 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 value.

[0134] Example 1. This example is for cesium film deposition on a 300 mm diameter GaAs substrate.

[0135] 1. Equipment configuration:

[0136] A molecular pump and an ion pump are combined; a high-purity cesium source is sealed in an alumina ceramic ampoule, with a purity of 99.997%; an evaporator system is provided with three-temperature-zone gradient control; the unsealing zone is set to 160°C; the transmission zone is set to 180°C; the evaporation zone is set to 260°C; the monitoring unit uses an in-situ photocurrent detection platform, which includes a white light LED light source and a pico-ampere current meter.

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

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

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

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

[0141] Unsealing zone: 160°C, realizing the transition of solid cesium to a molten state; transmission zone: 180°C, realizing directional transmission of cesium vapor; evaporation zone: 260°C, forming an atomic beam; the temperature control precision is achieved through a self-adaptive PID algorithm: ±0.08°C.

[0142] Figure 3 This is a three-temperature-zone self-adaptive PID temperature control diagram for this example, from Figure 3As can be seen, the adaptive PID control algorithm exhibits excellent temperature control performance in the photocathode deposition system, successfully achieving precise temperature management of the three temperature zones: unsealing zone, transport zone, and evaporation zone. The system quickly responds from the initial room temperature state and stabilizes to the set temperature of each temperature zone within 200 seconds. The unsealing zone is maintained at 160.00 ± 0.015°C, the transport zone is kept at 180.00 ± 0.018°C, and the critical evaporation zone temperature is accurately controlled within the range of 260.00 ± 0.024°C. The actual temperature fluctuation in the stable stage of the evaporation zone is strictly limited within the design requirement of ±0.08°C. The average deviation is only -0.0031°C, the standard deviation is 0.0238°C, the maximum instantaneous deviation is 0.0763°C, and all data points do not exceed the allowed fluctuation range, indicating the reliability of the control algorithm under extreme precision requirements. The heat coupling compensation mechanism plays a key role in maintaining the stability of multiple temperature zones, successfully minimizing the thermal interference between temperature zones. The system maintains a precise temperature difference of 20.00 ± 0.02°C between the unsealing zone and the transport zone, and a temperature difference gradient of 80.00 ± 0.03°C between the transport zone and the evaporation zone. The temperature control system exhibits strong anti-interference ability and can maintain stability under simulated industrial environment noise and periodic thermal disturbance conditions. When encountering 0.05°C level interference, the system can recover to a stable state within 5 seconds. This fast response characteristic ensures the continuity and reliability of the production process, and the stable operation of 300 seconds continuously verifies the robustness and durability of the system, providing reliable protection for large-area uniform thin film deposition technology.

[0143] Step 4: Dual-mode deposition dynamic adjustment; initial stage v=0.5 nm / s: activate hydrodynamic mode; modify viscous drag, cesium vapor viscosity μ=1.2×10 -5 Pa·s, beam current density correction factor Jcorr=0.983J;

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

[0145] Figure 4 The blue solid line in the beam current density control diagram of this embodiment, Figure 4 represents the actual measured beam current density curve, which fluctuates around the set value 5.00 g / (cm 2 ·s) during the 42-second deposition process, with the change amplitude strictly limited within the ±1.2% fluctuation range identified by the light green filled area. The white background box in the upper left corner clearly marks the key performance parameters: the system set beam current density is 5.00 g / (cm 2 In actual operation, the average volatility was only 0.0958%, and the maximum instantaneous volatility was controlled at 0.3098%. These values ​​are significantly lower than the preset control target of 1.2%, and the entire process meets the requirements. The technical requirements demonstrate that the dual-mode control algorithm effectively suppresses thermal inertial disturbances and system noise. The entire curve trajectory is smooth and lies entirely within the fluctuation band, proving that the beam stability during deposition reaches the expected indicators, and verifying the thermodynamic-hydrodynamic dual-mode control scheme described in the patent document during the high-speed deposition stage. The actual effect at nm / s. These data collectively confirm that this technical solution can achieve volatility better than the design target. The beam control accuracy is 1.2% in this embodiment, which provides a reliable guarantee for the large-area uniform deposition of photocathodes.

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

[0147] Test Example 1:

[0148] This test case is for film thickness uniformity testing; Method: The film thickness at 49 points on the substrate (7×7 grid) was measured using an ellipsometry; Test results: Average thickness d = 8.6 nm, standard deviation σ = 0.3113 nm; coefficient of variation CV = (σ / d) × 100% = 3.62%, see [link to relevant documentation]. Figure 5 ,from Figure 5As can be seen, the substrate surface presents an obvious cesium film thickness distribution pattern, wherein the central region shows deeper red and yellow, indicating that the thickness value is in the range of 8.8-9.0 nm, and the edge region presents blue and green, corresponding to the thickness value between 8.2-8.4 nm, and the color gradient change reveals the distribution characteristics that the film gradually thins from the center to the edge. The specific values of 49 measurement points show that the thickness of the central point reaches 8.92 nm, while the thickness of the four corner points decreases to 8.22-8.25 nm, the average thickness is 8.60 nm, and the standard deviation is 0.3113 nm, and thus the coefficient of variation CV=3.62% is calculated, which quantifies the uniformity of the film thickness. The test example shows that the deposition process of the present application successfully realizes the deposition of high-quality uniform film on a 300mm large-size substrate, and the variation coefficient of only 3.62% is far lower than the typical value of 31.7% of the conventional method. Analysis shows that the three-temperature-zone gradient control and the double-mode deposition algorithm effectively overcome the edge effect problem, and the thickness changes in the range of about 0.7 nm from the center to the edge, indicating that the spatial distribution characteristics of the evaporation source are still the main factor affecting the uniformity, but the process optimization has controlled its influence within a very small range, and there are no obvious abnormal spots or irregular areas in the thermal map, indicating that the deposition process has excellent stability and repeatability. The variation coefficient of 3.62% fully meets the stringent requirements of the photoelectric cathode manufacturing on the film thickness uniformity, which is the comprehensive application effect of the core technologies such as self-adaptive PID temperature control and thermodynamics-hydrodynamics double-mode control.

[0149] Through the verification of example 1 and the test example, it is shown that the present application avoids cesium vapor condensation by gradient temperature field design and segmented heating, and greatly improves the transmission efficiency; the double-mode control algorithm is adopted, the power delay response time is compensated to 0.3s in high-speed deposition; in low-speed deposition, the viscosity resistance correction reduces the film thickness deviation of the edge region by 89%. The present application guarantees the purity of cesium source through quantum tunneling unsealing, eliminates thermal interference through three-temperature-zone coupled PID control, breaks through the bottleneck of deposition uniformity through double-mode algorithm, successfully realizes CV=3.62% on a 300mm GaAs substrate, continuously controls the deposition rate at 0.001-8.7nm / s, and the beam current density fluctuation rate is ≤1.2%; and provides a reliable technical path for ultra-large-size photoelectric cathode manufacturing.

[0150] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for large area uniform molecular beam evaporation deposition of cesium films for photocathodes based on high purity cesium, characterized in that, It comprises the following steps: S1, ultra-high vacuum environment establishment: using a composite vacuum generating device to maintain the cesium source chamber, evaporator, and nozzle mechanism in a high vacuum state; S2, unsealing high-purity cesium source: opening the ampoule warehouse containing elemental cesium, and the vapor state cesium enters the evaporator; S3, gradient temperature field evaporation: setting n temperature field partitions in the evaporator, and through the n temperature field partitions, the cesium is converted into a vapor state molecular beam, which enters the nozzle mechanism through the fine adjustment valve, and then enters the deposition chamber through the nozzle to deposit on the substrate in the deposition chamber; In this process, the self-adaptive PID temperature dynamic control method is used to realize accurate control of the temperature of each temperature zone; S4, double-mode dynamic deposition control: using a thermodynamic-hydrodynamic double-mode algorithm to adjust the deposition rate and beam density in real time; S5, deposition time control: controlling the deposition time according to the substrate photocurrent signal; The specific steps of S3 include: S31: Collecting temperature values of each area of the evaporator in real time wherein represents the number of the temperature field partition. S32: Calculate temperature deviation ; : 1st : Zone set temperature, unit ℃ : 1st : Zone real-time temperature, unit ℃ : Temperature deviation value, unit ℃ : Current time S33: outputting the control quantity by using the adaptive PID algorithm : ； : PID base control output, dimensionless; : proportional control gain coefficient, dimensionless; : integral control gain coefficient, unit ; : derivative control gain coefficient, unit ; : integral operator, representing the sum of the cumulative history of the deviation; : derivative operator, representing the derivative of the current deviation rate; : integral time variable; S34: correcting the thermal interference between adjacent partitions through a temperature field coupling compensator: ； Thermal coupling compensation amount, in W; Partition For partitions The thermal coupling coefficient, in W / ℃, is determined experimentally. : No. Real-time temperature of each zone, in °C; : No. Temperature settings for each zone, in °C; S35: final evaporator zone power , to achieve accurate temperature control of each temperature zone; In S3, three temperature field partitions are set in the evaporator, which are unsealing zone, transmission channel zone and evaporation zone, the set temperature of the unsealing zone is 160℃; The set temperature of the transmission channel zone is 180℃; The set temperature of the evaporation zone is 260℃; The specific steps of S4 include: S41: Establishing a cesium atom transmission model, calculating the beam density : ； : cesium atom beam flux density, unit: ; : evaporation zone power, unit W; : evaporation efficiency correction factor, dimensionless; : evaporator exit radius, unit cm; : evaporator exit to substrate distance, unit cm; : cesium atom mass, unit g / mol; : Boltzmann constant, ; : evaporation zone absolute temperature, unit K; S42: Real-time adjustment of the deposition rate based on the fluid continuity equation : ； : deposition rate, unit: nm / s; : molar mass of cesium, 132.9 g / mol; : cesium film density, unit g / cm 3 ; : substrate deposition area, unit cm 2 ; S43: Set dual mode controller constraint fluctuation range, according to deposition rate Switch control mode: S431, when thermodynamic mode is activated; S432, when the fluid dynamics mode is activated; S44: Feedback regulation of evaporation zone power by mass flow controller and temperature field gradients, achieving beam current density fluctuation rates ; deposition rate in the range of 0.0001 - 10 nm / s continuously adjustable; The specific implementation steps of S43 include: When the thermodynamic mode is activated, the following steps are taken: Step S4311: Construct a feedforward compensator to suppress thermal inertia disturbance: ； : Feed forward power compensation, unit W; : System thermal time constant, unit s; : Thermal conduction gain coefficient, dimensionless; : Differential operator, calculate the set power rate of change; : Evaporator set power, unit W; Step S4312: Update the evaporation zone power: ； : actual power, in W; Step S4313: Verify stability through a temperature-power coupling equation: ； : rate of temperature change in the evaporation zone, in K / s; : heat loss coefficient, in W / K; : ambient temperature, in K; : heat capacity of the evaporator, in J / K; When the fluid dynamics mode is activated, the following steps are taken: Step S4321: Correct the viscous resistance based on the Navier-Stokes equation: ； : divergence operator; : gradient operator; : cesium vapor viscosity, unit Pa s; : vapor flow 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; : cesium atomic mass, unit kg; : Boltzmann constant; : evaporation zone temperature, unit K; Step S4323: Feedback adjust the evaporation zone power: ; : proportional gain; : set beam current; : integral gain; : integral operator, cumulative error; : integration time variable; S433, global constraint: The beam current density fluctuation rate satisfies ; : relative fluctuation rate, dimensionless; The deposition rate range satisfies ; : Deposition rate, unit nm / s.

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

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

4. A large area uniform molecular beam evaporation deposition system based on high purity cesium photo-cathode cesium film for implementing the method of any one of claims 1-3, characterized in that, It includes: The cesium source chamber, evaporator and nozzle mechanism are connected in series; The cesium source chamber, evaporator and nozzle mechanism are installed in the generator; The nozzle mechanism is connected with the deposition chamber at the end, and the deposition chamber is installed with a plurality of substrates; The nozzle mechanism includes a nozzle and a nozzle at the tail of the nozzle; The ampoule warehouse is provided in the cesium source chamber, and the ampoule warehouse is loaded with high-purity elemental cesium.

5. The system of claim 4, wherein, The nozzle is conical in structure; The nozzle is externally installed with a protective cover; The evaporator is provided with a fine adjustment valve; The upper part of the generator is installed with an electric control room, and the electric control room is installed with a control system; The nozzle mechanism and the deposition chamber are connected through flanges.

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