A method for processing a low-temperature atomic-level surface of a GaAs photocathode in an ultrahigh vacuum environment

Abstract

The present application relates to the specific use or application of B82Y nanostructure; the field of nanostructure manufacturing or processing technology, in particular to a processing method of GaAs photocathode low-temperature atomic surface under ultrahigh vacuum environment, comprising the following steps: S1: the photocathode after completing plasma cleaning is transmitted to a thermal cleaning cavity through a magnetic force rod, and is placed in the center of a furnace tray after being observed through a window, then the magnetic force rod is withdrawn, and a plug valve is closed; S2: while starting thermal cleaning, open RGA, select H2 (2), H2O (18), CO (28) and As (75) to analyze residual gas, and record the curve; S3: apply a furnace tray current of 12.00-15.00 A, a temperature rising rate of 10.00-15.00 A / m, and a holding time of 10-20 min; S4: apply a furnace tray current of 15.00-18.00 A, a temperature rising rate of 10.00-15.00 A / m, and a holding time of 10-20 min; the GaAs photocathode is heated by using a substrate heating mode, and the problems of frequent strip abnormality after cathode thermal cleaning, too high CO and H2O content during thermal cleaning and the like in the prior art are solved by optimizing thermal desorption process parameters.

Description

Technical Field

[0001] This invention relates to a specific use or application of B82Y nanostructures; the field of nanostructure manufacturing or processing technology, specifically a method for processing the low-temperature atomic-level surface of GaAs photocathodes under ultra-high vacuum conditions. Background Technology

[0002] Gallium arsenide (GaAs) photocathodes, with their negative electron affinity, possess advantages such as high quantum efficiency, low dark emission, and concentrated energy and angular distribution of emitted electrons. GaAs photocathodes are the core component in photodetector fabrication; their atomic-level surface quality affects electron emission efficiency and directly determines the overall performance of the photodetector. GaAs is a direct bandgap semiconductor. After surface activation with cesium-oxygen (Cs-O), its electron affinity becomes negative, allowing electrons at the bottom of the conduction band to escape directly into the vacuum. When irradiated with light of a specific spectrum, it emits photoelectrons, with the number of emitted photoelectrons proportional to the incident light intensity, thus converting the low-energy radiation image input to its surface into an electronic image.

[0003] GaAs photocathodes are fabricated in a vacuum environment by using high temperature and pressure to induce atomic diffusion between gallium arsenide epitaxial wafers and the surface of anti-halo glass windows (AVG), resulting in direct chemical bonding. The fabrication process of GaAs photocathodes differs from that of ordinary photocathodes, consisting of epitaxial layer growth and surface activation. Surface activation is a crucial step in the photocathode fabrication process; the cleanliness of the surface and the atomic-level (or nanostructure) surface treatment significantly impact the activation effect. Therefore, atomic-level surface treatment is necessary before activating GaAs photocathodes to meet activation requirements. Currently, most industry practices employ high-temperature atomic-level surface treatment to clean the nanostructured surface of GaAs photocathodes, removing oxides from the photocathode surface. However, this method also has several drawbacks:

[0004] (1) Since the surface molecular desorption of gallium arsenide cathodes begins at about 300°C in ultra-high vacuum environment, excessively high thermal cleaning temperature will cause severe desorption of surface arsenic (As), atomic-level surface reconstruction and destruction, forming nanostructure defects, increasing surface states, trapping electrons, reducing emission efficiency, and causing stress stripes, thereby reducing activation effect.

[0005] (2) If the temperature is too high, the surface structure atoms rearrange and the grains coarsen, resulting in a decrease in the quantum efficiency of the photocathode and a worse response. If the heat treatment temperature is insufficient, impurities such as oxides cannot be completely removed, resulting in black spots and subsequent abnormal activation.

[0006] (3) Excessive temperature will cause impurities, gases and residual water vapor in the substrate and cavity to be released more quickly. These substances will be firmly adsorbed on the surface of GaAs photocathode, forming a recombination center, increasing dark current and reducing lifespan.

[0007] (4) The atomic-level surface of GaAs is extremely sensitive to CO and H2O. The CO and H2O in the environment will increase rapidly under high temperature. Once the content exceeds a certain value, it will contaminate the surface, causing the Cs-O layer to fail to adsorb successfully, thereby reducing the quantum efficiency and affecting the atomic-level surface quality of GaAs photocathode.

[0008] Therefore, in order to avoid the adverse effects of excessively high thermal cleaning temperatures and to ensure the atomic-level surface quality of GaAs photocathodes, this invention designs a low-temperature atomic-level surface treatment method for GaAs photocathodes under ultra-high vacuum conditions to solve the above problems. Summary of the Invention

[0009] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0010] The technical solution adopted by this invention to solve its technical problem is: a method for low-temperature atomic-level surface treatment of GaAs photocathode under ultra-high vacuum environment, comprising the following steps:

[0011] S1: Transfer the photocathode that has been plasma cleaned to the hot cleaning chamber through the magnetic rod. After observing it through the viewing window, place it in the center of the furnace plate, then withdraw the magnetic rod and close the slide valve.

[0012] S2: Start the hot cleaning process and turn on the RGA. Select H2(2), H2O(18), CO(28), As(75) for residual gas analysis and record the curves.

[0013] S3: Apply furnace plate current of 12.00~15.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min;

[0014] S4: Apply furnace plate current of 15.00~18.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min;

[0015] S5: Apply furnace plate current of 19.00~21.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min;

[0016] S6: Apply furnace plate current of 21.00~22.50 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min;

[0017] S7: Observe the changes in H2O and CO content at each step of the program, and determine that the H2O and CO content should be reduced to a safe range before step 8;

[0018] S8: Apply furnace plate current of 23.00~25.10 A, heating rate of 10.00~15.00 A / m, and holding time of 90~150 min;

[0019] S9: Observe whether the As peak can be detected normally in the RGA curve, and confirm whether the As partial pressure reaches the standard level.

[0020] S10: After the hot cleaning is finished, use a flashlight to check the surface of the photocathode through the glass window to check for black spots or streaks, which are abnormal signs of hot cleaning. Also, observe the RGA curve to confirm whether the As partial pressure meets the standard and whether the partial pressures of the other gases are normal.

[0021] S11: Adjust the height of the hot cleaning chamber bracket, open the valve between the activation chamber and the hot cleaning chamber, and use the magnetic rod to transfer the photocathode to the activation chamber in preparation for activation.

[0022] Furthermore, all chambers are under ultra-high vacuum, with a vacuum level better than 1.0E-10 Torr.

[0023] Furthermore, the furnace plate in the S1 hot cleaning chamber is positioned horizontally and without tilting.

[0024] Furthermore, before S1, the process includes: observing the cathode surface and electrode film after plasma cleaning to confirm whether there is any residual particle contamination or abnormality; if not, the contamination is transferred to the thermal cleaning chamber via a magnetic rod.

[0025] Furthermore, in S2, before thermal cleaning, RGA is used to analyze the residual gas in the cavity to check the content of H2, H2O, CO, and As gases. If the proportion of other gases is within the normal range, thermal cleaning continues. If the gas content is abnormal, the thermal cleaning process is paused and the cavity vacuum is checked and repaired first.

[0026] Furthermore, in S3 to S8, the thermal cleaning steps are automatically completed by a computer program, and the gas partial pressure in the cavity is monitored by observing the changes in the RGA curve in real time.

[0027] Furthermore, in S10 and S11, after the thermal cleaning is completed, potential problems are predicted by the RGA curve, and the cathode surface is observed through the glass window of the cavity using a blue light flashlight. After confirming that there are no abnormal phenomena such as stripes or black spots, it is transferred to the next activation process. The overall time should not be too long to avoid the degradation of the cathode surface quality.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. The present invention describes a method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum conditions. The method uses substrate heating to heat the GaAs photocathode and optimizes the thermal desorption process parameters to solve the problems of frequent stripe abnormalities after cathode thermal cleaning and excessive CO and H2O content during thermal cleaning in the prior art.

[0030] 2. This invention combines thermal desorption curves to control the amount of As desorption, which can avoid thermal stress and result in a more complete interfacial bond.

[0031] 3. At the same time, the use of low-temperature atomic-level surface treatment can suppress impurity desorption, reduce the probability of secondary contamination of GaAs, and obtain a clean GaAs photocathode, which provides an effective guarantee for subsequent activation processes.

[0032] 4. This invention employs a low-temperature atomic-level surface treatment method. By reducing the heat load, while ensuring the cleanliness of the GaAs photocathode surface, it maximizes the protection of the photocathode surface activity, film structure, and interface state at low temperatures, effectively improving quantum efficiency, reducing cathode dark current, and enhancing product quality. Attached Figure Description

[0033] The invention will now be further described with reference to the accompanying drawings.

[0034] Figure 1 This is a schematic diagram of the thermal cleaning method of the present invention;

[0035] Figure 2 This is a schematic diagram of the process flow of the present invention;

[0036] Figure 3 This is a diagram of the thermal cleaning heating structure of the present invention. Detailed Implementation

[0037] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0038] like Figures 1 to 2 As shown in the embodiment of the present invention, a method for low-temperature atomic-level surface treatment of GaAs photocathode under ultra-high vacuum environment includes the following steps:

[0039] S1: Transfer the photocathode that has been plasma cleaned to the hot cleaning chamber through the magnetic rod. After observing it through the viewing window, place it in the center of the furnace plate, then withdraw the magnetic rod and close the slide valve.

[0040] S2: Start the hot cleaning process and turn on the RGA. Select H2(2), H2O(18), CO(28), As(75) for residual gas analysis and record the curves.

[0041] S3: Apply furnace plate current of 12.00~15.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min;

[0042] S4: Apply furnace plate current of 15.00~18.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min;

[0043] S5: Apply furnace plate current of 19.00~21.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min;

[0044] S6: Apply furnace plate current of 21.00~22.50 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min;

[0045] S7: Observe the changes in H2O and CO content at each step of the program, and determine that the H2O and CO content should be reduced to a safe range before step 8;

[0046] S8: Apply furnace plate current of 23.00~25.10 A, heating rate of 10.00~15.00 A / m, and holding time of 90~150 min;

[0047] S9: Observe whether the As peak can be detected normally in the RGA curve, and confirm whether the As partial pressure reaches the standard level.

[0048] S10: After the hot cleaning is finished, use a flashlight to check the surface of the photocathode through the glass window to check for black spots or streaks, which are abnormal phenomena of hot cleaning. Also, observe the RGA curve to confirm whether the As partial pressure meets the standard and whether the partial pressures of the other gases are normal.

[0049] S11: Adjust the height of the hot cleaning chamber bracket, open the valve between the activation chamber and the hot cleaning chamber, and use the magnetic rod to transfer the photocathode to the activation chamber in preparation for activation.

[0050] S1 is the preparation work for transferring the cathode after the previous plasma cleaning. It is necessary to observe the cathode surface and electrode film after plasma cleaning to confirm whether there are any abnormalities such as residual particle contamination. If not, it can be transferred to the thermal cleaning chamber for subsequent steps through the magnetic rod.

[0051] Before thermal cleaning, S2 uses RGA to analyze the residual gas in the cavity to ensure that the cavity environment is suitable for the thermal cleaning process. At the same time, the contents of H2(2), H2O(18), CO(28), and As(75) are checked. If the proportions of other gases are within the normal range, thermal cleaning can continue. If the gas contents are abnormal, it will affect the thermal cleaning process and have a bad impact on the cathode surface. In this case, the thermal cleaning process needs to be suspended and the cavity vacuum needs to be checked and repaired first.

[0052] S3-S9 describe the specific operation of thermal cleaning. The main feature of this invention is that the power supply current for the highest temperature thermal cleaning of the cathode has been reduced from 120~130 W to 80~90 W. The thermal cleaning steps are automatically completed by a computer program. The gas partial pressure in the cavity is monitored by observing the changes in the RGA curve in real time. Multiple measures are taken to ensure the normal operation of the thermal cleaning process and to predict and judge the results of thermal cleaning based on the curve.

[0053] S10-S11 describes the specific operation of thermal cleaning. The main feature of this invention is that the power supply current for the highest temperature thermal cleaning of the cathode has been reduced from the original 120~130 W to 80~90 W. The thermal cleaning steps are automatically completed by a computer program. The gas partial pressure in the cavity is monitored by observing the changes in the RGA curve in real time. Multiple measures are taken to ensure the normal operation of the thermal cleaning process and to predict and judge the results of thermal cleaning based on the curve.

[0054] S10-S11 is the inspection phase after hot cleaning and the transfer to the next activation process. After hot cleaning, potential problems are predicted using the RGA curve, and a blue light flashlight is used to observe the cathode surface through the glass window of the cavity to check for complete hot cleaning and the presence of abnormalities such as streaks or black spots. If any are found, it needs to be determined whether to continue operation or to remove the workstation. If none are found, the process can be transferred to the next activation process. The overall time should not be too long to avoid deterioration of the cathode surface quality. These step-by-step inspections ensure product qualification rates and enable timely anomaly analysis, effectively improving the overall production level of integrated tube manufacturing.

[0055] All chambers are under ultra-high vacuum, with a vacuum level better than 1.0E-10 Torr.

[0056] The furnace plate in the S1 hot cleaning chamber is horizontal and not tilted.

[0057] In summary, this thermal cleaning method for GaAs photocathodes in third-generation image intensifiers achieves high-temperature thermal cleaning at approximately 23.00–25.10 A (about 80–90 W) by appropriately reducing the power during the highest temperature cleaning stage. This allows for the thermal decomposition of the oxide layer on the cathode surface, removing the surface oxide layer and allowing a small amount of As to escape. The method is further aided by RGA (Radio Absorber Gauge) and vacuum gauges to control the vacuum level and partial pressures of various gases within the thermal cleaning chamber. This ensures that the gaseous influences during the thermal cleaning process, such as O2, CO, and H2O, remain within a controllable range, while also providing assistance for anomaly analysis.

[0058] Before S1, the process also includes: observing the cathode surface and electrode film after plasma cleaning to confirm whether there is any residual particle contamination or abnormality. If not, the contamination is transferred to the thermal cleaning chamber via a magnetic rod.

[0059] In S2, before hot cleaning, RGA is used to analyze the residual gas in the cavity and check the content of H2, H2O, CO, and As gases. If the proportion of other gases is within the normal range, hot cleaning continues. If the gas content is abnormal, the hot cleaning process is paused and the cavity vacuum is checked and repaired first.

[0060] In S3 to S8, the thermal cleaning steps are automatically completed by a computer program, and the gas partial pressure in the cavity is monitored by observing the changes in the RGA curve in real time.

[0061] In S10 and S11, after the thermal cleaning is completed, potential problems are predicted by the RGA curve, and the cathode surface is observed through the glass window of the cavity using a blue light flashlight. After confirming that there are no abnormal phenomena such as stripes or black spots, it is transferred to the next activation process. The overall time should not be too long to avoid the degradation of the cathode surface quality.

[0062] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum conditions, characterized in that: Includes the following steps: S1: Transfer the photocathode that has been plasma cleaned to the hot cleaning chamber through the magnetic rod. After observing it through the viewing window, place it in the center of the furnace plate, then withdraw the magnetic rod and close the slide valve. S2: Start the hot cleaning process and turn on the RGA. Select H2(2), H2O(18), CO(28), As(75) for residual gas analysis and record the curves. S3: Apply furnace plate current of 12.00~15.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min; S4: Apply furnace plate current of 15.00~18.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min; S5: Apply furnace plate current of 19.00~21.00 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min; S6: Apply furnace plate current of 21.00~22.50 A, heating rate of 10.00~15.00 A / m, and holding time of 10~20 min; S7: Observe the changes in H2O and CO content at each step of the program, and determine that the H2O and CO content should be reduced to a safe range before step 8; S8: Apply furnace plate current of 23.00~25.10 A, heating rate of 10.00~15.00 A / m, and holding time of 90~150 min; S9: Observe whether the RGA curve can detect the As peak normally, and confirm whether the As partial pressure reaches the standard level. S10: After the hot cleaning is finished, use a flashlight to check the surface of the photocathode through the glass window to check for black spots or streaks, which are abnormal signs of hot cleaning. Also, observe the RGA curve to confirm whether the As partial pressure meets the standard and whether the partial pressures of the other gases are normal. S11: Adjust the height of the hot cleaning chamber bracket, open the valve between the activation chamber and the hot cleaning chamber, and use the magnetic rod to transfer the photocathode to the activation chamber in preparation for activation.

2. The method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum environment according to claim 1, characterized in that: All chambers are under ultra-high vacuum, with a vacuum level better than 1.0E-10 Torr.

3. The method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum environment according to claim 1, characterized in that: The furnace plate in the S1 hot cleaning chamber is horizontal and not tilted.

4. The method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum environment according to claim 1, characterized in that: All cathode clamps are fully compatible with the current cathode size.

5. The method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum environment according to claim 1, characterized in that: Before S1, the process also includes: observing the cathode surface and electrode film after plasma cleaning to confirm whether there is any residual particle contamination or abnormality. If not, the contamination is transferred to the thermal cleaning chamber via a magnetic rod.

6. The method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum environment according to claim 1, characterized in that: In S2, before hot cleaning, RGA is used to analyze the residual gas in the cavity and check the content of H2, H2O, CO, and As gases. If the proportion of other gases is within the normal range, hot cleaning continues. If the gas content is abnormal, the hot cleaning process is paused and the cavity vacuum is checked and repaired first.

7. The method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum environment according to claim 1, characterized in that: In S3 to S8, the thermal cleaning steps are automatically completed by a computer program, and the gas partial pressure in the cavity is monitored by observing the changes in the RGA curve in real time.

8. The method for treating the low-temperature atomic-level surface of a GaAs photocathode under ultra-high vacuum environment according to claim 1, characterized in that: In S10 and S11, after the thermal cleaning is completed, potential problems are predicted by the RGA curve, and the cathode surface is observed through the glass window of the cavity using a blue light flashlight. After confirming that there are no abnormal phenomena such as stripes or black spots, it is transferred to the next activation process. The overall time should not be too long to avoid the degradation of the cathode surface quality.

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