A method for obtaining atomic-level cleanliness of GaAs photocathode

Abstract

The invention discloses a method for obtaining atomic-level cleanliness of a GaAs photocathode, comprising low-temperature thermal cleaning, ion stripping and atomic hydrogen reduction, etc., so as to obtain an activated surface with atomic-level cleanliness. The specific steps and principles are as follows: S1: low-temperature thermal cleaning: low-temperature thermal cleaning adopts a radiation heating method, and generates thermal radiation by heating a heating wire. The thermal radiation passes through AVG glass and irradiates the GaAs epitaxial layer, so as to heat it. By adopting the above scheme, product performance can be significantly improved and material cost can be reduced. Low-temperature thermal cleaning is adopted in cost control. On the one hand, the requirements for AVG glass in the GaAs photocathode are reduced, so that 7056 glass with higher cost performance can be adopted as a substitute, and the single material cost is reduced by about 50%; on the other hand, 7056 glass is adopted, and its bonding temperature is lower, thereby reducing the requirements for the bonding process and improving the qualified rate of bonding.

Description

Technical Field

[0001] The invention relates to the field of GaAs photocathode devices, and in particular to a method for obtaining atomic-level cleanliness of a GaAs photocathode. Background Art

[0002] At present, there are countless universities, research institutes, and companies studying the GaAs photocathode of the third-generation image tube in the world, but only a few countries (such as the United States and Russia) have achieved mass production of the third-generation image tube. The main factor limiting its mass production is the GaAs photocathode, and one of the key processes in the preparation of the GaAs photocathode is to obtain atomic-level cleanliness. It is also the most difficult process in the entire low-light image intensifier preparation process, which greatly affects the performance and pass rate of the third-generation image tube. (The three main indicators describing the GaAs photocathode are integral sensitivity, radiation sensitivity, and uniformity, and these three indicators are the core technical indicators of the third-generation image tube.

[0003] Most of the known processes for obtaining atomic-level cleanliness of GaAs photocathodes use high-temperature thermal cleaning, which heats the entire GaAs photocathode in a vacuum environment by thermal radiation, thereby decomposing the oxide on the surface and leaking the gallium arsenide layer that is easy to emit electrons. There are four problems:

[0004] 1) Low performance: This method requires a relatively high temperature (about 600°C) during the preparation process. High temperature will cause arsenic oxide and gallium oxide to decompose. However, the temperature at which gallium oxide decomposes is similar to that at which gallium arsenide decomposes. If the temperature is not controlled accurately, gallium arsenide will decompose and form gallium droplets on the surface. The gallium-rich surface is not conducive to activating the emission of electrons, thus reducing the performance of the product.

[0005] 2) Low pass rate: Before the atomic-level cleanliness of GaAs photocathodes is achieved, they undergo epitaxial growth, high-temperature bonding, directional corrosion, coating and other processes, which results in poor surface consistency of the product itself. When this method is used for further processing, different samples need to absorb different amounts of heat and time, but it is difficult to judge in the actual operation process, which results in a low pass rate for GaAs photocathodes;

[0006] 3) Poor uniformity: High-temperature thermal cleaning will destroy the structure of the entire emission layer, causing changes in local components, and the uniformity of the light source is not easy to control, which will cause differences in the uniformity of the product's emission layer, which is reflected in the product as some parts are bright and some parts are dark;

[0007] 4) High cost: The GaAs photocathode is composed of AVG glass and GaAs epitaxial wafer bonded together. Since thermal cleaning uses a high temperature method, on the one hand, it has high requirements on the transition point and softening point of the glass, and on the other hand, it has strict requirements on the bonding process, resulting in an increase in raw material and labor costs. Summary of the invention

[0008] In order to overcome the shortcomings of the prior art of low photocathode performance, low production qualification rate, poor emission layer uniformity and high production cost, the present invention provides a method for obtaining atomic-level cleanliness of a GaAs photocathode, which effectively reduces the problems of gallium arsenide decomposition, component changes and rising raw material costs caused by excessively high temperatures during the process of obtaining atomic-level cleanliness through low-temperature thermal cleaning technology, plasma stripping technology and atomic hydrogen cleaning technology, and through plasma stripping and atomic hydrogen cleaning technology, a surface activated like epitaxial growth can be obtained without damaging the internal components of the gallium arsenide emission layer, and the non-decomposable compounds and carbon on the surface can be effectively removed, thereby greatly improving the performance of the gallium arsenide photocathode.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for obtaining atomic-level cleanliness of a GaAs photocathode, comprising low-temperature thermal cleaning, ion stripping and atomic hydrogen reduction, etc., so as to obtain an activated surface with atomic-level cleanliness. The specific steps and principles are as follows:

[0010] S1: Low temperature thermal cleaning: Low temperature thermal cleaning uses radiation heating to generate thermal radiation by heating the heating wire. The thermal radiation passes through the AVG glass and irradiates the GaAs epitaxial layer, thereby heating it.

[0011] S2: Argon ion stripping: The ionized Ar+ is accelerated by the emission voltage, which makes it have greater kinetic energy to bombard the sample surface, destroying the molecular structure and thus achieving surface stripping; through argon ion stripping, substances on the surface that are not easily decomposed by heat, including gallium oxide, carbon and other oxides, can be effectively removed. At the same time, the surface can also be polished to improve the micro-roughness of the surface, preparing for the next step of cesium oxide activation of the GaAs photocathode;

[0012] S3: Atomic hydrogen cleaning: The hydrogen atom gun generates atomic hydrogen by thermal cracking, which generates local high temperature and reacts to remove harmful substances such as residual carbon and gallium oxide on the surface of the GaAs emitter layer. The generated gallium monoxide has a low evaporation point and can be easily sublimated, thus exposing a clean and activated GaAs emitter layer.

[0013] After the sample enters from a valve, the sample is transferred to the workstation through the lifting and conversion device, a heat radiation device is turned on, the power is set to W1, the working time is T1, the argon atom gun is turned on, the filament current is set to I1, the grid voltage is U1, the emission voltage is U2, and the working time is T2. Then, the sample is transferred to another workstation through the lifting and conversion device, the hydrogen atom gun is turned on, the filament current is set to I2, and the working time is T3. After the specified time, the sample is cleaned and transferred to the next process equipment.

[0014] As a preferred technical solution of the present invention, in the step S1, the thermal radiation source is placed on the large end face of AVG, 6-20 mm away from the GaAs epitaxial layer, the heating wire working power W1=60-100 W, the working time T1=30-60 min, and the reaction during the low-temperature thermal cleaning process is shown as follows:

[0015] As a preferred technical solution of the present invention, the S2 step needs to be carried out in a high vacuum environment, and the range is controlled within 1×10-5torr~1×10-7torr, and argon gas is introduced through a precision leakage valve to control the vacuum degree. Argon ions in the high vacuum form an electron cloud of a certain density through a metal gate, thereby increasing the probability of Ar gas colliding with it, thereby generating Ar+ of the required density. The argon ion gun filament current I1=2.5~3.5A, the gate voltage U1=150~200V, the emission voltage U2=2000~3000V, and the working time T2=10~60min used in the S2 step. In actual situations, the stripping speed can be controlled by adjusting the above parameters. The thickness of the stripped GaAs emission layer in the present invention is about 10~100nm.

[0016] As a preferred technical solution of the present invention, the hydrogen atom gun used in S3 generates atomic hydrogen by thermal cracking, the filament current I2=10~15A, the working time T3=5~30min, and the chemical reaction formula of harmful substances such as carbon and gallium oxide remaining on the surface is:

[0017] As a preferred technical solution of the present invention, the high vacuum environment in S2 includes but is not limited to an ultra-high vacuum chamber with a vacuum degree of ≤1×10-9torr when no load is applied, an effective working distance of an argon ion gun of 50~200mm, an effective working area of ​​≥20mm, a stripping speed of ≥0.5nm / min, a filament current of a hydrogen ion gun of ≥10A, and a maximum temperature of ≥1500°C.

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

[0019] 1. The above solution can significantly improve product performance and reduce material costs. Low-temperature thermal cleaning is used for cost control. On the one hand, the requirements for AVG glass in GaAs photocathode are reduced, so that 7056 glass with higher cost performance can be used as a replacement, and the cost of single material is reduced by about 50%; on the other hand, the bonding temperature of 7056 glass is lower, thereby reducing the requirements for bonding process and improving the bonding qualification rate.

[0020] 2. This method, by lowering the thermal cleaning temperature, more effectively alleviates the problem of the qualified rate caused by the poor consistency of the gallium arsenide cathode. And because this method improves the performance of the gallium arsenide cathode as a whole, the qualified rate of the cathode activation is also significantly improved, thereby improving the qualified rate of finished products and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0022] Figure 2 It is a schematic diagram of the structure of the working device of the present invention;

[0023] Figure 3 It is a top view of the structure of the working device of the present invention;

[0024] Figure 4 This is a structural flow chart of Embodiment 1 of the present invention;

[0025] Figure 5 It is a schematic structural diagram of low-temperature thermal cleaning in step S1 of the present invention.

[0026] 1. Gas analysis device; 2. Hydrogen atom gun; 3. Argon atom gun; 4. Lifting transmission device; 5. Valve; 6. Thermal radiation device. DETAILED DESCRIPTION

[0027] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments, but the following embodiments are only preferred embodiments of the present invention, not all. Based on the embodiments in the implementation mode, other embodiments obtained by those skilled in the art without creative work all belong to the protection scope of the present invention. The experimental methods in the following embodiments, unless otherwise specified, are conventional methods, and the materials, reagents, etc. used in the following embodiments, unless otherwise specified, can all be obtained from commercial channels.

[0028] Embodiment one:

[0029] like Figure 1As shown, a method for obtaining atomic-level cleanliness of a GaAs photocathode includes low-temperature thermal cleaning, ion stripping, and atomic hydrogen reduction, thereby obtaining an activated surface with atomic-level cleanliness. The specific steps and principles are as follows:

[0030] S1: Low temperature thermal cleaning: Low temperature thermal cleaning uses radiation heating to generate thermal radiation by heating the heating wire. The thermal radiation passes through the AVG glass and irradiates the GaAs epitaxial layer, thereby heating it.

[0031] S2: Argon ion stripping: The ionized Ar+ is accelerated by the emission voltage, giving it greater kinetic energy to bombard the sample surface, destroying the molecular structure and achieving surface stripping;

[0032] S3: Atomic hydrogen cleaning: The hydrogen atom gun generates atomic hydrogen by thermal cracking, which generates local high temperature and reacts to remove harmful substances such as residual carbon and gallium oxide on the surface of the GaAs emitter layer. The generated gallium monoxide has a low evaporation point and can be easily sublimated, thus exposing a clean and activated GaAs emitter layer.

[0033] After the sample enters from a valve 5, the sample is transferred to a workstation through the lifting and conversion device 4, a heat radiation device 6 is turned on, the power is set to W1, the working time is T1, the argon atom gun 3 is turned on, the filament current I1, the grid voltage U1, the emission voltage U2, and the working time T2 are set, and then the sample is transferred to another workstation through the lifting and conversion device 4, the hydrogen atom gun 2 is turned on, the filament current is set to I2, and the working time is T3. After the specified time, the sample is cleaned and transferred to the next process equipment. When in use, the gas composition inside is analyzed in real time through the gas analysis device 1.

[0034] In other embodiments, in step S1, the thermal radiation source is placed on the large end face of AVG, 6-20 mm away from the GaAs epitaxial layer, the heating wire working power W1=60-100 W, the working time T1=30-60 min, and the reaction during the low-temperature thermal cleaning process is shown as follows:

[0035] In other embodiments, step S2 needs to be performed in a high vacuum environment, and the range is controlled within 1×10-5torr~1×10-7torr, and argon gas is introduced through a precision leakage valve to control the vacuum degree. Argon ions in high vacuum form an electron cloud of a certain density through a metal gate, thereby increasing the probability of Ar gas colliding with it, thereby generating Ar+ of the required density. The argon ion gun filament current I1=2.5~3.5A, the gate voltage U1=150~200V, the emission voltage U2=2000~3000V, and the working time T2=10~60min used in step S2. In actual situations, the stripping speed can be controlled by adjusting the above parameters. The thickness of the stripped GaAs emission layer in the present invention is approximately 10~100nm.

[0036] In other embodiments, the hydrogen atom gun used in S3 generates atomic hydrogen by thermal cracking, the filament current I2=10~15A, the working time T3=5~30min, and the chemical reaction formula of harmful substances such as carbon and gallium oxide remaining on the surface is:

[0037]

[0038] In other embodiments, the high vacuum environment in S2 includes but is not limited to an ultra-high vacuum chamber with a vacuum degree of ≤1×10-9 torr when no load is applied, an effective working distance of an argon ion gun of 50~200mm, an effective working area of ​​≥20mm, a stripping speed of ≥0.5nm / min, a filament current of a hydrogen ion gun of ≥10A, and a maximum temperature of ≥1500°C. Example

[0039] In this embodiment, based on the first embodiment, the use effect can be achieved by adjusting the process sequence, including first performing argon ion stripping, then performing low-temperature thermal cleaning, and finally performing atomic hydrogen cleaning, or first performing low-temperature thermal cleaning, then performing atomic hydrogen cleaning, and finally performing argon ion stripping.

[0040] The above solutions can significantly improve product performance and reduce material costs:

[0041] ① Performance: The performance parameters for measuring the sensitivity of GaAs photocathode mainly include integral sensitivity, radiation sensitivity and uniformity, as shown in the following table

[0042] Table 1 Performance improvement comparison

[0043]

[0044] ②Cost:

[0045] Low-temperature thermal cleaning is used for cost control. On the one hand, it reduces the requirements for AVG glass in GaAs photocathode, so that more cost-effective 7056 glass can be used as a substitute, reducing the cost of single material by about 50%; on the other hand, the use of 7056 glass has a lower bonding temperature, which reduces the requirements for the bonding process and improves the bonding qualification rate.

[0046] Secondly, lowering the thermal cleaning temperature more effectively alleviates the problem of qualified rate caused by the poor consistency of GaAs cathodes. And because this method improves the performance of GaAs cathodes as a whole, the qualified rate of cathode activation is also significantly improved, thereby improving the qualified rate of finished products and reducing costs.

[0047] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0048] The above shows and describes 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 by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for obtaining atomic-level cleanliness of a GaAs photocathode, characterized in that: It includes low-temperature thermal cleaning, ion stripping and atomic hydrogen reduction to obtain an activated surface with atomic-level cleanliness. The specific steps and principles are as follows: S1: Low-temperature thermal cleaning: Low-temperature thermal cleaning uses radiation heating to heat the heating wire and generate thermal radiation. The thermal radiation passes through the AVG glass and irradiates the GaAs epitaxial layer to heat it. S2: Argon ion stripping: Argon ion stripping: The ionized Ar+ is accelerated by the emission voltage and has kinetic energy to bombard the sample surface, destroying the molecular structure to achieve surface stripping; S3: Atomic hydrogen cleaning: Atomic hydrogen cleaning: The hydrogen atom gun generates atomic hydrogen by thermal cracking, and generates local high temperature through the action of atomic hydrogen, which reacts to remove the residual carbon and gallium oxide harmful substances on the surface of the GaAs emission layer. The generated gallium monoxide has a low evaporation point and can sublimate to expose the clean and activated GaAs emission layer; After the sample enters from a valve, the sample is transferred to a workstation through a lifting and conversion device, a heat radiation device is turned on, the power is set to W1, the working time is T1, the argon atom gun is turned on, the filament current is set to I1, the grid voltage is U1, the emission voltage is U2, and the working time is T2, then the sample is transferred to another workstation through a lifting and conversion device, the hydrogen atom gun is turned on, the filament current is set to I2, and the working time is T3, after T3, the sample is cleaned and transferred to the next process equipment; In S1, the heat radiation source is placed on the large end face of AVG, 6-20 mm away from the GaAs epitaxial layer, the heating wire working power W1=60-100 W, the working time T1=30-60 min, and the reaction formula during the low-temperature thermal cleaning process is as follows: ； The S2 needs to be carried out in a high vacuum environment, and the range is controlled within 1×10-5torr~1×10-7torr, and argon gas is introduced through a precision leak valve to control the vacuum degree. Argon ions in the high vacuum form an electron cloud of a certain density through a metal gate, thereby increasing the probability of Ar gas colliding with it, thereby generating Ar+ of the required density. The argon ion gun filament current I1=2.5~3.5A, the gate voltage U1=150~200V, the emission voltage U2=2000~3000V, the working time T2=10~60min, and the thickness of the stripped GaAs emission layer is 10~100nm; The high vacuum environment in S2 is an ultra-high vacuum chamber with a vacuum degree of ≤1×10-9torr when no load is applied, an effective working distance of an argon ion gun of 50~200mm, an effective working area of ​​≥20mm, a stripping speed of ≥0.5nm / min, a filament current of a hydrogen ion gun of ≥10A, and a temperature of ≥1500℃; The hydrogen atom gun used in S3 generates atomic hydrogen by thermal cracking, the filament current I2=10~15A, the working time T3=5~30min, and the chemical reaction formula of the residual carbon and gallium oxide harmful substances on the surface is: 。

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