CN106558466A - A kind of preparation method of monocrystalline lanthanum hexaboride field emitter arrays - Google Patents

Abstract

The invention discloses a method for preparing a single crystal lanthanum hexaboride field emission array cathode, which belongs to the technical field of cathode field emission. The present invention adopts nanosecond pulse electrochemical corrosion process to etch to form single crystal lanthanum hexaboride field emission array cathode, and adjusts processing pulse current parameters and etching time to make The polarization overpotential produces a significant difference, which effectively overcomes the stray corrosion in the process of etching the cone array by the electrochemical corrosion process, improves the uniformity of the cone array cathode, and then improves and enhances the field emission performance of the cathode, making The single crystal lanthanum hexaboride field emission cone array cathode has a broad application prospect as an electron source in microwave devices such as traveling wave tubes and klystrons and large dynamic vacuum equipment.

Description

A preparation method of single crystal lanthanum hexaboride field emission array cathode

technical field

The invention belongs to the technical field of cathode field emission, and in particular relates to a preparation method of a single crystal lanthanum hexaboride field emission array cathode.

Background technique

Because Field emission array cathodes (Field emission arrays) have a series of advantages such as instant start, room temperature operation, and high emission current density, they have good application prospects in many fields. Various application environments have their own special requirements for the field emission cathode itself. However, even for various applications, the emission stability of the cathode is always an indispensable basic guarantee for the normal operation of a device itself.

According to the research, the existing main problems of the tapered field emission cathode are: low emission current density and unstable current emission. According to experiments and analysis, the reason why the overall current density of the array cathode is not high is that not all the cathode cones participate in the emission. The reason is as follows: in the cathode manufacturing process, the small inhomogeneity of the grid hole array caused by the microfabrication technology will lead to obvious differences between the emission cones, and from the principle of the formation of the cones See, the difference in their shape will also be inevitable. The difference in the geometry of the emitting cones will cause the difference in their surface electric fields, and according to the principle of field emission:

(F-N formula when T=0K)

The change of the emission current density J caused by the different emission electric field strength E is very obvious. During the cathode test, some cones with better shape and smaller tip curvature radius in the array will reach the electric field threshold before other cones, resulting in field emission, and when the gate voltage is gradually increased, it is expected that all the cones will emit. In the process of obtaining a larger emission current, these cones are often burned due to overheating due to high local current density. This kind of local heat damage is often easy to cause the melting of part of the grid, and what is more, it will cause the discharge between the electrodes, resulting in the failure of the entire array cathode. Therefore, solving the problem of electron emission uniformity has become the key to the practicality of field emission arrays. Therefore, how to improve the uniformity of the cone array, thereby increasing the emission level of the cathode, has become a technical problem to be solved in the research.

Experiments have proved that single crystal lanthanum hexaboride (LaB ₆ ) has high melting point, high electrical conductivity and good thermal stability, chemical stability, low work function and active cathode surface, therefore, single crystal lanthanum hexaboride (LaB 6 ) ₆ ) is a very ideal field emission cathode material. The preparation process of single crystal LaB ₆ cone field emission array cathode mainly includes the following steps: deposition of protective layer, patterning of protective layer and etching of LaB ₆ cone array. Among them, the etching of LaB ₆ cone array is the most difficult and critical step in the whole process. The etching methods of single crystal LaB ₆ cone arrays include: wet etching, oxygen plasma oxidation combined with argon plasma dry etching oxide layer, oxygen plasma oxidation combined with hydrochloric acid wet etching oxide layer, electrodeposition chemical corrosion etc. Among them, the corrosive solution in wet etching is easy to damage the mask, resulting in a change in the shape of the cone; the combination of oxygen plasma oxidation and argon plasma dry etching of the oxide layer will corrode the mask material , causing the mask material to fall off in advance; the combination of oxygen plasma oxidation and hydrochloric acid wet etching of the oxide layer has a long process cycle, which can easily lead to a decrease in the uniformity of the cone array. The electrochemical etching process is a widely used LaB ₆ cone array etching process. The traditional process uses DC electrochemical corrosion to etch the LaB ₆ substrate. The process is simple and the cone shape is relatively intact. However, due to the stray electrochemical reaction Corrosion phenomenon, resulting in poor localization of its processing. Therefore, in order to improve the uniformity of the cone array in the etching process of the cone array by using the electrochemical etching process, it is necessary to solve the localization problem of the cone array etching.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the above technical problems and provide a method for preparing a single crystal lanthanum hexaboride field emission array cathode, which specifically includes pretreatment of a single crystal lanthanum hexaboride substrate, deposition of a protective layer, protection Layer patterning and single crystal lanthanum hexaboride cone array etching, this preparation method can effectively reduce stray corrosion and improve the localization of etching, thereby obtaining single crystal lanthanum hexaboride with good uniformity of the cone array Field emission array cathode.

In order to realize the above-mentioned purpose of the invention, the present invention adopts the following technical solutions:

A method for preparing a single crystal lanthanum hexaboride field emission cathode array, characterized in that it comprises the following steps:

Step A: cleaning the single crystal hexaboride substrate after grinding and polishing;

Step B: depositing a protective layer on the substrate processed in step A, and forming a desired pattern on the protective layer by photolithography and etching;

Step C: immerse the single crystal lanthanum hexaboride substrate and the graphite rod prepared in step B into the electrolyte, then connect the single crystal lanthanum hexaboride to the positive pole of the power supply, connect the graphite rod to the negative pole of the power supply, and use an external Pulse current is used for etching to form a single crystal lanthanum hexaboride cone array; the remaining protective layer on the single crystal lanthanum hexaboride cone array is removed, and finally a single crystal lanthanum hexaboride field emission cathode array is produced.

According to the embodiment of the present invention, step A of the present invention is specifically to use the RCA cleaning process after polishing the single crystal lanthanum hexaboride substrate. The RCA cleaning process is to wash the substrate with deionized water, absolute ethanol, acetone , absolute ethanol, SC-1 cleaning agent and SC-2 cleaning agent for ultrasonic cleaning, each reagent is cleaned with deionized water after cleaning;

Specifically, the chemical composition of the SC-1 cleaning agent is NH ₄ OH, H ₂ O ₂ and H ₂ O, and its volume ratio is NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:5 ; The chemical composition of the SC-2 cleaning agent is HCl, H ₂ O ₂ and H ₂ O, and its volume ratio is HCl:H ₂ O ₂ :H ₂ O=1:1:6.

As a preferred embodiment, the material of the protective layer in step B of the present invention is SiN _x .

Specifically, the specific operation of making the protective layer form the required pattern in step B of the present invention is:

B1: Uniform glue; under the condition of avoiding light, uniformly coat a layer of photoresist on the above-mentioned single crystal hexaboride substrate;

B2: Exposure: The substrate is subjected to soft baking treatment, and then the mask plate is covered on the single crystal lanthanum hexaboride substrate coated with photoresist, and the single crystal lanthanum hexaboride substrate is fully irradiated with ultraviolet light for exposure deal with;

B3: Developing: developing the exposed single crystal lanthanum hexaboride substrate with a developer, and then hardening the fully developed single crystal lanthanum hexaboride substrate;

B4: Etching: Reactive ion etching is used to etch to remove the redundant protective layer to obtain a single crystal lanthanum hexaboride substrate with the desired pattern on the surface;

B5: Removing the photoresist; putting the single crystal lanthanum hexaboride substrate with the patterned protective layer into the reagent for cleaning, and removing the photoresist on the surface layer.

As a preferred embodiment, the process parameters of the reactive ion etching method in the step B are as follows: the etching gas is SF ₆ , the gas flow rate is 30 sccm, the etching power is 40-60 W, and the etching time is 5-10 minutes.

Further, in step C of the present invention, a hydrofluoric acid solution is specifically used to remove the remaining mask.

Further, the chemical composition of the electrolyte in Step C of the present invention is H ₃ PO ₄ , C ₂ H ₅ OH and H ₂ O, preferably, the volume ratio of each composition is H ₃ PO ₄ :C ₂ H ₅ OH: H ₂ O=1:8~12:8~12, wherein the volume ratio of each component is H ₃ PO ₄ :C ₂ H ₅ OH:H ₂ O=1:10:10 is the best.

Further, the pulse width of the pulse current in step C of the present invention is preferably 5 ns-100 ns, the duty ratio is preferably 1:9-12, and the pulse voltage is preferably 3.5 V-4V.

Based on the original DC electrochemical corrosion process, the present invention combines micro-processing technology, adopts nanosecond pulse electrochemical corrosion process to etch to form single crystal lanthanum hexaboride field emission array cathode. Both the substrate and the emitter of the cathode of the field emission array are made of single crystal lanthanum hexaboride (LaB ₆ ), which effectively reduces the turn-on voltage required for the cathode of the field emission array, and greatly improves the emission of the cathode compared with the current materials. Current density and emission stability; more importantly, the nanosecond pulse electrochemical corrosion process is used to etch the lanthanum hexaboride substrate, and by adjusting the processing pulse current parameters and etching time, the single crystal lanthanum hexaboride substrate The overpotential of the area (processing area) not covered by the protective layer is higher than the decomposition potential, and the current density is large. The electrochemical erosion of the single crystal lanthanum hexaboride material in this area is large; The overpotential of the area (non-processing area) is lower than the decomposition potential, and the current density is small. The single crystal lanthanum hexaboride material in this area hardly undergoes electrochemical reactions, thereby significantly enhancing the localized erosion ability and reducing strays that affect processing accuracy. Corrosion, to achieve micron-scale electrolytic machining.

Compared with the prior art, the present invention has the following beneficial effects:

In the present invention, by adopting nanosecond pulse electrochemical corrosion, the polarization overpotential of the single crystal lanthanum hexaboride substrate processing area and non-processing area is significantly different, thereby effectively reducing the stray corrosion in the process of etching the cone array, The uniformity of the cone array cathode is improved, and the field emission performance of the fabricated cathode is improved and enhanced, so that the single crystal lanthanum hexaboride field emission cone array cathode is used as an electron source in microwave devices such as traveling wave tubes and klystrons. And large dynamic vacuum equipment and other fields have broad application prospects.

Description of drawings

1 is a schematic diagram of depositing a silicon nitride SiN _x protective layer on the surface of a single crystal lanthanum hexaboride (LaB ₆ ) substrate according to an embodiment of the present invention;

2 is a schematic diagram of coating photoresist on the surface of a silicon nitride (SiN _x ) protective layer according to an embodiment of the present invention;

3 is a schematic diagram of ultraviolet light exposure of a silicon nitride (SiN _x ) protective layer coated with photoresist according to an embodiment of the present invention;

Fig. 4 is a schematic diagram of an embodiment of the present invention after developing a silicon nitride (SiN _x ) protective layer;

5 is a schematic diagram of an embodiment of the present invention after the silicon nitride (SiN _x ) protection layer is etched by reactive ion etching (RIE) and the photoresist is removed;

Fig. 6 is a schematic diagram of an embodiment of the present invention after adopting nanosecond pulse electrochemical etching;

7 is a schematic diagram of the embodiment of the present invention after removing the remaining mask on the top of the tapered emitter obtained by etching;

Fig. 8 is a schematic diagram of the geometry of a single crystal lanthanum hexaboride (LaB ₆ ) field emitter obtained in an embodiment of the present invention;

Fig. 9 is a schematic structural view of a single crystal lanthanum hexaboride (LaB ₆ ) field emission array cathode obtained in an embodiment of the present invention.

detailed description

The present invention is described in detail below in conjunction with accompanying drawing and specific embodiment of description:

The invention provides a method for preparing a single crystal lanthanum hexaboride field emission cathode array, which specifically includes pretreatment of a single crystal lanthanum hexaboride substrate, deposition of a protective layer, patterning of the protective layer, and single crystal lanthanum hexaboride tip Cone array etching, because the electrochemical parameters in the process of forming single-crystal lanthanum hexaboride cone arrays through electrochemical etching process directly determine the shape of the etched cones, which in turn determines the field emission performance of the array cathode. The present invention selects suitable processing pulse parameters, adjusts the polarization overpotential of the processing area and the non-processing area to make a significant difference between the two, so as to control the dissolution and erosion of single crystal lanthanum hexaboride material in different areas, thereby reducing the Stray corrosion that affects machining accuracy.

Example:

A method for preparing a single crystal lanthanum hexaboride field emission cathode array, comprising the following steps:

Step A: pretreatment of single crystal hexaboride substrate;

In the present invention, micropowders such as silicon carbide, magnesium oxide, silicon dioxide, and aluminum oxide with suitable particle sizes are used to grind the single crystal lanthanum hexaboride substrate to remove the surface mechanical damage layer, and then use aluminum oxide or hydrogen peroxide to perform polishing treatment The flatness and high-gloss substrate surface meeting the experimental requirements were obtained; the polished single crystal lanthanum hexaboride substrate was cleaned to remove molecular, ionic and atomic impurities; this embodiment uses semiconductor manufacturing The RCA cleaning process commonly used in the process is as follows: sequentially use deionized water, absolute ethanol, acetone, absolute ethanol, No. 1 standard cleaning solution (SC-1 cleaning solution) and No. 2 standard cleaning solution (SC-2 cleaning solution) ) ultrasonic cleaning, each reagent was cleaned with deionized water after cleaning. Among them, the chemical composition of the SC-1 cleaning solution is NH ₄ OH, H ₂ O ₂ and H ₂ O, and the volume ratio of these three is NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:5～ 1:2:7; the chemical composition of SC-2 cleaning solution is HCl, H ₂ O ₂ and H ₂ O, and its volume ratio is HCl:H ₂ O ₂ :H ₂ O=1:1:6～1: 2:8; In this embodiment, the SC-1 cleaning solution with a chemical ratio of NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:5 and the chemical ratio of HCl:H ₂ O ₂ :H ₂ are used O=1:1:6 SC-2 cleaning solution; the specific cleaning method used in this implementation is: put the single crystal lanthanum hexaboride substrate in deionized water for ultrasonic cleaning for 10 minutes, repeat 5 times, and use deionized cleaning clean; put it in anhydrous ethanol liquid for ultrasonic cleaning for 10 minutes, and use deionization to clean it; put it in acetone liquid for ultrasonic cleaning for 20 minutes, use deionized cleaning to clean it, put it in absolute ethanol liquid for ultrasonic cleaning for 10 minutes, use deionized After ion cleaning, put it into SC-1 cleaning solution, heat it to 80°C for ultrasonic cleaning for 15 minutes. Ultrasonic cleaning in deionized water for 15 minutes, repeated 5 times;

Step B: Depositing a protective layer and patterning the protective layer;

As shown in Figure 1, in this embodiment, a silicon nitride (SiN _x ) film with a thickness of 500 nm is deposited on the surface of the substrate by radio frequency magnetron sputtering as a monocrystalline lanthanum hexaboride (LaB ₆ ) emitter for etching. required protective layer;

In this embodiment, common photolithography and etching processes are used to pattern the protective layer on a single crystal lanthanum hexaboride (LaB ₆ ) substrate deposited with a silicon nitride (SiN _x ) film, and the specific steps are as follows:

B1: Coating; under the condition of darkening, use the spin coating method to evenly coat a layer of photoresist on the above-mentioned single crystal hexaboride substrate, wherein the speed of the coating table is 3000rpm, and the coating time is 30 seconds. The schematic diagram of the structure of the obtained sample is shown in Figure 2;

B2: Exposure: The substrate is subjected to soft baking treatment, and then the mask plate is covered on the single crystal lanthanum hexaboride substrate coated with photoresist, and the single crystal lanthanum hexaboride substrate is fully irradiated with ultraviolet light for exposure Treatment, the exposure time of the present embodiment is 90 seconds, and the structural representation of the obtained sample is shown in Figure 3;

B3: Development; develop the exposed single crystal lanthanum hexaboride substrate with 4% tetramethylammonium hydroxide solution, carefully observe the change of the photoresist on the surface of the substrate, and the development time in this implementation is 30 seconds The photoresist in the exposed area is basically removed, and then the fully developed single crystal lanthanum hexaboride substrate is rinsed repeatedly with deionized water, blown dry with nitrogen, and baked in an oven at 100°C for 10 minutes to achieve film hardening Processing, the structural representation of obtained sample is as shown in Figure 4;

B4: Etching; Reactive ion etching is used to etch and remove the redundant protective layer, because SF ₆ has no obvious etching effect on single crystal lanthanum hexaboride, so this embodiment uses SF ₆ as the etching gas, and adjusts The gas flow rate is 30sccm, the etching power is 50W, and the etching time is 8 minutes. According to the experiment, the etching effect is good under this process parameter;

B5: Removing the photoresist; put the single crystal lanthanum hexaboride substrate patterned on the protective layer into an acetone solution and ultrasonically clean it for 3 minutes to remove the photoresist on the surface layer. The structure diagram of the obtained sample is shown in Figure 5;

Step C: single crystal lanthanum hexaboride cone array etching;

The single crystal lanthanum hexaboride substrate prepared in step B is cleaned, and then placed in a nanosecond pulse electrochemical etching device for etching treatment, wherein the above-mentioned single crystal lanthanum hexaboride substrate is connected to the positive electrode of the power supply as The anode and the graphite rod are connected to the negative pole of the power supply as the cathode, and the electrolyte in the nanosecond pulse electrochemical etching device is H ₃ PO ₄ aqueous solution, and ethanol is added as a buffer to slow down the reaction rate. The volume ratio of each component is preferably 1:1: 10. Turn on the nano-pulse power supply, adjust the pulse voltage to 4V, the pulse width to 40ns, and the duty ratio to 1:10. After etching for 3 hours, a frustum-shaped single crystal lanthanum hexaboride emitter with a height of 2.5 μm is formed, and the obtained The structural diagram of the sample is shown in Figure 6. The remaining protective layer on the single crystal lanthanum hexaboride emitter is removed to finally obtain a single crystal lanthanum hexaboride field emission cathode array. The structural diagram of the obtained sample is shown in Figure 7 shown.

As shown in Figure 8, it is a schematic diagram of the geometric shape of the single crystal lanthanum hexaboride field emitter obtained in the embodiment of the present invention, which belongs to the Spindt type structure, and its geometric shape can usually be represented by a cone, and the top is approximately a cone. For tangent spheres, the radius of curvature of the spheres is very small, mostly on the order of nanometers; FIG. 9 is a schematic diagram of the structure of the single crystal lanthanum hexaboride (LaB ₆ ) field emission array cathode obtained in the embodiment of the present invention.

The above-mentioned embodiments only express the implementation manner of the present invention, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (9)

1. a kind of preparation method of monocrystalline lanthanum hexaboride field emission cathode array, it is characterised in that comprise the following steps：

Step A：Clean up after monocrystalline hexaboride substrate is ground polishing；

Step B：In monocrystalline hexaboride deposition on substrate protective layer obtained by Jing processing of step A, and caused by photoetching and etching Required figure is formed on the protective layer；

Step C：The monocrystalline lanthanum hexaboride substrate of surface protection pattern layers and graphite rod are immersed in electrolyte, then by monocrystalline Lanthanum hexaboride substrate is connected with positive source, and graphite rod is connected with power cathode, performs etching shape using applying pulse electric current Into monocrystalline lanthanum hexaboride pointed cone array, remaining protective layer on the monocrystalline lanthanum hexaboride pointed cone array is removed, it is final to be obtained Monocrystalline lanthanum hexaboride field emission cathode array.

2. the preparation method of a kind of monocrystalline lanthanum hexaboride field emission cathode array according to claim 1, it is characterised in that Step A is specially carries out monocrystalline lanthanum hexaboride substrate using RCA cleanings after rubbing down, and the RCA cleanings are by base Deionized water, dehydrated alcohol, acetone, dehydrated alcohol, SC-1 abluents and SC-2 abluents are cleaned by ultrasonic piece successively, often Cleaned up using deionized water after planting reagent cleaning.

3. the preparation method of a kind of monocrystalline lanthanum hexaboride field emission cathode array according to claim 2, it is characterised in that The chemical composition of the SC-1 abluents is NH₄OH、H₂O₂And H₂O, its volume proportion are NH₄OH∶H₂O₂∶H₂O=1: 1: 5；It is described The chemical composition of SC-2 abluents is HCl, H₂O₂And H₂O, its volume proportion are HCl: H₂O₂∶H₂O=1: 1: 6.

4. the preparation method of a kind of monocrystalline lanthanum hexaboride field emission cathode array according to claim 1, it is characterised in that In step B, protective layer material is SiN_x。

5. the preparation method of a kind of monocrystalline lanthanum hexaboride field emission cathode array according to claim 4, it is characterised in that So that the concrete operations that protective layer forms required figure are in step B：

B1：Spin coating；Under the conditions of lucifuge, one layer of photoresist is uniformly coated on above-mentioned monocrystalline hexaboride substrate；

B2：Exposure；Substrate is carried out into soft baking process, then mask plate is covered in the monocrystalline lanthanum hexaboride base for being coated with photoresist On piece, monocrystalline lanthanum hexaboride substrate is fully irradiated using ultraviolet light and is exposed process；

B3：Development；Monocrystalline lanthanum hexaboride substrate after exposure is developed with developer solution, then by the monocrystalline six of abundant development Lanthanum boride substrate carries out firmly treatment；

B4：Etching；Removal redundant protection layer is performed etching using reactive ion etching method, the list that surface has required figure is obtained Brilliant lanthanum hexaboride substrate；

B5：Remove photoresist；The monocrystalline lanthanum hexaboride substrate of protection pattern layers is put in reagent and is cleaned, go skim-coat photoetching Glue.

6. the preparation method of a kind of monocrystalline lanthanum hexaboride field emission cathode array according to claim 5, it is characterised in that The technological parameter of reactive ion etching method is as follows：Etching gas are SF₆, gas flow is 30sccm, etching power be 40～ 60W, etch period are 5～10 minutes.

7. the preparation method of a kind of monocrystalline lanthanum hexaboride field emission cathode array according to claim 1, it is characterised in that Step C specifically removes remaining mask using hydrofluoric acid solution.

8. the preparation method of a kind of monocrystalline lanthanum hexaboride field emission cathode array according to any one of claim 1 to 7, its It is characterised by, in step C, the chemical composition of electrolyte is H₃PO₄、C₂H₅OH and H₂O, wherein the volume ratio of each composition is H₃PO₄∶ C₂H₅OH∶H₂O=1: 8～12: 8～12.

9. the preparation method of a kind of monocrystalline lanthanum hexaboride field emission cathode array according to claim 8, it is characterised in that The pulsewidth of the pulse current is 5ns～100ns, and dutycycle is 1: 9～12, and pulse voltage is 3.5V～4V.