CN115513017A - Spindt cathode electron source and preparation method and application thereof - Google Patents

Abstract

The invention discloses a Spindt cathode electron source and a preparation method and application thereof, wherein the cathode electron source comprises the following structures: the silicon substrate, the insulating layer and the grid are sequentially arranged from bottom to top, and an insulating layer cavity is formed among the silicon substrate, the insulating layer and the grid through hole; an emission sharp cone arranged on the silicon substrate and positioned in the cavity of the insulating layer, wherein the emission sharp cone corresponds to the gate through hole; the coating layer is arranged on the silicon substrate, is positioned in the insulating layer cavity and completely covers the exposed silicon substrate in the insulating layer cavity; the attached oxide layer is positioned between the coating layer and the emission pointed cone and coats the lower side surface of the emission pointed cone; the upper side surface of the emission tip cone is exposed outside the incidental oxide layer. The cathode electron source structure avoids the unexpected electron emission of the three-combination point, thereby effectively preventing the common discharge along the network and the space arc failure caused by the discharge.

Description

A kind of Spindt cathode electron source and its preparation method and application

technical field

The invention relates to the technical field of vacuum electronics. More specifically, it relates to a Spindt cathode electron source and its preparation method and application.

Background technique

The field emission electron source based on the principle of electron escape induced by a strong electric field has the advantages of no external energy, room temperature operation, instant start and high current density. It can replace the traditional hot cathode electron source in vacuum electronic devices, and it is expected to retain the high frequency and high power of the device. , high temperature resistance, and radiation resistance, and at the same time achieve smaller volume and lighter weight, which has very good comprehensive advantages. Potential applications of field emission electron sources include various high-end analytical instruments, display devices, X-ray emitters, microwave power devices, high-energy particle acceleration devices, space propulsion devices and many other scenarios. The development of high-performance field emission electron sources is of great significance to the development and progress of vacuum electronic devices.

The Spindt cathode is the field emission electron source that was developed the earliest and is the most mature in development and application. It was used as a reference for many researches on field emission electron sources in the later period. The Spindt cathode is an array cathode with a large number of integrated micro-emission units. Figure 1 shows the structure of a typical unit. The components in Figure 1 are marked as: 101-silicon substrate, 201-insulating layer, 301-gate pole and 401-emitter tip. When working normally, applying a forward bias voltage on the 101-silicon substrate and the 301-gate can generate a strong electric field on the surface of the 401-emission cone, resulting in electron emission. As the gate bias voltage increases, the cell emission current can rapidly increase exponentially. A large number of micro-emitting units are integrated, so that the Spindt cathode can maintain a large current density and total current at the same time.

However, the Spindt cathode electron source often has arc failure in high current applications, which affects the reliability of the device. Relevant studies have shown that the main cause of arc failure is that when a high voltage is applied between the 301-gate and the 101-silicon substrate, an abnormality will occur at the junction of the 101-silicon substrate, the 201-insulating layer and the vacuum triple junction. The expected electron emission, the undesired electron emission climbs along the side wall of the 201-insulation layer to the 301-gate under the action of the electric field, during which the electrons are multiplied by constant collisions, and then discharge along the network is formed, and finally in the 301-gate and 401-Emitting a cone-induced arc causes damage. For this kind of arc failure, there have been two types of related patented technologies in the early stage.

One type of technology is to try to block the path of electron discharge along the network. The structure of Japanese patent JP-A8-321255, as shown in Figure 2, introduces a second insulating layer material, and these two insulating materials construct three alternating layers of insulating layers 201, 202 and 203. In fact, five layers and seven layers can also be constructed. A layer or more layer structure, using the difference in lateral corrosion caused by the different corrosion selection ratios of the two materials, can realize the insulating sidewall of the overall wrinkled structure. This wrinkled structure insulates the sidewall, making it more difficult for electrons to be generated from the three junctions of 101-silicon substrate, 201-insulating layer and vacuum, to move along the wall to the 301-gate and to generate discharge along the network. The US6075315A structure, as shown in FIG. 3 , also introduces another insulating layer material, but only uses it to construct the 204 -shielding layer between the 201 -insulating layer and the 301 -gate. The special structure design makes the 301-gate moderately retracted, and the 204-shielding layer is used to isolate the 101-silicon substrate, 201-insulating layer and vacuum triple junction from the space of the 301-gate, so that the undesired emission of electrons It is difficult to generate discharge along the grid to reach the 301-gate. However, this type of technology does not prevent undesired electron emission. Although it increases the difficulty of electron discharge along the network, it does not solve the fundamental problem. And the U.S. patented structure, due to the retraction of the 301-grid, greatly reduces the surface electric field intensity of the 401-emission cone under the same operating voltage, and weakens the electron emission capability of the Spindt cathode.

Another type of technology is trying to block the channel that generates space arc. U.S. Patent US6369496B1 structure, as shown in Figure 4, uses another insulating material to construct 205-insulating ring columns to surround 401-emission cones and isolate them from 201-insulating layers and 301-grids to avoid space arcs produce. The US005442193A structure, as shown in Figure 5, uses another insulating material to construct the 206-covering layer, and completely conformally covers the 201-insulating layer and 301-gate, in order to block it and the 401-emission cone to create a space arc. However, this type of technology does not fundamentally prevent undesired electron emission, and the isolation of the former is not complete, while the latter requires a higher operating voltage due to insulation covering, which will also lead to insulation breakdown and space arcing.

Contents of the invention

Based on the above facts, the object of the present invention is to provide a Spindt cathode electron source and its preparation method and application, which solves the problem that the undesired electron emission cannot be completely overcome in the prior art, and then can effectively prevent the common edge of the electron source with the traditional structure. Network discharge and space arc failure.

On the one hand, the invention provides a kind of Spindt cathode electron source, comprises in its structure:

A silicon substrate, an insulating layer, and a gate are sequentially arranged from bottom to top, and an insulating layer cavity is formed between the silicon substrate, the insulating layer, and the through hole of the gate;

an emission cone disposed on the silicon substrate and located in the cavity of the insulating layer, the emission cone corresponding to the gate through-hole; and,

a cladding layer disposed on the silicon substrate, the cladding layer being located in the cavity of the insulating layer and completely covering the silicon substrate exposed in the cavity of the insulating layer;

An incidental oxide layer located between the coating layer and the emitting cone and covering the lower side of the emitting cone; the upper side of the emitting cone is exposed to the incidental oxide layer.

Further, the coating layer is silicon dioxide obtained by thermal oxidation of the surface of the silicon substrate.

Further, the thickness of the coating layer is 30-100 nm.

Further, the height of the upper side of the emitting cone exposed to the incidental oxide layer is 0.3-0.4 μm.

Further, the material of the emitting cone is selected from pure metals with high melting point and low work function, preferably W or Mo.

Further, the emission cone has a bottom diameter of 0.6-1 μm, a height of 0.8-2.2 μm, and a top curvature radius of 20-50 nm.

Further, the height of the upper side of the emission cone exposed to the incidental oxide layer is 15-50% of the overall height of the emission cone.

Further, the material of the oxidized layer is obtained by thermal oxidation of the surface of the lower side of the emitting cone.

Further, the silicon substrate is selected from semiconductor process standard N-type doped silicon wafers.

Further, the resistivity of the silicon substrate is 0.005-5Ω·cm.

Further, the insulating layer material is selected from silicon dioxide or silicon nitride.

Further, the thickness of the insulating layer material is 0.8-2 μm.

Further, the material of the gate is selected from pure metals with high melting point, preferably W or Mo; preferably, the thickness of the gate is 100-200 nm, and the diameter of the through-hole of the gate is 0.8-1.2 μm.

In another aspect, the present invention provides the preparation method of Spindt cathode electron source as described above, comprising the steps:

forming an insulating layer on the silicon substrate;

vacuum coating, forming a gate layer on the insulating layer;

Through photolithography, and sequentially etch the gate layer and insulating layer until the silicon substrate, forming a gate and insulating layer cavity containing gate through holes;

The substrate is rotated, and only a sacrificial layer is vacuum-coated on the surface of the grid by adopting the method of small surface inclination to reduce the through-hole of the grid;

The surface is vertically vacuum-coated with a layer of emitting cone material to form an emitting cone in the cavity;

removing the sacrificial layer and the emission tip material deposited on the sacrificial layer;

The substrate is rotated, and a protective layer is only vacuum-coated on the surface of the gate and the upper side of the emission cone by adopting the method of large surface inclination;

The silicon substrate is thermally oxidized, the coating layer is formed on the surface of the silicon substrate in the cavity, and the unprotected part of the emission tip is incidentally oxidized to form an incidental oxide layer;

The protective layer is removed by etching to expose the grid and the upper side of the emission cone to obtain the Spindt cathode electron source.

In yet another aspect, the present invention provides the application of the Spindt cathode electron source as described above in devices for vacuum electronics.

The beneficial effects of the present invention are as follows:

In the Spindt cathode electron source provided by the invention, the cladding layer completely covers the silicon substrate, eliminating the triple junction structure formed by the silicon substrate, insulating layer and vacuum, and preventing the undesired electron emission from the structure point. Compared with the previous technology of blocking the transmission path of electron discharge along the network or the path of arc discharge, the present invention eliminates the source of electron emission that generates discharge and arc, and can effectively prevent the traditional electronic source from being prone to discharge along the network under high voltage and high current working conditions. and space arc failure, effectively improving the reliability of the electron source.

The manufacturing method of the Spindt cathode electron source provided by the present invention is only to implement the two-step process of manufacturing the emitting cone protective layer and manufacturing the base coating layer after completing the traditional structure.

Description of drawings

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 1 shows a schematic structural diagram of a Spindt cathode electron source showing a typical structure in the prior art.

FIG. 2 shows a schematic structural diagram of a Spindt cathode electron source with a multi-insulation layer wrinkled sidewall structure in the prior art.

FIG. 3 shows a schematic structural diagram of a Spindt cathode electron source with a grid shielding layer in the prior art.

Fig. 4 shows a schematic structural diagram of a Spindt cathode electron source with an emission tip insulating ring column isolation in the prior art.

Fig. 5 shows a schematic structural diagram of a Spindt cathode electron source with a covering layer in the prior art.

Fig. 6 shows a schematic structural view of a substrate-coated Spindt cathode electron source of the present invention.

Fig. 7a-Fig. 7h show a fabrication flow chart of a substrate-coated Spindt cathode electron source of the present invention.

Fig. 8a and Fig. 8b show a conventional aspect ratio Spindt cathode electron source photo and partial enlarged photo of the present invention with a base coating layer.

Figures 9a-9c show the scanning electron photographs of a Spindt cathode electron source with a large aspect ratio and a substrate cladding layer in the present invention, which is produced in one cycle and two cycles, and the emission cone array and the final partial enlarged emission unit.

Fig. 10a-Fig. 10b respectively show the emission performance test curves of Spindt cathode electron source obtained in embodiment 1 and embodiment 2 of the present invention.

detailed description

In order to illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not limit the protection scope of the present invention.

In view of the Spindt cathode electron source in the prior art, arc failure often occurs in high current applications, which affects the reliability of the device, and there is no related technology that can well overcome this problem. A specific embodiment of the present invention provides a A kind of Spindt cathode electron source, as shown in Figure 6, comprises in its structure:

A silicon substrate 101, an insulating layer 201, and a gate 301 are sequentially arranged from bottom to top, and an insulating layer cavity is formed between the silicon substrate 101, the insulating layer 201, and the through hole of the gate;

An emission cone 401 disposed on the silicon substrate 101 and located in the cavity of the insulating layer, the emission cone 401 corresponding to the gate through hole; and,

A cladding layer 207 disposed on the silicon substrate 101, the cladding layer 207 is located in the cavity of the insulating layer and completely covers the silicon substrate 101 exposed in the cavity of the insulating layer;

An incidental oxide layer 402 located between the coating layer 207 and the emitting cone 401 and covering the lower side of the emitting cone 401 ; the upper side of the emitting cone 401 is exposed to the incidental oxide layer 402 .

In this implementation manner, the diameter of the gate through hole is smaller than the diameter of the cavity of the insulating layer.

By constructing the cladding layer 207, the traditional Spindt cathode electron source is eliminated from the three-junction structure formed by the silicon substrate, insulating layer and vacuum, preventing the generation of undesired electron emission and the resulting discharge along the network. And space arc, thus improving the reliability of Spindt cathode electron source working under high voltage and high current.

The function of the cladding layer 207 is to effectively cover the silicon substrate 101 and requires a certain thickness to withstand electric field breakdown. The cladding layer 207 is located in the cavity formed by the silicon substrate 101, the emission cone 401 and the insulating layer 201, completely covers the silicon substrate 101 and isolates the vacuum, and eliminates the silicon substrate, the insulating layer and the vacuum in the traditional structure. composed of three junctions. In comprehensive consideration of the position of the coating layer and the realization of the process, the material of the 207-coating layer is thermally oxidized silicon dioxide. In order to effectively form a barrier, the thickness of the coating layer 207 is preferably 30-100 nm.

In some preferred examples, the coating layer is silicon dioxide obtained by thermal oxidation of the surface of the silicon substrate.

The function of the emission cone is to emit electrons. In a preferred example, the material of the emission cone 401 is selected from pure metals with high melting point and low work function, so as to achieve effective emission of electrons. For example, the material of the emission tip 401 can preferably be molybdenum (melting point 2620°C, work function 4.2eV) or tungsten (melting point 3420°C, work function 4.5eV), which can overcome the large work function and chemical Instability, poor electrical conductivity, poor thermal conductivity, etc., so as to provide high current and stable electron emission.

The shape of the emission cone 401 affects the strength of its surface electric field and thus affects field electron emission. The optimal position of the height of the cone is between the upper and lower surfaces of the gate, specifically determined by the thickness of the insulating layer 201 and the gate 301, and the range is preferably 0.8-2.2 μm; the curvature radius of the cone tip is specifically determined by the height of the emission cone 401 1. The diameter of the gate through hole 301 and the thickness of the deposited film layer in both directions of the fabrication of the cone are determined, and the optimization range is 20-50nm; the diameter of the bottom of the emission cone is determined by the diameter of the gate 301 hole and the thickness of the deposition in the oblique direction of the fabrication of the cone, The range is 0.6-1μm.

According to the principle of the Spindt cathode field emission electron source, the field electron emission only exists in a small area at the top of the emission cone 401 . Exemplarily, the height of the upper side of the emission cone exposed to the accompanying oxide layer is 15-50% of the overall height of the emission cone. Under this condition, the upper side (upper part) of the emission cone 401 maintains the original material properties, so that the Spindt cathode electron source maintains proper electron emission performance. The lower side (lower part) of the emitting cone 401 covered by the incidental oxide layer does not affect the performance of the electron source due to the position.

In still some preferred examples, the height of the upper side of the emitting cone exposed to the incidental oxide layer is 0.3-0.4 μm.

Exemplarily, the material with the oxide layer is obtained by thermal oxidation of the surface of the lower side of the emitting cone. The silicon base plays the role of carrying structure at the same time, and is suitable for the characteristics of micro-machining technology. The standard size silicon chip of microelectronics is selected; the silicon base 101 is responsible for providing the functions of emitting electrons and cathode conduction. The ratio is preferably 0.005-5Ω·cm.

The function of the insulating layer 201 is to resist the high operating voltage between the silicon substrate 101 and the gate 301 , which requires the insulating layer 201 to have a higher breakdown field strength and thickness. The thickness of the insulating layer is determined according to the comprehensive influence of the breakdown field strength and the diameter of the gate through hole and the shape of the emission cone 401, preferably in the range of 0.8-2 μm; the material of the insulating layer 201 is preferably made of process-compatible silicon dioxide or nitrogen More preferably, according to the process implementation method, when the thickness of the insulating layer 201 is 0.8-1.2 μm, the material is selected from thermally oxidized silicon dioxide with better comprehensive performance, and when the thickness is 1.2-2 μm, the material is selected from the prepared Process-optimized chemical vapor deposition of silicon nitride.

The function of the grid is to form a strong electric field on the surface of the emitting cone 401 to extract electrons through the applied high voltage, and it must carry structural strength and certain leakage heat power dissipation. The material of the gate 301 is selected from metal materials with a high melting point. In a preferred example, the material of the gate 301 is selected from molybdenum or tungsten. The thickness of the gate 301 is affected by structural strength and micro-processing technology, and is preferably 100-200 nm according to actual application conditions. The diameter of the gate through-hole affects the surface electric field intensity and electron emission performance of the emitting cone 401 under the condition of applying a voltage, and is preferably 0.8-1.2 μm according to actual application conditions.

According to another specific embodiment of the present invention, a kind of preparation method of Spindt cathode electron source is provided, and it comprises the steps:

1) An insulating layer 201 is formed on the silicon substrate 101 .

The material of the insulating layer is preferably thermally oxidized silicon dioxide, which is formed by direct oxidation of the silicon wafer material and has the best bonding effect with the silicon wafer; however, the thermal oxidation growth of silicon dioxide exceeds a certain thickness is extremely slow, so thermal oxidation is used when the insulating layer is thin. Oxide silicon dioxide, and silicon nitride by chemical vapor deposition method after exceeding a certain thickness. In one example, the thermally oxidized silicon dioxide insulating layer has a thickness in the range of 0.8-1.2 μm; in another example, the chemical vapor deposition silicon dioxide insulating layer has a thickness in the range of 1.2-2 μm. The chemical vapor deposition method can also deposit silicon nitride material as an insulating layer.

2) Vacuum coating, forming a gate layer 301 on the insulating layer 201, as shown in FIG. 7a.

The gate material is selected from metal materials with high melting point, preferably W or Mo. The gate 301 is formed by vacuum coating technology, preferably magnetron sputtering coating method, compared with other coating processes, sputtering coating can obtain better film bonding force. The thickness of the gate 301 can be adjusted according to actual application conditions, preferably 100-200 nm.

3) By photolithography, and sequentially etching the gate layer 301 and the insulating layer 201 until the silicon substrate 101, forming the gate 301 and the insulating layer cavity including gate through holes, as shown in FIG. 7b.

Conventional photolithography technology in semiconductor technology is used to form the masking layer of the gate through-hole pattern, and the pattern on the masking layer can be copied and transferred to the structural layer through a subsequent etching process. The structural layer in the present invention is the gate layer.

The gate 301 is etched through the pattern masking layer to form gate through-holes, and the etching method is preferably reactive ion etching; reactive ion etching is a highly anisotropic dry etching method, which can produce depth direction etching at the same time Basically keep the dimension in the width direction unchanged. For the gate through-hole etching in the present invention, the 301-gate 100-200nm depth direction etching can be completed, while maintaining the 0.8-1.2 μm gate through-hole diameter defined by the photolithographic masking layer basically unchanged, and obtaining approximately steep side wall.

Etch the insulating layer through the gate through hole to form a gate-controlled cavity in the insulating layer. The combination of reactive ion etching and wet chemical etching is preferred for etching; first, reactive ion etching realizes the etching of the insulating layer at a depth of 0.8-2 μm. , to ensure that there is no lateral undercutting during the process, so as to avoid the gate being suspended and the insulating layer bonded weakly; the wet chemical etching is used as a short-term rinse etching to ensure that the insulating layer cavity is etched directly to the silicon substrate. Since the wet chemical etching method has a good etching selection ratio, it can be ensured that the process only basically targets the insulating layer material and does not damage the silicon substrate. The short-term wet chemical etching process will produce slight lateral undercutting, making the lateral size of the insulating cavity slightly larger than the diameter of the 0.8-1.2 μm gate through-hole.

4) The substrate is rotated, and only one layer of sacrificial layer is vacuum-coated on the surface of the gate by adopting the method of a small surface inclination to reduce the through-hole of the gate, as shown in FIG. 7c.

The purpose of depositing the sacrificial layer at a small inclination angle is to reduce the hole diameter of the gate 301, thereby controlling the size of the bottom of the emission cone 401; The film layer and the gate 301 form an effective isolation.

The material of the sacrificial layer 501 is selected from materials having an etch selectivity with the silicon substrate 101, the insulating layer 201, the gates 301 and 401 and the emitter cone 401, preferably selected from metal oxide materials to facilitate the formation of a fine and uniform film layer. In a preferred example, it is selected from aluminum oxide.

The sacrificial layer 501 is selected from deposition at a small inclination angle. The purpose is that the material of the sacrificial layer 501 only exists on the surface of the gate 301, including the upper surface and the edge of the through hole of the gate, but does not enter the void formed by the silicon substrate 101 and 201-the insulating layer at the angle of sight. cavity inside. Preferably, the range of the small inclination angle is selected from an angle of 15-30 degrees with the grid plane.

The sacrificial layer 501 is vacuum-coated, preferably vacuum-evaporated from parallel beams. Parallel beams are injected to ensure the consistency of the grid closure of each unit on the Spindt cathode array; vacuum evaporation ensures that the deposited material particles are fine to form smooth edges in the grid through holes. In a preferred example, the vacuum coating is selected from electron beam evaporation coating.

The deposition thickness of the sacrificial layer 501 mainly depends on the reduction degree of the opening of the through hole of the grid 301 and is related to the incident angle of the deposition material beam. Preferably, the opening diameter of the gate through hole is reduced by about 0.2 μm, and correspondingly, the thickness of the sacrificial layer 501 is deposited in a range of 100-200 nm.

5) A layer of emitting cone material is vacuum-coated vertically on the surface to form an emitting cone 401 in the cavity, as shown in FIG. 7d.

The purpose of the surface vertical deposition is to form the emitting cone 401 . The vertically deposited material is partially deposited on the sacrificial layer 501 to form the incidental deposition layer 403; part of it is deposited on the silicon substrate 101 through the gate through hole narrowed by the sacrificial layer 501, because the continuously deposited material in the process will also Shrinking the through-holes of the gate leads to the continuous reduction of the range of materials deposited on the silicon substrate 101 , thereby forming a conical emission tip 401 .

The emission tip material is selected from pure metals with high melting point and low work function, such as preferably molybdenum or tungsten, so as to realize efficient emission of electrons. In another preferred example, a conductive non-metallic material with a high melting point and low work function, such as zirconium carbide, can also be deposited on the surface of the emission cone 401 as the electron emission material.

Emission cone material deposition is selected from vacuum evaporation, which ensures that the particles of the deposited material are fine and uniform, so as to form an emission cone with a dense structure and smooth surface; to meet the requirements of high melting point material deposition, the emission cone material deposition is selected from electron beam evaporation coating.

The deposition thickness of the emission cone material depends on the required height of the emission cone 401 , and the ratio between the two is basically (1-1.2):1. For the formation of pointed cones with a height in the range of 0.8-1 μm, the preferred deposition thickness is 1-1.2 μm. In view of the preferred structure, the deposition of the sacrificial layer 501 at a small angle has narrowed the gate through-hole to 0.6-1 μm. During the deposition of the emitter tip 401 material, since the gate through-hole will continue to shrink until it is completely closed, the deposited material cannot enter The cavity heightens the emission cone 401, and the height of the emission cone 401 formed by one material deposition will not exceed 1 μm. Therefore, for the formation of a cone with a height in the range of 1-2.2 μm, multiple emission cone material deposition processes are required.

6) Removing the sacrificial layer 501 and the emission tip material deposited on the sacrificial layer, as shown in FIG. 7e.

The material of the sacrificial layer 501 is selected from a material having an etching selectivity ratio with the silicon substrate 101, the insulating layer 201, the gate 301, the emission tip 401 and the subsequent cladding layer 207, so that when the sacrificial layer material is removed by etching, the etching solution does not Can damage other materials. In a preferred example, the material of the sacrificial layer is selected from aluminum oxide, and the corrosion solution is selected from hot phosphoric acid at 120° C., or potassium hydroxide solution with a concentration of 20%.

7) The substrate is rotated, and a protection layer 601 and 602 is vacuum-coated only on the surface of the gate 301 and the upper side of the emission cone 601 by adopting a method with a large surface inclination, as shown in FIG. 7f.

The purpose of depositing the protective layer at a large inclination angle is to form a layer of temporary protection on the surface of the gate 301 and the emitting cone 401, so that in the subsequent process of forming the cladding layer 207, the surface state of the gate 301 and the surface of the emitting cone 401 will not be affected. .

The protective layer material is selected from materials having an etching selectivity ratio with the silicon substrate 101, the insulating layer 201, the gate 301 and the emission tip 401, and is not affected by the subsequent process of forming the cladding layer 207, preferably selected from metal oxide materials In order to facilitate the formation of fine and uniform film layer. In a preferred example, it is selected from aluminum oxide.

The protection layer is selected from high-inclination-angle deposition, which is relative to the small-inclination-angle deposition of the aforementioned sacrificial layer. half of the surface; incidentally, the protective layer material may also exist in the upper half 601 of the sidewall of the insulating layer 201, and this part of the material has no practical use; but the protective layer material should ensure that the angle of sight does not reach the surface of the silicon substrate 101, to avoid It affects the formation of the subsequent cladding layer 207 . Preferably, the range of the large inclination angle is selected from an angle of 30-60 degrees with the grid 301 plane.

The protective layer is vacuum-coated, preferably vacuum-evaporated from parallel beams. Parallel beam flow ensures that no chaotic particles enter the cavity and reach the surface of the silicon substrate 101 during evaporation at an oblique angle; vacuum evaporation ensures that the deposited material particles are fine to form a uniform protection. In a preferred example, the vacuum coating is selected from electron beam evaporation coating.

The thickness of the protective layer is deposited on the basis of forming a continuous dense film on the surface of the gate 301 and the emitting cone 401 , preferably, the deposition thickness is in the range of 50-100 nm.

8) The silicon substrate 101 is thermally oxidized, the coating layer 207 is formed on the surface of the silicon substrate 101 in the cavity, and the unprotected part of the emission tip 401 is additionally oxidized to form an additional oxide layer 402, as shown in FIG. 7g.

The purpose of thermally oxidizing the silicon substrate 101 is to directly oxidize the silicon material, and the formed silicon dioxide forms a coating layer 207 on the surface of the silicon substrate 101 in the cavity, completely covering the silicon substrate, so as to eliminate the problems caused by the silicon substrate 101, the insulating layer 201 and Three junctions created by the vacuum inside the cavity. The cladding layer 207 requires a certain thickness to withstand electric field breakdown and effectively form an electron emission barrier, and the thickness is preferably 30-100 nm.

The silicon wafer can be naturally oxidized at room temperature, but the thickness of the oxide layer generally does not exceed 20nm, which cannot meet the requirements of the coating layer 207, so a high temperature oxidation method is used. Preferably, a lower temperature of 700-800° C. is used for the thermal oxidation of the silicon substrate 101 , so as to ensure the required thickness of the oxide layer and not excessively affect the combination of the emission tip 401 and the silicon substrate 101 . More preferably, dry oxygen thermal oxidation or water vapor thermal oxidation can be used for thermal oxidation, the former is slow to obtain a dense oxide layer, and the latter is fast to shorten the process time.

9) Etching and removing the protective layers 601, 602 and 603, exposing the gate 301 and the upper side of the emission cone 401 to obtain the Spindt cathode electron source, as shown in FIG. 7h.

Emitting cone protection layer 601 and gate protection 602 materials, selected from silicon substrate 101, insulating layer 201, gate 301, emitting cone 401 and cladding layer 207 have corrosion selectivity materials, when etching to remove the protection layer material , the corrosive liquid will not damage other materials. In a preferred example, the material of the sacrificial layer is selected from aluminum oxide, and the corrosion solution is selected from hot phosphoric acid at 120° C., or potassium hydroxide solution with a concentration of 20%.

Below, illustrate in conjunction with specific embodiment:

Example 1

A Spindt cathode electron source with a base cladding layer, the conventional aspect ratio of the emission cone is close to 1:1, and its structure is shown in Figure 6, including a silicon substrate 101, an emission cone 401 and An oxide layer 402 , a cladding layer 207 , an insulating layer 201 and a gate 301 are attached. Its preparation method comprises the following steps:

1) The silicon substrate 101 is a silicon wafer with N-type doping, <100> crystal orientation, and a resistivity of 0.01 Ω·cm, thermally oxidized at 1200° C. for 16 hours, and grows a layer of silicon dioxide with a thickness of 0.8 μm as the insulating layer 201 .

2) Using the radio frequency magnetron sputtering vacuum coating method, sputtering for 3 minutes at a power of 600W, depositing a layer of molybdenum with a thickness of 0.2 μm on the insulating layer 201 as the gate 301, as shown in FIG. 7a.

3) Coat the gate 301 with Shipley S1818 photoresist with a thickness of 1.4 μm, and use ultraviolet lithography to form an array of circular holes with a diameter of 1 μm on the photoresist layer as a masking layer; through the photoresist masking layer, through inductively coupled plasma method, using sulfur hexafluoride process atmosphere to etch the gate 301, with a discharge power of 500W and an etching power of 300W, and complete etching in 4 minutes to obtain the opening (through hole) of the gate 301; through the opening of the gate, through the induction Coupled plasma method, using trifluoromethane process atmosphere to etch the insulating layer 201, discharge power 500W, etching power 300W, etch to a depth of about 0.6 μm in 6 minutes, and then use BOE buffer solution (hydrofluoric acid: ammonium fluoride: water =3ml: 6g: 10ml) to continue etching, completely etch the silicon dioxide insulating layer to the silicon substrate 101 in 5 minutes, and at the same time produce a certain degree of lateral undercutting; remove the residual Shipley S1818 photoresist to form a gate-controlled cavity structure, As shown in Figure 7b.

4) The above-mentioned substrate is rotated at 30 RPM along the normal direction of the plane, and at the same time, in the direction of the included angle of 20 degrees, the Al2O3 is evaporated with an electron beam and deposited at a power of 2kW for 10 minutes to form a 200nm thick Al2O3 on the plane of the gate 301. Dialuminum is used as the sacrificial layer 501; the sacrificial layer completely wraps the upper surface of the gate 301 and the sides of the opening, and reduces the gate opening from 1 μm to 0.8 μm, as shown in FIG. 7c.

5) The above substrate is evaporated molybdenum with electron beam along the vertical direction, and the deposited material reaches 101-silicon substrate 101 through the opening of 301-grid 301. As the opening of the gate continues to shrink, emission Spike 401. 4kW power deposition for 40 minutes, deposited molybdenum layer thickness of 1.1 μm, resulting in emission cone 401 with a height of about 0.9 μm, and an incidental deposition layer 403 with a thickness of 1.1 μm formed on the plane of the sacrificial layer 501, as shown in Figure 7d.

6) Use hot phosphoric acid with a concentration of 85% and a temperature of 120°C to etch the sacrificial layer 501 and completely dissolve it in 1 minute, and the incidental deposition layer 403 on the sacrificial layer 501 is peeled off from the substrate, leaving the silicon substrate 101, the emission cone 401, and the insulating layer 201 and grid 301 constitute the traditional Spindt cathode electron source structure, as shown in FIG. 7e.

7) The above-mentioned substrate is rotated at 30 RPM along the normal direction of the plane, and at the same time, in the direction of 45 degrees included in the plane, Al2O3 is evaporated with an electron beam and deposited for 2 minutes at a power of 2kW to form a 50nm thick grid on the grid 301 plane The protective layer 602 completely wraps the upper surface of the grid 301 and the sides of the opening, and forms a 50nm-thick emission cone protection layer 601 on the upper half of the emission cone 401 to completely wrap the electron emission part at the top of the emission cone 401; at the same time, the insulating layer 201 The sidewalls form an accompanying protective layer, as shown in Figure 7f.

8) Carry out thermal oxidation, dry oxygen oxidation at 800°C for 5 hours, and form a silicon dioxide 207-coating layer 207 with a thickness of 30nm on the surface of the cavity 101-silicon substrate 101, and at the same time, 401-the lower half of the emission cone is not exposed. The protected portion incidentally forms an oxidized surface incidentally with an oxide layer 402, as shown in FIG. 7g.

9) Use hot phosphoric acid with a concentration of 85% and a temperature of 120°C to corrode the protective layer 601 of the emission tip, the protective layer 602 of the gate and the protective layer 603, and completely dissolve it in 1 minute, exposing the upper part of the gate 301 and the upper part of the tip of the emission 401, and obtain The substrate-coated Spindt cathode electron source is shown in Fig. 7h.

The substrate-coated Spindt cathode electron source is obtained by the above process, the diameter of the gate opening of the emission array unit is 1 μm, the thickness of the insulating layer is 0.8 μm, the thickness of the gate is 0.2 μm, the height of the emission cone is 0.9 μm, and the radius of curvature of the tip of the emission cone is 50nm , the thickness of the cladding layer is 30nm, the scanning electron photos of the Spindt cathode electron source array and the partially enlarged emission unit are shown in Fig. 8a and 8b respectively.

Example 2

A Spindt cathode electron source with a base cladding layer, the conventional aspect ratio of the emission cone is close to 1.5:1, and its structure is shown in Figure 6, including a silicon substrate 101, an emission cone 401 and An oxide layer 402 , a cladding layer 207 , an insulating layer 201 and a gate 301 are attached. Its preparation method comprises repeating embodiment 1, difference is:

In step 1, 201-insulating layer 201 is grown by chemical vapor deposition, and tetraethylorthosilicate (TEOS) is decomposed at 640°C for 120 minutes to obtain a silicon dioxide insulating layer with a thickness of 1.2 μm.

In step 3, the insulating layer 201 is etched using a trifluoromethane process atmosphere with constant process parameters, and the silicon dioxide is etched to a depth of approximately 1 μm in 15 minutes.

Steps 4-6 need to be repeated twice: in the first cycle, the thickness of the molybdenum layer deposited in step 5 is 0.6 μm, and the height of the emitting cone 401 is about 0.5 μm. In the second cycle, in step 4, the electron beam evaporates aluminum oxide to form a sacrificial layer 501 with a thickness of 250 nm on the plane of the gate 301, reducing the gate opening from 1 μm to 0.7 μm; in step 5, depositing a molybdenum layer with a thickness of 1 μm, 0.8 μm is superimposed on the already 0.5 μm height of emission cone 401 .

In step 8, thermal oxidation was performed with water vapor at 800° C. for 2 hours to form a silicon dioxide coating layer 207 with a thickness of 100 nm on the surface of the silicon substrate 101 in the cavity.

The substrate-coated Spindt cathode electron source is obtained by the above process, the diameter of the gate opening of the emission array unit is 1 μm, the thickness of the insulating layer is 1.2 μm, the thickness of the gate is 0.2 μm, the height of the emission cone is 1.3 μm, and the radius of curvature of the tip of the emission cone is 40nm , the thickness of the cladding layer is 100nm, the scanning electron photos of the Spindt cathode electron source for the first and second cycles of manufacturing the emission cone array and the final partial enlarged emission unit are shown in Figures 9a, 9b and 9c, respectively.

The verification results of the above examples show that the substrate-coated Spindt cathode electron source proposed by the present invention can effectively eliminate the undesirable electron emission generated by the silicon substrate, the insulating layer and the vacuum triple junction, thereby avoiding the resulting vacuum arc electron source Invalidation problem.

Taking the structural parameters of the embodiment (mainly the diameter of the grid hole, the height of the emission tip and the radius of curvature of the tip of the tip) and the material as an example, the Spindt cathode electron source without the base cladding layer structure generates the grid voltage for electron emission The threshold value is 70-80V, and the emission current increases with the increase of the grid voltage, but when the grid voltage exceeds 120-130V, an obvious vacuum arc may be generated, resulting in damage to the cathode electron source. However, the Spindt cathode electron source with a substrate-coated structure in Example 1 basically does not change the gate voltage threshold for electron emission, and can still work stably when the gate voltage exceeds 130V, maintaining high current and reliable emission. Example 2 and other examples show similar results, indicating that the present invention can better solve the problem of vacuum arc failure caused by undesired electrons at triple junctions of the Spindt cathode electron source.

Figure 10 shows the emission performance test curves of two Spindt cathode electron sources with a substrate-coated structure, and the vacuum degree of the test environment is 2×10 ^-7 Pa. The test adopts a three-pole test with an external anode. A fixed high voltage is applied to the external anode, and the grid voltage is gradually increased to test the emission current. The total emission current includes the anode current and the grid interception current. Figure 10a corresponds to the Spindt cathode obtained in Example 1 that contains 11,000 emitting unit arrays and a unit center spacing of 5 μm. It starts to generate electron emission at a gate voltage of 70V, and obtains a stable emission current of 24.62mA at 148V. The corresponding emission current density 8.7A/cm ² . Figure 10b corresponds to the Spindt cathode obtained in Example 2, which contains 25 emitting unit arrays and a unit center spacing of 5 μm. It starts to generate electron emission at a gate voltage of 80V, and obtains a stable emission current of 159 μA at 160V, corresponding to an emission current density of 25.4 A/cm ² .

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those of ordinary skill in the art can also make It is impossible to exhaustively list all the implementation modes here, and any obvious changes or changes derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims (10)

1. A Spindt cathode electron source, characterized in that the structure comprises:

the silicon substrate, the insulating layer and the grid are sequentially arranged from bottom to top, and an insulating layer cavity is formed among the silicon substrate, the insulating layer and the grid through hole;

an emission sharp cone arranged on the silicon substrate and positioned in the cavity of the insulating layer, wherein the emission sharp cone corresponds to the gate through hole; and the number of the first and second groups,

a coating layer arranged on the silicon substrate, wherein the coating layer is positioned in the insulating layer cavity and completely covers the silicon substrate exposed in the insulating layer cavity;

the attached oxide layer is positioned between the coating layer and the emission tip cone and coated on the lower side surface of the emission tip cone; the upper side surface of the emission tip cone is exposed outside the incidental oxide layer.

2. The Spindt cathode electron source of claim 1, wherein the coating layer is silicon dioxide obtained by thermal oxidation of the surface of the silicon substrate;

preferably, the coating layer has a thickness of 30-100nm.

3. A Spindt cathode electron source according to claim 1, wherein the upper side of the emission tip is exposed outside the incidental oxide layer to a height of 0.3-0.4 μm;

preferably, the material of the emission tip cone is selected from pure metals with high melting point and low work function, preferably W or Mo;

preferably, the diameter of the bottom of the emission sharp cone is 0.6-1 μm, the height is 0.8-2.2 μm, and the radius of curvature of the top is 20-50nm.

4. A Spindt cathode electron source according to claim 1, wherein the upper side of the emission tip is exposed outside the incidental oxide layer to a height of 15-50% of the overall height of the emission tip.

5. A Spindt cathode electron source according to claim 1, wherein the incidental oxide layer is thermally oxidised from the surface of the underside of the emission cusp.

6. The Spindt cathode electron source of claim 1, wherein the silicon substrate is selected from a semiconductor process standard N-type doped silicon wafer; preferably, the silicon substrate has a resistivity of 0.005 to 5 Ω · cm.

7. A Spindt cathode electron source according to claim 1, wherein the insulating layer material is selected from silicon dioxide or silicon nitride; preferably, the thickness of the insulating layer material is 0.8-2 μm.

8. A Spindt cathode electron source according to claim 1, wherein the material of the grid is selected from a high melting point pure metal, preferably W or Mo; preferably, the thickness of the grid electrode is 100-200nm, and the diameter of the grid through hole is 0.8-1.2 μm.

9. A method of producing a Spindt cathode electron source according to any of claims 1 to 8, comprising the steps of:

forming an insulating layer on the silicon substrate;

vacuum coating, forming a grid layer on the insulating layer;

etching the grid layer and the insulating layer in sequence until reaching the silicon substrate by photoetching to form a grid containing a grid through hole and an insulating layer cavity;

rotating the substrate, and performing vacuum coating on the surface of the grid only by adopting a method with a small surface inclination angle to form a sacrificial layer and reduce the through holes of the grid;

vacuum coating a layer of emission pointed cone material on the surface of the hollow cavity in a vertical manner to form an emission pointed cone in the hollow cavity;

removing the sacrificial layer and the emission pointed cone material deposited on the sacrificial layer;

rotating the substrate, and performing vacuum coating on the surface of the grid and the upper side surface of the emission pointed cone only by adopting a method of large surface inclination angle to form a protective layer;

thermally oxidizing the silicon substrate, wherein the coating layer is formed on the surface of the silicon substrate in the cavity, and the unprotected part of the emission sharp cone is subjected to oxidation to form an attached oxidation layer;

and corroding and removing the protective layer to expose the grid and the upper side surface of the emission pointed cone to obtain the Spindt cathode electron source.

10. Use of a Spindt cathode electron source according to any of the claims 1-8 in a device for vacuum electronics.

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