Method for welding molybdenum field emission array and molybdenum substrate in field emission device

Abstract

The invention belongs to the field of vacuum microelectronics, and particularly relates to a method for welding a molybdenum field emission array and a molybdenum substrate in a field emission device, which comprises the following steps of: firstly, etching an inverted pyramid pit array on a silicon wafer covered with a silicon dioxide mask; performing thermal oxidation treatment on the silicon wafer etched with the inverted pyramid pit array to form a silicon dioxide layer; evaporating a molybdenum emitter layer on the silicon dioxide layer to obtain a molybdenum field emission array; and finally welding the molybdenum field emission array with the molybdenum substrate. According to the invention, the inverted pyramid pit array is etched on the silicon wafer coated with the silicon dioxide mask, so that the surface roughness is enhanced, and the connection strength is improved. Under the combined action of the silicon dioxide layer formed by performing thermal oxidation treatment on the silicon wafer etched with the inverted pyramid pit array and the molybdenum layer deposited on the upper surface of the silicon dioxide layer, the tight connection between the molybdenum field emission array and the molybdenum-molybdenum substrate is realized while the silicon is prevented from being eroded by the welding flux.

Description

Technical Field

[0001] The invention belongs to the field of vacuum microelectronics, and in particular relates to a method for welding a molybdenum field emission array and a molybdenum substrate in a field emission device. Background Art

[0002] Traditional hot cathode vacuum devices have the disadvantages of large size, high power consumption, and low life, and are no longer suitable for the rapid development of various fields. Field emission cathodes have the advantages of small size, high integration, and low power consumption. They have been widely used in vacuum microelectronic devices. The reverse molding technology makes a field emission array cone by making a silicon wafer reverse mold, depositing the emitter, and transferring the emitter layer. The molybdenum-molybdenum substrate has the characteristics of low thermal expansion coefficient, low resistivity, high temperature resistance, and corrosion resistance. Therefore, the silicon wafer can be connected to the molybdenum-molybdenum substrate by welding technology to facilitate the transfer of the cathode layer; at the same time, it can be used as an electrode to realize the function of field emission.

[0003] The traditional connection method of reverse molding technology is to use electrostatic bonding to connect the molybdenum field emission array and the glass substrate. Under high temperature, high vacuum and high voltage, the molybdenum field emission array and the glass substrate are connected together. Electrostatic bonding is the process of Na + The ions drift toward the negative electrode, forming a depletion layer on the glass surface next to the silicon wafer, and the metal layer and the glass are in close contact through electrostatic attraction. However, since the glass substrate is not conductive and the depletion layer is only a few microns, it is difficult to extract the electrode, which affects the field emission function test. Summary of the invention

[0004] The purpose of the present invention is to provide a method for welding a molybdenum field emission array and a molybdenum substrate in a field emission device to improve the connection strength and product performance of the existing inverted molding technology, in order to solve the problems of difficulty in extracting electrodes and affecting field emission in the prior art inverted molding technology.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical scheme:

[0006] A method for welding a molybdenum field emission array and a molybdenum substrate in a field emission device comprises the following steps: firstly etching an inverted pyramid pit array on a silicon wafer covered with a silicon dioxide mask; then thermally oxidizing the silicon wafer etched with the inverted pyramid pit array; then vapor-depositing a molybdenum emitter layer on the thermally oxidized silicon wafer to obtain a molybdenum field emission array; and finally welding the molybdenum field emission array to the molybdenum substrate.

[0007] As a preferred embodiment, the method comprises the following steps:

[0008] S1, etching an inverted pyramid pit array on a silicon wafer covered with a silicon dioxide mask by wet etching;

[0009] S2, performing thermal oxidation treatment on the silicon wafer having the inverted pyramid pit array to form a silicon dioxide layer on its surface;

[0010] S3, depositing a molybdenum emitter layer on the silicon dioxide layer to obtain a molybdenum field emission array;

[0011] S4. Brazing the molybdenum field emission array and the molybdenum substrate.

[0012] As a preferred embodiment, the method comprises the following steps:

[0013] S1. The solution for wet etching the silicon wafer is a mixed solution, and the etching time is 20 minutes to 25 minutes; the mixed solution is prepared by 15% tetramethylammonium hydroxide and 16% isopropyl alcohol in a 1:1 ratio.

[0014] S2, using thermal oxidation technology to perform thermal oxidation treatment on the silicon wafer with the inverted pyramid pit array etched, the thermal oxidation treatment temperature is 1000° C. to 1200° C., preferably 1000° C.; the oxidation time is 0.5 to 1.5 hours, and the oxygen flow rate is 30 to 60 sccm, preferably 50 sccm;

[0015] S3, using conventional thin film deposition technology to evaporate the molybdenum emitter layer on the silicon dioxide layer, the system vacuum degree is 4×10 -4 Pa, the thickness of the molybdenum emitter layer is 3-5 μm;

[0016] S4, stack the silver-copper-titanium alloy sheet and the silicon sheet with the molybdenum emitter layer in sequence in a sintering furnace for high vacuum sintering; the vacuum degree is 3×10 -3 Pa, the sintering temperature is 840°C, the thickness of the silver-copper-titanium alloy is 0.06-0.08mm; the thickness of the molybdenum substrate is 0.4-0.8mm.

[0017] As a preferred embodiment, step S4 of the method is further as follows:

[0018] S4, stack the molybdenum substrate, the silver-copper-titanium alloy sheet, and the silicon sheet with the molybdenum emitter layer deposited in sequence in a sintering furnace for high vacuum sintering with a vacuum degree of 3×10 -3 Pa, the sintering temperature is 840℃, the thickness of the silver-copper-titanium alloy is 0.06mm; the thickness of the molybdenum substrate is 0.7mm.

[0019] After adopting the above technical solution, the present invention has the following beneficial effects:

[0020] (1) The present invention enhances the surface roughness and improves the connection strength by etching an inverted pyramid pit array on a silicon wafer covered with a silicon dioxide mask.

[0021] (2) The present invention uses a silicon dioxide layer formed by thermally oxidizing a silicon wafer etched with an inverted pyramid pit array and a molybdenum layer deposited on the upper surface of the silicon dioxide layer to block solder from corroding silicon while further improving the connection strength between silicon and molybdenum. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the electrostatic bonding structure of the traditional reverse molding technology;

[0023] Figure 2 A schematic diagram of a welding structure according to a welding method of the present invention;

[0024] Figure 3 TEM image of Example 4;

[0025] Figure 4 This is the EDS diagram of Example 4. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0027] Example 1

[0028] A method for welding a molybdenum field emission array and a molybdenum substrate comprises the following steps:

[0029] S1. Wet etching is used to etch inverted pyramid pits on a silicon wafer; the selected etching solution is a mixed solution of 15% tetramethylammonium hydroxide and 16% isopropanol in a ratio of 1:1, and the etching time is 20 minutes.

[0030] S2. The silicon wafer etched with the inverted pyramid pits is subjected to thermal oxidation treatment by using thermal oxidation technology to form a silicon dioxide layer on the surface of the silicon wafer etched with the inverted pyramid pits. The thermal oxidation treatment temperature is 1000° C., the time is 1 hour, and the oxygen flow rate is 50 sccm.

[0031] S3, using conventional thin film deposition technology to evaporate the molybdenum emitter layer on the silicon dioxide layer, the system vacuum degree is 4×10 -4 Pa, the thickness of the molybdenum emitter layer is 3 μm. The conventional thin film deposition technology of this embodiment uses magnetron sputtering technology.

[0032] S4, stack the molybdenum substrate, silver-copper-titanium alloy sheet, and the silicon wafer with the molybdenum emitter layer deposited in sequence in a sintering furnace for high vacuum sintering with a vacuum degree of 3×10 -3 Pa, the sintering temperature is 840℃, the thickness of the silver-copper-titanium alloy is 0.06mm; the thickness of the molybdenum substrate is 0.4mm.

[0033] Example 2

[0034] A method for welding a molybdenum field emission array and a molybdenum substrate comprises the following steps:

[0035] S1. Wet etching is used to etch inverted pyramid pits on a silicon wafer; the selected etching solution is a mixed solution of 15% tetramethylammonium hydroxide and 16% isopropanol in a ratio of 1:1, and the etching time is 20 minutes.

[0036] S2. The silicon wafer etched with the inverted pyramid pits is subjected to thermal oxidation treatment by using thermal oxidation technology to form a silicon dioxide layer on the surface of the silicon wafer etched with the inverted pyramid pits. The thermal oxidation treatment temperature is 1000° C., the time is 1 hour, and the oxygen flow rate is 50 sccm.

[0037] S3, using conventional thin film deposition technology to evaporate the molybdenum emitter layer on the silicon dioxide layer, the system vacuum degree is 4×10 -4 Pa, the thickness of the Mo emitter layer is 3 μm;

[0038] S4, stack the molybdenum substrate, silver-copper-titanium alloy sheet, and the silicon wafer with the molybdenum emitter layer deposited in sequence in a sintering furnace for high vacuum sintering with a vacuum degree of 3×10 -3 Pa, sintering temperature is 840℃, the thickness of silver-copper-titanium alloy is 0.08mm; the thickness of molybdenum substrate is 0.4mm; its final structure is as follows Figure 2 shown.

[0039] Example 3

[0040] A method for welding a molybdenum field emission array and a molybdenum substrate comprises the following steps:

[0041] S1. Wet etching is used to etch inverted pyramid pits on a silicon wafer; the selected etching solution is a mixed solution of 15% tetramethylammonium hydroxide and 16% isopropanol in a ratio of 1:1, and the etching time is 20 minutes.

[0042] S2. The silicon wafer etched with the inverted pyramid pits is subjected to thermal oxidation treatment by using thermal oxidation technology to form a silicon dioxide layer on the surface of the silicon wafer etched with the inverted pyramid pits. The thermal oxidation treatment temperature is 1000° C., the time is 1 hour, and the oxygen flow rate is 50 sccm.

[0043] S3, using conventional thin film deposition technology to evaporate the molybdenum emitter layer on the silicon dioxide layer, the system vacuum degree is 4×10 -4 Pa, the thickness of the Mo emitter layer is 3 μm;

[0044] S4, stack the molybdenum substrate, silver-copper-titanium alloy sheet, and the silicon wafer with the molybdenum emitter layer deposited in sequence in a sintering furnace for high vacuum sintering with a vacuum degree of 3×10 -3Pa, the sintering temperature is 840℃, the thickness of the silver-copper-titanium alloy is 0.06mm; the thickness of the molybdenum substrate is 0.7mm.

[0045] Example 4

[0046] A method for welding a molybdenum field emission array and a molybdenum substrate comprises the following steps:

[0047] S1. Wet etching is used to etch inverted pyramid pits on a silicon wafer; the selected etching solution is a mixed solution of 15% tetramethylammonium hydroxide and 16% isopropanol in a ratio of 1:1, and the etching time is 20 minutes.

[0048] S2. The silicon wafer etched with the inverted pyramid pits is subjected to thermal oxidation treatment by using thermal oxidation technology to form a silicon dioxide layer on the surface of the silicon wafer etched with the inverted pyramid pits. The thermal oxidation treatment temperature is 1000° C., the time is 1 hour, and the oxygen flow rate is 50 sccm.

[0049] S3, using conventional thin film deposition technology to evaporate the molybdenum emitter layer on the silicon dioxide layer, the system vacuum degree is 4×10 -4 Pa, the thickness of the molybdenum emitter layer is 3 μm.

[0050] S4, stack the molybdenum substrate, silver-copper-titanium alloy sheet, and the silicon wafer with the molybdenum emitter layer deposited in sequence in a sintering furnace for high vacuum sintering with a vacuum degree of 3×10 -3 Pa, the sintering temperature is 840℃, the thickness of the silver-copper-titanium alloy is 0.08mm; the thickness of the molybdenum substrate is 0.7mm.

[0051] Comparative Example

[0052] S1. Wet etching is used to etch inverted pyramid pits on a silicon wafer; the selected etching solution is a mixed solution of 15% tetramethylammonium hydroxide and 16% isopropanol in a ratio of 1:1, and the etching time is 20 minutes.

[0053] S2. The silicon wafer etched with the inverted pyramid pits is subjected to thermal oxidation treatment by using thermal oxidation technology to form a silicon dioxide layer on the surface of the silicon wafer etched with the inverted pyramid pits. The thermal oxidation treatment temperature is 1000° C., the time is 1 hour, and the oxygen flow rate is 50 sccm.

[0054] S3, using conventional thin film deposition technology to evaporate the molybdenum emitter layer on the silicon dioxide layer, the system vacuum degree is 4×10 -4 Pa, the thickness of the Mo emitter layer is 3 μm;

[0055] S4, stack the glass molybdenum substrate and the molybdenum-coated silicon wafer in sequence in an electrostatic bonding device, and perform high vacuum, high voltage, and high temperature electrostatic bonding. The vacuum degree is 3×10 -3Pa, voltage is 800V, temperature is 400℃; the final welding structure is as follows Figure 1 shown.

[0056] When the conventional electrostatic bonding method of the control example 1 is used for connection, the electrodes cannot be brought out and there is no conductivity between the glass substrate and the silicon wafer. However, in the welding method of the present invention, the silicon dioxide layer can block solder erosion and can bring out the electrodes, which greatly improves the application scenarios of field emission and improves efficiency.

[0057] Figure 3 is the TEM image of Example 4; Figure 3 The TEM images given show that the molybdenum field emission array is well connected to the molybdenum substrate without obvious cracks, indicating that welding is feasible and effective;

[0058] Figure 4 is the EDS diagram of Example 4; Figure 4 It can be seen that the contents of Mo and Cu indicate that the solder diffuses into the MoFEA, and the mutual diffusion between the MoFEA and the solder enhances the bonding force between them.

[0059] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for welding a molybdenum field emission array and a molybdenum substrate in a field emission device, characterized in that: First, an inverted pyramid pit array is etched on a silicon wafer covered with a silicon dioxide mask; then the silicon wafer etched with the inverted pyramid pit array is thermally oxidized to form a silicon dioxide layer; then a molybdenum emitter layer is evaporated on the silicon dioxide layer to obtain a molybdenum field emission array, and finally the molybdenum field emission array is welded to the molybdenum substrate.

2. The method according to claim 1, characterized in that: The steps include: S1, etching an inverted pyramid pit array on a silicon wafer covered with a silicon dioxide mask by wet etching; S2, performing thermal oxidation treatment on the silicon wafer having the inverted pyramid pit array to form a silicon dioxide layer on its surface; S3, depositing a molybdenum emitter layer on the silicon dioxide layer to obtain a molybdenum field emission array; S4. Brazing the molybdenum field emission array and the molybdenum substrate.

3. The method according to claim 1, characterized in that The steps include: S1. The solution for wet etching the silicon wafer is a mixed solution, and the etching time is 20 min to 25 min; the mixed solution is prepared by 15% tetramethylammonium hydroxide and 16% isopropanol in a ratio of 1:1; S2, using thermal oxidation technology to perform thermal oxidation treatment on the silicon wafer with the inverted pyramid pit array etched, the thermal oxidation treatment temperature is 1000° C. to 1200° C., preferably 1000° C.; the oxidation time is 0.5 to 1.5 hours, and the oxygen flow rate is 30-60 sccm, preferably 50 sccm; S3, using thin film deposition technology to evaporate the molybdenum emitter layer on the silicon dioxide layer, the system vacuum degree is 4×10 -4 Pa, the thickness of the molybdenum emitter layer is 3-5 μm; S4, stack the molybdenum substrate, the silver-copper-titanium alloy sheet, and the silicon sheet with the molybdenum emitter layer deposited thereon in sequence in a sintering furnace for high vacuum sintering; the vacuum degree is 3×10 -3 Pa, the sintering temperature is 840°C, the thickness of the silver-copper-titanium alloy is 0.06-0.08mm; the thickness of the molybdenum substrate is 0.4-0.8mm.

4. The method according to claim 3, characterized in that In step S4 of the method, the thickness of the silver-copper-titanium alloy is 0.06 mm; the thickness of the molybdenum substrate is 0.7 mm.

5. The method according to claim 3, characterized in that: In step S2, the thermal oxidation treatment temperature is 1000° C., the oxidation time is 1 hour, and the oxygen is 50 sccm; In step S3, a molybdenum emitter layer with a thickness of 3 μm is evaporated on the silicon dioxide layer using conventional thin film deposition technology.

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