GaAs photoelectric cathode assembly based on separated hot-pressing bonding and preparation method thereof

Abstract

The invention discloses a GaAs photoelectric cathode assembly based on separated hot-pressing bonding and a preparation method of the GaAs photoelectric cathode assembly. The assembly is composed of a GaAs epitaxial wafer and light window glass, wherein the light window glass is formed by compounding low-melting-point glass and anti-halation light window glass through a hydrophilic bonding process; precise assembly is achieved through a specially-made separated hot-pressing bonding mold, the mold comprises a hot-pressing graphite base, an epitaxial wafer graphite limiting seat, a light window glass graphite limiting ring and other components, and assembly separated positioning is achieved in cooperation with a spring supporting system. According to the preparation method, the hot pressing temperature of 610-670 DEG C and the vacuum environment of 5 * 10 <-6 > Pa are adopted, and reliable bonding of the light window glass and the GaAs epitaxial wafer is achieved through staged heating degassing and pressure control. According to the invention, the damage of high temperature to GaAs material in the traditional process is effectively avoided, the composite structure of the light window glass improves the anti-halation performance, the separated design of the mold ensures the accurate alignment of the assembly, and the yield is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of vacuum semiconductor, and particularly relates to a GaAs photocathode assembly based on separated thermal compression bonding and a preparation method thereof. Background Art

[0002] In recent years, third-generation low-light-level image intensifiers featuring negative electron affinity GaAs photocathodes have been widely used in the low-light-level night vision field and developed rapidly due to their high sensitivity, high resolution, and low noise. Among them, the photocathode is the core component of the low-light-level image intensifier, and the quality of the photocathode directly affects the sensitivity of the device and the detection ability of weak light signals. Therefore, it is crucial to develop GaAs photocathodes with low defects and high flatness.

[0003] Thermal compression bonding technology is a key process technology in the preparation of GaAs photocathodes, which realizes the transfer of the photocathode epitaxial material to the optical window glass substrate. First, the flatness and warpage of the GaAs epitaxial wafer and the optical window glass surface have a great impact on the quality of the thermal compression bonding interface, easily causing high stress and many defects in the thermal compression assembly, thereby affecting the sensitivity of the GaAs photocathode and the imaging quality of the image intensifier. Second, it is required that the GaAs epitaxial wafer and the optical window glass be firmly bonded without falling off and without bubbles, have good chemical stability, be able to withstand chemical corrosion during substrate thinning, and have good thermal stability, be able to withstand high-temperature baking during the degassing process of the whole tube.

[0004] During the thermal compression bonding process, too high a temperature will cause the lattice quality of the photocathode material to decline, reduce the generation and transport ability of photoelectrons in the photocathode material, and ultimately result in low sensitivity of the GaAs photocathode; too high a pressure will damage the bonding interface of the thermal compression assembly, generate thermal stress, thereby leading to poor quality of the thermal compression bonding interface, and ultimately affecting the imaging quality of the image intensifier; while too low a temperature and pressure will cause the thermal compression assembly to be poorly bonded, resulting in the photocathode material falling off or obvious pinholes during the subsequent substrate thinning process, thereby affecting the quality of the photocathode. Summary of the Invention

[0005] The purpose of the present invention is to provide a GaAs photocathode assembly based on separated thermal compression bonding and a preparation method thereof, which reduces thermal stress and improves the quality of the bonding interface, thereby improving the imaging quality of the image intensifier.

[0006] To achieve the purpose of the present invention, on the one hand, the present invention provides a GaAs photocathode assembly based on separated thermal compression bonding, including a GaAs epitaxial wafer and an optical window glass;

[0007] The GaAs epitaxial wafer (1) is used for generating and emitting electrons when the GaAs photocathode is irradiated by light;

[0008] The light window glass (2) is used for light to pass through the GaAs photocathode, thereby exciting the GaAs epitaxial wafer to generate electrons. The split hot-pressing bonding mold separates the GaAs epitaxial wafer and the light window glass from each other, and then applies pressure to bond the light window glass and the GaAs epitaxial wafer to obtain the GaAs photocathode assembly.

[0009] The light window glass includes a low-melting-point glass and an anti-halation light window glass. The low-melting-point glass and the anti-halation light window glass are bonded through a hydrophilic bonding process to obtain the light window glass.

[0010] The split hot-pressing bonding mold includes a hot-pressing graphite base, an epitaxial wafer graphite limiting seat, a light window glass graphite limiting ring, a graphite pressing block, a fixed support rod, and a spring;

[0011] The hot-pressing graphite base is placed on the table, and there are holes on its periphery. The epitaxial wafer graphite limiting seat is placed on the upper surface of the hot-pressing graphite base. The GaAs epitaxial wafer is placed face up in the epitaxial wafer graphite limiting seat. The fixed support rod is fixed in the peripheral holes of the hot-pressing graphite base, and the spring is sleeved on the fixed support rod; the light window glass is placed in the light window glass graphite limiting ring, and its assembly is sleeved on the fixed support rod. The spring is used to support the light window glass graphite limiting ring to separate the GaAs epitaxial wafer from the light window glass; the graphite pressing block presses on the light window glass.

[0012] Further, the melting point of the low-melting-point glass is greater than 400 °C and less than or equal to 550 °C.

[0013] Further, the hot-pressing graphite base is made of electronic-grade graphite, and there are 4 holes on its periphery with a hole diameter of 5 mm and a depth of 10 mm. Its upper surface is a polished high-flatness surface.

[0014] Further, the epitaxial wafer graphite limiting seat is made of electronic-grade graphite, with an outer diameter of 31 mm, an inner diameter of 25 mm, and a thickness of 5 mm.

[0015] Further, the light window glass graphite limiting ring is made of electronic-grade graphite, and there are 4 through holes on its periphery with a hole diameter of 5 mm. The center of the light window glass graphite limiting ring is hollowed out, and its thickness is adapted to the step height of the light window glass.

[0016] Further, the graphite pressing block is made of electronic-grade graphite, and its shape is a cylinder or a cube. The upper surface of the graphite pressing block is flat and is in direct contact with the pressure device press head to apply pressure.

[0017] Further, the fixed support rod has a diameter of 5 mm, a length of 100 mm, and the number is 4 and they have the same shape; the spring is a high-temperature and high-pressure resistant spring, and its inner diameter is greater than 5 mm.

[0018] On the other hand, the present invention also provides a method for preparing a GaAs photocathode component based on separated thermal compression bonding, comprising the following steps:

[0019] Step 1: Treat the low-melting-point glass and the anti-halation window glass with RCA solution or piranha solution to form a hydrophilic surface on their surfaces. Then, at room temperature, bond the low-melting-point glass and the anti-halation window glass with hydrophilic surfaces together and place them in a mold, and then put them into a bonding device for high-temperature annealing. The annealing temperature is 300°C - 400°C to obtain the window glass;

[0020] Step 2: Clean the GaAs epitaxial wafer and the window glass. The cleaning includes rinsing, ultrasonic cleaning, and spin-drying, and then store them in a clean container for standby;

[0021] Step 3: Place the thermal compression graphite base on the tabletop. There are holes around it. Place the epitaxial wafer graphite limiting seat on the upper surface of the thermal compression graphite base. Place the GaAs epitaxial wafer face up in the epitaxial wafer graphite limiting seat. Fix the fixed support rod in the peripheral holes of the thermal compression graphite base, and sleeved the spring on the fixed support rod; Place the window glass into the window glass graphite limiting ring, and sleeve its assembly on the fixed support rod. The spring is used to support the window glass graphite limiting ring, so as to separate the GaAs epitaxial wafer from the window glass; Press the graphite pressing block on the window glass to complete the assembly of the separated thermal compression bonding mold;

[0022] Step 4: Place the assembled separated thermal compression bonding mold into a thermal compression device, evacuate the thermal compression device, and start heating and degassing after the vacuum degree reaches 5×10 -6 Pa;

[0023] Step 5: After heating up to the thermal compression bonding temperature, the thermal compression bonding temperature is 610°C - 670°C, control the pressure device to lower the pressure plate, so that the window glass slowly descends until it contacts the GaAs epitaxial wafer, and apply pressure to bond the two together to complete the thermal compression bonding;

[0024] Step 6: Lift the pressure plate. After the temperature of the thermal compression device drops below 80°C, break the airtightness of the thermal compression device to obtain the thermally compression-bonded GaAs photocathode component.

[0025] Compared with the prior art, the remarkable progress of the present invention lies in: (1) Before hot pressing and bonding, the anti-halation window glass is pre-bonded in the present invention, and a layer of low-melting-point glass is bonded to its stepped surface by a hydrophilic bonding method, so that it can better match with the GaAs epitaxial wafer during hot pressing and bonding, reduce stress release, and obtain a hot pressing and bonding interface quality with high flatness and low stress; (2) Before bonding, the window glass is supported by a spring in the present invention to separate it from the GaAs epitaxial wafer. After heating to the bonding temperature, pressure is applied to make the two contact and bond, effectively baking and degassing the bonding interface of the two, and avoiding phenomena such as bubbles and water marks on the bonded interface.

[0026] To more clearly illustrate the functional characteristics and structural parameters of the present invention, the following further explains in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of this application. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0028] Figure 1 is a schematic diagram of the hot pressing and bonding structure of the present invention;

[0029] Figure 2 is a cross-sectional view of the split hot pressing and bonding mold of the present invention;

[0030] Figure 3 is the hot pressing and bonding temperature change curve of the present invention.

[0031] The reference numerals in the drawings are: 1 - GaAs epitaxial wafer; 2 - window glass; 2a - low-melting-point glass; 2b - anti-halation window glass; 3 - hot pressing graphite base; 4 - epitaxial wafer graphite limit seat; 5 - window glass graphite limit ring; 6 - graphite pressing block; 7 - fixed support rod; 8 - spring. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] A GaAs photocathode component based on split hot pressing and bonding of the present invention, combined with Figure 1 , includes a GaAs epitaxial wafer 1 and a window glass 2;

[0034] The GaAs epitaxial wafer (1) is used to generate and emit electrons when the GaAs photocathode is illuminated.

[0035] The optical window glass (2) is used for light to pass through the GaAs photocathode, thereby exciting the GaAs epitaxial wafer to generate electrons. The split thermocompression bonding mold separates the GaAs epitaxial wafer 1 and the optical window glass 2 from each other, and then applies pressure to make the optical window glass 2 slowly descend until it is bonded to the GaAs epitaxial wafer 1 to obtain the GaAs photocathode assembly.

[0036] The optical window glass 2 includes a low-melting-point glass 2a and an anti-halation optical window glass 2b. The low-melting-point glass 2a and the anti-halation optical window glass 2b are bonded by a hydrophilic bonding process to obtain the optical window glass 2.

[0037] The split thermocompression bonding mold includes a thermocompression graphite base 3, an epitaxial wafer graphite limit seat 4, an optical window glass graphite limit ring 5, a graphite pressing block 6, a fixed support rod 7, and a spring 8.

[0038] Combined Figure 2 , the thermocompression graphite base 3 is placed on the tabletop, and there are holes around it. The epitaxial wafer graphite limit seat 4 is placed on the upper surface of the thermocompression graphite base 3. The GaAs epitaxial wafer 1 is placed face up in the epitaxial wafer graphite limit seat 4. The fixed support rod 7 is fixed in the holes around the thermocompression graphite base 3. The spring 8 is sleeved on the fixed support rod 7. The optical window glass 2 is placed into the optical window glass graphite limit ring 5, and its assembly is sleeved on the fixed support rod 7. The spring 8 is used to support the optical window glass graphite limit ring 5, thereby separating the GaAs epitaxial wafer 1 from the optical window glass 2. The graphite pressing block 6 presses on the optical window glass 2.

[0039] The melting point of the low-melting-point glass 2a should generally be greater than 400 °C and less than or equal to 550 °C.

[0040] The thermocompression graphite base 3 is made of electronic-grade graphite. There are 4 holes around it with a hole diameter of 5 mm and a depth of 10 mm. Its upper surface is a polished high-flatness surface.

[0041] The epitaxial wafer graphite limit seat 4 is made of electronic-grade graphite. Its outer diameter is 31 mm, inner diameter is 25 mm, and thickness is 5 mm.

[0042] The optical window glass graphite limit ring 5 is made of electronic-grade graphite. There are 4 through holes around it with a hole diameter of 5 mm. The center of the optical window glass graphite limit ring 5 is hollowed out, and its thickness is adapted to the step height of the optical window glass 2.

[0043] The graphite briquette 6 is electronic-grade graphite, and its shape is a cylinder or a cube. The upper surface of the graphite briquette 6 is flat and is in direct contact with the pressure head of the pressure device to apply pressure.

[0044] The material of the fixed support rod 7 can be selected from stainless steel, ceramics, quartz, etc. Its diameter is 5 mm, its length is 100 mm, and the number is 4 and the shapes are exactly the same; the spring 8 is a high-temperature and high-pressure resistant spring, and its inner diameter is greater than 5 mm, and the height is variable.

[0045] On the other hand, a preparation method of a GaAs photocathode assembly based on split thermal compression bonding of the present invention includes the following steps:

[0046] Step 1: Treat the low-melting-point glass 2a and the anti-halation window glass 2b with an RCA solution (a mixed solution of ammonia water and hydrogen peroxide) or a piranha solution (a mixed solution of concentrated sulfuric acid and hydrogen peroxide) to form a hydrophilic surface with a relatively high density of hydroxyl -OH on their surfaces. Water molecules in the atmospheric environment are easily adsorbed on this hydrophilic surface. Then, at room temperature, the low-melting-point glass 2a and the anti-halation window glass 2b with hydrophilic surfaces are bonded and placed in a mold. A weak intermolecular force adsorption force will be formed at the interface between the two. Then, it is put into a bonding device for high-temperature annealing, and the annealing temperature is 300°C - 400°C. During the hydrophilic bonding process, since the annealing temperature is relatively low, the low-melting-point glass 2a will not melt, and it can achieve hydrophilic bonding with the anti-halation window glass 2b. The weak intermolecular force between the two interfaces will be transformed into a stronger Si-O-Si covalent bond, and the window glass 2 with a firm bonding interface is obtained.

[0047] Step 2: Clean the GaAs epitaxial wafer 1 and the window glass 2. The cleaning includes rinsing, ultrasonic cleaning, and spin-drying, and then store them in a clean container for standby.

[0048] Step 3: Place the hot-pressed graphite base 3 on the tabletop. There are holes around it. The epitaxial wafer graphite limit seat 4 is placed on the upper surface of the hot-pressed graphite base 3. The GaAs epitaxial wafer 1 is placed face up in the epitaxial wafer graphite limit seat 4. The fixed support rod 7 is fixed in the holes around the hot-pressed graphite base 3. The spring 8 is sleeved on the fixed support rod 7. The window glass 2 is placed in the window glass graphite limit ring 5, and its assembly is sleeved on the fixed support rod 7. The spring 8 is used to support the window glass graphite limit ring 5, so as to separate the GaAs epitaxial wafer 1 from the window glass 2. The graphite briquette 6 is pressed on the window glass 2 to complete the assembly of the split thermal compression bonding mold.

[0049] Step 4: Put the assembled split thermal compression bonding mold into a hot-pressing device, evacuate the hot-pressing device, and wait until the vacuum degree reaches 5×10 -6Start heating and degassing after Pa, and the heating and cooling rate curve is as Figure 3 shown. The heating and cooling rate should be reasonably controlled and should be slow rather than fast;

[0050] Step 5: After heating up to the hot pressing bonding temperature, the hot pressing bonding temperature is 610°C - 670°C. Control the pressure device to lower the pressure plate, so that the optical window glass 2 slowly descends until it contacts the GaAs epitaxial wafer 1, and apply pressure to bond the two to each other. At this time, since the hot pressing bonding temperature is higher than the softening temperature of the low melting point glass 2a, the low melting point glass 2a can melt at this time, so as to form a thin molten dense layer between the GaAs epitaxial wafer 1 and the anti-halation optical window glass 2, making the hot pressing bonding interface more uniform and free of stress lines, and completing the hot pressing bonding;

[0051] Step 6: Lift the pressure plate. After the temperature of the hot pressing equipment drops below 80°C, the hot pressing equipment breaks the air to obtain the hot pressing bonded GaAs photocathode assembly.

[0052] In addition, before the hot pressing bonding assembly, it is necessary to clean the hot pressing bonding mold to ensure the cleanliness of the mold.

[0053] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0054] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A GaAs photocathode assembly based on separate hot-press bonding, characterized in that: It comprises a GaAs epitaxial wafer (1) and a light window glass (2); The GaAs epitaxial wafer (1) is used for the GaAs photocathode to generate and emit electrons when illuminated; The light window glass (2) is used for irradiating light through the GaAs photocathode to stimulate the GaAs epitaxial wafer to generate electrons; The separate hot-pressing bonding mold separates the GaAs epitaxial wafer (1) and the light window glass (2) from each other, and then applies pressure to bond the light window glass (2) and the GaAs epitaxial wafer (1) to each other, thereby obtaining the GaAs photocathode assembly.

2. A GaAs photocathode assembly based on separate thermal compression bonding according to claim 1, characterized in that: The light window glass (2) comprises a low melting point glass (2a) and an anti-halation light window glass (2b); the low melting point glass (2a) and the anti-halation light window glass (2b) are bonded by a hydrophilic bonding process to obtain the light window glass (2).

3. A GaAs photocathode assembly based on separate thermal compression bonding according to claim 1, characterized in that: The separate hot-pressing bonding mold comprises a hot-pressing graphite base (3), an epitaxial wafer graphite limiting seat (4), a window glass graphite limiting ring (5), a graphite pressing block (6), a fixed support rod (7), and a spring (8); The hot-pressed graphite base (3) is placed on a table, and holes are arranged on its periphery; the epitaxial wafer graphite limit seat (4) is placed on the upper surface of the hot-pressed graphite base (3); the GaAs epitaxial wafer (1) is placed in the epitaxial wafer graphite limit seat (4) with its front side facing upward; the fixed support rod (7) is fixed in the peripheral holes of the hot-pressed graphite base (3); the spring (8) is sleeved on the fixed support rod (7); the light window glass (2) is placed in the light window glass graphite limit ring (5), and its assembly is sleeved on the fixed support rod (7); the spring (8) is used to support the light window glass graphite limit ring (5), so as to separate the GaAs epitaxial wafer (1) from the light window glass (2); and the graphite pressing block (6) is pressed on the light window glass (2).

4. A GaAs photocathode assembly based on separate thermal compression bonding according to claim 2, characterized in that: The melting point of the low-melting-point glass (2a) is greater than 400°C and less than or equal to 550°C.

5. A GaAs photocathode assembly based on separate thermal compression bonding according to claim 3, characterized in that: The hot-pressed graphite base (3) is electronic-grade graphite, and is provided with four holes on its periphery, with a hole diameter of 5 mm and a depth of 10 mm, and its upper surface is a polished high-flatness surface.

6. A GaAs photocathode assembly based on separate thermal compression bonding according to claim 3, characterized in that: The epitaxial wafer graphite limit seat (4) is made of electronic grade graphite, with an outer diameter of 31 mm, an inner diameter of 25 mm and a thickness of 5 mm.

7. A GaAs photocathode assembly based on separate thermal compression bonding according to claim 3, characterized in that: The light window glass graphite limiting ring (5) is made of electronic grade graphite and has four through holes on its periphery, with a hole diameter of 5 mm. The center of the light window glass graphite limiting ring (5) is hollowed out, and its thickness is adapted to the step height of the light window glass (2).

8. A GaAs photocathode assembly based on separate thermal compression bonding according to claim 3, characterized in that: The graphite pressing block (6) is electronic grade graphite and is in the shape of a cylinder or a cube. The upper surface of the graphite pressing block (6) is flat and is in direct contact with the pressure head of the pressure device to apply pressure.

9. A GaAs photocathode assembly based on separate thermal compression bonding according to claim 3, characterized in that: The fixed support rod (7) has a diameter of 5 mm and a length of 100 mm, and is 4 in number and has the same shape; the spring (8) is a high temperature and high pressure resistant spring, and has an inner diameter greater than 5 mm.

10. A method for preparing a GaAs photocathode assembly based on separate hot-press bonding according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: using RCA solution or piranha solution to treat low-melting-point glass (2a) and anti-halation window glass (2b) to form a hydrophilic surface on the surface; then, at room temperature, the low-melting-point glass (2a) with the hydrophilic surface and the anti-halation window glass 2b are bonded and loaded into a mold, and then placed in a bonding device for high-temperature annealing, the annealing temperature being 300° C.-400° C., to obtain the light window glass (2); Step 2, cleaning the GaAs epitaxial wafer (1) and the optical window glass (2), wherein the cleaning comprises rinsing, ultrasonic cleaning and drying, and then storing them in a clean container for later use; Step 3, placing the hot-pressed graphite base (3) on a table, with holes arranged on its periphery, the epitaxial wafer graphite limit seat (4) placed on the upper surface of the hot-pressed graphite base (3), the GaAs epitaxial wafer (1) placed in the epitaxial wafer graphite limit seat (4) with its front side facing upward, the fixed support rod (7) fixed in the peripheral holes of the hot-pressed graphite base (3), the spring (8) sleeved on the fixed support rod (7); the light window glass (2) placed in the light window glass graphite limit ring (5), its assembly sleeved on the fixed support rod (7), the spring (8) used to support the light window glass graphite limit ring (5), so as to separate the GaAs epitaxial wafer (1) from the light window glass (2); the graphite pressing block (6) pressed on the light window glass (2), completing the assembly of the separate hot pressing bonding mold; Step 4: Place the assembled separate hot pressing bonding mold into the hot pressing equipment, evacuate the hot pressing equipment, and wait until the vacuum degree reaches 5×10 -6 After Pa, the temperature starts to rise and degassing begins; Step 5, after the temperature is raised to the hot pressing bonding temperature, which is 610° C.-670° C., the pressure device is controlled to lower the pressure plate, so that the light window glass (2) is slowly lowered until it contacts the GaAs epitaxial wafer (1), and pressure is applied to make the two bond to each other, thereby completing the hot pressing bonding; Step 6: lift the pressure plate, wait for the temperature of the hot pressing device to drop below 80° C., break the hot pressing device, and obtain a hot-pressed and bonded GaAs photocathode assembly.

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