Pressure-free step-temperature thermal bonding method

Abstract

A pressure-free step-temperature thermal bonding method includes two steps: optical bonding and pressure-free step-temperature thermal bonding. The surface roughness of materials such as glass is processed and then optically bonded to form two layers of composite materials; the two layers of materials are bonded using a pressure-free step-temperature thermal bonding process; the pressure-free step-temperature thermal bonding process increases the pre-bonding step temperature during the heat treatment stage, so that the gas remaining at the optical bonding interface can be slowly released without pressure without causing optical bonding failure, thereby preventing separation at the interface after heating or dust particles from entering between interfaces. The adverse effects of interface stress and deformation caused by pressure are reduced. The interlayer bonding force of the planar waveguide prepared by the invention can reach 10MPa or more, which is better than the strength of the material used for the planar waveguide, and the thickness of the bonding sub-interface between the interfaces is not more than 13nm.

Description

Technical Field

[0001] The present invention is a non-pressure step-by-step temperature-raising thermal bonding process, and in particular relates to a glass-to-glass thermal bonding process for preparing a planar waveguide laser gain medium, and belongs to the technical field of thermal bonding and solid lasers. Background Art

[0002] Solid-state lasers are widely used in military, medical and scientific research. They are often used in laser radar ranging, laser guidance, laser surgery, holography and other fields. However, a large amount of waste heat is generated during the laser emission process. Excessive heat will limit the laser efficiency and affect the beam quality. Based on the above background, a planar waveguide structure is proposed. Since the planar waveguide has the characteristics of a large cooling area, it can accelerate the heat dissipation and thus increase the power of the laser; in addition, the planar waveguide laser has many unique advantages: high-efficiency operation can be achieved through high-intensity pumping, high beam quality and power scaling along the plane direction can be obtained through waveguide mode selection, and the multi-reflection optical path structure provided can provide high-gain amplification; the planar waveguide has a large aspect ratio and can suppress nonlinear effects.

[0003] Common methods for preparing planar waveguides include ion exchange, ion implantation, and chemical vapor deposition, but these methods have two unavoidable disadvantages. One is that the thickness of the waveguide layer of the obtained planar waveguide is small, about 10nm to 1μm. The second is that the doping concentration of the obtained waveguide layer material is limited. These two points make these methods unsuitable for the preparation of laser gain media. Therefore, bonding is currently the most suitable technology for the preparation of laser gain media.

[0004] The bonding process is widely used in crystal bonding and was first proposed by Lord Rayleigh in 1936. The application of bonding technology to prepare planar optical waveguides is easy to control the interface morphology and waveguide layer thickness, and can combine materials of different qualities. The process and principle are simple and suitable for large-scale production. Common traditional bonding methods include anodic bonding, surface activated low-temperature bonding and thermal bonding. These bonding methods have strict requirements on bonding conditions and need to be completed in a clean room; in terms of equipment, anodic bonding requires corresponding bonding equipment, while surface activated low-temperature bonding often requires complex surface activation equipment and the development of appropriate chemical reagent ratios (EPA Pat. No. 0209173).

[0005] The most suitable bonding method for bonding two pieces of glass is thermal bonding, that is, heating to make the molecules at the connection between the two pieces of glass diffuse and move to form a bond. In traditional thermal bonding, the two pieces of glass are first connected together through an optical bonding process and then heated to improve the quality of the bonding interface. However, a certain amount of gas will remain in the microstructure between the interfaces after optical bonding. During the thermal bonding process, the gas molecules move under the heat, which will form bubbles between the interfaces or cause the optical bonding to fail. It is often necessary to pressurize the materials to stick together (US Pat. No. 5441803). Most thermal bonding processes apply a pressure of 10-500 kg / cm2. As described in patents and articles such as CN. Pat. No. 109942209A, CN. Pat. No. 2789986Y, CN. Pat. No. 1295508, Mukhin, I., (2012). Laser Opt. Tech. Dig. However, the application of pressure is likely to have the unexpected adverse effect of sealing off the gas before it can escape, thereby trapping the gas prematurely in the interface region. When this technology is used on single wafers, the applied pressure can produce microcracks at temperatures that do not allow plastic deformation. If the processing temperature is increased to a level sufficient to prevent microcracks, the plastic deformation of the wafer will destroy the crystal structure. In addition to the mechanical damage that is easily caused to the bonding interface when applied under high-power laser conditions, the pressure can also cause deformation of the bonding interface, which is not conducive to the total reflection of light in the planar waveguide.

[0006] From the above analysis, it can be found that applying pressure during thermal bonding has a great impact on the quality of the planar waveguide interface. This problem is also a key problem to be solved in the process of thermal bonding to prepare planar waveguides. Therefore, a solution that can bond without pressure is needed.

[0007] Therefore, the present invention provides a pressure-free step-by-step temperature rise thermal bonding process, which can effectively solve the above problems. For thermal bonding, temperature and time are the two most important factors. By controlling the temperature rise and fall speed, bonding temperature and time of the bonding heat treatment, the stress of the bonding interface and the quality of the bonding interface can be adjusted. The present invention innovatively adds a pre-bonding step temperature step to slowly release the residual gas at the optical bonding interface, so that the molecules at the connection of the two pieces of glass diffuse and move to form bonds. By controlling the pre-bonding step temperature and time, it is possible to bond the molecules at the bonding interface, and prevent the failure of optical bonding after heating, which leads to separation at the interface or dust particles entering the interface. The bonding interface effect can be achieved without pressure, so that the quality of the bonding interface is good. However, controlling the pre-bonding step temperature range requires a lot of exploratory experiments and data. If the pre-bonding step temperature is too low, the molecular diffusion rate at the glass connection is slow, and a large number of bonds cannot be formed, resulting in voids in the bonding interface; if the bonding pre-bonding step temperature is too high, the optical glue will fail, resulting in bubbles in the bonding interface or even bonding failure. Therefore, it is necessary to select appropriate pre-bonding step temperature and time to achieve good bonding effect. Summary of the invention

[0008] The purpose of the present invention is to solve the shortcomings of the above-mentioned commonly used thermal bonding process, and provide a pressure-free step-temperature thermal bonding method for preparing a glass-to-glass thermal bonding process for a planar waveguide laser gain medium. For preparing a glass planar waveguide with a core layer thickness of 10 μm to 3 mm, the present invention uses a suitable step temperature and time to achieve a pressure-free step-temperature thermal bonding process, which can make the bonding strength of the prepared planar waveguide reach 11.63 MPa, and the thickness of the bonding sub-interface between the interfaces is not more than 13 nm. The bonding interface quality is good, without voids and bubbles.

[0009] The present invention adopts a pressure-free step-temperature thermal bonding process to prepare a planar waveguide. The specific steps include optical bonding and pressure-free step-temperature thermal bonding. Optical bonding refers to the two polished smooth surfaces being tightly fitted together through intermolecular electrostatic attraction. However, in order to form a permanent bond between the bonding interfaces, in addition to forming a sufficiently strong electrostatic force at the bonding interface, it is also necessary to ensure that an oxidation reaction can occur between the bonding interfaces to form an oxidation transition layer, thereby achieving permanent connection of the materials. This is done by heat treatment for bonding, which in the present invention is pressure-free step-temperature thermal bonding.

[0010] Therefore, the present invention mainly includes two aspects: surface processing and optical bonding, and pressure-free step-temperature thermal bonding.

[0011] 1. Surface processing and optical bonding: Cut the materials to be bonded according to the designed size and then use a suitable polishing method for surface processing. The surface roughness of the polished material is controlled between 3nm and 5nm, and the surface shape is controlled between λ / 5 and λ / 10. The surface of the obtained material is tested, and the qualified samples are cleaned and optically bonded.

[0012] 2. Pressure-free step-heating thermal bonding: The optically bonded samples are subjected to pressure-free step-heating thermal bonding in a vacuum annealing furnace, with a relative vacuum degree of -0.1Mpa to -1Mpa. The bonding time-temperature curve used in the pressure-free step-heating thermal bonding is divided into three stages: heating stage (t1-t2), insulation stage (t2-t3), and cooling stage (t3-t4). Different temperatures and heating rates are used in each stage.

[0013] The obtained sample is used as one side of the intermediate layer for surface processing, optical bonding and pressure-free step-temperature thermal bonding; according to the design, the above steps can be repeated to prepare a multi-cladding planar waveguide structure. Due to the limitations of polishing and thinning technology, this technology is mainly aimed at planar waveguides or three-layer glass bonded structures with intermediate waveguide layer thickness ranging from 10μm to 3mm.

[0014] The method is characterized by adding a pre-bonding step temperature step and no pressure is applied during the thermal bonding process, which will not increase the bonding interface stress or cause the interface to deform and the bonding interface quality is good. The innovation of the present invention lies in that by designing and adopting a suitable thermal bonding time-temperature curve, the two layers of materials on the optical bonding can be bonded together through a pressure-free step-temperature thermal bonding process by adding a pre-bonding step temperature step. The planar waveguide bonded by the present invention has advantages in heat dissipation and suppression of nonlinear effects, and is of great significance in the research of new optical devices and new solid-state lasers.

[0015] The advantages of the present invention are as follows: the stress and deformation of the bonding interface can be reduced, mechanical damage can be reduced, and the light transmission quality in the device can be improved by the pressure-free step-temperature thermal bonding process. By increasing the pre-bonding step temperature, the molecules at the bonding interface can be bonded, and the failure of optical bonding after heating can be prevented, resulting in separation at the interface or dust particles entering between the interfaces. The bubbles and voids at the bonding interface are reduced, and the bonding strength and yield rate are improved. In addition, the method adopted by the present invention has low requirements on the operating environment, low cost, simple operation, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of the present invention

[0017] Figure 2 The time-temperature diagram used in the present invention is

[0018] Figure 3 This is a planar waveguide image prepared by Example 1 of the present invention. a is a physical image of a three-layer erbium-ytterbium co-doped phosphate glass planar waveguide, and b is a side micrograph of the planar waveguide.

[0019] Figure 4 This is the EPMA test image of the planar waveguide interface obtained by bonding. Where a is the Yb3+ content image on the scanning path, and b is the test scanning path.

[0020] Figure 5 This is a planar waveguide image prepared by Example 2 of the present invention. a is a real image of a planar waveguide with a core layer of erbium-ytterbium co-doped phosphate glass and upper and lower cladding layers of silicate glass, and b is a side micrograph of the planar waveguide. DETAILED DESCRIPTION

[0021] For the convenience of description and understanding, the Figure 1 , i.e., a flow chart of the present invention, describes in detail a specific implementation mode of the present invention.

[0022] First, the material of designed size is cut. The material is subjected to appropriate coarse grinding, fine grinding and polishing processes. The surface roughness of the polished material is controlled between 3nm and 6nm, and the surface shape is controlled between λ / 5 and λ / 10.

[0023] After the qualified materials are ultrasonically cleaned, wipe the glass surface with a dust-free cloth in a fume hood to ensure that there is no visible dust on the surface under a microscope. Use a white light interferometer to determine the surface matching of the materials to be optically bonded, and determine the two sides with the highest matching degree for optical bonding.

[0024] The optically bonded sample is placed in a vacuum annealing furnace for pressure-free step-by-step thermal bonding, with a relative vacuum degree of -0.1Mpa to -1Mpa. Next, the time-temperature curve of the pressure-free step-by-step thermal bonding needs to be set according to the material used, where the pre-bonding step temperature is in the heating stage. The schematic diagram of the temperature curve used in the present invention is shown in the attached figure. Figure 2 As shown:

[0025] The time-temperature curve of pressure-free step-heating thermal bonding can be divided into three stages:

[0026] 1. Heating stage (t1-t2): In the heating stage, the starting temperature T1 is room temperature, and T2 is set to the pre-bonding step temperature. b Between T1 and αT b (0.3≤α≤0.6), the pre-bonding step temperature holding time is coordinated with T2 and is between 15 hours and 30 hours. The heating rate is between 30℃ / h and 50℃ / h.

[0027] 2. Insulation stage (t2-t3): During the insulation stage, the bonding insulation temperature T is determined based on the lower Tg temperature of the two materials. b , T b =βTg(0.6≤β≤0.8). Insulation time and T b The coordination period is between 15 hours and 45 hours.

[0028] 3. Cooling stage (t3-t4): Multi-stage annealing can be used in the cooling stage, and the cooling rate is between 10℃ / h and 30℃ / h.

[0029] The sample that has undergone pressure-free step-temperature thermal bonding is used as the material surface of one side of the middle layer, and the above-mentioned polishing, testing, optical bonding and pressure-free step-temperature thermal bonding steps are repeated to obtain a planar waveguide of a three-layer composite material.

[0030] Example 1

[0031] The material used for the core layer is erbium-ytterbium co-doped phosphate glass (A), and the material used for the cladding layer is phosphate glass (B), with a Tg temperature of 550°C. The size of the erbium-ytterbium co-doped phosphate glass and the phosphate glass is 20mm×10mm×2mm. After cutting, rough grinding, fine grinding and polishing, the surface roughness reaches 5nm and the surface shape is λ / 5. After ultrasonic cleaning, A and B are wiped in a fume hood, and optical bonding is performed after the surface is free of dust. The optically bonded sample is placed in a vacuum annealing furnace with a relative vacuum degree of -0.1Mpa for pressure-free step-by-step thermal bonding. During the heating stage, the starting temperature is 25°C, and the pre-bonding insulation temperature is set to 200°C. The heating rate is 30°C / h. During the insulation stage, the bonding insulation temperature is 440°C, and the insulation time is 25 hours. During the cooling stage, the cooling rate is 13°C / h. After obtaining the two-layer bonded sample, the core material is polished to the designed thickness of 100μm, and the other cladding is optically bonded again, using the same pressure-free step-by-step thermal bonding process. Figure 3 As shown in FIG. 1 , a three-layer Er-Yb co-doped phosphate glass planar waveguide is finally obtained. The thickness of the bonding sub-interface between the obtained planar waveguide interfaces is no more than 13 nm. Figure 4 -a as shown.

[0032] Example 2

[0033] The core layer is made of Er-Yb co-doped phosphate glass (A), and the cladding is made of silicate glass (B). The lower Tg temperature of the two is 550℃ for phosphate glass. The size of Er-Yb co-doped phosphate glass and silicate glass is 20mm×20mm×4mm. After cutting, rough grinding, fine grinding and polishing, the surface roughness reaches 4.5nm and the surface shape is λ / 6. After ultrasonic cleaning, A and B are wiped in a fume hood, and optical bonding is performed after the surface is free of dust. The optically bonded sample is placed in a vacuum annealing furnace with a relative vacuum degree of -0.3Mpa for pressure-free step-by-step thermal bonding. During the heating stage, the starting temperature is 25℃, and the pre-bonding insulation temperature is set to 220℃. The heating rate is 50℃ / h. During the insulation stage, the bonding insulation temperature is 400℃, and the insulation time is 30 hours. During the cooling stage, the cooling rate is 30℃ / h. After obtaining the two-layer bonded sample, the core material was polished to a thickness of 1 mm, and the other cladding was optically bonded again, using the same pressure-free step-by-step thermal bonding process. Figure 3 As shown in the figure on the left, a planar waveguide is finally obtained, with the core layer being erbium-ytterbium co-doped phosphate glass and the upper and lower cladding layers being silicate glass.

[0034] Example 3

[0035] The core layer is made of erbium-ytterbium co-doped phosphate glass (A), the inner cladding is made of phosphate glass (B), and the outer cladding is made of silicate glass (C). The lowest Tg temperature among the three is 550°C. The size of erbium-ytterbium co-doped phosphate glass and phosphate glass is 20mm×30mm×4mm, and the size of silicate glass is 20mm×30mm×7mm. After cutting, rough grinding, fine grinding and polishing, the surface roughness reaches 6nm and the surface shape is λ / 5. First, bond AB, and then wipe the surface of A and B in a fume hood after ultrasonic cleaning. Optically bond after the surface is free of dust. The optically bonded sample is placed in a vacuum annealing furnace with a relative vacuum degree of -0.5Mpa for pressure-free step-by-step thermal bonding. During the heating stage, the starting temperature is 25°C, and the pre-bonding insulation temperature is set to 200°C. The heating rate is 35°C / h. During the insulation stage, the bonding insulation temperature is 400°C and the insulation time is 25 hours. During the cooling stage, the cooling rate is 13°C / h. After obtaining two layers of bonded samples, the core material of erbium-ytterbium co-doped phosphate glass is polished to 0.01mm, and another inner cladding B and outer cladding C are optically bonded to the core layer A again, and the outer cladding C is optically bonded to the outer layer of the inner cladding B, using the same pressure-free step-by-step thermal bonding process. Finally, a five-layer erbium-ytterbium co-doped phosphate glass planar waveguide is obtained, with the inner cladding being phosphate glass and the outer cladding being silicate glass.

Claims

1. A pressure-free step-by-step thermal bonding method, characterized in that: The method comprises the following steps: Step 1: surface polishing treatment: obtaining the glass to be processed with a surface roughness controlled between 3nm and 5nm and a surface shape controlled between λ / 5 and λ / 10; Step 2, optically bonding the polished surfaces of the two pieces of glass to be processed; Step 3: Heat-treat the two pieces of glass to be processed after optical bonding, which is divided into three stages: The first stage is the heating stage t1-t2, that is, the temperature is raised from the room temperature T1 at the starting time t1 to the pre-bonding insulation temperature T 2， After keeping warm for a while, continue to heat up to the bonding temperature T b ; The second stage is the insulation stage t2-t 3， That is, from time t2 to time t3, the bonding insulation temperature T b Perform heat treatment; The third stage is the cooling stage t3-t 4， That is, heat treatment is performed at a certain cooling rate from time t3 to time t4 until the temperature reaches room temperature; Step 4: Using the sample obtained in step 3 as an intermediate layer, re-performing the surface polishing, optical gluing and pressure-free step-temperature thermal bonding of steps 1 to 3 to obtain a planar waveguide structure with three or more layers; The bonding insulation temperature T b =βTg, 0.7≤β≤0.8, wherein Tg is the Tg temperature of the glass to be processed with a lower Tg temperature, and the pre-bonding insulation temperature T 2＝ αT b , 0.4≤α≤0.

6.

2. The pressure-free step-by-step temperature increase thermal bonding method according to claim 1, characterized in that: The thickness of the intermediate layer is 10 μm to 3 mm.

3. The pressure-free step-by-step thermal bonding method according to claim 1, characterized in that: The heat preservation time of the heating stage is 15-30h.

4. The pressure-free step-by-step temperature increase thermal bonding method according to claim 1, characterized in that: The heating rate in the heating stage is between 30°C / h and 50°C / h, and the cooling rate in the cooling stage is between 10°C / h and 30°C / h.

5. The pressure-free step-by-step temperature increase thermal bonding method according to claim 1, characterized in that: The insulation time of the insulation stage t2-t3 is b The coordination period is between 15 hours and 45 hours.

6. The pressure-free step-by-step thermal bonding method according to any one of claims 1 to 4, characterized in that: Before the step 1, the glass to be processed needs to be cut to meet the sizes required by different requirements.

7. The pressure-free step-by-step thermal bonding method according to any one of claims 1 to 4, characterized in that: The heat treatment adopts a vacuum annealing furnace with a relative vacuum degree between -0.1Mpa and -1Mpa.

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