A bonding method for nano-twinned copper deposition substrate

Abstract

The present invention discloses a bonding method for a nano-twinned copper deposition substrate, comprising pre-treating a ceramic substrate, magnetron sputtering of a Ti layer, preparing an electrostatic spray-assisted magnetron sputtered nano-twinned copper layer using a magnetron sputtering device, and sintering the resulting connection to a GaN power module. The present invention allows for efficient diffusion of highly oriented nano-twinned copper with nano-silver paste at relatively low temperatures, resulting in a more effective bonding strength. Furthermore, sintering can be performed in both air and a protective gas. Compared to conventional DBC bonding methods, the method achieves higher bond strength and aging performance in terms of materials, experimental conditions, and sintering conditions, while significantly reducing the economic cost compared to silver-plated plates.

Description

Technical Field

[0001] The present invention relates to a bonding method for a nano-twinned copper precipitate substrate, in particular to a bonding method for a ceramic substrate based on a nano-twinned copper thin layer and a gallium nitride device, belonging to the technical field of microelectronic packaging. Background Art

[0002] Generally speaking, third-generation semiconductors, represented by gallium nitride (GaN), are widely used in high-end displays, aerospace, 5G communications, and other fields due to their high thermal conductivity, wide bandgap, and excellent radiation resistance. Specifically, GaN-based power chips can withstand temperatures as high as 600°C. During operation, the accumulated heat inside the device can reach nearly 200°C. However, the tin-containing solder used in current welding technology typically operates below 200°C due to its melting point of 232°C. During high-temperature service, Kirkendall voids and severe remelting are prone to occur, causing short circuits in power devices.

[0003] Copper is an excellent conductive material, far superior to other common metals. It also has extremely high thermal conductivity and good mechanical properties. Compared with other precious metals such as gold and silver, copper is relatively cheap and can be used as a raw material for large-area ceramic substrates, which helps reduce the manufacturing cost of electronic equipment and makes copper more cost-effective in electronic packaging. Nano-twinned copper with a specified orientation inherits the excellent mechanical, electrical and thermal properties of traditional randomly oriented polycrystalline copper, while also possessing higher resistance to electromigration and a higher interface diffusion coefficient. This enables nano-twinned copper to perform well in power device packaging, especially in the field of welding substrates and devices.

[0004] Nano silver paste has a series of advantages such as large specific surface area, high diffusion coefficient, and stable chemical properties. It has huge advantages in microelectronic packaging, especially in the packaging of power devices of third-generation semiconductors represented by GaN: First, nano silver paste can be pressurelessly sintered and diffused at a relatively low temperature (below 200°C), and after the sintering process, it achieves various properties close to those of bulk silver; second, it has excellent electrical and thermal conductivity. Compared with traditional lead-free solder paste, nano silver paste can be sintered under nearly the same welding conditions, while meeting higher service temperatures and more reliable service stability. The use of nano silver paste for bonding and packaging substrates and high-power devices has huge application potential.

[0005] Patent publication number CN110760903A discloses a copper thin film material and its electrodeposition preparation method. The electrodeposited copper thin film material's microstructure is composed of a mixture of copper columnar crystals containing nanotwins and nanocrystals. Compared to conventional copper, the introduction of nanotwins enhances the performance of conventional copper materials, resulting in superior mechanical properties, hardness, and conductivity. Furthermore, its deposition rate is faster than that of a fully nanotwinned structure, improving the interconnect performance and service reliability of electronic products while maintaining manufacturing efficiency. It offers low production costs and is fully compatible with microelectronics and MEMS packaging processes. However, in current power electronics packaging, especially in automotive electronics, solder is commonly used to bond bare copper substrates to power modules. However, since the solder used is tin paste, it often experiences failures such as short circuits after prolonged high-temperature aging, damaging the power modules. Furthermore, when bonding nanosilver paste to traditional direct bond copper (DBC) ceramic substrates, the metal layer, consisting of a standard random polycrystalline copper layer, exhibits suboptimal bonding efficiency, prolonged bonding times, and excessive temperatures. During this process, the excessively high temperatures and durations often cause severe electromigration of the silver, resulting in the formation of large voids. These voids, formed during the bonding process, grow larger over time, ultimately leading to cracking of the bond layer. To address these aging issues, silver-plated ceramic substrates have been employed, but these require a silver layer of a certain thickness and quality. A series of requirements such as long bonding time, strict bonding conditions, and the quality and thickness of the silver layer have seriously increased the packaging cost of power devices, greatly hindering the development of the power device and substrate packaging market and industry. Summary of the Invention

[0006] The purpose of the present invention is to provide a bonding method for a nano-twinned copper deposition substrate in order to solve at least one of the above-mentioned technical problems. The bonding method uses nano-silver paste to bond a ceramic substrate prepared by magnetron sputtering to a GaN power module, thereby improving the service life of the packaged module while reducing industrial costs.

[0007] The present invention achieves the above-mentioned object through the following technical solutions: a bonding method of a nano-twinned copper deposition substrate, the bonding method comprising a nano-twinned copper deposition substrate, the nano-twinned copper deposition substrate consisting of a ceramic substrate, a magnetron sputtered Ti layer, an electrostatic spray-assisted magnetron sputtered nano-twinned copper layer, a nano-silver bonding layer and a GaN power module;

[0008] The ceramic substrate is located at the bottom layer of the nano-twinned copper deposition substrate, and the upper surface of the ceramic substrate is sequentially adhered with a magnetron sputtered Ti layer and an electrostatic spray-assisted magnetron sputtered nano-twinned copper layer. A plurality of GaN power modules are arranged in a one-to-one correspondence with the nano-silver bonding layer, and the GaN power modules are connected to the upper surface of the electrostatic spray-assisted magnetron sputtered nano-twinned copper layer through the nano-silver bonding layer.

[0009] The bonding method comprises the following steps:

[0010] S1, pretreatment of the ceramic substrate, cleaning the surface of the ceramic substrate, placing the ceramic substrate in a hydrofluoric acid cleaning solution, heating it in a water bath under an ultrasonic cleaning device, ultrasonically cleaning it after reaching the target temperature, and then cleaning it with deionized water and anhydrous ethanol for later use;

[0011] S2. Magnetron sputtering of Ti layer coating: using a magnetron sputtering device to prepare a Ti layer on the cleaned ceramic substrate to attach a magnetron sputtered Ti layer to the surface of the ceramic substrate;

[0012] S3, electrostatic seeding of nano-twinned copper layer, electrostatic seeding of nano-copper seeds on the prepared Ti layer-coated ceramic substrate, and then using magnetron sputtering equipment to prepare electrostatic spray-assisted magnetron sputtering nano-twinned copper layer;

[0013] S4, GaN power module sintering connection, the ceramic substrate with electrostatic spray assisted magnetron sputtering nano twin copper layer is printed with nano silver paste using screen printing technology, and the formed nano silver bonding layer and GaN power module are pressurelessly sintered under atmosphere to obtain the finished module.

[0014] As a further solution of the present invention: in step S1, the mass fraction of the hydrofluoric acid cleaning solution is 45wt%; and the temperature of the water bath heating is 65°C.

[0015] As a further solution of the present invention: in step S1, the ceramic substrate is ultrasonically cleaned using deionized water and anhydrous ethanol respectively, and the ultrasonic cleaning time is 90 seconds.

[0016] As a further solution of the present invention: in step S2, the magnetron sputtering of the Ti layer coating includes the following steps:

[0017] S21, fixing the ceramic substrate pretreated in step S1 on the conductive base of the sample chamber, and installing a high-purity Ti target with a purity of 99.995% and a high-purity Cu target with a purity of 99.999% on the sputtering port of the magnetron sputtering equipment;

[0018] S22. Use a mechanical pump to perform preliminary vacuum extraction. After 20 minutes, the pressure in the sample chamber reaches 6 Pa. When the actual vacuum degree in the sample chamber reaches the preset pressure, use a molecular pump to extract high vacuum in the sample chamber until the vacuum degree in the sample chamber reaches 9.6×10 -4 Pa, and at the same time, slowly heat the temperature in the sample chamber and maintain it at 35°C;

[0019] S23. Introduce 99.99% pure argon gas into the sample chamber. Start ignition when the pressure reaches 2.5 Pa. After observing that the ignition in the sample chamber is normal and stable for 60 seconds, adjust the argon flow until the pressure in the sample chamber is stable, and automatically rotate the sample stage to start pre-sputtering.

[0020] S24. After 10 minutes of pre-sputtering, observe the interior of the sample chamber. If normal, remove the baffle and start formal sputtering.

[0021] S25. After sputtering for 3 hours, the sputtering was terminated and the argon gas was refilled. The sample chamber was allowed to return to normal temperature and pressure, and the sample was taken out to obtain a 250nm Ti layer. The surface of the ceramic substrate was cleaned with deionized water, dried with argon gas, and placed back into the sample chamber. The target material was replaced with a high-purity copper target with a purity of 99.999%.

[0022] As a further solution of the present invention: when magnetron sputtering Ti, the flow rate of argon gas is 175 sccm; when magnetron sputtering Ti, during pre-sputtering, the pressure in the sample chamber is 0.25 Pa;

[0023] The parameters set during formal sputtering and pre-sputtering are the same: base temperature is 580°C, internal total gas pressure is 0.25Pa, RF power is 105W, and sputtering current is 0.5A.

[0024] As a further solution of the present invention: in step S3, electrostatic seeding of the nano-twinned copper layer includes the following steps:

[0025] S31, fix the ceramic substrate completed in step S2 on the conductive base of the sample chamber, use a mechanical pump to perform preliminary vacuum extraction, and after 20 minutes, the pressure in the sample chamber reaches 6Pa; when the actual vacuum degree in the sample chamber reaches the preset pressure, use a molecular pump to extract high vacuum degree in the sample chamber until the vacuum degree in the sample chamber reaches 9.6×10 -4 Pa, and at the same time, slowly heat the temperature in the sample chamber and maintain it at 35°C;

[0026] S32, the prepared nano-copper powder is mixed with a mixture of 85wt% methanol, 14wt% n-hexane, and 1wt% stabilizer according to the ratio to prepare a nano-copper suspension, and 5ml of the prepared nano-copper suspension is placed in the suspension reagent tank of the electrostatic nozzle;

[0027] S33. Start the regulator to control the outflow rate of the nano-copper suspension to 0.05 ml / min; apply a higher bias voltage through power control to ionize the nano-copper suspension without causing unstable arcing. The ionized charged aerosol will be attracted to the conductive base along the electric field lines, thereby seeding the aerosol with nano-copper powder onto the Ti layer. The whole process lasts for 5 seconds; after the electrostatic seeding is completed, the base is heated to a stable temperature and pretreated for 10 minutes; since the nano-level copper powder has a large specific surface area and extremely high surface activity, it can be well combined with the Ti layer after pretreatment, and at the same time provides active sites for the subsequent magnetron sputtering of highly oriented nano-twin copper.

[0028] As a further solution of the present invention, magnetron sputtering of the nano-twinned copper layer includes the following steps:

[0029] S34. Introduce 99.99% pure argon gas into the sample chamber. Start ignition when the pressure reaches 2.5 Pa. After observing that the ignition in the sample chamber is normal and stable for 60 seconds, adjust the argon flow until the pressure in the chamber is stable, and automatically rotate the sample stage to start pre-sputtering. After 10 minutes of pre-sputtering, observe the interior of the chamber. If it is normal, remove the baffle and start formal sputtering.

[0030] S35. Turn on the base bias power supply and set the parameters during formal sputtering. Since electrostatic seeding pre-constructs Cu atom slots on the Ti layer, the bombarded Cu atoms are sputtered in the slots, thereby reducing the nucleation potential of the twin copper and promoting twin nucleation between the bombarded precipitated Cu atoms and the seeded nano-copper atoms, resulting in continuous layered growth. At the same time, since the base adds negative pressure, in this process: high-energy argon ions are attracted and continuously bombard the Cu layer being formed, thereby enhancing the mobility of the adsorbed Cu atoms. These Cu atoms with high mobility continuously migrate to the plane with the lowest surface energy to form a stable structure. In this process, a stable nano-twin copper layer gradually grows on the Ti layer. The growth rate of the Cu layer is 0.5nm / s. After 6h of sputtering, a 10um nano-twin copper layer is obtained, and the nano-twin copper ceramic substrate is completed. After the sample chamber returns to room temperature and pressure, the ceramic substrate is immediately taken out and cleaned with anhydrous ethanol, and then dried with argon for bonding.

[0031] As a further solution of the present invention: when electrostatically seeding nano-copper seeds, the solute of the suspension used is: 15nm nano-copper powder; the mass ratio of the suspension used is 1:40; the voltage controlled by the power supply is 40kV; and the base temperature during pretreatment is 150°C.

[0032] When the nano-twinned copper layer is formally magnetron sputtered, the base temperature is 600°C; the pressure in the chamber is 0.25Pa; the RF power supply power is 200W; the base bias voltage is -75V; and the sputtering current is 0.5A.

[0033] As a further solution of the present invention: in S4, the bonding of the GaN power module specifically includes the following steps:

[0034] S41, dividing the ceramic substrate of nano-twinned copper prepared by magnetron sputtering in step S3 into 10×10 mm rectangular blocks using a laser, with intervals of 3 to 10 mm between the blocks, and the rectangular blocks are used for bonding with the GaN power module;

[0035] S42. Use a screen printing steel mesh to apply nano silver paste to the designated area, attach the power module, and press it using a tablet press to complete the bonding area.

[0036] S43, placing the module and substrate after patching into an atmosphere furnace for sintering, first performing pre-sintering, and then performing formal sintering to complete pressureless sintering.

[0037] As a further solution of the present invention: the screen printing thickness is 80 μm; the tablet press provides a pressure of 20 g, and the pressure lasts for 5 seconds;

[0038] During pre-sintering, 99.99% argon gas was introduced with a flow rate of 250 sccm, and the temperature was raised from room temperature to 120°C at a rate of 5°C / min. The pre-sintering was carried out for 15 minutes. During the formal sintering, the temperature was raised to 260°C at a rate of 10°C / min, kept at this temperature for 60 minutes, and then naturally cooled to room temperature.

[0039] The beneficial effects of the present invention are: 1) the present invention can efficiently diffuse highly oriented nano-twinned copper and nano-silver paste at a lower temperature, ensuring a more efficient bonding strength in packaging bonding compared to traditional DBC ceramic plates or other bare copper substrates;

[0040] 2) When bonding substrates, the present invention can be sintered in both air and protective gas. Although the performance of samples sintered in air deviates from that sintered in a protective atmosphere, they still have good bonding strength. Compared with the traditional DBC bonding method, it can achieve higher bonding strength and aging performance in terms of materials, experimental conditions, sintering conditions, etc., and at the same time, it has a significant reduction in economic cost compared to silver-plated plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic diagram of a magnetron sputtering device with an electrostatic nozzle device used in the present invention;

[0042] Figure 2FIB slice SEM characterization of nano-twinned copper prepared by the present invention Figure 1 ;

[0043] Figure 3 FIB slice SEM characterization of nano-twinned copper prepared by the present invention Figure 2 ;

[0044] Figure 4 XRD of the nano-twinned copper layer prepared by the present invention;

[0045] Figure 5 Schematic diagram of the bonding module of the present invention;

[0046] Figure 6 This is a cross-sectional SEM image of Example 2 of the present invention;

[0047] Figure 7 This is a cross-sectional SEM image of Example 3 of the present invention;

[0048] Figure 8 This is a cross-sectional SEM image of Example 4 of the present invention;

[0049] Figure 9 This is a cross-sectional SEM image of Example 5 of the present invention;

[0050] Figure: 1. Ceramic substrate; 2. Magnetron sputtered Ti layer; 3. Electrostatic spray-assisted magnetron sputtered nano-twinned copper layer; 4. Nano-silver bonding layer; 5. GaN power module. DETAILED DESCRIPTION

[0051] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0052] Description: Unless otherwise specified, the materials and equipment used in this technical solution should be understood as the materials and equipment commonly used in the industry. Unless otherwise specified, the experimental methods used in this technical solution should be understood as the experimental methods commonly used in the industry. The main equipment used in this technical solution is magnetron sputtering equipment, and its general structure is a common model in the industry, such as Figure 1As shown in the figure, the magnetron sputtering equipment mainly includes an inflation valve, target material, rotating shaft, pre-baffle, main baffle, exhaust valve, mechanical regulating valve, conductive sample stage, and bias power supply. However, the sample chamber is equipped with an electrostatic nozzle, power supply, regulator, and suspension reagent station. The power supply enables the electrostatic nozzle to generate a voltage of 0 to 43 kV. The vertical distance between the electrostatic nozzle and the sample stage is 40 mm, and the regulator is used to control the flow rate of the colloidal suspension device. The modified magnetron sputtering equipment can meet the requirements of seeding copper without interference from foreign impurities. The integrated equipment reduces intermediate steps and enables more efficient experiments.

[0053] Example 1, as Figure 5 As shown, this embodiment provides a bonding method for a nano-twinned copper deposition substrate, including a nano-twinned copper deposition substrate, wherein the nano-twinned copper deposition substrate is composed of a ceramic substrate 1, a magnetron sputtered Ti layer 2, an electrostatic spray-assisted magnetron sputtered nano-twinned copper layer 3, a nano-silver bonding layer 4, and a GaN power module 5;

[0054] A ceramic substrate 1 is located at the bottom layer of a nano-twinned copper deposition substrate. A magnetron sputtered Ti layer 2 and an electrostatic spray-assisted magnetron sputtered nano-twinned copper layer 3 are sequentially attached to the upper surface of the ceramic substrate 1. Several GaN power modules 5 are arranged in a one-to-one correspondence with nano-silver bonding layers 4, and the GaN power modules 5 are connected to the upper surface of the electrostatic spray-assisted magnetron sputtered nano-twinned copper layer 3 via the nano-silver bonding layer 4.

[0055] The bonding method of the nano-twinned copper deposition substrate comprises the following steps:

[0056] S1, pretreatment of the ceramic substrate, cleaning and pretreatment of the surface of the ceramic substrate 1, placing the ceramic substrate 1 in a hydrofluoric acid cleaning solution, heating it in a water bath under an ultrasonic cleaning device, ultrasonically cleaning it after reaching the target temperature, and then cleaning it with deionized water and anhydrous ethanol for later use;

[0057] S2, magnetron sputtering of Ti layer coating, using a magnetron sputtering device to prepare a Ti layer on the cleaned ceramic substrate 1, so as to attach a magnetron sputtered Ti layer 2 to the surface of the ceramic substrate 1;

[0058] S3, electrostatic seeding of nano-twinned copper layer, electrostatic seeding of nano-copper seeds on the prepared Ti layer-coated ceramic substrate 1, and then using magnetron sputtering equipment to prepare electrostatic spray-assisted magnetron sputtering nano-twinned copper layer 3;

[0059] S4. Sintering and connecting the GaN power module. The ceramic substrate 1 with the electrostatic spray-assisted magnetron sputtering nano-twinned copper layer 3 is printed with nano-silver paste using screen printing technology. The formed nano-silver bonding layer 4 and the GaN power module 5 are pressurelessly sintered under atmosphere to obtain a finished module.

[0060] Example 2, as Figures 2 to 6 As shown, a bonding method for a nano-twinned copper deposition substrate, the bonding method specifically includes:

[0061] S1. Pretreatment of ceramic substrates: Clean and pretreat the surface of commonly used ceramic substrates, place the ceramic substrate in a hydrofluoric acid cleaning solution with a mass fraction of 45wt%, heat it in a water bath under an ultrasonic cleaning device, and raise the temperature from room temperature to 65℃ at a rate of 5℃ / min. After reaching the target temperature, perform ultrasonic cleaning at this temperature for 10 minutes and then take it out. Place it in anhydrous ethanol for ultrasonic cleaning for 90 seconds and then take it out. Use an argon air gun to blow it dry and set it aside.

[0062] S2. Sputtering coating:

[0063] (1) Fix the ceramic substrate processed in step S1 on the conductive base of the sample chamber (the bottom of the ceramic substrate is fixed on the conductive base of the sample chamber using conductive glue, and the side of the ceramic substrate is wrapped with conductive glue), and install a high-purity Ti target with a purity of 99.995% and a high-purity Cu target with a purity of 99.999% on the sputtering port;

[0064] (2) Use a mechanical pump to perform preliminary vacuum extraction. After 20 minutes, the pressure in the sample chamber reaches 6 Pa. When the actual vacuum degree in the sample chamber reaches the preset pressure, use a molecular pump to extract high vacuum in the sample chamber until the vacuum degree in the sample chamber reaches 9.6×10 -4 Pa, and at the same time, slowly heat the temperature in the sample chamber and maintain it at 35°C;

[0065] (3) Introduce 99.99% pure argon gas into the chamber at a flow rate of 175 sccm. Start ignition when the pressure reaches 2.5 Pa. After observing that the ignition in the sample chamber is normal and stable for 60 seconds, adjust the argon flow rate until the pressure in the chamber is stable at 0.25 Pa, and automatically rotate the sample stage to start pre-sputtering;

[0066] (4) After 10 minutes of pre-sputtering, observe the interior of the chamber. If everything is normal, remove the baffle and start formal sputtering. The parameters set for formal sputtering and pre-sputtering are the same: base temperature is 580℃, internal total pressure is 0.25Pa, RF power is 105W, and sputtering current is 0.5A.

[0067] (5) After sputtering for 3 hours, the sputtering was terminated and the argon gas was refilled. The sample chamber was allowed to return to normal temperature and pressure, and the sample was taken out to obtain a 250nm Ti layer. The substrate surface was cleaned with deionized water, dried with argon gas, and returned to the sample chamber. The target material was replaced with a high-purity copper target with a purity of 99.999%.

[0068] (6) Electrostatic seeding: Repeat the operations in (1) and (2) to fill the sample chamber with a protective atmosphere. The liquid in the suspension is a nano-copper powder suspension. The nano-copper powder is prepared using a polyol one-step reduction method. The powder size is small and the preparation efficiency is high. Nano-copper powder with a diameter of 15nm can be prepared. The prepared nano-copper powder is mixed with a mixture of 85wt% methanol, 14wt% n-hexane and 1wt% stabilizer in a ratio of 1:40 to prepare a nano-copper suspension. Take 5 ml of the obtained suspension and place it in the suspension reagent chamber of the electrostatic nozzle. Start the regulator to control the outflow rate of the suspension colloid to 0.05 ml / min. The voltage controlled by the power supply is 40 kV. By applying a higher bias voltage, the suspension is ionized without unstable arcing. The ionized charged aerosol will be attracted to the conductive base along the electric field lines, thereby seeding the aerosol with nano-copper powder onto the Ti layer. The whole process lasts for 5 seconds. After the electrostatic seeding is completed, the base is heated to 150 ° C for 10 minutes of pretreatment. Since the nano-level copper powder has a large specific surface area and extremely high surface activity, it can be well combined with the Ti layer after pretreatment, and at the same time provides active sites for the subsequent magnetron sputtering of highly oriented nano-twinned copper.

[0069] (7) Sputtering of nano-twinned copper layer: After (6), repeat the step (3) to start pre-sputtering. After 10 minutes of pre-sputtering, observe the interior of the chamber. If it is normal, remove the baffle and start formal sputtering. During formal sputtering, the base temperature is 600℃, the internal total air pressure is 0.25Pa, the RF power is 200W, the base bias power is turned on, the base bias is set to -75V, and the sputtering current is 0.5A. Since electrostatic seeding pre-constructs Cu atomic slots on the Ti layer, the bombarded Cu atoms are sputtered in the slots, thereby reducing the nucleation potential of the twinned copper and promoting twin nucleation between the bombarded precipitated Cu atoms and the seeded nano-copper atoms, resulting in continuous layered growth. At the same time, due to the negative pressure applied to the base, high-energy argon ions are attracted and continuously bombard the forming Cu layer during this process, thereby enhancing the mobility of the adsorbed Cu atoms. These highly mobile Cu atoms continuously migrate to the plane with the lowest surface energy, forming a stable structure. In this process, a stable nano-twinned copper layer gradually grows on the Ti layer, with a growth rate of 0.5nm / s. After 6 hours of sputtering, a 10μm nano-twinned copper layer is obtained, and the nano-twinned copper ceramic substrate is prepared. After the sample chamber returns to normal temperature and pressure, the substrate is immediately removed and cleaned with anhydrous ethanol. After drying with argon gas, bonding is performed.

[0070] The cross section of the prepared nanotwinned copper layer is shown in Figure 2. Figure 2 and Figure 3 As shown, the XRD characterization of the prepared nano-twinned copper layer is as follows Figure 4 shown.

[0071] S3. Bonding experiment:

[0072] (1) The ceramic substrate of nano-twinned copper prepared in S2 is divided into 10×10 mm rectangular blocks by laser, and the intervals between the blocks are divided into 3 to 10 mm. The rectangular blocks are used for bonding with the GaN power module;

[0073] (2) Use an 80 μm screen printing steel mesh to apply nanosilver paste (particle diameter 35 nm) to the designated area, attach the power module, and use a tablet press to provide a pressure of 20 g for 5 seconds to complete the bonding area;

[0074] (3) Place the completed module and substrate into an atmosphere furnace for sintering. Introduce 99.99% argon gas with a flow rate of 250 sccm. Raise the temperature from room temperature to 120°C at a rate of 5°C / min. Pre-sinter for 15 minutes. Raise the temperature to 260°C at a rate of 10°C / min. Keep warm for 60 minutes and then cool naturally to room temperature to complete pressureless sintering. The schematic diagram of the prepared module is shown in the figure. Figure 5 shown.

[0075] Example 3, as Figure 7 As shown, a bonding method for a nano-twinned copper deposition substrate, the bonding method specifically includes:

[0076] S1. Substrate Pretreatment: Clean and pretreat the surface of a commonly used ceramic substrate. Place the ceramic substrate in a 45wt% hydrofluoric acid cleaning solution and heat it in a water bath under an ultrasonic cleaning device, raising the temperature from room temperature to 65°C at a rate of 5°C / min. After reaching the target temperature, ultrasonically clean the substrate at that temperature for 10 minutes before removing it from the heat source. Ultrasonic clean the substrate in anhydrous ethanol for 90 seconds before removing it from the heat source. Use an argon gas gun to blow dry the substrate and set aside.

[0077] S2. Sputtering coating:

[0078] (1) Fix the ceramic substrate processed in step S1 on the conductive base of the sample chamber, and install a high-purity Ti target with a purity of 99.995% and a high-purity Cu target with a purity of 99.999% on the sputtering port;

[0079] (2) Use a mechanical pump to perform preliminary vacuum extraction. After 20 minutes, the pressure in the sample chamber reaches 6 Pa. When the actual vacuum degree in the sample chamber reaches the preset pressure, use a molecular pump to extract high vacuum in the sample chamber until the vacuum degree in the sample chamber reaches 9.6×10 -4 Pa, and at the same time, slowly heat the temperature in the sample chamber and maintain it at 35°C;

[0080] (3) Introduce 99.99% pure argon gas into the chamber at a flow rate of 175 sccm. Start ignition when the pressure is 2.5 Pa. After observing that the ignition in the sample chamber is normal and stable for 60 seconds, adjust the argon flow rate until the pressure in the chamber is stable at 0.25 Pa, and automatically rotate the sample stage to start pre-sputtering.

[0081] (4) After 10 minutes of pre-sputtering, observe the interior of the chamber. If normal, remove the baffle and start formal sputtering. The parameters set for formal sputtering and pre-sputtering are the same: base temperature is 580℃, internal total pressure is 0.25Pa, RF power is 105W, and sputtering current is 0.5A.

[0082] (5) After 3 hours of sputtering, the sputtering was terminated and the argon gas was refilled. The sample chamber was allowed to return to normal temperature and pressure, and the sample was removed to obtain a 250nm Ti layer. The substrate surface was cleaned with deionized water, dried with argon gas, and returned to the sample chamber. The target material was replaced with a high-purity copper target with a purity of 99.999%.

[0083] (6) Electrostatic seeding: Repeat the operations in (1) and (2) to fill the sample chamber with a protective atmosphere. Add the prepared nano-copper powder to a mixture of 85 wt% methanol, 14 wt% n-hexane, and 1 wt% stabilizer at a ratio of 1:40 to prepare a nano-copper suspension. Place 5 ml of the suspension in the reagent chamber. Start to control the outflow rate of the suspension colloid at 0.05 ml / min and the nozzle voltage at 40 kV. After 5 seconds of electrostatic seeding, heat the base to 150 ° C for 10 minutes of pretreatment.

[0084] (7) Sputtering of nano-twinned copper layer: After (6), repeat the steps of (3) to start pre-sputtering. After 10 minutes of pre-sputtering, observe the interior of the chamber. If it is normal, remove the baffle and start formal sputtering. During formal sputtering, the base temperature is 600℃, the internal total pressure is 0.25Pa, the RF power is 200W, the base bias power is set to -75V, the sputtering current is 0.5A, and the growth rate of the Cu layer is 0.5nm / s. After 6 hours of sputtering, a 10um nano-twinned copper layer is obtained. The nano-twinned copper ceramic substrate is prepared. After the sample chamber returns to normal temperature and pressure, the substrate is immediately taken out and cleaned with anhydrous ethanol. After drying with argon gas, bonding operation is performed.

[0085] S3. Bonding experiment:

[0086] (1) The ceramic substrate of nano-twinned copper prepared in S2 is divided into 10×10 mm rectangular blocks by laser for bonding with the GaN power module;

[0087] (2) Screen printing thickness is 80 μm, apply nano silver paste (particle diameter 35 nm) to the designated area, attach the power module, and use a tablet press to provide 20 g pressure for 5 seconds to complete the bonding area;

[0088] (3) Place the module and substrate after patching into an atmosphere furnace for sintering. Do not introduce protective atmosphere, but introduce air normally. Raise the temperature from room temperature to 120°C at a rate of 5°C / min, pre-sinter for 15 minutes, and then raise the temperature to 260°C at a rate of 10°C / min. Keep warm for 60 minutes and then cool naturally to room temperature to complete pressureless air sintering.

[0089] Example 4, as Figure 8 As shown, a bonding method for a nano-twinned copper deposition substrate, the bonding method specifically includes:

[0090] S1. Pretreatment of substrate:

[0091] The commonly used direct copper plate (DBC) substrate was ultrasonically cleaned in the following order: anhydrous ethanol cleaning for 300 seconds, acetone cleaning for 180 seconds, isopropyl alcohol cleaning for 180 seconds, 22.5wt% dilute nitric acid cleaning for 90 seconds, and anhydrous ethanol cleaning for 120 seconds to remove oil stains and oxidized impurities on the surface of the direct copper plate;

[0092] S2. Bonding experiment:

[0093] (1) The DBC substrate processed in step S1 is divided into 10×10 mm rectangular blocks using a laser for bonding with the GaN power module. Nanosilver paste (particle diameter 35 nm) is applied to the designated area using screen printing with a thickness of 80 μm. The power module is bonded on top and a tablet press is used to apply a pressure of 20 g for 5 seconds to complete the bonding of the bonding area.

[0094] (2) Place the completed module and substrate into an atmosphere furnace for sintering, introduce 99.99% argon gas with a flow rate of 250 sccm, raise the temperature from room temperature to 120°C at a rate of 5°C / min, pre-sinter for 15 minutes, raise the temperature to 260°C at a rate of 10°C / min, keep warm for 60 minutes, and then naturally cool to room temperature to complete pressureless sintering.

[0095] Example 5, as Figure 9 As shown, a bonding method for a nano-twinned copper deposition substrate, the bonding method specifically includes:

[0096] S1. Pretreatment of substrate:

[0097] The commonly used direct copper plate (DBC substrate) was ultrasonically cleaned in the following order: anhydrous ethanol cleaning for 300 s, acetone cleaning for 180 s, isopropyl alcohol cleaning for 180 s, 22.5 wt% dilute nitric acid cleaning for 90 s, and anhydrous ethanol cleaning for 120 s to remove oil stains and oxidized impurities on the surface of the direct copper plate.

[0098] S2. Bonding experiment:

[0099] (1) The DBC substrate processed in step S1 was divided into 10 × 10 mm rectangular blocks using a laser for bonding with the GaN power module. Nanosilver paste (particle diameter 35 nm) was applied to the designated area using screen printing with a thickness of 80 μm. The power module was attached and a tablet press was used to apply a pressure of 20 g for 5 seconds to complete the bonding of the bonding area.

[0100] (2) Place the module and substrate after patching into an atmosphere furnace for sintering. Do not introduce protective atmosphere, but introduce air normally. Raise the temperature from room temperature to 120°C at a rate of 5°C / min, pre-sinter for 15 minutes, and then raise the temperature to 260°C at a rate of 10°C / min. Keep warm for 60 minutes and then cool naturally to room temperature to complete pressureless air sintering.

[0101] The shear strength test was performed on the substrate prepared by bonding in the above embodiment:

[0102] Test method: After the modules sintered without pressure in different atmospheres were aged in air at 300°C for 100 hours, a shear force test was performed at a shear height of 10 μm and a speed of 100.0 μm / s.

[0103] Test results: Example 2 is 25.4 MPa, Example 3 is 19.8 MPa, Example 4 is 17.5 MPa, and Example 5 is 11.1 MPa.

[0104] The porosity test was performed on the substrate prepared by bonding in the above embodiment:

[0105] Test method: Modules pressurelessly sintered in different atmospheres were aged in air at 300°C for 100 hours, then cold-mounted with resin. After polishing with sandpaper and alumina suspension, the interface morphology of the sample joints was observed under a scanning electron microscope, and the porosity was calculated using software.

[0106] Test results: Example 2 is 2.5%, Example 3 is 4.4%, Example 4 is 11.5%, and Example 5 is 28.2%.

[0107] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0108] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for bonding a nano-twinned copper deposition substrate, characterized in that: The nano-twinned copper deposition substrate is composed of a ceramic substrate (1), a magnetron sputtered Ti layer (2), an electrostatic spray-assisted magnetron sputtered nano-twinned copper layer (3), a nano-silver bonding layer (4), and a GaN power module (5); The ceramic substrate (1) is located at the bottom layer of the nano-twinned copper deposition substrate, and the upper plate surface of the ceramic substrate (1) is sequentially attached with a magnetron sputtered Ti layer (2) and an electrostatic spray-assisted magnetron sputtered nano-twinned copper layer (3), and a plurality of GaN power modules (5) are provided in a one-to-one correspondence with the nano-silver bonding layer (4), and the GaN power module (5) is connected to the upper surface of the electrostatic spray-assisted magnetron sputtered nano-twinned copper layer (3) through the nano-silver bonding layer (4); The bonding method of the nano-twinned copper deposition substrate comprises the following steps: S1, pretreatment of the ceramic substrate, cleaning and pretreatment of the surface of the ceramic substrate (1), placing the ceramic substrate (1) in a hydrofluoric acid cleaning solution, heating it in a water bath under an ultrasonic cleaning device, ultrasonically cleaning it after reaching the target temperature, and then cleaning it with deionized water and anhydrous ethanol for later use; S2, magnetron sputtering of a Ti layer coating, using a magnetron sputtering device to prepare a Ti layer on the cleaned ceramic substrate (1), so as to attach a magnetron sputtered Ti layer (2) to the surface of the ceramic substrate (1); S3, electrostatic seeding of nano-twinned copper layer, electrostatic seeding of nano-copper seeds on the prepared Ti layer-coated ceramic substrate (1), and then using magnetron sputtering equipment to prepare electrostatic spray-assisted magnetron sputtering nano-twinned copper layer (3); S4, GaN power module sintering connection, the ceramic substrate (1) with the electrostatic spray assisted magnetron sputtering nano twin copper layer (3) is printed with nano silver paste using screen printing technology, and the formed nano silver bonding layer (4) and the GaN power module (5) are pressurelessly sintered under atmosphere to obtain a finished module.

2. The bonding method according to claim 1, wherein: In S1, the mass fraction of the hydrofluoric acid cleaning solution is 45 wt %; and the water bath heating temperature is 65° C.

3. The bonding method according to claim 2, wherein: In S1, the ceramic substrate (1) is ultrasonically cleaned using deionized water and anhydrous ethanol, respectively, and the ultrasonic cleaning time is 90 seconds.

4. The bonding method according to claim 1, wherein: In S2, the magnetron sputtering of the Ti layer coating comprises the following steps: S21, fixing the ceramic substrate (1) pre-treated in step S1 on the conductive base of the sample chamber, and installing a high-purity Ti target with a purity of 99.995% and a high-purity Cu target with a purity of 99.999% on the sputtering port of the magnetron sputtering equipment; S22. Use a mechanical pump to perform preliminary vacuum extraction. After 20 minutes, the pressure in the sample chamber reaches 6 Pa. When the actual vacuum degree in the sample chamber reaches the preset pressure, use a molecular pump to extract high vacuum in the sample chamber until the vacuum degree in the sample chamber reaches 9.6×10 -4 Pa, while heating the sample chamber to maintain the temperature at 35°C; S23. Introduce 99.99% pure argon gas into the sample chamber. Start ignition when the pressure reaches 2.5 Pa. After observing that the ignition in the sample chamber is normal and stable for 60 seconds, adjust the argon flow until the pressure in the sample chamber is stable, and automatically rotate the sample stage to start pre-sputtering. S24. After 10 minutes of pre-sputtering, observe the interior of the sample chamber. If normal, remove the baffle and start formal sputtering. S25. After sputtering for 3 hours, the sputtering is terminated and the argon gas is refilled. The sample chamber is allowed to return to normal temperature and pressure. The sample is taken out to obtain a 250nm Ti layer. The surface of the ceramic substrate (1) is cleaned with deionized water, dried with argon gas, and returned to the sample chamber. The target material is replaced with a high-purity copper target with a purity of 99.999%.

5. The bonding method according to claim 4, wherein: When magnetron sputtering Ti, the flow rate of argon gas is 175 sccm; when magnetron sputtering Ti, the pressure in the sample chamber during pre-sputtering is 0.25 Pa; The parameters set during formal sputtering and pre-sputtering are the same: base temperature is 580°C, internal total gas pressure is 0.25Pa, RF power is 105W, and sputtering current is 0.5A.

6. The bonding method according to claim 5, wherein: In S3, the electrostatic seeding of the nano-twinned copper layer includes the following steps: S31, fix the ceramic substrate (1) completed in step S2 on the conductive base of the sample chamber, use a mechanical pump to perform preliminary vacuum extraction, and after 20 minutes, the pressure in the sample chamber reaches 6Pa. When the actual vacuum degree in the sample chamber reaches the preset pressure, use a molecular pump to extract the high vacuum degree in the sample chamber until the vacuum degree in the sample chamber reaches 9.6×10 -4 Pa, while heating the sample chamber to maintain the temperature at 35°C; S32, the prepared nano-copper powder is mixed with a mixture of 85wt% methanol, 14wt% n-hexane, and 1wt% stabilizer according to the ratio to prepare a nano-copper suspension, and 5ml of the prepared nano-copper suspension is placed in the suspension reagent tank of the electrostatic nozzle; S33. Start the regulator to control the outflow rate of the nano-copper suspension to 0.05 ml / min; apply bias voltage through power control to ionize the nano-copper suspension without causing unstable arcing. The ionized charged aerosol will be attracted to the conductive base along the electric field lines, thereby seeding the aerosol with nano-copper powder onto the Ti layer. The whole process lasts for 5 seconds; after the electrostatic seeding is completed, the base is heated to a stable temperature and pretreated for 10 minutes; due to the specific surface area and surface activity of nano-level copper powder, it can be combined with the Ti layer after pretreatment, and at the same time provide active sites for the subsequent magnetron sputtering of highly oriented nano-twin copper.

7. The bonding method according to claim 6, wherein: The magnetron sputtering of the nano-twinned copper layer comprises the following steps: S34. Introduce 99.99% pure argon gas into the sample chamber. Start ignition when the pressure reaches 2.5 Pa. After observing that the ignition in the sample chamber is normal and stable for 60 seconds, adjust the argon flow until the pressure in the sample chamber is stable. Then rotate the sample stage automatically and start pre-sputtering. After 10 minutes of pre-sputtering, observe the interior of the sample chamber. If it is normal, remove the baffle and start formal sputtering. S35. Turn on the base bias power supply and set the parameters during the formal sputtering. Since electrostatic seeding pre-constructs Cu atom slots on the Ti layer, the bombarded Cu atoms are sputtered in the slots, thereby reducing the nucleation potential of the twin copper and promoting twin nucleation between the bombarded precipitated Cu atoms and the seeded nano-copper atoms, resulting in continuous layered growth. At the same time, since the base adds negative pressure, in this process: high-energy argon ions are attracted and continuously bombard the Cu layer being formed, thereby enhancing the mobility of the adsorbed Cu atoms. These Cu atoms with high mobility continuously migrate to the plane with the lowest surface energy to form a stable structure. In this process, a stable nano-twin copper layer gradually grows on the Ti layer. The growth rate of the Cu layer is 0.5nm / s. After 6h of sputtering, a 10um nano-twin copper layer is obtained, and the nano-twin copper ceramic substrate is prepared. After the sample chamber returns to normal temperature and pressure, take out the ceramic substrate (1), clean it with anhydrous ethanol, blow it dry with argon gas, and then perform bonding operations.

8. The bonding method according to claim 7, wherein: When electrostatic seeding of nano-copper seeds, the solute of the suspension used is: 15nm nano-copper powder; the mass ratio of the suspension used is 1:40; the voltage controlled by the power supply is 40kV; the base temperature during pretreatment is 150℃; When the nano-twinned copper layer is formally magnetron sputtered, the base temperature is 600°C; the pressure in the chamber is 0.25Pa; the RF power is 200W; and the base bias voltage is -75V. The sputtering current was 0.5A.

9. The bonding method according to claim 1, wherein: In said S4, the bonding of the GaN power module (5) specifically includes the following steps: S41, dividing the nano-twinned copper ceramic substrate (1) prepared by magnetron sputtering in step S3 into 10×10 mm rectangular blocks using a laser, with intervals of 3 to 10 mm between the blocks, and the rectangular blocks are used for bonding with the GaN power module (5); S42. Use a screen printing steel mesh to apply nano silver paste to the designated area, attach the power module, and press it using a tablet press to complete the bonding area. S43, placing the module and substrate after patching into an atmosphere furnace for sintering, first performing pre-sintering, and then performing formal sintering to complete pressureless sintering.

10. The bonding method according to claim 9, wherein: The screen printing thickness is 80 μm; the tablet press provides a pressure of 20 g, and the pressure lasts for 5 seconds; During pre-sintering, 99.99% argon gas was introduced with a flow rate of 250 sccm, and the temperature was raised from room temperature to 120°C at a rate of 5°C / min. The pre-sintering was carried out for 15 minutes. During the formal sintering, the temperature was raised to 260°C at a rate of 10°C / min, kept at this temperature for 60 minutes, and then naturally cooled to room temperature.

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