A wafer trench high-precision filling method based on airflow assistance

Abstract

The application belongs to the field of electronic packaging, and specifically discloses a wafer groove high-precision filling method based on airflow assistance, which specifically comprises the following steps: filling nanosilver paste into a wafer groove on a substrate by using ink direct writing technology, and simultaneously cooperating with airflow assistance filling technology to make the nanosilver paste uniformly spread in the wafer groove; laser sintering the filling material by using a gradient sintering process; repeating the above steps according to the filling times until the filling is completed, and finally performing high-temperature laser sintering at 330 DEG C to 380 DEG C to optimize the temperature resistance of the nanosilver paste. The application can assist the nanosilver paste to flow in the wafer groove, make it more uniformly distributed and avoid the generation of holes in the infiltration process, while filling the nanosilver paste, and simultaneously cooperate with the gradient sintering process, so that the solidification efficiency is improved while the wafer is prevented from being damaged, and the material organization after sintering is more uniform.

Description

Technical Field

[0001] This application belongs to the field of electronic packaging, and more specifically, relates to a high-precision filling method for wafer trenches based on airflow assistance. Background Technology

[0002] With the continuous advancement of integrated circuit technology, chip integration is constantly increasing, and 3D packaging has become the mainstream solution. During wafer-level bonding, wafer thinning leads to heat accumulation, and the stacking of multiple chips increases the total power consumption per unit area, generating more heat, yet there is no effective heat dissipation channel. To reduce residual stress generated during wafer thinning, improve wafer heat dissipation capacity, and avoid hot spots, developing a thermally conductive filler with a coefficient of thermal expansion similar to silicon-based materials to fill the wafer trenches is a simple and effective method. Currently, high-density plasma-enhanced chemical vapor deposition (PECVD) is commonly used to fill wafer trenches; however, this method is inefficient, costly, and has strict environmental requirements, hindering its development in wafer trench filling applications. Therefore, an alternative filling solution is urgently needed.

[0003] Due to the small particle size of silver particles and their excellent electrical and thermal conductivity, nano-silver paste has become an important alternative to traditional encapsulation materials. However, the high solids content and low viscosity of traditional nano-silver paste cannot be simultaneously satisfied, which can easily lead to defects such as voids and cracks when filling micro-grooves, hindering the improvement of filling efficiency. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a high-precision wafer trench filling method based on airflow assistance, aiming to solve the problem of voids and cracks easily generated when filling micro trenches with nano-silver paste.

[0005] This application provides a high-precision wafer trench filling method based on airflow assistance, specifically as follows: S1 uses ink direct writing technology to fill the wafer trenches on the substrate with nano silver paste, and at the same time, it uses airflow-assisted filling technology to make the nano silver paste spread evenly in the wafer trenches. S2 uses a gradient sintering process to laser sinter the filler material. The sintering power is selected according to the number of filler layers to ensure that the sintering temperature of the bottom layer is 80℃~100℃, the sintering temperature difference between adjacent layers is 10℃~30℃, and the sintering temperature of the top layer does not exceed 150℃. S3 repeats steps S1-S2 according to the number of filling cycles until the filling is completed. Finally, high-temperature laser sintering is performed at 330℃~380℃ to optimize the temperature resistance of the nano silver paste.

[0006] Compared with the prior art, the above-described technical solutions conceived in this application, by combining the filling of nano-silver paste with airflow for auxiliary filling, can assist the nano-silver paste to flow in the wafer trenches, making its distribution more uniform and avoiding the generation of pores during the penetration process. At the same time, by combining with the gradient sintering process, it can improve the curing efficiency while avoiding wafer damage, resulting in a more uniform material structure after sintering.

[0007] As a further preferred embodiment, in step S1, in the ink direct writing technology, the extrusion pressure of the nano silver paste is 100kPa to 200kPa, the distance between the extrusion needle and the substrate is 0mm to 0.5mm, and the substrate moving speed is 50mm / s to 200mm / s.

[0008] As a further preferred embodiment, in the airflow-assisted filling technology, the airflow nozzle is tilted and the angle between it and the extrusion needle of the ink direct writing technology is less than 30°, and the airflow ejected by the airflow nozzle flows in the opposite direction to the moving direction of the substrate in the horizontal direction.

[0009] As a further preferred embodiment, in the airflow-assisted filling technology, the airflow nozzle is located above the extrusion needle of the ink direct writing technology, and the vertical distance between the end of the airflow nozzle and the end of the extrusion needle is 5mm to 8mm, and the airflow pressure of the airflow nozzle is 200kPa to 500kPa.

[0010] As a further preferred embodiment, in step S1, the wafer trench is pretreated before filling, thereby activating the surface of the wafer trench.

[0011] As a further preferred method, the wafer trenches are pretreated using a plasma surface activation method.

[0012] As a further preferred embodiment, in step S1, a modified silver nanoparticle paste is filled into the wafer trench. The modified silver nanoparticle paste is prepared by mixing a dispersant with small-sized silver nanoparticles to obtain a precursor silver nanoparticle paste, and then mixing the precursor silver nanoparticle paste with a conventional silver nanoparticle paste and adding a strongly polar solvent to obtain a modified silver nanoparticle paste. The small-sized silver nanoparticles have a particle size of 50 nm to 100 nm, and the conventional silver nanoparticle paste has a particle size of 0.5 μm to 1 μm.

[0013] As a further preferred embodiment, the mass ratio of small-sized silver nanoparticles to traditional silver nanoparticles in the modified silver nanoparticle paste is 1:10 to 1:30.

[0014] As a further preferred embodiment, the dispersant includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and sodium dodecyl sulfate, and the mass ratio of the dispersant to the small-sized silver nanoparticles is 1:0.5 to 1:2. The strong polar solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylformamide, and the amount of the strong polar solvent added is 5% to 10% of the mass of the conventional silver nanoparticle paste.

[0015] As a further preferred option, the method for determining the number of filling operations in step S3 is as follows: When the aspect ratio of the wafer trench is less than 1, the filling number is 2 times; When the aspect ratio of the wafer trench is 1 to 2, the filling number is 4 times; When the aspect ratio of the wafer trench is greater than 2, the wafer trench is filled and sintered in layers, with the aspect ratio of each trench being less than 2 and the filling number of each trench being 2 to 4 times.

[0016] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages: 1. This application combines the filling of nano-silver paste with airflow-assisted filling technology, which can assist the nano-silver paste to flow in the wafer trench, making its distribution more uniform and avoiding the formation of pores during the penetration process. This is conducive to the nano-silver paste filling the entire wafer trench. At the same time, combined with the gradient sintering process, it can avoid wafer damage and avoid excessive temperature causing the surface solvent to dry too quickly and the internal solvent to overflow and cause bulging. This results in a more uniform material structure and higher curing quality after sintering. 2. In particular, the present application pre-treats the wafer trenches before filling, which can increase the surface energy of the wafer trenches to increase the adhesion between the nano silver paste and the wafer trenches, thereby alleviating the interlayer splitting phenomenon caused by insufficient adhesion during the silver paste curing process. 3. Meanwhile, this application uses dual-modal silver nanoparticles to prepare modified silver nanoparticle paste, which can improve the density of the silver nanoparticle paste after curing. The surface of the silver nanoparticles is modified by using a dispersant, which can enhance its dispersibility and stability. The flowability of the silver nanoparticle paste is optimized by using a strong polar solvent, thereby further improving the fluidity and uniformity of the silver nanoparticle paste in the wafer trench and avoiding the formation of pores during the penetration process. Attached Figure Description

[0017] Figure 1 This is a flowchart of a high-precision wafer trench filling process based on airflow-assisted materials provided in an embodiment of this application; Figure 2 This is a high-precision filling process diagram of wafer trenches based on airflow-assisted materials provided in the embodiments of this application; Figure 3 This is a cross-sectional view of the wafer trench and laser gradient curing in the high-precision wafer trench filling method based on airflow-assisted materials provided in the embodiments of this application; Figure 4 These are scanning electron microscope images (×40000x magnification) of the modified silver nanoparticle paste and the traditional silver nanoparticle paste prepared in Example 1 of this application after curing, where a is the traditional silver nanoparticle paste and b is the modified silver nanoparticle paste; Figure 5 These are scanning electron microscope images of the wafer trenches after filling in Embodiment 1 and Comparative Example 1 of this application, where a is Comparative Example 1 and b is Embodiment 1.

[0018] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-Substrate, 11-Wafer trench, 12-Substrate, 13-Device, 2-Extrusion needle, 3-Airflow nozzle. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] like Figure 1 As shown, this application provides a high-precision wafer trench filling method based on airflow assistance, specifically: S1 sets the initial parameters and number of filling processes based on the specific shape and size of the wafer trench 11. It uses ink direct writing technology to fill the wafer trench 11 on the substrate 1 with nano silver paste. At the same time, it uses airflow-assisted filling technology to make the nano silver paste spread evenly in the wafer trench 11. Specifically, the airflow-assisted filling technology is to set an airflow nozzle 3 next to the extrusion needle 2 and use the airflow sprayed by the airflow nozzle 3 to make the silver paste spread evenly. S2 employs a gradient sintering process to laser-sinter the filler material to evaporate the solvent in the nano-silver paste. The sintering power is selected based on the number of filler layers to ensure that the sintering temperature of the bottom layer is 80℃~100℃, thus avoiding damage to the wafer substrate 1 due to excessively high sintering temperatures. The sintering temperature difference between adjacent layers is 10℃~30℃, and the sintering temperature of the top layer does not exceed 150℃ to prevent bulging caused by excessively rapid solvent evaporation on the surface of the nano-silver paste and overflow of internal solvent during the evaporation process. This ensures a stable curing process and guarantees curing quality. S3 repeats steps S1-S2 according to the number of filling cycles until the filling is completed. Finally, high-temperature laser sintering is performed at 330℃~380℃ to completely solidify the nano-silver paste, thereby optimizing the temperature resistance of the nano-silver paste.

[0021] This application combines the filling of nano-silver paste with airflow-assisted filling technology, which assists the nano-silver paste in flowing within the wafer trench 11, making its flow smoother and its distribution more uniform. Simultaneously, the airflow can drive the nano-silver paste at the needle tip towards the bottom of the wafer trench 11, preventing the formation of bubbles or pores in the nano-silver paste during the filling process due to excessive viscosity and surface tension. This facilitates the nano-silver paste filling the entire wafer trench 11, effectively solving the problem that traditional nano-silver paste cannot simultaneously meet the requirements of high solids content and low viscosity, which easily leads to voids and cracks. Furthermore, when a conical needle is used in the nano-silver paste extrusion process, the airflow-assisted filling technology can also prevent the nano-silver paste from flowing to the outer surface of the needle through wetting when printing is paused, thus avoiding difficulties in continuous printing.

[0022] Meanwhile, this application, combined with a gradient sintering process, can achieve precise selective local sintering, reduce the heat-affected zone, and lower the thermal impact on the wafer substrate. Low-power curing is selected at the bottom of the wafer trench 11 to ensure that the sintering temperature is between 80℃ and 100℃, avoiding hot spots during sintering and causing wafer damage. Higher-power curing is selected in areas far from the bottom of the trench, and the sintering temperature of the top layer is ensured not to exceed 150℃. This can improve curing efficiency while maintaining a low overall power, evaporating most of the solvent at a lower temperature. Finally, a high-power laser is used for high-temperature laser sintering to complete the filling curing process, making the material structure more uniform after sintering and optimizing the temperature resistance of the nano-silver paste. This improves curing efficiency while avoiding wafer damage, resulting in a more uniform material structure after sintering.

[0023] Furthermore, in step S1, in the ink direct writing technology, the extrusion pressure of the nano silver paste is 100kPa to 200kPa, the distance between the extrusion needle 2 and the substrate 1 is 0mm to 0.5mm, and the moving speed of the substrate 1 is 50mm / s to 200mm / s, so that the nano silver paste fills the entire channel as much as possible during the extrusion process and does not overflow onto the wafer surface.

[0024] Furthermore, in the airflow-assisted filling technology, the airflow nozzle 3 is located above the extrusion needle 2, and the vertical distance between the end of the airflow nozzle 3 and the end of the extrusion needle 2 is 5mm to 8mm. The airflow nozzle 3 is tilted, and the angle between it and the extrusion needle 2 is less than 30°. If the distance between the end of the airflow nozzle 3 and the end of the extrusion needle 2 is too small, it will easily lead to excessive airflow concentration, causing nano-silver paste to splash. If the distance is too large, it will be difficult to ensure the effect of assisting the flow of nano-silver paste. The airflow with a certain tilt angle is more likely to promote the flow of the paste. However, if the tilt angle is too large, it can only act on the surface of the nano-silver paste and it is difficult to eliminate internal pore defects. Simultaneously, the airflow ejected by the airflow nozzle 3 flows in the opposite direction to the movement of the substrate 1 in the horizontal direction, causing the nano-silver paste to flow away from the substrate 1. This ensures a more uniform nano-silver paste in the wafer trench 11. Since the substrate 1 moves during the printing and filling process, the airflow ejected by the airflow nozzle 3, flowing in the opposite direction to the substrate 1 in the horizontal direction, allows the airflow to directly sweep away the freshly extruded nano-silver paste. As the nano-silver paste loses shear force and its viscosity increases, increasing the airflow disrupts its surface tension, making it easier to contact the inner wall of the trench and reducing internal pores. The airflow nozzle 3 is circular, and its opening diameter is adjusted according to the trench width. The preferred airflow component is dry nitrogen. The airflow pressure of the airflow nozzle 3 is 200 kPa to 500 kPa. If the airflow pressure is too high, it can easily cause the nano-silver paste to splash or overflow, causing contamination; if the airflow pressure is too low, the effect is not significant.

[0025] Furthermore, in step S1, the wafer trench 11 is pretreated before filling, thereby activating the surface of the wafer trench 11, increasing the surface energy of the wafer trench 11 to increase the adhesion between the nano silver paste and the wafer trench 11, thereby alleviating the interlayer splitting phenomenon caused by insufficient adhesion during the silver paste curing process.

[0026] Preferably, the wafer trench 11 is pretreated by plasma surface activation. There are no restrictions on the plasma treatment efficiency and treatment time. Preferably, the plasma treatment power is 100W and the treatment time is 2min to 5min.

[0027] Further, in step S1, modified nano-silver paste is filled into the wafer trench 11. The modified nano-silver paste is prepared by mixing a dispersant with small-sized nano-silver particles and mixing them evenly using ultrasonic and mechanical stirring to obtain a precursor nano-silver paste. This allows the dispersant to uniformly modify the surface of the small-sized nano-silver particles or to have a steric hindrance effect, thereby reducing the agglomeration of the nano-silver particles and optimizing their dispersion effect. Then, the precursor nano-silver paste is mixed with traditional nano-silver paste and a strong polar solvent is added. The mixture is then uniformly mixed using a high-speed ball milling dispersion process to obtain the modified nano-silver paste. The particle size of the small-sized nano-silver particles is 50nm to 100nm, while the particle size of the traditional nano-silver particles in the traditional nano-silver paste is 0.5μm to 1μm. The use of two different particle size distributions of silver particles forms a dual-mode particle size distribution structure, which can improve the density of the nano-silver paste after curing. Adding a highly polar solvent to traditional silver nanoparticle paste can reduce its viscosity and enhance its fluidity, which is beneficial for the dispersion of small-sized silver nanoparticles. Furthermore, the high solvent capacity of the highly polar solvent can promote uniform mixing between the nanoparticles and organic matter. By using dual-modal silver nanoparticles to prepare modified silver nanoparticle paste, the fluidity and uniformity of the paste in wafer trenches can be further improved, avoiding the formation of voids during the infiltration process. If voids exist, the coefficient of thermal expansion at the void locations will change, easily leading to stress concentration during processing and causing wafer warping. Modified silver nanoparticle paste, with its stronger fluidity, avoids defects caused by voids.

[0028] More preferably, the dispersant includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and sodium dodecyl sulfate, and the mass ratio of the dispersant to the small-sized silver nanoparticles is 1:0.5 to 1:2, thereby ensuring uniform dispersion and maintaining a high solid content in the modified silver nanoparticle paste; the strong polar solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylformamide, and the amount of the strong polar solvent added is 5% to 10% of the mass of the traditional silver nanoparticle paste, thereby improving its fluidity and maintaining a high solid content in the modified silver nanoparticle paste.

[0029] More preferably, the mass ratio of small-sized silver nanoparticles to traditional silver nanoparticles in the modified silver nanoparticle paste is 1:5 to 1:25.

[0030] More preferably, the ball milling dispersion process uses a rotation speed of 300 rpm to 500 rpm and a time of 2 h to 8 h to ensure that the various materials in the modified nano silver paste are dispersed evenly.

[0031] In a preferred embodiment of this application, the viscosity of the conventional nano-silver paste used is 167 Pa·s at a shear rate of 1 / s, exhibiting shear thinning phenomenon, where its viscosity decreases as the shear rate increases, making it suitable for direct ink writing processes.

[0032] The modified silver nanoparticle paste prepared in this application has good fluidity and can be directly used in various processes such as ink direct writing and screen printing. The cured material has low porosity, good electrical and thermal conductivity, and good filling effect for wafer trench 11 filling, making it suitable for the field of electronic packaging.

[0033] Further, in step S3, the substrate 1 includes a substrate 12 and devices 13 disposed on the substrate 12. Wafer trenches 11 are formed between adjacent devices 13. The number of filling operations is determined according to the aspect ratio of the wafer trenches 11. The specific method for determining this is as follows: When the aspect ratio of the wafer trench 11 is less than 1, the filling times are preferably 2 times, so as to obtain a better filling effect while ensuring filling efficiency. When the aspect ratio of the wafer trench 11 is 1 to 2, the filling number is preferably 4 times. If the filling number is reduced, it may result in incomplete filling or excessive filling amount each time, making it difficult to cure evenly. Increasing the filling number will reduce the filling efficiency. When the aspect ratio of the wafer trench 11 is greater than 2, the wafer trench 11 is filled and sintered in layers. The aspect ratio of each trench is less than 2 and the filling times of each trench are preferably 2 to 4 times. After the filling and sintering of each trench is completed, high-temperature laser sintering is performed to ensure the filling quality.

[0034] The technical solutions provided in this application will be further described below with reference to specific embodiments.

[0035] Example 1 To prepare the modified silver nanoparticle paste, 0.25 g of small-sized silver nanoparticles (100 nm in diameter) and 0.25 g of polyvinylpyrrolidone solution were placed in an experimental bottle and magnetically stirred for 30 min to obtain 0.5 g of precursor silver nanoparticle paste. The 0.5 g precursor silver nanoparticle paste was added to 5 g of conventional silver nanoparticle paste (the conventional silver nanoparticles had a particle size of 1 μm and a mass fraction of 80 wt%), and 0.25 g of the highly polar solvent N-methylpyrrolidone was added. The mixture was then dispersed by high-speed ball milling at 300 rpm for 2 h. After filtration, the modified silver nanoparticle paste was obtained.

[0036] The specific filling process includes: Step 1: Pre-process the etched wafer trench 11 Wafer trenches 11 with a width of 100μm and a depth of 50μm were selected for the filling process. The spacing between wafer trenches 11 was 10mm. The inner wall of the wafer trenches 11 after etching was not completely vertical, but had a certain tilt angle. The cross-section is shown below. Figure 3As shown. The wafer trench 11 was treated with plasma technology. The plasma power was 100W and the treatment time was 3 minutes to activate its inner surface and enhance the adhesion of the nano silver paste.

[0037] Step 2: Based on the specific shape and size of the wafer trench 11, set the initial parameters for the filling process and determine the number of filling operations. Based on the selected wafer trench 11, the extrusion pressure is set to 130 kPa, the needle-to-substrate height is 0.2 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the selected wafer trench 11 has a depth-to-width ratio of 1:2, and the filling times are determined to be 2. The moving trajectory is based on the interval between the wafer trenches 11, starting from the edge trench and moving in a serpentine pattern, first laterally and then longitudinally, until all trenches are filled.

[0038] Step 3: Extrude nano-silver paste using ink direct writing technology, and use airflow-assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; The modified silver nanoparticle paste was extruded according to the initial parameters in step two, with the airflow setting position and direction as follows. Figure 2 As shown, the angle between the airflow nozzle 3 and the extrusion needle 2 is 10°, the vertical distance between the end of the airflow nozzle 3 and the end of the extrusion needle 2 is 6mm, the airflow pressure is set to 250kPa, and dry nitrogen gas is blown uniformly into the wafer trench 11 to enhance the fluidity of the high viscosity nano silver paste, while breaking its surface tension, avoiding the generation of bubbles and pores, and improving the filling effect.

[0039] Step 4: Control the laser power according to the filling depth and perform gradient sintering and solidification of the filling material.

[0040] After the wafer trench 11 is filled, laser sintering and curing begins. After the first filling, the laser power is set to 30W, the laser focal length is set to 100μm, the stage moving speed is 3mm / s, and the moving trajectory is the same as during printing and filling, thus ensuring that the sintering temperature of the bottom layer is approximately 80℃.

[0041] Step 5: Repeat steps 3 and 4 to complete the filling; After the second layer filling is completed, the laser sintering power is set to 40W, while other parameters remain unchanged, ensuring that the sintering temperature of the second layer is approximately 100℃. After curing, the laser power is set to 100W, while other parameters remain unchanged, ensuring that the sintering temperature is approximately 350℃ to completely solidify the material. This gradient sintering process can reduce the damage to the wafer substrate and devices caused by high temperatures and improve the filling quality.

[0042] Example 2 To prepare the modified silver nanoparticle paste, 0.25 g of small-sized silver nanoparticles (50 nm in diameter) and 0.5 g of polyvinyl alcohol solution were placed in an experimental bottle and magnetically stirred for 30 min to obtain 0.75 g of precursor silver nanoparticle paste. The 0.75 g precursor silver nanoparticle paste was added to 7.5 g of conventional silver nanoparticle paste (conventional silver nanoparticles with a particle size of 1 μm and a mass fraction of 80 wt%), and 0.75 g of the highly polar solvent dimethyl sulfoxide was added. The mixture was then dispersed by high-speed ball milling at 300 rpm for 2 h. After filtration, the modified silver nanoparticle paste was obtained.

[0043] The specific filling process includes: Step 1: Pre-process the etched wafer trench 11 Wafer trenches 11 with a width and depth of 100 μm were selected for the filling process. The spacing between the wafer trenches 11 was 10 mm. After etching, the inner wall of the wafer trenches 11 was not completely perpendicular, but had a certain tilt angle. The cross-section is shown below. Figure 3 As shown. The wafer trench 11 was treated with plasma technology. The plasma power was 100W and the treatment time was 3 minutes to activate its inner surface and enhance the adhesion of the nano silver paste.

[0044] Step 2: Based on the specific shape and size of the wafer trench 11, set the initial parameters for the filling process and determine the number of filling operations. Based on the selected wafer trench 11, the extrusion pressure is set to 130 kPa, the needle-to-substrate height is 0 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the selected wafer trench 11 has a depth-to-width ratio of 1:1, and the filling times are determined to be 3 times. The moving trajectory is based on the interval between the wafer trenches 11, starting from the edge trench and moving in a serpentine manner, first laterally and then longitudinally, until all trenches are filled.

[0045] Step 3: Extrude nano-silver paste using ink direct writing technology, and use airflow-assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; The modified silver nanoparticle paste was extruded according to the initial parameters in step two, with the airflow setting position and direction as follows. Figure 2 As shown, the angle between the airflow nozzle 3 and the extrusion needle 2 is 30°, the vertical distance between the end of the airflow nozzle 3 and the end of the extrusion needle 2 is 5mm, the airflow pressure is set to 500kPa, and dry nitrogen gas is blown uniformly into the wafer trench 11 to enhance the fluidity of the high viscosity nano silver paste, while breaking its surface tension, avoiding the generation of bubbles and pores, and improving the filling effect.

[0046] Step 4: Control the laser power according to the filling depth and perform gradient sintering and solidification of the filling material.

[0047] After the wafer trench 11 is filled, laser sintering and curing begins. After the first filling, the laser power is set to 40W, the laser focal length is set to 100μm, the stage moving speed is 3mm / s, and the moving trajectory is the same as during printing and filling, thus ensuring that the sintering temperature of the bottom layer is approximately 100℃.

[0048] Step 5: Repeat steps 3 and 4 to complete the filling; After the second filling, the laser sintering power was set to 45W, with other parameters remaining constant, ensuring a sintering temperature of approximately 120°C for the second layer. After the third filling, the laser sintering power was set to 50W, with other parameters remaining constant, ensuring a sintering temperature of approximately 150°C for the third layer. After curing, the laser power was set to 105W, with other parameters remaining constant, ensuring a sintering temperature of approximately 380°C to completely solidify the material. This gradient sintering process reduces high-temperature damage to the wafer substrate and devices, improving the filling quality.

[0049] Example 3 To prepare the modified silver nanoparticle paste, 0.5 g of small-sized silver nanoparticles (100 nm in diameter) and 0.25 g of polyethylene glycol solution were placed in an experimental bottle and magnetically stirred for 30 min to obtain 0.75 g of precursor silver nanoparticle paste. The 0.75 g precursor silver nanoparticle paste was added to 18.75 g of conventional silver nanoparticle paste (conventional silver nanoparticles with a diameter of 0.5 μm and a mass fraction of 80 wt%), and 0.975 g of the highly polar solvent N,N-dimethylformamide was added. The mixture was then dispersed by high-speed ball milling at 300 rpm for 2 h. After filtration, the modified silver nanoparticle paste was obtained.

[0050] The specific filling process includes: Step 1: Pre-process the etched wafer trench 11 Wafer trenches 11 with a width of 100μm and a depth of 50μm were selected for the filling process. The spacing between wafer trenches 11 was 10mm. The inner wall of the wafer trenches 11 after etching was not completely vertical, but had a certain tilt angle. The cross-section is shown below. Figure 3 As shown. The wafer trench 11 was treated with plasma technology. The plasma power was 100W and the treatment time was 3 minutes to activate its inner surface and enhance the adhesion of the nano silver paste.

[0051] Step 2: Based on the specific shape and size of the wafer trench 11, set the initial parameters for the filling process and determine the number of filling operations. Based on the selected wafer trench 11, the extrusion pressure is set to 130 kPa, the needle-to-substrate height is 0.2 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the selected wafer trench 11 has a depth-to-width ratio of 1:2, and the filling times are determined to be 2. The moving trajectory is based on the interval between the wafer trenches 11, starting from the edge trench and moving in a serpentine pattern, first laterally and then longitudinally, until all trenches are filled.

[0052] Step 3: Extrude nano-silver paste using ink direct writing technology, and use airflow-assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; The modified silver nanoparticle paste was extruded according to the initial parameters in step two, with the airflow setting position and direction as follows. Figure 2 As shown, the angle between the airflow nozzle 3 and the extrusion needle 2 is 10°, the vertical distance between the end of the airflow nozzle 3 and the end of the extrusion needle 2 is 8mm, the airflow pressure is set to 200kPa, and dry nitrogen gas is blown uniformly into the wafer trench 11 to enhance the fluidity of the high viscosity nano silver paste, while breaking its surface tension, avoiding the generation of bubbles and pores, and improving the filling effect.

[0053] Step 4: Control the laser power according to the filling depth and perform gradient sintering and solidification of the filling material.

[0054] After the wafer trench 11 is filled, laser sintering and curing begins. After the first filling, the laser power is set to 30W, the laser focal length is set to 100μm, the stage moving speed is 3mm / s, and the moving trajectory is the same as during printing and filling, thus ensuring that the sintering temperature of the bottom layer is approximately 80℃.

[0055] Step 5: Repeat steps 3 and 4 to complete the filling; After the second layer of filling is completed, the laser sintering power is set to 40W, while other parameters remain unchanged, ensuring that the sintering temperature of the second layer is approximately 100℃. After curing, the laser power is set to 95W, while other parameters remain unchanged, ensuring that the sintering temperature is approximately 330℃ to completely solidify the material. This gradient sintering process can reduce the damage to the wafer substrate and devices caused by high temperatures and improve the filling quality.

[0056] Example 4 To prepare the modified silver nanoparticle paste, 0.2 g of small-sized silver nanoparticles (80 nm in diameter) and 0.2 g of sodium dodecyl sulfate solution were placed in an experimental bottle and magnetically stirred for 30 min to obtain 0.4 g of precursor silver nanoparticle paste. The 0.4 g precursor silver nanoparticle paste was added to 2.5 g of conventional silver nanoparticle paste (conventional silver nanoparticles with a diameter of 0.5 μm and a mass fraction of 80 wt%), and 0.16 g of the highly polar solvent N,N-dimethylformamide was added. The mixture was then dispersed by high-speed ball milling at 300 rpm for 2 h. After filtration, the modified silver nanoparticle paste was obtained.

[0057] The specific filling process includes: Step 1: Pre-process the etched wafer trench 11 Wafer trenches 11 with a width of 100μm and a depth of 50μm were selected for the filling process. The spacing between wafer trenches 11 was 10mm. The inner wall of the wafer trenches 11 after etching was not completely vertical, but had a certain tilt angle. The cross-section is shown below. Figure 3 As shown. The wafer trench 11 was treated with plasma technology. The plasma power was 100W and the treatment time was 3 minutes to activate its inner surface and enhance the adhesion of the nano silver paste.

[0058] Step 2: Based on the specific shape and size of the wafer trench 11, set the initial parameters for the filling process and determine the number of filling operations. Based on the selected wafer trench 11, the extrusion pressure is set to 130 kPa, the needle-to-substrate height is 0.2 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the selected wafer trench 11 has a depth-to-width ratio of 1:2, and the filling times are determined to be 2. The moving trajectory is based on the interval between the wafer trenches 11, starting from the edge trench and moving in a serpentine pattern, first laterally and then longitudinally, until all trenches are filled.

[0059] Step 3: Extrude nano-silver paste using ink direct writing technology, and use airflow-assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; The modified silver nanoparticle paste was extruded according to the initial parameters in step two, with the airflow setting position and direction as follows. Figure 2 As shown, the angle between the airflow nozzle 3 and the extrusion needle 2 is 10°, the vertical distance between the end of the airflow nozzle 3 and the end of the extrusion needle 2 is 5mm, the airflow pressure is set to 200kPa, and dry nitrogen gas is blown uniformly into the wafer trench 11 to enhance the fluidity of the high viscosity nano silver paste, while breaking its surface tension, avoiding the generation of bubbles and pores, and improving the filling effect.

[0060] Step 4: Control the laser power according to the filling depth and perform gradient sintering and solidification of the filling material.

[0061] After the wafer trench 11 is filled, laser sintering and curing begins. After the first filling, the laser power is set to 30W, the laser focal length is set to 100μm, the stage moving speed is 3mm / s, and the moving trajectory is the same as during printing and filling, thus ensuring that the sintering temperature of the bottom layer is approximately 80℃.

[0062] Step 5: Repeat steps 3 and 4 to complete the filling; After the second layer filling is completed, the laser sintering power is set to 40W, while other parameters remain unchanged, ensuring that the sintering temperature of the second layer is approximately 100℃. After curing, the laser power is set to 100W, while other parameters remain unchanged, ensuring that the sintering temperature is approximately 350℃ to completely solidify the material. This gradient sintering process can reduce the damage to the wafer substrate and devices caused by high temperatures and improve the filling quality.

[0063] Example 5 To prepare the modified silver nanoparticle paste, 0.25 g of small-sized silver nanoparticles (100 nm in diameter) and 0.5 g of polyvinylpyrrolidone solution were placed in an experimental bottle and magnetically stirred for 30 min to obtain 0.75 g of precursor silver nanoparticle paste. The 0.75 g precursor silver nanoparticle paste was added to 7.5 g of conventional silver nanoparticle paste (conventional silver nanoparticles with a diameter of 0.8 μm and a mass fraction of 80 wt%), along with 0.75 g of the highly polar solvent N-methylpyrrolidone. The mixture was then dispersed by high-speed ball milling at 300 rpm for 2 h. After filtration, the modified silver nanoparticle paste was obtained.

[0064] The specific filling process includes: Step 1: Pre-process the etched wafer trench 11 Wafer trenches 11 with a width of 100μm and a depth of 50μm were selected for the filling process. The spacing between wafer trenches 11 was 10mm. The inner wall of the wafer trenches 11 after etching was not completely vertical, but had a certain tilt angle. The cross-section is shown below. Figure 3 As shown. The wafer trench 11 was treated with plasma technology. The plasma power was 100W and the treatment time was 3 minutes to activate its inner surface and enhance the adhesion of the nano silver paste.

[0065] Step 2: Based on the specific shape and size of the wafer trench 11, set the initial parameters for the filling process and determine the number of filling operations. Based on the selected wafer trench 11, the extrusion pressure is set to 130 kPa, the needle-to-substrate height is 0.2 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the selected wafer trench 11 has a depth-to-width ratio of 1:2, and the filling times are determined to be 2. The moving trajectory is based on the interval between the wafer trenches 11, starting from the edge trench and moving in a serpentine pattern, first laterally and then longitudinally, until all trenches are filled.

[0066] Step 3: Extrude nano-silver paste using ink direct writing technology, and use airflow-assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; The modified silver nanoparticle paste was extruded according to the initial parameters in step two, with the airflow setting position and direction as follows. Figure 2 As shown, the angle between the airflow nozzle 3 and the extrusion needle 2 is 10°, the vertical distance between the end of the airflow nozzle 3 and the end of the extrusion needle 2 is 8mm, the airflow pressure is set to 250kPa, and dry nitrogen gas is blown uniformly into the wafer trench 11 to enhance the fluidity of the high viscosity nano silver paste, while breaking its surface tension, avoiding the generation of bubbles and pores, and improving the filling effect.

[0067] Step 4: Control the laser power according to the filling depth and perform gradient sintering and solidification of the filling material.

[0068] After the wafer trench 11 is filled, laser sintering and curing begins. After the first filling, the laser power is set to 30W, the laser focal length is set to 100μm, the stage moving speed is 3mm / s, and the moving trajectory is the same as during printing and filling, thus ensuring that the sintering temperature of the bottom layer is approximately 80℃.

[0069] Step 5: Repeat steps 3 and 4 to complete the filling; After the second layer filling is completed, the laser sintering power is set to 40W, while other parameters remain unchanged, ensuring that the sintering temperature of the second layer is approximately 100℃. After curing, the laser power is set to 100W, while other parameters remain unchanged, ensuring that the sintering temperature is approximately 350℃ to completely solidify the material. This gradient sintering process can reduce the damage to the wafer substrate and devices caused by high temperatures and improve the filling quality.

[0070] Comparative Example 1 Same as Example 1, except that the airflow-assisted filling process was not used during filling.

[0071] Figure 4 These are scanning electron microscope images of the modified silver nanoparticle paste prepared in Example 1 and the traditional silver nanoparticle paste after curing. As can be seen from the images, the small-sized silver nanoparticles in the modified silver nanoparticle paste fill the spaces between the large-sized silver nanoparticles, making it more compact.

[0072] Figure 5 These are scanning electron microscope images of the wafer trench cross-sections after filling in Embodiment 1 and Comparative Example 1 of this application. It can be seen from the images that defects caused by residual bubbles will exist if the airflow-assisted filling process is not used. Therefore, the high-precision wafer trench filling method based on airflow assistance provided in this application can effectively avoid the generation of holes.

[0073] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0074] Furthermore, throughout this specification, references to "an embodiment"; "an embodiment," "an example," or similar language indicate that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. Therefore, the appearance of the phrase "in one embodiment;" throughout this specification, and similar language, may, but not necessarily, refer to the same embodiment.

[0075] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for high-precision filling of a wafer trench based on airflow assistance, characterized in that, Specifically: S1 uses ink direct writing technology to fill the wafer trench on the substrate (1) with nano silver paste, and at the same time, it uses airflow-assisted filling technology to make the nano silver paste spread evenly in the wafer trench. In the ink direct writing technology, the extrusion pressure of the nano silver paste is 100kPa~200kPa, the distance between the extrusion needle (2) and the substrate (1) is 0mm~0.5mm, and the moving speed of the substrate (1) is 50mm / s~200mm / s. In the airflow-assisted filling technology, the airflow nozzle (3) is tilted and the angle between it and the extrusion needle (2) of the ink direct writing technology is less than 30°. At the same time, the airflow ejected by the airflow nozzle (3) flows in the opposite direction to the moving direction of the substrate (1) in the horizontal direction. S2 uses a gradient sintering process to laser sinter the filler material to ensure that the sintering temperature of the bottom layer is 80℃~100℃, the sintering temperature difference between adjacent layers is 10℃~30℃, and the sintering temperature of the top layer does not exceed 150℃. S3 repeats steps S1-S2 according to the number of filling cycles until the filling is completed. Finally, high-temperature laser sintering is performed at 330℃~380℃ to optimize the temperature resistance of the nano silver paste.

2. The high-precision filling method for wafer trenches as described in claim 1, characterized in that, In the airflow-assisted filling technology, the airflow nozzle (3) is located above the extrusion needle (2) of the ink direct writing technology, and the vertical distance between the end of the airflow nozzle (3) and the end of the extrusion needle (2) is 5mm to 8mm, and the airflow pressure of the airflow nozzle (3) is 200kPa to 500kPa.

3. The high-precision filling method for wafer trenches as described in claim 1, characterized in that, In step S1, the wafer trench is pretreated before filling, thereby activating the surface of the wafer trench.

4. The high-precision filling method for wafer trenches as described in claim 3, characterized in that, The wafer trenches were pretreated using a plasma surface activation method.

5. The high-precision filling method for wafer trenches as described in claim 1, characterized in that, In step S1, modified silver nanoparticle paste is filled into the wafer trench. The modified silver nanoparticle paste is prepared by mixing a dispersant with small-sized silver nanoparticles to obtain a precursor silver nanoparticle paste, then mixing the precursor silver nanoparticle paste with a conventional silver nanoparticle paste and adding a strongly polar solvent to obtain a modified silver nanoparticle paste. The small-sized silver nanoparticles have a particle size of 50 nm to 100 nm, and the conventional silver nanoparticle paste has a particle size of 0.5 μm to 1 μm.

6. The high-precision filling method for wafer trenches as described in claim 5, characterized in that, The modified silver nanoparticle paste has a mass ratio of small-sized silver nanoparticles to traditional silver nanoparticles of 1:10 to 1:

30.

7. The high-precision filling method for wafer trenches as described in claim 5, characterized in that, The dispersant includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and sodium dodecyl sulfate. The mass ratio of the dispersant to the small-sized silver nanoparticles is 1:0.5 to 1:

2. The strong polar solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide. The amount of the strong polar solvent added is 5% to 10% of the mass of the traditional silver nanoparticle paste.

8. The high-precision wafer trench filling method according to any one of claims 1 to 7, characterized in that, In step S3, the method for determining the number of filling operations is as follows: When the aspect ratio of the wafer trench is less than 1, the filling number is 2 times; When the aspect ratio of the wafer trench is 1 to 2, the filling number is 4 times; When the aspect ratio of the wafer trench is greater than 2, the wafer trench is filled and sintered in layers, with the aspect ratio of each trench being less than 2 and the filling number of each trench being 2 to 4 times.

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