Wafer groove high-precision filling method based on airflow assistance

Abstract

The invention belongs to the field of electronic packaging, and particularly discloses a wafer groove high-precision filling method based on airflow assistance, and the method specifically comprises the steps: filling a wafer groove in a substrate with nano-silver paste through employing an ink direct writing technology, and enabling the nano-silver paste to be uniformly spread in the wafer groove through cooperation with an airflow-assisted filling technology; carrying out laser sintering on the filling material by adopting a gradient sintering process; and repeating the steps according to the filling times until filling is finished, and finally performing high-temperature laser sintering at 330-380 DEG C to optimize the temperature resistance of the nano-silver paste. According to the method, auxiliary filling is carried out in cooperation with airflow while filling of the nano-silver paste is carried out, the nano-silver paste can be assisted to flow in a wafer groove, distribution of the nano-silver paste is more uniform, holes are prevented from being generated in the permeation process, meanwhile, in cooperation with the gradient sintering technology, wafer damage can be avoided, meanwhile, the curing efficiency is improved, and the product quality is improved. And the structure of the sintered material 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 air flow assistance. Background Art

[0002] With the continuous progress of integrated circuit technology, the integration degree of chips has been continuously improved, and three-dimensional packaging has become the mainstream solution. During the wafer-level bonding process, after the wafer is thinned, heat accumulation will occur. At the same time, the stacking of multiple layers of chips leads to an increase in the total power consumption per unit area, resulting in more heat generation, yet there is no effective heat dissipation channel. In order to reduce the residual stress generated during the wafer thinning process, improve the heat dissipation ability of the wafer, and avoid the generation of hot spots, developing a thermal conductive filler with a coefficient of thermal expansion similar to that of silicon-based materials and filling it in the wafer trenches is a simple and effective way. Currently, high-density plasma-enhanced chemical vapor deposition technology (PECVD) is generally used as a method for filling wafer channels, but this filling method has low efficiency, high cost, and strict environmental requirements, which hinder its development in wafer channel filling applications. There is an urgent need for an alternative filling solution.

[0003] Nano silver paste has become an important alternative to traditional packaging materials due to its small silver particle size and excellent electrical conductivity and good thermal conductivity. However, the high solid content and low viscosity of traditional nano silver paste cannot be satisfied simultaneously, and defects such as voids and cracks are likely to occur when filling micro trenches, which is not conducive to improving the filling efficiency. Summary of the Invention

[0004] Aiming at the defects of the prior art, this application provides a high-precision filling method for wafer trenches based on air flow assistance, aiming to solve the problem that holes and cracks are likely to occur when nano silver paste fills micro trenches.

[0005] A high-precision filling method for wafer trenches based on air flow assistance provided by this application is specifically as follows: S1 Use inkjet printing technology to fill nano silver paste into the wafer trenches on the substrate, and at the same time cooperate with the air flow assistance filling technology to make the nano silver paste spread evenly in the wafer trenches; S2 Use a gradient sintering process to laser sinter the filling material. The sintering power is selected according to the number of filling layers to ensure that the sintering temperature of the bottom layer is 80°C to 100°C, the sintering temperature difference between adjacent layers is 10°C to 30°C, and the sintering temperature of the top layer does not exceed 150°C; S3 Repeat steps S1 - S2 according to the number of filling times until the filling is completed, and finally perform high-temperature laser sintering at 330°C to 380°C to optimize the temperature resistance of the nano silver paste.

[0006] Through the above technical solution conceived in this application, compared with the prior art, since this application fills the nano-silver paste while assisting with air flow for filling, it can assist the nano-silver paste to flow in the wafer trench, making its distribution more uniform and avoiding the generation of holes during the penetration process. At the same time, in combination with the gradient sintering process, it can improve the curing efficiency while avoiding wafer damage, making the sintered material structure more uniform.

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

[0008] As a further preference, in the air flow assisted filling technology, the air flow nozzle is inclined and the included angle with the extrusion needle of the inkjet writing technology is less than 30°. At the same time, the flowing direction of the air flow ejected by the air flow nozzle in the horizontal direction is opposite to the moving direction of the substrate.

[0009] As a further preference, in the air flow assisted filling technology, the air flow nozzle is located above the extrusion needle of the inkjet writing technology, and the distance between the end of the air flow nozzle and the end of the extrusion needle in the vertical direction is 5 mm to 8 mm, and the air flow pressure of the air flow nozzle is 200 kPa to 500 kPa.

[0010] As a further preference, in step S1, the wafer trench is pretreated before filling, so as to activate the surface of the wafer trench.

[0011] As a further preference, the wafer trench is pretreated by the method of plasma surface activation.

[0012] As a further preference, in step S1, a modified nano-silver paste is filled into the wafer trench. The preparation method of the modified nano-silver paste is: mixing a dispersant with small-sized nano-silver particles to obtain a precursor nano-silver paste, and then mixing the precursor nano-silver paste with a traditional nano-silver paste and adding a strongly polar solvent to obtain a modified nano-silver paste, wherein the particle size of the small-sized nano-silver particles is 50 nm to 100 nm, and the particle size of the traditional nano-silver particles in the traditional nano-silver paste is 0.5 μm to 1 μm.

[0013] As a further preference, the mass ratio of the small-sized nano-silver particles to the traditional nano-silver particles in the modified nano-silver paste is 1:10 to 1:30.

[0014] As a further preference, 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, N,N-dimethylformamide, and N,N-dimethylformamide. The addition amount of the strong polar solvent is 5% to 10% of the mass of the traditional silver nanopaste.

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

[0016] Generally speaking, compared with the prior art through the above technical solution conceived by the present application, the following technical advantages are mainly presented: 1. The present application combines the gas flow-assisted filling technology while filling the silver nanopaste, which can assist the silver nanopaste to flow in the wafer trench, make its distribution more uniform and avoid the generation of holes during the penetration process, which is beneficial to filling the entire wafer trench with the silver nanopaste. At the same time, combined with the gradient sintering process, it can avoid wafer damage while preventing the surface solvent from evaporating too fast due to too high temperature, and avoid the bulging phenomenon during the evaporation and overflow of the internal solvent, thereby making the sintered material structure more uniform and the curing quality higher; 2. In particular, the present application pre-treats the wafer trench before filling, which can increase the surface energy of the wafer trench surface to increase the adhesion between the silver nanopaste and the wafer trench, thereby alleviating the interlayer splitting phenomenon caused by insufficient adhesion during the silver paste curing process; 3. At the same time, the present application uses bimodal silver nanoparticles to prepare modified silver nanopaste, which can improve the density of the silver nanopaste after curing, and uses a dispersant to modify the surface of the silver nanoparticles, which can enhance its dispersibility and stability. Combining with a strong polar solvent to optimize the leveling property of the silver nanopaste, it can further improve the fluidity and uniformity of the silver nanopaste in the wafer trench and avoid the generation of holes during the penetration process. Description of the Drawings

[0017] Figure 1 is a high-precision filling process flow chart of a wafer trench based on a gas flow-assisted material provided by an embodiment of the present application; Figure 2 is a high-precision filling process diagram of a wafer trench based on a gas flow-assisted material provided by an embodiment of the present application; Figure 3 It is a cross-sectional view of a wafer trench and laser gradient curing in the high-precision filling method of a wafer trench based on an air flow-assisted material provided by an embodiment of the present application; Figure 4 It is a scanning electron microscope image (magnified 40,000 times) after curing of the modified nano silver paste and the traditional nano silver paste prepared in Embodiment 1 of the present application, where a is the traditional nano silver paste and b is the modified nano silver paste; Figure 5 It is a scanning electron microscope image of the cross-section of the wafer trench after filling in Embodiment 1 of the present application and Comparative Example 1, where a is Comparative Example 1 and b is Embodiment 1.

[0018] In all the drawings, the same reference numerals are used to represent the same elements or structures, where: 1 - Substrate, 11 - Wafer trench, 12 - Substrate, 13 - Device, 2 - Extrusion needle, 3 - Air flow nozzle. Detailed implementation manners

[0019] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0020] As Figure 1 shown, the present application provides a high-precision filling method for a wafer trench based on air flow assistance, specifically: S1 Set the initial parameters and filling times of the filling process based on the specific shape and size of the wafer trench 11, and use the inkjet printing technology to fill the nano silver paste into the wafer trench 11 on the substrate 1. At the same time, cooperate with the air flow-assisted filling technology to make the nano silver paste spread evenly in the wafer trench 11. The air flow-assisted filling technology is specifically to set an air flow nozzle 3 beside the extrusion needle 2, and make the silver paste spread evenly through the air flow ejected by the air flow nozzle 3; S2 Use the gradient sintering process to laser sinter the filling material to evaporate the solvent in the nano silver paste. The sintering power is selected according to the filling layer number to ensure that the sintering temperature of the bottom layer is 80°C to 100°C, so as to avoid damaging the wafer substrate 1 due to too high sintering temperature. The sintering temperature difference between adjacent layers is 10°C to 30°C, and the sintering temperature of the top layer does not exceed 150°C, to avoid the phenomenon of bulging during the evaporation of the internal solvent due to too fast evaporation of the solvent on the surface of the nano silver paste at too high temperature. Thus, the curing process is stable and the curing quality is ensured; S3 Repeat steps S1 - S2 according to the filling times until the filling is completed, and finally perform high-temperature laser sintering at 330°C to 380°C to completely cure the nano silver paste, so as to optimize the temperature resistance of the nano silver paste.

[0021] The present application uses airflow-assisted filling technology while filling the nano-silver paste, which can assist the nano-silver paste to flow in the wafer groove 11, making its flow smoother and distribution more even. At the same time, the airflow can drive the nano-silver paste at the needle tip to flow to the bottom of the wafer groove 11, avoiding the formation of bubbles or holes in the nano-silver paste due to excessive viscosity and surface tension during the filling process, which is conducive to the nano-silver paste filling the entire wafer groove 11, and effectively solves the defect that the high solid content and low viscosity of traditional nano-silver paste cannot be met at the same time, which easily leads to voids and cracks; at the same time, when a conical needle tip is used in the nano-silver paste extrusion process, the airflow-assisted filling technology can also avoid the problem that the nano-silver paste flows to the outer surface of the needle tip through infiltration when printing is paused, causing continuous printing difficulties.

[0022] At the same time, the present application can achieve precise selective local sintering in conjunction with the gradient sintering process, reduce the heat-affected zone, and reduce the thermal impact on the wafer substrate. Low-power curing is selected at the bottom of the wafer groove 11 to ensure that the sintering temperature is between 80°C and 100°C, avoiding the generation of hot spots during the sintering process and causing wafer damage; higher-power curing is selected in the area away from the bottom of the groove, and the sintering temperature of the top layer is ensured not to exceed 150°C. The overall power can be maintained at a lower level while improving the curing efficiency, and most of the solvent can be evaporated at a lower temperature. Finally, a high-power laser is used for high-temperature laser sintering to complete the filling and curing process, so that the material structure after sintering is more uniform, and the temperature resistance of the nano-silver paste is optimized, thereby improving the curing efficiency while avoiding wafer damage, and making the material structure after sintering more uniform.

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

[0024] Further, in the air flow assisted filling technique, the air flow nozzle 3 is located above the extrusion needle 2, and the distance between the end of the air flow nozzle 3 and the end of the extrusion needle 2 in the vertical direction is 5 mm to 8 mm. Moreover, the air flow nozzle 3 is inclined, and the included angle with the extrusion needle 2 is less than 30°. If the distance between the end of the air flow nozzle 3 and the end of the extrusion needle 2 is too small, it is easy to cause the air flow to be too concentrated, resulting in the splashing of the nano silver paste. If the distance is too large, it is difficult to ensure the effect of assisting the flow of the nano silver paste. And having a certain inclination angle of the air flow is more likely to promote the flow of the paste. However, when the inclination angle is too large, it can only act on the surface of the nano silver paste and is difficult to eliminate the internal pore defects. At the same time, the flow direction of the air flow ejected by the air flow nozzle 3 in the horizontal direction is opposite to the moving direction of the substrate 1, so that the nano silver paste flows in the direction away from the substrate 1, thereby ensuring that the nano silver paste in the wafer groove 11 is more uniform. Since the substrate 1 moves during the printing and filling process, the flow direction of the air flow ejected by the air flow nozzle 3 in the horizontal direction being opposite to the moving direction of the substrate 1 can directly blow the freshly extruded nano silver paste. When the viscosity of the nano silver paste increases due to the loss of the shear force, increasing the air flow can break its surface tension, making it easier to contact the inner wall of the channel and reducing the internal holes. The shape of the air flow nozzle 3 is circular, and the opening diameter is adjusted according to the groove width. Preferably, the air flow component is dry nitrogen. The air flow pressure of the air flow nozzle 3 is 200 kPa to 500 kPa. If the air flow pressure is too high, it is easy to cause the splashing or overflow of the nano silver paste, resulting in pollution. When the air flow pressure is too low, the effect is not obvious.

[0025] Further, in step S1, before filling, the wafer groove 11 is pretreated, so as to activate the surface of the wafer groove 11, increase the surface energy of the surface of the wafer groove 11 to increase the adhesion between the nano silver paste and the wafer groove 11, and further alleviate the interlayer splitting phenomenon caused by insufficient adhesion during the silver paste curing process.

[0026] Preferably, the wafer groove 11 is pretreated by the method of plasma surface activation. There is no limit to the processing efficiency and processing time of the plasma. Preferably, the plasma processing power is 100 W, and the processing time is 2 min to 5 min.

[0027] Further, in step S1, the modified nano silver paste is filled into the wafer trench 11. The preparation method of the modified nano silver paste is as follows: a dispersant is mixed with small-sized nano silver particles, and ultrasonic wave is used in combination with mechanical stirring to mix them evenly to obtain a precursor nano silver paste, so that the dispersant uniformly modifies the surface of the small-sized nano silver particles or has a steric hindrance effect itself, compared with the aggregation of nano silver particles, optimizing its dispersion effect; then the precursor nano silver paste is mixed with the traditional nano silver paste and a strongly polar solvent is added, and they are mixed evenly by 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 50 nm to 100 nm, and the particle size of the traditional nano silver particles in the traditional nano silver paste is 0.5 μm to 1 μm. Using silver particles with two different particle size distributions to form a bimodal particle size distribution structure can improve the density after the nano silver paste is cured. Adding a strongly polar solvent to the traditional nano silver paste can, on the one hand, reduce the viscosity of the nano silver paste, enhance its fluidity, and is conducive to the dispersion of small-sized nano silver particles. On the other hand, the solvent ability of the strongly polar solvent is high, which can promote the uniform mixing between nano particles and organic substances. By using bimodal nano silver particles to prepare the modified nano silver paste, the fluidity and uniformity of the nano silver paste in the wafer trench can be further improved, avoiding the generation of holes during the penetration process. If there are hole defects, the coefficient of thermal expansion at the holes will change, and stress concentration is likely to occur during the processing, resulting in wafer warping. The modified nano silver paste has stronger fluidity, avoiding the defects caused by holes.

[0028] More preferably, the dispersant includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, sodium dodecyl sulfate, and the mass ratio of the dispersant to the small-sized nano silver particles is 1:0.5 to 1:2, so as to make it disperse evenly and keep the modified nano silver paste with a high solid content; the strongly polar solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylformamide, and the addition amount of the strongly polar solvent is 5% to 10% of the mass of the traditional nano silver paste, so as to improve its fluidity and keep the modified nano silver paste with a high solid content.

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

[0030] More preferably, the rotation speed of the ball milling dispersion process is 300 rpm to 500 rpm, and the time is 2 h to 8 h, so as to ensure that each material in the modified nano silver paste is dispersed evenly.

[0031] In a preferred embodiment of the present application, the viscosity of the traditional nano silver paste used at a shear rate of 1 / s is 167 Pa·s, and it has a shear thinning phenomenon. Its viscosity will decrease when the shear rate becomes higher, which is suitable for the inkjet printing process.

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

[0033] Further, in step S3, the substrate 1 includes a substrate 12 and a device 13 disposed on the substrate 12. A wafer trench 11 is formed between adjacent devices 13. The number of filling times is determined according to the aspect ratio of the wafer trench 11. The specific determination method is as follows: When the aspect ratio of the wafer trench 11 is less than 1, the number of filling times is preferably 2 times, so as to obtain a better filling effect while ensuring the filling efficiency; When the aspect ratio of the wafer trench 11 is 1-2, the number of filling times is preferably 4 times. If the number of filling times is reduced, it may lead to incomplete filling or too much filling amount each time, making it difficult to cure evenly, while increasing the number of filling times 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 layer of trench is less than 2 and the number of filling times for each layer of trench is preferably 2 to 4 times. And high-temperature laser sintering is performed after the filling and sintering of each layer of trench, so as to ensure the filling quality.

[0034] The technical solution provided by this application will be further described below according to specific embodiments.

[0035] Example 1 Prepare a modified nano-silver paste. Take 0.25 g of small-sized nano-silver particles (particle size of 100 nm) and 0.25 g of polyvinylpyrrolidone solution and put them into an experimental bottle. Magnetically stir for 30 min to obtain 0.5 g of precursor nano-silver paste; add 0.5 g of precursor nano-silver paste to 5 g of traditional nano-silver paste (the particle size of traditional nano-silver particles is 1 μm, and the mass fraction of traditional nano-silver particles is 80 wt%), and add 0.25 g of strongly polar solvent N-methylpyrrolidone. Mix them evenly by high-speed ball milling dispersion process. Set the ball milling speed to 300 rpm and the ball milling time to 2 h. After filtration, the modified nano-silver paste is obtained.

[0036] The specific filling process includes: Step 1. Pretreat the etched wafer trench 11 Select a wafer trench 11 with a width of 100 μm and a depth of 50 μm for the filling process. The interval between the wafer trenches 11 is 10 mm. The inner wall of the wafer trench 11 obtained after etching is not completely vertical and has a certain inclination angle. The cross-section is as Figure 3As shown in the figure. The wafer trench 11 is processed using plasma technology with a plasma power of 100 W and a processing time of 3 min to activate its inner surface and enhance the adhesion of the nano silver paste.

[0037] Step 2: Set the initial parameters of the filling process based on the specific shape and size of the wafer trench 11 and determine the number of filling times. According to the selected wafer trench 11, an extrusion air pressure of 130 kPa, a height of the needle head from the substrate of 0.2 mm, and a substrate moving speed of 60 mm / s are selected. In this embodiment, the aspect ratio of the selected wafer trench 11 is 1:2, and the number of filling times is determined to be 2 times. The moving trajectory starts from the edge trench according to the spacing distance between the wafer trenches 11, moves in a serpentine manner, first horizontally and then vertically until all channels are filled.

[0038] Step 3: Extrude the nano silver paste using inkjet direct writing technology, and use the air flow assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11. Extrude the prepared modified nano silver paste according to the initial parameters in Step 2. The position and direction of the air flow setting are as Figure 2 shown. The included angle between the air flow nozzle 3 and the extrusion needle 2 is 10°, the vertical distance between the end of the air flow nozzle 3 and the end of the extrusion needle 2 is 6 mm, the air flow pressure is set to 250 kPa, and dry nitrogen is evenly blown 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 holes, and improving the filling effect.

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

[0040] After the filling of the wafer trench 11 is completed, laser sintering and curing start. After the first filling, a laser power of 30 W is selected, the laser focal length is set to 100 μm, the moving speed of the base is 3 mm / s, and the moving trajectory is the same as that during printing and filling, so as to ensure that the sintering temperature of the bottom layer is about 80 °C.

[0041] Step 5: Repeat Steps 3 to 4 to complete the filling. After the second filling is completed, the power of laser sintering and curing is set to 40 W, and other parameters remain unchanged, so as to ensure that the sintering temperature of the second layer is about 100 °C. After the curing is completed, the laser power is set to 100 W, and other parameters remain unchanged, so as to ensure that the sintering temperature is about 350 °C to completely cure the material. Using this gradient sintering process can reduce the damage to the wafer substrate and devices caused by high temperature and improve the filling quality.

[0042] Example 2 To prepare the modified nano silver paste, 0.25 g of small-sized nano silver particles (with a particle size of 50 nm) and 0.5 g of polyvinyl alcohol solution are placed into an experimental flask, and magnetically stirred for 30 min to obtain 0.75 g of precursor nano silver paste; 0.75 g of the precursor nano silver paste is added to 7.5 g of traditional nano silver paste (the particle size of traditional nano silver particles is 1 μm, and the mass fraction of traditional nano silver particles is 80 wt%), and 0.75 g of strongly polar solvent dimethyl sulfoxide is added, and they are mixed evenly by high-speed ball milling dispersion process. The ball milling speed is set at 300 rpm, and the ball milling time is set at 2 h. After filtration, the modified nano silver paste is obtained.

[0043] The specific filling process includes: Step 1: Pretreat the etched wafer trench 11 Select the wafer trench 11 with a width of 100 μm and a depth of 100 μm for the filling process. The interval between the wafer trenches 11 is 10 mm. The inner wall of the wafer trench 11 obtained after etching is not completely vertical and has a certain inclination angle. The cross-section is as Figure 3 shown. The wafer trench 11 is treated using plasma technology. The power of the plasma is 100 W, and the treatment time is 3 min to activate its inner surface and enhance the adhesion of the nano silver paste.

[0044] Step 2: Set the initial parameters of the filling process based on the specific shape and size of the wafer trench 11, and determine the filling times According to the selected wafer trench 11, select an extrusion air pressure of 130 kPa, the height of the needle head from the substrate is 0 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the aspect ratio of the selected wafer trench 11 is 1:1, and the filling times are determined to be 3 times. The moving trajectory starts from the edge trench according to the interval distance between the wafer trenches 11, moves in a serpentine manner, first horizontally and then vertically until all channels are filled.

[0045] Step 3: Extrude the nano silver paste using inkjet direct writing technology, and use gas-assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; Extrude the prepared modified nano silver paste according to the initial parameters in Step 2. The position and direction of the gas flow are as Figure 2 shown. The included angle between the gas flow nozzle 3 and the extrusion needle 2 is 30°. The distance between the end of the gas flow nozzle 3 and the end of the extrusion needle 2 in the vertical direction is 5 mm. The gas flow pressure is set at 500 kPa, and dry nitrogen is evenly blown into the wafer trench 11 to enhance the fluidity of the high-viscosity nano silver paste, and at the same time break its surface tension, avoid the generation of bubbles and holes, and improve the filling effect.

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

[0047] After the filling of the wafer trench 11 is completed, laser sintering and curing are started. After the first filling, the laser power is selected to be 40 W, the laser focal length is set to 100 μm, the moving speed of the base is 3 mm / s, and the moving trajectory is the same as that during printing and filling, so as to ensure that the sintering temperature of the bottom layer is about 100 °C.

[0048] Step Five: Repeat Step Three to Step Four to complete the filling; After the second filling is completed, the power of laser sintering and curing is set to 45 W, and other parameters remain unchanged, so as to ensure that the sintering temperature of the second layer is about 120 °C. After the third filling is completed, the power of laser sintering and curing is set to 50 W, and other parameters remain unchanged, so as to ensure that the sintering temperature of the third layer is about 150 °C. After the curing is completed, the laser power is set to 105 W, and other parameters remain unchanged, so as to ensure that the sintering temperature is about 380 °C to completely cure the material. Adopting this gradient sintering process can reduce the damage of high temperature to the wafer substrate and devices and improve the filling quality.

[0049] Example 3 Prepare the modified nano-silver paste. Take 0.5 g of small-sized nano-silver particles (particle size of 100 nm) and 0.25 g of polyethylene glycol solution and put them into an experimental bottle. Use magnetic stirring for 30 min to obtain 0.75 g of precursor nano-silver paste; add 0.75 g of precursor nano-silver paste to 18.75 g of traditional nano-silver paste (the particle size of traditional nano-silver particles is 0.5 μm, and the mass fraction of traditional nano-silver particles is 80 wt%), and add 0.975 g of strong polar solvent N,N-dimethylformamide. Mix them evenly by high-speed ball milling dispersion process. Set the ball milling speed to 300 rpm and the ball milling time to 2 h. After filtration, the modified nano-silver paste is obtained.

[0050] The specific filling process includes: Step One: Pretreat the etched wafer trench 11 Select the wafer trench 11 with a width of 100 μm and a depth of 50 μm for the filling process. The interval between the wafer trenches 11 is 10 mm. The inner wall of the wafer trench 11 obtained after etching is not completely vertical and has a certain inclination angle. The cross-section is as Figure 3 shown. Use plasma technology to treat the wafer trench 11. The power of the plasma is 100 W and the treatment time is 3 min to activate its inner surface and enhance the adhesion of the nano-silver paste.

[0051] Step Two: Set the initial parameters of the filling process based on the specific shape and size of the wafer trench 11 and determine the filling times According to the selected wafer trench 11, the extrusion air pressure is selected as 130 kPa, the height between the needle and the substrate is 0.2 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the aspect ratio of the selected wafer trench 11 is 1:2, the filling times are determined to be 2 times, and the moving trajectory starts from the edge trench according to the interval distance between the wafer trenches 11, moving in a serpentine manner, first horizontally and then vertically until all channels are filled.

[0052] Step 3: Extrude the nano silver paste by inkjet direct writing technology, and adopt the air flow assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; Extrude the prepared modified nano silver paste according to the initial parameters in Step 2. The position and direction of the air flow setting are as Figure 2 shown. The included angle between the air flow nozzle 3 and the extrusion needle 2 is 10°, the vertical distance between the end of the air flow nozzle 3 and the end of the extrusion needle 2 is 8 mm, the air flow pressure is set to 200 kPa, and dry nitrogen is evenly blown into the wafer trench 11 to enhance the fluidity of the high-viscosity nano silver paste, and at the same time break its surface tension, avoid the generation of bubbles and holes, and improve the filling effect.

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

[0054] After the wafer trench 11 is filled, laser sintering and curing start. After the first filling, the laser power is selected as 30 W, the laser focal length is set to 100 μm, the base platform moving speed is 3 mm / s, and the moving trajectory is the same as that during printing and filling, so as to ensure that the sintering temperature of the bottom layer is about 80 °C.

[0055] Step 5: Repeat Step 3 to Step 4 to complete the filling; After the second filling is completed, set the power of laser sintering and curing to 40 W, and keep other parameters unchanged, so as to ensure that the sintering temperature of the second layer is about 100 °C. After the curing is completed, set the laser power to 95 W, and keep other parameters unchanged, so as to ensure that the sintering temperature is about 330 °C to completely cure the material. Adopting this gradient sintering process can reduce the damage to the wafer substrate and devices caused by high temperature and improve the filling quality.

[0056] Example 4 To prepare the modified nano silver paste, 0.2 g of small-sized nano silver particles (with a particle size of 80 nm) and 0.2 g of sodium dodecyl sulfate solution are placed into an experimental flask, and magnetic stirring is carried out for 30 min to obtain 0.4 g of precursor nano silver paste; 0.4 g of the precursor nano silver paste is added to 2.5 g of traditional nano silver paste (the particle size of traditional nano silver particles is 0.5 μm, and the mass fraction of traditional nano silver particles is 80 wt%), and 0.16 g of strong polar solvent N,N-dimethylformamide is added, and they are mixed evenly through a high-speed ball milling and dispersion process. The ball milling speed is set at 300 rpm, the ball milling time is set at 2 h, and the modified nano silver paste is obtained after filtration.

[0057] The specific filling process includes: Step 1: Pretreat the etched wafer trench 11 Select the wafer trench 11 with a width of 100 μm and a depth of 50 μm for the filling process. The interval between the wafer trenches 11 is 10 mm. The inner wall of the wafer trench 11 obtained after etching is not completely vertical and has a certain inclination angle. The cross-section is as Figure 3 shown. The wafer trench 11 is treated using plasma technology. The power of the plasma is 100 W, and the treatment time is 3 min to activate its inner surface and enhance the adhesion of the nano silver paste.

[0058] Step 2: Set the initial parameters of the filling process based on the specific shape and size of the wafer trench 11 and determine the filling times According to the selected wafer trench 11, the extrusion air pressure is selected as 130 kPa, the height between the needle and the substrate is 0.2 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the depth-to-width ratio of the selected wafer trench 11 is 1:2, and the filling times are determined to be 2 times. The moving trajectory starts from the edge trench according to the interval distance between the wafer trenches 11, moves in a serpentine manner, first horizontally and then vertically until all channels are filled.

[0059] Step 3: Extrude the nano silver paste using the inkjet direct writing technology, and use the gas flow assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; Extrude the prepared modified nano silver paste according to the initial parameters in Step 2. The position and direction of the gas flow setting are as Figure 2 shown. The included angle between the gas flow nozzle 3 and the extrusion needle 2 is 10°, the distance between the end of the gas flow nozzle 3 and the end of the extrusion needle 2 in the vertical direction is 5 mm, the gas flow pressure is set at 200 kPa, and dry nitrogen is evenly blown into the wafer trench 11 to enhance the fluidity of the high-viscosity nano silver paste, and at the same time break its surface tension, avoid the generation of bubbles and holes, and improve the filling effect.

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

[0061] After the filling of the wafer trench 11 is completed, laser sintering and curing are started. After the first filling, the laser power is selected to be 30 W, the laser focal length is set to 100 μm, the moving speed of the base is 3 mm / s, and the moving trajectory is the same as that during printing and filling, so as to ensure that the sintering temperature of the bottom layer is about 80 °C.

[0062] Step Five: Repeat Step Three to Step Four to complete the filling; After the second filling is completed, the power of laser sintering and curing is set to 40 W, and other parameters remain unchanged, so as to ensure that the sintering temperature of the second layer is about 100 °C. After the curing is completed, the laser power is set to 100 W, and other parameters remain unchanged, so as to ensure that the sintering temperature is about 350 °C to completely cure the material. Adopting this gradient sintering process can reduce the damage to the wafer substrate and devices caused by high temperature and improve the filling quality.

[0063] Example 5 Prepare the modified nano silver paste. Take 0.25 g of small-sized nano silver particles (particle size is 100 nm) and 0.5 g of polyvinylpyrrolidone solution and put them into an experimental bottle. Use magnetic stirring treatment for 30 min to obtain 0.75 g of precursor nano silver paste; add 0.75 g of precursor nano silver paste to 7.5 g of traditional nano silver paste (the particle size of traditional nano silver particles is 0.8 μm, and the mass fraction of traditional nano silver particles is 80 wt%), and add 0.75 g of strongly polar solvent N-methylpyrrolidone, and mix them evenly through a high-speed ball milling and dispersion process. Set the ball milling speed to 300 rpm and the ball milling time to 2 h. After filtration, the modified nano silver paste is obtained.

[0064] The specific filling process includes: Step One: Pretreat the etched wafer trench 11 Select the wafer trench 11 with a width of 100 μm and a depth of 50 μm for the filling process. The interval between the wafer trenches 11 is 10 mm. The inner wall of the wafer trench 11 obtained after etching is not completely vertical and has a certain inclination angle. The cross-section is as Figure 3 shown. Use plasma technology to treat the wafer trench 11. The power of the plasma is 100 W and the treatment time is 3 min to activate its inner surface and enhance the adhesion of the nano silver paste.

[0065] Step Two: Set the initial parameters of the filling process based on the specific shape and size of the wafer trench 11 and determine the number of fillings According to the selected wafer trench 11, the extrusion air pressure is selected as 130 kPa, the height between the needle and the substrate is 0.2 mm, and the substrate moving speed is 60 mm / s. In this embodiment, the aspect ratio of the selected wafer trench 11 is 1:2, the filling times are determined to be 2 times, and the moving trajectory starts from the edge trench according to the interval distance between the wafer trenches 11, moving in a serpentine manner, first horizontally and then vertically until all channels are filled.

[0066] Step 3: Extrude the modified nano silver paste using the inkjet direct writing technology, and adopt the gas flow assisted filling technology during the material extrusion process to make it spread evenly in the wafer trench 11; Extrude the prepared modified nano silver paste according to the initial parameters in Step 2. The position and direction of the gas flow setting are as Figure 2 shown. The included angle between the gas flow nozzle 3 and the extrusion needle 2 is 10°, the vertical distance between the end of the gas flow nozzle 3 and the end of the extrusion needle 2 is 8 mm, the gas flow pressure is set to 250 kPa, and dry nitrogen is evenly blown 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 holes, and improving the filling effect.

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

[0068] After the wafer trench 11 is filled, start laser sintering and curing. After the first filling, select the laser power as 30 W, set the laser focal length to 100 μm, the moving speed of the base is 3 mm / s, and the moving trajectory is the same as that during printing and filling, so as to ensure that the sintering temperature of the bottom layer is about 80 °C.

[0069] Step 5: Repeat Step 3 to Step 4 to complete the filling; After the second filling is completed, set the power of laser sintering and curing to 40 W, and keep other parameters unchanged, so as to ensure that the sintering temperature of the second layer is about 100 °C. After the curing is completed, set the laser power to 100 W, and keep other parameters unchanged, so as to ensure that the sintering temperature is about 350 °C to completely cure the material. Adopting this gradient sintering process can reduce the damage to the wafer substrate and devices caused by high temperature and improve the filling quality.

[0070] Comparative Example 1 Same as Example 1, only the gas flow assisted filling process is not used during filling.

[0071] Figure 4 Figure 27 is the scanning electron microscope image of the modified nano silver paste and the traditional nano silver paste prepared in Example 1 after curing. It can be seen from the figure that the small-sized nano silver particles in the modified nano silver paste are filled between the large-sized nano silver particles, making it more dense.

[0072] Figure 5 It is a scanning electron microscope image of the cross-section of a wafer trench after filling in Embodiment 1 and Comparative Example 1 of the present application. It can be seen from the figure that defects caused by bubble residues will occur without using the gas flow-assisted filling process. Therefore, the high-precision wafer trench filling method based on gas flow assistance provided by the present application can effectively avoid the generation of holes.

[0073] In the description of the present application, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more, unless otherwise specifically defined.

[0074] In addition, the reference to "one embodiment" throughout this specification; the phrase "in one embodiment", "an example" or similar language means that the specific features, structures or characteristics described in connection with the embodiment are included in at least one embodiment of the present application. Thus, the appearances of the phrase "in one embodiment" and similar language throughout this specification may or may not all refer to the same embodiment.

[0075] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A high-precision wafer groove filling method based on airflow assistance, characterized in that: Specifically: S1 uses ink direct writing technology to fill nano silver paste into the wafer grooves on the substrate (1), and uses airflow assisted filling technology to evenly spread the nano silver paste in the wafer grooves; S2 uses a gradient sintering process to laser sinter the filling material to ensure that the sintering temperature of the bottom layer is 80℃~100℃, the sintering temperature difference between two 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 times until the filling is completed, and finally performs high-temperature laser sintering at 330° C. to 380° C. to optimize the temperature resistance of the nano silver paste.

2. The high-precision wafer trench filling method according to claim 1, characterized in that: In step S1, in the ink direct writing technology, the extrusion pressure of the nano silver paste is 100 kPa to 200 kPa, the distance between the extrusion needle (2) and the substrate (1) is 0 mm to 0.5 mm, and the moving speed of the substrate (1) is 50 mm / s to 200 mm / s.

3. The high-precision wafer trench filling method according to claim 1, characterized in that: 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 degrees, and the flow direction of the airflow ejected by the airflow nozzle (3) in the horizontal direction is opposite to the moving direction of the substrate (1).

4. The high-precision wafer trench filling method according to 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 5 mm to 8 mm, and the airflow pressure of the airflow nozzle (3) is 200 kPa to 500 kPa.

5. The high-precision wafer trench filling method according to claim 1, characterized in that: In step S1 , the wafer trench is pre-treated before filling, so as to activate the surface of the wafer trench.

6. The high-precision wafer trench filling method according to claim 5, characterized in that: The wafer grooves are pretreated by plasma surface activation.

7. The high-precision wafer trench filling method according to claim 1, characterized in that: In step S1, a modified nano-silver paste is filled into the wafer grooves. The preparation method of the modified nano-silver paste is as follows: a dispersant is mixed with small-sized nano-silver particles to obtain a precursor nano-silver paste, and then the precursor nano-silver paste is mixed with a traditional nano-silver paste and a strong polar solvent is added to obtain a modified nano-silver paste, wherein the particle size of the small-sized nano-silver particles is 50nm to 100nm, and the particle size of the traditional nano-silver particles in the traditional nano-silver paste is 0.5μm to 1μm.

8. The high-precision wafer trench filling method according to claim 7, characterized in that: The mass ratio of the small-sized nano-silver particles to the traditional nano-silver particles in the modified nano-silver paste is 1:10 to 1:

30.

9. The high-precision wafer trench filling method according to claim 7, characterized in that: The dispersant includes one or more of polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and sodium dodecyl sulfate, and the mass ratio of the dispersant to the small-sized nano silver particles 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. The added amount of the strong polar solvent is 5% to 10% of the mass of the traditional nano silver paste.

10. The high-precision wafer trench filling method according to any one of claims 1 to 9, characterized in that: In step S3, the method for determining the number of filling times is: When the aspect ratio of the wafer trench is less than 1, the number of filling times is 2; When the aspect ratio of the wafer trench is 1 to 2, the number of filling times is 4; When the aspect ratio of the wafer groove is greater than 2, the wafer groove is filled and sintered in layers, the aspect ratio of each layer of grooves is less than 2 and the number of filling times of each layer of grooves is 2 to 4 times.

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