Non-pressure silver sintering process for improving reliability of SiC chip

Abstract

The invention discloses a non-pressure silver sintering process for improving the reliability of a SiC chip, and relates to the technical field of semiconductor chips, and the process comprises the following steps: powder heating: after nano-silver particles are heated to reach the thermal decomposition temperature of an organic layer, forming a sintering neck among the nano-silver particles, and carrying out dense diffusion, silver atoms in the nano-silver paste are migrated to a sintering neck area through diffusion and cooled, the SiC chip is placed in a sintering layer, the bonded SiC chip assembly is placed in a high-temperature environment, and metal particles are melted and mutually diffused. According to the non-pressure silver sintering process for improving the reliability of the SiC chip, a low-temperature nano-silver welding technology is adopted, and the components of a sintering connection layer of the SiC chip are set to comprise one or more of gold, silver and copper, so that organic coating layer residues in a sintering joint are reduced, the sintering sufficiency is improved, and the reliability strength of the SiC chip is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor chips, and in particular to a pressureless silver sintering process for improving the reliability of SiC chips. Background Art

[0002] SiC chip is a semiconductor device based on silicon carbide, mainly used in power electronics applications under high temperature, high pressure and high frequency conditions. Silicon carbide (SiC) chips are widely used in many high-end fields due to the unique properties of the material. Silicon carbide has the characteristics of large bandgap, strong thermal stability, high thermal conductivity and strong radiation resistance. These advantages enable SiC chips to operate stably in extreme environments. Compared with traditional silicon-based semiconductors, SiC chips can withstand higher voltages and temperatures, which makes them have broad application prospects in power electronics, new energy vehicles, uninterruptible power supplies and other fields.

[0003] SiC power modules are the current market trend and have significant advantages in improving power conversion efficiency, system performance and reliability. SiC chips can work reliably and stably under conditions above 300°C. It is expected that the junction temperature of SiC power modules can reach 170 to 200°C. Traditional vacuum reflow soldering materials such as solder sheets and tin belong to a type of soft soldering, and their melting points are generally below 300°C. Limited by the melting point of the solder, at temperatures of 175 to 200°C, the performance of the solder layer degrades, and the creep fatigue effect is obvious, which seriously affects reliability. Therefore, traditional solders cannot give full play to the advantages of SiC materials. At the same time, when the sintering temperature is too low or the sintering time is too short, the organic layer in the nano-silver paste will not volatilize and decompose completely, and there will still be a lot of organic coating residues inside the sintered joint, resulting in insufficient sintering.

[0004] Therefore, a pressureless silver sintering process for improving the reliability of SiC chips is proposed to solve the above-mentioned problems. Summary of the invention

[0005] The object of the present invention is to provide a pressureless silver sintering process for improving the reliability of SiC chips, so as to solve the problems raised in the above background technology.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A pressureless silver sintering process for improving the reliability of SiC chips comprises the following steps:

[0008] Step 1: Powder heating. After the nanosilver particles are heated to the thermal decomposition temperature of the organic layer, a sintering neck is formed between the nanosilver particles. Then the sintering neck gradually disappears, and the nanosilver paste polymerizes and interconnects to form a whole, and diffuses atoms with the interconnecting material.

[0009] Step 2: Diffusion and densification. The silver atoms in the nanosilver paste migrate to the sintering neck area by diffusion. As the sintering neck continues to grow, the distance between adjacent silver particles gradually decreases, forming a continuous pore network.

[0010] Step 3: Cooling, put in the SiC chip, pre-bake and cool it to remove organic solvents and other harmful components in the sintered material to obtain a SiC chip assembly.

[0011] Step 4: Sintering layer: Place the bonded SiC chip assembly in a high temperature environment to melt the metal particles and diffuse them into each other, completing the pressureless silver sintering process of the SiC chip.

[0012] The inert gas in the sintering process is set to nitrogen, and the oxygen concentration is set to ≤5000ppm.

[0013] By adopting the above technical solution, the organic layer in the nano silver paste is completely volatilized and decomposed, the organic coating layer residue inside the sintered joint is reduced, and the sintering adequacy is increased.

[0014] The size of the nanosilver particles is 8 to 100 nm;

[0015] The size of the SiC chip is 8-12 mm.

[0016] By adopting the above technical solution, since the melting point of silver is as high as 961°C, during the high-temperature sintering process, the typical fatigue effect that occurs in the soft solder connection layer with a melting point less than 300°C will not occur, making the SIC chip have extremely high reliability.

[0017] The decomposition temperature of the organic layer during the powder heating is set at 80 to 100°C, and the heating rate is 5°C / min.

[0018] By adopting the above technical solution, the SiC chip has extremely high reliability.

[0019] The interconnect material includes a dispersant, an antioxidant, Al2O3 to Y2O3 (YAG) and a polymer;

[0020] The mass ratio of the dispersant, antioxidant, Al2O3 to Y2O3 (YAG) and polymer is 1 to 3: 1 to 3: 0.5 to 2: 2 to 5;

[0021] The dispersant includes one or more of sodium citrate, sodium humate, sodium phosphate, sodium silicate, sodium carbonate, sodium metasilicate, sodium polyacrylate, polyacrylamide, styrene to maleic anhydride copolymer, sodium pyrophosphate and sodium silicate complex, and potassium citrate and sodium polymetaphosphate complex;

[0022] The antioxidant comprises one or more of silicon nitride, titanium boride and zirconium boride,

[0023] By adopting the above technical solution, the composition of the SiC chip sintering connection layer is set to include one or more of gold, silver and copper, so that the chip has excellent electrical and thermal conductivity. When the nanosilver particles are sintered, when the sintering temperature is too low or the sintering time is too short, the organic layer in the nanosilver paste is completely volatilized and decomposed.

[0024] The pre-baking temperature is set to 80°C for 60 minutes.

[0025] By adopting the above technical solution, the preheating temperature conditions of the pressureless silver sintering process are determined.

[0026] The powder was diffused and densely heated at 250°C for 60 minutes.

[0027] By adopting the above technical solution, the heating temperature conditions of the pressureless silver sintering process are determined.

[0028] The cooling rate is set at 5°C / min.

[0029] By adopting the above technical solution, the cooling temperature conditions of the pressureless silver sintering process are determined.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. In the present invention, by adopting a pressureless silver sintering process, the composition of the SiC chip sintering connection layer is set to include one or more of gold, silver and copper, so that the chip has excellent electrical and thermal conductivity, so that when the nano silver particles are sintered, when the sintering temperature is too low or the sintering time is too short, the organic layer in the nano silver paste is completely volatilized and decomposed, and the organic coating layer residue is reduced inside the sintered joint, thereby increasing the sintering adequacy;

[0032] 2. In the present invention, since the melting point of silver is as high as 961°C, the typical fatigue effect that occurs in the solder connection layer with a melting point of less than 300°C will not occur during the high-temperature sintering process, so that the SiC chip has extremely high reliability and increases the reliable strength of the SiC chip. By adding Al2O3 to Y2O3, Al2O3 and Y2O3 can form a garnet structure with a cubic crystal system, which gives the material excellent optical and mechanical properties;

[0033] 3. In the present invention, by using sintered silver atomic material, the sintered material has a sintering temperature similar to that of traditional soft solder, and the sintered material does not contain lead, and is an environmentally friendly material, which increases the practicality of SiC silicon carbide chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1This is a schematic diagram of the overall process flow of a pressureless silver sintering process for improving the reliability of SiC chips according to the present invention;

[0035] Figure 2 This is a schematic diagram of temperature conditions for a pressureless silver sintering process for improving the reliability of SiC chips according to the present invention. DETAILED DESCRIPTION

[0036] Example 1

[0037] See also Figure 1 , a pressureless silver sintering process for improving the reliability of SiC chips, comprising the following steps:

[0038] Step 1: Powder heating. After the nanosilver particles are heated to the thermal decomposition temperature of the organic layer, a sintering neck is formed between the nanosilver particles. Then the sintering neck gradually disappears, and the nanosilver paste polymerizes and interconnects to form a whole, and diffuses atoms with the interconnecting material.

[0039] Step 2: Diffusion and densification. The silver atoms in the nanosilver paste migrate to the sintering neck area by diffusion. As the sintering neck continues to grow, the distance between adjacent silver particles gradually decreases, forming a continuous pore network.

[0040] Step 3: Cooling, put in the SiC chip, pre-bake and cool it to remove organic solvents and other harmful components in the sintered material to obtain a SiC chip assembly.

[0041] Step 4: Sintering layer: Place the bonded SiC chip assembly in a high temperature environment to melt the metal particles and diffuse them into each other, completing the pressureless silver sintering process of the SiC chip.

[0042] The inert gas in the sintering process is set to nitrogen, and the oxygen concentration is set to ≤5000ppm.

[0043] The size of nanosilver particles ranges from 8 to 100 nm;

[0044] The size of the SiC chip is 8-12 mm.

[0045] The decomposition temperature of the organic layer during the powder heating was set at 80 to 100°C, and the heating rate was 5°C / min.

[0046] Interconnect materials include dispersants, antioxidants, Al2O3 to Y2O3 (YAG) and polymers;

[0047] The mass ratio of the dispersant, antioxidant, Al2O3 to Y2O3 (YAG) and polymer is 1 to 3: 1 to 3: 0.5 to 2: 2 to 5;

[0048] The dispersant includes one or more of sodium citrate, sodium humate, sodium phosphate, sodium silicate, sodium carbonate, sodium metasilicate, sodium polyacrylate, polyacrylamide, styrene to maleic anhydride copolymer, sodium pyrophosphate and sodium silicate complex, and potassium citrate and sodium polymetaphosphate complex;

[0049] The antioxidant includes one or more of silicon nitride, titanium boride and zirconium boride.

[0050] The use steps of the present invention are as follows: when the pressureless silver sintering process is performed on the SiC chip, the composition of the sintering connection layer of the SiC chip is set to include one or more of gold, silver and copper by adopting the pressureless silver sintering process, so that the chip has excellent electrical and thermal conductivity. When the nano-silver particles are sintered, when the sintering temperature is too low or the sintering time is too short, the organic layer in the nano-silver paste is completely volatilized and decomposed, the organic coating layer residue is reduced inside the sintered joint, and the sintering adequacy is increased.

[0051] Example 2

[0052] See also Figure 1 Based on Example 1, a pressureless silver sintering process for improving the reliability of SiC chips includes the following steps:

[0053] Step 1: Powder heating. After the nanosilver particles are heated to the thermal decomposition temperature of the organic layer, a sintering neck is formed between the nanosilver particles. Then the sintering neck gradually disappears, and the nanosilver paste polymerizes and interconnects to form a whole, and diffuses atoms with the interconnecting material.

[0054] Step 2: Diffusion and densification. The silver atoms in the nanosilver paste migrate to the sintering neck area by diffusion. As the sintering neck continues to grow, the distance between adjacent silver particles gradually decreases, forming a continuous pore network.

[0055] Step 3: Cooling, put in the SiC chip, pre-bake and cool it to remove organic solvents and other harmful components in the sintered material to obtain a SiC chip assembly.

[0056] Step 4: Sintering layer: Place the bonded SiC chip assembly in a high temperature environment to melt the metal particles and diffuse them into each other, completing the pressureless silver sintering process of the SiC chip.

[0057] The pre-baking temperature was set to 80°C for 60 minutes.

[0058] The powders were diffusion densified by heating at 250 °C for 60 min.

[0059] The cooling rate was set at 5°C / min.

[0060] The use steps of the present invention are as follows: The present invention adopts sintered silver atomic material so that the sintered material has a sintering temperature similar to that of traditional soft solder, and the sintered material does not contain lead, and is an environmentally friendly material, thereby increasing the practicality of SiC silicon carbide chips. Since the melting point of silver is as high as 961°C, during the high-temperature sintering process, the typical fatigue effect that occurs in the soft solder connection layer with a melting point of less than 300°C will not occur, thereby making the SiC chip extremely reliable and increasing the reliable strength of the SiC chip. By adding Al2O3 to Y2O3, Al2O3 and Y2O3 can form a garnet structure with a cubic crystal system, which gives the material excellent optical and mechanical properties.

[0061] When the pressureless silver sintering process is performed on the SiC chip, the nanosilver particles are first heated to reach the thermal decomposition temperature of the organic layer, and a sintering neck is formed between the nanosilver particles. Then the sintering neck gradually disappears, and the nanosilver paste is polymerized and interconnected to gradually form a whole, and the atoms diffuse with the interconnection material. By adopting the pressureless silver sintering process, the composition of the sintering connection layer of the SiC chip is set to include one or more of gold, silver and copper, so that the chip has excellent electrical and thermal conductivity. When the nanosilver particles are sintered, when the sintering temperature is too low or the sintering time is too short, the organic layer in the nanosilver paste is completely volatilized and decomposed, and the organic coating layer residue is reduced inside the sintering joint, thereby increasing the sintering adequacy; the silver atoms in the nanosilver paste are Diffusion migrates to the sintering neck area. As the sintering neck continues to grow, the distance between adjacent silver particles gradually decreases, forming a continuous pore network. Since the melting point of silver is as high as 961°C, during the high-temperature sintering process, the typical fatigue effect that occurs in the soft solder connection layer with a melting point of less than 300°C will not occur, making the SiC chip extremely reliable and increasing the reliable strength of the SiC chip. By adding Al2O3 to Y2O3, Al2O3 and Y2O3 can form a garnet structure with a cubic crystal system, which gives the material excellent optical and mechanical properties; put the SiC chip in, pre-bake and cool it to remove organic solvents and other harmful components in the sintered material to obtain a SiC chip component. The bonded SiC chip assembly is placed in a high-temperature environment to melt the metal particles and diffuse with each other, completing the pressureless silver sintering process of the SiC chip. By using sintered silver atomic materials, the sintered material has a sintering temperature similar to that of traditional soft solder, and the sintered material does not contain lead, which is an environmentally friendly material, which increases the practicality of the SiC silicon carbide chip. Silver atoms migrate to the sintering neck area by diffusion, so that the sintering neck continues to grow, and the distance between adjacent silver particles gradually decreases, forming a continuous pore network. As the sintering process proceeds, the holes gradually become smaller, and the sintering density and strength increase significantly. In the final stage of sintering, most of the holes are completely divided, small holes gradually disappear, and large holes gradually become smaller until the final density is reached.

[0062] The test results of the pressureless silver sintering process are shown in Table 1 below:

[0063] Table 1:

[0064]

[0065] From the test results in the above table, it can be seen that the organic layer in the nano silver paste is completely volatilized and decomposed, and the organic coating residue inside the sintered joint is reduced, which increases the practicality of the SiC silicon carbide chip.

[0066] By comparing a pressureless silver sintering process for improving the reliability of SiC chips in the prior art with the pressureless silver sintering process in the present application, it can be found that the pressureless silver sintering process in the present application has the following obvious differences compared with the prior art: 1. By adopting the pressureless silver sintering process, the composition of the sintering connection layer of the SiC chip is set to include one or more of gold, silver and copper, so that the chip has excellent electrical and thermal conductivity, so that when the nanosilver particles are sintered, when the sintering temperature is too low or the sintering time is too short, the organic layer in the nanosilver paste is completely volatilized and decomposed, and the sintering 1. Reduce the organic coating residue inside the junction and increase the sintering adequacy; 2. Since the melting point of silver is as high as 961°C, during the high-temperature sintering process, the typical fatigue effect that occurs in the soft solder connection layer with a melting point of less than 300°C will not occur, making the SiC chip extremely reliable and increasing the reliable strength of the SiC chip; 3. By using sintered silver atomic material, the sintering material has a sintering temperature similar to that of traditional soft solder, and the sintered material does not contain lead, which is an environmentally friendly material, increasing the practicality of the SiC silicon carbide chip.

[0067] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A pressureless silver sintering process for improving the reliability of SiC chips, characterized in that: The following steps are involved: Step 1: Powder heating. After the nanosilver particles are heated to the thermal decomposition temperature of the organic layer, a sintering neck is formed between the nanosilver particles. Then the sintering neck gradually disappears, and the nanosilver paste polymerizes and interconnects to form a whole, and diffuses atoms with the interconnecting material. Step 2: Diffusion and densification. The silver atoms in the nanosilver paste migrate to the sintering neck area by diffusion. As the sintering neck continues to grow, the distance between adjacent silver particles gradually decreases, forming a continuous pore network. Step 3: Cooling, put in the SiC chip, pre-bake and cool to remove organic solvents and other harmful components in the sintered material to obtain a SiC chip assembly. Step 4: Sintering layer: Place the bonded SiC chip assembly in a high temperature environment to melt the metal particles and diffuse them into each other, completing the pressureless silver sintering process of the SiC chip.

2. A pressureless silver sintering process for improving the reliability of SiC chips according to claim 1, characterized in that: The inert gas in the sintering process is set to nitrogen, and the oxygen concentration is set to ≤5000ppm.

3. The pressureless silver sintering process for improving the reliability of SiC chips according to claim 1, characterized in that: The size of the nanosilver particles is 8 to 100 nm; The size of the SiC chip is 8-12 mm.

4. The pressureless silver sintering process for improving the reliability of SiC chips according to claim 1, characterized in that: The decomposition temperature of the organic layer during the powder heating is set at 80 to 100° C., and the heating rate is 5° C. / min.

5. The pressureless silver sintering process for improving the reliability of SiC chips according to claim 1, characterized in that: The interconnect material includes a dispersant, an antioxidant, Al2O3 to Y2O3 (YAG) and a polymer; The mass ratio of the dispersant, antioxidant, Al2O3 to Y2O3 (YAG) and polymer is 1 to 3: 1 to 3: 0.5 to 2: 2 to 5; The dispersant includes one or more of sodium citrate, sodium humate, sodium phosphate, sodium silicate, sodium carbonate, sodium metasilicate, sodium polyacrylate, polyacrylamide, styrene to maleic anhydride copolymer, sodium pyrophosphate and sodium silicate complex, and potassium citrate and sodium polymetaphosphate complex; The antioxidant includes one or more of silicon nitride, titanium boride and zirconium boride.

6. The pressureless silver sintering process for improving the reliability of SiC chips according to claim 1, characterized in that: The pre-baking temperature was set to 80° C. for 60 minutes.

7. The pressureless silver sintering process for improving the reliability of SiC chips according to claim 1, characterized in that: The powder was diffusion densified by heating at 250°C for 60 minutes.

8. The pressureless silver sintering process for improving the reliability of SiC chips according to claim 1, characterized in that: The cooling rate was set to 5°C / min.

Images