A method for reducing black point defects of silicon nitride substrate based on regulating atmosphere during glue discharge process

Abstract

The application discloses a method for reducing black point defects of a silicon nitride substrate based on atmosphere regulation during a glue removal process, and belongs to the technical field of advanced ceramic substrate manufacturing. The method comprises the following steps: placing a silicon nitride substrate blank in a glue removal furnace; introducing an atmosphere containing water vapor and ammonia into the glue removal furnace during the glue removal process, wherein the water vapor is used for promoting the oxidative volatilization of organic group cracking products, and the ammonia is used for nitriding modification on residual carbonized areas; and performing sintering treatment after the glue removal is completed. By introducing water vapor and ammonia to regulate the atmosphere during the glue removal process, the black point defects on the surface of the silicon nitride substrate are effectively reduced, the appearance consistency and reliability of the substrate are improved, and the method is suitable for the preparation of high-reliability IGBT power module packaging substrates.

Description

Technical Field

[0001] This invention relates to the field of advanced ceramic substrate manufacturing technology, and in particular to a method for reducing black spot defects in silicon nitride substrates by controlling the atmosphere during the adhesive removal process. Background Technology

[0002] Silicon nitride ceramic substrates have excellent thermal conductivity, electrical insulation and mechanical strength, making them an important substrate for high-reliability power device packaging (such as IGBT modules) and one of the preferred materials for high-temperature and high-pressure applications.

[0003] The reliability of silicon nitride substrates depends not only on the mechanical and thermal properties of the material itself, but also on the overall defects, surface blemishes / black spots, and internal foreign matter, as well as the uniformity of appearance. In actual production, organic binders, dispersants, and various auxiliary materials are required during the molding stage of silicon nitride ceramic substrates. During the subsequent debinding (degreasing) heat treatment, these organic components undergo thermal decomposition. Residual carbon components, organic decomposition products, and incomplete reaction products easily form carbonized, locally colored, or dark areas on or near the substrate surface, i.e., so-called "black spot" defects. These defects become local electric and thermal field concentration points during subsequent metallization, packaging, and reliability testing, thus significantly reducing the long-term thermal cycling, damp heat aging, and high-voltage breakdown reliability of IGBT modules.

[0004] Existing debinding processes mainly rely on temperature control and unstable atmosphere emission, with inert or weakly reducing atmospheres being commonly used. However, these processes cannot effectively remove deep-seated residues and lack the ability to actively remove residual carbonaceous matter, leading to a high incidence of black spot defects. Consequently, product yield and reliability fail to meet the application requirements of high-end power electronic devices. Summary of the Invention

[0005] To address the technical problems of incomplete decomposition of organic components and residual carbonaceous matter leading to black spot defects in existing silicon nitride substrate descaling processes, this invention provides a method for reducing black spot defects in silicon nitride substrates by regulating the atmosphere during the descaling process. This method optimizes the decomposition path of organic groups and removes residual carbonaceous matter through atmosphere regulation.

[0006] This invention is achieved through the following technical solution: A method for reducing black spot defects in silicon nitride substrates by controlling the atmosphere during the desizing process includes the following steps: placing a silicon nitride substrate blank in a desizing furnace; during the desizing process, introducing an atmosphere containing one or two gases, namely water vapor and ammonia, into the desizing furnace, wherein the water vapor is used to promote the oxidative volatilization of organic group pyrolysis products, and the ammonia is used to nitridate and modify the residual carbonized areas; after the desizing is completed, sintering is performed to obtain a silicon nitride ceramic substrate.

[0007] Preferably, the volume content of water vapor in the atmosphere is 0.1% to 5%, and the volume content of ammonia is 0.1% to 3%.

[0008] Preferably, the temperature range of the glue removal process is 50℃~800℃, and the temperature range of the water vapor and ammonia gas introduced is 200℃~650℃.

[0009] Preferably, the introduction rate of the atmosphere containing water vapor and ammonia is 0.1 L / min to 10 L / min.

[0010] Preferably, during the glue discharge process, the ratio of water vapor and ammonia and the flow rate are adjusted in segments according to the preset temperature and time curves.

[0011] Preferably, water vapor and ammonia are introduced sequentially, in stages, or simultaneously during the glue removal process.

[0012] Preferably, the debinding furnace is also circulated with a basic inert atmosphere or a weak reducing atmosphere.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) With the participation of water vapor, the decomposition products and products of residual organic components can be further oxidized, making the residual carbonized substances more volatile or converted into gaseous products for discharge, thereby reducing the formation of local carbon black spots. (2) The addition of ammonia can chemically interact with the local carbonized area or trace non-ideal phase on the surface, change the chemical state of local defects, realize the nitriding modification of the residual carbonized area, and further suppress the formation of dark residue and defects. (3) By adjusting atmospheric parameters such as the ratio of water vapor to ammonia, the injection rate and the temperature curve, the glue removal process can be flexibly optimized to meet the defect control requirements of substrates of different product specifications. (4) After the black spot defects on the substrate surface are reduced, the appearance consistency is improved. At the same time, the concentration of local electrothermal gradient can be reduced, which is conducive to improving the electrical and thermal reliability of IGBT power modules. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 This is a schematic diagram of the temperature curve and atmosphere introduction sequence during the glue removal process of the present invention; Figure 3 A physical image of the substrate surface prepared using the original process method; Figure 4 This is a physical image of the substrate surface prepared by the method of the present invention. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0016] Implementation Method 1: After the silicon nitride substrate blank is formed according to conventional methods, it is placed in a debinding furnace. In the initial stage of debinding, inert nitrogen gas is introduced into the furnace as a base atmosphere, and the substrate temperature is slowly raised to 200-400°C. Simultaneously, a mixture of 0.5%-3% water vapor by volume is introduced to maintain an oxidizing environment for organic groups during thermal decomposition. In the later stages of debinding, ammonia gas with a volume content of 0.2%-2% is introduced within the temperature range of 400-650°C, and the proportion of water vapor introduced is gradually reduced to allow for trace nitriding modification in the remaining carbonized areas. Finally, the introduction of water vapor and ammonia is stopped at 650-800°C, leaving only an inert atmosphere to complete the debinding process. After debinding, the temperature is increased at 5°C per minute to a sintering temperature of 1900°C and held for 2 hours for high-temperature sintering densification treatment, resulting in a silicon nitride ceramic substrate with low black spot defects.

[0017] Implementation Method Two: This method employs a segmented atmosphere control strategy. Different mixing ratios of water vapor and ammonia are set at different temperature ranges during the debinding process. Specifically, in the initial stage of debinding (200-300℃), a higher water vapor ratio (3-5%) is used to promote the oxidative decomposition of organic matter. In the middle stage (300-400℃), a reactive atmosphere dominated by ammonia (1-3%) is transitioned to nitriding modification of residual carbonized areas. In the later stage (400-600℃), a low-content water vapor is used to "wash" away residues (0.1-1.5%), achieving a more thorough removal of residual components. The switching points, atmosphere ratios, and inlet rates for each temperature range are adjusted according to the specific substrate formulation and dimensions.

[0018] Implementation Method 3: The atmosphere control method of this invention is applicable to silicon nitride substrate blanks prepared by different molding methods (such as tape casting, slip casting, etc.), and also to substrate products of different specifications and sizes. By pre-setting the proportion and flow rate curves of water vapor and / or ammonia, optimal debinding control for different products can be achieved. During the debinding process, the volume content of water vapor can be adjusted within the range of 0.1% to 5%, the volume content of ammonia can be adjusted within the range of 0.1% to 3%, and the total introduction rate of the mixed atmosphere can be adjusted within the range of 0.1 L / min to 10 L / min. The specific parameters are determined according to factors such as the organic content in the substrate, the substrate thickness, and the furnace loading. After debinding, the number of black spot defects on the surface of the obtained substrate is significantly reduced, to below 2%, and the substrate consistency and reliability are improved.

[0019] according to Figure 3 Figure 4 A comparison of the substrate surface prepared by the original process method and the substrate surface prepared by the method of the present invention shows that the substrate surface prepared by the original process method has obvious black spots. Figure 3 (circled in the middle) The number of black spot defects on the substrate surface prepared by the method of the present invention is significantly reduced.

Claims

1. A method for reducing black spot defects in silicon nitride substrates by controlling the atmosphere during the adhesive removal process, characterized in that, Includes the following steps: Place the silicon nitride substrate blank in a debinding furnace; During the debinding process, an atmosphere containing one or two gases, namely water vapor and ammonia, is introduced into the debinding furnace. The water vapor is used to promote the oxidative volatilization of organic group pyrolysis products, and the ammonia is used to nitridate and modify the residual carbonized area. After the adhesive is removed, a sintering process is performed to obtain a silicon nitride ceramic substrate.

2. The method according to claim 1, characterized in that, The volume content of water vapor in the atmosphere is 0.1% to 5%.

3. The method according to claim 1, characterized in that, The volume content of ammonia in the atmosphere is 0.1% to 3%.

4. The method according to claim 1, characterized in that, The temperature range for the glue removal process is 50℃~800℃, and the temperature range for introducing water vapor and ammonia is 200℃~650℃.

5. The method according to claim 1, characterized in that, The atmosphere containing water vapor and ammonia is introduced at a rate of 0.1 L / min to 10 L / min.

6. The method according to claim 5, characterized in that, During the glue discharge process, the ratio of water vapor and ammonia and the flow rate are adjusted in segments according to the preset temperature and time curves.

7. The method according to claim 6, characterized in that, During the glue removal process, water vapor and ammonia are introduced sequentially, in stages, or simultaneously.

8. The method according to claim 1, characterized in that, The debinding furnace is also purged with a basic inert atmosphere or a weak reducing atmosphere.

9. The method according to claim 1, characterized in that, The silicon nitride ceramic substrate is used as a packaging substrate for IGBT power modules.

10. A silicon nitride ceramic substrate, characterized in that, Prepared by the method according to any one of claims 1 to 9.

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