Method for manufacturing active metal brazed ceramic substrates

Abstract

A method for manufacturing an active metal brazed ceramic substrate includes performing atomic layer deposition on the upper and lower surfaces of a ceramic substrate, forming surface optimization layers on the upper and lower surfaces of the ceramic substrate, performing atomic layer deposition again to form a first brazing material layer on the surface optimization layer, forming a third brazing material layer on the surfaces of two copper plates facing the upper and lower surfaces of the ceramic substrate, and finally stacking the ceramic substrate and the two copper plates one on top of the other to form a layered structure. The layered structure is then brazed at high temperature and under hot pressure to form an active metal brazed ceramic substrate.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an active metal brazing ceramic substrate, and more particularly to a manufacturing method that reduces porosity after brazing in an active metal brazing step. [Background technology]

[0002] The active metal brazing (AMB) process is a method of joining ceramic to metal by using a reaction layer formed by reacting a small amount of active elements contained in the brazing material with ceramic and then wetting it with liquid brazing material.

[0003] Typically, active metal brazing material is first printed on the ceramic surface, then sandwiched between oxygen-free copper, and then high-temperature brazing is carried out in a vacuum brazing furnace. Once the bonding is complete, a wet etching process similar to that used for PCB boards is used to create circuits on the surface, and finally the surface is plated to produce a product with reliable performance.

[0004] AMB substrates are bonded by chemically reacting ceramic with active metal brazing paste at high temperatures, resulting in high bond strength and reliability. However, this method is expensive, there are few suitable brazing materials, and the reliability of the brazing material has a significant impact. Currently, only a few Japanese companies have mastered reliable active metal brazing technology.

[0005] Currently, the porosity of the ceramic interface is one of the important factors in substrate quality, so controlling the porosity at the ceramic interface is important. If the interface porosity is good, service reliability under high temperature and large current can be guaranteed.

[0006] Taking Ag-Cu-Ti active brazing filler metal as an example, the causes of void formation are as follows. (1) Surface quality of raw materials: Scratches, pits, oxidation, organic contamination, and other issues on the surface of ceramic, oxygen-free copper, and brazing filler metal before brazing have a negative impact on the wetting and spreading of the brazing filler metal, leading to potential void risks at the brazing interface. In this regard, there are generally several types of surface contamination and defects in Si3N4 ceramic materials: particle contamination, surface roughness, surface cracks, surface contamination, point defects, dislocations, microcracks, and impurities. Of these, point defects, dislocations, microcracks, impurities, and surface contamination have the greatest impact, and if not treated properly, after wetting the surface with titanium, surface defects can easily penetrate into the ceramic substrate, causing voids, which can have negative effects such as weakening the strength of the substrate-copper film bonding interface, and even posing a risk of voids forming. (2) Inactivation of active elements: The active element (Ti) of Ag-Cu-Ti is sensitive enough to oxygen, so that it is inactivated in the high-temperature brazing process. -3 A vacuum level of better than Pa is often required. If the vacuum level cannot meet the brazing requirements, the Ti oxidation will become inactive, and the brazing filler metal will not be able to wet the Si3N4 ceramic surface, resulting in large-area brazing defects and brazing leaks. (3) Brazing process parameters: Ag-Cu-Ti active brazing filler metal often cannot wet the Si3N4 surface unless the temperature is above 800°C. If the brazing temperature is too low or the heating time is too short, the reaction between Ti and the ceramic surface is insufficient, and the brazing filler metal cannot fully wet the ceramic surface. (4) Brazing paste printing quality: In the process of printing large areas of brazing paste, problems such as missing or uneven printing of the brazing paste are easily encountered. If the brazing material does not spread to cover the missing areas after melting, voids will be formed directly. (5) Gas release from brazing paste: During the brazing process, the gas volatilized from the brazing paste is covered by the flux and forms bubbles. In addition, bubbles are generated by the reaction between the organic acid in the flux and the metal oxide. As the reaction progresses, the bubbles gradually grow larger. The released bubbles leave dense pores on the surface of the brazing paste. Similarly, the unreleased bubbles remain at the brazing interface as the brazing material melts and solidifies, forming voids and posing a risk of the substrate copper film bonding interface cracking during long-term operation.

[0007] A common method for reducing porosity is to remove oil and oxidation from the ceramic and copper pieces during the AMB process to produce silicon nitride copper clad substrates, thereby providing a higher vacuum brazing environment. This is a well-known method for reducing interfacial porosity, but its effectiveness remains limited, and an effective solution is urgently needed.

[0008] Therefore, in this application, a surface optimization layer (silicon nitride, aluminum oxide, or aluminum nitride) is first formed on the upper and lower surfaces of the ceramic substrate by ALD, covering surface defects and planarizing the upper and lower surfaces of the ceramic substrate, thereby reducing the chance of voids. Furthermore, ALD is further used to form a first brazing material layer (titanium or titanium nitride) on the surface optimization layer, and a third brazing material layer (silver) on the copper plate surface. This results in an active metal brazed ceramic substrate, which is then stacked on top of the ceramic substrate and two copper plates and brazed at high temperature and under hot pressure, significantly reducing the chance of voids. Therefore, this invention should be an optimal solution. Summary of the Invention

[0009] The present invention is a method for manufacturing an active metal brazed ceramic substrate, the method comprising: (1) performing atomic layer deposition on the upper and lower surfaces of a ceramic substrate to form a surface optimization layer on the upper and lower surfaces of the ceramic substrate, wherein the surface optimization layer is composed of silicon nitride, aluminum oxide, or aluminum nitride; (2) performing atomic layer deposition on the surface-optimized layer to form a first brazing filler metal layer on the surface-optimized layer, the first brazing filler metal layer comprising titanium; (3) forming a third brazing filler metal layer on the two copper plate surfaces facing the upper and lower surfaces of the ceramic substrate, the third brazing filler metal layer comprising at least copper and silver; (4) The ceramic substrate and two copper plates are stacked one on top of the other to form a layered structure, and the layered structure is subjected to high-temperature, hot-pressure brazing to form an active metal brazed ceramic substrate.

[0010] More specifically, the surface optimization layer is used to cover surface defects on the top and bottom surfaces of the ceramic substrate.

[0011] More specifically, the upper and lower surfaces of the ceramic substrate are first subjected to an atomic layer etching process, then subjected to an atomic layer deposition process to form the surface optimization layer, and then subjected to an atomic layer etching process to remove surface defects on the upper and lower surfaces of the ceramic substrate.

[0012] More specifically, the thickness of the surface optimization layer is 1 nm to 1 μm.

[0013] More specifically, a second brazing material layer is further formed on the first brazing material layer, and the second brazing material layer is made of titanium nitride.

[0014] More specifically, the thickness of the second brazing material layer is 0.1 to 100 nm.

[0015] More specifically, the thickness of the first brazing material layer is 0.1 to 100 nm.

[0016] More specifically, the thickness of the third brazing material layer is 0.1 μm to 100 μm.

[0017] More specifically, the composition of the third braze layer further includes titanium.

[0018] More specifically, the temperature of the high-temperature hot pressure brazing is 750 to 950°C. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a flow chart showing the manufacturing process of the active metal brazing ceramic substrate of the present invention. [Figure 2A] 1 is a structural separation diagram of an active metal brazing ceramic substrate according to a method for producing an active metal brazing ceramic substrate of the present invention; [Figure 2B] 3 is a structural diagram of an active metal brazed ceramic substrate after hot pressing according to the method for producing an active metal brazed ceramic substrate of the present invention. FIG. [Figure 3] 10 is a diagram showing another embodiment of the structure of a ceramic substrate and a first brazing material layer in the method for producing an active metal brazing ceramic substrate of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] Other technical contents, features and effects of the present invention will become apparent from the following detailed description of preferred embodiments, which will be given in conjunction with the accompanying drawings.

[0021] As shown in FIG. 1, the manufacturing method of the active metal brazing ceramic substrate is as follows. (1) Atomic layer deposition is performed on the upper and lower surfaces of the ceramic substrate to form a surface optimization layer on the upper and lower surfaces of the ceramic substrate, the surface optimization layer being composed of silicon nitride, aluminum oxide, or aluminum nitride 101. (2) A first brazing filler metal layer is formed on the surface-optimized layer by atomic layer deposition, and the first brazing filler metal layer is composed of titanium 102. (3) A third brazing filler metal layer is formed on the two copper plate surfaces facing the upper and lower surfaces of the ceramic substrate. The third brazing filler metal layer is composed of at least copper and silver 103. (4) A ceramic substrate and two copper plates are stacked one on top of the other to form a layered structure, and then the layered structure is subjected to high-temperature, hot-pressure brazing to form an active metal brazed ceramic substrate 104 .

[0022] The temperature for high temperature hot pressure brazing is 750~950℃.

[0023] 2A, the active metal brazing ceramic substrate includes a ceramic substrate 11 and two copper plates 12 and 13. Surface optimization layers 14 are attached to the top and bottom surfaces of the ceramic substrate 11. The material of the surface optimization layer 14 is Si3N4, AlN, or Al2O3.

[0024] The surface optimization layer 14 has a thickness of 1 nm to 1 μm.

[0025] The surface optimization layer 14 is used to cover surface defects on the upper and lower surfaces of the ceramic substrate 11 .

[0026] Onto the surface optimization layer 14 a first braze layer 15 (titanium) may be deposited.

[0027] The two copper plates 12, 13 each have a third brazing filler metal layer 17 (copper, silver, titanium) attached to the surface facing the ceramic substrate 11. The third brazing filler metal layer 17 is composed of silver, copper, and titanium (of which the proportion of silver is 66 to 72%, the proportion of copper is 28 to 32%, and the proportion of titanium is 0 to 6%).

[0028] The third brazing material layer 17 is formed on the surfaces of the two copper plates 12, 13 by sputtering or atomic layer deposition.

[0029] The thickness of the first brazing material layer 15 is 0.1 to 100 nm.

[0030] The third brazing material layer 17 has a thickness of 0.1 μm to 100 μm.

[0031] The copper plates 12 and 13 have a thickness of 100 to 1000 μm.

[0032] As shown in FIG. 2B, a layered structure is formed by stacking the layers one on top of the other, and then this layered structure is subjected to high-temperature, hot-pressure brazing to form an active metal brazed ceramic substrate 1.

[0033] Atomic layer deposition (ALD) is a conventional process that involves reacting a chemical gas containing the components to be deposited with a ceramic substrate, then using a large amount of inert gas (e.g., nitrogen or argon) to remove the chemical gas, and then repeating step a described above. This ensures that all reactions occur solely on the surface of the ceramic substrate, forming a single atomic thin film per cycle. This allows for thickness precision of the plating film to be achieved at the atomic level (approximately 0.1 nm) with excellent uniformity. Furthermore, because the growth process is limited to the surface of the ceramic substrate, favorable coverage and uniformity are achieved on the surface of the structure.

[0034] Atomic layer deposition (ALD) can be used to cover defects on the top and bottom surfaces of ceramic substrates to achieve planarization, including point defects, dislocations, microcracks, impurities, and surface contamination.

[0035] In the present invention, surface defects can be covered using atomic layer deposition (ALD), but better results can be obtained if atomic layer etching (ALE) is first used to remove surface micro-defects and then atomic layer deposition (ALD) is further used to cover the surface defects.

[0036] Therefore, the upper and lower surfaces of the ceramic substrate 11 are first subjected to atomic layer etching, and then subjected to atomic layer deposition to form a surface optimization layer on the upper and lower surfaces of the ceramic substrate 11. The atomic layer etching is used to remove surface defects on the upper and lower surfaces of the ceramic substrate 11.

[0037] The atomic layer etching (ALE) process is a conventional technology in which etching gas and inert gas are supplied together to a reaction space using a mass flow controller, and then etching is performed using plasma. Inert gas or nitrogen gas supplied to the reaction space is used as the basic reaction gas to generate plasma, and oxidizing gas or reducing gas such as hydrogen is added to control the etching rate, and the manufacturing process temperature is controlled to approximately 0 to 250 degrees.

[0038] Atomic Layer Etching (ALE) is used to remove defects on the top and bottom surfaces of ceramic substrates, including point defects, dislocations, microcracks, and surface contamination.

[0039] The surface optimization layer 14, the first brazing filler metal layer 15, and the second brazing filler metal layer 16 on the upper and lower surfaces of the ceramic substrate 11 are brought into contact with the third brazing filler metal layer 17 of the copper plates 12 and 13, and then vacuum-packed using a heat-conducting material to obtain a layered structure. The vacuum degree of the vacuum packing is 10 -1 Less than Pa. The thermally conductive material is a flexible metal foil pouch.

[0040] As shown in FIG. 3 , a second brazing filler metal layer 16 may be further formed on the first brazing filler metal layer 15. The second brazing filler metal layer 16 is made of titanium nitride. The second brazing filler metal layer 16 has oxidation resistance and prevents or reduces the possibility of oxidation of the first brazing filler metal layer 15. The present invention may be implemented by forming only the first brazing filler metal layer 15, or by forming both the first brazing filler metal layer 15 and the second brazing filler metal layer 16. The outermost layer of the multi-layer structure is either the first brazing filler metal layer 15 or the second brazing filler metal layer 16.

[0041] The second brazing material layer 16 has a thickness of 0.1 to 100 nm.

[0042] The second braze layer 16 primarily serves to prevent oxidation of titanium metal during subsequent high temperature treatment of the first braze layer 15 and effectively controls intermetallic formation.

[0043] The ceramic substrate 11 is further subjected to a degreasing process, and the first brazing material layer 15 and the second brazing material layer 16 are heated and degreased in an inert gas or reducing gas atmosphere to be attached to the upper and lower surfaces of the ceramic substrate 11. The inert gas includes nitrogen or argon, and the reducing gas includes hydrogen, a mixed gas of nitrogen and hydrogen, or an acidic gas.

[0044] The copper plates 12 and 13 are subjected to a degreasing treatment, and the third brazing material layer 17 is heated and degreased in an inert gas or reducing gas atmosphere to be attached onto the surfaces of the copper plates 12 and 13 .

[0045] The present invention can reduce the rate of voids after treating the upper and lower surfaces of a ceramic substrate using atomic layer etching (ALE) and atomic layer deposition (ALD).

[0046] The first brazing filler metal layer is formed using atomic layer deposition (ALD), which allows its thickness to be controlled with high precision and its surface to be uniformly flat, thereby achieving good bonding with the ceramic substrate. In addition, the uniform thickness of the coating of the first brazing filler metal layer is sufficiently thin, allowing the intermetallic layer between the ceramic substrate and the brazing filler metal to be effectively controlled and formed.

[0047] The method for manufacturing an active metal brazing ceramic substrate provided by the present invention has the following advantages over other prior arts: (1) This application uses atomic layer etching (ALE) to treat the top and bottom surfaces of the ceramic substrate (removing minute defects on the surface), thereby reducing the rate of voids and increasing the yield of active metal brazing ceramic substrates. (2) This application uses atomic layer deposition (ALD) to form a surface optimization layer (silicon nitride, aluminum oxide, or aluminum nitride) on the upper and lower surfaces of a ceramic substrate, resulting in a more favorable processed surface (covering surface defects), while also reducing the incidence of voids and increasing the yield of active metal brazed ceramic substrates. (3) This application uses atomic layer etching (ALE) and atomic layer deposition (ALD) to enhance the wetting ability of the first brazing material layer (titanium) to the ceramic substrate, thereby increasing the bonding strength between the copper and the substrate.

[0048] The present invention has been disclosed by the above-mentioned embodiments, but they are not intended to limit the present invention. Anyone skilled in the art can understand the above-mentioned technical features and embodiments of the present invention and make various changes and modifications within the scope of the present invention without departing from the spirit and scope of the present invention. Therefore, the patent protection scope of the present invention is as defined in the claims attached hereto. [Explanation of symbols]

[0049] 1. Active metal brazing ceramic substrate 11 Ceramic substrate 12 Copper plate 13 Copper plate 14 Surface optimization layer 15 First brazing layer 16 Second brazing layer 17 Third brazing layer

Claims

1. A method for manufacturing an active metal brazing ceramic substrate, comprising: performing an atomic layer deposition process on the upper and lower surfaces of the ceramic substrate to form a surface optimization layer on the upper and lower surfaces of the ceramic substrate, the surface optimization layer being composed of silicon nitride, aluminum oxide, or aluminum nitride; performing an atomic layer deposition process on the surface-optimized layer to form a first brazing filler metal layer on the surface-optimized layer, the first brazing filler metal layer comprising titanium; a third brazing filler metal layer is formed on the two copper plate surfaces facing the upper and lower surfaces of the ceramic substrate, and the components of the third brazing filler metal layer are at least copper and silver; The ceramic substrate and two copper plates are stacked one on top of the other to form a layered structure, and the layered structure is subjected to high-temperature hot pressure brazing to form an active metal brazed ceramic substrate. A method for manufacturing active metal brazed ceramic substrates.

2. 2. The method for manufacturing an active metal brazing ceramic substrate according to claim 1, wherein the surface optimization layer is used to cover surface defects on the upper and lower surfaces of the ceramic substrate.

3. 2. The method for manufacturing an active metal brazing ceramic substrate according to claim 1, wherein the upper and lower surfaces of the ceramic substrate are first subjected to an atomic layer etching process, then subjected to an atomic layer deposition process to form the surface optimization layer, and then subjected to an atomic layer etching process to remove surface defects on the upper and lower surfaces of the ceramic substrate.

4. 2. The method for manufacturing an active metal brazing ceramic substrate according to claim 1, wherein the thickness of the surface optimization layer is 1 nm to 1 μm.

5. 2. The method for manufacturing an active metal brazed ceramic substrate according to claim 1, further comprising forming a second brazing material layer on the first brazing material layer, the second brazing material layer comprising titanium nitride.

6. 6. The method for manufacturing an active metal brazed ceramic substrate according to claim 5, wherein the thickness of the second brazing material layer is 0.1 to 100 nm.

7. 2. The method for manufacturing an active metal brazed ceramic substrate according to claim 1, wherein the thickness of the first brazing material layer is 0.1 to 100 nm.

8. 2. The method for manufacturing an active metal brazed ceramic substrate according to claim 1, wherein the thickness of the third brazing material layer is 0.1 μm to 100 μm.

9. 2. The method for manufacturing an active metal brazed ceramic substrate according to claim 1, wherein the components of said third brazing material layer further include titanium.

10. 2. The method for manufacturing an active metal brazed ceramic substrate according to claim 1, wherein the high-temperature hot pressure brazing temperature is 750 to 950°C.

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