Composite material

Abstract

Provided is a composite material capable of suppressing a problem of thermal stress in association with bonding in manufacturing an SiC semiconductor power device or the like and a thermal cycle during use of a semiconductor. The composite material comprises a low thermal expansion material and a high thermal expansion material, and has a diffusion layer at the interface between the low thermal expansion material and the high thermal expansion material. When the total thickness of the low thermal expansion material and the high thermal expansion material is defined as 100, a Y value calculated according to (the thickness ratio of the low thermal expansion material x Vickers hardness of the low thermal expansion material) / (the thickness ratio of the high thermal expansion material x Vickers hardness of the high thermal expansion material) exceeds 0.72.

Description

Composite material

[0001] The present invention relates to a composite material suitable, for example, for lead wires and heat sinks connected to semiconductor chips, insulating substrates and the like.

[0002] In semiconductor products such as Si semiconductor power devices, Cu, Al and the like have been conventionally used as lead wires and heat sinks connected to semiconductor chips, insulating substrates and the like. Here, there is a large difference in thermal expansion coefficient between Si constituting the semiconductor chip and Cu or Al constituting the lead wire or heat sink. When a semiconductor chip is bonded to a lead wire, a heat sink or the like, the generation of thermal stress caused by the difference in thermal expansion between the semiconductor chip and the lead wire or heat sink may cause peeling at the bonded portion between the semiconductor chip and the lead wire or heat sink formed by solder or brazing filler metal. In addition, due to thermal cycles of temperature rise and drop that occur during use of the semiconductor, in addition to an increase in electrical resistance of the lead wire, the generation of the aforementioned thermal stress may also cause peeling at the bonded portion between the semiconductor chip and the lead wire or heat sink formed by solder or brazing filler metal.

[0003] Therefore, there is a demand for a metal material that has a low coefficient of thermal expansion close to that of semiconductor chips and insulating substrates, and also exhibits high thermal conductivity and low electrical resistance. For example, in Patent Document 1, as a lead wire, a composite material composed of Cu / invar / Cu having a laminated structure in which both surfaces of an Fe-Ni alloy (hereinafter also referred to as invar), which is a low thermal expansion material, are sandwiched by Cu, which is a high thermal expansion material having high thermal conductivity, has been put into practical use. According to Patent Document 1, it is specified that for this composite material composed of Cu / invar / Cu, the coefficient of thermal expansion is about 6 ppm / ° C when the thickness ratio is 1:3:1, and about 3 ppm / ° C when the thickness ratio is 1:8:1.

[0004] Japanese Unexamined Patent Publication No. 2023-40253

[0005] The composite material disclosed in Patent Document 1, mentioned above, is advantageous in that it suppresses the problems of bonding during semiconductor manufacturing and thermal expansion associated with temperature rise during semiconductor use. On the other hand, in recent years, with the practical application of silicon carbide (SiC) semiconductor power devices, which have superior switching performance and high-temperature operating characteristics compared to the Si semiconductor power devices mentioned above, the problem of thermal stress based on the difference in thermal expansion between the semiconductor chip and lead wires or heat sinks due to thermal cycles of temperature rise and fall that occur during semiconductor use is becoming more pronounced. Therefore, there is a need for a composite material that can further reduce thermal expansion while keeping the ratio of Invar at or below the level of Patent Document 1. The object of the present invention is to provide a composite material that can suppress the problems of thermal stress associated with bonding during semiconductor manufacturing and thermal cycles during semiconductor use.

[0006] The inventors of the present invention have discovered that even with the same configuration as the composite material having a laminated structure of low thermal expansion material and high thermal expansion material described above, a composite material can be obtained in which the problem of thermal stress can be suppressed by adopting a specific layer configuration in which the thermal expansion coefficient and Vickers hardness of each layer are within a predetermined range, thereby arriving at the present invention.

[0007] In other words, the composite material of the present invention comprises a low thermal expansion material and a high thermal expansion material, and has a diffusion layer at the interface between the low thermal expansion material and the high thermal expansion material, wherein when the total thickness of the low thermal expansion material and the high thermal expansion material is 100, the value calculated by (thickness ratio of the low thermal expansion material × Vickers hardness of the low thermal expansion material) / (thickness ratio of the high thermal expansion material × Vickers hardness of the high thermal expansion material) is greater than 0.72.

[0008] In the composite material of the present invention, it is preferable that the low thermal expansion material is an Fe-Ni alloy.

[0009] In the composite material of the present invention, it is preferable that the low thermal expansion material is an Fe-Ni-Co alloy.

[0010] In the present invention, it is preferable that the high thermal expansion material is selected from Cu or a Cu alloy.

[0011] In the present invention, it is preferable that the high thermal expansion material is one selected from Al or an Al alloy.

[0012] The composite material of the present invention preferably has a Vickers hardness of 75 HV or less when Cu or a Cu alloy is selected as the high thermal expansion material.

[0013] The composite material of the present invention preferably has a Vickers hardness of 40 HV or less when Al or an Al alloy is selected as the high thermal expansion material.

[0014] In the composite material of the present invention, when the total thickness of the low thermal expansion material and the high thermal expansion material is set to 100, it is preferable that the thickness ratio of the low thermal expansion material is greater than 15% and less than 70%.

[0015] The composite material of the present invention can provide a composite material that can suppress problems of thermal stress associated with bonding during semiconductor manufacturing and thermal cycling during semiconductor use, and therefore, it is a useful technology for manufacturing SiC semiconductor power devices, for example.

[0016] An example of a schematic cross-sectional diagram of the composite material of the present invention.

[0017] Figure 1 shows an example of a schematic cross-sectional view of the composite material of the present invention. The composite material 1 of the present invention comprises a low thermal expansion material 2 and a high thermal expansion material 3. The composite material of the present invention has a structure in which a diffusion layer (composition gradient region) is formed at the interface between the low thermal expansion material 2 and the high thermal expansion material 3 due to the elemental diffusion of both materials, by diffusion bonding of the low thermal expansion material 2 and the high thermal expansion material 3. In the composite material of the present invention, when the total thickness of the low thermal expansion material and the high thermal expansion material is 100, the Y value calculated as (thickness ratio of the low thermal expansion material × Vickers hardness of the low thermal expansion material) / (thickness ratio of the high thermal expansion material × Vickers hardness of the high thermal expansion material) is greater than 0.72. The characteristics will be described below.

[0018] The thermal expansion coefficient of composite materials such as Cu / Invar / Cu can generally be calculated using a composite law based on the thermal expansion coefficient of each layer, the Young's modulus of each layer, and the volume ratio of each layer. On the other hand, the composite material of the present invention can obtain a thermal expansion coefficient that is 20% or more lower than the thermal expansion coefficient calculated by the composite law by adjusting the thickness ratio of the low thermal expansion material and the high thermal expansion material, as well as adjusting the Vickers hardness of the low thermal expansion material and the high thermal expansion material. The composite material of the present invention uses the aforementioned Vickers hardness as an index, and when the total thickness of the low thermal expansion material and the high thermal expansion material is set to 100, the Y value calculated as (thickness ratio of the low thermal expansion material × Vickers hardness of the low thermal expansion material) / (thickness ratio of the high thermal expansion material × Vickers hardness of the high thermal expansion material) is set to be greater than 0.72.

[0019] Here, in Patent Document 1, a composite member composed of Cu / Invar / Cu with a thermal expansion coefficient of approximately 3 ppm / °C is specifically described, and it is necessary to have a thickness ratio of 1:8:1. This results in a thickness ratio of 20% for Cu (high thermal expansion material in this invention) and 80% for Invar (low thermal expansion material in this invention). As a result, the proportion of Invar, which has inferior conductivity and thermal conductivity (heat dissipation) compared to Cu, becomes larger, raising concerns about deterioration of conductivity and thermal conductivity (heat dissipation).

[0020] In contrast, the composite material of the present invention, for example, employs Invar as the low thermal expansion material, adjusting its thickness ratio to 60% and its Vickers hardness to 137 HV, and employs oxygen-free copper (C1020) as defined in JIS H 3100 as the high thermal expansion material, adjusting its thickness ratio to 40% and its Vickers hardness to 63 HV, and by setting the Y value calculated as (thickness ratio of low thermal expansion material × Vickers hardness of low thermal expansion material) / (thickness ratio of high thermal expansion material × Vickers hardness of high thermal expansion material) to 3.26, the thermal expansion coefficient of the resulting composite material can be set to 3.5 ppm / °C. In other words, the composite material of the present invention, by adjusting not only the thickness ratio of the low thermal expansion material and the high thermal expansion material, but also the Vickers hardness of the low thermal expansion material and the high thermal expansion material, can ensure an excellent thermal expansion coefficient even when the thickness ratio of the low thermal expansion material is 20% thinner than that of the conventional material described above. Furthermore, the composite material of the present invention can achieve a low coefficient of thermal expansion even when the thickness ratio of the low thermal expansion material is 20% thinner than that of the conventional material described above. Therefore, it can also be expected to improve conductivity and thermal conductivity (heat dissipation), which are easily inhibited by low thermal expansion materials. In addition, for the same reasons as above, the composite material according to the embodiment of the present invention preferably has a Y value of 0.75 or higher, more preferably 0.80 or higher, and even more preferably 1.00 or higher. In addition, for the same reasons as above, the composite material according to the embodiment of the present invention preferably has a Y value of 12.0 or lower, and more preferably 10.0 or lower.

[0021] The composite material of the present invention employs a low thermal expansion material, thereby achieving a low thermal expansion coefficient close to that of semiconductor chips and insulating substrates. This reduces the effects of thermal stress associated with bonding during semiconductor manufacturing and thermal cycling during semiconductor use. In the embodiments of the present invention, the composite material preferably uses a material with a thermal expansion coefficient of 10.0 ppm / °C or less in the temperature range of 30 to 200°C as the low thermal expansion material. From the viewpoint of availability and processability, it is preferable to use Fe-Ni alloys such as Invar or Fe-Ni-Co alloys such as Kovar, which have a thermal expansion coefficient of 6.0 ppm / °C or less, and more preferably a thermal expansion coefficient of 4.0 ppm / °C or less. Here, the Ni content of the above Fe-Ni alloy is preferably 34 to 38 mass%. Furthermore, it is preferable that the other elements are C < 0.1 mass%, Si < 0.5 mass%, and Mn < 1.0 mass%. Furthermore, the composite material may contain unavoidable impurities such as P, S, Cr, Cu, Al, Mo, Ti, B, Nb, V, Sn, and Co, but it is preferable that each be 0.1% by mass or less. In addition, the Ni content of the above Fe-Ni-Co alloy is preferably 28 to 35% by mass, and the Co content is preferably 7 to 18% by mass. More preferably, the Co content is 4 to 8% by mass, and more preferably 7 to 8% by mass. In addition, it is preferable that the other elements are C < 0.1% by mass, Si < 0.5% by mass, and Mn < 1.0% by mass. Furthermore, the composite material according to the embodiment of the present invention preferably has a low thermal expansion material thickness in the range of 0.01 to 3.00 mm. Furthermore, in the embodiments of the present invention, the Vickers hardness of the low thermal expansion material is preferably in the range of 120 to 260 HV, and more preferably 200 HV or higher. The Vickers hardness of the low thermal expansion material can be adjusted by heat treatment.

[0022] The composite material of the present invention ensures conductivity and thermal conductivity (heat dissipation) for use as a lead wire or heat sink by diffusion bonding the low thermal expansion material and the high thermal expansion material described above. In the composite material according to the embodiment of the present invention, it is preferable to use Cu, Cu alloys, Al, Al alloys, etc., as the high thermal expansion material, which has a thermal expansion coefficient of more than 10.0 ppm / °C in the temperature range of 30 to 200°C, from the viewpoint of improving conductivity and thermal conductivity (heat dissipation). In particular, if it is a Cu-based material, it is preferable to use oxygen-free copper (C1020) as defined in JIS H 3100, and if it is an Al-based material, it is preferable to use pure Al (A1050) as defined in JIS H 4000. Here, the thermal expansion coefficient of the high expansion material is more preferably more than 16.0 ppm / °C, and even more preferably more than 20.0 ppm / °C. Furthermore, in the composite material according to the embodiment of the present invention, it is preferable to set the thickness of the high thermal expansion material to a range of 0.01 to 3.00 mm. Furthermore, in the composite material according to the embodiment of the present invention, when Cu or a Cu alloy is selected as the high thermal expansion material, the Vickers hardness is preferably 75 HV or less, and more preferably 50 HV or more. Furthermore, in the composite material according to the embodiment of the present invention, when Al or an Al alloy is selected as the high thermal expansion material, the Vickers hardness is preferably 40 HV or less, and more preferably 30 HV or less. In the composite material according to the embodiment of the present invention, when Al or an Al alloy is selected as the high thermal expansion material, the Vickers hardness is preferably 10 HV or more. In the composite material according to the embodiment of the present invention, by controlling the hardness of the high thermal expansion material to the above range, it becomes easier to control the Y value to a desired range, and it becomes easier to obtain a low thermal expansion coefficient while reducing the thickness ratio of the low thermal expansion material. The Vickers hardness of the high thermal expansion material can be adjusted by heat treatment.

[0023] The composite material according to the embodiment of the present invention is diffusion-bonded in a structure in which a low thermal expansion material and a high thermal expansion material are adjacent to each other. The number of bonding layers is not particularly limited, and odd-numbered layered structures such as the three-layer structure composed of high thermal expansion material 3 / low thermal expansion material 2 / high thermal expansion material 3 shown in Figure 1, or the five-layer structure composed of high thermal expansion material / low thermal expansion material / high thermal expansion material / low thermal expansion material / high thermal expansion material can be applied. Furthermore, the composite material according to the embodiment of the present invention can also be even-numbered layered structures such as the two-layer structure composed of high thermal expansion material / low thermal expansion material, or the four-layer structure composed of high thermal expansion material / low thermal expansion material / high thermal expansion material / low thermal expansion material. Regardless of the number of bonding layers, the composite material according to the embodiment of the present invention has a structure in which a diffusion layer (composition gradient region) is formed at the interface of adjacent diffusion-bonded layers due to elemental diffusion of both materials. As a result, the composite material according to the embodiment of the present invention can secure an excellent coefficient of thermal expansion even when the thickness ratio of the low thermal expansion material is thinner than that of conventional materials, and is also expected to have the effect of improving conductivity and thermal conduction (heat dissipation), which are easily inhibited by the low thermal expansion material. Furthermore, for the same reasons as above, it is more preferable that the thickness ratio of the low thermal expansion material in the composite material according to the embodiment of the present invention be 67% or less, and even more preferable that it be 62% or less.

[0024] The composite material of the present invention can be applied to semiconductor products such as power devices, specifically to components where thermal expansion differences are a problem, such as semiconductor chips and insulating substrates. For example, in addition to applications to components such as leads, clips, spacers, and heat spreaders used for current conduction and heat dissipation with chips, it can also be used as a substitute for structural components such as Cu and Al provided on substrates using insulators such as resins and ceramics. Furthermore, the composite material of the present invention can be used as a component to mitigate thermal expansion differences by being inserted between components such as semiconductor chips and insulating substrates and metal components such as Cu and Al, and can also be applied to components that control thermal expansion inside a product. Moreover, the composite material of the present invention is not limited to applications to semiconductor products such as power devices as described above, but can also be applied to various components or their surrounding components where problems arise due to thermal expansion differences.

[0025] Composite materials representing the present invention, conventional examples, and comparative examples were fabricated, and their properties were investigated. Specifically, first, materials for low thermal expansion (Fe-Ni alloy consisting of 36% Ni-Fe with a thermal expansion coefficient of 2.5 ppm / °C and Fe-Ni-Co alloy consisting of 29% Ni-17% Co-Fe with a thermal expansion coefficient of 3.3 ppm / °C) and materials for high thermal expansion (C1020 with a thermal expansion coefficient of 17.7 ppm / °C and A1050 with a thermal expansion coefficient of 24.0 ppm / °C) were prepared as shown in Table 1. Then, pressure welding, diffusion annealing, intermediate rolling, intermediate annealing, finish rolling, and finish annealing were performed to obtain a composite material with a thickness of 0.5 mm in the configuration shown in Table 1, resulting in a three-layer structure of high thermal expansion material 3 / low thermal expansion material 2 / high thermal expansion material 3 as shown in Figure 1. Furthermore, it was confirmed that each composite material obtained above has a structure in which a diffusion layer (composition gradient region) is formed at the interface between the low thermal expansion material and the high thermal expansion material due to elemental diffusion of both materials, through diffusion bonding. For the composite materials No. 1 to 29 obtained above, the thermal expansion coefficient was measured using a push-rod type dilatometer with a quartz glass detection rod. The measurement temperature range for the thermal expansion coefficient was set to 30 to 200°C. The results are shown in Table 1.

[0026]

[0027] In all of the comparative composite materials, samples No. 22 to 29, when the total thickness of the low-thermal-expansion material and the high-thermal-expansion material is set to 100, the Y value calculated as (thickness ratio of the low-thermal-expansion material × Vickers hardness of the low-thermal-expansion material) / (thickness ratio of the high-thermal-expansion material × Vickers hardness of the high-thermal-expansion material) was set to 0.72 or less, confirming that the thermal expansion coefficient exceeded 11.0 ppm / °C, indicating a high thermal expansion coefficient.

[0028] In contrast, the composite materials of samples No. 1 to 21, which are examples of the present invention, all have a low thermal expansion coefficient, as confirmed by setting the Y value, calculated as (thickness ratio of low thermal expansion material × Vickers hardness of low thermal expansion material) / (thickness ratio of high thermal expansion material × Vickers hardness of high thermal expansion material), to over 0.72 when the total thickness of the low thermal expansion material and high thermal expansion material is set to 100. Furthermore, even when the thickness ratio of the low thermal expansion material is less than 50%, the composite materials of the present invention achieve a low thermal expansion coefficient of 5.9 ppm / °C or less, and are expected to have the effect of mitigating thermal stress associated with bonding during semiconductor manufacturing and thermal cycling during semiconductor use. In addition, the composite materials of samples No. 1 to 21, which are examples of the present invention, all have a thickness ratio of the low thermal expansion material within the range of less than 65%, and among them, sample No. 6 and sample No. As with material 9, even within the range of 21% to 59% for the thickness ratio of the low thermal expansion material, the thermal expansion coefficient is below 6.0 ppm / °C. This means that even with a reduced thickness ratio of the low thermal expansion material, an excellent thermal expansion coefficient can be secured, and it is also expected to improve conductivity and thermal conduction (heat dissipation), which are often inhibited by low thermal expansion materials.

[0029] 1. Composite materials 2. Low thermal expansion materials 3. High thermal expansion materials

Claims

1. A composite material comprising a low thermal expansion material and a high thermal expansion material, wherein a diffusion layer is present at the interface between the low thermal expansion material and the high thermal expansion material, and the Y value calculated by (thickness ratio of the low thermal expansion material × Vickers hardness of the low thermal expansion material) / (thickness ratio of the high thermal expansion material × Vickers hardness of the high thermal expansion material) is greater than 0.72 when the total thickness of the low thermal expansion material and the high thermal expansion material is 100.

2. The composite material according to claim 1, wherein the low thermal expansion material is an Fe-Ni alloy.

3. The composite material according to claim 1, wherein the low thermal expansion material is an Fe-Ni-Co alloy.

4. The composite material according to claim 2 or 3, wherein the high thermal expansion material is selected from Cu or a Cu alloy.

5. The composite material according to claim 2 or 3, wherein the high thermal expansion material is selected from Al or an Al alloy.

6. The composite material according to claim 4, wherein the Vickers hardness of the high thermal expansion material is 75 HV or less.

7. The composite material according to claim 5, wherein the Vickers hardness of the high thermal expansion material is 40 HV or less.

8. The composite material according to claim 1, wherein when the total thickness of the low thermal expansion material and the high thermal expansion material is 100, the thickness ratio of the low thermal expansion material is greater than 15% and less than 70%.

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