JP2015123485A - Bonding method and power semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonding method and a power semiconductor device capable of obtaining bonding which responds to high temperature and is excellent in heat conductivity.SOLUTION: A method of performing bonding by producing a metallic compound (CuSn) between bonding objects M1, M2 opposite to each other includes a process of forming a mixed layer of a first metal (Cu) and a second metal (Sn), a process of overlapping the bonding objects M1, M2 so as to put the mixing layer between the bonding objects and a process of heating the mixed layer to a temperature in the middle of a melting point of the first metal and a melting point of the second metal to produce the metallic compound (CuSn) between the bonding objects M1, M2. Therein, in the process of forming the mixed layer, the mixed layer is formed by deposition on the bonding surface of at least one side bonding object (M1).

Description

  The present invention relates to a method for producing an intermetallic compound and joining objects to be joined, and particularly to a joining method suitable for manufacturing a power semiconductor device.

  Conventionally, solder bonding has been extremely useful and widely used as a method for bonding electronic devices such as power semiconductor devices. However, since lead (Pb) contained in solder has an influence on the human body, development of Pb-free solder not containing Pb has been performed. As a bonding material for a power semiconductor device, a low-temperature solder having a melting point of about 183 ° C. and a high-temperature solder having a melting point of about 300 ° C. are used depending on the process. Also, in electronic components that generate heat, such as power semiconductor devices, heat dissipation members are used to efficiently transmit generated heat to the heat sink by joining with heat dissipation fins and heat sinks so as to eliminate gaps. .

  On the other hand, with the recent technological advancement, in order to improve the output and miniaturization of power semiconductor devices, by adopting power semiconductor elements called wide band gap semiconductors such as silicon carbide (SiC), high current There is a tendency of higher density and higher operating temperature. Therefore, it is necessary to form a bonding layer and a heat dissipation layer that can withstand high temperatures. Therefore, a technique has been developed in which two kinds of metals are reacted to form an intermetallic compound, and a bonding layer having a heat resistant temperature higher than the temperature at the time of bonding is formed. Specifically, a metal foil in which each type of metal particle is mixed is formed in advance, and is inserted between objects to be bonded and heat-treated (for example, see Patent Document 1), or one type of metal layer. Has been proposed (see, for example, Patent Document 2) and the like in which the other type of metal layer is interposed therebetween.

JP 2002-301588 A (paragraphs 0018 to 0021, FIG. 1 to FIG. 2, paragraph 0042, FIG. 3) JP 2009-290007 A (paragraph 0018, FIG. 1, paragraphs 0025 to 0027, FIGS. 2 to 3)

  However, when the intermetallic compound is produced by reacting the metal foil inserted between the objects to be joined, voids may remain at the boundary part (joining interface) between the object to be joined and the intermetallic compound. There is a possibility that the heat transfer path is broken and the heat transfer performance is impaired. Moreover, when making it react between metal layers, since a joining state changes with thickness directions, the heat-transfer path | route in the thickness direction may be obstructed and heat conductivity may be impaired. Therefore, it is difficult to efficiently dissipate the generated heat, and it is difficult to obtain a power semiconductor device with high output and high reliability.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a joint that can cope with a high temperature and has excellent thermal conductivity.

  The joining method according to the present invention is a method for producing an intermetallic compound between joining objects to be opposed to each other, forming a mixed layer of a first metal and a second metal, and the mixed layer. And the step of superimposing the joining objects so as to sandwich them, and heating to a temperature intermediate between the melting point of the first metal and the melting point of the second metal to produce the intermetallic compound between the joining objects. And the step of forming the mixed layer includes forming the mixed layer by precipitation on at least one of the bonding surfaces to be bonded.

  According to the present invention, it is possible to obtain a joint that suppresses voids at the joint interface and efficiently radiates the generated heat without changing the joining state in the thickness direction. Further, by applying this bonding method, a power semiconductor device with high output and high reliability can be obtained.

It is a cross-sectional schematic diagram of the junction part for every process for demonstrating the joining method concerning Embodiment 1 of this invention. It is a cross-sectional schematic diagram for demonstrating the structure of the power semiconductor device concerning Embodiment 1 of this invention. It is a cross-sectional schematic diagram of the junction part in a process in the joining method concerning the modification of Embodiment 1 of this invention. It is a cross-sectional schematic diagram of the junction part by the joining method concerning Embodiment 2 of this invention. It is a cross-sectional schematic diagram of the junction part for every process for demonstrating the joining method concerning Embodiment 3 of this invention. It is a cross-sectional schematic diagram of the junction part by the joining method concerning Embodiment 4 of this invention. It is a cross-sectional schematic diagram of the junction part for every process for demonstrating the joining method concerning Embodiment 5 of this invention.

  Below, the joining method concerning each embodiment of the present invention and the power semiconductor device manufactured using this joining method (manufacturing method of a power semiconductor device) are explained in detail. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. Moreover, in the drawings shown below, since it is a schematic description, the scale of each member may differ from the actual scale.

Embodiment 1 FIG.
1 to 3 are diagrams for explaining a bonding method according to a first embodiment of the present invention and a power semiconductor device manufactured by using the bonding method. FIG. 1 is a view for explaining a method of joining opposing objects to be joined using an intermetallic compound, and FIGS. 1A to 1E are schematic cross-sectional views showing states of joined portions in respective steps. . FIG. 2 is a schematic cross-sectional view showing the configuration of the power semiconductor device manufactured by using the bonding method according to the first embodiment. FIG. 3 is a schematic cross-sectional view of a joining portion at a certain step in the joining method according to the modification, and corresponds to the step of FIG.

Prior to the description of the bonding method, which is a feature of the present invention, the configuration of the power semiconductor device will be described with reference to FIG.
The power semiconductor device 10 manufactured using the bonding method (power semiconductor device manufacturing method) according to the present embodiment or each embodiment described later has, for example, excellent thermal conductivity as shown in FIG. Insulating substrate 4 in which conductor layers 4f and 4r such as a copper foil layer and an aluminum foil layer are formed on both surfaces of ceramic substrate 4i, and metal on one surface (lower side in the figure: heat dissipation surface) of insulating substrate 4 A heat sink 5 mainly composed of a material having high thermal conductivity such as aluminum (Al) or copper (Cu) joined through a joint 3-3 by intermetallic compound, and the other surface of the insulating substrate 4 (in the drawing) The power semiconductor element 1 having the back electrode 1r joined to the upper side (circuit surface) via the junction 3-2 and the electrode 1e on the main surface of the power semiconductor element 1 via the junction 3-1. And a lead terminal 2 having one end joined thereto. In addition, a lead terminal (not shown) is joined to the conductor layer 4f, and electrical connection between the power semiconductor element 1 and an external circuit is possible. The circuit surface side is sealed with a sealing body 6 so as to enclose the power semiconductor element 1 and packaged.

  The power semiconductor element 1 is usually composed of silicon or silicon carbide as a main material. In general, a semiconductor material such as silicon carbide (SiC) called a wide band gap semiconductor material has a wider band gap than silicon (Si), and a power semiconductor device 1 using a wide band gap semiconductor material has a high band gap. It can be used in a high temperature range up to about 300 ° C. with high efficiency (large current). Therefore, when a SiC chip is used, heat resistance and high heat dissipation are required rather than a Si chip.

Next, a bonding method for forming each of the bonding parts 3-1 to 3-3 (collectively the bonding part 3), which is a method for manufacturing the power semiconductor device 10 described above, will be described with reference to FIG.
In addition, the joining object in each joining part 3 is called and referred to as the joining object M1 and the joining object M2. First, as shown in FIG. 1A, one joining object M1 is installed in a sputtering apparatus (not shown). And as shown in FIG.1 (b), the joining material layer 3R by which the particle | grains 3Rp of copper (Cu) were mixed in the base material 3Rb of tin (Sn) on the joining surface of the joining object M1 by sputtering. To form. When a bonding material layer 3R having a required thickness is formed on the bonding surface as shown in FIG. 1C, the bonding material layer 3R is taken out from the sputtering apparatus and installed in a bonding apparatus (not shown), as shown in FIG. The other joining object M2 is overlapped so as to sandwich the joining material layer 3R therebetween.

And if it continues heating at 232 degreeC or more which is melting | fusing point of Sn (below melting | fusing point of Cu, and also below heat-resistant temperature of the power semiconductor element 1 etc.), the fuse | melted Sn will spread | diffuse in the Cu particle 3Rp (erosion), The Cu particles 3Rp are eroded inward in the process of compounding (alloying) from the surface layer of the particles 3Rp and increasing the thickness of the intermetallic compound layer. As the intermetallic compound layer grows in this way, Sn is depleted and the Cu concentration in Sn increases, and the freezing point rises while the intermetallic compound layers are in contact with each other. In other words, liquid layer diffusion bonding is achieved by raising the freezing point. The bonding material layer 3R is formed so that the molar ratio of Cu and Sn is 3: 1. As shown in FIG. 1E, the bonding portion 3 mainly composed of an intermetallic compound (Cu ₃ Sn) is formed. It is formed. In FIG. 1 (e), for the purpose of facilitating understanding, the portion where the Cu particles 3Rp are present is indicated by a dotted line for the sake of convenience. The part which was 3Rb is united with the same composition.

At that time, the joining object M1 and the joining object M2 are firmly joined at the joining part 3 composed of an intermetallic compound (Cu ₃ Sn) whose freezing point is higher than the joining temperature (the melting point of Sn in the above example). The Since the bonding material layer 3R is formed by being directly deposited on the bonding target M1 by sputtering, almost no voids are generated at the interface between the bonding target M1 and the bonding portion 3, and the bonding material layer 3R is transmitted like an integrated object. Good thermal properties. Therefore, the temperature gradient from the joining object M1 to the joining part 3 becomes smooth, and it becomes possible to maintain high joining strength without applying extreme stress.

  Note that a void similar to that in Patent Document 1 may occur between the bonding object M2 and the bonding portion 3, but the bonding material layer 3R is formed on the side close to the heat source or on the side having a small bonding area. Thus, the influence can be suppressed. For example, in the power semiconductor device 10 illustrated in FIG. 2, the bonding material layer 3 </ b> R is formed on the power semiconductor element 1 side (on the electrode 1 e and the electrode 1 r) if the bonding portions 3-1 and 3-2 are performed. In the case of the bonding portion 3-3, it is desirable to form the bonding material layer 3R on the insulating substrate 4 side (on the conductive layer 4r). Alternatively, for example, as shown in FIG. 3, if the bonding material layer 3R is formed on the bonding target M2 as well as the bonding target M1, the generation of voids at the interface is suppressed, and good at any interface. Heat transfer performance can be demonstrated. Here, for example, when there are a plurality of bonding targets (on both surfaces) for a certain bonding target Mi, the same effect can be obtained by forming the bonding material layer 3R on each surface. In the first embodiment and the following embodiments, it is described that the joining method described above is used for all of the joint portions 3, but it goes without saying that it may be used for some of the joint portions. Yes.

  For the base material 3Rb and the particles 3Rp constituting the bonding material layer 3R, an intermetallic compound is generated, and the selected intermetallic compound has a melting point higher than the melting point of one metal. do it. In addition to Sn shown in this embodiment, indium (In) or the like can be used as a metal species having a melting point lower than the melting point of the generated intermetallic compound. As the other metal species, metals such as silver (Ag), gold (Au), nickel (Ni), and cobalt (Co) can be used in addition to Cu shown in the present embodiment.

  And it is preferable to use the metal species having the lower melting point in the combination for the base material 3Rb. In the above example, it is Sn or In, but it is not necessarily limited to a single kind of metal, and the particle 3Rp and the metal It may be an alloy capable of forming an intermetallic compound. And the junction part 3 by an intermetallic compound can be formed by heat-processing at the temperature more than melting | fusing point of base material 3Rb and below melting | fusing point of particle | grain 3Rp. The shape of the particle 3Rp is preferably a spherical shape or a cylindrical shape.

  The bonding targets M1 and M2 may be any material that can be bonded to the intermetallic compound, and Cu, Ag, Au, Ni, and Co that generate an intermetallic compound with the base material 3Rb are particularly desirable. On the other hand, for materials such as aluminum (Al) that are not intermetallic compounded with Sn or bonded, the surface may be covered with a bondable material. For example, when the joining object M1 or M2 is the heat sink 5 or the lead terminal 2 made of Al, a coating such as Ni strike may be formed on the surface. Further, when the bonding target M1 or M2 is the Al electrode 1r or 1e of the power semiconductor element 1, an Au coating may be provided on the electrode surface.

  In addition, although sputter | spatter was shown as an example of the formation method of the joining material layer 3R in which particle | grain 3Rp mixes in base material 3Rb, it does not restrict to this, It forms by depositing on a joining surface, such as vapor deposition and plating. If it is the method to do, it becomes possible to suppress generation | occurrence | production of the void in a joining interface. Moreover, since the bonding material layer 3R in which the particles 3Rp are mixed in the base material 3Rb is used, for example, compared to the case where two kinds of metals are formed in layers, an intermetallic compound can be formed in a short time. It is possible to easily form the strong joint 3.

  That is, since each junction part 3 in the power semiconductor device 10 shown in FIG. 2 is formed by the joining method described above, the power semiconductor device can be applied to a high temperature operation and has excellent heat conductivity and high reliability. 10 can be obtained.

As described above, according to the bonding method according to the first embodiment, an intermetallic compound (for example, Cu ₃ Sn) is generated and bonded between the bonding objects M1 and M2 facing each other. Forming a mixed layer (bonding material layer 3R) of a first metal (for example, Cu) and a second metal (Sn) (for generating an intermetallic compound), and a mixed layer (bonding material layer 3R) The process of superimposing the joining objects M1 and M2 so as to be sandwiched between them, and heating to the intermediate temperature (closer to 232 ° C) between the melting point of the first metal (1084 ° C) and the melting point of the second metal (232 ° C) A step of forming an intermetallic compound (Cu ₃ Sn) between the bonding targets M1 and M2, and forming a mixed layer (bonding material layer 3R), wherein at least one of the bonding targets (M1) is bonded On the surface, a mixed layer (bonding) by precipitation (such as sputtering or plating) Since the material layer 3R) is formed, it is possible to suppress the generation of voids at the bonding interface, to cope with a high temperature, and to obtain a bond with excellent thermal conductivity. Further, since there are few voids at the bonding interface, the temperature gradient near the interface becomes uniform with the surroundings, and stress concentration is avoided and bonding reliability is improved.

  The first metal is any one of Cu, Ag, Au, Ni, and Co. If the second metal is Sn or In, the first metal is bonded at a temperature lower than the temperature that affects the members of the power semiconductor device 10. In addition, it is possible to obtain a joint that is compatible with high temperatures and excellent in thermal conductivity.

  The mixed layer (bonding material layer 3R) is obtained by mixing particles 3Rp of the first metal in the base material 3Rb of the second metal (Sn and In) having a melting point lower than that of the first metal (Cu and the above-described metal species). Therefore, the bonding time can be shortened, and a good bonding portion 3 is formed.

  In addition, if the mixed layer (bonding material layer 3R) is formed on the bonding surface of the other bonding target M2 by precipitation, the generation of voids at both bonding interfaces is suppressed, and the heat transfer is more excellent. Bonding is obtained. Therefore, the joining reliability is also improved.

Embodiment 2. FIG.
In the joining method according to the second embodiment, the content ratio of the base material and the particles is changed with respect to the first embodiment so that the number of particles increases. FIG. 4 shows the structure of the joint formed by the joining method according to the second embodiment, and corresponds to FIG. 1 (e) in the first embodiment. In the figure, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Further, the portions other than FIG. 1E in the first embodiment are also used in the second embodiment.

In the second embodiment, the constituent ratio of Sn constituting the base material 3Rb and Cu constituting the particles 3Rp in the bonding material layer 3R is higher than the molar ratio of Cu from 1: 3 as compared with the first embodiment. It is intended to be higher. That is, the ratio of Cu constituting the particles 3Rp is set higher than the stoichiometric ratio for forming the intermetallic compound (Cu ₃ Sn). As a result, as shown in FIG. 4, the bonded portion 3 after bonding includes a nucleus 3c in which the single metal portion of Cu is left in the intermetallic compound portion without being converted into an intermetallic compound from the particles 3Rp. Will be. Other configurations and processes, or application of modification examples are the same as those in the first embodiment.

Thus, by adjusting the compounding ratio of the metal in the bonding material layer 3R so that the ratio of Cu (particle 3Rp) is larger than the composition ratio, the single metal nucleus 3c is included in the intermetallic compound phase. The remaining joint 3 can be formed. By using this configuration, the highly conductive Cu core 3c becomes a heat transfer path, and heat dissipation performance can be improved. Further, the linear expansion coefficient of the core 3c remaining in the joint 3 (in the case of copper: about 16.6 ppm / K) is the linear expansion coefficient of the intermetallic compound phase (in the case of Cu ₃ Sn: about 18.0 ppm / K). Therefore, there is an effect on stress relaxation.

  In the second embodiment, a mode has been described in which the ratio becomes higher than the stoichiometric ratio for forming an intermetallic compound that is assumed to have a particle-side ratio with respect to the intermetallic compound of Sn and Cu. Needless to say, the present invention can also be applied to combinations of these metal species. In addition, the bonding method according to each of the following embodiments including the second embodiment may be applied to any of the respective bonding portions 3 of the power semiconductor device 10 according to the first embodiment, and further different bonding. You may combine methods.

As described above, according to the bonding method according to the second embodiment, the ratio of the first metal (Cu) to the second metal (Sn) in the mixed layer (bonding material layer 3R) is such that the intermetallic compound (Cu ₃ Sn) stoichiometric ratio for generating (in a molar ratio of 3: since to be larger than 1), nuclear 3c of high conductivity Cu becomes heat transfer path, it is possible to improve the heat dissipation performance it can. Furthermore, there is an effect on stress relaxation.

Embodiment 3
In the bonding method according to the third embodiment, among the particles contained in the bonding material layer as compared with the first embodiment, a particle having a particle size used for thickness adjustment is used. FIG. 5 shows the structure of the joining part for each step in the joining method according to the third embodiment. FIGS. 5 (a) and 5 (b) are the same as FIGS. This corresponds to e). In the figure, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Further, portions other than those in FIGS. 1D and 1E in the first embodiment are also used in the third embodiment.

  In the joining method according to the third embodiment, as shown in FIG. 5, in order to define the thickness t3 of the joint 3 in the joining material layer 3R, the particle 3Rp corresponds to the thickness t3. Particles having a particle size of 3 Rps were used. Other configurations are the same as those in the first embodiment. Thus, in the step of melting the base material 3Rb, the particles 3Rps dispersed in the surface support the spacer Sp, and the interval between the joining objects M1 and M2 is the particle size even when the joining pressure is increased. Kept in minutes. That is, even if the bonding pressure is increased in order to increase the bonding strength, the thickness of the bonding portion 3 is maintained, so that an arbitrary bonding strength can be obtained and the height can be formed to match the loading space. .

  For example, when used as an under-chip bonding layer (bonding portion 3-2), in order to quickly diffuse the heat generated in the power semiconductor element 1, the size of the particles 3Rps is made smaller than that of other bonding portions, and bonding is performed. It is possible to cope with the formation such that the thickness of the portion 3-2 is reduced. Moreover, when using as a board | substrate lower joining layer (joining part 3-3), in order to utilize effectively the heat sink 5 etc. which are formed under the insulated substrate 4, the size of particle | grain 3Rps is set rather than another joining part. By increasing the thickness, the thickness of the joint portion 3-3 is made thicker than other joint portions, and the heat released to the outside can be spread and diffused according to the heat sink 5.

  As described above, the size of the particle 3 Rps is selected in accordance with the application portion of the bonding portion 3, whereby the bonding portion 3 that meets the purpose can be formed. In addition, if the particles 3Rps are blended to such an extent that they are appropriately dispersed in the joint surface, the thickness t3 can be defined. Therefore, for example, in order to adjust the blending ratio with the base material 3Rb, particles 3Rp having a particle diameter smaller than 3Rps may be mixed.

  As described above, according to the bonding method according to the third embodiment, the mixed layer (bonding material layer 3R) has a plurality of particles having a predetermined diameter that is the maximum diameter among the first metal particles 3Rp. Since 3 Rps is dispersed in the joint surface, the thickness of the joint portion 3 can be easily defined. Therefore, the bonding pressure can be increased by increasing the bonding pressure.

Embodiment 4 FIG.
In the bonding method according to the fourth embodiment, the content ratio of the base material and the particles is changed so as to increase the number of particles as compared with the third embodiment. FIG. 6 shows the structure of the joint formed by the joining method according to the fourth embodiment, and corresponds to FIG. 5B in the third embodiment. In the figure, the same parts as those in the third embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Further, the portions other than FIG. 1E in the first embodiment and FIG. 5A in the third embodiment are also used in the fourth embodiment.

In the fourth embodiment, the particles 3Rps for defining the thickness 3t are used, and the composition ratio of Sn and Cu in the bonding material layer 3R is higher than the stoichiometric ratio for forming Cu ₃ Sn. It is a thing. As a result, as shown in FIG. 6, in the bonded portion 3 after bonding, a nucleus in which a single metal portion of Cu remains in the Cu ₃ Sn intermetallic compound portion without being converted into an intermetallic compound from the particles 3Rp. 3c will be included. In particular, the particle 3Rps having a predetermined maximum diameter is likely to remain as the nucleus 3c of the single metal portion as compared with other particles, so that the size can be easily defined. That is, the thickness 3t of the joint portion 3 can be defined, and improvement in heat dissipation and stress relaxation can be achieved.

As described above, according to the bonding method according to the fourth embodiment, the ratio of the first metal (Cu) to the second metal (Sn) in the mixed layer (bonding material layer 3R) is such that the intermetallic compound (Cu ₃ Sn) stoichiometric ratio for generating (in a molar ratio of 3: since to be larger than 1), nuclear 3c of high conductivity Cu becomes heat transfer path, it is possible to improve the heat dissipation performance it can. Furthermore, there is an effect on stress relaxation. In particular, particles 3Rps having a predetermined maximum diameter functioning as a spacer remain as nuclei 3c, and the thickness can be easily defined.

Embodiment 5 FIG.
In the joining method according to the fifth embodiment, a buffer plate is inserted into the intermediate portion in the thickness direction with respect to the joint described in the first to fourth embodiments. FIG. 7 shows the structure of the joining portion for each step in the joining method according to the fifth embodiment, and FIGS. 7 (a) and 7 (b) are the same as FIGS. This corresponds to e). In the figure, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Further, portions other than those in FIGS. 1D and 1E in the first embodiment are also used in the fifth embodiment.

  In the fifth embodiment, as shown in FIG. 7 (a), a metal buffer plate 9 (a composite material in which the bonding material layer 3R described in each of the above embodiments is provided on both sides of a thickness of 1 μm to 90 μm). The bonding material layer 30R is formed, and the bonding objects M1 and M2 are pressed from both sides of the composite bonding material layer 30R, and heat-treated at a temperature not lower than the melting point of Sn and not higher than the melting point of Cu as described in the first embodiment. 7B, the objects to be joined M1 and M2 are joined by the composite joining portion 30. As shown in FIG.

  The buffer plate 9 is a metal that is thinner than the objects to be joined M1 and M2, and is not particularly limited as a material to be joined to the joint portion 3. For example, Cu, Al, Ag, Au, Ni, Co Metals such as can be applied. The bonding material layers 3R formed on both surfaces of the buffer plate 9 may have the same specifications, but may have a combination of different specifications (bonding material layers 3R shown in different embodiments). Further, similarly to the above-described embodiments, the bonding material layer 3R may be formed on the bonding objects M1 and M2 side, and in that case, different specifications may be combined.

  As described above, the buffer plate 9 sandwiched between the bonding targets M1 and M2 absorbs the swell generated in the bonding target M1 and the bonding target M2, so that the bonding can be easily performed, and the buffer plate 9 is provided. The stress applied to the composite joint 30 can be absorbed, and the joining reliability can be improved. Moreover, if the particle 3Rps that defines the size is mixed in the particle 3Rp as in the third or fourth embodiment, the thickness of the composite joint 30 can be selected, so that higher stress relaxation and higher heat dissipation are obtained. It is possible. Therefore, the composite joint portion 30 is particularly suitable for the joint portion 3-3.

  As described above, according to the joining method according to the fifth embodiment, the buffer plate 9 having a thickness smaller than that of the joining objects M1 and M2 is inserted in the middle portion in the thickness direction of the mixed layer (joining material layer 30R). Therefore, it is possible to obtain higher stress relaxation and higher heat dissipation.

  That is, if the power semiconductor device 10 is manufactured (forms the junction 3) by the bonding method according to each of the above embodiments, the power semiconductor device 10 with high output and high reliability can be obtained.

  In the power semiconductor device 10 to which each of the first to fifth embodiments is applied, the power semiconductor element 1 functioning as a switching element (transistor) or a rectifier element (diode) is formed of silicon carbide. showed that. However, the present invention is not limited to this, and it may be formed of generally used silicon. However, when using silicon carbide, which can form a so-called wide gap semiconductor, or a gallium nitride-based material or diamond, which has a larger band gap than silicon, the operating temperature is high and the current handled is large, so the amount of heat generated is also large. Therefore, the effect by this invention can be exhibited further.

  Needless to say, both the switching element and the rectifying element may be formed of a wide band gap semiconductor, or one of the elements may be formed of a wide band gap semiconductor.

1: power semiconductor element, 2: lead terminal (wiring member), 3: joint, 3R: bonding material layer (mixed layer), 3Rb: base material, 3Rp: particles, 3Rps: particles defining the thickness,
4: Insulating substrate, 4f, 4r: Conductive layer, 4i: Ceramic base material, 5: Heat sink, 6: Sealing body, 9: Buffer plate, 30: Composite bonding material layer (mixed layer),
M1, M2: Joining targets.

Claims (10)

A method for producing and joining an intermetallic compound between opposing joining objects,
Forming a mixed layer of a first metal and a second metal;
A step of superimposing the joining objects so as to sandwich the mixed layer;
Heating to a temperature intermediate between the melting point of the first metal and the melting point of the second metal, and generating the intermetallic compound between the objects to be joined,
In the step of forming the mixed layer, the mixed layer is formed by precipitation on at least one of the bonding surfaces to be bonded. The first metal is any one of Cu, Ag, Au, Ni, and Co;
The bonding method according to claim 1, wherein the second metal is Sn or In.   3. The joining method according to claim 1, wherein the mixed layer is obtained by mixing particles of the first metal in a base material of the second metal having a melting point lower than that of the first metal. .   4. The bonding according to claim 3, wherein among the particles of the first metal, the mixed layer has a plurality of particles having a predetermined diameter that is a maximum diameter dispersed in the bonding surface. Method.   The bonding method according to claim 3 or 4, wherein a ratio of the first metal to the second metal in the mixed layer is larger than a stoichiometric ratio for generating the intermetallic compound.   The joining method according to claim 1, wherein the mixed layer is also formed by precipitation on the joining surface of the other joining target.   The joining method according to any one of claims 1 to 6, wherein a buffer plate having a thickness smaller than that of the joining target is inserted in an intermediate portion in the thickness direction of the mixed layer. A power semiconductor element having a back electrode bonded to one surface of a circuit board;
A wiring member bonded to the surface electrode of the power semiconductor element;
A cooling member joined to the other surface of the circuit board,
8. At least one of joining of the power semiconductor element and the circuit board, joining of the power semiconductor element and the wiring member, and joining of the circuit board and the cooling member is performed. A power semiconductor device comprising the bonding method according to any one of the above.   The power semiconductor device according to claim 8, wherein the power semiconductor element is formed of a wide band gap semiconductor material.   10. The power semiconductor device according to claim 9, wherein the wide band gap semiconductor material is any one of silicon carbide, gallium nitride-based material, and diamond.

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