Semiconductor device and method for producing semiconductor device

Abstract

This semiconductor device is provided with a semiconductor element (1) and a metal member (2) to be joined. The semiconductor device is provided with a sintered layer (3) of metal particles, which is provided so as to be in direct contact with both the semiconductor element (1) and the metal member (2) to be joined, and a solder (4) that is interposed in a gap at the bonding interface between the metal member (2) to be joined and the sintered layer (3). As a result, it is possible to provide a semiconductor device provided with a bonding layer having high heat resistance, high reliability, and excellent heat dissipation.

Description

Semiconductor device and manufacturing method thereof

[0001] The present disclosure relates to a semiconductor device and a method for manufacturing the semiconductor device.

[0002] In recent years, there has been a strong demand for technologies to improve the heat resistance, reliability, and heat dissipation of bonding layers in semiconductor devices. In particular, there is a strong demand for improved heat resistance, reliability, and heat dissipation of bonding layers that bond semiconductor elements and terminals or other metal-based bonded members, which have large differences in thermal expansion coefficients. Conventionally, semiconductor elements have often been made from silicon (Si), and their operating temperatures range from 100°C to 125°C. Meanwhile, as next-generation devices aimed at energy conservation, active development is underway for devices made from silicon carbide (SiC) or gallium nitride (GaN). To reduce power loss, the operating temperatures of SiC and GaN devices are expected to be 175°C or higher, and it is said that they may reach 250°C in the future.

[0003] In conventional Si devices, lead-containing solders such as Sn-38Pb (mass%) and Pb-5Sn (mass%), and Sn-based solders such as Sn-3Ag-0.5Cu (mass%) or Sn-9Zn (mass%) and Sn-0.7Cu (mass%) have been used as joining materials. Gallium arsenide devices, on the other hand, have used Au-containing solders such as 80Au-20Sn (mass%) and Sn-10Au (mass%). However, from the perspective of reducing environmental impact, Pb-based solders containing large amounts of harmful lead (Pb) are problematic, and Au-containing solders are costly due to the rising cost of precious metals and limited reserves. For these reasons, Sn-based solders are a candidate joining material for Si, SiC, and GaN devices. However, Sn has a low melting point of 232°C, and the above-mentioned Sn-3Ag-0.5Cu solder is a eutectic solder, so its melting point is even lower, at approximately 220°C. To increase the melting point of Sn-based solders, Sn-5Sb (mass%) or Sn-10Sb (mass%), in which Sb is added to Sn, are available. However, since the melting point is only increased by about 20°C, from 230°C to 240°C, the heat resistance of the bonding layer remains a problem at the operating temperatures of the semiconductor elements during actual operation. Furthermore, even if a high-melting-point metal is added to Sn above the eutectic composition, the difference between the liquidus and solidus increases, resulting in poor wetting during solder bonding. Furthermore, shrinkage cavities and voids are frequently generated, which reduces the reliability of the bonding layer. Furthermore, at low temperatures (below freezing), Sn undergoes a phase transformation from β-Sn to brittle α-Sn. Therefore, when a heat cycle test, which involves repeating low-temperature (-) and high-temperature (+) cycles—a type of reliability test—is conducted, cracks occur early, resulting in failure and insufficient reliability of the bonding layer. Furthermore, when cracks occur in the bonding layer, the heat dissipation properties of the bonding layer are reduced, causing the bonded semiconductor element to heat up more during actual operation. This creates a negative spiral in which further cracks occur in the bonding layer, potentially causing thermal runaway in the semiconductor element. Therefore, when solder is used as a bonding material for semiconductor elements, the heat resistance, reliability, and heat dissipation properties of the bonding layer are insufficient.

[0004] Therefore, sintered bonding materials have been attracting attention as an alternative bonding material to solder. Sintered bonding materials include those formed by blending nano- or micro-sized metal particles, known as sinterable metals or metal pastes, with organic solvents. In these sintered bonding materials, the organic components covering the surfaces of the metal particles decompose due to heat, sintering the metal particles together to form a bonding layer, resulting in sintered bonding. The heat resistance temperature of the bonding layer after sintering is approximately the same as the melting point of the metal particles used (e.g., 960°C for Ag), resulting in a higher heat resistance than solder. Depending on the organic component, organic solvents decompose at approximately 200–300°C, allowing bonding at temperatures that do not degrade the bonded components. Furthermore, when using a blend of metal particles and organic solvents as a sintered bonding material, pressure is required to densely sinter the metal particles after the organic components volatilize to enhance heat dissipation. When bonding without pressure, there is a limit to how much the heat generated during sintering alone can promote the diffusion of the metal particles, resulting in insufficient bonding strength and low bonding layer reliability. Furthermore, when bonding is performed without pressure, if the bonded members undergo deformation such as warping due to thermal expansion or the like, the sintered bonding material does not melt, and therefore cannot follow the deformation, which may cause peeling at the bonding interface between the bonded members and the sintered body layer. If peeling occurs, heat dissipation will deteriorate. If high pressure, for example, 100 MPa or more, is applied to bond the members in order to form a bonding layer with high reliability and heat dissipation, the semiconductor element will be destroyed and will not function normally electrically.

[0005] Patent Document 1 discloses a semiconductor device in which a semiconductor element and a circuit board are bonded using both a sintered bonding material and a solder. The semiconductor device described in Patent Document 1 has a structure in which the semiconductor element and the circuit board are directly bonded with solder, and a sintered body layer formed by sintering metal particles as a sintered bonding material is provided in a bonding interface region between the solder bonding layer and the circuit board.

[0006] JP 2015-106654 A

[0007] The semiconductor device described in Patent Document 1 uses both a sintered bonding material and a solder bonding material, but of the bonding layers that bond the semiconductor element to the circuit board, the sintered body layer is provided only on the circuit board side, and the proportion of the solder layer in the bonding layer is still high, so as described above, the heat resistance, reliability, and heat dissipation of the bonding layer are insufficient.

[0008] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a semiconductor device having a bonding layer that has high heat resistance, high reliability, and high heat dissipation properties, and a method for manufacturing the semiconductor device.

[0009] The semiconductor device according to the present disclosure is a semiconductor device comprising a semiconductor element and a member to be joined made of metal, and comprises a sintered layer of metal particles that joins the semiconductor element and the member to be joined and is provided so as to be in direct contact with the semiconductor element and the member to be joined, and solder that is interposed in the gap at the joining interface between the member to be joined and the sintered layer.

[0010] The method for manufacturing a semiconductor device according to the present disclosure includes a metal particle layer forming step of forming a metal particle layer having a sintering temperature lower than the melting point of solder on an upper surface of a semiconductor element; a member-to-be-joined arrangement step of arranging a member to be joined so that the member is in direct contact with the upper surface of the metal particle layer; a solder supplying step of supplying the solder to the member to be joined so that the solder does not come into contact with the metal particle layer; a first joining step of heating at a first temperature lower than the melting point of the solder and equal to or higher than the sintering temperature to sinter the metal particle layer, thereby forming a sintered body layer and joining the semiconductor element and the member to be joined; and a second joining step of heating at a second temperature equal to or higher than the melting point of the solder to melt the solder, and interposing the molten solder in a gap at the joining interface between the member to be joined and the sintered body layer to join the member to be joined and the sintered body layer.

[0011] According to the semiconductor device and the method for manufacturing the semiconductor device according to the present disclosure, it is possible to provide a semiconductor device and a method for manufacturing the semiconductor device that include a bonding layer that has high heat resistance, high reliability, and high heat dissipation properties.

[0012] 1 is a schematic cross-sectional view of a semiconductor device according to a first embodiment taken along the line X-X in FIG. 2; FIG. 2 is a schematic top view of a semiconductor device according to a first embodiment; FIG. 3 is an enlarged view of a region A in FIG. 1 of a semiconductor device according to a first embodiment; FIG. 4 is a flowchart showing a procedure of a method for manufacturing a semiconductor device according to a first embodiment; FIG. 5 is a schematic cross-sectional view of a semiconductor device according to a first embodiment taken along the line X-X in FIG. 6, illustrating a method for manufacturing a semiconductor device according to a first embodiment; FIG. 6 is a schematic top view of a semiconductor device according to a modification of the first embodiment, illustrating a semiconductor element and terminals of a semiconductor device according to a second embodiment; FIG. 9 is a schematic cross-sectional view of a semiconductor device according to a second embodiment; FIG. 10 is a schematic top view of a semiconductor device according to a second embodiment;

[0013] <Introduction> One side in a direction parallel to the depth direction of a semiconductor device is referred to as "top" and the other side as "bottom." Of the two main surfaces of a semiconductor element 1, layer, or other member, one surface is referred to as the top surface and the other surface is referred to as the bottom surface. The directions of "top" and "bottom" are not limited to the direction of gravity or the directions when the semiconductor device is mounted.

[0014] Furthermore, the drawings are schematic, and the relative sizes and positions of images shown in different drawings are not necessarily accurately depicted and may be changed as appropriate. In the following description, similar components are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions thereof may be omitted.

[0015] First Embodiment. The first embodiment will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a semiconductor device 100 according to the first embodiment. FIG. 2 is a schematic top view of the semiconductor device 100 according to the first embodiment. Note that FIG. 1 shows a cross section taken along dashed line X-X shown in FIG. 2. Also, FIG. 3 is an enlarged view of region A shown in FIG. 1.

[0016] The configuration of the semiconductor device 100 will be described with reference to Figures 1 to 3. As shown in Figure 2, the semiconductor device 100 includes a semiconductor element 1, a member to be joined 2, and a joining layer 5 made of a sintered body layer 3 and solder 4.

[0017] The semiconductor element 1 is made of various semiconductor materials such as silicon (Si), silicon carbide (SiC), or gallium nitride (GaN). The thickness of the semiconductor element 1 is preferably 100 μm or more to prevent the semiconductor element 1 from cracking due to external force. As shown in FIG. 2 , the shape of the semiconductor element 1 may be rectangular when viewed from above, and one side of the semiconductor element 1 may be 5 mm or more when viewed from above.

[0018] Although not shown, the semiconductor element 1 has an electrode layer on the upper surface thereof. The electrode layer may be made of an aluminum alloy. For example, the electrode layer may be made of an aluminum-silicon alloy (Al—Si alloy).

[0019] A plating layer may also be provided on the upper surface of the electrode layer. The plating layer may be composed of, for example, Au, nickel or a nickel alloy, or palladium. The plating layer may also have, for example, a laminated structure including two or more metal layers. The laminated structure may be composed of, for example, a Ni layer, a Pd layer, and an Au layer, and preferably formed in the order Ni, Pd, and Au from the upper surface side of the semiconductor element 1. By forming Pd on Ni, diffusion of Ni to the bonding interface between the semiconductor element 1 and the sintered body layer 3 described below can be suppressed. Note that, for example, the thickness of the Ni layer may be 15 μm, the thickness of the Pd layer may be 100 nm, and the thickness of the Au layer may be 200 nm. The electrode layer and plating layer may also be collectively referred to as the electrode layer.

[0020] The members to be joined 2 are intended to be members made of a metal that can be sintered with a sintered bonding material, which will be described later. In this embodiment, the members to be joined 2 are terminals, as shown in FIGS. 1 and 2 . The terminals are preferably made of copper, for example. By using copper, adhesion to the solder and the sintered bonding material and heat dissipation can be further improved. Furthermore, in order to ensure heat dissipation and formability for forming the openings 2 a, which will be described later, the thickness of the members to be joined 2 is preferably 1 mm or more. The members to be joined 2 may also be mounted components, such as capacitors.

[0021] 1 and 2, the members to be joined 2 preferably have an opening 2a penetrating the top and bottom surfaces of the members to be joined 2. As shown in FIG. 2, the inner wall 2b of the members to be joined 2 that forms the opening 2a is preferably perpendicular to the joining interface between the members to be joined 2 and the sintered body layer 3. In FIG. 1, the width of the opening 2a is exaggerated compared to its actual width. In order to allow the molten solder to flow through the opening 2a, the width of the opening 2a is preferably 1 mm or more. In this embodiment, the shape of the opening 2a is rectangular, as shown in FIG. 2.

[0022] 1 and 2, the members to be joined 2 may have a metal plating portion 6 at a location where the sintered body layer 3 and the solder 4 come into contact. By applying metal plating to the members to be joined 2 at this location, it is possible to improve the adhesion between the members to be joined 2 and the sintered body layer 3 and solder 4. The metal plating portion 6 is made of, for example, Ag, Au, Sn, or an alloy plating containing any of these as the main component.

[0023] As shown in FIGS. 1 and 3 , the sintered body layer 3 bonds the semiconductor element 1 and the workpiece 2 and is provided so as to be in direct contact with the semiconductor element 1 and the workpiece 2. In this embodiment, the sintered body layer 3 is provided on an electrode layer provided on the upper surface of the semiconductor element 1. The sintered body layer 3 is formed by sintering metal particles, which are sintered bonding materials. The metal particles are preferably composed of Ag, Cu, Au, Ni, or an alloy containing these as their main components, which have high thermal conductivity. However, Au is costly, Cu reduces sintered density due to oxidation, and Ni is inferior to Ag in terms of sintered density reduction due to oxidation and heat dissipation. Therefore, the metal particles are preferably composed of Ag or an alloy containing Ag as its main component. Furthermore, the particle size of the metal particles is arbitrary as long as the sintering temperature of the metal particles is lower than the melting point of the solder. In this embodiment, the particle size of the metal particles is 100 nm or more and less than 10 μm. When the particle size of metal particles is on the nano-order, they can be sintered at a temperature lower than the inherent melting point of the metal, so in some cases it is desirable to make the particle size less than 1 μm in relation to the solder material.

[0024] As shown in FIGS. 1 and 3 , the solder 4 is provided so as to fill the gap at the bonding interface between the workpiece 2 and the sintered body layer 3. Specifically, if a gap occurs in the region between the workpiece 2 and the sintered body layer 3, it is desirable that the solder 4 be provided so as to fill the gap. The solder 4 referred to here also includes intermetallic compounds formed by a reaction between the solder and the workpiece 2 or the sintered body layer 3, and the solder 4 may be composed solely of the intermetallic compounds. As shown in FIGS. 1 and 3 , it is desirable that the solder 4 be provided so as to fill the entire gap at the bonding interface between the workpiece 2 and the sintered body layer 3. Specifically, if a gap occurs in the region between the workpiece 2 and the sintered body layer 3, it is desirable that the solder 4 be provided so as to fill the entire gap. Furthermore, as shown in FIG. 1 , it is desirable that the solder 4 be in contact with the inner wall 2 b of the workpiece 2. The solder may be made of, for example, Sn, In, Bi, Zn, Al, or an alloy containing these as its main component, and is preferably made of Sn or an alloy containing Sn as its main component.

[0025] The semiconductor device 100 of this embodiment is configured as described above. By providing the sintered body layer 3 that bonds the semiconductor element 1 and the bonded member 2 and is provided so as to be in direct contact with the semiconductor element 1 and the bonded member 2, and the bonding layer 5 made of the solder 4 that is interposed in the gap at the bonding interface between the bonded member 2 and the sintered body layer 3, it is possible to provide a semiconductor device and a method for manufacturing a semiconductor device that include a bonding layer that has high heat resistance, high reliability, and high heat dissipation. The reason for this will be explained below.

[0026] First, by sintering and bonding the semiconductor element 1 and the workpiece 2 using a sintering bonding material, the proportion of the sintered body layer 3 in the bonding layer 5 can be increased, resulting in a highly heat-resistant and highly reliable bonding layer. Furthermore, by interposing solder 4 in the gap at the bonding interface between the workpiece 2 and the sintered body layer 3, even if the workpiece 2 deforms due to thermal expansion or other factors during sintering, delamination at the bonding interface between the workpiece 2 and the sintered body layer 3 can be suppressed. As a result, a highly heat-resistant, highly reliable, and highly heat-dissipating bonding layer can be formed, enabling semiconductor devices to operate at high temperatures. Furthermore, by interposing solder 4 in the entire gap at the bonding interface between the workpiece 2 and the sintered body layer 3, delamination at the bonding interface between the workpiece 2 and the sintered body layer 3 can be further suppressed. Furthermore, since the solder 4 contacts the inner wall 2b of the workpiece 2, the contact area between the workpiece 2 and the solder 4 increases, resulting in a stronger and more heat-dissipating bonding layer.

[0027] In the present invention, since the semiconductor element 1 is not easily thermally deformed, i.e., peeling is unlikely to occur at the bonding interface between the semiconductor element 1 and the sintered body layer 3, the solder 4 is interposed only at the bonding interface between the sintered body layer 3 and the member to be joined 2, which is generally more susceptible to thermal deformation than the semiconductor element 1. However, the solder 4 may also be interposed at the bonding interface between the semiconductor element 1 and the sintered body layer 3. The ease of peeling also varies depending on the positional relationship in the direction of gravity. An object placed below the direction of gravity is more likely to adhere to the sintered body layer 3 due to the influence of gravity than an object placed above the direction of gravity, i.e., peeling is less likely to occur. Therefore, it is desirable to interpose the solder 4 at the bonding interface between the sintered body layer 3 and an object placed above the direction of gravity.

[0028] Furthermore, in this embodiment, the members to be joined 2 have metal plated portions 6 at locations that come into contact with the sintered body layer 3 and the solder 4. As described above, by applying metal plating to these locations of the members to be joined 2, it is possible to improve the adhesion between the members to be joined 2 and the sintered body layer 3 and the solder 4, thereby further improving heat dissipation. Therefore, it is possible to further realize high-temperature operation of the semiconductor device.

[0029] Furthermore, when the semiconductor element 1 is made of SiC, the breakdown voltage is higher than that of Si, and therefore a higher voltage is applied during use of the semiconductor device, and the temperature is likely to rise. Therefore, SiC is required to have higher heat dissipation properties. By applying the present invention, even when the semiconductor element 1 is made of SiC, a bonding layer having high heat resistance, high reliability, and high heat dissipation properties can be formed, thereby realizing high-temperature operation of the semiconductor device.

[0030] Furthermore, by using Ag as the metal particles as in this embodiment, the heat dissipation properties of the sintered body layer 3 can be further improved, making it possible to form a bonding layer with even higher heat dissipation properties, and further enabling the semiconductor device to operate at higher temperatures.

[0031] Next, an example of a method for manufacturing a semiconductor device according to this embodiment will be described with reference to FIGS. 4 to 6 . FIG. 4 is a flowchart showing an example of the steps of the method for manufacturing a semiconductor device according to this embodiment. FIG. 5 is a schematic cross-sectional view showing a semiconductor device after the metal particle layer forming step, the bonded member arranging step, and the solder supplying step of the method for manufacturing a semiconductor device according to this embodiment have been performed, and before the first bonding step has been performed. FIG. 6 is a schematic top view showing a semiconductor device after the metal particle layer forming step, the bonded member arranging step, and the solder supplying step of the method for manufacturing a semiconductor device according to this embodiment have been performed, and before the first bonding step has been performed. Note that the method for manufacturing a semiconductor device according to this embodiment is partially similar to conventional methods for manufacturing semiconductor devices, and therefore the following description will mainly focus on the differences from conventional methods for manufacturing semiconductor devices.

[0032] As shown in FIG. 4, the method for manufacturing a semiconductor device includes a metal particle layer forming step, a bonded member arranging step, a solder supplying step, a first bonding step, a second bonding step, and a cooling step.

[0033] First, the metal particle layer formation process will be described. A metal particle layer 7 having a sintering temperature lower than the melting point of the solder is formed on the upper surface of the semiconductor element 1. In this embodiment, the metal particle layer 7 is formed on an electrode layer provided on the upper surface of the semiconductor element 1. In this embodiment, the metal particle layer 7 is composed of Ag. Here, an example of a method for forming the metal particle layer 7 will be described. For example, a method can be used in which a paste containing metal particles and a solvent is prepared and then applied to the upper surface of the semiconductor element 1. The application method can be, for example, metal mask printing or dispense application. The solvent is selected to have a low boiling point so that it evaporates completely during the heating process performed in the first bonding process. Examples of solvents that can be used include Texanol, butyl carbitol, butyl carbitol acetate, and hexyl carbitol. Note that if the proportion of solvent in the paste is high, the solvent may not evaporate completely during heating. Furthermore, the spacing between the metal particles may increase, making it difficult for the metal particles to sinter. Therefore, a low proportion of solvent in the paste is preferable. For example, it is desirable that the solvent content in the paste be 15 wt % or less.

[0034] Next, the bonded member placement process will be described. The bonded members 2 are placed so that they are in direct contact with the upper surfaces of the metal particle layer 7. It is desirable to pressurize the bonded members 2 toward the semiconductor element 1 with a pressure large enough to ensure that the metal particle layer 7 adheres to the entire bonded surface of the bonded members 2, but not so large that the metal particles spread to the side surfaces 2c and upper surfaces of the bonded members 2 other than the bonded surface. Note that, depending on the viscosity of the solvent contained in the paste for the metal particle layer 7, a pressure of 3 to 10 N is used, for example. In this embodiment, the bonded members 2 have openings 2a penetrating the upper and lower surfaces of the bonded members 2. Furthermore, as described above, the bonded members 2 may have a metal-plated portion 6. In this case, the metal-plated portion of the bonded members 2 may be in direct contact with the upper surface of the metal particle layer 7, as shown in FIG. 5 . Note that in this embodiment, the bonded members 2 are terminals. The metal plating portion 6 can be formed by wet plating methods such as electrolytic plating and electroless plating, but dry plating methods such as sputtering, ion plating, and hot-dip plating may also be used.

[0035] Next, the solder supplying step will be described. As shown in FIGS. 5 and 6 , the solder 4 is supplied to the workpieces 2 so as not to come into contact with the metal particle layer 7. In this embodiment, the solder 4 is made of Sn. If the solder 4 comes into contact with the metal particle layer 7 during supplying the solder, the solder 4 and the metal particles will react during heating in the first and second joining steps, forming a large amount of intermetallic compound. This may result in failure to achieve a sintered bond between the semiconductor element 1 and the workpieces 2 and a soldered bond between the workpieces 2 and the sintered body layer 3. Therefore, in order to form an appropriate amount of intermetallic compound, it is necessary to prevent the solder 4 from coming into contact with the metal particles during heating in the first joining step. Therefore, in the solder supplying step, the solder 4 is supplied so as not to come into contact with the metal particles. In this embodiment, the solder 4 is supplied to the upper surface of the workpieces 2 so that the solder 4 is positioned above the opening 2 a. This prevents the solder 4 from coming into contact with the metal particle layer 7. The solder 4 must melt at a temperature higher than the heating temperature used in the first joining step, i.e., the sintering temperature of the metal particles. Therefore, a solder 4 having a melting point higher than the sintering temperature of the metal particles used is used. The solder 4 may be in the form of a sheet, thread, or pellet, for example, but in this embodiment, a sheet-like solder 4 is used, which makes it easier to control the amount of solder 4 supplied.

[0036] Next, the first bonding step will be described. The metal particle layer 7 is sintered by heating at a first temperature lower than the melting point of the solder 4 but equal to or higher than the sintering temperature of the metal particles, forming a sintered body layer 3 and bonding the semiconductor element 1 and the workpiece 2. A sintering process using a paste containing metal particles and a solvent as the sintering bonding material will be described. The organic components covering the surfaces of the metal particles are decomposed by heat, sintering the metal particles together to form a sintered body layer 3, thereby sinter-bonding the semiconductor element 1 and the workpiece 2. When a paste containing metal particles and a solvent is used as the sintering bonding material, sinter-bonding can be achieved without applying pressure during sintering. The heat-resistant temperature of the sintered body layer 3 after sinter-bonding is approximately the same as the melting point of the metal particles used (e.g., 960°C for Ag), providing higher heat resistance than solder. Note that, although depending on the organic component, organic solvents decompose at approximately 200–300°C, allowing sinter-bonding at temperatures that do not degrade the workpiece 2. An example of a heating method is to place a semiconductor device composed of the joined member 2, the solder 4, the metal particle layer 7, and the semiconductor element 1 combined in the above-described process in a normal pressure heating furnace filled with an inert gas such as nitrogen, and to heat the device by setting the temperature inside the heating furnace to the above-described first temperature.

[0037] Next, the second joining step will be described. The solder 4 is melted by heating at a second temperature equal to or higher than the melting point of the solder 4, and the molten solder 4 is interposed in the gap at the joining interface between the joined member 2 and the sintered body layer 3, thereby joining the joined member 2 and the sintered body layer 3. One example of a heating method is a method in which the temperature inside a heating furnace is set to the second temperature after the first joining step. Note that the second temperature is preferably 10°C or more higher than the melting point of the solder 4 in order to completely melt the solder 4. Furthermore, in the solder supplying step in this embodiment, the solder 4 is supplied onto the upper surface of the joined member 2 so that the solder 4 is positioned above the opening 2a. Therefore, in the second joining step, the solder 4 arranged on the opening 2 a melts, and the molten solder 4 passes through the opening 2 a provided in the workpiece 2, permeating the sintered body layer 3 from the portion of the sintered body layer 3 located directly below the opening 2 a toward the outside. As a result, the molten solder 4 can be interposed in the gaps at the joining interface between the workpiece 2 and the sintered body layer 3, as shown in FIG. 1 . It is desirable to interpose the molten solder 4 in the gaps at the entire joining interface between the workpiece 2 and the sintered body layer 3, and the amount of solder 4 supplied in the solder supplying step may be appropriately changed so that the molten solder 4 is interposed in the gaps at the entire joining interface between the workpiece 2 and the sintered body layer 3. Furthermore, when Ag-based metal particles and Sn-based solder 4 are used as in this embodiment, Sn easily permeates Ag, and therefore the molten solder 4 easily permeates the sintered body layer 3 in the second joining step. Therefore, it is possible to easily interpose the molten solder 4 in the gap at the joining interface between the joined members 2 and the sintered body layer 3. Furthermore, in the second joining step, by controlling the heating temperature and heating time, it is possible to cause the solder 4 to react with the joined members 2 or the sintered body layer 3 to form an intermetallic compound. At this time, the solder 4 itself may be eliminated to leave only the intermetallic compound, or the solder 4 may be left to contain both the intermetallic compound and the solder 4. When the solder 4 itself is eliminated, it is possible to leave only the intermetallic compound, which has a higher heat resistance than the solder 4, and therefore it is possible to form a joining layer 5 that is more heat resistant than when the solder 4 is left.Furthermore, when the solder 4 is left, the solder 4, which has higher ductility than the intermetallic compound, can be interposed, so the bonding layer 5 is less likely to crack than when the solder 4 itself is removed, and a highly reliable bonding layer 5 can be formed. Furthermore, when metal particles composed of Ag-based metal particles and solder 4 composed of Sn-based metal particles are used as in this embodiment, the intermetallic compound can be configured to contain Sn and Ag, and a bonding layer 5 with higher heat dissipation and higher reliability can be formed.

[0038] Finally, the cooling step will be described. The semiconductor device is cooled, and the sintered body layer 3 and the solder 4 are cooled to complete the bonding.

[0039] The semiconductor device 100 is fabricated through the above-described steps. In the first bonding step, a paste containing a mixture of metal particles and a solvent is used as the sintering bonding material. However, a sheet of solidified powdered metal particles may also be used as the sintering bonding material. However, if a sheet of solidified powdered metal particles is used, pressure must be applied during sintering in the first bonding step to sinter the materials. Therefore, it is preferable to use a paste containing a mixture of metal particles and a solvent that can be sinter-bonded without pressure during sintering. In the past, when a mixture of metal particles and an organic solvent was used as the sintering bonding material in the first bonding step, pressure was required to densely sinter the metal particles to enhance heat dissipation after the organic components volatilized. However, bonding without pressure limited the ability to promote diffusion of the metal particles using heat alone during sintering, resulting in a problem of insufficient bonding strength and low reliability of the bonding layer 5. Furthermore, in conventional bonding without pressure, if the workpieces 2 are deformed due to thermal expansion or the like, the sinter bonding material does not melt, and therefore cannot follow the deformation, which can result in peeling at the bonding interface between the workpieces 2 and the sintered body layer 3. When peeling occurs, there is a problem of deterioration in heat dissipation. However, in this embodiment, even when sinter bonding is performed without pressure, the molten solder 4 can be interposed in the gaps between the metal particles, ensuring the heat dissipation and reliability of the bonding layer 5.

[0040] Furthermore, in the above, in the solder supplying step, the solder 4 is supplied to the upper surface of the workpiece 2 so that the solder 4 is positioned over the opening 2a, but the solder may be supplied not only over the opening 2a but also to the side surface 2c of the workpiece 2. For example, paste solder may be used and applied to the side surface 2c of the workpiece 2. By supplying the solder to the side surface 2c in the solder supplying step, the solder 4 supplied to the side surface 2c of the workpiece 2 melts in the second joining step, and the molten solder 4 flows over the side surface 2c of the workpiece 2, allowing the molten solder 4 to permeate the sintered body layer 3 from the outer portion toward the inside. Therefore, by supplying solder to both the opening 2 a and the side surface 2 c of the workpiece 2 in the solder supplying step, the molten solder 4 can penetrate the sintered body layer 3 from both the outside and the inside of the sintered body layer in the second joining step, and the molten solder 4 can be more reliably interposed in gaps throughout the entire joining interface between the workpiece 2 and the sintered body layer 3. Note that if solder is supplied not only to the opening 2 a but also to the side surface 2 c of the workpiece 2, there is a possibility that the solder 4 will fall onto the semiconductor element 1 and that the solder 4 will come into contact with the metal particle layer 7. Therefore, by using methods such as making the size of the workpiece 2 smaller than the size of the electrode layer provided on the upper surface of the semiconductor element 1, inclining the side surface 2 c of the workpiece 2 so that it has a trapezoidal shape, or appropriately controlling the amount of solder 4 supplied, it is possible to prevent the solder 4 from falling onto the semiconductor element 1 and the solder 4 from coming into contact with the metal particle layer 7.

[0041] Next, a modification of the first embodiment will be described with reference to Fig. 7. In Fig. 7, the size of the opening 2a in the member to be joined 2 is exaggerated compared to the actual size of the opening 2a. Fig. 7 is a schematic top view showing the semiconductor element 1 and the member to be joined 2 of the semiconductor device according to the first modification. In Fig. 7, a terminal is shown as an example of the member to be joined 2.

[0042] As shown in Figures 7(a), (b), (c), and (d), the shape of the opening 2a of the terminal may be changed as appropriate. As shown in Figure 7(a), the opening 2a may be circular, or as shown in Figure 7(b), the opening 2a may be rectangular. As shown in Figure 7(c), the opening 2a may be semi-elliptical. Furthermore, as shown in Figure 7(d), multiple openings 2a may be provided in a mesh-like pattern. Note that, considering ease of manufacture, it is preferable that the openings 2a be circular. Furthermore, by providing multiple openings 2a in a mesh-like pattern, the molten solder 4 can be evenly distributed in the gaps at the bonding interface between the workpiece 2 and the sintered body layer 3.

[0043] Second Embodiment A semiconductor device 200 according to a second embodiment will be described with reference to Figures 8 to 10. Figure 8 is a schematic cross-sectional view of the semiconductor device 200 according to the second embodiment. Figure 9 is a schematic top view of the semiconductor device 200 according to the second embodiment. Note that Figure 8 shows a cross section taken along the dashed dotted line X-X shown in Figure 9. Figure 10 is an enlarged view of region A shown in Figure 8. Note that in Figures 8 to 10, the members to be joined 2 are shown as terminals.

[0044] As shown in Figures 8 to 10, the semiconductor device 200 of embodiment 2 differs from the semiconductor device 100 of embodiment 1 in that the member 2 to be joined does not have an opening 2a that penetrates the upper and lower surfaces of the member 2 to be joined.

[0045] As shown in Figures 8 and 10, the sintered body layer 3 bonds the semiconductor element 1 and the workpiece 2, and is provided so as to be in direct contact with the semiconductor element 1 and the workpiece 2, as in the first embodiment. Also, as in the first embodiment, the solder 4 is provided so as to be interposed in the gap at the bonding interface between the workpiece 2 and the sintered body layer 3, as shown in Figures 8 and 10. Also, as in the first embodiment, the solder 4 includes an intermetallic compound formed by a reaction between the solder and the workpiece 2 or the sintered body layer 3, and the solder 4 may be composed solely of the intermetallic compound. Note that in the second embodiment, as shown in Figures 8 and 10, the solder 4 is provided over the entire lower surface of the workpiece 2, but as in the first embodiment, it is sufficient that the solder 4 is provided so as to be interposed at least in the gap at the bonding interface between the workpiece 2 and the sintered body layer 3.

[0046] The semiconductor device 200 of embodiment 2 is configured as described above. As in embodiment 1, the semiconductor device 200 of embodiment 2 is provided with a sintered body layer 3 that bonds the semiconductor element 1 and the bonded member 2 and is provided so as to be in direct contact with the semiconductor element 1 and the bonded member 2, and a bonding layer 5 made of solder 4 that is interposed in the gap at the bonding interface between the bonded member 2 and the sintered body layer 3. Therefore, the semiconductor device 200 of embodiment 2 can achieve the same effects as embodiment 1.

[0047] Next, a method for manufacturing a semiconductor device according to a second embodiment will be described with reference to Figures 11 and 12. Figure 11 is a schematic cross-sectional view showing a semiconductor device after the metal particle layer forming step, the bonded member arranging step, and the solder supplying step of the method for manufacturing a semiconductor device according to the second embodiment have been performed, and before the first bonding step. Figure 12 is a schematic top view showing a semiconductor device after the metal particle layer forming step, the bonded member arranging step, and the solder supplying step of the method for manufacturing a semiconductor device according to the second embodiment have been performed, and before the first bonding step.

[0048] The method for manufacturing a semiconductor device according to the second embodiment differs from that according to the first embodiment in that the member to be joined 2 does not have an opening 2a penetrating the upper and lower surfaces of the member to be joined 2, and therefore the solder supplying step and the second joining step are partially different. The following description will focus on the differences between the solder supplying step and the second joining step, and the rest of the method is the same as that according to the first embodiment.

[0049] First, an example of the solder supplying process will be described for a case where the workpieces 2 do not have openings 2a penetrating the top and bottom surfaces of the workpieces 2. As shown in FIGS. 11 and 12 , the solder 4 is supplied to the workpieces 2 so as not to come into contact with the metal particle layer 7. In the second embodiment, as shown in FIGS. 11 and 12 , the solder 4 is supplied to the top and side surfaces 2c of the workpieces 2. As described above, when solder is supplied to the side surfaces 2c of the workpieces 2, there is a possibility that the solder 4 will fall onto the semiconductor element 1 and that the solder 4 will come into contact with the metal particle layer 7. Therefore, by using methods such as reducing the size of the workpieces 2 relative to the size of the electrode layer provided on the top surface of the semiconductor element 1, inclining the side surfaces 2c of the workpieces 2, or appropriately controlling the amount of solder 4 supplied, it is possible to prevent the solder 4 from falling onto the semiconductor element 1 and the solder 4 from coming into contact with the metal particle layer 7. In the second embodiment, a paste solder is used and applied to the top and side surfaces of the workpieces 2. 11 and 12, the solder 4 is supplied to both the top surface and the side surface 2c of the member 2 to be joined, but it is sufficient that the solder 4 is supplied to at least the side surface 2c of the member 2 to be joined.

[0050] Next, an example of the second joining step will be described for a case where the workpieces 2 do not have an opening 2a penetrating the top and bottom surfaces thereof. The workpieces 2 are heated to a second temperature equal to or higher than the melting point of the solder 4 to melt the solder 4, and the molten solder 4 is interposed in the gap at the joining interface between the workpieces 2 and the sintered body layer 3, thereby joining the workpieces 2 and the sintered body layer 3. In the second embodiment, the solder 4 is supplied to at least the side surface 2c of the workpieces 2 in the solder supplying step. Therefore, in the second joining step, the solder 4 supplied to the side surface 2c of the workpieces 2 melts and flows over the side surface 2c of the workpieces 2, permeating the sintered body layer 3 from the outer portion toward the inside. As a result, the molten solder 4 can be interposed in the gap at the joining interface between the workpieces 2 and the sintered body layer 3, as shown in FIG. 1 . Furthermore, in the second joining step, as in the first embodiment, by controlling the heating temperature and heating time, it is possible to form an intermetallic compound by causing the solder 4 to react with the joined member 2 or the sintered body layer 3. In this case, the solder 4 may be eliminated to leave only the intermetallic compound, or the solder 4 may be left to contain both the intermetallic compound and the solder 4.

[0051] The semiconductor device 200 is fabricated through the above-described steps.

[0052] The configurations shown in the above embodiments are merely examples of the contents of the present disclosure and may be combined with other known technologies. Furthermore, it is also possible to combine the embodiments with each other and the modified examples with each other. Furthermore, it is also possible to omit or modify part of the configurations without departing from the scope of the present disclosure.

[0053] Various aspects of the present disclosure are summarized below as appendices.

[0054] (Supplementary Note 1) A semiconductor device comprising a semiconductor element and a member to be joined made of metal, the semiconductor element and the member to be joined being joined together, and a sintered body layer of metal particles provided so as to be in direct contact with the semiconductor element and the member to be joined; and solder interposed in a gap at a joining interface between the member to be joined and the sintered body layer. (Supplementary Note 2) The semiconductor device according to Supplementary Note 1, wherein the solder includes an intermetallic compound of solder. (Supplementary Note 3) The semiconductor device according to Supplementary Note 1 or 2, wherein the solder is provided so as to be interposed in a gap across the entire joining interface between the member to be joined and the sintered body layer. (Supplementary Note 4) The semiconductor device according to any one of Supplements 1 to 3, wherein the member to be joined has a metal-plated portion in a portion that comes into contact with the sintered body layer and the solder. (Supplementary Note 5) The semiconductor device according to any one of Supplements 1 to 4, wherein the member to be joined has an opening penetrating an upper surface and a lower surface of the member to be joined. (Supplementary Note 6) The semiconductor device according to Supplementary Note 5, wherein the solder contacts an inner wall of the member to be joined that defines the opening. (Supplementary Note 7) The semiconductor device according to Supplementary Note 5 or 6, wherein a plurality of openings are provided in the member to be joined. (Supplementary Note 8) The semiconductor device according to any one of Supplementary Notes 1 to 7, wherein the member to be joined is a terminal. (Supplementary Note 9) The semiconductor device according to any one of Supplementary Notes 1 to 8, wherein the metal particles are made of Ag. (Supplementary Note 10) The semiconductor device according to any one of Supplementary Notes 1 to 9, wherein the solder is made of Sn. (Supplementary Note 11) The semiconductor device according to any one of Supplementary Notes 1 to 10, wherein the semiconductor element is made of SiC.(Appendix 12) A method for manufacturing a semiconductor device, comprising: a metal particle layer forming step of forming a metal particle layer having a sintering temperature lower than the melting point of solder on an upper surface of a semiconductor element; a member-to-be-joined arrangement step of arranging a member to be joined so that it is in direct contact with the upper surface of the metal particle layer; a solder supplying step of supplying the solder to the member to be joined so as not to come into contact with the metal particle layer; a first joining step of heating at a first temperature lower than the melting point of the solder and equal to or higher than the sintering temperature to sinter the metal particle layer to form a sintered body layer and join the semiconductor element and the member to be joined; and a second joining step of heating at a second temperature equal to or higher than the melting point of the solder to melt the solder and join the member to be joined and the sintered body layer by interposing the molten solder in a gap at a joining interface between the member to be joined and the sintered body layer. (Appendix 13) A method for manufacturing a semiconductor device according to Appendices 12, wherein in the second joining step, the solder reacts with the member to be joined or the sintered body layer to further form an intermetallic compound. (Appendix 14) The method for manufacturing a semiconductor device according to Appendix 13, wherein in the second joining step, the solder is reacted with the members to be joined or the sintered body layer to further form an intermetallic compound and cause the solder to disappear. (Appendix 15) The method for manufacturing a semiconductor device according to any one of Appendices 12 to 14, wherein the members to be joined have openings penetrating upper and lower surfaces of the members to be joined, the solder supplying step supplies the solder to the upper surfaces of the members to be joined so that the solder is disposed over the openings, and the second joining step joins the members to be joined and the sintered body layer by passing the molten solder through the openings and thereby interposing the molten solder in a gap at the joining interface between the members to be joined and the sintered body layer. (Supplementary Note 16) The method for manufacturing a semiconductor device according to any one of Supplementary Notes 12 to 14, wherein in the solder supplying step, the solder is supplied to at least a side surface of the workpiece, and in the second joining step, the molten solder flows over the side surface of the workpiece, thereby interposing the molten solder in a gap at a joining interface between the workpiece and the sintered body layer, thereby joining the workpiece and the sintered body layer. (Supplementary Note 17) The method for manufacturing a semiconductor device according to any one of Supplementary Notes 12 to 16, wherein the workpiece is a terminal.

[0055] REFERENCE SIGNS LIST 1 semiconductor element, 2 bonded member, 2a opening, 2b inner wall, 2c side surface, 3 sintered body layer, 4 solder, 5 bonding layer, 6 metal plated portion, 7 metal particle layer

Claims

1. A semiconductor device comprising a semiconductor element and a bonded member made of metal, the semiconductor element and the bonded member being bonded together, a sintered layer of metal particles provided so as to be in direct contact with the semiconductor element and the bonded member, and solder interposed in the gap at the bonding interface between the bonded member and the sintered layer.

2. The semiconductor device according to claim 1, wherein the solder contains an intermetallic compound of solder.

3. The semiconductor device according to claim 1 or 2, wherein the solder is provided so as to be interposed in the gaps across the entire bonding interface between the member to be bonded and the sintered body layer.

4. The semiconductor device according to any one of claims 1 to 3, wherein the member to be joined has a metal-plated portion at a portion that comes into contact with the sintered body layer and the solder.

5. The semiconductor device according to any one of claims 1 to 4, wherein the members to be joined have an opening penetrating the upper and lower surfaces of the members to be joined.

6. The semiconductor device according to claim 5, wherein the solder contacts the inner wall of the member to be joined that defines the opening.

7. The semiconductor device according to claim 5 or 6, wherein a plurality of openings are provided in the member to be joined.

8. The semiconductor device according to any one of claims 1 to 7, wherein the member to be joined is a terminal.

9. The semiconductor device according to any one of claims 1 to 8, wherein the metal particles are made of Ag.

10. The semiconductor device according to any one of claims 1 to 9, wherein the solder is made of Sn.

11. The semiconductor device according to any one of claims 1 to 10, wherein the semiconductor element is made of SiC.

12. A method for manufacturing a semiconductor device, comprising: a metal particle layer forming step of forming a metal particle layer having a sintering temperature lower than the melting point of solder on the upper surface of a semiconductor element; a member to be joined positioning step of positioning a member to be joined so that it is in direct contact with the upper surface of the metal particle layer; a solder supplying step of supplying the solder to the member to be joined so that it does not come into contact with the metal particle layer; a first joining step of heating at a first temperature lower than the melting point of the solder and equal to or higher than the sintering temperature to sinter the metal particle layer, thereby forming a sintered layer and joining the semiconductor element and the member to be joined; and a second joining step of heating at a second temperature equal to or higher than the melting point of the solder to melt the solder, and interposing the molten solder in a gap at the joining interface between the member to be joined and the sintered layer, thereby joining the member to be joined and the sintered layer.

13. The method for manufacturing a semiconductor device according to claim 12, wherein in the second joining step, the solder is reacted with the member to be joined or the sintered body layer to further form an intermetallic compound.

14. A method for manufacturing a semiconductor device as described in claim 13, wherein in the second joining step, the solder is reacted with the joined member or the sintered body layer to further form an intermetallic compound, and the solder is then eliminated.

15. A method for manufacturing a semiconductor device according to any one of claims 12 to 14, wherein the members to be joined have openings penetrating the top and bottom surfaces of the members to be joined, and in the solder supplying step, the solder is supplied to the top surface of the members to be joined so that the solder is positioned above the opening, and in the second joining step, the molten solder passes through the opening, thereby interposing the molten solder in a gap at the joining interface between the members to be joined and the sintered body layer, thereby joining the members to be joined and the sintered body layer.

16. A method for manufacturing a semiconductor device according to any one of claims 12 to 14, wherein in the solder supplying step, the solder is supplied to at least the side surface of the member to be joined, and in the second joining step, the molten solder flows over the side surface of the member to be joined, thereby interposing the molten solder in a gap at the joining interface between the member to be joined and the sintered body layer, thereby joining the member to be joined and the sintered body layer.

17. The method for manufacturing a semiconductor device according to any one of claims 12 to 16, wherein the member to be joined is a terminal.

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