Bonded body, circuit board, semiconductor device, and method for manufacturing bonded body

Abstract

This joined body according to an embodiment is characterized by comprising: a ceramic substrate; a copper plate; and a joining layer disposed on at least one surface of the ceramic substrate to join the ceramic substrate and the copper plate together. The joined body is further characterized in that: the joining layer contains Ag, Cu, Ti, and a first element which is one or two selected from Sn and In; a Ti alloy is present at the junction interface between the copper plate and the joining layer; the Ti alloy comprises Ti and at least one selected from Ag, Cu, Sn and In; and the abundance ratio of the Ti alloy per 30 µm of the length of the junction interface is 30%.

Description

Technical Field

[0001] The embodiments described below relate to a bonded body, a circuit board, a semiconductor device, and a method for manufacturing the bonded body.

Background Art

[0002] A bonded body of a ceramic substrate and a copper plate is used as a circuit board on which semiconductor elements and the like are mounted. International Publication No. 2018 / 021472 (Patent Document 1) discloses a ceramic copper circuit board in which a ceramic substrate and a copper plate are bonded. In Patent Document 1, a brazing material containing Ag, Cu, Ti, etc. is used for the bonding layer. In Patent Document 1, heat bonding is performed under a pressure of 1×10 -3 Pa or less. Such a pressure of 1×10 -3 Pa or less is called a vacuum. The bonding method using Ti is called an active metal bonding method. Since Ti is an active metal, it is easily nitrided or oxidized. In the active metal bonding method, in order to prevent Ti from being nitrided or oxidized before bonding, bonding is performed in a vacuum. To bond in a vacuum, the inside of the bonding apparatus must be evacuated. Since the temperature is raised after evacuation, only batch processing could be applied to the heat bonding process. The heat bonding process includes four processes of evacuation, temperature rise, bonding, and cooling per batch. It took more than 24 hours per batch. Therefore, mass productivity was not good. On the other hand, International Publication No. 2018 / 199060 (Patent Document 2) discloses performing a heat bonding process in a continuous furnace. In the example of Patent Document 2, bonding is performed at a furnace length of 3 m and a conveyance speed of 10 cm / min. Heat bonding can be performed in about 2 hours including the holding time in the middle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] In Patent Document 1 and Patent Document 2, the brazing filler metal contains 40 wt% or more of Ag. Further, Sn or In is also used in the brazing filler metal. Ag is an element that easily diffuses into the copper plate. Along with the diffusion of Ag, Sn and In also diffuse into the copper plate. When Sn or In diffuses into the copper plate, the melting point of the copper plate decreases. When the melting point of the copper plate decreases, it causes deformation during bonding and deterioration of Temperature Cycling Test (TCT) characteristics. In order to prevent the diffusion of Sn or In into the copper plate, it has been found that it is effective to have Ti present at the interface between the copper plate and the bonding layer. The present invention is for dealing with such problems, and provides a joined body in which the distribution of Ti in the bonding layer is controlled.

MEANS FOR SOLVING THE PROBLEMS

[0005] The joined body according to the embodiment includes a ceramic substrate, a copper plate, and a bonding layer disposed on at least one surface of the ceramic substrate for joining the ceramic substrate and the copper plate. The bonding layer contains Ag, Cu, Ti, and a first element selected from one or two of Sn and In. At the bonding interface between the copper plate and the bonding layer, a Ti alloy of Ti and at least one selected from Ag, Cu, Sn, and In exists, and the Ti alloy exists at 30% or more per 30 μm in length of the bonding interface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0007] The joined body according to the embodiment includes a ceramic substrate, a copper plate, and a joining layer disposed on at least one surface of the ceramic substrate for joining the ceramic substrate and the copper plate. The joining layer contains Ag, Cu, Ti, and a first element selected from one or two of Sn and In. At the joining interface between the copper plate and the joining layer, a Ti alloy of Ti and at least one selected from Ag, Cu, Sn, and In exists, and the Ti alloy is present at 30% or more per 30 μm of the length of the joining interface. FIG. 1 is a schematic diagram showing an example of a joined body. In FIG. 1, 1 is the joined body, 2 is the ceramic substrate, 3 is the copper plate, and 4 is the joining layer. FIG. 1 shows a joined body 1 in which copper plates 3 are respectively disposed on both surfaces of the ceramic substrate 2 via the joining layer 4. In the example of FIG. 1, the vertical and horizontal sizes of the ceramic substrate 2 and the copper plate 3 are the same as each other. The joined body according to the embodiment is not limited to such a form and may have a structure in which the copper plate 3 is provided only on one side of the ceramic substrate 2. Also, the vertical and horizontal sizes of the ceramic substrate 2 and the copper plate 3 may be different from each other.

[0008] Examples of the ceramic substrate 2 include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and an AlZr substrate. The thickness of the ceramic substrate 2 is preferably 0.1 mm or more and 1 mm or less. If the substrate thickness is less than 0.1 mm, the strength of the ceramic substrate 2 may decrease. Also, if the substrate thickness is thicker than 1 mm, the ceramic substrate becomes a heat resistor, which may reduce the heat dissipation of the joined body. The three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more. Further, the thermal conductivity is preferably 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, the substrate thickness can be reduced. For this reason, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, more preferably 700 MPa or more. The substrate thickness of the silicon nitride substrate can be reduced to 0.40 mm or less, more preferably 0.30 mm or less. The three-point bending strength of the aluminum nitride substrate is about 300 - 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or more. Since the strength of the aluminum nitride substrate is low, the substrate thickness is preferably 0.60 mm or more. The three-point bending strength of the aluminum oxide substrate is about 300 - 450 MPa, but the aluminum oxide substrate is inexpensive. Also, the three-point bending strength of the Ardel substrate is as high as about 550 MPa, but the thermal conductivity is about 30 - 50 W / m·K. The ceramic substrate 2 is preferably either a silicon nitride substrate or an aluminum nitride substrate. The silicon nitride substrate and the aluminum nitride substrate are nitride ceramic substrates. The nitride ceramics react with an active metal brazing material containing Ti to form titanium nitride. Also, the oxide ceramics react with an active metal brazing material containing Ti to form titanium oxide. For the copper plate 3, a pure copper plate or a copper alloy plate can be used. The copper plate 3 is preferably oxygen-free copper. Regarding oxygen-free copper, as shown in JIS-H-3100 (ISO1337, etc.), the copper purity is 99.96 wt% or more.

[0009] The bonding layer contains Ag, Cu, Ti, and a first element selected from one or two of Sn and In. Ag (silver), Cu (copper), and Ti (titanium) are essential constituent elements. In addition to these essential constituent elements, the bonding layer contains one or two selected from Sn (tin) and In (indium). Cu (copper) is an element that serves as the base material of the bonding layer. Even if Cu diffuses into the copper plate, it will not deteriorate the copper plate. Ti (titanium) is an effective element for reacting with the ceramic substrate to form a strong bond. Ag (silver) is an element that easily alloys with Ti. Sn (tin) or In (indium) is an effective element for lowering the melting point of the bonding solder material that forms the bonding layer. As will be described later, in order to obtain the desired bonding layer, it is effective to increase the heating rate. For this purpose, it is necessary to contain Sn or In.

[0010] At the bonding interface between the copper plate and the bonding layer, there exists a Ti alloy of Ti and one or more selected from Ag, Cu, Sn, and In. The Ti alloy is characterized by being present at 30% or more per 30 μm in length of the bonding interface. Figure 2 shows an example of the bonding layer. In Figure 2, 2 is the ceramic substrate, 3 is the copper plate, 4 is the bonding layer, 5 is the Ti alloy region, 6 is the Ti poor region, and 7 is the diffusion region. For measuring the presence or absence of the Ti alloy and the mass ratio of each element at the bonding interface between the copper plate 3 and the bonding layer 4, Scanning Electron Microscope - Energy Dispersive X-ray spectroscopy (SEM-EDX) is used. Hereinafter, an example in which the bonding layer and the Ti alloy contain Sn will be described. The cross-section of the bonded body 1 is taken as the measurement area. The cross-section of the bonded body 1 is parallel to the direction perpendicular to the surface of the ceramic substrate 2. As the SEM, a JSM-IT100 manufactured by JEOL Ltd. or an apparatus having equivalent performance is used. As the EDX, an EX-9440IT4L11 manufactured by JEOL Ltd. or an apparatus having equivalent performance is used. First, area analysis is performed by EDX in the range of 30 μm × the thickness of the bonding layer of the measurement area. The 30 μm in the measurement area is the length in the direction parallel to the surface of the ceramic substrate 2. Also, the thickness of the bonding layer in the measurement area only needs to include the interface between the copper plate and the bonding layer and the central region of the bonding layer in the measurement area.

[0011] At the bonding interface between the copper plate and the bonding layer, there exists a Ti alloy composed of Ti and one or more selected from Ag, Cu, Sn, and In. Examples of the Ti alloy include TiAg alloy, TiCu alloy, TiSn alloy, TiIn alloy, etc. It may be a Ti alloy containing two or more of Ag, Cu, Sn, or In. Further, the Ti alloy may be a compound or intermetallic compound containing Ti. The Ti alloy also includes a reaction product formed by the reaction of constituent elements and a mixture formed by the phase separation and mixing of constituent elements. That is, the Ti alloy indicates a state in which Ti and one or more selected from Ag, Cu, Sn, and In are mixed. The Ti alloy is present at 30% or more per 30 μm of the length of the bonding interface. The fact that it is present at 30% or more per 30 μm of the length of the bonding interface indicates that the Ti alloy is present at 9 μm or more per 30 μm. It is not necessary for a single mass of the Ti alloy to be present at 30% or more per 30 μm of the length of the bonding interface, and the Ti alloy may be present in multiple separated masses. It is only necessary for the total of the Ti alloy to be present at 30% or more per 30 μm of the length of the bonding interface. The presence of the Ti alloy at the bonding interface can suppress the diffusion of Ag, Sn, and In into the copper plate. When Ag diffuses into the copper plate, there is a possibility that Ag precipitates on the surface of the copper plate. When there is Ag on the surface of the copper plate, the wettability of the solder during mounting of the semiconductor element decreases. Also, when Sn or In diffuses into the copper plate, the melting point of the copper plate decreases. When the melting point of the copper plate decreases, the copper plate may be deformed during bonding or the TCT test. The presence of the Ti alloy at the bonding interface can suppress the diffusion of elements that have an adverse effect on the copper plate.

[0012] When performing surface analysis on the cross-section of the bonding layer, the mass ratio of Ag is preferably 20 mass% or less. Also, when performing surface analysis on the cross-section of the bonding layer, the mass M Cu of Ag to the mass M Ag of Cu, the ratio M Ag / M Cu is preferably 1 / 6 or less. By setting the Ag amount in the surface analysis to 20 mass% or less, it becomes easier to form the TiAg alloy. For this reason, the Ag amount is preferably 1 mass% or more and 20 mass% or less. The mass ratio M when performing surface analysisAg / M Cu being 1 / 6 or less indicates that the amount of Cu in the bonding layer is six times or more the amount of Ag. By reducing the amount of Ag and increasing the amount of Cu, it becomes easier to form the Ti alloy. Also, when performing surface analysis of the cross-section of the bonding layer, the mass M of Ag Ag and the mass M of Ti Ti For the sum of, the mass M of Ag Ag ratio M of Ag / (M Ag +M Ti ) is preferably 0.65 or less. Perform surface analysis on an arbitrary cross-section of the bonding layer 4 by EDX. Set the measurement magnification of SEM-EDX to 1000 times. Set the thickness direction of the measurement area to the range where the bonding layer 4 between the ceramic substrate 2 and the copper plate 3 is located. Set the lateral width of the measurement area for surface analysis to 30 μm. The lateral width is the dimension in the direction parallel to the surface of the ceramic substrate 2. Set the length in the thickness direction of the measurement area for surface analysis to the thickness of the bonding layer 4. The bonding interface between the ceramic substrate 2 and the bonding layer 4 is the bonding interface between the ceramic substrate 2 and the Ti agglomerated layer. If the ceramic substrate 2 is a nitride-based ceramic substrate, the Ti agglomerated layer contains titanium nitride (TiN). The atomic ratio of titanium to nitrogen in the titanium nitride contained in the Ti agglomerated layer may be other than 1:1. The bonding interface between the bonding layer 4 and the copper plate 3 is the farthest location (the location farthest from the ceramic substrate 2) where the components of the bonding layer are connected to contact the copper plate 3 within the measurement area. Since the bonding layer 4 contains Ti, Ag, Sn, or In, the bonding interface between the bonding layer 4 and the copper plate 3 is judged based on the diffusion state of these elements. Also, if the ceramic substrate 2 is an oxide-based ceramic substrate, the Ti agglomerated layer contains titanium oxide. As titanium oxide as the Ti agglomerated layer, compounds with various atomic ratios such as TiO2, TiO, and Ti2O3 may exist. Measure three arbitrary non-overlapping measurement areas by EDX and obtain the average value of the mass of each element. Thereby, the mass ratio of Ag and Ti in the bonding layer 4 can be grasped. Mass ratio M Ag / (M Ag +M Ti) being 0.65 or less indicates that the amount of Ag in the bonding layer is small. Thus, the barrier effect of Ag by Ti can be enhanced. At least a part of the Ti alloy is an alloy containing Ti and Ag. The Ti alloy preferably includes a Ti-rich region containing Ti and Ag. In the Ti-rich region, the mass M of Ag Ag to the mass M of Ti Ti ratio M Ti / M Ag is 0.6 or more. Among the Ti alloys 5, the region where M Ti / M Ag is 0.6 or more is defined as the Ti-rich region. The Ti-rich region may be a part of the Ti alloy 5 or may be the entire Ti alloy 5. Hereinafter, the Ti alloy 5 will also be referred to as the Ti-rich region 5. Ag is an element that easily diffuses into the copper plate. On the other hand, Ag is an element that easily alloys with Ti. By providing an alloy containing Ti and Ag with a mass ratio M Ti / M Ag of 0.6 or more, the diffusion of Ag into the copper plate can be suppressed. When the mass ratio M Ti / M Ag is 0.5 or less, since there is a large amount of Ag, the diffusion effect into the copper plate may decrease. Hereinafter, the alloy containing Ti and Ag may also be referred to as a TiAg alloy. Also, from the results of the surface analysis mentioned above, it can be determined that a TiAg alloy is formed in the region where the area where Ti exists overlaps with the area where Ag exists. Regarding Sn, In, Cu, and C described later, from the results of the surface analysis, if the area where these elements exist overlaps with the area where Ti exists, it can be determined that these elements exist in the Ti alloy. For measuring the mass ratio of elements in the Ti alloy, point analysis by SEM-EDX is used. The measuring device is as described above. The measuring magnification of the point analysis is set to 1000 times. Point analysis is a measuring method with a narrowed X-ray beam spot diameter. It is effective for measuring the mass ratio in a narrow range. From the surface analysis mentioned above, the region where the mass ratio M Ti / M Ag is 0.6 or more, and the region where the mass ratio M Ti / M AgGrasp the region where it is 0.5 or less. Arbitrarily select five locations from the region to be measured and measure them by point analysis, and use the average value of the mass of each element as the composition of the Ti alloy. For example, for the mass ratio M Ti / M Ag When it is desired to measure the composition of a Ti-rich region where is 0.6 or more, arbitrarily select five locations from the Ti-rich region and measure them by point analysis. The Ti-rich region can suppress the diffusion of Sn or In into the copper plate. That is, the Ti-rich region functions as a barrier layer that suppresses the diffusion of Ag, Sn, or In into the copper plate. The Ti-rich region is preferably at least a part of the Ti alloy present at the bonding interface. More preferably, the area ratio of the Ti alloy is 50% or more and 100% or less.

[0013] At least a part of the Ti alloy is an alloy containing Ti and a first element. In the alloy containing Ti and the first element, the mass M of the first element E1 to the mass M of Ti Ti The ratio M of Ti / M E1 It is preferable that there is a Ti-rich region where is 0.4 or more. The Ti alloy at the bonding interface functions as a barrier layer. When the mass ratio M Ti / M E1 is 0.4 or more, Ti can suppress the diffusion of Sn or In into the copper plate. Hereinafter, an alloy containing Ti and Sn may also be referred to as a TiSn alloy. An alloy containing Ti and In may also be referred to as a TiIn alloy. The TiSn alloy or TiIn alloy may contain Ag. That is, a TiAgSn alloy or a TiAgIn alloy may exist. For this reason, the TiAg alloy may exist in the same region as the TiSn alloy or the TiIn alloy. The presence of a Ti alloy containing a large amount of Ti by mass ratio improves the function as a barrier layer.

[0014] FIG. 3 is a partially enlarged view of the bonding layer of the bonded body according to the embodiment. FIG. 3 shows a state where 100% of the Ti alloy is a Ti-rich region. As shown in FIG. 3, the bonding layer 4 includes a region 4a located between the ceramic substrate 2 and the Ti-rich region 5. When comparing the Cu amount in the central portion 5a of the Ti-rich region with the Cu amount in the region 4a of the bonding layer 4, it is preferable that the Cu amount in the central portion 5a is less. The fact that the Cu amount in the central portion 5a is small indicates that elements other than Cu are concentrated in the Ti-rich region 5. In other words, it indicates that the Ti-rich region 5 functions as a barrier layer. On the ceramic substrate side as viewed from the Ti-rich region, it is preferable that there is a region where Cu is 70% or more by mass ratio. The region on the ceramic substrate side as viewed from the Ti-rich region is a region located about 1 to 3 μm on the ceramic substrate side from the Ti-rich region, for example, the region 4a shown in FIG. 3. It is preferable that there is a region where Cu is 90% or more by mass ratio between the Ti-rich region and the copper plate. The fact that there is a region where the mass ratio of Cu is 90% or more between the Ti-rich region and the copper plate indicates that the Ti-rich region 5 exists at the bonding interface between the copper plate 3 and the bonding layer 4. In the confirmation of the mass ratio, the Cu amount in the region located about 1 to 3 μm on the copper plate side from the Ti-rich region 5 is measured. The Ti-rich region 5 exists at the bonding interface between the copper plate 3 and the bonding layer 4. It is preferable that there is a region where Cu is less than 90% on the ceramic substrate 2 side of the Ti-rich region 5. Also, it is preferable that there is a region where Cu is 90% or more by mass ratio between the copper plate 3 and the Ti-rich region 5. This indicates that there is a difference in the mass ratio of Cu between the two regions sandwiching the Ti-rich region 5. The Ti-rich region 5 has a barrier effect on Ag, Sn, and In, resulting in a difference in the mass ratio of Cu. The higher the function of the Ti-rich region 5 as a barrier layer, the greater the difference in the mass ratio of Cu between the two regions sandwiching the Ti-rich region 5. For the measurement of the mass ratio of Cu in these regions, the above-described surface analysis is used. The Ti-rich region preferably contains carbon. By adding carbon to the brazing filler metal, the fluidity and wettability of the brazing filler metal can be controlled. The fact that the Ti-rich region 5 contains carbon indicates that the Ti-rich region 5 also functions as a barrier layer that traps carbon. In addition, for the measurement of the Cu amount in the central portion 5a of the Ti-rich region 5 and the Cu amount in the region 4a of the bonding layer 4, point analysis by SEM-EDX is used. For the central portion of the Ti-rich region, point analysis is performed near the center of the Ti-rich region. For the above-mentioned region of the bonding layer, point analysis is performed on a region located about 1 to 3 μm on the ceramic substrate side from the Ti-rich region. The point analysis may be performed at any one location. For the measurement of the Cu amount between the copper plate and the Ti-rich region, point analysis is performed on a region located about 1 to 3 μm on the copper plate side from the Ti-rich region.

[0015] Preferably, a Ti-poor region exists in the central portion of the bonding layer. In the Ti-poor region, the mass M Ag of Ti to the mass M Ti of Ag Ti has a ratio M Ag / M of 0.1 or less. The central portion of the bonding layer is the center in the thickness direction of the bonding layer 4. The region located in the middle between the interface of the ceramic substrate 2 and the bonding layer 4 and the interface of the bonding layer 4 and the copper plate 3 is called the central portion. The Ti content of the Ti-rich region is higher than the Ti content of the Ti-poor region. Ti / M Ag being 0.1 or less in the central portion of the bonding layer indicates that the amount of Ti is significantly less than the amount of Ag. The active metal bonding layer includes a Ti agglomeration layer formed on the surface of the ceramic substrate 2. The Ti agglomeration layer of the nitride-based ceramic substrate 2 contains titanium nitride (TiN). In addition, the Ti agglomeration layer of the oxide-based ceramic substrate 2 contains titanium oxide. By forming a Ti agglomeration layer on the surface of the ceramic substrate 2, the bonding strength can be improved. The fact that the abundance of Ti is low in the central part of the bonding layer indicates that Ti in the bonding layer exists as a Ti agglomerated layer and a Ti alloy at the bonding interface between the copper plate 3 and the bonding layer 4. That is, it shows that Ti in the bonding layer has both functions of improving the bonding strength and suppressing the diffusion of Ag or the like into the copper plate. In addition, in the bonding layer, there may be a region where the mass ratio M Ti / M Ag exceeds 0.1. As long as it does not connect to the Ti-rich region at the interface between the Ti agglomerated layer on the surface of the ceramic substrate 2 and the bonding layer 4 of the copper plate 3, there may be a region in the bonding layer where the mass ratio M Ti / M Ag exceeds 0.1. It is effective that the Ti agglomerated layer and the Ti-rich region are separated from each other by a region where the mass ratio M Ti / M Ag is 0.1 or less. In the Ti poor region, the ratio M Cu of the mass M Ag of Ag to the mass M Ag / M Cu is preferably 0.1 or less with respect to Cu. The fact that the mass ratio M Ag / M Cu is 0.1 or less in the Ti poor region at the center of the bonding layer indicates that the amount of Ag in the bonding layer is small. When the amount of Ag is large, the mass ratio M Ti / M Ag in the Ti alloy at the bonding interface between the copper plate 3 and the bonding layer 4 tends to be 0.5 or less. Further, the Ti poor region preferably exists in 50% or more of the central part of the bonding layer. In addition, the composition analysis of the Ti poor region is obtained by measuring an arbitrary area analysis of 50 μm × 3 μm on the horizontal line passing through the center of the bonding layer 4 and taking the average value. When it cannot be analyzed in one field of view, the average value may be obtained using the analysis results of a plurality of areas.

[0016] When the amount of Ag in the Ti-rich region is A (wt%) and the amount of Ag at a position 30 μm deep into the copper plate from the bonding interface is B (wt%), it is preferable that A > B. As shown in FIG. 2, a diffusion region 7 is defined from the bonding interface between the copper plate 3 and the bonding layer 4 to a position 30 μm deep into the copper plate 3. The bonding interface between the copper plate 3 and the bonding layer 4 can be determined from the position of the Ti alloy 5 having a Ti-rich region. The fact that A > B indicates that the amount of Ag diffused into the copper plate is less than that in the Ti-rich region at the bonding interface between the copper plate 3 and the bonding layer 4. Ag is an element that easily diffuses into the copper plate. Even considering the narrow diffusion region 7 of 30 μm, the fact that A > B indicates that the Ti-rich region functions as a barrier layer. When the amount of Sn in the Ti-rich region is D (wt%) and the amount of Sn at a position 30 μm deep into the copper plate from the bonding interface is E (wt%), it is preferable that D > E. This indicates that the diffusion of Sn into the copper plate can be suppressed. The same applies when Sn is replaced with In. The thickness of the copper plate is preferably 0.3 mm or more. The Ti-rich region at the bonding interface between the copper plate 3 and the bonding layer 4 can suppress the diffusion of Ag, Sn, or In into the copper plate. The thicker the copper plate, the more susceptible it is to the influence of the diffusion of Ag, Sn, or In. Since the diffusion can be suppressed, even if the thickness of the copper plate is increased to 0.3 mm or more, and further to 0.6 mm or more, the occurrence of problems can be suppressed.

[0017] The bonded body as described above is suitable for a circuit board. Further, a semiconductor element can be mounted on the circuit board according to the embodiment and used for a semiconductor device. FIG. 4 is a schematic diagram showing an example of a circuit board. FIG. 5 is a schematic diagram showing an example of a semiconductor device. In FIGS. 4 and 5, 8 is a copper circuit portion, 9 is a heat sink, 10 is a semiconductor element, 11 is a lead frame, 20 is a circuit board, and 30 is a semiconductor device. In the circuit board 20 shown in FIG. 4, the copper plate 3 on the front side of the joined body 1 is processed into a copper circuit portion 8, and the copper plate 3 on the back side is processed into a heat sink 9. A circuit shape is imparted to the copper plate 3 of the joined body 1 to produce the circuit board 20. In the semiconductor device 30 shown in FIG. 5, a semiconductor element 10 is mounted on the copper circuit portion 8 of the circuit board 20. In the semiconductor device 30, in addition to the semiconductor element 10, a lead frame 11 or the like may be mounted as necessary. In the example shown in FIG. 4, the circuit board 20 has a structure in which two copper circuit portions 8 are provided, but the structure of the circuit board 20 is not limited to this example. As necessary, the number and size of the copper circuit portions 8 can be changed. The number of each of the semiconductor element 10 and the lead frame 11 can also be arbitrarily changed. Further, in FIG. 4, the copper plate 3 on the back side is used as the heat sink 9, but a circuit structure may be imparted to the copper plates 3 on both sides respectively. As necessary, an inclined shape may be imparted to the side surface of the copper circuit portion 8 and the side surface of the heat sink 9. As necessary, the joining layer 4 may be provided with a protruding portion protruding from the side end portion of the copper circuit portion 8 and the side end portion of the heat sink 9. It is preferable to use an etching process for imparting a circuit structure and an inclined shape to the side surface of the copper plate.

[0018] Next, a method for manufacturing the joined body according to the embodiment will be described. As long as the joined body according to the embodiment has the above configuration, its manufacturing method is not limited. Here, an example of a method for obtaining the joined body according to the embodiment with good yield is given. First, a ceramic substrate 2 is prepared. Examples of the ceramic substrate 2 include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and an aldyl substrate. The aldyl substrate is a substrate in which aluminum oxide and zirconium oxide are mixed. As the copper plate 3, an oxygen-free copper plate or a copper alloy plate can be used. The copper plate is preferably an oxygen-free copper. As shown in JIS-H-3100 (ISO1337, etc.), the oxygen-free copper is a copper plate with a copper purity of 99.96 wt% or more. Next, prepare a brazing filler metal. As the brazing filler metal, it is preferable to contain 50 mass% or more of Cu, 4 mass% or more and 30 mass% or less of Ti, 5 mass% or more and 40 mass% or less of one or two selected from Sn and In, 1 mass% or more and 20 mass% or less of Ag, and 0 mass% or more and 2 mass% or less of carbon. Conventional active metal brazing filler metals contain 40 mass% or more of Ag. By setting the Ag amount to 1 mass% or more and 20 mass% or less, the mass ratio M Ti / M Ag tends to form a Ti-rich region of 0.6 or more. Further, as the brazing filler metal, prepare a brazing filler metal that can be joined even when a rapid heating process with a heating rate of 20 °C / min or more is performed. The brazing filler metal preferably has an endothermic peak in the range of 520 °C or more and 590 °C or less in the DSC curve of the heating process with a heating rate of 20 °C / min.

[0019] The DSC curve is obtained by using a differential scanning calorimeter (DSC) to apply heat to a sample and measure the presence or absence of endothermic and exothermic reactions. When an endothermic or exothermic reaction occurs, a peak appears in the DSC curve. A peak in the minus direction is an endothermic reaction, and a peak in the plus direction is an exothermic reaction. An endothermic reaction indicates that melting, decomposition, etc. of the sample are occurring. An exothermic reaction indicates that the constituent elements of the sample are reacting to form a compound (including alloying) or are being solidified. It can be seen that the larger the peak, the larger the heat of reaction. Here, a peak in the minus direction is called an endothermic peak, and a peak in the plus direction is called an exothermic peak. Also, the apex of the peak is called the peak top. Also, the difference between the maximum and minimum points of the peak is called the peak height. For example, since the endothermic peak is in the minus direction, it goes up, down, and then up. The endothermic peak includes a change from maximum point → minimum point → maximum point. This minimum point (the lowest point) becomes the peak top. Of the maximum points on the low-temperature side and high-temperature side of the minimum point, the larger value (the larger peak in the plus direction) is taken as the most extreme maximum point. The peak height is the value obtained by subtracting the minimum point from the most extreme maximum point. For example, since the heat generation peak is in the positive direction, it decreases, increases, and then decreases again. The heat generation peak includes changes from a minimum point → a maximum point → a minimum point. This maximum point (the highest point) becomes the peak top. Among the minimum points on the low-temperature side and high-temperature side of the maximum point, the one with the smaller value (a large peak in the negative direction) is taken as the most extreme minimum point. The peak height is the value obtained by subtracting the most extreme minimum point from the maximum point. Note that the end point of the endothermic peak (a peak in the negative direction) may appear to be the heat generation peak (a peak in the positive direction), but here it is counted as the heat generation peak. It is also possible to draw a baseline and determine each peak. As the DSC, a TGA-DSC simultaneous thermal analyzer STA449-F3-Jupiter manufactured by NETZSCH or a device having equivalent performance is used. Also, the measurement is carried out in an Ar (argon) flow by dropping an appropriate amount of brazing material into an alumina container. The measurement is performed with the lid of the alumina container closed. It is necessary to prevent the brazing material from reacting with the atmosphere by measuring in an Ar atmosphere. Note that the dropped amount (mg) is measured with a balance. Also, a sample with a solid content of 15 mg or more is used.

[0020] The temperature profile for obtaining the DSC curve consists of the above-mentioned heating process, holding process, and cooling process. The heating process is a process of heating from room temperature to 950 °C at a heating rate of 20 °C / min. The holding process is a process of holding at 950 °C for 20 minutes. The cooling process is a process of cooling from 950 °C to room temperature at a cooling rate of 20 °C / min. The holding process is carried out after the heating process, and the cooling process is carried out after the holding process. Hereinafter, the DSC curve of the heating process at a heating rate of 20 °C / min may also be referred to as the DSC curve of the heating process. The DSC curve of the cooling process at a cooling rate of 20 °C / min may also be referred to as the DSC curve of the cooling process. In the DSC curve, those with a difference in heat flow of 0.02 mW / mg or more between the baseline and the apex of the protrusion were counted as peaks.

[0021] FIG. 6 shows the DSC curve (500 to 600 °C) of the heating process of the brazing filler metal used in Example 1. FIG. 7 shows the DSC curve (800 to 900 °C) of the heating process of the brazing filler metal used in Example 1. In FIGS. 6 and 7, the horizontal axis represents temperature (°C) and the vertical axis represents heat flow (mW / mg). In FIGS. 6 and 7, the heat flow is denoted as DSC. The DSC curve of the heating process at a heating rate of 20 °C / min preferably has an endothermic peak in the range of 520 °C or higher and 590 °C or lower. Also, the DSC curve of the heating process preferably has an endothermic peak in the range of 810 °C or higher and 890 °C or lower. The endothermic peak within the range of 520 °C or higher and 590 °C or lower in the DSC curve of the heating process is called the first endothermic peak. When there are two or more endothermic peaks within the range of 520 °C or higher and 590 °C or lower in the DSC curve of the heating process, the largest peak is taken as the first endothermic peak. The largest peak means the peak with a large value on the negative side. Also, the endothermic peak within the range of 810 °C or higher and 890 °C or lower in the DSC curve of the heating process is called the second endothermic peak. When there are two or more endothermic peaks within the range of 810 °C or higher and 890 °C or lower in the DSC curve of the heating process, the largest peak is taken as the second endothermic peak. The largest peak means the peak with a large value on the negative side. FIG. 6 is a diagram showing an example of the first endothermic peak. FIG. 7 is a diagram showing an example of the second endothermic peak.

[0022] The first endothermic peak indicates that the decomposition reaction of TiH₂ is occurring. The decomposed hydrogen has the effect of removing impurity oxygen in the brazing filler metal and activating the metal components. As the conventional active metal brazing filler metal, an AgCuSnTi brazing filler metal containing 40 mass% or more of Ag has been used. In the conventional active metal brazing filler metal, the decomposition reaction of TiH₂ occurred at 480 to 500 °C. That is, there was no first endothermic peak in the DSC curve of the conventional active metal brazing filler metal. By shifting the decomposition reaction of TiH₂ to the high-temperature side, it is possible to suppress the nitridation of the joining brazing filler metal. When joining a nitride-based ceramic substrate and a copper plate using an active metal brazing filler metal, a Ti aggregation layer is formed on the surface of the ceramic substrate. By shifting the decomposition reaction of TiH₂ to the high-temperature side, it is possible to suppress the nitridation of Ti in the brazing filler metal before reacting with the ceramic substrate. For this reason, joining in a nitrogen atmosphere becomes possible.

[0023] The second endothermic peak indicates the melting reaction of Cu and the first element. This melting reaction may include the melting reactions of Ag and copper. Cu and the first element are the elements that become the base material of the joining brazing filler metal. For this reason, the second endothermic peak indicates that the reaction in which the joining brazing filler metal melts to generate a liquid phase is occurring. Regarding the conventional active metal brazing filler metal, the decomposition reaction of TiH₂ occurred at 480 to 500 °C. That is, in the conventional active metal brazing filler metal, the first endothermic peak did not occur. By using a joining brazing filler metal in which the first endothermic peak occurs, the temperature difference between the peak indicating the decomposition reaction of TiH₂ and the second endothermic peak indicating the melting reaction of Cu and the first element can be reduced. Thereby, even if the heating rate in the joining process becomes fast, the joinability can be maintained.

[0024] The DSC curve of the cooling process at a cooling rate of 20°C / min preferably has an exothermic peak. The exothermic peak in the cooling process indicates that the formation or solidification of the compound (alloy) in the bonding layer is occurring. The thermal stress is the greatest when the molten solder solidifies. This is because after the bonding interface is formed, members with different coefficients of thermal expansion are constrained, and stress due to the difference in thermal expansion occurs during cooling. Therefore, the DSC curve of the cooling process preferably has an exothermic peak at 890°C or lower. The DSC curve may have two or more exothermic peaks. Having two or more exothermic peaks indicates that the formation or solidification of the compound (alloy) in the bonding layer occurs in multiple steps. Thereby, the stress relaxation effect of the bonded body is improved. Also, the DSC curve of the cooling process at a cooling rate of 20°C / min preferably has an exothermic peak at 450°C or higher and 550°C or lower. The exothermic peak at 450°C or higher and 550°C or lower in the DSC curve of the cooling process at a cooling rate of 20°C / min is called the first exothermic peak. When there are two or more exothermic peaks in this temperature range, the peak with the maximum value shall be regarded as the first exothermic peak. If the exothermic peak in the cooling process is less than 450°C, the solidification temperature is too low and the reliability of the bond may decrease. On the other hand, if the exothermic peak exceeds 550°C and is too high, the thermal stress may increase. Also, when comparing the peak top temperatures of the first endothermic peak in the heating process and the first exothermic peak in the cooling process, it is preferable that the peak top temperature of the first exothermic peak is lower. The first endothermic peak is mainly caused by the decomposition reaction of TiH2. On the other hand, the first exothermic peak in the cooling process is an exothermic reaction caused by the solidification of the bonding layer or the formation of Ti compounds. By setting the peak top position of the first exothermic peak in the cooling process at a temperature lower than the peak top position of the first endothermic peak in the heating process, the generation of thermal stress in the cooling process can be suppressed. Note that if the cooling process has an exothermic peak, the first exothermic peak may not be present. Also, by having two or more exothermic peaks in the DSC curve of the cooling process, the same effect can be obtained.

[0025] The brazing filler metal as described above can be joined even when the heating rate is 20°C / min or more or the cooling process is 20°C / min or more. Also, the brazing atmosphere may be in a vacuum or a nitrogen atmosphere. Note that the vacuum refers to an atmosphere of 1×10 -3 Pa or less. Also, the nitrogen atmosphere refers to an atmosphere in which nitrogen is 70 vol% or more. Also, examples of components other than nitrogen include argon gas and air.

[0026] To control the DSC curve, it is effective to control the filler metal composition. As the brazing filler metal, it is preferably contained 50 mass% or more of Cu, 4 mass% or more and 30 mass% or less of Ti, 5 mass% or more and 40 mass% or less of one or two selected from Sn and In, 1 mass% or more and 20 mass% or less of Ag, and 0 mass% or more and 2 mass% or less of carbon. Carbon is preferably 0.1 mass% or more and 1 mass% or less. It is preferable that the total of Cu, Ti, and the first element is 80 mass% or more, and further 90 mass% or more and 99 mass% or less. It is preferable that the total of Cu and the first element is 70 mass% or more. By reducing the proportion of Ag present, the melting point of the filler metal can be raised. Thereby, even if the heating rate and the cooling rate are increased, a filler metal having the target DSC curve can be obtained.

[0027] Regarding the Cu powder used as the raw material of the filler metal, the average particle size D 50 is preferably 12.0 μm or less, and further preferably 10.0 μm or less. Also, the average particle size D 50 of the TiH2 powder is preferably 6.0 μm or less, and further preferably 4.0 μm or less. The average particle size D 50 of the Sn powder or In powder is preferably 16.0 μm or less, and further preferably 14.0 μm or less. The average particle size D 50 of the C powder is preferably 6.0 μm or less, and further preferably 4.0 μm or less. The average particle size D 50 of the Ag powder is preferably 3.0 μm or less, and further preferably 2.0 μm or less. By controlling the particle size of the powder, the reaction of each powder can be made uniform. The average particle size D 50 of the Cu powder is the average particle size D 50It is preferably smaller. As described above, Cu and the first element serve as the base material for the brazing material composition. Compared with Cu, Sn and In are elements with low melting points. By increasing the particle size of Sn or In, the reaction between the Sn powder and the Cu powder or the reaction between the In powder and the Cu powder can be made homogeneous. Thereby, even if the heating rate or the cooling rate is increased, joining can be achieved.

[0028] A step of joining a ceramic substrate and a copper plate is performed using the brazing material for joining as described above. The brazing material is mixed with an organic substance to prepare a brazing paste. The brazing paste is applied to the surface of the ceramic substrate 2 (or the copper plate 3) to form a brazing paste layer. The copper plate 3 (or the ceramic substrate 2) is disposed on the brazing paste layer. The heating and joining step is performed in a vacuum or a nitrogen atmosphere. The vacuum means under a pressure of 1×10 -3 Pa or less. Also, the nitrogen atmosphere means an atmosphere in which nitrogen is 70 vol% or more. The nitrogen atmosphere preferably has a nitrogen content of 70 vol% or more, more preferably 85 vol% or more and 100 vol% or less. The nitrogen atmosphere may contain argon gas or air in addition to nitrogen. When heating and joining in a nitrogen atmosphere, it can be performed under various conditions such as normal pressure, reduced pressure, and pressurization.

[0029] In the heating step of the heating and joining step, the heating rate is set to 20 °C / min or more. In the conventional active metal bonding method, the heating rate was 5 °C / min or less. By using the brazing material having the DSC curve as described above, joining is possible even if the heating rate is increased. The upper limit of the heating rate is not particularly limited, but is preferably 100 °C / min or less. If it is faster than 100 °C / min, the joinability may decrease. Therefore, the heating rate is preferably 20 °C / min or more and 100 °C / min or less, more preferably 30 °C / min or more and 70 °C / min or less. In the heating process, the temperature is raised to the bonding temperature. The bonding temperature is set to 750 °C or higher. Also, the bonding temperature is set to a temperature higher than the peak temperature of the second endothermic peak. The second endothermic peak is at 810 - 890 °C. By setting the bonding temperature to a temperature higher than the peak temperature of the second endothermic peak, the melting reaction of the brazing material can be properly induced. Therefore, the bonding temperature is preferably 750 °C or higher, more preferably 800 °C or higher. Note that the upper limit of the bonding temperature is preferably 1000 °C or lower. If it exceeds 1000 °C and is too high, it will be close to the melting point of copper (1085 °C), and the copper plate may deform. The bonding temperature is preferably maintained for 10 minutes or more. The time of holding at the bonding temperature is called the heating holding time. The heating holding time is preferably 10 minutes or more and 100 minutes or less. If the heating holding time is less than 10 minutes, there may be insufficient time for the brazing material to melt and solidify. Also, if it exceeds 100 minutes and is too long, Sn or In may diffuse excessively into the copper plate.

[0030] After the heating holding time ends, a cooling process is performed. The cooling process is the process of cooling from the bonding temperature to room temperature. The cooling rate is set to 20 °C / min or more. In the conventional active metal bonding method, the cooling rate was about 5 °C / min. By using the brazing material for bonding having the DSC curve as described above, even if the cooling rate is increased, bonding is possible. The upper limit of the cooling rate is not particularly limited, but it is preferably 100 °C / min or less. If it is faster than 100 °C / min, the bondability may decrease. Therefore, the cooling rate is preferably 20 °C / min or more and 100 °C / min or less, more preferably 30 °C / min or more and 70 °C / min or less. Also, if necessary, the heating and bonding process may be performed while placing a weight on the bonded body 1.

[0031] Through the bonding process as described above, the bonded body 1 can be manufactured. By increasing the heating rate in the heating process and the cooling rate in the cooling process, the amount of heat applied to the bonded body 1 can be reduced. As a result, the distribution of the Ti alloy at the bonding interface between the copper plate 3 and the bonding layer 4 can be controlled. Also, the diffusion amount of Ag, Sn, or In into the copper plate can be reduced. Since the amount of heat transferred to the bonded body 1 can be reduced, warping of the bonded body 1 and distortion of the copper plate 3 can also be reduced. The obtained bonded body 1 is subjected to etching and processed into the circuit board 20. Further, if necessary, multiple bonding may be performed. Multiple bonding is a method of cutting a large bonded body to obtain a small bonded body. There are also methods of dividing the bonded body or dividing the ceramic copper circuit board. In order to facilitate division, scribing may be performed.

[0032] (Example) (Examples 1 to 5, Comparative Example 1) The brazing materials shown in Tables 1 and 2 were prepared. Table 1 shows the particle size of the raw material powder. Table 2 shows the composition ratio.

[0033] [Table 1]

[0034] [Table 2]

[0035] The brazing material components according to the examples and comparative examples were mixed with an organic binder to prepare a brazing paste. For each brazing paste, a DSC curve was measured using DSC. As the DSC, a TGA-DSC simultaneous thermal analyzer STA449-F3-Jupiter manufactured by NETZSCH was used. The measurement was carried out by dropping an appropriate amount of the brazing material into an alumina container in an Ar flow. The measurement was performed with the lid of the alumina container closed. The temperature program was a heating rate of 20 °C / min, holding at 950 °C for 20 minutes, and a cooling rate of 20 °C / min. A sample with a solid content of 15 mg was used. The presence or absence of the first endothermic peak and the second endothermic peak in the heating process was examined. In addition, the temperature at the peak top was examined. The results are shown in Table 3.

[0036] [Table 3]

[0037] As can be seen from the table, for the brazing filler metal according to the examples, the first endothermic peak and the second endothermic peak were observed. On the other hand, in Comparative Example 1, the endothermic peak indicating the decomposition reaction of TiH₂ was less than 520 °C. That is, the first endothermic peak was not observed. Also, in Comparative Example 1, the endothermic peak indicating the melting reaction of Cu and the first element was 722 °C. That is, the second endothermic peak was not observed. Next, a silicon nitride substrate was prepared as the ceramic substrate. A silicon nitride substrate with a thermal conductivity of 90 W / m·K, a three-point bending strength of 600 MPa, a length of 50 mm × a width of 40 mm × a plate thickness of 0.32 mm was used. As the copper plate, an oxygen-free copper plate with a length of 50 mm × a width of 40 mm × a plate thickness of 0.5 mm was prepared. Brazing paste was applied to both sides of the ceramic substrate at 30 μm each, and the copper plates were respectively placed thereon. Next, a heat joining process was carried out. The joining atmosphere was unified to a nitrogen atmosphere. Also, the joining conditions were unified to 850 °C × 20 minutes. The heating rate and the cooling rate were set to the conditions shown in Table 4.

[0038] [Table 4]

[0039] Through the above steps, joined bodies were manufactured. Ten joined bodies according to each of the examples and comparative examples were manufactured. Next, the cross-sectional structure of the obtained joined body was observed. The cross-section of the joined body was observed by SEM-EDX. Surface analysis was performed in the range of a measurement area of 30 μm × the thickness of the joining layer in the joining layer. At three arbitrary locations, surface analysis was performed in the range of a measurement area of 30 μm × the thickness of the joining layer. Using the average value of the mass of each element obtained by surface analysis, the Ag amount and the mass ratio M Ag / M Cu in the joining layer were determined. Also, the presence or absence of the Ti alloy at the joining interface between the copper plate 3 and the joining layer 4 and the presence ratio of the Ti alloy per 30 μm in length were determined. Using point analysis of SEM-EDX, the mass ratio M Ti / M Ag in the Ti alloy, the mass M of Sn SnThe mass M of Ti with respect to Ti The ratio M Ti / M Sn was determined. The mass ratio M Ti / M Ag at the center of the bonding layer, and the mass ratio M Ag / M Cu in the cross-section of the bonding layer were measured. A comparison was made between the amount of Cu in the Ti-rich region and the amount of Cu in a part of the bonding layer between the Ti-rich region and the ceramic substrate. As the amount of Cu in the Ti-rich region, the value obtained by point analysis was used. The amount of Cu in a part of the bonding layer was determined using the value obtained by surface analysis of the corresponding part. It was examined whether the amount of Cu between the Ti-rich region and the copper plate is 90 wt% or more. It was also examined whether the amount of Cu in the region located below the Ti-rich region is 70 wt% or more. Furthermore, it was examined whether the Ti-rich region contains carbon. Regarding the region between the Ti-rich region and the copper plate, a point located 2 μm on the copper plate side from the Ti-rich region was measured. Also, regarding the region located below the Ti-rich region, a point located 2 μm on the ceramic substrate side from the Ti-rich region was measured. The amounts of Ag and Sn in the diffusion region 7 that is 30 μm deep into the copper plate from the bonding interface were also measured. Let the amount of Ag in the Ti-rich region existing at the bonding interface between the copper plate and the bonding layer be A (wt%), and the amount of Ag at a location 30 μm deep from the bonding interface of the copper plate be B (wt%), and it was confirmed whether A > B is satisfied. Also, when the amount of Sn in the Ti-rich region is D (wt%) and the amount of Sn at a location 30 μm deep from the bonding interface of the copper plate is E (wt%), it was confirmed whether D > E is satisfied. The results are shown in Tables 5, 6, and 7.

[0040]

Table 5

[0041]

Table 6

[0042]

Table 7

[0043] As can be seen from the table, in the joined body according to the example, a Ti alloy was present at the joining interface between the copper plate and the joining layer. Also, 50% or more and 100% or less of the Ti alloy was a TiAg alloy with a mass ratio M Ti / M Ag of 0.6 or more. Also, in the joined body according to the example, the amount of Ag in the diffusion region 30 μm deep from the joining interface of the copper plate was less than the amount of Ag in the Ti alloy at the joining interface. Similarly, the amount of Sn in the diffusion region of the copper plate was less than the amount of Sn in the Ti alloy at the joining interface. It can be seen that the Ti alloy at the joining interface between the copper plate and the joining layer serves as a barrier layer that suppresses diffusion into the copper plate. On the other hand, in Comparative Example 1, the proportion of the Ti alloy at the interface between the copper plate and the joining layer was small. Also, since an Ag-rich solder material was used, although a Ti-rich region was formed, the proportion of the Ti-rich region present at the joining interface between the copper plate and the joining layer was small. Also, the Ti-rich region of Comparative Example 1 did not contain carbon.

[0044] Next, the warpage amount of the obtained joined body and the joining strength of the copper plate were measured. The warpage amount was measured for the warpage amount on the long side. All 10 with a warpage amount of 0.3 mm or less were rated as excellent products (◎). Also, those with 1 to 3 having a warpage amount exceeding 0.3 mm were rated as good products (〇). Those with 4 or more having a warpage amount exceeding 0.3 mm were rated as defective products (×). Also, the joining strength of the copper plate was taken as the peel strength. Specifically, in each example and comparative example, a sample for the peel test was prepared. The sample was a strip-shaped copper plate joined to a ceramic substrate. At that time, one end of the copper plate was joined so as to protrude from the ceramic substrate. The peel strength was measured by vertically pulling the protruding copper plate. The results are shown in Table 8. Also, an example in which the heating rate and the cooling rate of Example 1 were 5 °C / min was taken as Reference Example 1. An example in which the heating rate and the cooling rate of Comparative Example 1 were 5 °C / min was taken as Reference Example 2.

[0045]

Table 8

[0046] As can be seen from the table, the bonded body according to the example was excellent in both the amount of warpage and the bonding strength. On the other hand, in Comparative Example 1, since the amount of Ag was large, when the heating rate and the cooling rate were fast, proper bonding could not be achieved. The amount of warpage in Reference Example 1 was small, but the bonding strength decreased. It can be seen that the brazing filler metal of the example is suitable for a brazing process with a fast heating rate of 20 °C / min or more. The same applies to Reference Example 2. In a nitrogen atmosphere, nitridation progressed in the brazing filler metal containing a large amount of Ag, and the bonding strength decreased. From the above, it was found that for a brazing filler metal having a DSC curve with a heating rate and a cooling rate of 20 °C / min and having a predetermined peak, excellent bondability can be obtained even if the heating rate and the cooling rate in the brazing process are increased to 20 °C / min or more. Therefore, it can be seen that the bonded body according to the embodiment has a small amount of warpage and is excellent in mass productivity.

[0047] As described above, some embodiments of the present invention have been illustrated. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope. In addition, the above-described embodiments can be implemented in combination with each other.

Explanation of Reference Numerals

[0048] 1... Bonded body, 2... Ceramic substrate, 3... Copper plate, 4... Bonding layer, 5... Ti alloy region, 6... Ti poor region, 7... Diffusion region, 8... Copper circuit portion, 9... Copper heat sink, 10... Semiconductor element, 11... Lead frame, 20... Circuit board, 30... Semiconductor device

Claims

1. A ceramic substrate, a copper plate, a joined body comprising a joining layer disposed on at least one surface of the ceramic substrate for joining the ceramic substrate and the copper plate, wherein the joining layer contains 1% by mass or more and 20% by mass or less of Ag, 50% by mass or more of Cu, 4% by mass or more and 30% by mass or less of Ti, and one or two selected from Sn and In as a first element of 5% by mass or more and 40% by mass or less, in a cross section of the joined body in a first direction perpendicular to the surface of the ceramic substrate, when analyzing a measurement area where the length in a second direction parallel to the surface is 30 μm and the length in the first direction is the thickness of the joining layer by SEM-EDX, and regarding a location where the components of the joining layer are connected at the interface between the joining layer and the copper plate, in contact with the copper plate, and farthest from the ceramic substrate as the joining interface between the joining layer and the copper plate, a Ti alloy of Ti and at least one selected from Ag, Cu, Sn, and In exists at the joining interface, when analyzing any three measurement areas in the cross section by SEM-EDX and measuring the total length of the Ti alloy present per 30 μm of the length of the joining interface in the second direction, the Ti alloy exists 30% or more per 30 μm of the length on average of the three measurement areas, the joined body being characterized thereby.

2. When the measurement area in the cross section of the bonding layer is subjected to surface analysis by EDX at a measurement magnification of 1000 times, the mass M of Cu Ｃｕ to the mass M of Ag Ａｇ ratio (M Ａｇ / M Ｃｕ ) is 1 / 6 or less, the bonded body according to claim 1, characterized in that.

3. At least a part of the Ti alloy is an alloy containing Ti and Ag, In the cross section, when point analysis of the alloy containing Ti and the first element is performed at a measurement magnification of 1000 times, in the alloy containing Ti and Ag, the mass M Ａｇ of Ti with respect to the mass M Ｔｉ of Ag (M Ｔｉ / M Ａｇ ) has a Ti-rich region of 0.6 or more. The joined body according to any one of claims 1 to 2, characterized in that.

4. At least a part of the Ti alloy is an alloy containing Ti and the first element, In the cross-section, when point analysis of the alloy containing Ti and the first element is performed at a measurement magnification of 1000 times, in the alloy containing Ti and the first element, the mass M Ｅ１ of Ti with respect to the mass M Ｔｉ of the first element, there exists a Ti-rich region where the ratio (M Ｔｉ / M Ｅ１ ) is 0.4 or more. The bonded body according to any one of claims 1 to 3, characterized in that.

5. A part of the joining layer is located between the Ti-rich region and the ceramic substrate, The joined body according to any one of Claims 3 to 4, characterized in that the amount of Cu in the central part of the Ti-rich region is less than the amount of Cu in the part of the joining layer.

6. When surface analysis is performed on the measurement area in the cross section of the joining layer by EDX at a measurement magnification of 1000 times, the joined body according to any one of Claims 3 to 5, characterized in that a region having a mass ratio of Cu of 90% or more exists between the Ti-rich region and the copper plate.

7. The joined body according to any one of Claims 3 to 6, characterized in that the Ti-rich region contains carbon.

8. At the center of the bonding layer in the direction connecting the ceramic substrate and the copper plate, there is a mass M of Ag Ａｇ and a mass M of Ti Ｔｉ with a ratio (M Ｔｉ / M Ａｇ ) of 0.1 or less, and a Ti poor region exists. The bonded body according to any one of claims 1 to 7, characterized in that.

9. The bonded body according to any one of claims 1 to 8, characterized in that the thickness of the copper plate is 0.3 mm or more.

10. A circuit board comprising the bonded body according to any one of claims 1 to 9.

11. A semiconductor device comprising the circuit board according to claim 10 and a semiconductor element mounted on the circuit board.

12. A method for manufacturing the bonded body according to any one of claims 1 to 9, comprising: using a brazing filler metal containing 50% by mass or more of Cu, 4% by mass or more and 30% by mass or less of Ti, 5% by mass or more and 40% by mass or less of one or two selected from Sn and In, 1% by mass or more and 20% by mass or less of Ag, and 0% by mass or more and 2% by mass or less of carbon, and having an endothermic peak at 520°C or more and 590°C or less in the DSC curve of the heating process when measuring the DSC curve with a heating rate of 20°C / min, to bond the ceramic substrate and the copper plate.

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